WO2013087999A1 - Alumina material having a multiscale structure, including an aluminum-oxide binder having good mechanical strength, and method for preparing same - Google Patents

Alumina material having a multiscale structure, including an aluminum-oxide binder having good mechanical strength, and method for preparing same Download PDF

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WO2013087999A1
WO2013087999A1 PCT/FR2012/000490 FR2012000490W WO2013087999A1 WO 2013087999 A1 WO2013087999 A1 WO 2013087999A1 FR 2012000490 W FR2012000490 W FR 2012000490W WO 2013087999 A1 WO2013087999 A1 WO 2013087999A1
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particles
alumina
diameter
small
median diameter
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PCT/FR2012/000490
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French (fr)
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Stefânia CASSIANO-GASPAR
Delphine Bazer-Bachi
Loïc ROULEAU
Eric Lecolier
Jérôme CHEVALIER
Yves Jorand
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IFP Energies Nouvelles
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    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
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    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/44—Dehydration of aluminium oxide or hydroxide, i.e. all conversions of one form into another involving a loss of water
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Definitions

  • the present invention relates to the field of alumina-based materials, in the form of a millimetric object, porous and having good mechanical strength. More specifically, it relates to a multiscale structure material resulting from a hierarchical assembly of small and large particles preferentially spherical, micrometric and porous alumina-based and a binder consisting of aluminum oxide as well as its preparation process.
  • alumina-based materials made up of at most a single class of particles bound together by a binder, in the form of a millimetric and porous object, are widely described in the prior art such as, for example, in patent US6780817.
  • the particles that constitute these materials are particles of alumina or particles originating from solid precursors of alumina (oxides, oxyhydroxides or aluminum hydroxides), and in this case which do not disperse during the process of setting form, and which will therefore be present within the final material.
  • the binder used is also a solid precursor of alumina but with a better dispersion capacity than those of the particles, during the forming process.
  • the textural properties (BET surface area, mesoporous and macroporous volume, mesopore diameter) of the material are directly related to the textural properties of the particles and the binder used in the preparation of said materials.
  • the mesoporous and macroporous volumes are influenced by the amount of particles and binder.
  • a large macroporous volume can be obtained if the binder content is low, and in this case the mechanical properties of the material are strongly degraded.
  • An improvement in the mechanical strength can be sought by increasing the binder content, which implies a decrease in the macroporous volume but also a decrease in the amount of particles within the material.
  • the mesoporosity of the material may be degraded due to a small amount of porous particles, and therefore the mesoporosity provided to the material and from said particles is less important.
  • the characteristics of the mesopores are attributed to the organization of the alumina crystallites which depends on the preparation process and in particular on the synthesis of the alumina precursor or on the forming of millimetric objects.
  • the improvement of the textural properties of said particles such as the increase of the specific surface area, the mesoporous volume or the size of the mesopores may be sought and obtained by synthesis or post-synthesis treatment. However, these characteristics partially degrade during formatting.
  • the present invention relates to a material based on alumina, in millimetric object form, with a multiscale structure, porous and having a good mechanical strength which results from an assembly hierarchical structure of small and large micrometric and porous particles based on alumina and a binder consisting of aluminum oxide ensuring the cohesion of said material and on its preparation process.
  • the interest of the invention relates to the hierarchical organization of small and large micrometric porous particles of alumina, which makes it possible to maximize the content of particles within the material and consequently to increase the mesoporous volume of said material.
  • the hierarchical organization also minimizes the amount of binder because the space between the large particles is filled by the small particles, and therefore, the binder content necessary to ensure the cohesion of the material is minimized.
  • This binder makes it possible to ensure a macroporous volume that is minimal but sufficient for accessibility to the porosity of said micrometric particles.
  • the hierarchical organization ensures proper mechanical properties. Moreover, an improvement of these properties can be obtained by the use of a specific binder.
  • an object of the present invention relates to a material, in the form of a millimetric object, consisting of large particles of alumina having a median diameter of between 10 and 200 ⁇ m, said large particles being distant, from an interface to the other, less than 10 ⁇ m, small particles of alumina having a median diameter of between 0.5 and 10 ⁇ , said small particles being distant, from one interface to another, of less than 5 ⁇ m and being located in the space between the large particles, and a binder consisting of aluminum oxide, said binder being located in the space between said small and large particles, said material having a mesoporous volume, measured by porosimetry to a mercury content of between 0.2 and 2 ml / g, a macroporous volume, measured by mercury porosimetry, of between 0.05 and 0.2 ml / g and a BET specific surface area of between 90 and 350 m 2 / g; .
  • Another object of the present invention relates to a process for preparing said material which comprises at least the following steps:
  • step b) drying the raw material obtained at the end of step b) and;
  • An advantage of the present invention is to provide a material having a maximized proportion of small and large porous particles due to the hierarchical organization of said particles within the material and thus to provide a material having a very wide range of texture, in particular a mesoporous volume up to the value of 2mL / g much greater than the mesoporous volume values generally observed for alumina-based materials consisting of up to a single class of particles collected by a binder of the prior art.
  • Another advantage of the present invention is to provide a material having enhanced strength properties. This is due to the combined effect of the hierarchical organization of the small and large particles of alumina material according to the invention and the cohesion of said material provided by the presence of a specific binder.
  • the material according to the invention has a maximized lateral crushing strength up to very high values of force, up to 100 N for a material according to the invention of cylindrical shape, with a diameter of 2 mm. and of length equal to 4 mm, which are force values much greater than those observed for alumina materials consisting of a single class of particles collected by a binder of the prior art.
  • Another advantage of the present invention is also to provide a method of preparation for obtaining said material having increased mechanical strength properties by mixing in a step a) micrometric particles of alumina with a solid precursor of alumina and an acidic solution having a very high ratio (introduced acid mass) / (mass of introduced alumina solid precursor), leading to the in situ generation of a specific binder at the end of a calcination step dried and shaped material.
  • step a) a good flow of the mixture obtained in step a) during step b) which limits the generation of geometric defects and micrometric defects on the surface of the raw material thus improving the appearance and strength of the material as a millimetric object obtained according to the invention; the formation of defects related to the densification of the binder during steps c) and d) is minimized because of its location in the small space between the micrometric particles of alumina which improves the mechanical strength of the material in form millimetric object obtained according to the invention.
  • the present invention relates to a material, in the form of a millimetric object, consisting of large particles of alumina having a median diameter of between 10 and 200 ⁇ m, said large particles being distant, from one interface to another, of less than 10 ⁇ m, small alumina particles having a median diameter of between 0.5 and 10 ⁇ m, said small particles being spaced, from one interface to another, of less than 5 ⁇ m and being located in the space between the large particles and a binder consisting of aluminum oxide, said binder being located in the space between said small and large particles, said material having a mesoporous volume, measured by mercury porosimetry, of between 0.2 and 2 mL / g, a macroporous volume, measured by mercury porosimetry, of between 0.05 and 0.2 mL / g and a BET specific surface area of between 90 and 350 m 2 / g.
  • mesoporous volume is meant the volume of pores whose diameter is between 3.6 and 50 nm.
  • the mesoporous volume is measured by mercury porosimetry, the method of which is described below. More particularly, the term mesoporous volume, a pore volume corresponding to the volume of mercury which is entered into the pores with a diameter of between 3.6 and 50 nm.
  • macroporous volume the volume of pores whose diameter is between 50 and 7000 nm.
  • the macroporous volume is measured by mercury porosimetry, the method of which is described below. More particularly, by macroporous volume, a pore volume corresponding to the volume of mercury which is entered into the pores with a diameter of between 50 and 7000 nm.
  • Mercury porosimetry is performed according to ASTM D4284-83, using a surface tension of 480 dyne / cm and a contact angle of 140 °. The wetting angle was taken as 140 ° following the recommendations of the book "Techniques of the Engineer, analyzed analysis and characterization, P 1050-5, written by Jean Charpin and Bernard Rasneur".
  • BET specific surface area is understood to mean a specific surface area determined by nitrogen adsorption according to ASTM D 3663-78 established from the BET method (Brunauer-Emmett-Teller) described in US Pat. Periodical "The Journal of the American Society", 60, 309 (1938).
  • the large particles and the small particles of alumina which constitute the material according to the invention are, by their size, micrometric particles.
  • the material according to the present invention is advantageously constituted by the hierarchical organization of small and large micrometric porous particles of alumina.
  • micrometric particles refers throughout the text to all large and small particles. The total amount of micrometric particles is therefore the sum of the large
  • micrometric particles which constitute the material according to the invention are transition aluminas.
  • the micrometric alumina particles are transition aluminas chosen from chi, kappa, rho, eta, theta, gamma and delta alumina, alone or as a mixture, and preferably the transition alumina is alumina. gamma.
  • the small and large particles or micrometric particles which constitute the material according to the present invention are advantageously porous particles.
  • said particles are of rounded shape and even more preferably of spherical shape.
  • Said small and large particles are advantageously agglomerates of> 5 nanometer crystallites of alumina.
  • These crystallites are in the form of platelets, fibers or "blocks" whose dimensions are advantageously between 2 and 150 nm, preferably between 4 and 150 nm and preferably between 4 and 100 nm.
  • the crystallites of alumina are the elementary entities which constitute the micrometric particles.
  • the inter-crystallite space is responsible for the presence of the mesoporosity within said particles.
  • the size of the crystallite agglomerates constituting the micrometric particles is analyzed by scanning electron microscopy (SEM).
  • SEM scanning electron microscopy
  • the average size of the crystallite agglomerates constituting the micrometric particles is determined from scanning electron microscopy (SEM) images of the material according to the invention using SMile View software. SEM images must be made on the material in fracture mode and with a secondary electron detector.
  • the large particles of alumina constituting the material according to the invention have a median diameter of between 10 and 200 ⁇ m, preferably between 10 and 100 ⁇ m, and preferably between 10 and 80 ⁇ m.
  • the term "median diameter” refers to the D50, i.e., the diameter of the equivalent disc such that 50% by number of said coarse particles has a size less than said diameter.
  • the distribution of the particle size of said large particles of alumina within the material according to the invention is represented by the dimension DX, defined as the diameter of the equivalent disc such that X% in number of said large particles has a size less than said diameter. More precisely, the distribution of the particle size of said large particles is advantageously represented by the three dimensions D10, D50 and D90.
  • Said material according to the invention advantageously has a distribution of the particle size of said large particles of alumina within said material such that the diameter D 0 is at most 3 times lower than the median diameter D 50 and preferably at most 2 times smaller than the median diameter D50 and such that the diameter D90 is at most 3 times greater than the median diameter D50 and preferably at most 2 times greater than the median diameter D50.
  • the diameter of the large particles is determined, in the material according to the invention, from scanning electron microscopy (SEM) images of the material according to the invention, on a polished section, using the SMile View software.
  • the median diameter is calculated from the average of the diameters determined on a number of measurements that the person skilled in the art deems necessary and sufficient and preferably on at least 200 measurements.
  • said large particles are spaced, from one interface to another, less than 10 ⁇ m, preferably less than 8 ⁇ m, and preferably less than 6 ⁇ m.
  • the distance between the interface of a large particle and the interface of the closest large particle is determined from scanning electron microscopy (SEM) images of the material according to the invention, on a polished section, at using the SMile View software.
  • SEM scanning electron microscopy
  • the measurements are made on a number of measurements that the person skilled in the art deems necessary and sufficient and preferably on 50 images in order to determine an average distance from one interface to the other.
  • Said large particles advantageously have a median diameter less than 1/10 times the mean diameter of the smallest dimension of the material according to the invention, and preferably less than 1/50 times the average diameter of the smallest dimension of said material, so to ensure complete filling of the space of said material.
  • the large particles constituting the material according to the invention can advantageously be composed of two populations of particles having distinct median diameters.
  • Said large particles may optionally comprise a proportion of particles, called “lower fat” particles, having a median diameter of between 10 and 60 ⁇ m and preferably between 15 and 30 ⁇ and a proportion of particles called “larger” particles having a median diameter of between 60 and 200 ⁇ m and preferably between 100 and 180 ⁇ m.
  • said material according to the invention advantageously has a distribution of the particle size of said "coarse” particles of alumina within said material such as that the diameter D10 is at most 3 times smaller than the median diameter D50 and preferably at most 2 times less than the median diameter D50 and such that the diameter D90 is at most 3 times greater than the median diameter D50 and preferably at most 2 times greater at the median diameter D50 and a distribution of the particle size of said "larger” particles of alumina in said material such that the diameter D10 is at most 3 times smaller than the median diameter D50 and preferably at most 2 times less than the median diameter D50 and such that the diameter D90 is at most 3 times greater than the median diameter D50 and preferably at most 2 times greater than the median diameter D50.
  • the small particles which constitute the material according to the invention have a median diameter of between 0.5 and 10 ⁇ m, preferably between 0.5 and 6 ⁇ m and, preferably
  • diameter refers to the D50, i.e., the diameter of the equivalent disc such that 50% by number of said small particles has a size smaller than said diameter.
  • the distribution of the particle size of said small particles of alumina within the material according to the invention is represented by the dimension DX, defined as the diameter of the equivalent disk such that X% by number of said small particles has a size smaller than said diameter. More precisely, the distribution of the particle size of said small particles is advantageously represented by the three dimensions D10, D50 and D90.
  • Said material according to the invention advantageously has a distribution of the particle size of said small particles of alumina within said material such that the diameter D10 is at most 3 times smaller than the median diameter D50 and preferably at most 2 times smaller than the median diameter D50 and such that the diameter D90 is at most 3 times greater than the median diameter D50 and preferably at most 2 times greater than the median diameter D50.
  • the diameter of said small particles is determined, in the material according to the invention, from scanning electron microscopy (SEM) images of the material according to the invention on a polished section, using the software Sile View.
  • the median diameter is calculated from the average of the diameters determined on a number of measurements that the person skilled in the art deems necessary and sufficient and preferably on at least 200 measurements.
  • said small particles are spaced, from one interface to another, less than 5 ⁇ m, preferably less than 3 ⁇ m, and preferably less than 2 ⁇ m.
  • the distance between the interface of a small particle and the interface of the smallest particle closest is determined by scanning electron microscopy (SEM) images of the material according to the invention, on a polished section, using SMile View software. The measurements are made on a number of measurements that the person skilled in the art deems necessary and sufficient and preferably on 50 images in order to determine an average distance from one interface to the other.
  • Said small particles advantageously have a median diameter less than 1/5 times the median diameter of the large particles, and preferably a median diameter less than 1/10 times the median diameter of the large particles. This makes it possible to fill the space between said large particles, said small particles being located in the space between said large particles.
  • the proportion of said small particles is determined so as to fill the space between said large particles.
  • the proportions of the small and large particles of alumina constituting the material according to the invention are expressed as surface percentages with respect to the total surface area of the SEM image of the material according to the invention, so as to indicate the area that the small and large particles occupy within the material, as well as the proportion of lower fat particles having a median diameter between 10 and 60 ⁇ .
  • the surface percentages of the micrometric particles are determined from the SEM image analysis of the material according to the invention, on a polished section.
  • the resolution of the scanning electron microscope (SEM) is advantageously adapted to the median diameter of said micrometric particles so as to have an image representative of all the material according to the invention.
  • the area occupied by the small particles is determined as follows: the diameter of all the small particles is measured using SMile View software, in order to calculate the area occupied by each of said small particles. The sum of each of the areas occupied by each of said small particles corresponds to the total area occupied by all of said small particles in the SEM image.
  • the area occupied by the large particles is determined from the GIMP and Analysis software as follows: the edges of each of the large particles are delimited using the GIMP software. The area occupied by all of said large particles is then expressed as a percentage from the Analysis software.
  • the proportion of small and large particles occupying the surface of the SEM image of the material according to the invention is expressed as a percentage by surface area relative to the total surface area of the SEM image of the material according to the invention. It is calculated according to the formula: (area occupied by small or large particles / total area of the SEM image) x100. Percentages surface areas are determined on a number of images that the person skilled in the art deems necessary and sufficient and preferably, on 10 images.
  • the surface percentage of the small particles relative to the total surface of the SEM image of the material according to the invention is advantageously between 5 and 55%, preferably between 10 and 45% and preferably between 10 and 30%.
  • the surface percentage of the large particles is advantageously between 35 and 85%, preferably between 45 and 80% and preferably between 60 and 80% relative to the total surface of the SEM image of the material according to the invention.
  • the complement of the surface fraction that is to say, the sum of the surface percentages of the 3 small and large particles subtracted from 100%, corresponds to the surface percentage occupied by the binder consisting of aluminum oxide and the vacuum residual.
  • the presence of residual vacuum in the SEM image, that is to say unfilled space is related to the existence of a macroporous volume within the material.
  • said small particles are located in the space between the large particles.
  • This assembly of small and large particles is at the origin of the hierarchical organization of said micrometric particles within the material.
  • Said material according to the invention advantageously has a hierarchical organization.
  • the hierarchical organization of said micrometric particles within said material leads to a very extensive texture domain, in particular of mesoporous volume measured by mercury porosimetry on said material of between 0.2 and 2 micrograms.
  • a binder consisting of aluminum oxide is located in the space between small and large particles.
  • said small particles fill the gap between the coarse particles and said binder fills the residual space between the small and coarse particles and the residual space between the small particles.
  • Said binder fills the space between said micrometric particles so as to ensure the cohesion of the material according to the invention, and consequently, so as to minimize the residual vacuum, that is to say the unfilled space between said particles micrometric.
  • the existence of residual vacuum is to say the unfilled space between said particles micrometric.
  • the binder present in the space between the micrometric particles makes it possible to minimize the macroporous volume within the material according to the invention so that said macroporous volume of said material is between 0.05 and 0.2 mL / g, preferably included between 0.07 and 0.17 ml / g, and preferably between 0.1 and 0.15 ml / g.
  • the binder must not disturb the hierarchical organization of small and large particles, that is to say, that the binder must not move micrometric particles away from each other.
  • said binder makes it possible to maintain a distance from one interface to another between the small particles of less than 5 ⁇ m, preferably less than 3 ⁇ m, and preferably less than 2 ⁇ m, and distance from one interface to another between coarse particles less than 10 ⁇ m, preferably less than 8 ⁇ m and preferably less than 6 ⁇ m.
  • said binder consisting of aluminum oxide.
  • Said binder is advantageously present in the material according to the invention in the form of particles having a mean size of less than 1 ⁇ m.
  • the size of the particles constituting the binder can advantageously be measured, in the material according to the invention, by SEM image analysis of the material according to the invention, with the aid of SMile View software.
  • the SEM images must be made on the material according to the invention in fracture mode and with a secondary electron detector.
  • said material has a mesoporous volume measured by mercury porosimetry of between 0.2 and 2 ml / g, preferably between 0.25 and 1.5 ml / g and preferably between 0, 25 and 1.0 mL g.
  • said material has a macroporous volume measured by mercury porosimetry of between 0.05 and 0.2 ml / g, preferably between 0.07 and 0.17 ml / g and preferably between 0.1 and 0.15 mL / g.
  • said material has a median mesopore diameter measured by mercury porosimetry between 8 and 25 nm, preferably between 10 and 25 nm and preferably between 10 and 23 nm.
  • said material has a BET specific surface area of between 90 and 350 m 2 / g, preferably between 100 and 300 m 2 / g and preferably between 30 and 280 m 2 / g.
  • said material is in the form of a millimeter object.
  • the mean diameter of the smallest dimension of the material according to the invention is advantageously between 0.5 and 10 mm, preferably between 0.7 and 5 mm, and preferably between 1.0 and 4.0. mm.
  • the dimensions of the millimetric object can be obtained with any measuring tool adapted to the dimensions of said material and in particular with a vernier caliper.
  • Said material is advantageously in the form of a granule or an extrusion and preferably in the form of an extrudate.
  • the material according to the invention thus has maximized proportions of micrometric particles porous because of this hierarchical organization, resulting in a porous material and having good mechanical strength.
  • the material according to the present invention has excellent strength properties. This is due to the combined effect of the hierarchical organization of small and large particles of alumina of the material according to the invention and the cohesion of said material provided by the presence of a specific binder.
  • the material according to the invention has a mechanical resistance to lateral crushing determined by the grain-to-grain (EGG) crushing test advantageously between 50 and 100 N, preferably between 60 and 100 N and so preferred between 80 and 100 N, expressed by force in the case of the materials according to the invention in the form of granules, and a mechanical resistance to lateral crushing advantageously between 0.8 and 2.5 daN / mm, preferably between 0.85 and 2 daN / mm and preferably between 0.85 and 1.8 daN / mm, expressed in force per unit length in the case of the materials according to the invention in the form of extrudates.
  • GSG grain-to-grain
  • the mechanical strength of the material according to the invention determined by the grain-to-grain (GGE) crushing test.
  • GGE grain-to-grain
  • ASTM D4179-01 a standardized test that involves subjecting a material in the form of a millimeter object, such as a granule or extrusion, to a compressive force that causes the rupture. This test is therefore a measure of the tensile strength of the material. The analysis is repeated on a number of solids taken individually and typically on a number of solids between 10 and 200. The average of the lateral forces of rupture measured is the average EGG which is expressed in the case of the granules in unit of force (N), and in the case of extrusions in unit of force per unit length (daN / mm).
  • Another subject of the present invention relates to a process for preparing said material comprising at least the following steps:
  • micrometric particles es having a mesoporous volume of between 0.2 and 2.5 mL / g, and a median mesopore diameter of between 7 and 25 nm
  • the large particles and the small particles of alumina referred to as the "micrometric particles" used in the mixing step a) of the preparation process according to the invention are advantageously transition aluminas chosen from chi, kappa alumina. , rho, eta, theta, gamma and delta, alone or as a mixture, and preferably gamma-alumina, or are advantageously solid precursors of alumina selected from hydrargillite, gibbsite, nordstrandite, bayerite, boehmite or pseudo-boehmite.
  • the micrometric particles are solid precursors of alumina
  • said precursors must be little dispersible in the acid solution introduced in the mixing step a) of the preparation process, that is to say in such a way that that the median diameter of said micrometric particles is little reduced during step a) and that the hierarchical organization of small and large particles can be observed within the material at the end of step d) of preparation according to the characterization techniques described in detail above.
  • step d) of calcination a phase transformation takes place so as to obtain the transition aluminas within said material.
  • the micrometric alumina particles used in the mixing step a) of the preparation process are transition aluminas or solid precursors of alumina which are poorly dispersible in the acid solution used. in said step a) of the preparation process, and which will be converted to transition alumina at the end of step d) of calcination.
  • step a) of mixing the preparation process according to the invention small particles of alumina with a median diameter of between 0.5 and 10 ⁇ m are mixed with large particles of alumina with a median diameter of between 10 and 200 pm.
  • said large particles of alumina have a median diameter of between 10 and 100 ⁇ m, and preferably between 10 and 80 ⁇ m.
  • Said large particles mixed in step a) of the preparation process according to the invention may advantageously be composed of two populations of particles having distinct median diameters.
  • Said large particles may optionally comprise a proportion of particles, called “lower fat” particles, having a median diameter of between 10 and 60 ⁇ m and preferably between 15 and 30 ⁇ m and a proportion of particles called “larger” particles having a median diameter between 60 and 200 pm and preferably between 100 and 180 pm.
  • said small alumina particles have a diameter of between 0.5 and 6 ⁇ m and preferably between 0.5 and 3 ⁇ m.
  • Said micrometric alumina particles mixed in step a) of the preparation process are advantageously used in powder form.
  • the size distribution of said micrometric alumina particles in the powders used in said mixing step a) is measured by laser diffraction granulometry, based on the Mie diffraction theory (GBJ de Boer, C. de Weerd, D Thoenes, HWJ Goossens, Charact 4 (1987) 14-19).
  • the distribution of the particle size of the micrometric alumina particles in the powders is represented by the dimension DvX, defined as the diameter of the equivalent sphere such that X% by volume of said particles has a size less than said diameter.
  • the distribution of the particle size of said particles is represented by the three dimensions Dv10, Dv50 and Dv90.
  • the term "median diameter” used in the description of the preparation process according to the invention denotes the Dv50, that is to say the diameter of the equivalent sphere such that 50% by volume of said particles has a size less than said diameter.
  • the distribution of the particle size of the small particles is such that the diameter Dv10 is at most 3 times smaller than the median diameter Dv50 and preferably at most 2 times less than the median diameter Dv50 and such that the diameter Dv90 is at most 3 times greater than the diameter.
  • the distribution of the particle size of the larger particles and the particle size distribution of the "coarse" particles is advantageously identical to the particle size distribution of the small particles.
  • the particle size distribution of the small particles is preferably monomodal, and the particle size distribution of the coarse particles may be monomodal or bimodal, in the case where said coarse particles are composed of said larger and lower coarse particles.
  • the textural properties of said micrometric alumina particles are respectively determined by nitrogen adsorption and mercury porosimetry.
  • the BET surface area, the mesoporous volume and the pore size distribution of the micrometric particles constituting the material according to the invention can be very variable depending on the process for preparing the alumina precursor used to prepare the micrometric particles and the operating conditions. .
  • Said micrometric particles advantageously have a BET specific surface area of between 100 and 480 m 2 / g, preferably between 120 and 300 m 2 / g, and preferably between 120 and 250 m 2 / g.
  • said micrometric particles advantageously have a mesoporous volume of between 0.2 and 2.5 ml of g, preferably of between 0.3 and 2.0 ml / g, and preferably of between 0.3. and 1.5 mL / g.
  • said micrometric particles advantageously have a median mesopore diameter of between 7 and 25 nm, preferably between 7 and 24 nm, and preferably between 7.5 and 23 nm.
  • the proportions of small and large particles introduced into the mixture of step a) is an essential criterion of the preparation method according to the present invention because said proportions define the compactness of the mixture of small and large particles. Said proportions lead to the hierarchical organization of small and large particles within the material obtained at the end of said preparation process. More specifically, the proportions of small and large particles are
  • the porosity gives information on the volume of voids between the small and the large particles, and consequently, allows to define the proportion of binder necessary to fill the space between said small and large particles. This also makes it possible to define the proportion of solid precursor of alumina necessary for obtaining said
  • step a) of mixing the preparation process according to the invention 10 to 60% and preferably 15 to 35% by weight of small alumina particles with a median diameter of between 0.5 and 10 m and 40 to 90% and preferably 65 to 85% by weight of large: alumina particles of median diameter between 10 and 200 pm, the percentages being expressed relative to the total amount of micrometer particles.
  • the hierarchical organization of micrometric particles of alumina will not be optimal given the large amount of small particles and the maximization of the proportion of micrometric particles of alumina. It can not be reached because of a less compact organization.
  • the proportion of large particles is too high and in particular greater than 90% by weight, the quantity of small particles will not be sufficient to fill the voids between the large particles, and the hierarchical organization of micrometric particles of Alumina will not be optimal because of a less compact organization.
  • Another essential criterion of the preparation process according to the invention is the introduction into step a) of a mixture of a solid precursor of alumina and of an acid in solution allowing the generation in situ. a binder consisting of aluminum oxide, after step d) of calcination of the preparation process according to the invention.
  • the solid precursor of alumina and the acid in solution must be introduced in said step a) in the proportions as claimed.
  • the generation of said binder consisting of aluminum oxide requires a solid precursor of alumina which in the presence of the acidic solution is more reactive than the micrometric alumina particles also introduced in step a) of mixing the preparation process according to the invention.
  • the solid precursor of alumina must be capable of dispersing predominantly or dissolving predominantly in the acid solution used and forming particles of average size less than 1 ⁇ between the micrometric particles.
  • the micrometric alumina particles must be slightly degraded in the presence of said acid solution, that is to say that the median diameter of said alumina particles must be maintained in the presence of the acid in solution introduced in the presence of during step a) of the preparation process according to the invention.
  • the solid precursor of alumina is advantageously chosen from aluminum oxides, aluminum hydroxides and aluminum oxyhydroxides which are soluble or dispersible in the acid solution employed, preferably from aluminum hydroxides and aluminum oxyhydroxides.
  • said solid alumina precursor is an aluminum oxyhydroxide and more preferably said solid alumina precursor is boehmite or pseudo-boehmite.
  • Said alumina precursor is advantageously in the form of a powder consisting of solid particles having a median diameter, determined by laser diffraction granulometry, of between 9 and 80 ⁇ m, preferably between 10 and 60 ⁇ m, and preferably between 15 and 45 pm.
  • the particles of the solid precursor of alumina are advantageously constituted by agglomerates of elementary units, called crystallites, whose dimensions are advantageously between 2 and 150 nm, preferably between 4 and 150 nm and preferably between 4 and 100 nm. determined by transmission electron microscopy (TEM).
  • TEM transmission electron microscopy
  • the proportion of the solid precursor of alumina is between 5 and 50% by weight relative to the total amount of solid particles, preferably between 10 and 30% by weight, and preferably between 15 and 25% by weight.
  • the total amount of solid particles is the sum of the micrometric particles (small and large alumina particles) and particles of the solid alumina precursor.
  • the amount of solid precursor of alumina is less than 5% by weight relative to the total amount of solid particles introduced, the amount of aluminum oxide binder which will be formed in situ after step d) of calcination, will not be sufficient to ensure the cohesion of the hierarchical organization of small and large micrometric particles of alumina.
  • the amount of solid precursor of alumina is greater than 50% by weight relative to the total amount of solid particles, the amount of aluminum oxide binder which will be formed in situ after step d) of calcination will be greater than the amount necessary to fill the residual voids between the micrometric particles, and consequently, the micrometric particles will be dispersed in an unorganized manner within said binder and the proportion of micrometric particles present in the material obtained at the end of the process of preparation according to the final invention will not be maximum.
  • an acid in solution is chosen from acetic acid, hydrochloric acid, sulfuric acid, formic acid, citric acid and nitric acid, alone or as a mixture, is introduced, provided that after step d) of the preparation process according to the invention, said acid is decomposed and lead to a binder consisting of aluminum oxide .
  • said acid is nitric acid.
  • the role of the acid solution is to promote the dispersion of the particles which constitute the solid precursor of alumina.
  • the particles of the solid precursor of alumina which initially have a median diameter of about ten micron become submicron colloidal particles, thanks to the action of the acid solution associated with the mechanical energy provided.
  • step a) of mixing the process for preparing the material according to the invention These colloidal particles re-aggregate to form particles having an average size of less than 1 ⁇
  • the solid precursor of alumina and the acid in solution chosen from acetic acid, hydrochloric acid, sulfuric acid, formic acid, the citric acid and the nitric acid, alone or as a mixture are introduced in proportions such that the ratio of the mass of acid introduced into the solid precursor mass of introduced alumina is between 2.5 and 115% by weight, preferably between 7.4 and 74% by weight and preferably between 30 and 62% by weight.
  • step a) of the preparation process according to the invention makes it possible at the same time to disperse well the particles having a median diameter of about ten micron which constitute the solid precursor of alumina in submicron colloidal particles, but also to promote the partial dissolution of said solid precursor of alumina and in a minority, micrometric particles of alumina.
  • This high acid ratio dissolution favors the formation of alumina species which modify the rheology of the mixture resulting from stage a) of the preparation process according to the invention and also act as binders in stages c) and d). ) of heat treatments of said preparation process.
  • step d) of calcination makes it possible to improve the adhesion between the micrometric particles of alumina and the binder consisting of aluminum oxide formed at the end of the step d) calcination. Consequently, this makes it possible, after step d) of calcination, to increase the cohesion of the hierarchical organization of the small and large micrometric particles of alumina and thus of the material obtained by the preparation process according to the invention. 'invention.
  • an organic binder may optionally be added in step a) of mixing.
  • the presence of said organic binder facilitates shaping by extrusion.
  • Said organic binder can advantageously be chosen from methylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, carboxymethylcellulose and polyvinyl alcohol.
  • the proportion of said organic binder is advantageously between 0 and 5% by weight, preferably between 0 and 3% by weight and preferably between 0 and 1% by weight, relative to the total amount of solid particles.
  • step d) of calcination of the preparation process according to the invention said organic binder is decomposed, that is to say that at the end of step d) calcination, said Organic binder is no longer present within the material according to the invention.
  • step a) of the preparation process according to the invention is advantageously carried out in a single step or in two steps.
  • step a) differs according to the shaping technique used in step b) of the preparation process according to the invention.
  • the mixing step a) is preferably carried out in a single step.
  • the micrometric alumina particles, the solid precursor of alumina, the acid in solution and optionally an organic binder are mixed all at once using a batch mixer, preferably with a cam or an arm. Z, or using a twin-screw mixer-mixer.
  • the mixing conditions are adjusted in a manner known to those skilled in the art and aim to obtain a homogeneous and extrudable paste.
  • the extrudability of the paste can advantageously be adjusted with the addition of water to the acid in solution, in order to obtain a paste suitable for carrying out the extrusion forming step b).
  • the mixing step a) is preferably carried out in two steps.
  • the small and large micrometric particles of alumina are advantageously dry mixed for a period of between 1 and 5 min and preferably between 2 and 4 min.
  • the mixture is preferably made using a mixer such as, for example, a bezel or a rotating drum.
  • the solid precursor of alumina and the acid in solution are then advantageously introduced into said dry mixture of micrometric alumina particles, in the form of a binder solution formed with the solid precursor of alumina dispersed in said acidic solution.
  • the acid in solution and the solid precursor of alumina dispersed in said acid solution are advantageously introduced in a second step, using a spray nozzle, to ensure the contact between the components of the mixture. and allow the progressive agglomeration of micrometric alumina particles during rotation of the bezel or rotating drum.
  • the addition in a second step of the solid precursor of alumina dispersed in the acid in solution makes it possible to ensure the shaping by wet granular growth during the granulation shaping step b).
  • the shaping conditions are adjusted in a manner known to those skilled in the art and are aimed at obtaining spherical granules of desired size.
  • step a) The mixture resulting from step a) is then shaped according to step b) of the process for preparing the material according to the invention.
  • the shaping step b) makes it possible to obtain a raw material 10.
  • raw material is meant the material shaped and having not undergone any heat treatment steps.
  • Said b) shaping step can advantageously be carried out by wet granulation or by extrusion.
  • said shaping step b) is carried out by extrusion in a manner known to those skilled in the art.
  • the mixture resulting from stage a), that is to say the paste resulting from stage a) advantageously passes through a die, for example using a piston or a continuous twin-screw or single-screw extruder.
  • the diameter of the die is advantageously variable and is between 10 and 5 mm.
  • the shape of the die, and therefore the form of the millimeter solid obtained in extruded form, is advantageously cylindrical, trilobal, quadrilobed or multilobed.
  • the green material from step b) can therefore be in the form of granules or extrudates and preferably in the form of extrudates.
  • step b) of the preparation process according to the invention is then subjected to the heat treatments of steps c) and d).
  • step c) of the preparation process according to the invention the raw material obtained at the end of step b) undergoes a drying step.
  • drying step c) is advantageously carried out according to the techniques known to those skilled in the art to evaporate in a controlled manner the solvent from the acid solution present in the shaped green material obtained at the end of step b) and imparting a first solidification to said material.
  • the drying step c) may advantageously be carried out under vacuum or under air or in moist air, in one or more substeps of determined conditions of temperature, vacuum or gas.
  • the drying step c) is advantageously carried out at a temperature between 40 and 200 ° C, preferably between 50 and 150 ° C, and preferably between 70 and 100 ° C.
  • the drying step c) is advantageously carried out for a period of between 12 and 72 hours, and preferably between 12 and 24 hours.
  • Said step c) of drying is advantageously carried out under ambient air or in humid air, with a water vapor content between 20 and 100% volume.
  • step d) of the preparation process according to the invention the dried material obtained at the end of the drying step c) undergoes a calcination step.
  • Said step d) of calcination is advantageously carried out according to the techniques known to those skilled in the art.
  • Said step d) can be carried out under air or under air with steam, in one or more substeps of determined conditions of temperature or gas.
  • Said d) calcination step is advantageously carried out at a temperature between 400 and 1000 ° C, preferably between 450 and 850 ° C, and preferably between 500 and 700 ° C.
  • the d) calcination step is advantageously carried out for a period of between 1 to 6 hours and preferably between 2 and 3 hours, under ambient air or under air and steam.
  • Said step d) of calcination is advantageously carried out under ambient air.
  • Said step d) of calcination makes it possible to generate the binder constituted by aluminum oxide and to ensure the cohesion of the hierarchical organization of small and large micrometric particles of alumina and therefore of the material obtained by the preparation process according to the invention.
  • invention thanks, in particular, to the transformation of the solid alumina precursor into a transition alumina, and the presence of aluminum species in the medium, originating from the partial dissolution of said solid precursor of alumina and in a minority, micrometric particles of alumina in the presence of a high acid ratio.
  • the material in the form of millimetric object according to the invention is obtained.
  • material in the form of a millimeter object is meant a material having dimensions of the order of one millimeter.
  • the material in the form of millimetric object, preferably in extruded form, prepared according to the sequence of steps a), b), c) and d) of the preparation process according to the invention can be characterized according to the following techniques : nitrogen adsorption for the determination of the specific surface according to the BET method; mercury porosimetry for mesoporous and macroporous volume measurements and pore size distribution; scanning electron microscopy (SEM) for the microstructure analysis to observe the hierarchical organization and dimensions of the small and large micrometric alumina particles assembled by the aluminum oxide binder; a grain-to-grain crushing test for evaluating the mechanical strength of the material.
  • nitrogen adsorption for the determination of the specific surface according to the BET method
  • mercury porosimetry for mesoporous and macroporous volume measurements and pore size distribution
  • SEM scanning electron microscopy
  • the preparation method of the invention ensures the formation of said material but also: a good sliding of the micrometric particles of alumina with respect to each other during the mixing step a) which limits, on the one hand, the degradation of the particles and thus makes it possible to maintain a high porosity of the material and what on the other hand limits the generation of micrometric defects within the mixture and thus makes it possible to improve its
  • step b) a good flow of the mixture obtained in step a) during step b) which limits the generation of geometric defects and micrometric defects on the surface of the raw material thus improving the appearance and strength of the material as a millimetric object obtained according to the invention
  • Example 1 preparation of an alumina-based material, in the form of a millimetric, porous object, with a hierarchical organization of two classes of micrometric particles assembled by a binder consisting of aluminum oxide and prepared at an acid ratio of 61% by weight.
  • the large particle population consists of alumina Puralox Scfa-140 (Sasol). These particles have a BET specific surface area of 144 m 2 / g determined by nitrogen adsorption (ASAP 2420 - Micromeritics), a mesoporous volume of 0.45 mL / g and a median mesopore diameter of 1.15 ⁇ m determined by mercury porosimetry (Autopore 9500 - Micromeritics). The median diameter, i.e., the Dv50 of said large particles is about 19 ⁇ m, the Dv10 is about 7 ⁇ m, and the Dv90 is about 38 ⁇ m, determined by laser diffraction particle size. (Mastersizer 2000 - Malvern).
  • the small micrometric alumina particles are obtained by spray drying of a boehmite sol prepared from the Pural SB3 powder (Sasol).
  • the sol is prepared so as to obtain a mass ratio (mass of boehmite / mass of water) ⁇ 100 of 3.4% by weight and a level of acid (mass of nitric acid / mass of alumina formed from boehmite after calcination) of 4.6% by weight.
  • the powder Pural SB3 referenced (Sasol) is introduced into the acid solution, and the mixture is subjected to strong stirring for 2 hours. After the mixing time, the sol is centrifuged for 20 min at a speed of 4000 rpm to remove the undispersed boehmite sediments.
  • the boehmite sol is then spray-dried using a laboratory spray dryer (Buchi B-290).
  • the atomization conditions such as the feed rate, the compressed air flow, the inlet and outlet temperatures, and the suction flow rate are optimized so that to produce in the separation cyclone small spherical particles whose median diameter is about 2 ⁇ m.
  • the particles obtained by spray drying are then calcined in a muffle furnace at 600 ° C. for 2 hours in order to ensure the conversion of boehmite to gamma-alumina, and thus to obtain the small micrometric and spherical particles of alumina.
  • These particles have, after calcination, a BET surface area of 212 m 2 / g determined by nitrogen adsorption (ASAP 2420 - Micromeritics), a mesoporous volume of 0.35 ml / g and a median diameter of 7.5 mesopores. nm, determined by mercury porosimetry (Autopore 9500 - Micromeritics).
  • the median diameter, i.e., the Dv50 of said small particles is about 1.7 ⁇ m
  • the Dv10 is about 0.75 ⁇ m
  • the Dv90 is about 3.4 ⁇ m, determined by laser diffraction granulometry (Mastersizer 2000 - Malvern).
  • the solid precursor of alumina, necessary for the formation of the binder consisting of aluminum oxide, is the powder referenced Pural SB3 (Sasol), and it is a highly dispersible boehmite in acid solution.
  • the large micrometric particles (Puralox Scfa-140 - Sasol), the small micrometric particles obtained by spray drying of a boehmite sol, and the solid alumina precursor referenced Pural SB3 (Sasol), are dry blended in such a way that to obtain, respectively, the proportions of 80% and 20% by weight of large and small particles, and 19% by weight of solid precursor of alumina.
  • the proportions of large and small particles are expressed in relation to the total amount of micrometric particles, and the proportion of solid precursor of alumina is expressed in relation to the total amount of solid.
  • the dry blending is carried out using a cam blender (Brabender 50 EHT) at an arm rotation speed of 10 rpm for 2 minutes.
  • a solution of nitric acid is introduced using a syringe pump, so as to obtain an acid ratio (mass of introduced nitric acid / solid precursor mass of introduced alumina) x100 of 61% in weight.
  • the water is added with the acid solution so as to obtain a cohesive, homogeneous and extrudable paste.
  • the kneading is continued at a rotation speed of the arms of 16 revolutions / min for 30 minutes, after the end of the addition of the acid solution.
  • the nitric acid solution associated with the mechanical energy provided during the kneading make it possible to disperse the micrometric crystallite agglomerates of the solid precursor of alumina, and at the end of the mixing process, the formed dough consists of coarse and micrometric small particles of alumina bound by a binder whose particles have an average size of the order of a hundred nanometers.
  • the high acid ratio promotes the partial dissolution of the solid alumina precursor and in a minor way, the micrometric alumina particles, and therefore promotes the formation of alumina species which will help form the binder.
  • the paste obtained is shaped using a piston extruder (MTS), equipped with a cylindrical die 3 mm in diameter and 6 mm in length, to form the millimeter object.
  • the extrusions are then dried in a ventilated oven at 80 ° C for 16 hours in ambient air, in order to evaporate the solvent from the acid solution.
  • the dried extrudates are then calcined in a muffle furnace at 600 ° C. for 2 hours in ambient air, in order to ensure the solidification of the material by virtue of the conversion of the aluminum precursor, in this example, the boehmite into gamma alumina. and thus forming the binder consisting of aluminum oxide.
  • the extrudates obtained are characterized according to the following techniques: nitrogen adsorption, for the determination of the BET specific surface area; mercury porosimetry for mesoporous and macroporous volume measurements and mesopore diameter distribution; by scanning electron microscopy (JEOL JSM 6340F) for the observation of the hierarchical organization of small and large micrometric particles of alumina and in particular the distance from one interface to another between said large particles (Dg r0SS es) and from one interface to another between said small particles ⁇ D pe tites) and the surface percentage of small (S pet ites) and large particles (Sg rosses ) with respect to the total surface of the SEM image; and the grain-to-grain (GGE) crush test to determine the lateral crushing strength of the material.
  • GGE grain-to-grain
  • Example 1 The characteristics of the material obtained according to the formulation of Example 1 are summarized in Table 1. It is observed that the material according to the invention obtained according to Example 1 has a good mechanical strength due to the hierarchical organization of small and large particles assembled by a binder consisting of aluminum oxide. The distances Dg r0SS es and D pe tjtes and the surface percentages Sgrosses and S pe tites are essential criteria for obtaining the hierarchical organization of said small and large particles and are consistent with those of the material of the invention.
  • the textural properties of the material obtained are related to the textural properties of the micrometric alumina particles and are consistent with the expected properties of the material according to the invention.
  • the hierarchical organization makes it possible to increase the mesoporous volume of the material, by maximizing the proportion of micrometric particles with respect to the binder content.
  • the hierarchical organization also makes it possible to have good sliding of the small and large micrometric alumina particles relative to each other, which results in a low mixing torque of the order of 7 Nm.
  • Example 2 preparation of an alumina-based material, in the form of a millimetric object, highly porous, with a hierarchical organization of two classes of micrometric particles assembled by a binder consisting of oxide of aluminum and prepared at a high acid ratio of 61% by weight.
  • the large micrometric and porous alumina particles are obtained from calcination in a muffle furnace at 600 ° C. for 2 hours, under ambient air, with the Pural TH100 powder (Sasol), in order to transform the starting boehmite into alumina. gamma.
  • the micrometric particles After calcination, the micrometric particles have a specific surface area of 142 m 2 / g determined by nitrogen adsorption (ASAP 2420 - Micromeritics), a mesoporous volume of 0.87 ml / g and a median mesopore diameter of 22.5 ⁇ m. nm determined by mercury porosimetry (Autopore 9500 - Micromeritics). The median diameter, that is to say the Dv50 of said large particles is about 40 ⁇ , the Dv10 is about 15 pm, and the Dv90 is about 77 pm, determined by laser diffraction granulometry (Mastersizer 2000 - Malvern).
  • the small micrometric particles are obtained by spray drying of a boehmite sol prepared from the powder Pural TH100 (Sasol).
  • Said boehmite sol is prepared according to the same conditions described in Example 1; and the atomization parameters are optimized to produce in the separation cyclone small spherical particles having a median diameter of about 3 ⁇ m.
  • the particles obtained by spray drying are subjected to the same heat treatment as Example 1, in order to ensure the conversion of boehmite to gamma-alumina, and thus to obtain small micrometric and spherical particles of alumina.
  • These particles have, after calcination, a BET specific surface area of 130 m 2 / g determined by nitrogen adsorption (ASAP 2420 - Micromeritics), a mesoporous volume of 0.78 ml of g and a median diameter of the mesopores of 23 nm, determined by mercury porosimetry (Autopore 9500 - Micromeritics).
  • the median diameter, i.e., the Dv50 of said small particles is about 2.7 ⁇ m
  • the Dv10 is about 1.7 ⁇ m
  • the Dv90 is about 8 ⁇ m, determined by particle size distribution.
  • the solid precursor of alumina, necessary for the formation of the binder consisting of aluminum oxide, is the powder referenced Pural TH100 (Sasol).
  • the large micrometric particles obtained after calcination of the powder referenced Pural 100 (Sasol), the small micrometric particles obtained by spray drying of a boehmite sol, and the solid precursor of alumina referenced Pural 100 (Sasol), are mixed with in the same proportions and under the same conditions described in Example 1. Then, a solution of nitric acid is introduced in the same way as that described in Example 1, and in order to obtain an acid ratio. (Mass of introduced nitric acid / mass of introduced alumina solid precursor) x100 of 61% by weight. The mixing is continued under the same conditions as in Example 1. The water is added with the acid solution so as to obtain a cohesive, homogeneous and extrudable paste. The high acid ratio associated with the mechanical energy provided to the kneading, lead to the same technical effects described in Example 1.
  • the paste obtained is then shaped according to the same conditions as in Example 1.
  • Example 1 The extrudates are then dried and calcined according to the conditions described in Example 1; and characterized according to the same techniques described in the same example.
  • the characteristics of the material obtained according to the formulation of Example 2 are collated in Table 1.
  • the material according to the invention obtained according to Example 1 has a good mechanical strength due to the hierarchical organization of small and large particles assembled by a binder consisting of aluminum oxide.
  • the distances D gr0 sses and Dpies and the surface percentages Sgrosses and S pe iites are essential criteria for obtaining the hierarchical organization of said small and large particles and are consistent with those of the material of the invention.
  • the textural properties of the material obtained are related to the textural properties of the micrometric alumina particles and are consistent with the expected properties of the material according to the invention.
  • the hierarchical organization makes it possible to increase the mesoporous volume of the material, by maximizing the proportion of micrometric particles with respect to the binder content.
  • the hierarchical organization also makes it possible to have good sliding of the small and large micrometric particles of alumina with respect to each other, which results in a low mixing torque of the order of 9 Nm.
  • Example 3 preparation of an alumina-based material, in the form of a millimetric, porous object, with a hierarchical organization of three classes of micrometric particles assembled by a binder consisting of aluminum oxide and prepared at a high acid ratio of 61% by weight.
  • the large particles of alumina are composed of two populations of particles whose median diameter is distinct, and which are identified as: a population of so-called lower fat particles and referenced Puralox Scfa-140 (Sasol) and a so-called larger population referenced Puralox SCCa 150/200 (Sasol).
  • a population of so-called lower fat particles and referenced Puralox Scfa-140 (Sasol)
  • a so-called larger population referenced Puralox SCCa 150/200 Sasol.
  • the characteristics of the alumina powder referenced Puralox Scfa-140 are described in Example 1.
  • the alumina powder referenced Puralox SCCa 150/200 has a BET specific surface area of 199 m 2 / g determined by nitrogen adsorption ( ASAP 2420 - Micromeritics), a mesoporous volume of 0.43 mIg and a mesopore median diameter of 8.7 nm determined by mercury porosimetry (Autopore 9500 - Micromeritics).
  • the median diameter, i.e., the Dv50 of said larger fat particles is about 160 ⁇ m
  • the Dv10 is about 104 ⁇ m
  • the Dv90 is about 247 ⁇ m, determined by laser diffraction particle size ( Mastersizer 2000 - Malvern).
  • the small particles are obtained in the same manner as described in Example 1 and their characteristics are also described in the same example.
  • the solid precursor of alumina is the boehmite referenced Pural SB3 (Sasol), also used in Example 1.
  • the conditions for mixing the alumina particles with the solid alumina precursor and the acid solution, the mixing conditions, the extrusion shaping and the heat treatments, are identical to those described in Example 1, but with 4 powders instead of 3 powders.
  • the proportions of coarse particles, that is to say of the whole of the coarse lower and upper coarse particles, and small micrometric particles of alumina are respectively 76% and 24% by weight, expressed relative to the total quantity of particles. micrometric, and the proportion of solid precursor of alumina is 13% by weight relative to the total amount of solid.
  • the proportion of so-called smaller particles relative to the totality of large particles is 40% by weight.
  • the ratio of acid (mass of introduced nitric acid) / (mass of solid precursor of alumina) ⁇ 100 used is 61%.
  • the material according to the invention obtained according to Example 3 has good mechanical strength due to the hierarchical organization of small and large particles assembled by a binder consisting of aluminum oxide.
  • the distances D large s and D pe t es and the surface percentages Sg ra sses and Suites are essential criteria for obtaining the hierarchical organization of said small and large particles and are consistent with those of the material of the invention.
  • the textural properties of the material obtained are related to the textural properties of the micrometric alumina particles and are consistent with the expected properties of the material according to the invention.
  • the hierarchical organization makes it possible to increase the mesoporous volume of the material, by maximizing the proportion of micrometric particles with respect to the binder content.
  • the hierarchical organization also makes it possible to have good sliding of the small and large micrometric alumina particles relative to each other, which results in a low mixing torque of the order of 12 Nm.
  • Example 4 preparation of an alumina-based material, in the form of a millimetric, porous object, with a single class of micrometric particles assembled by a binder consisting of aluminum oxide and prepared at a ratio of high acid of 61% by weight.
  • micrometric and porous alumina particles come from the powder Puralox SCfa-140 referenced (Sasol) whose characteristics are described in Example 1.
  • the solid precursor of alumina is the boehmite referenced Pural SB3 (Sasol), also used in Example 1.
  • the conditions for mixing the alumina particles with the solid alumina precursor and the acid solution, the mixing conditions, the extrusion shaping and the heat treatments, are identical to those described in Example 1, but with 2 powders instead of 3 powders.
  • the proportions of micrometric particles of alumina and alumina solid precursor relative to the total amount of solid are respectively 74 and 26% by weight.
  • the ratio of acid (mass of introduced nitric acid) / (mass of solid precursor of alumina) ⁇ 100 used is 61%.
  • a lower mechanical resistance is observed with respect to the materials of Examples 1, 2 and 3 according to the invention because of the presence of a single class of micrometric alumina particles, which also leads to a mesoporous volume and a specific surface area. BET lower compared to the examples according to the invention. A higher macroporous volume is also observed because of the lack of hierarchical organization of small and large particles in this material. The sliding of the micrometric particles of alumina with respect to each other is less favored which results in a mixing torque of the order of 20 Nm.
  • Example 5 (Comparative !: Preparation of an Alumina-Based Material, in the form of a Porous Millimetric Object, with a Single Class of Micrometric Particles Assembled by a Binder of Aluminum Oxide and Prepared at a Density Ratio weak acid of 2.37% weight.
  • micrometric and porous alumina particles come from the powder Puralox SCfa-140 referenced (Sasol) whose characteristics are described in Example 1.
  • the solid precursor of alumina is the boehmite referenced Pural SB3 (Sasol), also used in Example 1.
  • the mixing conditions of the alumina particles with the solid alumina precursor and the acid solution, the mixing conditions, the extrusion shaping and the heat treatments, are identical to those described in Example 4, but with 2 powders instead of 3 powders.
  • the proportions of micrometric particles of alumina and alumina solid precursor relative to the total amount of solid are respectively 74 and 26% by weight.
  • the ratio of acid (mass of introduced nitric acid) / (mass of solid precursor of alumina) ⁇ 100 used is 2.37%.
  • a lower mechanical resistance is observed with respect to the materials of Examples 1, 2 and 3 according to the invention because of the presence of a single class of micrometric particles of alumina and a binder prepared with a low acid ratio.
  • a higher macroporous volume is also observed because of the lack of hierarchical organization of small and large particles in this material.
  • Examples 1 to 3 according to the invention having both a hierarchical organization of small and large particles of alumina and comprising a binder consisting of aluminum oxide prepared at a high acid ratio, have increased mechanical properties compared to the material of the prior art (Example 5) or low acid level (Example 4).
  • the hierarchical organization also makes it possible to increase the mesoporous volume of the material, thanks to a maximization of the proportion of micrometric particles with respect to the binder content (Examples 1 to 3). Even higher textural properties can be achieved from the use of micrometer particles of high porosity alumina.

Abstract

The invention relates to a material in the form of a millimeter-scale object consisting of: large alumina particles having a median diameter of between 10 and 200 pm, said large particles being separated, from one interface to the other, by at least 10 pm; small alumina particles having a median diameter of between 0.5 and 10 pm, said small particles being separated, from one interface to the other, by at least 5 pm and located in the space between the large particles; and a binder consisting of aluminum oxide, said binder being located in the space between said small and large particles, said material having a mesoporous volume, measured by mercury porosimetry, of between 0.2 and 2 mL/g, a macroporous volume, measured by mercury porosimetry, of between 0.05 and 0.2 mL/g, and a BET specific surface area of between 90 and 350 m2/g.

Description

MATERIAU A BASE D'ALUMINE A STRUCTURE MULTIECHELLE, COMPRENANT UN LIANT OXYDE D'ALUMINIUM AYANT UNE BONNE RESISTANCE MECANIQUE ET SON PROCEDE DE PREPARATION  ALUMINA MATERIAL HAVING A MULTI-HELL STRUCTURE, COMPRISING AN ALUMINUM OXIDE BINDER HAVING GOOD MECHANICAL RESISTANCE AND PROCESS FOR PREPARING THE SAME
DOMAINE TECHNIQUE TECHNICAL AREA
La présente invention se rapporte au domaine des matériaux à base d'alumine, sous la forme d'objet millimétrique, poreux et ayant une bonne résistance mécanique. Plus précisément, elle se rapporte à un matériau à structure multiéchelle résultant d'un assemblage hiérarchisé de petites et grosses particules préférentiellement sphériques, micrométriques et poreuses à base d'alumine et d'un liant constitué d'oxyde d'aluminium ainsi qu'à son procédé de préparation. The present invention relates to the field of alumina-based materials, in the form of a millimetric object, porous and having good mechanical strength. More specifically, it relates to a multiscale structure material resulting from a hierarchical assembly of small and large particles preferentially spherical, micrometric and porous alumina-based and a binder consisting of aluminum oxide as well as its preparation process.
ART ANTERIEUR PRIOR ART
Les matériaux à base d'alumine constitués au maximum d'une seule classe de particules rassemblées par un liant, sous forme d'objet millimétrique et poreux sont largement décrits dans l'art antérieur tel que par exemple dans le brevet US6780817. Les particules qui constituent ces matériaux sont des particules d'alumine ou des particules provenant des précurseurs solides de l'alumine (oxydes, oxyhydroxydes ou hydroxydes d'aluminium), et dans ce cas qui ne se dispersent pas au cours du procédé de mise en forme, et qui seront donc présentes au sein du matériau final. Le liant utilisé est également un précurseur solide d'alumine mais avec une meilleure capacité de dispersion que celles des particules, au cours du procédé de mise en forme. Les propriétés texturales (surface spécifique BET, volume mésoporeux et macroporeux, diamètre des mésopores) du matériau sont directement liées aux propriétés texturales des particules et du liant employés dans la préparation desdits matériaux. Par ailleurs, les volumes mésoporeux et macroporeux sont influencés par la quantité de particules et de liant. En fait, un important volume macroporeux peut être obtenu si la teneur en liant est faible, et dans ce cas les propriétés mécaniques du matériau sont fortement dégradées. Une amélioration de la tenue mécanique peut être recherchée par l'augmentation de la teneur en liant, ce qui implique une diminution du volume macroporeux mais également une diminution de la quantité de particules au sein du matériau. Dans ce cas, la mésoporosité du matériau peut être dégradée du fait d'une faible quantité de particules poreuses, et par conséquent, la mésoporosité apportée au matériau et provenant desdites particules est moins importante. Les caractéristiques des mésopores sont attribuées à l'organisation des cristallites d'alumine qui dépend du procédé de préparation et notamment de la synthèse du précurseur d'alumine ou de la mise sous forme d'objet millimétrique. L'amélioration des propriétés texturales desdites particules telles que l'augmentation de la surface spécifique, du volume mésoporeux ou de la taille des mésopores peut être recherchée et obtenue par synthèse ou traitement post-synthèse. Cependant ces caractéristiques se dégradent partiellement au cours de la mise en forme.  The alumina-based materials made up of at most a single class of particles bound together by a binder, in the form of a millimetric and porous object, are widely described in the prior art such as, for example, in patent US6780817. The particles that constitute these materials are particles of alumina or particles originating from solid precursors of alumina (oxides, oxyhydroxides or aluminum hydroxides), and in this case which do not disperse during the process of setting form, and which will therefore be present within the final material. The binder used is also a solid precursor of alumina but with a better dispersion capacity than those of the particles, during the forming process. The textural properties (BET surface area, mesoporous and macroporous volume, mesopore diameter) of the material are directly related to the textural properties of the particles and the binder used in the preparation of said materials. In addition, the mesoporous and macroporous volumes are influenced by the amount of particles and binder. In fact, a large macroporous volume can be obtained if the binder content is low, and in this case the mechanical properties of the material are strongly degraded. An improvement in the mechanical strength can be sought by increasing the binder content, which implies a decrease in the macroporous volume but also a decrease in the amount of particles within the material. In this case, the mesoporosity of the material may be degraded due to a small amount of porous particles, and therefore the mesoporosity provided to the material and from said particles is less important. The characteristics of the mesopores are attributed to the organization of the alumina crystallites which depends on the preparation process and in particular on the synthesis of the alumina precursor or on the forming of millimetric objects. The improvement of the textural properties of said particles such as the increase of the specific surface area, the mesoporous volume or the size of the mesopores may be sought and obtained by synthesis or post-synthesis treatment. However, these characteristics partially degrade during formatting.
OBJET ET INTÉRÊT DE L'INVENTION OBJECT AND INTEREST OF THE INVENTION
La présente invention porte sur un matériau à base d'alumine, sous forme d'objet millimétrique, à structure multiéchelle, poreux et ayant une bonne résistance mécanique qui résulte d'un assemblage hiérarchisé de petites et grosses particules micrométriques et poreuses à base d'alumine et d'un liant constitué d'oxyde d'aluminium assurant la cohésion dudit matériau et sur son procédé de préparation. The present invention relates to a material based on alumina, in millimetric object form, with a multiscale structure, porous and having a good mechanical strength which results from an assembly hierarchical structure of small and large micrometric and porous particles based on alumina and a binder consisting of aluminum oxide ensuring the cohesion of said material and on its preparation process.
L'intérêt de l'invention porte sur l'organisation hiérarchisée de petites et grosses particules i micrométriques poreuses d'alumine, qui permet de maximiser la teneur de particules au sein du matériau et par conséquent, d'augmenter le volume mésoporeux dudit matériau. L'organisation hiérarchisée permet également de minimiser la quantité de liant car l'espace entre les grosses particules est rempli par les petites particules, et par conséquent, la teneur en liant nécessaire pour assurer la cohésion du matériau est minimisée. Ce liant permet d'assurer un volume macroporeux i minimal mais suffisant pour l'accessibilité à la porosité desdites particules micrométriques. D'autre part, l'organisation hiérarchisée assure des propriétés mécaniques convenables. Par ailleurs, une amélioration de ces propriétés peut être obtenue par l'emploi d'un liant spécifique. The interest of the invention relates to the hierarchical organization of small and large micrometric porous particles of alumina, which makes it possible to maximize the content of particles within the material and consequently to increase the mesoporous volume of said material. The hierarchical organization also minimizes the amount of binder because the space between the large particles is filled by the small particles, and therefore, the binder content necessary to ensure the cohesion of the material is minimized. This binder makes it possible to ensure a macroporous volume that is minimal but sufficient for accessibility to the porosity of said micrometric particles. On the other hand, the hierarchical organization ensures proper mechanical properties. Moreover, an improvement of these properties can be obtained by the use of a specific binder.
En particulier, un objet de la présente invention concerne un matériau, sous forme d'objet i millimétrique, constitué de grosses particules d'alumine présentant un diamètre médian compris entre 10 et 200 pm, lesdites grosses particules étant distantes, d'une interface à l'autre, de moins de 10 pm, de petites particules d'alumine présentant un diamètre médian compris entre 0,5 et 10 μιτι, lesdites petites particules étant distantes, d'une interface à l'autre, de moins de 5 pm et étant localisées dans l'espace entre les grosses particules, et d'un liant constitué d'oxyde d'aluminium, ledit liant étant i localisé dans l'espace entre lesdites petites et grosses particules, ledit matériau présentant un volume mésoporeux, mesuré par porosimétrie au mercure, compris entre 0,2 et 2 mL/g, un volume macroporeux, mesuré par porosimétrie au mercure, compris entre 0,05 et 0,2 ml_/g et une surface spécifique BET comprise entre 90 et 350 m2/g. In particular, an object of the present invention relates to a material, in the form of a millimetric object, consisting of large particles of alumina having a median diameter of between 10 and 200 μm, said large particles being distant, from an interface to the other, less than 10 μm, small particles of alumina having a median diameter of between 0.5 and 10 μιτι, said small particles being distant, from one interface to another, of less than 5 μm and being located in the space between the large particles, and a binder consisting of aluminum oxide, said binder being located in the space between said small and large particles, said material having a mesoporous volume, measured by porosimetry to a mercury content of between 0.2 and 2 ml / g, a macroporous volume, measured by mercury porosimetry, of between 0.05 and 0.2 ml / g and a BET specific surface area of between 90 and 350 m 2 / g; .
Un autre objet de la présente invention concerne un procédé de préparation dudit matériau qui comprend au moins les étapes suivantes: Another object of the present invention relates to a process for preparing said material which comprises at least the following steps:
a) le mélange de 10 à 60% en poids de petites particules d'alumine de diamètre médian compris entre 0,5 et 10 pm et de 40 à 90% en poids de grosses particules d'alumine de diamètre médian compris entre 10 et 200 pm, de 5 à 50 % en poids d'un précurseur solide d'alumine, les pourcentages de petites et grosses particules d'alumine étant exprimés par rapport à la quantité totale de particules micrométriques, et le pourcentage de précurseur solide d'alumine étant exprimé par rapport à la quantité totale de solide, et d'un acide en solution choisi parmi l'acide acétique, l'acide chlorhydrique, l'acide sulfurique, l'acide formique, l'acide citrique et l'acide nitrique, seul ou en mélange, dans des proportions tel que le rapport de la masse d'acide introduit sur la masse de précurseur solide d'alumine introduit soit compris entre 2,5 et 1 15% en poids, lesdites grosses particules et petites particules d'alumine, désignées sous le terme particules micrométriques, présentant un volume mésoporeux compris entre 0,2 et 2,5 mL g, et un diamètre médian de mésopores compris entre 7 et b) la mise en forme du mélange issu de l'étape a) ; a) mixing 10 to 60% by weight of small alumina particles with a median diameter of between 0.5 and 10 μm and 40 to 90% by weight of large alumina particles with a median diameter of between 10 and 200; pm, from 5 to 50% by weight of a solid precursor of alumina, the percentages of small and large alumina particles being expressed relative to the total amount of micrometric particles, and the percentage of solid alumina precursor being expressed with respect to the total amount of solid, and an acid in solution selected from acetic acid, hydrochloric acid, sulfuric acid, formic acid, citric acid and nitric acid, alone or in a mixture, in proportions such that the ratio of the mass of acid introduced into the solid precursor mass of introduced alumina is between 2.5 and 1 15% by weight, said large particles and small particles of alumina , referred to as micrometric particles, near with a mesoporous volume of between 0.2 and 2.5 mL g, and a median mesopore diameter of between 7 and b) shaping the mixture from step a);
c) le séchage du matériau cru obtenu à l'issue de l'étape b) et ; c) drying the raw material obtained at the end of step b) and;
d) la calcination du matériau séché issu de l'étape c). d) calcination of the dried material from step c).
Un avantage de la présente invention est de fournir un matériau présentant une proportion maximisée de petites et grosses particules poreuses du fait de l'organisation hiérarchisée desdites particules au sein du matériau et donc de fournir un matériau présentant un domaine de texture très étendu, notamment un volume mésoporeux pouvant atteindre la valeur de 2mL/g largement supérieure aux valeurs de volume mésoporeux généralement observées pour des matériaux à base d'alumine constitués au maximum d'une seule classe de particules rassemblées par un liant de l'art antérieur.  An advantage of the present invention is to provide a material having a maximized proportion of small and large porous particles due to the hierarchical organization of said particles within the material and thus to provide a material having a very wide range of texture, in particular a mesoporous volume up to the value of 2mL / g much greater than the mesoporous volume values generally observed for alumina-based materials consisting of up to a single class of particles collected by a binder of the prior art.
Un autre avantage de la présente invention est de fournir un matériau présentant des propriétés de résistance mécanique accrues. Ceci est dû à l'effet combiné de l'organisation hiérarchisée des petites et grosses particules d'alumine du matériau selon l'invention et de la cohésion dudit matériau assurée par la présence d'un liant spécifique. En particulier, le matériau selon l'invention présente une résistance mécanique à l'écrasement latéral maximisée pouvant atteindre des valeurs de force très élevées, jusqu'à 100 N pour un matériau selon l'invention de forme cylindrique, de diamètre égal à 2 mm et de longueur égale à 4 mm, qui sont des valeurs de force largement supérieures à celles observées pour des matériaux à base d'alumine constitués d'une seule classe de particules rassemblées par un liant de l'art antérieur. Another advantage of the present invention is to provide a material having enhanced strength properties. This is due to the combined effect of the hierarchical organization of the small and large particles of alumina material according to the invention and the cohesion of said material provided by the presence of a specific binder. In particular, the material according to the invention has a maximized lateral crushing strength up to very high values of force, up to 100 N for a material according to the invention of cylindrical shape, with a diameter of 2 mm. and of length equal to 4 mm, which are force values much greater than those observed for alumina materials consisting of a single class of particles collected by a binder of the prior art.
Un autre avantage de la présente invention est également de fournir un procédé de préparation permettant l'obtention dudit matériau présentant des propriétés de résistance mécanique accrues grâce au mélange dans une étape a) de particules micrométriques d'alumine avec un précurseur solide d'alumine et d'une solution acide présentant un rapport (masse d'acide introduit)/(masse de précurseur solide d'alumine introduit) très élevé, conduisant à la génération in situ d'un liant spécifique à l'issue d'une étape de calcination du matériau séché et mis en forme. Another advantage of the present invention is also to provide a method of preparation for obtaining said material having increased mechanical strength properties by mixing in a step a) micrometric particles of alumina with a solid precursor of alumina and an acidic solution having a very high ratio (introduced acid mass) / (mass of introduced alumina solid precursor), leading to the in situ generation of a specific binder at the end of a calcination step dried and shaped material.
Un autre avantage de la présente invention est également de fournir un procédé de préparation permettant : Another advantage of the present invention is also to provide a preparation method for:
un bon glissement des particules micrométriques d'alumine les unes par rapport aux autres au cours de l'étape a) de mélange ce qui limite d'une part, la dégradation des particules et permet ainsi de maintenir une grande porosité du matériau et ce qui limite d'autre part la génération de défauts micrométriques au sein du mélange et permet ainsi d'améliorer sa résistance mécanique ;  a good sliding of the micrometric particles of alumina with respect to each other during the mixing step a) which limits, on the one hand, the degradation of the particles and thus makes it possible to maintain a high porosity of the material and what on the other hand limits the generation of micrometric defects within the mixture and thus makes it possible to improve its mechanical strength;
un bon écoulement du mélange obtenu à l'étape a) au cours de l'étape b) ce qui limite la génération de défauts de géométrie et de défauts micrométriques à la surface du matériau cru améliorant ainsi l'aspect et la résistance mécanique du matériau sous forme d'objet millimétrique obtenu selon l'invention ; la formation des défauts liés à la densification du liant au cours des étapes c) et d) est minimisée du fait de sa localisation dans l'espace de faible dimension entre les particules micrométriques d'alumine ce qui améliore la résistance mécanique du matériau sous forme d'objet millimétrique obtenu selon l'invention. a good flow of the mixture obtained in step a) during step b) which limits the generation of geometric defects and micrometric defects on the surface of the raw material thus improving the appearance and strength of the material as a millimetric object obtained according to the invention; the formation of defects related to the densification of the binder during steps c) and d) is minimized because of its location in the small space between the micrometric particles of alumina which improves the mechanical strength of the material in form millimetric object obtained according to the invention.
DESCRIPTION DE L'INVENTION DESCRIPTION OF THE INVENTION
La présente invention concerne un matériau, sous forme d'objet millimétrique, constitué de grosses particules d'alumine présentant un diamètre médian compris entre 10 et 200 pm, lesdites grosses particules étant distantes, d'une interface à l'autre, de moins de 10 pm, de petites particules d'alumine présentant un diamètre médian compris entre 0,5 et 10 pm, lesdites petites particules étant distantes, d'une interface à l'autre, de moins de 5 pm et étant localisées dans l'espace entre les grosses particules et d'un liant constitué d'oxyde d'aluminium, ledit liant étant localisé dans l'espace entre lesdites petites et grosses particules, ledit matériau présentant un volume mésoporeux, mesuré par porosimétrie au mercure, compris entre 0,2 et 2 mL/g, un volume macroporeux, mesuré par porosimétrie au mercure, compris entre 0,05 et 0,2 mL/g et une surface spécifique BET comprise entre 90 et 350 m2/g. The present invention relates to a material, in the form of a millimetric object, consisting of large particles of alumina having a median diameter of between 10 and 200 μm, said large particles being distant, from one interface to another, of less than 10 μm, small alumina particles having a median diameter of between 0.5 and 10 μm, said small particles being spaced, from one interface to another, of less than 5 μm and being located in the space between the large particles and a binder consisting of aluminum oxide, said binder being located in the space between said small and large particles, said material having a mesoporous volume, measured by mercury porosimetry, of between 0.2 and 2 mL / g, a macroporous volume, measured by mercury porosimetry, of between 0.05 and 0.2 mL / g and a BET specific surface area of between 90 and 350 m 2 / g.
Dans toute la suite du texte, on entend par volume mésoporeux, le volume des pores dont le diamètre est compris entre 3,6 et 50 nm. Conformément à l'invention, le volume mésoporeux est mesuré par porosimétrie au mercure dont la méthode est décrite ci-dessous. Plus particulièrement, on entend par volume mésoporeux, un volume poreux correspondant au volume de mercure qui est rentré dans les pores de diamètre compris entre 3,6 et 50 nm. Throughout the remainder of the text, by mesoporous volume is meant the volume of pores whose diameter is between 3.6 and 50 nm. According to the invention, the mesoporous volume is measured by mercury porosimetry, the method of which is described below. More particularly, the term mesoporous volume, a pore volume corresponding to the volume of mercury which is entered into the pores with a diameter of between 3.6 and 50 nm.
Dans toute la suite du texte, on entend par volume macroporeux, le volume des pores dont le diamètre est compris entre 50 et 7000 nm. Conformément à l'invention, le volume macroporeux est mesuré par porosimétrie au mercure dont la méthode est décrite ci-dessous. Plus particulièrement, on entend par volume macroporeux, un volume poreux correspondant au volume de mercure qui est rentré dans les pores de diamètre compris entre 50 et 7000 nm. Throughout the remainder of the text, the term macroporous volume, the volume of pores whose diameter is between 50 and 7000 nm. According to the invention, the macroporous volume is measured by mercury porosimetry, the method of which is described below. More particularly, by macroporous volume, a pore volume corresponding to the volume of mercury which is entered into the pores with a diameter of between 50 and 7000 nm.
Dans toute la suite du texte, on entend par volume mesuré par porosimétrie au mercure, le volume mesuré par la technique de pénétration du mercure dans laquelle on applique la loi de Kelvin- Washburn qui donne la relation entre la pression, le diamètre du plus petit pore dans lequel le mercure pénètre à ladite pression, l'angle de mouillage et la tension superficielle selon la formule : P = (4ycos9)/d, dans laquelle γ est la tension superficielle, Θ est l'angle de mouillage du mercure avec le matériau, d représente le diamètre du pore, et P la pression. La porosimétrie au mercure est réalisée selon la norme ASTM D4284-83, utilisant une tension de surface de 480 dyne/cm et un angle de contact de 140°. L'angle de mouillage a été pris égal à 140° en suivant les recommandations de l'ouvrage "Techniques de l'Ingénieur, traité analyse et caractérisation, P 1050-5, écrites par Jean Charpin et Bernard Rasneur". Throughout the rest of the text, the volume measured by mercury porosimetry is the volume measured by the mercury penetration technique in which the Kelvin-Washburn law is applied, which gives the relationship between the pressure and the diameter of the smallest pore in which the mercury penetrates at said pressure, the wetting angle and the surface tension according to the formula: P = (4ycos9) / d, wherein γ is the surface tension, Θ is the wetting angle of the mercury with the material, d represents the diameter of the pore, and P the pressure. Mercury porosimetry is performed according to ASTM D4284-83, using a surface tension of 480 dyne / cm and a contact angle of 140 °. The wetting angle was taken as 140 ° following the recommendations of the book "Techniques of the Engineer, analyzed analysis and characterization, P 1050-5, written by Jean Charpin and Bernard Rasneur".
Dans toute la suite du texte, on entend par surface spécifique BET, une surface spécifique déterminée 5 par adsorption d'azote conformément à la norme ASTM D 3663-78 établie à partir de la méthode BET (Brunauer - Emmett - Teller) décrite dans le périodique "The Journal of the American Society", 60, 309 (1938). Throughout the rest of the text, BET specific surface area is understood to mean a specific surface area determined by nitrogen adsorption according to ASTM D 3663-78 established from the BET method (Brunauer-Emmett-Teller) described in US Pat. Periodical "The Journal of the American Society", 60, 309 (1938).
Les grosses particules et les petites particules d'alumine qui constituent le matériau selon l'invention 10 sont, de part leur taille, des particules micrométriques. The large particles and the small particles of alumina which constitute the material according to the invention are, by their size, micrometric particles.
Le matériau selon la présente invention est avantageusement constitué de l'organisation hiérarchisée de petites et de grosses particules micrométriques poreuses d'alumine.  The material according to the present invention is advantageously constituted by the hierarchical organization of small and large micrometric porous particles of alumina.
Le terme "particules micrométriques" désigne dans toute la suite du texte l'ensemble des grosses et des petites particules. La quantité totale de particules micrométriques est donc la somme des grosses The term "micrometric particles" refers throughout the text to all large and small particles. The total amount of micrometric particles is therefore the sum of the large
15 et des petites particules d'alumine. And small alumina particles.
Lesdites particules micrométriques qui constituent le matériau selon l'invention, sont des alumines de transition. En particulier, les particules micrométriques d'alumine sont des alumines de transition choisies parmi l'alumine chi, kappa, rho, eta, thêta, gamma et delta, seules ou en mélange, et de préférence l'alumine de transition est l'alumine gamma.  Said micrometric particles which constitute the material according to the invention are transition aluminas. In particular, the micrometric alumina particles are transition aluminas chosen from chi, kappa, rho, eta, theta, gamma and delta alumina, alone or as a mixture, and preferably the transition alumina is alumina. gamma.
20 Les petites et les grosses particules ou particules micrométriques qui constituent le matériau selon la présente invention sont avantageusement des particules poreuses. De préférence, lesdites particules sont de forme arrondie et de manière encore plus préférée de forme sphérique.  The small and large particles or micrometric particles which constitute the material according to the present invention are advantageously porous particles. Preferably, said particles are of rounded shape and even more preferably of spherical shape.
Lesdites petites et les grosses particules sont avantageusement des agglomérats de cristallites >5 nanométriques d'alumine. Ces cristallites se présentent sous forme de plaquettes, de fibres ou de "blocs" dont les dimensions sont avantageusement comprises entre 2 et 150 nm, de préférence entre 4 et 150 nm et de manière préférée entre 4 et 100 nm. Said small and large particles are advantageously agglomerates of> 5 nanometer crystallites of alumina. These crystallites are in the form of platelets, fibers or "blocks" whose dimensions are advantageously between 2 and 150 nm, preferably between 4 and 150 nm and preferably between 4 and 100 nm.
Les cristallites d'alumine sont les entités élémentaires qui constituent les particules micrométriques. ?0 L'espace inter-cristallites est responsable de la présence de la mésoporosité au sein même desdites particules. The crystallites of alumina are the elementary entities which constitute the micrometric particles. The inter-crystallite space is responsible for the presence of the mesoporosity within said particles.
La taille des agglomérats de cristallites qui constituent les particules micrométriques est analysée par microscopie électronique à balayage (MEB). En particulier, la taille moyenne des agglomérats de cristallites qui constituent les particules micrométriques, est déterminée à partir d'images de 55 microscopie électronique à balayage (MEB) du matériau selon l'invention à l'aide du logiciel SMile View. Les images MEB doivent être réalisées sur le matériau en mode fracture et avec un détecteur d'électrons secondaires. Conformément à l'invention, les grosses particules d'alumine constituant le matériau selon l'invention présentent un diamètre médian compris entre 10 et 200 pm, de préférence entre 10 et 100 pm et de manière préférée entre 10 et 80 pm. Le terme "diamètre médian" désigne le D50, c'est-à-dire le diamètre du disque équivalent tel que 50 % en nombre desdites grosses particules a une taille inférieure audit diamètre. The size of the crystallite agglomerates constituting the micrometric particles is analyzed by scanning electron microscopy (SEM). In particular, the average size of the crystallite agglomerates constituting the micrometric particles is determined from scanning electron microscopy (SEM) images of the material according to the invention using SMile View software. SEM images must be made on the material in fracture mode and with a secondary electron detector. According to the invention, the large particles of alumina constituting the material according to the invention have a median diameter of between 10 and 200 μm, preferably between 10 and 100 μm, and preferably between 10 and 80 μm. The term "median diameter" refers to the D50, i.e., the diameter of the equivalent disc such that 50% by number of said coarse particles has a size less than said diameter.
La distribution de la granulométrie desdites grosses particules d'alumine au sein du matériau selon l'invention est représentée par la dimension DX, définie comme étant le diamètre du disque équivalent tel que X % en nombre desdites grosses particules a une taille inférieure audit diamètre. Plus précisément, la distribution de la granulométrie desdites grosses particules est avantageusement représentée par les trois dimensions D10, D50 et D90.  The distribution of the particle size of said large particles of alumina within the material according to the invention is represented by the dimension DX, defined as the diameter of the equivalent disc such that X% in number of said large particles has a size less than said diameter. More precisely, the distribution of the particle size of said large particles is advantageously represented by the three dimensions D10, D50 and D90.
Ledit matériau selon l'invention présente avantageusement une distribution de la granulométrie desdites grosses particules d'alumine au sein dudit matériau tel que le diamètre D 0 est au plus 3 fois inférieur au diamètre médian D50 et de préférence au plus 2 fois inférieur au diamètre médian D50 et tel que le diamètre D90 est au plus 3 fois supérieur au diamètre médian D50 et de préférence au plus 2 fois supérieur au diamètre médian D50.  Said material according to the invention advantageously has a distribution of the particle size of said large particles of alumina within said material such that the diameter D 0 is at most 3 times lower than the median diameter D 50 and preferably at most 2 times smaller than the median diameter D50 and such that the diameter D90 is at most 3 times greater than the median diameter D50 and preferably at most 2 times greater than the median diameter D50.
Le diamètre des grosses particules est déterminé, dans le matériau selon l'invention, à partir d'images de microscopie électronique à balayage (MEB) du matériau selon l'invention, sur section polie, à l'aide du logiciel SMile View. Le diamètre médian est calculé à partir de la moyenne des diamètres déterminés sur un nombre de mesures que l'Homme de l'art juge nécessaire et suffisant et de préférence, sur au moins 200 mesures. The diameter of the large particles is determined, in the material according to the invention, from scanning electron microscopy (SEM) images of the material according to the invention, on a polished section, using the SMile View software. The median diameter is calculated from the average of the diameters determined on a number of measurements that the person skilled in the art deems necessary and sufficient and preferably on at least 200 measurements.
Conformément à l'invention, lesdites grosses particules sont distantes, d'une interface à l'autre, de moins de 10 pm, de préférence de moins de 8 pm, et de manière préférée de moins de 6 pm. According to the invention, said large particles are spaced, from one interface to another, less than 10 μm, preferably less than 8 μm, and preferably less than 6 μm.
La distance entre l'interface d'une grosse particule et l'interface de la grosse particule la plus proche, est déterminée à partir d'images de microscopie électronique à balayage (MEB) du matériau selon l'invention, sur section polie, à l'aide du logiciel SMile View. Les mesures sont réalisées sur un nombre de mesures que l'Homme de l'art juge nécessaire et suffisant et de préférence, sur 50 images afin de déterminer une distance moyenne d'une interface à l'autre. The distance between the interface of a large particle and the interface of the closest large particle is determined from scanning electron microscopy (SEM) images of the material according to the invention, on a polished section, at using the SMile View software. The measurements are made on a number of measurements that the person skilled in the art deems necessary and sufficient and preferably on 50 images in order to determine an average distance from one interface to the other.
Lesdites grosses particules présentent avantageusement un diamètre médian inférieur à 1/10 fois le diamètre moyen de la plus petite dimension du matériau selon l'invention, et de préférence inférieur à 1/50 fois le diamètre moyen de la plus petite dimension dudit matériau, afin d'assurer le remplissage complet de l'espace dudit matériau. Les grosses particules constituant le matériau selon l'invention peuvent avantageusement être composées de deux populations de particules présentant des diamètres médians distincts. Said large particles advantageously have a median diameter less than 1/10 times the mean diameter of the smallest dimension of the material according to the invention, and preferably less than 1/50 times the average diameter of the smallest dimension of said material, so to ensure complete filling of the space of said material. The large particles constituting the material according to the invention can advantageously be composed of two populations of particles having distinct median diameters.
Lesdites grosses particules peuvent éventuellement comprendre une proportion de particules, appelée particules "grosses inférieures", présentant un diamètre médian compris entre 10 et 60 pm et de préférence compris entre 15 et 30 μπι et une proportion de particules appelée particules "grosses supérieures" présentant un diamètre médian compris entre 60 et 200 pm et de préférence compris entre 100 et 180 pm. Said large particles may optionally comprise a proportion of particles, called "lower fat" particles, having a median diameter of between 10 and 60 μm and preferably between 15 and 30 μπι and a proportion of particles called "larger" particles having a median diameter of between 60 and 200 μm and preferably between 100 and 180 μm.
Dans le cas où lesdites grosses particules sont composées de particules "grosses inférieures" et de particules "grosses supérieures", ledit matériau selon l'invention présente avantageusement une distribution de la granulométrie desdites particules "grosses inférieures" d'alumine au sein dudit matériau tel que le diamètre D10 est au plus 3 fois inférieur au diamètre médian D50 et de préférence au plus 2 fois inférieur au diamètre médian D50 et tel que le diamètre D90 est au plus 3 fois supérieur au diamètre médian D50 et de préférence au plus 2 fois supérieur au diamètre médian D50 et une distribution de la granulométrie desdites particules "grosses supérieures" d'alumine au sein dudit matériau tel que le diamètre D10 est au plus 3 fois inférieur au diamètre médian D50 et de préférence au plus 2 fois inférieur au diamètre médian D50 et tel que le diamètre D90 est au plus 3 fois supérieur au diamètre médian D50 et de préférence au plus 2 fois supérieur au diamètre médian D50. Conformément à l'invention, les petites particules qui constituent le matériau selon l'invention présentent un diamètre médian compris entre 0,5 et 10 pm, de préférence entre 0,5 et 6 pm et de manière préférée, entre 0,5 et 3 pm.  In the case where said large particles are composed of "coarse" particles and "larger" particles, said material according to the invention advantageously has a distribution of the particle size of said "coarse" particles of alumina within said material such as that the diameter D10 is at most 3 times smaller than the median diameter D50 and preferably at most 2 times less than the median diameter D50 and such that the diameter D90 is at most 3 times greater than the median diameter D50 and preferably at most 2 times greater at the median diameter D50 and a distribution of the particle size of said "larger" particles of alumina in said material such that the diameter D10 is at most 3 times smaller than the median diameter D50 and preferably at most 2 times less than the median diameter D50 and such that the diameter D90 is at most 3 times greater than the median diameter D50 and preferably at most 2 times greater than the median diameter D50. According to the invention, the small particles which constitute the material according to the invention have a median diameter of between 0.5 and 10 μm, preferably between 0.5 and 6 μm and, preferably, between 0.5 and 3 μm. pm.
Le terme "diamètre médian" désigne le D50, c'est-à-dire le diamètre du disque équivalent tel que 50 % en nombre desdites petites particules a une taille inférieure audit diamètre.  The term "median diameter" refers to the D50, i.e., the diameter of the equivalent disc such that 50% by number of said small particles has a size smaller than said diameter.
La distribution de la granulométrie desdites petites particules d'alumine au sein du matériau selon l'invention est représentée par la dimension DX, définie comme étant le diamètre du disque équivalent tel que X % en nombre desdites petites particules a une taille inférieure audit diamètre. Plus précisément, la distribution de la granulométrie desdites petites particules est avantageusement représentée par les trois dimensions D10, D50 et D90. The distribution of the particle size of said small particles of alumina within the material according to the invention is represented by the dimension DX, defined as the diameter of the equivalent disk such that X% by number of said small particles has a size smaller than said diameter. More precisely, the distribution of the particle size of said small particles is advantageously represented by the three dimensions D10, D50 and D90.
Ledit matériau selon l'invention présente avantageusement une distribution de la granulométrie desdites petites particules d'alumine au sein dudit matériau tel que le diamètre D10 est au plus 3 fois inférieur au diamètre médian D50 et de préférence au plus 2 fois inférieur au diamètre médian D50 et tel que le diamètre D90 est au plus 3 fois supérieur au diamètre médian D50 et de préférence au plus 2 fois supérieur au diamètre médian D50. Said material according to the invention advantageously has a distribution of the particle size of said small particles of alumina within said material such that the diameter D10 is at most 3 times smaller than the median diameter D50 and preferably at most 2 times smaller than the median diameter D50 and such that the diameter D90 is at most 3 times greater than the median diameter D50 and preferably at most 2 times greater than the median diameter D50.
Le diamètre desdites petites particules est déterminé, dans le matériau selon l'invention, à partir d'images de microscopie électronique à balayage (MEB) du matériau selon l'invention sur section polie, à l'aide du logiciel S ile View. Le diamètre médian est calculé à partir de la moyenne des diamètres déterminés sur un nombre de mesures que l'Homme de l'art juge nécessaire et suffisant et de préférence, sur au moins 200 mesures. The diameter of said small particles is determined, in the material according to the invention, from scanning electron microscopy (SEM) images of the material according to the invention on a polished section, using the software Sile View. The median diameter is calculated from the average of the diameters determined on a number of measurements that the person skilled in the art deems necessary and sufficient and preferably on at least 200 measurements.
Conformément à l'invention, lesdites petites particules sont distantes, d'une interface à l'autre, de moins de 5 pm, de préférence de moins de 3 pm, et de manière préférée de moins de 2 pm. La distance entre l'interface d'une petite particule et l'interface de la petite particule la plus proche, est déterminée par images de microscopie électronique à balayage (MEB) du matériau selon l'invention, sur section polie, à l'aide du logiciel SMile View. Les mesures sont réalisées sur un nombre de mesures que l'Homme de l'art juge nécessaire et suffisant et de préférence, sur 50 images afin de déterminer une distance moyenne d'une interface à l'autre. According to the invention, said small particles are spaced, from one interface to another, less than 5 μm, preferably less than 3 μm, and preferably less than 2 μm. The distance between the interface of a small particle and the interface of the smallest particle closest, is determined by scanning electron microscopy (SEM) images of the material according to the invention, on a polished section, using SMile View software. The measurements are made on a number of measurements that the person skilled in the art deems necessary and sufficient and preferably on 50 images in order to determine an average distance from one interface to the other.
Lesdites petites particules présentent avantageusement un diamètre médian inférieur à 1/5 fois le diamètre médian des grosses particules, et de préférence un diamètre médian inférieur à 1/10 fois le diamètre médian des grosses particules. Ceci permet d'assurer le remplissage de l'espace entre lesdites grosses particules, lesdites petites particules étant localisées dans l'espace entre lesdites grosses particules. Said small particles advantageously have a median diameter less than 1/5 times the median diameter of the large particles, and preferably a median diameter less than 1/10 times the median diameter of the large particles. This makes it possible to fill the space between said large particles, said small particles being located in the space between said large particles.
De plus, la proportion desdites petites particules est déterminée de manière à remplir l'espace entre lesdites grosses particules. Les proportions des petites et des grosses particules d'alumine constituant le matériau selon l'invention sont exprimées en pourcentages surfaciques par rapport à la surface totale de l'image MEB du matériau selon l'invention, de manière à indiquer la surface que les petites et les grosses particules occupent au sein du matériau, ainsi que la proportion des particules grosses inférieures présentant un diamètre médian compris entre 10 et 60 μηι. Les pourcentages surfaciques des particules micrométriques sont déterminés à partir de l'analyse d'images MEB du matériau selon l'invention, sur section polie. La résolution du microscope électronique à balayage (MEB) est avantageusement adaptée au diamètre médian desdites particules micrométriques de manière à avoir une image représentative de l'ensemble du matériau selon l'invention. La surface occupée par les petites particules est déterminée de la façon suivante : le diamètre de la totalité des petites particules est mesuré à l'aide du logiciel SMile View, afin de calculer la surface occupée par chacune desdites petites particules. La somme de chacune des surfaces occupées par chacune desdites petites particules correspond à la surface totale occupée par l'ensemble desdites petites particules dans l'image MEB.  In addition, the proportion of said small particles is determined so as to fill the space between said large particles. The proportions of the small and large particles of alumina constituting the material according to the invention are expressed as surface percentages with respect to the total surface area of the SEM image of the material according to the invention, so as to indicate the area that the small and large particles occupy within the material, as well as the proportion of lower fat particles having a median diameter between 10 and 60 μηι. The surface percentages of the micrometric particles are determined from the SEM image analysis of the material according to the invention, on a polished section. The resolution of the scanning electron microscope (SEM) is advantageously adapted to the median diameter of said micrometric particles so as to have an image representative of all the material according to the invention. The area occupied by the small particles is determined as follows: the diameter of all the small particles is measured using SMile View software, in order to calculate the area occupied by each of said small particles. The sum of each of the areas occupied by each of said small particles corresponds to the total area occupied by all of said small particles in the SEM image.
La surface occupée par les grosses particules est déterminée à partir des logiciels GIMP et Analysis de la façon suivante : les bords de chacune des grosses particules sont délimités à l'aide du logiciel GIMP. La surface occupée par l'ensemble desdites grosses particules est ensuite exprimée en pourcentage à partir du logiciel Analysis. The area occupied by the large particles is determined from the GIMP and Analysis software as follows: the edges of each of the large particles are delimited using the GIMP software. The area occupied by all of said large particles is then expressed as a percentage from the Analysis software.
La proportion des petites et des grosses particules qui occupent la surface de l'image MEB du matériau selon l'invention est exprimée en pourcentage surfacique par rapport à la surface totale de l'image MEB du matériau selon l'invention. Elle est calculée selon la formule : (surface occupée par les petites ou les grosses particules / surface totale de l'image MEB) x100. Les pourcentages surfaciques sont déterminées sur un nombre d'images que l'Homme de l'art juge nécessaire et suffisant et de préférence, sur 10 images. The proportion of small and large particles occupying the surface of the SEM image of the material according to the invention is expressed as a percentage by surface area relative to the total surface area of the SEM image of the material according to the invention. It is calculated according to the formula: (area occupied by small or large particles / total area of the SEM image) x100. Percentages surface areas are determined on a number of images that the person skilled in the art deems necessary and sufficient and preferably, on 10 images.
Le pourcentage surfacique des petites particules par rapport à la surface totale de l'image MEB du 5 matériau selon l'invention est avantageusement compris entre 5 et 55%, de préférence entre 10 et 45% et de manière préférée entre 10 et 30%. Le pourcentage surfacique des grosses particules est avantageusement compris entre 35 et 85%, de préférence entre 45 et 80% et de manière préférée entre 60 et 80% par rapport à la surface totale de l'image MEB du matériau selon l'invention. Le complément de la fraction surfacique, c'est-à-dire, la somme des pourcentages surfaciques des 3 petites et des grosses particules soustraite de 100%, correspond au pourcentage surfacique occupé par le liant constitué d'oxyde d'aluminium et le vide résiduel. La présence de vide résiduel dans l'image MEB, c'est-à-dire d'espace non rempli, est liée à l'existence d'un volume macroporeux au sein du matériau. The surface percentage of the small particles relative to the total surface of the SEM image of the material according to the invention is advantageously between 5 and 55%, preferably between 10 and 45% and preferably between 10 and 30%. The surface percentage of the large particles is advantageously between 35 and 85%, preferably between 45 and 80% and preferably between 60 and 80% relative to the total surface of the SEM image of the material according to the invention. The complement of the surface fraction, that is to say, the sum of the surface percentages of the 3 small and large particles subtracted from 100%, corresponds to the surface percentage occupied by the binder consisting of aluminum oxide and the vacuum residual. The presence of residual vacuum in the SEM image, that is to say unfilled space, is related to the existence of a macroporous volume within the material.
5 Conformément à l'invention, lesdites petites particules sont localisées dans l'espace entre les grosses particules. Cet assemblage de petites et de grosses particules est à l'origine de l'organisation hiérarchisée desdites particules micrométriques au sein du matériau. Ledit matériau selon l'invention présente avantageusement une organisation hiérarchisée. According to the invention, said small particles are located in the space between the large particles. This assembly of small and large particles is at the origin of the hierarchical organization of said micrometric particles within the material. Said material according to the invention advantageously has a hierarchical organization.
L'organisation hiérarchisée desdites particules micrométriques au sein dudit matériau conduit à un ) domaine de texture très étendu, notamment de volume mésoporeux mesuré par porosimétrie au mercure sur ledit matériau compris entre 0,2 et 2 mIJg.  The hierarchical organization of said micrometric particles within said material leads to a very extensive texture domain, in particular of mesoporous volume measured by mercury porosimetry on said material of between 0.2 and 2 micrograms.
Conformément à l'invention, un liant constitué d'oxyde d'aluminium est localisé dans l'espace entre les petites et les grosses particules. De préférence, lesdites petites particules remplissent l'espace entre 5 les grosses particules et ledit liant remplit l'espace résiduel entre les petites et les grosses particules et l'espace résiduel entre les petites particules. According to the invention, a binder consisting of aluminum oxide is located in the space between small and large particles. Preferably, said small particles fill the gap between the coarse particles and said binder fills the residual space between the small and coarse particles and the residual space between the small particles.
Ledit liant remplit l'espace entre lesdites particules micrométriques de manière à assurer la cohésion du matériau selon l'invention, et par conséquent, de manière à minimiser le vide résiduel, c'est-à-dire l'espace non rempli entre lesdites particules micrométriques. L'existence de vide résiduel est Said binder fills the space between said micrometric particles so as to ensure the cohesion of the material according to the invention, and consequently, so as to minimize the residual vacuum, that is to say the unfilled space between said particles micrometric. The existence of residual vacuum is
) responsable de la présence d'un volume macroporeux au sein du matériau. ) responsible for the presence of a macroporous volume within the material.
Le liant présent dans l'espace entre les particules micrométriques permet de minimiser le volume macroporeux au sein du matériau selon l'invention de sorte que ledit volume macroporeux dudit matériau soit compris entre 0,05 et 0,2 mL/g, de préférence compris entre 0,07 et 0,17 mL/g, et de manière préférée compris entre 0,1 et 0,15 mL/g.  The binder present in the space between the micrometric particles makes it possible to minimize the macroporous volume within the material according to the invention so that said macroporous volume of said material is between 0.05 and 0.2 mL / g, preferably included between 0.07 and 0.17 ml / g, and preferably between 0.1 and 0.15 ml / g.
> Par ailleurs, le liant ne doit pas perturber l'organisation hiérarchisée de petites et grosses particules, c'est-à-dire, que le liant ne doit pas éloigner les particules micrométriques les unes des autres.  > Moreover, the binder must not disturb the hierarchical organization of small and large particles, that is to say, that the binder must not move micrometric particles away from each other.
Ainsi, ledit liant permet de maintenir une distance d'une interface à l'autre entre les petites particules inférieure à 5 pm, de préférence inférieure à 3 pm, et de manière préférée inférieure à 2 pm, et une distance d'une interface à l'autre entre les grosses particules inférieure à 10 μηι, de préférence inférieure à 8 pm et de manière préférée inférieure à 6 pm. Ainsi, la cohésion des particules micrométriques est assurée par la présence dudit liant constitué d'oxyde d'aluminium. Thus, said binder makes it possible to maintain a distance from one interface to another between the small particles of less than 5 μm, preferably less than 3 μm, and preferably less than 2 μm, and distance from one interface to another between coarse particles less than 10 μm, preferably less than 8 μm and preferably less than 6 μm. Thus, the cohesion of the micrometric particles is ensured by the presence of said binder consisting of aluminum oxide.
Ledit liant se présente avantageusement, dans le matériau selon l'invention, sous la forme de particules ayant une taille moyenne inférieure à 1 pm. La taille des particules constituant le liant peut avantageusement être mesurée, dans le matériau selon l'invention, par analyse d'images MEB du matériau selon l'invention, avec l'aide du logiciel SMile View. Les images MEB doivent être réalisées sur le matériau selon l'invention en mode fracture et avec un détecteur d'électrons secondaires. Said binder is advantageously present in the material according to the invention in the form of particles having a mean size of less than 1 μm. The size of the particles constituting the binder can advantageously be measured, in the material according to the invention, by SEM image analysis of the material according to the invention, with the aid of SMile View software. The SEM images must be made on the material according to the invention in fracture mode and with a secondary electron detector.
Conformément à l'invention, ledit matériau présente un volume mésoporeux mesuré par porosimétrie au mercure compris entre 0,2 et 2 ml_/g, de préférence compris entre 0,25 et 1 ,5 mL/g et de manière préférée compris entre 0,25 et 1 ,0 mL g. According to the invention, said material has a mesoporous volume measured by mercury porosimetry of between 0.2 and 2 ml / g, preferably between 0.25 and 1.5 ml / g and preferably between 0, 25 and 1.0 mL g.
Conformément à l'invention, ledit matériau présente un volume macroporeux mesuré par porosimétrie au mercure compris entre 0,05 et 0,2 ml_/g, de préférence compris entre 0,07 et 0,17 ml_/g et de manière préférée compris entre 0,1 et 0,15 mL/g.  According to the invention, said material has a macroporous volume measured by mercury porosimetry of between 0.05 and 0.2 ml / g, preferably between 0.07 and 0.17 ml / g and preferably between 0.1 and 0.15 mL / g.
De préférence, ledit matériau présente un diamètre médian des mésopores mesuré par porosimétrie au mercure compris entre 8 et 25 nm, de préférence compris entre 10 et 25 nm et de manière préférée compris entre 10 et 23 nm.  Preferably, said material has a median mesopore diameter measured by mercury porosimetry between 8 and 25 nm, preferably between 10 and 25 nm and preferably between 10 and 23 nm.
Conformément à l'invention, ledit matériau présente une surface spécifique BET comprise entre 90 et 350 m2/g, de préférence comprise entre 100 et 300 m2/g et de manière préférée comprise entre 30 et 280 m2/g. According to the invention, said material has a BET specific surface area of between 90 and 350 m 2 / g, preferably between 100 and 300 m 2 / g and preferably between 30 and 280 m 2 / g.
Conformément à l'invention, ledit matériau se présente sous la forme d'un objet millimétrique. De préférence, le diamètre moyen de la plus petite dimension du matériau selon l'invention est avantageusement compris entre 0,5 et 10 mm, de préférence entre 0,7 et 5 mm, et de manière préférée entre 1 ,0 et 4,0 mm. Les dimensions de l'objet millimétrique peuvent être obtenues avec n'importe quel outil de mesure adapté aux dimensions dudit matériau et notamment avec un pied à coulisse.  According to the invention, said material is in the form of a millimeter object. Preferably, the mean diameter of the smallest dimension of the material according to the invention is advantageously between 0.5 and 10 mm, preferably between 0.7 and 5 mm, and preferably between 1.0 and 4.0. mm. The dimensions of the millimetric object can be obtained with any measuring tool adapted to the dimensions of said material and in particular with a vernier caliper.
Ledit matériau se présente avantageusement sous forme de granule ou d'extrudé et de préférence sous forme d'extrudé.  Said material is advantageously in the form of a granule or an extrusion and preferably in the form of an extrudate.
Le matériau selon l'invention présente ainsi des proportions maximisées en particules micrométriques poreuses du fait de cette organisation hiérarchisée, résultant en un matériau poreux et ayant une bonne résistance mécanique. The material according to the invention thus has maximized proportions of micrometric particles porous because of this hierarchical organization, resulting in a porous material and having good mechanical strength.
Le matériau selon la présente invention possède d'excellentes propriétés de résistance mécanique. Ceci est dû à l'effet combiné de l'organisation hiérarchisée des petites et grosses particules d'alumine du matériau selon l'invention et de la cohésion dudit matériau assurée par la présence d'un liant spécifique. En particulier, le matériau selon l'invention présente une résistance mécanique à l'écrasement latéral déterminée par le test d'écrasement grain à grain (EGG) avantageusement comprise entre 50 et 100 N, de préférence comprise entre 60 et 100 N et de manière préférée comprise entre 80 et 100 N, exprimée en force dans le cas des matériaux selon l'invention sous forme de granules, et une résistance mécanique à l'écrasement latéral avantageusement comprise entre 0,8 et 2,5 daN/mm, de préférence comprise entre 0,85 et 2 daN/mm et de manière préférée comprise entre 0,85 et 1 ,8 daN/mm, exprimée en force par unité de longueur dans le cas des matériaux selon l'invention sous forme d'extrudés. The material according to the present invention has excellent strength properties. This is due to the combined effect of the hierarchical organization of small and large particles of alumina of the material according to the invention and the cohesion of said material provided by the presence of a specific binder. In particular, the material according to the invention has a mechanical resistance to lateral crushing determined by the grain-to-grain (EGG) crushing test advantageously between 50 and 100 N, preferably between 60 and 100 N and so preferred between 80 and 100 N, expressed by force in the case of the materials according to the invention in the form of granules, and a mechanical resistance to lateral crushing advantageously between 0.8 and 2.5 daN / mm, preferably between 0.85 and 2 daN / mm and preferably between 0.85 and 1.8 daN / mm, expressed in force per unit length in the case of the materials according to the invention in the form of extrudates.
On entend par résistance mécanique à l'écrasement latéral, la résistance mécanique du matériau selon l'invention déterminée par le test d'écrasement grain à grain (EGG). Il s'agit d'un test normalisé (norme ASTM D4179-01) qui consiste à soumettre un matériau sous forme d'objet millimétrique, comme une granule ou un extrudé, à une force de compression générant la rupture. Ce test est donc une mesure de la résistance en traction du matériau. L'analyse est répétée sur un certain nombre de solides pris individuellement et typiquement sur un nombre de solides compris entre 10 et 200. La moyenne des forces latérales de rupture mesurées constitue l'EGG moyen qui est exprimé dans le cas des granules en unité de force (N), et dans le cas des extrudés en unité de force par unité de longueur (daN/mm). By mechanical resistance to lateral crushing, the mechanical strength of the material according to the invention determined by the grain-to-grain (GGE) crushing test. This is a standardized test (ASTM D4179-01) that involves subjecting a material in the form of a millimeter object, such as a granule or extrusion, to a compressive force that causes the rupture. This test is therefore a measure of the tensile strength of the material. The analysis is repeated on a number of solids taken individually and typically on a number of solids between 10 and 200. The average of the lateral forces of rupture measured is the average EGG which is expressed in the case of the granules in unit of force (N), and in the case of extrusions in unit of force per unit length (daN / mm).
Procédé de préparation Preparation process
Un autre objet de la présente invention concerne un procédé de préparation dudit matériau comprenant au moins les étapes suivantes :  Another subject of the present invention relates to a process for preparing said material comprising at least the following steps:
a) le mélange de 10 à 60% en poids de petites particules d'alumine de diamètre médian compris entre 0,5 et 10 μηι et de 40 à 90% en poids de grosses particules d'alumine de diamètre médian compris entre 10 et 200 μιτι, de 5 à 50 % en poids d'un précurseur solide d'alumine, les pourcentages de petites et grosses particules d'alumine étant exprimés par rapport à la quantité totale de particules micrométriques, et le pourcentage de précurseur solide d'alumine étant exprimé par rapport à la quantité totale de solide, et d'un acide en solution choisi parmi l'acide acétique, l'acide chlorhydrique, l'acide sulfurique, l'acide formique, l'acide citrique et l'acide nitrique, seul ou en mélange, dans des proportions tel que le rapport de la masse d'acide introduit sur la masse de précurseur solide d'alumine introduit soit compris entre 2,5 et 115% en poids, lesdites grosses particules et petites particules d'alumine, désignées sous le terme particules micrométriques, présentant un volume mésoporeux compris entre 0,2 et 2,5 mL/g, et un diamètre médian de mésopores compris entre 7 et 25 nm, a) mixing 10 to 60% by weight of small alumina particles with a median diameter of between 0.5 and 10 μηι and 40 to 90% by weight of large alumina particles with a median diameter of between 10 and 200; μιτι, from 5 to 50% by weight of a solid precursor of alumina, the percentages of small and large particles of alumina being expressed relative to the total amount of micrometric particles, and the percentage of solid precursor of alumina being expressed with respect to the total amount of solid, and an acid in solution selected from acetic acid, hydrochloric acid, sulfuric acid, formic acid, citric acid and nitric acid, alone or in a mixture, in proportions such that the ratio of the mass of acid introduced onto the mass of introduced alumina solid precursor is between 2.5 and 115% by weight, said large particles and small particles of alumina, referred to as micrometric particles es, having a mesoporous volume of between 0.2 and 2.5 mL / g, and a median mesopore diameter of between 7 and 25 nm,
b) la mise en forme du mélange issu de l'étape a), b) shaping the mixture resulting from step a),
c) le séchage du matériau cru obtenu à l'issue de l'étape b) et, c) drying the raw material obtained at the end of step b) and,
d) la calcination du matériau séché issu de l'étape c). Les grosses particules et les petites particules d'alumine, désignées sous le terme "particules micrométriques" utilisées dans l'étape a) de mélange du procédé de préparation selon l'invention sont avantageusement des alumines de transition choisies parmi l'alumine chi, kappa, rho, eta, thêta, gamma et delta, seules ou en mélange, et de préférence l'alumine gamma, ou sont avantageusement des précurseurs solides d'alumine choisis parmi l'hydrargillite, la gibbsite, la nordstrandite, la bayerite, la boehmite ou pseudo-boehmite. Dans le cas où les particules micrométriques sont des précurseurs solides d'alumine, lesdits précurseurs doivent être peu dispersibles dans la solution acide introduite dans l'étape a) de mélange du procédé de préparation, c'est-à-dire de manière à ce que le diamètre médian desdites particules micrométriques soit peu réduit au cours de l'étape a) et que l'organisation hiérarchisée de petites et grosses particules puisse être observée au sein du matériau à l'issue de l'étape d) de préparation selon les techniques de caractérisation décrites en détail ci-dessus. d) calcination of the dried material from step c). The large particles and the small particles of alumina, referred to as the "micrometric particles" used in the mixing step a) of the preparation process according to the invention are advantageously transition aluminas chosen from chi, kappa alumina. , rho, eta, theta, gamma and delta, alone or as a mixture, and preferably gamma-alumina, or are advantageously solid precursors of alumina selected from hydrargillite, gibbsite, nordstrandite, bayerite, boehmite or pseudo-boehmite. In the case where the micrometric particles are solid precursors of alumina, said precursors must be little dispersible in the acid solution introduced in the mixing step a) of the preparation process, that is to say in such a way that that the median diameter of said micrometric particles is little reduced during step a) and that the hierarchical organization of small and large particles can be observed within the material at the end of step d) of preparation according to the characterization techniques described in detail above.
Dans ce cas, à l'issue de l'étape d) de calcination, une transformation de phase a lieu de manière à obtenir les alumines de transition au sein dudit matériau. In this case, at the end of step d) of calcination, a phase transformation takes place so as to obtain the transition aluminas within said material.
Dans toute la suite de la description du procédé de préparation, les particules micrométriques d'alumine utilisées dans l'étape a) de mélange du procédé de préparation sont des alumines de transition ou des précurseurs solides d'alumine peu dispersibles dans la solution acide employée dans ladite étape a) du procédé de préparation, et qui seront transformés en alumine de transition à l'issue de l'étape d) de calcination.  Throughout the rest of the description of the preparation process, the micrometric alumina particles used in the mixing step a) of the preparation process are transition aluminas or solid precursors of alumina which are poorly dispersible in the acid solution used. in said step a) of the preparation process, and which will be converted to transition alumina at the end of step d) of calcination.
Dans l'étape a) de mélange du procédé de préparation selon l'invention, des petites particules d'alumine de diamètre médian compris entre 0,5 et 10 pm sont mélangées à des grosses particules d'alumine de diamètre médian compris entre 10 et 200 pm. In step a) of mixing the preparation process according to the invention, small particles of alumina with a median diameter of between 0.5 and 10 μm are mixed with large particles of alumina with a median diameter of between 10 and 200 pm.
De préférence, lesdites grosses particules d'alumine présentent un diamètre médian compris entre 10 et 100 pm et de manière préférée entre 10 et 80 pm.  Preferably, said large particles of alumina have a median diameter of between 10 and 100 μm, and preferably between 10 and 80 μm.
Lesdites grosses particules mélangées dans l'étape a) du procédé de préparation selon l'invention peuvent avantageusement être composées de deux populations de particules présentant des diamètres médians distincts.  Said large particles mixed in step a) of the preparation process according to the invention may advantageously be composed of two populations of particles having distinct median diameters.
Lesdites grosses particules peuvent éventuellement comprendre une proportion de particules, appelée particules "grosses inférieures", présentant un diamètre médian compris entre 10 et 60 pm et de préférence compris entre 15 et 30 pm et une proportion de particules appelée particules "grosses supérieures" présentant un diamètre médian compris entre 60 et 200 pm et de préférence compris entre 100 et 180 pm.  Said large particles may optionally comprise a proportion of particles, called "lower fat" particles, having a median diameter of between 10 and 60 μm and preferably between 15 and 30 μm and a proportion of particles called "larger" particles having a median diameter between 60 and 200 pm and preferably between 100 and 180 pm.
De préférence, lesdites petites particules d'alumine présentent un diamètre compris entre 0,5 et 6 pm et de manière préférée, entre 0,5 et 3 pm.  Preferably, said small alumina particles have a diameter of between 0.5 and 6 μm and preferably between 0.5 and 3 μm.
Lesdites particules micrométriques d'alumine mélangées dans l'étape a) du procédé de préparation sont avantageusement utilisées sous forme de poudre. La distribution de taille desdites particules micrométriques d'alumine au sein des poudres utilisées dans ladite étape a) de mélange est mesurée par granulométrie à diffraction laser, basée sur la théorie de la diffraction de Mie (G. B. J. de Boer, C. de Weerd, D. Thoenes, H. W. J. Goossens, Part. Charact. 4 (1987) 14-19). La distribution de la granulométrie des particules d'alumine micrométriques au sein des poudres est représentée par la dimension DvX, définie comme étant le diamètre de la sphère équivalente tel que X % en volume desdites particules a une taille inférieure audit diamètre. Plus précisément, la distribution de la granulométrie desdites particules est représentée par les trois dimensions Dv10, Dv50 et Dv90. Le terme "diamètre médian" employé dans la description du procédé de préparation selon l'invention désigne le Dv50, c'est-à-dire le diamètre de la sphère équivalente tel que 50 % en volume desdites particules a une taille inférieure audit diamètre. Said micrometric alumina particles mixed in step a) of the preparation process are advantageously used in powder form. The size distribution of said micrometric alumina particles in the powders used in said mixing step a) is measured by laser diffraction granulometry, based on the Mie diffraction theory (GBJ de Boer, C. de Weerd, D Thoenes, HWJ Goossens, Charact 4 (1987) 14-19). The distribution of the particle size of the micrometric alumina particles in the powders is represented by the dimension DvX, defined as the diameter of the equivalent sphere such that X% by volume of said particles has a size less than said diameter. More precisely, the distribution of the particle size of said particles is represented by the three dimensions Dv10, Dv50 and Dv90. The term "median diameter" used in the description of the preparation process according to the invention denotes the Dv50, that is to say the diameter of the equivalent sphere such that 50% by volume of said particles has a size less than said diameter.
La distribution de la granulométrie des petites particules est telle que le diamètre Dv10 est au plus 3 fois inférieur au diamètre médian Dv50 et de préférence au plus 2 fois inférieur au diamètre médian Dv50 et telle que le diamètre Dv90 est au plus 3 fois supérieur au diamètre médian Dv50 et de préférence au plus 2 fois supérieur au diamètre médian Dv50. The distribution of the particle size of the small particles is such that the diameter Dv10 is at most 3 times smaller than the median diameter Dv50 and preferably at most 2 times less than the median diameter Dv50 and such that the diameter Dv90 is at most 3 times greater than the diameter. median Dv50 and preferably at most 2 times greater than the median diameter Dv50.
La distribution de la granulométrie des particules grosses supérieures et la distribution de la granulométrie des particules "grosses inférieures" est avantageusement identique à la distribution de la granulométrie des petites particules.  The distribution of the particle size of the larger particles and the particle size distribution of the "coarse" particles is advantageously identical to the particle size distribution of the small particles.
Ainsi, la distribution de la granulométrie des petites particules est de préférence monomodale, et la distribution de la granulométrie des grosses particules peut être monomodale ou bimodale, dans le cas où lesdites grosses particules sont composées desdites particules grosses inférieures et grosses supérieures.  Thus, the particle size distribution of the small particles is preferably monomodal, and the particle size distribution of the coarse particles may be monomodal or bimodal, in the case where said coarse particles are composed of said larger and lower coarse particles.
Les propriétés texturales desdites particules micrométriques d'alumine, telles que la surface spécifique BET, le volume mésoporeux et le diamètre médian des mésopores, sont déterminées respectivement, par adsorption d'azote et porosimétrie au mercure. La surface spécifique BET, le volume mésoporeux et la distribution de taille des pores des particules micrométriques constituant le matériau selon l'invention peuvent être très variables en fonction du procédé de préparation du précurseur d'alumine utilisé pour préparer les particules micrométriques et des conditions opératoires. The textural properties of said micrometric alumina particles, such as the BET surface area, the mesoporous volume and the mesopore median diameter, are respectively determined by nitrogen adsorption and mercury porosimetry. The BET surface area, the mesoporous volume and the pore size distribution of the micrometric particles constituting the material according to the invention can be very variable depending on the process for preparing the alumina precursor used to prepare the micrometric particles and the operating conditions. .
Lesdites particules micrométriques présentent avantageusement une surface spécifique BET comprise entre 100 et 480 m2/g, de préférence comprise entre 120 et 300 m2/g, et de manière préférée comprise entre 120 et 250 m /g. Said micrometric particles advantageously have a BET specific surface area of between 100 and 480 m 2 / g, preferably between 120 and 300 m 2 / g, and preferably between 120 and 250 m 2 / g.
Conformément à l'invention, lesdites particules micrométriques présentent avantageusement un volume mésoporeux compris entre 0,2 et 2,5 mL g, de préférence compris entre 0,3 et 2,0 mL/g, et de manière préférée compris entre 0,3 et 1 ,5 mL/g. Conformément à l'invention, lesdites particules micrométriques présentent avantageusement un diamètre médian de mésopores compris entre 7 et 25 nm, de préférence compris entre 7 et 24 nm, et de manière préférée compris entre 7,5 et 23 nm. According to the invention, said micrometric particles advantageously have a mesoporous volume of between 0.2 and 2.5 ml of g, preferably of between 0.3 and 2.0 ml / g, and preferably of between 0.3. and 1.5 mL / g. According to the invention, said micrometric particles advantageously have a median mesopore diameter of between 7 and 25 nm, preferably between 7 and 24 nm, and preferably between 7.5 and 23 nm.
5 Les proportions en petites et grosses particules introduites dans le mélange de l'étape a) est un critère essentiel du procédé de préparation selon la présente invention car lesdites proportions définissent la compacité du mélange de petites et grosses particules. Lesdites proportions conduisent à l'organisation hiérarchisée des petites et grosses particules au sein du matériau obtenu à l'issue dudit procédé de préparation. Plus précisément, les proportions de petites et grosses particules sontThe proportions of small and large particles introduced into the mixture of step a) is an essential criterion of the preparation method according to the present invention because said proportions define the compactness of the mixture of small and large particles. Said proportions lead to the hierarchical organization of small and large particles within the material obtained at the end of said preparation process. More specifically, the proportions of small and large particles are
10 choisies de manière à avoir un mélange entre petites et grosses particules qui conduise à une compacité satisfaisante. Ladite compacité du mélange des petites et grosses particules est déterminée par une mesure classique de densité de remplissage tassée (DRT). A l'issue de cette mesure, il est possible de calculer la compacité (C) du mélange des poudres à partir de la formule : C = DRT / Dg, où DRT est la densité de remplissage tassée du mélange des poudres et Dg est la i5 densité de grain dudit mélange des poudres. A partir de la compacité (C), il est possible de déterminer la porosité (ε) du mélange des poudres où ε = 1 - C. La porosité renseigne sur le volume de vides entre les petites et les grosses particules, et par conséquent, permet de définir la proportion de liant nécessaire au remplissage de l'espace entre lesdites petites et grosses particules. Cela permet également de définir la proportion de précurseur solide d'alumine nécessaire à l'obtention de ladite10 selected so as to have a mixture of small and large particles which leads to a satisfactory compactness. Said compactness of the mixture of small and large particles is determined by a conventional packed fill density (TDD) measurement. At the end of this measurement, it is possible to calculate the compactness (C) of the mixture of powders from the formula: C = DRT / Dg, where DRT is the packed filling density of the powder mixture and Dg is the i5 grain density of said mixture of powders. From the compactness (C), it is possible to determine the porosity (ε) of the mixture of the powders where ε = 1 - C. The porosity gives information on the volume of voids between the small and the large particles, and consequently, allows to define the proportion of binder necessary to fill the space between said small and large particles. This also makes it possible to define the proportion of solid precursor of alumina necessary for obtaining said
:0 proportion en liant. : 0 proportion by binding.
Conformément à l'étape a) de mélange du procédé de préparation selon l'invention, on mélange de 10 à 60% et de préférence de 15 à 35% en poids de petites particules d'alumine de diamètre médian compris entre 0,5 et 10 m et de 40 à 90% et de préférence de 65 à 85% en poids de grosses :5 particules d'alumine de diamètre médian compris entre 10 et 200 pm, les pourcentages étant exprimés par rapport à la quantité totale de particules micrométriques. According to step a) of mixing the preparation process according to the invention, 10 to 60% and preferably 15 to 35% by weight of small alumina particles with a median diameter of between 0.5 and 10 m and 40 to 90% and preferably 65 to 85% by weight of large: alumina particles of median diameter between 10 and 200 pm, the percentages being expressed relative to the total amount of micrometer particles.
Si la proportion de grosses particules est inférieure à 40% en poids, l'organisation hiérarchisée de particules micrométriques d'alumine ne sera pas optimale compte tenu de la grande quantité de petites particules et la maximisation de la proportion de particules micrométriques d'alumine ne pourra 0 pas être atteinte du fait d'une organisation moins compacte. Par ailleurs, si la proportion de grosses particules est trop élevée et en particulier supérieure à 90% en poids, la quantité de petites particules ne sera pas suffisante pour remplir les vides entre les grosses particules, et l'organisation hiérarchisée de particules micrométriques d'alumine ne sera pas optimale du fait d'une organisation moins compacte.  If the proportion of coarse particles is less than 40% by weight, the hierarchical organization of micrometric particles of alumina will not be optimal given the large amount of small particles and the maximization of the proportion of micrometric particles of alumina. It can not be reached because of a less compact organization. On the other hand, if the proportion of large particles is too high and in particular greater than 90% by weight, the quantity of small particles will not be sufficient to fill the voids between the large particles, and the hierarchical organization of micrometric particles of Alumina will not be optimal because of a less compact organization.
5  5
Un autre critère essentiel du procédé de préparation selon l'invention est l'introduction dans l'étape a) de mélange, d'un précurseur solide d'alumine et d'un acide en solution permettant la génération in situ d'un liant constitué d'oxyde d'aluminium, après l'étape d) de calcination du procédé de préparation selon l'invention. Another essential criterion of the preparation process according to the invention is the introduction into step a) of a mixture of a solid precursor of alumina and of an acid in solution allowing the generation in situ. a binder consisting of aluminum oxide, after step d) of calcination of the preparation process according to the invention.
Par ailleurs, le précurseur solide d'alumine et l'acide en solution doivent être introduits dans ladite étape a) dans les proportions telles que revendiquées.  Moreover, the solid precursor of alumina and the acid in solution must be introduced in said step a) in the proportions as claimed.
La génération dudit liant constitué d'oxyde d'aluminium nécessite un précurseur solide d'alumine qui en présence de la solution acide soit plus réactif que les particules micrométriques d'alumine également introduites dans l'étape a) de mélange du procédé de préparation selon l'invention. En effet, le précurseur solide d'alumine doit être capable de se disperser majoritairement ou de se dissoudre majoritairement dans la solution acide employée et former des particules de taille moyenne inférieure à 1 μηι entre les particules micrométriques. En particulier, les particules micrométriques d'alumine doivent être peu dégradées en présence de ladite solution acide, c'est-à-dire que le diamètre médian desdites particules d'alumine doit être majoritairement maintenu en présence de l'acide en solution introduit au cours de l'étape a) du procédé de préparation selon l'invention.  The generation of said binder consisting of aluminum oxide requires a solid precursor of alumina which in the presence of the acidic solution is more reactive than the micrometric alumina particles also introduced in step a) of mixing the preparation process according to the invention. Indeed, the solid precursor of alumina must be capable of dispersing predominantly or dissolving predominantly in the acid solution used and forming particles of average size less than 1 μηι between the micrometric particles. In particular, the micrometric alumina particles must be slightly degraded in the presence of said acid solution, that is to say that the median diameter of said alumina particles must be maintained in the presence of the acid in solution introduced in the presence of during step a) of the preparation process according to the invention.
Le précurseur solide d'alumine est avantageusement choisi parmi les oxydes d'aluminium, les hydroxydes d'aluminium et les oxyhydroxydes d'aluminium solubles ou dispersibles dans la solution acide employée, de préférence parmi les hydroxydes d'aluminium et les oxyhydroxydes d'aluminium. De manière très préférée, ledit précurseur solide d'alumine est un oxyhydroxyde d'aluminium et de manière plus préférée ledit précurseur solide d'alumine est la boehmite ou la pseudo-boehmite. The solid precursor of alumina is advantageously chosen from aluminum oxides, aluminum hydroxides and aluminum oxyhydroxides which are soluble or dispersible in the acid solution employed, preferably from aluminum hydroxides and aluminum oxyhydroxides. . Very preferably, said solid alumina precursor is an aluminum oxyhydroxide and more preferably said solid alumina precursor is boehmite or pseudo-boehmite.
Ledit précurseur d'alumine se présente avantageusement sous forme de poudre constituée de particules solides présentant un diamètre médian, déterminé par granulométrie à diffraction laser, compris entre 9 et 80 pm, de préférence compris entre 10 et 60 pm et de manière préférée entre 15 et 45 pm. Les particules du précurseur solide d'alumine sont avantageusement constituées d'agglomérats d'unités élémentaires, dites cristallites, dont les dimensions sont avantageusement comprises entre 2 et 150 nm, de préférence entre 4 et 150 nm et de manière préférée entre 4 et 100 nm déterminées par microscopie électronique à transmission (MET). La morphologie des cristallites, la taille et la manière dont les cristallites sont organisées, dépendent principalement de la voie de synthèse du précurseur d'alumine utilisé pour préparer lesdites particules micrométriques. Said alumina precursor is advantageously in the form of a powder consisting of solid particles having a median diameter, determined by laser diffraction granulometry, of between 9 and 80 μm, preferably between 10 and 60 μm, and preferably between 15 and 45 pm. The particles of the solid precursor of alumina are advantageously constituted by agglomerates of elementary units, called crystallites, whose dimensions are advantageously between 2 and 150 nm, preferably between 4 and 150 nm and preferably between 4 and 100 nm. determined by transmission electron microscopy (TEM). The morphology of the crystallites, the size and the manner in which the crystallites are organized depend mainly on the synthesis route of the alumina precursor used to prepare said micrometric particles.
Conformément à l'étape a) du procédé de préparation selon l'invention, la proportion du précurseur solide d'alumine est comprise entre 5 et 50% en poids par rapport à la quantité totale de particules solides, de préférence entre 10 et 30% en poids, et de manière préférée entre 15 et 25% en poids. La quantité totale de particules solides est la somme des particules micrométriques (petites et grosses particules d'alumine) et des particules du précurseur solide d'alumine. According to step a) of the preparation process according to the invention, the proportion of the solid precursor of alumina is between 5 and 50% by weight relative to the total amount of solid particles, preferably between 10 and 30% by weight, and preferably between 15 and 25% by weight. The total amount of solid particles is the sum of the micrometric particles (small and large alumina particles) and particles of the solid alumina precursor.
Si la quantité de précurseur solide d'alumine est inférieure à 5% en poids par rapport à la quantité totale de particules solides introduites, la quantité de liant constitué d'oxyde d'aluminium qui sera formé in situ après l'étape d) de calcination, ne sera pas suffisante pour assurer la cohésion de l'organisation hiérarchisée des petites et grosses particules micrométriques d'alumine. Par ailleurs, si la quantité de précurseur solide d'alumine est supérieure à 50% en_ poids par rapport à la quantité totale de particules solides, la quantité de liant constitué d'oxyde d'aluminium qui sera formé in situ après l'étape d) de calcination sera supérieure à la quantité nécessaire pour remplir les vides résiduels entre les particules micrométriques, et par conséquent, les particules micrométriques seront dispersées de façon non organisée au sein dudit liant et la proportion de particules micrométriques présentes dans le matériau obtenu à l'issue du procédé de préparation selon l'invention final ne sera pas maximale. If the amount of solid precursor of alumina is less than 5% by weight relative to the total amount of solid particles introduced, the amount of aluminum oxide binder which will be formed in situ after step d) of calcination, will not be sufficient to ensure the cohesion of the hierarchical organization of small and large micrometric particles of alumina. Moreover, if the amount of solid precursor of alumina is greater than 50% by weight relative to the total amount of solid particles, the amount of aluminum oxide binder which will be formed in situ after step d) of calcination will be greater than the amount necessary to fill the residual voids between the micrometric particles, and consequently, the micrometric particles will be dispersed in an unorganized manner within said binder and the proportion of micrometric particles present in the material obtained at the end of the process of preparation according to the final invention will not be maximum.
Conformément à l'étape a) du procédé de préparation selon l'invention, un acide en solution est choisi parmi l'acide acétique, l'acide chlorhydrique, l'acide sulfurique, l'acide formique, l'acide citrique et l'acide nitrique, seul ou en mélange, est introduit, à condition qu'à l'issue de l'étape d) du procédé de préparation selon l'invention, ledit acide soit décomposé et conduise à un liant constitué d'oxyde d'aluminium. De préférence, ledit acide est l'acide nitrique.  According to step a) of the preparation process according to the invention, an acid in solution is chosen from acetic acid, hydrochloric acid, sulfuric acid, formic acid, citric acid and nitric acid, alone or as a mixture, is introduced, provided that after step d) of the preparation process according to the invention, said acid is decomposed and lead to a binder consisting of aluminum oxide . Preferably, said acid is nitric acid.
Le rôle de la solution acide est de promouvoir la dispersion des particules qui constituent le précurseur solide d'alumine. De cette manière, les particules du précurseur solide d'alumine qui ont au départ un diamètre médian de l'ordre de la dizaine du micron deviennent des particules colloïdales submicroniques, grâce à l'action de la solution acide associée à l'énergie mécanique apportée pendant l'étape a) de mélange du procédé de préparation du matériau selon l'invention. Ces particules colloïdales se ré-agrègent pour former des particules présentant une taille moyenne inférieure à 1 μπν The role of the acid solution is to promote the dispersion of the particles which constitute the solid precursor of alumina. In this way, the particles of the solid precursor of alumina which initially have a median diameter of about ten micron become submicron colloidal particles, thanks to the action of the acid solution associated with the mechanical energy provided. during step a) of mixing the process for preparing the material according to the invention. These colloidal particles re-aggregate to form particles having an average size of less than 1 μπν
Conformément à l'étape a) du procédé de préparation selon l'invention, le précurseur solide d'alumine et l'acide en solution choisi parmi l'acide acétique, l'acide chlorhydrique, l'acide sulfurique, l'acide formique, l'acide citrique et l'acide nitrique, seul ou en mélange, sont introduits dans des proportions telles que le rapport de la masse d'acide introduit sur la masse de précurseur solide d'alumine introduit soit compris entre 2,5 et 115% en poids, de préférence entre 7,4 et 74% en poids et de manière préférée, entre 30 et 62% en poids. According to step a) of the preparation process according to the invention, the solid precursor of alumina and the acid in solution chosen from acetic acid, hydrochloric acid, sulfuric acid, formic acid, the citric acid and the nitric acid, alone or as a mixture, are introduced in proportions such that the ratio of the mass of acid introduced into the solid precursor mass of introduced alumina is between 2.5 and 115% by weight, preferably between 7.4 and 74% by weight and preferably between 30 and 62% by weight.
L'emploi d'un rapport d'acide élevé (masse d'acide introduit) / (masse de précurseur solide d'alumine introduit) dans l'étape a) du procédé de préparation selon l'invention permet à la fois de bien disperser les particules présentant un diamètre médian de l'ordre de la dizaine du micron qui constituent le précurseur solide d'alumine en des particules colloïdales submicroniques, mais également, de favoriser la dissolution partielle dudit précurseur solide d'alumine et minoritairement, des particules micrométriques d'alumine. Cette dissolution à rapport d'acide élevé favorise la formation d'espèces aluminiques qui modifient la rhéologie du mélange issu de l'étape a) du procédé de préparation selon l'invention et jouent aussi le rôle de liant dans les étapes c) et d) de traitements thermiques dudit procédé de préparation. La présence d'espèces aluminiques permet d'améliorer l'adhésion entre les particules micrométriques d'alumine et le liant constitué d'oxyde d'aluminium formé à l'issue de l'étape d) de calcination. Par conséquent, ceci permet, à l'issue de l'étape d) de calcination, d'augmenter la cohésion de l'organisation hiérarchisée des petites et grosses particules micrométriques d'alumine et donc du matériau obtenu par le procédé de préparation selon l'invention. The use of a high acid ratio (mass of introduced acid) / (mass of introduced alumina solid precursor) in step a) of the preparation process according to the invention makes it possible at the same time to disperse well the particles having a median diameter of about ten micron which constitute the solid precursor of alumina in submicron colloidal particles, but also to promote the partial dissolution of said solid precursor of alumina and in a minority, micrometric particles of alumina. This high acid ratio dissolution favors the formation of alumina species which modify the rheology of the mixture resulting from stage a) of the preparation process according to the invention and also act as binders in stages c) and d). ) of heat treatments of said preparation process. The presence of aluminum species makes it possible to improve the adhesion between the micrometric particles of alumina and the binder consisting of aluminum oxide formed at the end of the step d) calcination. Consequently, this makes it possible, after step d) of calcination, to increase the cohesion of the hierarchical organization of the small and large micrometric particles of alumina and thus of the material obtained by the preparation process according to the invention. 'invention.
Dans le cas où la mise en forme du mélange issu de l'étape a) est réalisée par extrusion dans l'étape b), un liant organique peut éventuellement être ajouté dans l'étape a) de mélange. La présence dudit liant organique facilite la mise en forme par extrusion. Ledit liant organique peut avantageusement être choisi parmi le méthylcellulose, l'hydroxypropylméthylcellulose, l'hydroxyéthylcellulose, le carboxymethylcellulose et l'alcool polyvinylique. La proportion dudit liant organique est avantageusement comprise entre 0 et 5% en poids, de préférence entre 0 et 3% en poids et de manière préférée entre 0 et 1 % en poids, par rapport à la quantité totale de particules solides. In the case where the shaping of the mixture resulting from step a) is carried out by extrusion in step b), an organic binder may optionally be added in step a) of mixing. The presence of said organic binder facilitates shaping by extrusion. Said organic binder can advantageously be chosen from methylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, carboxymethylcellulose and polyvinyl alcohol. The proportion of said organic binder is advantageously between 0 and 5% by weight, preferably between 0 and 3% by weight and preferably between 0 and 1% by weight, relative to the total amount of solid particles.
A l'issue de l'étape d) de calcination du procédé de préparation selon l'invention, ledit liant organique est décomposé, c'est-à-dire qu'à l'issue de l'étape d) de calcination, ledit liant organique n'est plus présent au sein du matériau selon l'invention. At the end of step d) of calcination of the preparation process according to the invention, said organic binder is decomposed, that is to say that at the end of step d) calcination, said Organic binder is no longer present within the material according to the invention.
Le mélange de l'étape a) du procédé de préparation selon l'invention est avantageusement réalisé en une seule étape ou en deux étapes. The mixture of step a) of the preparation process according to the invention is advantageously carried out in a single step or in two steps.
En effet, la mise en oeuvre de ladite étape a) de mélange diffère selon la technique de mise en forme utilisée dans l'étape b) du procédé de préparation selon l'invention.  Indeed, the implementation of said mixing step a) differs according to the shaping technique used in step b) of the preparation process according to the invention.
Dans le cas où l'étape b) de mise en forme est réalisée par extrusion, l'étape a) de mélange est de préférence réalisée en une seule étape. Les particules micrométriques d'alumine, le précurseur solide d'alumine, l'acide en solution et éventuellement un liant organique sont mélangés en une seule fois à l'aide d'un malaxeur batch, de préférence à bras à cames ou à bras en Z, ou bien à l'aide d'un malaxeur-mélangeur bi-vis. Les conditions de malaxage sont ajustées de manière connue de l'Homme du métier et visent à obtenir une pâte homogène et extrudable. L'extrudabilité de la pâte peut avantageusement être ajustée avec l'ajout de l'eau à l'acide en solution, afin d'obtenir une pâte adaptée à la réalisation de l'étape b) de mise en forme par extrusion.  In the case where the shaping step b) is carried out by extrusion, the mixing step a) is preferably carried out in a single step. The micrometric alumina particles, the solid precursor of alumina, the acid in solution and optionally an organic binder are mixed all at once using a batch mixer, preferably with a cam or an arm. Z, or using a twin-screw mixer-mixer. The mixing conditions are adjusted in a manner known to those skilled in the art and aim to obtain a homogeneous and extrudable paste. The extrudability of the paste can advantageously be adjusted with the addition of water to the acid in solution, in order to obtain a paste suitable for carrying out the extrusion forming step b).
Dans le cas où l'étape b) de mise en forme est réalisée par granulation humide, l'étape a) de mélange est de préférence réalisée en deux étapes. Dans un premier temps, les petites et grosses particules micrométriques d'alumine sont avantageusement mélangées à sec pendant une durée comprise entre 1 et 5 min et de préférence comprise entre 2 et 4 mn. Le mélange est de préférence réalisé à l'aide d'un mélangeur tel que par exemple, un drageoir ou un tambour tournant. Le précurseur solide d'alumine et l'acide en solution sont ensuite avantageusement introduits audit mélange à sec de particules micrométriques d'alumine, sous forme d'une solution liante formée avec le précurseur solide d'alumine dispersé dans ladite solution acide. L'acide en solution et le précurseur solide d'alumine dispersé dans ladite solution acide, sont avantageusement introduits dans un deuxième temps, à l'aide d'une buse de pulvérisation, afin d'assurer la mise en contact entre les composants du mélange et permettre l'agglomération progressive des particules micrométriques d'alumine au cours de la rotation du drageoir ou du tambour tournant. L'ajout dans une deuxième étape du précurseur solide d'alumine dispersé dans l'acide en solution permet d'assurer la mise en forme par croissance granulaire humide au cours de l'étape b) de mise en forme par granulation. Les conditions de mise en 5 forme sont ajustées de manière connue de l'Homme du métier et visent à l'obtention de granules sphériques de taille souhaitée. In the case where the shaping step b) is carried out by wet granulation, the mixing step a) is preferably carried out in two steps. In a first step, the small and large micrometric particles of alumina are advantageously dry mixed for a period of between 1 and 5 min and preferably between 2 and 4 min. The mixture is preferably made using a mixer such as, for example, a bezel or a rotating drum. The solid precursor of alumina and the acid in solution are then advantageously introduced into said dry mixture of micrometric alumina particles, in the form of a binder solution formed with the solid precursor of alumina dispersed in said acidic solution. The acid in solution and the solid precursor of alumina dispersed in said acid solution are advantageously introduced in a second step, using a spray nozzle, to ensure the contact between the components of the mixture. and allow the progressive agglomeration of micrometric alumina particles during rotation of the bezel or rotating drum. The addition in a second step of the solid precursor of alumina dispersed in the acid in solution makes it possible to ensure the shaping by wet granular growth during the granulation shaping step b). The shaping conditions are adjusted in a manner known to those skilled in the art and are aimed at obtaining spherical granules of desired size.
Le mélange issu de l'étape a) est ensuite mis en forme conformément à l'étape b) du procédé de préparation du matériau selon l'invention. L'étape b) de mise en forme permet d'obtenir un matériau 10 cru. The mixture resulting from step a) is then shaped according to step b) of the process for preparing the material according to the invention. The shaping step b) makes it possible to obtain a raw material 10.
On entend par matériau cru, le matériau mis en forme et n'ayant pas subi d'étapes de traitement thermique .  By raw material is meant the material shaped and having not undergone any heat treatment steps.
Ladite étape b) de mise en forme peut avantageusement être réalisée par granulation humide ou par 5 extrusion. De préférence, ladite étape b) de mise en forme est réalisée par extrusion d'une manière connue de l'Homme du métier. Said b) shaping step can advantageously be carried out by wet granulation or by extrusion. Preferably, said shaping step b) is carried out by extrusion in a manner known to those skilled in the art.
Dans ce cas, le mélange issu de l'étape a) c'est-à-dire la pâte issue de l'étape a) passe avantageusement à travers une filière, à l'aide par exemple, d'un piston ou d'une extrudeuse continue double vis ou monovis. Le diamètre de la filière est avantageusement variable et est compris entre 1 10 et 5 mm. La forme de la filière, et par conséquent, la forme du solide millimétrique obtenu sous forme d'extrudé, est avantageusement cylindrique, trilobée, quadrilobée ou bien multilobée.  In this case, the mixture resulting from stage a), that is to say the paste resulting from stage a) advantageously passes through a die, for example using a piston or a continuous twin-screw or single-screw extruder. The diameter of the die is advantageously variable and is between 10 and 5 mm. The shape of the die, and therefore the form of the millimeter solid obtained in extruded form, is advantageously cylindrical, trilobal, quadrilobed or multilobed.
Le matériau cru issu de l'étape b) peut donc être sous forme de granule ou d'extrudé et de préférence sous forme d'extrudé. The green material from step b) can therefore be in the form of granules or extrudates and preferably in the form of extrudates.
!5  ! 5
Le matériau cru mis en forme selon l'étape b) du procédé de préparation selon l'invention, est ensuite soumis aux traitements thermiques des étapes c) et d).  The raw material shaped according to step b) of the preparation process according to the invention is then subjected to the heat treatments of steps c) and d).
Conformément à l'étape c) du procédé de préparation selon l'invention, le matériau cru obtenu à l'issue de l'étape b) subit une étape de séchage.  According to step c) of the preparation process according to the invention, the raw material obtained at the end of step b) undergoes a drying step.
0 Ladite étape c) de séchage est avantageusement réalisée selon les techniques connues de l'Homme du métier pour évaporer de manière contrôlée le solvant de la solution acide présent dans le matériau cru mis en forme obtenu à l'issue de l'étape b), et conférer une première solidification audit matériau. L'étape c) de séchage peut avantageusement être réalisée sous vide ou sous air ou sous air humide, en une ou plusieurs sous-étapes de conditions déterminées de température, de vide ou de gaz. Ladite Said drying step c) is advantageously carried out according to the techniques known to those skilled in the art to evaporate in a controlled manner the solvent from the acid solution present in the shaped green material obtained at the end of step b) and imparting a first solidification to said material. The drying step c) may advantageously be carried out under vacuum or under air or in moist air, in one or more substeps of determined conditions of temperature, vacuum or gas. said
5 étape c) de séchage est avantageusement réalisée à une température comprise entre 40 et 200°C, de préférence comprise entre 50 et 150°C, et de manière préférée comprise entre 70 et 100°C. L'étape c) de séchage est avantageusement réalisée pendant une durée comprise entre 12 et 72h, et de préférence comprise entre 12 et 24h. Ladite étape c) de séchage est avantageusement effectuée sous air ambiant ou sous air humide, avec une teneur en vapeur d'eau comprise entre 20 et 100% volume. The drying step c) is advantageously carried out at a temperature between 40 and 200 ° C, preferably between 50 and 150 ° C, and preferably between 70 and 100 ° C. The drying step c) is advantageously carried out for a period of between 12 and 72 hours, and preferably between 12 and 24 hours. Said step c) of drying is advantageously carried out under ambient air or in humid air, with a water vapor content between 20 and 100% volume.
Conformément à l'étape d) du procédé de préparation selon l'invention, le matériau séché obtenu à l'issue de l'étape c) de séchage subit une étape de calcination. According to step d) of the preparation process according to the invention, the dried material obtained at the end of the drying step c) undergoes a calcination step.
Ladite étape d) de calcination est avantageusement réalisée selon les techniques connues de l'Homme du métier. Ladite étape d) peut être réalisée sous air ou sous air avec de la vapeur d'eau, en une ou plusieurs sous-étapes de conditions déterminées de température ou de gaz. Ladite étape d) de calcination est avantageusement réalisée à une température comprise entre 400 et 1000°C, de préférence comprise entre 450 et 850°C, et de manière préférée comprise entre 500 et 700°C. L'étape d) de calcination est avantageusement réalisée pendant une durée comprise entre 1 à 6 h et de préférence entre 2 et 3h, sous air ambiant ou sous air et vapeur d'eau. Ladite étape d) de calcination est avantageusement effectuée sous air ambiant. Ladite étape d) de calcination permet de générer le liant constitué d'oxyde d'aluminium et d'assurer la cohésion de l'organisation hiérarchisée de petites et grosses particules micrométriques d'alumine et donc du matériau obtenu par le procédé de préparation selon l'invention grâce notamment, à la transformation du précurseur solide d'alumine en une alumine de transition, et de la présence d'espèces aluminiques dans le milieu, provenant de la dissolution partielle dudit précurseur solide d'alumine et minoritairement, des particules micrométriques d'alumine en présence d'un rapport d'acide élevé.  Said step d) of calcination is advantageously carried out according to the techniques known to those skilled in the art. Said step d) can be carried out under air or under air with steam, in one or more substeps of determined conditions of temperature or gas. Said d) calcination step is advantageously carried out at a temperature between 400 and 1000 ° C, preferably between 450 and 850 ° C, and preferably between 500 and 700 ° C. The d) calcination step is advantageously carried out for a period of between 1 to 6 hours and preferably between 2 and 3 hours, under ambient air or under air and steam. Said step d) of calcination is advantageously carried out under ambient air. Said step d) of calcination makes it possible to generate the binder constituted by aluminum oxide and to ensure the cohesion of the hierarchical organization of small and large micrometric particles of alumina and therefore of the material obtained by the preparation process according to the invention. invention thanks, in particular, to the transformation of the solid alumina precursor into a transition alumina, and the presence of aluminum species in the medium, originating from the partial dissolution of said solid precursor of alumina and in a minority, micrometric particles of alumina in the presence of a high acid ratio.
A l'issue de l'étape d) de calcination du procédé de préparation selon l'invention, le matériau sous forme d'objet millimétrique selon l'invention est obtenu. On entend par matériau sous forme d'objet millimétrique, un matériau présentant des dimensions de l'ordre du millimètre. At the end of step d) of calcination of the preparation process according to the invention, the material in the form of millimetric object according to the invention is obtained. By material in the form of a millimeter object is meant a material having dimensions of the order of one millimeter.
Le matériau sous forme d'objet millimétrique, de préférence sous forme d'extrudé, préparé selon l'enchainement des étapes a), b), c) et d) du procédé de préparation selon l'invention peut être caractérisé selon les techniques suivantes : l'adsorption d'azote pour la détermination de la surface spécifique selon la méthode BET; la porosimétrie au mercure pour les mesures des volumes mésoporeux et macroporeux et de la distribution de taille des pores ; la microscopie électronique à balayage (MEB) pour l'analyse de la microstructure permettant d'observer l'organisation hiérarchisée et les dimensions des petites et grosses particules micrométriques d'alumine assemblées par le liant constitué d'oxyde d'aluminium; un test d'écrasement grain à grain pour l'évaluation de la tenue mécanique du matériau. The material in the form of millimetric object, preferably in extruded form, prepared according to the sequence of steps a), b), c) and d) of the preparation process according to the invention can be characterized according to the following techniques : nitrogen adsorption for the determination of the specific surface according to the BET method; mercury porosimetry for mesoporous and macroporous volume measurements and pore size distribution; scanning electron microscopy (SEM) for the microstructure analysis to observe the hierarchical organization and dimensions of the small and large micrometric alumina particles assembled by the aluminum oxide binder; a grain-to-grain crushing test for evaluating the mechanical strength of the material.
Le procédé de préparation de l'invention assure la formation dudit matériau mais également : un bon glissement des particules micrométriques d'alumine les unes par rapport aux autres au cours de l'étape a) de mélange ce qui limite d'une part, la dégradation des particules et permet ainsi de maintenir une grande porosité du matériau et ce qui limite d'autre part la génération de défauts micrométriques au sein du mélange et permet ainsi d'améliorer saThe preparation method of the invention ensures the formation of said material but also: a good sliding of the micrometric particles of alumina with respect to each other during the mixing step a) which limits, on the one hand, the degradation of the particles and thus makes it possible to maintain a high porosity of the material and what on the other hand limits the generation of micrometric defects within the mixture and thus makes it possible to improve its
5 résistance mécanique ; Mechanical resistance;
un bon écoulement du mélange obtenu à l'étape a) au cours de l'étape b) ce qui limite la génération de défauts de géométrie et de défauts micrométriques à la surface du matériau cru améliorant ainsi l'aspect et la résistance mécanique du matériau sous forme d'objet millimétrique obtenu selon l'invention ;  a good flow of the mixture obtained in step a) during step b) which limits the generation of geometric defects and micrometric defects on the surface of the raw material thus improving the appearance and strength of the material as a millimetric object obtained according to the invention;
10 - la formation des défauts liés à la densification du liant au cours des étapes c) et d) est minimisée du fait de sa localisation dans l'espace de faible dimension entre les particules micrométriques d'alumine ce qui améliore la résistance mécanique du matériau sous forme d'objet millimétrique obtenu selon l'invention. i5 Les exemples suivants illustrent l'invention sans toutefois en limiter la portée.  The formation of the defects related to the densification of the binder during steps c) and d) is minimized because of its location in the small space between the micrometric particles of alumina, which improves the mechanical strength of the material as millimetric object obtained according to the invention. The following examples illustrate the invention without, however, limiting its scope.
Exemple 1 (selon l'invention) : préparation d'un matériau à base d'alumine, sous forme d'objet millimétrique, poreux, avec une organisation hiérarchisée de deux classes de particules micrométriaues assemblée par un liant constitué d'oxyde d'aluminium et préparé à un rapport !0 d'acide élevé de 61 % en poids. Example 1 (according to the invention): preparation of an alumina-based material, in the form of a millimetric, porous object, with a hierarchical organization of two classes of micrometric particles assembled by a binder consisting of aluminum oxide and prepared at an acid ratio of 61% by weight.
La population des grosses particules est constituée d'alumine référencée Puralox Scfa-140 (Sasol). Ces particules présentent une surface spécifique BET de 144 m2/g déterminée par adsorption d'azote (ASAP 2420 - Micromeritics), un volume mésoporeux de_ 0,45 mL/g et un diamètre médian des mésopores de 1 1 ,5 nm déterminés par porosimétrie au mercure (Autopore 9500 - Micromeritics). Le :5 diamètre médian, c'est-à-dire le Dv50 desdites grosses particules est d'environ 19 pm, le Dv10 est d'environ 7 pm, et le Dv90 est d'environ 38 pm, déterminés par granulométrie à diffraction laser (Mastersizer 2000 - Malvern). The large particle population consists of alumina Puralox Scfa-140 (Sasol). These particles have a BET specific surface area of 144 m 2 / g determined by nitrogen adsorption (ASAP 2420 - Micromeritics), a mesoporous volume of 0.45 mL / g and a median mesopore diameter of 1.15 μm determined by mercury porosimetry (Autopore 9500 - Micromeritics). The median diameter, i.e., the Dv50 of said large particles is about 19 μm, the Dv10 is about 7 μm, and the Dv90 is about 38 μm, determined by laser diffraction particle size. (Mastersizer 2000 - Malvern).
Les petites particules micrométriques d'alumine sont obtenues par séchage par atomisation d'un sol ;0 de boehmite préparé à partir de la poudre référencée Pural SB3 (Sasol). Le sol est préparé de manière à obtenir un rapport massique (masse de boehmite / masse d'eau)x 100 de 3,4% en poids et un taux d'acide (masse d'acide nitrique / masse d'alumine formée à partir de la boehmite après calcination) de 4,6% en poids. La poudre référencée Pural SB3 (Sasol) est introduite dans la solution acide, et le mélange est soumis à forte agitation pendant 2h. Après le temps de mélange, le sol est i5 centrifugé pendant 20 min à une vitesse de 4000 tours/min, afin d'enlever les sédiments de boehmite non dispersée. Le sol de boehmite est ensuite séché par atomisation à l'aide d'un séchoir par atomisation de laboratoire (Buchi B-290). Les conditions d'atomisation tels que le débit d'alimentation, le débit d'air comprimé, les températures d'entrée et sortie, et le débit d'aspiration sont optimisés afin de produire dans le cyclone de séparation, des petites particules sphériques dont le diamètre médian est d'environ 2 pm. Les particules obtenues par séchage par atomisation sont ensuite calcinées en four à moufle à 600°C pendant 2h afin d'assurer la transformation de la boehmite en alumine gamma, et ainsi d'obtenir les petites particules micrométriques et sphériques d'alumine. Ces particules présentent, après calcination, une surface spécifique BET de 212 m2/g déterminée par adsorption d'azote (ASAP 2420 - Micromeritics), un volume mésoporeux de 0,35 mL/g et un diamètre médian des mésopores de 7,5 nm, déterminés par porosimétrie au mercure (Autopore 9500 - Micromeritics). Le diamètre médian, c'est-à-dire le Dv50 desdites petites particules est d'environ 1 ,7 pm, le Dv10 est d'environ 0,75 pm, et le Dv90 est d'environ 3,4 pm, déterminés par granulométrie à diffraction laser (Mastersizer 2000 - Malvern). The small micrometric alumina particles are obtained by spray drying of a boehmite sol prepared from the Pural SB3 powder (Sasol). The sol is prepared so as to obtain a mass ratio (mass of boehmite / mass of water) × 100 of 3.4% by weight and a level of acid (mass of nitric acid / mass of alumina formed from boehmite after calcination) of 4.6% by weight. The powder Pural SB3 referenced (Sasol) is introduced into the acid solution, and the mixture is subjected to strong stirring for 2 hours. After the mixing time, the sol is centrifuged for 20 min at a speed of 4000 rpm to remove the undispersed boehmite sediments. The boehmite sol is then spray-dried using a laboratory spray dryer (Buchi B-290). The atomization conditions such as the feed rate, the compressed air flow, the inlet and outlet temperatures, and the suction flow rate are optimized so that to produce in the separation cyclone small spherical particles whose median diameter is about 2 μm. The particles obtained by spray drying are then calcined in a muffle furnace at 600 ° C. for 2 hours in order to ensure the conversion of boehmite to gamma-alumina, and thus to obtain the small micrometric and spherical particles of alumina. These particles have, after calcination, a BET surface area of 212 m 2 / g determined by nitrogen adsorption (ASAP 2420 - Micromeritics), a mesoporous volume of 0.35 ml / g and a median diameter of 7.5 mesopores. nm, determined by mercury porosimetry (Autopore 9500 - Micromeritics). The median diameter, i.e., the Dv50 of said small particles is about 1.7 μm, the Dv10 is about 0.75 μm, and the Dv90 is about 3.4 μm, determined by laser diffraction granulometry (Mastersizer 2000 - Malvern).
Le précurseur solide d'alumine, nécessaire à la formation du liant constitué d'oxyde d'aluminium, est la poudre référencée Pural SB3 (Sasol), et il s'agit d'une boehmite très dispersible en solution acide. Les grosses particules micrométriques (Puralox Scfa-140 - Sasol), les petites particules micrométriques obtenues par séchage par atomisation d'un sol de boehmite, et le précurseur solide d'alumine référencé Pural SB3 (Sasol), sont mélangés à sec de manière à obtenir respectivement, les proportions de 80% et 20% en poids de grosses et petites particules, et 19% en poids de précurseur solide d'alumine. Les proportions de grosses et petites particules sont exprimées par rapport à la quantité totale de particules micrométriques, et la proportion de précurseur solide d'alumine est exprimée par rapport à la quantité totale de solide. Le mélange à sec est réalisé à l'aide d'un malaxeur bras à cames (Brabender 50 EHT) à une vitesse de rotation des bras de 10 tours/min pendant 2 minutes. Ensuite, une solution d'acide nitrique est introduite à l'aide d'une pompe seringue, de manière à obtenir un rapport d'acide (masse d'acide nitrique introduit / masse de précurseur solide d'alumine introduit)x100 de 61 % en poids. L'eau est rajoutée avec la solution acide de manière à obtenir une pâte cohésive, homogène et extrudable. Le malaxage est poursuivi à une vitesse de rotation des bras de 16 tours/min pendant 30 minutes, après la fin de l'ajout de la solution acide. The solid precursor of alumina, necessary for the formation of the binder consisting of aluminum oxide, is the powder referenced Pural SB3 (Sasol), and it is a highly dispersible boehmite in acid solution. The large micrometric particles (Puralox Scfa-140 - Sasol), the small micrometric particles obtained by spray drying of a boehmite sol, and the solid alumina precursor referenced Pural SB3 (Sasol), are dry blended in such a way that to obtain, respectively, the proportions of 80% and 20% by weight of large and small particles, and 19% by weight of solid precursor of alumina. The proportions of large and small particles are expressed in relation to the total amount of micrometric particles, and the proportion of solid precursor of alumina is expressed in relation to the total amount of solid. The dry blending is carried out using a cam blender (Brabender 50 EHT) at an arm rotation speed of 10 rpm for 2 minutes. Then, a solution of nitric acid is introduced using a syringe pump, so as to obtain an acid ratio (mass of introduced nitric acid / solid precursor mass of introduced alumina) x100 of 61% in weight. The water is added with the acid solution so as to obtain a cohesive, homogeneous and extrudable paste. The kneading is continued at a rotation speed of the arms of 16 revolutions / min for 30 minutes, after the end of the addition of the acid solution.
La solution d'acide nitrique associée à l'énergie mécanique apportée pendant le malaxage, permettent de disperser majoritairement les agglomérats micrométriques de cristallites du précurseur solide d'alumine, et à la fin du processus de mélange, la pâte formée est constituée de grosses et petites particules micrométriques d'alumine liées par un liant dont les particules ont une taille moyenne de l'ordre de la centaine de nanomètre. En plus, le rapport d'acide élevé favorise la dissolution partielle du précurseur solide d'alumine et minoritairement, des particules micrométriques d'alumine, et par conséquent, favorise la formation d'espèces aluminiques qui vont contribuer à former le liant. The nitric acid solution associated with the mechanical energy provided during the kneading, make it possible to disperse the micrometric crystallite agglomerates of the solid precursor of alumina, and at the end of the mixing process, the formed dough consists of coarse and micrometric small particles of alumina bound by a binder whose particles have an average size of the order of a hundred nanometers. In addition, the high acid ratio promotes the partial dissolution of the solid alumina precursor and in a minor way, the micrometric alumina particles, and therefore promotes the formation of alumina species which will help form the binder.
La pâte obtenue est mise en forme à l'aide d'une extrudeuse piston (MTS), équipée d'une filière cylindrique de 3 mm de diamètre et de 6 mm de longueur, afin de former l'objet millimétrique. Les extrudes sont ensuite séchés en étuve ventilée à 80°C pendant 16h sous air ambiant, afin d'évaporer le solvant de la solution acide. Les extrudés séchés, sont ensuite calcinés en four à moufle à 600°C pendant 2h sous air ambiant, afin d'assurer la solidification du matériau grâce à la transformation du précurseur d'aluminium, dans cet exemple, de la boehmite en alumina gamma, et ainsi former le liant constitué d'oxyde d'aluminium. The paste obtained is shaped using a piston extruder (MTS), equipped with a cylindrical die 3 mm in diameter and 6 mm in length, to form the millimeter object. The extrusions are then dried in a ventilated oven at 80 ° C for 16 hours in ambient air, in order to evaporate the solvent from the acid solution. The dried extrudates are then calcined in a muffle furnace at 600 ° C. for 2 hours in ambient air, in order to ensure the solidification of the material by virtue of the conversion of the aluminum precursor, in this example, the boehmite into gamma alumina. and thus forming the binder consisting of aluminum oxide.
Les extrudés obtenus sont caractérisés selon les techniques suivantes : l'adsorption d'azote, pour la détermination de la surface spécifique BET; la porosimétrie au mercure pour les mesures des volumes mésoporeux et macroporeux et de la distribution du diamètre des mésopores; par microscopie électronique à balayage (JEOL JSM 6340F) pour l'observation de l'organisation hiérarchisée de petites et grosses particules micrométriques d'alumine et en particulier la distance d'une interface à l'autre entre lesdites grosses particules (Dgr0SSes) et d'une interface à l'autre entre lesdites petites particules <Dpetites) et le pourcentage surfacique des petites (Spetites) et des grosses particules (Sgrosses) par rapport à la surface totale de l'image MEB; et le test d'écrasement grain à grain (EGG) pour déterminer la résistance mécanique à l'écrasement latéral du matériau. The extrudates obtained are characterized according to the following techniques: nitrogen adsorption, for the determination of the BET specific surface area; mercury porosimetry for mesoporous and macroporous volume measurements and mesopore diameter distribution; by scanning electron microscopy (JEOL JSM 6340F) for the observation of the hierarchical organization of small and large micrometric particles of alumina and in particular the distance from one interface to another between said large particles (Dg r0SS es) and from one interface to another between said small particles <D pe tites) and the surface percentage of small (S pet ites) and large particles (Sg rosses ) with respect to the total surface of the SEM image; and the grain-to-grain (GGE) crush test to determine the lateral crushing strength of the material.
Les caractéristiques du matériau obtenu selon la formulation de l'exemple 1 , sont rassemblées dans le Tableau 1 . On observe que le matériau selon l'invention obtenu selon l'exemple 1 présente une bonne résistance mécanique du fait de l'organisation hiérarchisée des petites et des grosses particules assemblée par un liant constitué d'oxyde d'aluminium. Les distances Dgr0SSes et Dpetjtes et les pourcentages surfaciques Sgrosses et Spetites sont des critères indispensables à l'obtention de l'organisation hiérarchisée desdites petites et grosses particules et sont conformes à celles du matériau de l'invention. Les propriétés texturales du matériau obtenu sont liées aux propriétés texturales des particules micrométriques d'alumine et sont conformes aux propriétés attendues du matériau selon l'invention. L'organisation hiérarchisée permet d'augmenter le volume mésoporeux du matériau, grâce à une maximisation de la proportion de particules micrométriques par rapport à la teneur en liant. L'organisation hiérarchisée permet également d'avoir un bon glissement des petites et grosses particules micrométriques d'alumine les unes par rapport aux autres ce qui se traduit par un faible couple de malaxage de l'ordre de 7 Nm. The characteristics of the material obtained according to the formulation of Example 1 are summarized in Table 1. It is observed that the material according to the invention obtained according to Example 1 has a good mechanical strength due to the hierarchical organization of small and large particles assembled by a binder consisting of aluminum oxide. The distances Dg r0SS es and D pe tjtes and the surface percentages Sgrosses and S pe tites are essential criteria for obtaining the hierarchical organization of said small and large particles and are consistent with those of the material of the invention. The textural properties of the material obtained are related to the textural properties of the micrometric alumina particles and are consistent with the expected properties of the material according to the invention. The hierarchical organization makes it possible to increase the mesoporous volume of the material, by maximizing the proportion of micrometric particles with respect to the binder content. The hierarchical organization also makes it possible to have good sliding of the small and large micrometric alumina particles relative to each other, which results in a low mixing torque of the order of 7 Nm.
Exemple 2 (selon l'invention) : préparation d'un matériau à base d'alumine, sous forme d'objet millimétrique, très poreux, avec une organisation hiérarchisée de deux classes de particules micrométriques assemblée par un liant constitué d'oxyde d'aluminium et préparé à un rapport d'acide élevé de 61 % poids. Les grosses particules micrométriques et poreuses d'alumine sont obtenues à partir de la calcination en four à moufle à 600°C pendant 2h, sous air ambiant, de la poudre référencée Pural TH100 (Sasol), afin de transformer la boehmite de départ en alumine gamma. Les particules micrométriques présentent, après calcination, une surface spécifique de 142 m2/g déterminée par adsorption d'azote (ASAP 2420 - Micromeritics), un volume mésoporeux de 0,87 mL/g et un diamètre médian des mésopores de 22,5 nm déterminés par porosimétrie au mercure (Autopore 9500 - Micromeritics). Le diamètre médian, c'est-à-dire le Dv50 desdites grosses particules est d'environ 40 μιτι, le Dv10 est d'environ 15 pm, et le Dv90 est d'environ 77 pm, déterminés par granulométrie à diffraction laser (Mastersizer 2000 - Malvern). Example 2 (according to the invention): preparation of an alumina-based material, in the form of a millimetric object, highly porous, with a hierarchical organization of two classes of micrometric particles assembled by a binder consisting of oxide of aluminum and prepared at a high acid ratio of 61% by weight. The large micrometric and porous alumina particles are obtained from calcination in a muffle furnace at 600 ° C. for 2 hours, under ambient air, with the Pural TH100 powder (Sasol), in order to transform the starting boehmite into alumina. gamma. After calcination, the micrometric particles have a specific surface area of 142 m 2 / g determined by nitrogen adsorption (ASAP 2420 - Micromeritics), a mesoporous volume of 0.87 ml / g and a median mesopore diameter of 22.5 μm. nm determined by mercury porosimetry (Autopore 9500 - Micromeritics). The median diameter, that is to say the Dv50 of said large particles is about 40 μιτι, the Dv10 is about 15 pm, and the Dv90 is about 77 pm, determined by laser diffraction granulometry (Mastersizer 2000 - Malvern).
Les petites particules micrométriques sont obtenues par séchage par atomisation d'un sol de boehmite préparé à partir de la poudre référencée Pural TH100 (Sasol). Ledit sol de boehmite est préparé selon les mêmes conditions décrites dans l'exemple 1 ; et les paramètres d'atomisation sont optimisés afin de produire dans le cyclone de séparation, des petites particules sphériques dont le diamètre médian est d'environ 3 pm. Les particules obtenues par séchage par atomisation sont soumises au même traitement thermique que l'exemple 1 , afin d'assurer la transformation de la boehmite en alumine gamma, et ainsi d'obtenir les petites particules micrométriques et sphériques d'alumine. Ces particules présentent, après calcination, une surface spécifique BET dé 130 m2/g déterminée par adsorption d'azote (ASAP 2420 - Micromeritics), un volume mésoporeux de 0,78 ml_ g et un diamètre médian des mésopores de 23 nm, déterminés par porosimétrie au mercure (Autopore 9500 - Micromeritics). Le diamètre médian, c'est-à-dire le Dv50 desdites petites particules est d'environ 2,7 pm, le Dv10 est d'environ 1 ,7 pm, et le Dv90 est d'environ 8 pm, déterminés par granulométrie à diffraction laser (Mastersizer 2000 - Malvern). The small micrometric particles are obtained by spray drying of a boehmite sol prepared from the powder Pural TH100 (Sasol). Said boehmite sol is prepared according to the same conditions described in Example 1; and the atomization parameters are optimized to produce in the separation cyclone small spherical particles having a median diameter of about 3 μm. The particles obtained by spray drying are subjected to the same heat treatment as Example 1, in order to ensure the conversion of boehmite to gamma-alumina, and thus to obtain small micrometric and spherical particles of alumina. These particles have, after calcination, a BET specific surface area of 130 m 2 / g determined by nitrogen adsorption (ASAP 2420 - Micromeritics), a mesoporous volume of 0.78 ml of g and a median diameter of the mesopores of 23 nm, determined by mercury porosimetry (Autopore 9500 - Micromeritics). The median diameter, i.e., the Dv50 of said small particles is about 2.7 μm, the Dv10 is about 1.7 μm, and the Dv90 is about 8 μm, determined by particle size distribution. laser diffraction (Mastersizer 2000 - Malvern).
Le précurseur solide d'alumine, nécessaire à la formation du liant constitué d'oxyde d'aluminium, est la poudre référencée Pural TH100 (Sasol).  The solid precursor of alumina, necessary for the formation of the binder consisting of aluminum oxide, is the powder referenced Pural TH100 (Sasol).
Les grosses particules micrométriques obtenues après calcination de la poudre référencée Pural ΤΉ100 (Sasol), les petites particules micrométriques obtenues par séchage par atomisation d'un sol de boehmite, et le précurseur solide d'alumine référencé Pural ΤΉ100 (Sasol), sont mélangés à sec dans les mêmes proportions et dans les mêmes conditions décrites dans l'exemple 1. Ensuite, une solution d'acide nitrique est introduite de la même façon que celle décrite dans l'exemple 1 , et afin d'obtenir un rapport d'acide (masse d'acide nitrique introduit / masse de précurseur solide d'alumine introduit)x100 de 61 % en poids. Le malaxage est poursuivi dans les mêmes conditions de l'exemple 1. L'eau est rajoutée avec la solution acide de manière à obtenir une pâte cohésive, homogène et extrudable. Le rapport d'acide élevé associé à l'énergie mécanique apportée au malaxage, conduisent aux mêmes effets techniques décrits dans l'exemple 1 . The large micrometric particles obtained after calcination of the powder referenced Pural 100 (Sasol), the small micrometric particles obtained by spray drying of a boehmite sol, and the solid precursor of alumina referenced Pural 100 (Sasol), are mixed with in the same proportions and under the same conditions described in Example 1. Then, a solution of nitric acid is introduced in the same way as that described in Example 1, and in order to obtain an acid ratio. (Mass of introduced nitric acid / mass of introduced alumina solid precursor) x100 of 61% by weight. The mixing is continued under the same conditions as in Example 1. The water is added with the acid solution so as to obtain a cohesive, homogeneous and extrudable paste. The high acid ratio associated with the mechanical energy provided to the kneading, lead to the same technical effects described in Example 1.
La pâte obtenue est ensuite mise en forme selon les mêmes conditions de l'exemple 1. The paste obtained is then shaped according to the same conditions as in Example 1.
Les extrudés sont ensuite séchés et calcinés selon les conditions décrites dans l'exemple 1 ; et caractérisés selon les mêmes techniques décrites dans le même exemple. Les caractéristiques du matériau obtenu selon la formulation de l'exemple 2 sont rassemblées dans le Tableau 1. The extrudates are then dried and calcined according to the conditions described in Example 1; and characterized according to the same techniques described in the same example. The characteristics of the material obtained according to the formulation of Example 2 are collated in Table 1.
On observe que le matériau selon l'invention obtenu selon l'exemple 1 présente une bonne résistance mécanique du fait de l'organisation hiérarchisée des petites et des grosses particules assemblée par un liant constitué d'oxyde d'aluminium. Les distances Dgr0sses et Dpe«tes et les pourcentages surfaciques Sgrosses et Speiites sont des critères indispensables à l'obtention de l'organisation hiérarchisée desdites petites et grosses particules et sont conformes à celles du matériau de l'invention. Les propriétés texturales du matériau obtenu sont liées aux propriétés texturales des particules micrométriques d'alumine et sont conformes aux propriétés attendues du matériau selon l'invention. L'organisation hiérarchisée permet d'augmenter le volume mésoporeux du matériau, grâce à une maximisation de la proportion de particules micrométriques par rapport à la teneur en liant. It is observed that the material according to the invention obtained according to Example 1 has a good mechanical strength due to the hierarchical organization of small and large particles assembled by a binder consisting of aluminum oxide. The distances D gr0 sses and Dpies and the surface percentages Sgrosses and S pe iites are essential criteria for obtaining the hierarchical organization of said small and large particles and are consistent with those of the material of the invention. The textural properties of the material obtained are related to the textural properties of the micrometric alumina particles and are consistent with the expected properties of the material according to the invention. The hierarchical organization makes it possible to increase the mesoporous volume of the material, by maximizing the proportion of micrometric particles with respect to the binder content.
L'organisation hiérarchisée permet également d'avoir un bon glissement des petites et grosses particules micrométriques d'alumine les unes par rapport aux autres ce qui se traduit par un faible couple de malaxage de l'ordre de 9 Nm. The hierarchical organization also makes it possible to have good sliding of the small and large micrometric particles of alumina with respect to each other, which results in a low mixing torque of the order of 9 Nm.
Exemple 3 (selon l'invention) : préparation d'un matériau à base d'alumine, sous forme d'objet millimétrique, poreux, avec une organisation hiérarchisée de trois classes de particules micrométriques assemblée par un liant constitué d'oxyde d'aluminium et préparé à un rapport d'acide élevé de 61% poids. Example 3 (according to the invention): preparation of an alumina-based material, in the form of a millimetric, porous object, with a hierarchical organization of three classes of micrometric particles assembled by a binder consisting of aluminum oxide and prepared at a high acid ratio of 61% by weight.
Les grosses particules d'alumine sont composées de deux populations de particules dont le diamètre médian est distinct, et qui sont identifiées comme : une population de particules dites grosses inférieures et référencée Puralox Scfa-140 (Sasol) et une population dites grosses supérieures référencée Puralox SCCa 150/200 (Sasol). Les caractéristiques de la poudre d'alumine référencée Puralox Scfa-140 sont décrites dans l'exemple 1. La poudre d'alumine référencée Puralox SCCa 150/200 présente une surface spécifique BET de 199 m2/g déterminée par adsorption d'azote (ASAP 2420 - Micromeritics), un volume mésoporeux de 0,43 mIJg et un diamètre médian des mésopores de 8,7 nm déterminés par porosimétrie au mercure (Autopore 9500 - Micromeritics). Le diamètre médian, c'est-à-dire le Dv50 desdites particules grosses supérieures est d'environ 160 pm, le Dv10 est d'environ 104 pm, et le Dv90 est d'environ 247 pm, déterminés par granulométrie à diffraction laser (Mastersizer 2000 - Malvern). Les petites particules sont obtenues de la même manière décrite dans l'exemple 1 et leurs caractéristiques sont également décrites dans le même exemple. The large particles of alumina are composed of two populations of particles whose median diameter is distinct, and which are identified as: a population of so-called lower fat particles and referenced Puralox Scfa-140 (Sasol) and a so-called larger population referenced Puralox SCCa 150/200 (Sasol). The characteristics of the alumina powder referenced Puralox Scfa-140 are described in Example 1. The alumina powder referenced Puralox SCCa 150/200 has a BET specific surface area of 199 m 2 / g determined by nitrogen adsorption ( ASAP 2420 - Micromeritics), a mesoporous volume of 0.43 mIg and a mesopore median diameter of 8.7 nm determined by mercury porosimetry (Autopore 9500 - Micromeritics). The median diameter, i.e., the Dv50 of said larger fat particles is about 160 μm, the Dv10 is about 104 μm, and the Dv90 is about 247 μm, determined by laser diffraction particle size ( Mastersizer 2000 - Malvern). The small particles are obtained in the same manner as described in Example 1 and their characteristics are also described in the same example.
Le précurseur solide d'alumine est la boehmite référencée Pural SB3 (Sasol), également utilisée dans l'exemple 1. The solid precursor of alumina is the boehmite referenced Pural SB3 (Sasol), also used in Example 1.
Les conditions de mélange des particules d'alumine avec le précurseur solide d'alumine et la solution acide, les conditions de malaxage, la mise en forme par extrusion et les traitements thermiques, sont identiques à ceux décrits dans l'exemple 1 , mais avec 4 poudres au lieu de 3 poudres. Les proportions de grosses, c'est-à-dire de l'ensemble des particules grosses inférieures et grosses supérieures, et petites particules micrométriques d'alumine sont respectivement de 76% et 24% en poids exprimées par rapport à la quantité totale de particules micrométriques, et la proportion de précurseur solide d'alumine est de 13% en poids par rapport à la quantité totale de solide. La proportion des particules dites grosses inférieures par rapport à la totalité de grosses particules est de 40% en poids. Le rapport d'acide (masse d'acide nitrique introduit) / (masse de précurseur solide d'alumine)x100 utilisé est de 61 %. Les caractéristiques du matériau obtenu selon la formulation de l'exemple 3, et déterminées selon les techniques décrites dans l'exemple 1 , sont rassemblées dans le Tableau 1. The conditions for mixing the alumina particles with the solid alumina precursor and the acid solution, the mixing conditions, the extrusion shaping and the heat treatments, are identical to those described in Example 1, but with 4 powders instead of 3 powders. The proportions of coarse particles, that is to say of the whole of the coarse lower and upper coarse particles, and small micrometric particles of alumina are respectively 76% and 24% by weight, expressed relative to the total quantity of particles. micrometric, and the proportion of solid precursor of alumina is 13% by weight relative to the total amount of solid. The proportion of so-called smaller particles relative to the totality of large particles is 40% by weight. The ratio of acid (mass of introduced nitric acid) / (mass of solid precursor of alumina) × 100 used is 61%. The characteristics of the material obtained according to the formulation of Example 3, and determined according to the techniques described in Example 1, are summarized in Table 1.
On observe que la matériau selon l'invention obtenu selon l'exemple 3 présente une bonne résistance mécanique du fait de l'organisation hiérarchisée des petites et des grosses particules assemblée par un liant constitué d'oxyde d'aluminium. Les distances Dgrosses et Dpet„es et les pourcentages surfaciques Sgrasses et Suites sont des critères indispensables à l'obtention de l'organisation hiérarchisée desdites petites et grosses particules et sont conformes à celles du matériau de l'invention. Les propriétés texturales du matériau obtenu sont liées aux propriétés texturales des particules micrométriques d'alumine et sont conformes aux propriétés attendues du matériau selon l'invention. L'organisation hiérarchisée permet d'augmenter le volume mésoporeux du matériau, grâce à une maximisation de la proportion de particules micrométriques par rapport à la teneur en liant. It is observed that the material according to the invention obtained according to Example 3 has good mechanical strength due to the hierarchical organization of small and large particles assembled by a binder consisting of aluminum oxide. The distances D large s and D pe t es and the surface percentages Sg ra sses and Suites are essential criteria for obtaining the hierarchical organization of said small and large particles and are consistent with those of the material of the invention. The textural properties of the material obtained are related to the textural properties of the micrometric alumina particles and are consistent with the expected properties of the material according to the invention. The hierarchical organization makes it possible to increase the mesoporous volume of the material, by maximizing the proportion of micrometric particles with respect to the binder content.
LOrganisation hiérarchisée permet également d'avoir un bon glissement des petites et grosses particules micrométriques d'alumine les unes par rapport aux autres ce qui se traduit par un faible couple de malaxage de l'ordre de 12 Nm. The hierarchical organization also makes it possible to have good sliding of the small and large micrometric alumina particles relative to each other, which results in a low mixing torque of the order of 12 Nm.
Exemple 4 (comparatif) : préparation d'un matériau à base d'alumine, sous forme d'objet millimétrique, poreux, avec une seule classe de particules micrométriques assemblée par un liant constitué d'oxyde d'aluminium et préparé à un rapport d'acide élevé de 61% poids. Example 4 (comparative): preparation of an alumina-based material, in the form of a millimetric, porous object, with a single class of micrometric particles assembled by a binder consisting of aluminum oxide and prepared at a ratio of high acid of 61% by weight.
Les particules micrométriques et poreuses d'alumine proviennent de la poudre référencée Puralox SCfa-140 (Sasol) dont les caractéristiques sont décrites dans l'exemple 1.  The micrometric and porous alumina particles come from the powder Puralox SCfa-140 referenced (Sasol) whose characteristics are described in Example 1.
Le précurseur solide d'alumine est la boehmite référencée Pural SB3 (Sasol), également utilisée dans l'exemple 1. The solid precursor of alumina is the boehmite referenced Pural SB3 (Sasol), also used in Example 1.
Les conditions de mélange des particules d'alumine avec le précurseur solide d'alumine et la solution acide, les conditions de malaxage, la mise en forme par extrusion et les traitements thermiques, sont identiques à ceux décrits dans l'exemple 1 , mais avec 2 poudres au lieu de 3 poudres. Les proportions de particules micrométriques d'alumine et de précurseur solide d'alumine par rapport à la quantité totale de solide sont respectivement, 74 et 26% en poids. Le rapport d'acide (masse d'acide nitrique introduit) / (masse de précurseur solide d'alumine)x100 utilisé est de 61 %. The conditions for mixing the alumina particles with the solid alumina precursor and the acid solution, the mixing conditions, the extrusion shaping and the heat treatments, are identical to those described in Example 1, but with 2 powders instead of 3 powders. The proportions of micrometric particles of alumina and alumina solid precursor relative to the total amount of solid are respectively 74 and 26% by weight. The ratio of acid (mass of introduced nitric acid) / (mass of solid precursor of alumina) × 100 used is 61%.
Les caractéristiques du matériau obtenu selon la formulation de l'exemple 4, et déterminées selon les techniques décrites dans l'exemple 1 , sont rassemblées dans le Tableau 1. The characteristics of the material obtained according to the formulation of Example 4, and determined according to the techniques described in Example 1, are summarized in Table 1.
On observe une résistance mécanique plus faible par rapport aux matériaux des exemples 1 , 2 et 3 selon l'invention du fait de la présence d'une seule classe de particules micrométriques d'alumine ce qui conduit également à un volume mésoporeux et une surface spécifique BET plus faible par rapport aux exemples selon l'invention. On observe également un volume macroporeux plus élevé du fait de l'absence d'organisation hiérarchisée de petites et grosses particules dans ce matériau. Le glissement des particules micrométriques d'alumine les unes par rapport aux autres est moins favorisé ce qui se traduit par un couple de malaxage de l'ordre de 20 Nm. A lower mechanical resistance is observed with respect to the materials of Examples 1, 2 and 3 according to the invention because of the presence of a single class of micrometric alumina particles, which also leads to a mesoporous volume and a specific surface area. BET lower compared to the examples according to the invention. A higher macroporous volume is also observed because of the lack of hierarchical organization of small and large particles in this material. The sliding of the micrometric particles of alumina with respect to each other is less favored which results in a mixing torque of the order of 20 Nm.
Exemple 5 (comparatif! : préparation d'un matériau à base d'alumine, sous forme d'objet millimétrique, poreux, avec une seule classe de particules micrométriques assemblée par un liant constitué d'oxyde d'aluminium et préparé à un rapport d'acide faible de 2.37% poids. Example 5 (Comparative !: Preparation of an Alumina-Based Material, in the form of a Porous Millimetric Object, with a Single Class of Micrometric Particles Assembled by a Binder of Aluminum Oxide and Prepared at a Density Ratio weak acid of 2.37% weight.
Les particules micrométriques et poreuses d'alumine proviennent de la poudre référencée Puralox SCfa-140 (Sasol) dont les caractéristiques sont décrites dans l'exemple 1.  The micrometric and porous alumina particles come from the powder Puralox SCfa-140 referenced (Sasol) whose characteristics are described in Example 1.
Le précurseur solide d'alumine est la boehmite référencée Pural SB3 (Sasol), également utilisée dans l'exemple 1. The solid precursor of alumina is the boehmite referenced Pural SB3 (Sasol), also used in Example 1.
Les conditions de mélange des particules d'alumine avec le précurseur solide d'alumine et la solution acide, les conditions de malaxage, la mise en forme par extrusion et les traitements thermiques, sont identiques à ceux décrits dans l'exemple 4, mais avec 2 poudres au lieu de 3 poudres. Les proportions de particules micrométriques d'alumine et de précurseur solide d'alumine par rapport à la quantité totale de solide sont respectivement, 74 et 26% en poids. Le rapport d'acide (masse d'acide nitrique introduit) / (masse de précurseur solide d'alumine)x100 utilisé est de 2,37 %. The mixing conditions of the alumina particles with the solid alumina precursor and the acid solution, the mixing conditions, the extrusion shaping and the heat treatments, are identical to those described in Example 4, but with 2 powders instead of 3 powders. The proportions of micrometric particles of alumina and alumina solid precursor relative to the total amount of solid are respectively 74 and 26% by weight. The ratio of acid (mass of introduced nitric acid) / (mass of solid precursor of alumina) × 100 used is 2.37%.
Les caractéristiques du matériau obtenu selon la formulation de l'exemple 5, et déterminées selon les techniques décrites dans l'exemple 1 , sont rassemblées dans le Tableau 1. The characteristics of the material obtained according to the formulation of Example 5, and determined according to the techniques described in Example 1, are summarized in Table 1.
On observe une résistance mécanique plus faible par rapport aux matériaux des exemples 1 , 2 et 3 selon l'invention du fait de la présence d'une seule classe de particules micrométriques d'alumine et d'un liant préparé avec un rapport d'acide faible. On observe également un volume macroporeux plus élevé du fait de l'absence d'organisation hiérarchisée de petites et grosses particules dans ce matériau. A lower mechanical resistance is observed with respect to the materials of Examples 1, 2 and 3 according to the invention because of the presence of a single class of micrometric particles of alumina and a binder prepared with a low acid ratio. A higher macroporous volume is also observed because of the lack of hierarchical organization of small and large particles in this material.
5 Le glissement des particules micrométriques d'alumine les unes par rapport aux autres est moins favorisé ce qui se traduit par un couple de malaxage de l'ordre de 24 Nm. The sliding of the micrometric particles of alumina with respect to each other is less favored, which results in a mixing torque of the order of 24 Nm.
Tableau 1 Table 1
Figure imgf000028_0001
Figure imgf000028_0001
aAdsorption d'azote; Porosimétrie au mercure; cTest d'écrasement grain à grain (EGG); MEB; nonaAdsorption of nitrogen; Mercury porosimetry; c Grain-to-grain (GGE) crush test; SEM; no
10 déterminé 10 determined
Les exemples démontrent que les matériaux des exemples 1 à 3 selon l'invention présentant à la fois une organisation hiérarchisée de petites et de grosses particules d'alumine et comprenant un liant constitué d'oxyde d'aluminium préparé à rapport d'acide élevé, présentent des propriétés mécaniques 15 accrues par rapport au matériau de l'art antérieur (exemple 5) ou à faible taux d'acide (exemple 4). The examples demonstrate that the materials of Examples 1 to 3 according to the invention having both a hierarchical organization of small and large particles of alumina and comprising a binder consisting of aluminum oxide prepared at a high acid ratio, have increased mechanical properties compared to the material of the prior art (Example 5) or low acid level (Example 4).
L'organisation hiérarchisée permet également d'augmenter le volume mésoporeux du matériau, grâce à une maximisation de la proportion de particules micrométriques par rapport à la teneur en liant (exemples 1 à 3). Des propriétés texturales encore plus élevées peuvent être atteintes à partir de l'utilisation des particules micrométriques d'alumine à forte porosité.  The hierarchical organization also makes it possible to increase the mesoporous volume of the material, thanks to a maximization of the proportion of micrometric particles with respect to the binder content (Examples 1 to 3). Even higher textural properties can be achieved from the use of micrometer particles of high porosity alumina.

Claims

REVENDICATIONS
1. Matériau, sous forme d'objet millimétrique, constitué de grosses particules d'alumine présentant un diamètre médian compris entre 10 et 200 pm, lesdites grosses particules étant distantes, d'une interface à l'autre, de moins de 10 pm, de petites particules d'alumine présentant un diamètre médian compris entre 0,5 et 10 pm, lesdites petites particules étant distantes, d'une interface à l'autre, de moins de 5 pm et étant localisées dans l'espace entre les grosses particules et d'un liant constitué d'oxyde d'aluminium, ledit liant étant localisé dans l'espace entre lesdites petites et grosses particules, ledit matériau présentant un volume mésoporeux, mesuré par porosimétrie au mercure, compris entre 0,2 et 2 mL/g, un volume macroporeux, mesuré par porosimétrie au mercure, compris entre 0,05 et 0,2 mL/g et une surface spécifique BET comprise entre 90 et 350 m2/g. 1. Material, in the form of a millimetric object, consisting of large particles of alumina having a median diameter of between 10 and 200 μm, said large particles being spaced, from one interface to another, of less than 10 μm, small alumina particles having a median diameter of between 0.5 and 10 μm, said small particles being spaced from one interface to another by less than 5 μm and being located in the space between the large particles and a binder consisting of aluminum oxide, said binder being located in the space between said small and large particles, said material having a mesoporous volume, measured by mercury porosimetry, between 0.2 and 2 mL / g, a macroporous volume, measured by mercury porosimetry, of between 0.05 and 0.2 mL / g and a BET specific surface area of between 90 and 350 m 2 / g.
2. Matériau selon la revendication 1 dans lequel lesdites grosses particules d'alumine présentent un diamètre médian compris entre 0 et 80 pm. 2. Material according to claim 1 wherein said large particles of alumina have a median diameter of between 0 and 80 pm.
3. Matériau selon l'une des revendications 1 ou 2 dans lequel ledit matériau présente une distribution de la granulométrie desdites grosses particules d'alumine au sein dudit matériau telle que le diamètre D10 est au plus 3 fois inférieur au diamètre médian D50 et telle que le diamètre D90 est au plus 3 fois supérieur au diamètre médian D50. 3. Material according to one of claims 1 or 2 wherein said material has a distribution of the particle size of said large particles of alumina in said material such that the diameter D10 is at most 3 times less than the median diameter D50 and such that the diameter D90 is at most 3 times greater than the median diameter D50.
4. Matériau selon l'une des revendications 1 à 3 dans lequel lesdites grosses particules présentent un diamètre médian inférieur à 1/10 fois le diamètre moyen de la plus petite dimension du matériau. 4. Material according to one of claims 1 to 3 wherein said large particles have a median diameter less than 1/10 times the average diameter of the smallest dimension of the material.
5. Matériau selon l'une des revendications 1 à 4 dans lequel lesdites grosses particules sont distantes, d'une interface à l'autre, de moins de 6 pm. 5. Material according to one of claims 1 to 4 wherein said large particles are spaced from one interface to another, less than 6 pm.
6. Matériau selon l'une des revendications 1 à 5 dans lequel lesdites grosses particules comprennent une proportion de particules, appelée particules grosses inférieures, présentant un diamètre médian compris entre 0 et 60 pm et une proportion de particules, appelées particules grosses supérieures, présentant un diamètre médian compris entre 60 et 200 pm. 6. Material according to one of claims 1 to 5 wherein said coarse particles comprise a proportion of particles, called lower coarse particles, having a median diameter of between 0 and 60 pm and a proportion of particles, called larger particles greater, having a median diameter of between 60 and 200 μm.
7. Matériau selon la revendication 6 dans lequel ledit matériau présente une distribution de la granulométrie desdites particules grosses inférieures au sein dudit matériau tel que le diamètre D 0 est au plus 3 fois inférieur au diamètre médian D50 et tel que le diamètre D90 est au plus 3 fois supérieur au diamètre médian D50 et une distribution de la granulométrie desdites particules grosses supérieures au sein dudit matériau tel que le diamètre D10 est au plus 3 fois inférieur au diamètre médian D50 et tel que le diamètre D90 est au plus 3 fois supérieur au diamètre médian D50. 7. The material of claim 6 wherein said material has a distribution of the particle size of said lower coarse particles within said material such that the diameter D 0 is at most 3 times less than the median diameter D50 and such that the diameter D90 is at most 3 times greater than the median diameter D50 and a distribution of the particle size of said larger larger particles within said material such that the diameter D10 is at most 3 times smaller than the median diameter D50 and such that the diameter D90 is at most 3 times greater than the diameter median D50.
8. Matériau selon l'une des revendications 1 à 7 dans lequel dans lequel lesdites petites particules présentent un diamètre médian compris entre 0,5 et 3 pm. 8. Material according to one of claims 1 to 7 wherein wherein said small particles have a median diameter of between 0.5 and 3 pm.
9. Matériau selon l'une des revendications 1 à 8 dans lequel ledit matériau présente une distribution de la granulométrie desdites petites particules d'alumine au sein dudit matériau telle que le diamètre9. Material according to one of claims 1 to 8 wherein said material has a distribution of the particle size of said small particles of alumina within said material such as the diameter
D10 est au plus 3 fois inférieur au diamètre médian D50 et telle que le diamètre D90 est au plus 3 fois supérieur au diamètre médian D50. D10 is at most 3 times smaller than the median diameter D50 and such that the diameter D90 is at most 3 times greater than the median diameter D50.
10. Matériau selon l'une des revendications 1 à 9 dans lequel lesdites petites particules présentent un diamètre médian inférieur à 1/5 fois le diamètre médian des grosses particules, 10. Material according to one of claims 1 to 9 wherein said small particles have a median diameter less than 1/5 times the median diameter of large particles,
11. Matériau selon l'une des revendications 1 à 10 dans lequel le pourcentage surfacique des petites particules compris entre 5 et 55% par rapport à la surface totale de l'image MEB dudit matériau. 11. Material according to one of claims 1 to 10 wherein the surface percentage of small particles between 5 and 55% relative to the total surface of the SEM image of said material.
12. Matériau selon l'une des revendications 1 à 11 dans lequel le pourcentage surfacique des grosses particules est compris entre 35 et 85% par rapport à la surface totale de l'image MEB dudit matériau. 12. Material according to one of claims 1 to 11 wherein the surface percentage of large particles is between 35 and 85% relative to the total surface of the SEM image of said material.
13. Procédé de préparation dudit matériau comprenant au moins les étapes suivantes : 13. A process for preparing said material comprising at least the following steps:
a) le mélange de 10 à 60% en poids de petites particules d'alumine de diamètre médian compris entre 0,5 et 10 pm et de 40 à 90% en poids de grosses particules d'alumine de diamètre médian compris entre 10 et 200 pm, de 5 à 50 % en poids d'un précurseur solide d'alumine, les pourcentages de petites et grosses particules d'alumine étant exprimés par rapport à la quantité totale de particules micrométriques, et le pourcentage de précurseur solide d'alumine étant exprimé par rapport à la quantité totale de solide, et d'un acide en solution choisi parmi l'acide acétique, l'acide chlorhydrique, l'acide sulfurique, l'acide formique, l'acide citrique et l'acide nitrique, seul ou en mélange, dans des proportions tel que le rapport de la masse d'acide introduit sur la masse de précurseur solide d'alumine introduit soit compris entre 2,5 et 115% en poids, lesdites grosses particules et petites particules d'alumine, désignées sous le terme particules micrométriques, présentant un volume mésoporeux compris entre 0,2 et 2,5 mL/g, et un diamètre médian de mésopores compris entre 7 et 25 nm, a) mixing 10 to 60% by weight of small alumina particles with a median diameter of between 0.5 and 10 μm and 40 to 90% by weight of large alumina particles with a median diameter of between 10 and 200; pm, from 5 to 50% by weight of a solid precursor of alumina, the percentages of small and large alumina particles being expressed relative to the total amount of micrometric particles, and the percentage of solid alumina precursor being expressed with respect to the total amount of solid, and an acid in solution selected from acetic acid, hydrochloric acid, sulfuric acid, formic acid, citric acid and nitric acid, alone or in a mixture, in proportions such that the ratio of the mass of acid introduced onto the mass of introduced alumina solid precursor is between 2.5 and 115% by weight, said large particles and small particles of alumina, referred to as micrometric particles, presages having a mesoporous volume of between 0.2 and 2.5 mL / g, and a median mesopore diameter of between 7 and 25 nm,
b) la mise en forme du mélange issu de l'étape a), b) shaping the mixture resulting from step a),
c) le séchage du matériau cru obtenu à l'issue de l'étape b) et, c) drying the raw material obtained at the end of step b) and,
d) la calcination du matériau séché issu de l'étape c). d) calcination of the dried material from step c).
14. Procédé selon la revendication 13 dans lequel ledit précurseur solide d'alumine est choisi parmi les oxydes d'aluminium, les hydroxydes d'aluminium et les oxyhydroxydes d'aluminium solubles ou dispersibles dans la solution acide. 14. The method of claim 13 wherein said solid precursor of alumina is selected from aluminum oxides, aluminum hydroxides and aluminum oxyhydroxides soluble or dispersible in the acid solution.
15. Procédé selon l'une des revendications 13 ou 14 dans lequel ledit rapport de la masse d'acide introduit sur la masse de précurseur solide d'alumine introduit est compris entre 30 et 62% en poids. 15. Method according to one of claims 13 or 14 wherein said ratio of the mass of acid introduced on the solid precursor mass of introduced alumina is between 30 and 62% by weight.
16. Procédé selon l'une des revendications 13 à 15 dans lequel ladite étape b) de mise en forme est réalisée par granulation ou par extrusion. 16. Method according to one of claims 13 to 15 wherein said step b) shaping is carried out by granulation or extrusion.
PCT/FR2012/000490 2011-12-14 2012-11-27 Alumina material having a multiscale structure, including an aluminum-oxide binder having good mechanical strength, and method for preparing same WO2013087999A1 (en)

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