WO2006008385A1 - Method for selectively producing ordered carbon nanotubes - Google Patents

Method for selectively producing ordered carbon nanotubes Download PDF

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Publication number
WO2006008385A1
WO2006008385A1 PCT/FR2005/001542 FR2005001542W WO2006008385A1 WO 2006008385 A1 WO2006008385 A1 WO 2006008385A1 FR 2005001542 W FR2005001542 W FR 2005001542W WO 2006008385 A1 WO2006008385 A1 WO 2006008385A1
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WO
WIPO (PCT)
Prior art keywords
catalyst
ferrous metal
metal deposition
grains
microns
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PCT/FR2005/001542
Other languages
French (fr)
Inventor
Philippe Kalck
Philippe Serp
Massimiliano Corrias
Original Assignee
Institut National Polytechnique De Toulouse
Arkema France
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Publication date
Application filed by Institut National Polytechnique De Toulouse, Arkema France filed Critical Institut National Polytechnique De Toulouse
Priority to EP05778658A priority Critical patent/EP1771379A1/en
Priority to CA002570587A priority patent/CA2570587A1/en
Priority to BRPI0512398-4A priority patent/BRPI0512398A/en
Priority to US11/629,028 priority patent/US20080193367A1/en
Priority to JP2007517354A priority patent/JP4866345B2/en
Priority to CN2005800212288A priority patent/CN101018736B/en
Publication of WO2006008385A1 publication Critical patent/WO2006008385A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/74—Iron group metals
    • B01J23/745—Iron
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
    • B82B3/00—Manufacture or treatment of nanostructures by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
    • B82B3/0009—Forming specific nanostructures
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/158—Carbon nanotubes
    • C01B32/16—Preparation
    • C01B32/162—Preparation characterised by catalysts
    • B01J35/393—
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2202/00—Structure or properties of carbon nanotubes
    • C01B2202/06—Multi-walled nanotubes
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2202/00—Structure or properties of carbon nanotubes
    • C01B2202/20—Nanotubes characterized by their properties
    • C01B2202/36—Diameter

Definitions

  • the invention relates to the production of ordered carbon nanotubes.
  • Ordered carbon nanotubes in the sense of the present invention have a tabular structure with a diameter of between 0.4 nm and 30 nm and a length greater than 100 times their diameter, in particular between 1000 and 100,000 times their diameter. They may be associated with metal catalyst particles or free of these particles (following purification). Carbon nanotubes have been described for a long time (S. Iijima "Helical nanotubes of graphitic carbon” Nature, 354, 56 (1991)), but are not yet exploited on an industrial scale. They could nonetheless be the subject of numerous applications, and in particular be greatly useful and advantageous in the manufacture of composite materials, flat screens, spikes for atomic force microscopes, storage of hydrogen or other gases, as catalytic supports ...
  • WO-03002456 discloses a method for selectively producing ordered fluidized bed carbon nanotubes in the presence of a supported iron-on-alumina catalyst comprising from 1% to 5% by weight of highly fluidized CVD-dispersed atomic iron on alumina grains of about 120 ⁇ m or 150 ⁇ m.
  • the deposited iron particles are dispersed and have a size of the order of 3 to 6 nm. This method makes it possible to obtain a good selectivity and a good yield (greater than 90%) with respect to the carbon source.
  • the highly dispersed catalysts with low metal loading make it possible to obtain good metallic catalytic activity A * (grams of nanotubes formed per gram of metal per hour) and catalytic activity.
  • the object of the invention is to propose a process which makes it possible simultaneously to obtain a high productivity, in particular of the order of or greater than 25%, a high activity, in particular of the order of or greater than 10%, and a selectivity. very high - especially greater than 90%, or even close to 100% - in carbon nanotubes produced - especially in multiwall nanotubes -.
  • the object of the invention is more particularly to provide a method for producing ordered carbon nanotubes-in particular multiwall nanotubes-having a kinetics and a performance compatible with the constraints of an industrial scale operation.
  • the invention relates to a process for the selective production of ordered carbon nanotubes by decomposition of a source of carbon in the gaseous state brought into contact with at least one solid catalyst supported in the form of grains, called catalyst, porous alumina support carrying a so-called ferrous, non-oxidized metal deposition of at least one transition metal whose iron characterized in that a supported catalyst mainly formed of catalyst grains is used:
  • the ferrous metal deposition covers more than 75% of the surface of the macroscopic form (without taking into account the porosity) of the alumina support.
  • the ferrous metal deposit is in the form of at least one cluster formed of a plurality of agglutinated metal bulbs.
  • the ferrous metal deposit forms a homogeneous continuous ferrous metal surface layer. formed of metal bulbs.
  • Each cluster-in particular the ferrous metal layer- is formed of bulbs, that is to say of rounded and globular swellings agglutinated to each other.
  • the inventors have indeed found that the specific catalyst that constitutes a non-oxidized ferrous metal deposition - in particular made in the form of clusters, or a continuous layer of bulbs - covering more than 75% of the alumina support, has a much higher performance than the known catalysts, and in particular simultaneously makes it possible to obtain high activity and productivity with carbon nanotube selectivity close to 100% .
  • the ferrous metal deposition is adapted to cover the alumina support so that its pores are rendered inaccessible. It should be noted that the fact that these pores (mesopores in the case of a mesoporous alumina) are made inaccessible by the metal deposition can be easily verified by a simple measurement of the variation of the specific surface area due to the presence of the deposit. Ferrous metal and / or by the calculation of the volume of mesopores and / or residual micropores and / or XPS analysis to demonstrate that the constituent chemical elements of the alumina support are no longer accessible on the surface.
  • the composition according to the invention has a specific surface area corresponding to that of grains whose pores are inaccessible.
  • each catalyst grain has a non-oxidized ferrous metal deposit forming a homogeneous continuous surface layer extending in at least a portion of a closed surface around a porous alumina core.
  • Continuous layer means that it is possible to travel continuously throughout the surface of this layer, without having to cross a portion of another kind (including a portion free of non-oxidized ferrous metal deposition).
  • the ferrous metal deposit is not dispersed on the surface of each grain of alumina, but instead forms a continuous layer of area apparently corresponding to that of the grains.
  • This layer is moreover “homogeneous” in that it is formed of iron or a plurality of metals including iron, and has a solid composition identical in all its volume.
  • the expression "closed surface” is used in the topological sense of the term, that is to say a surface that delimits and surrounds an internal finite space which is the heart of the grain, and which can take various forms (sphere, polyhedron). , prism, torus, cylinder, cone ).
  • the ferrous metal deposition forms the outer layer of the catalyst grains immediately after its manufacture and if the catalyst composition is not brought into contact with an oxidizing medium. If the catalyst composition is vented to atmosphere, an oxide layer may form at the periphery. This oxide layer can, if necessary, be removed by a step of
  • the ferrous metal deposit is derived from an elemental metal deposit (that is to say in which one (or more) metal (s) is (are) deposited (s) in the state element (s), that is to say in atomic or ionic form) made in a single step on the alumina support.
  • the ferrous metal layer is part of an elemental ferrous metal deposit made in a single step on the solid alumina support.
  • a single-stage elemental metal deposit can result in particular from a vacuum evaporation deposition (PVD), or a chemical vapor deposition (CVD), or an electrochemical deposition.
  • the catalyst composition used in a process according to the invention differs in particular from a composition obtained by grinding metallurgically manufactured pure metal parts.
  • a single-stage elemental metal deposit is formed of crystalline microdomains of the metal (s).
  • Such a metal deposit elementary is formed of bulbs (rounded and globular bulges) metallic agglutinated to each other.
  • the bulbs have an average size of between 10 nm and 1 ⁇ m, in particular between 30 nm and 100 nm.
  • the ferrous metal deposition covers from 90% to 100% of the surface of the macroscopic form (envelope surface considered without taking into account the porosity) of the grains, which is itself a closed surface.
  • This proportion of coverage of the alumina support surface by ferrous metal deposition can be determined by XPS analysis.
  • the ferrous metal deposit thus extends 90% to 100% of a closed surface.
  • the ferrous metal deposition extends over a thickness greater than 0.5 ⁇ m, in particular of the order of 2 to 20 ⁇ m.
  • the ferrous metal deposition of each catalyst grain extends superficially with an average apparent surface area (on the outside surface of the grain) greater than 2.10 3 ⁇ m 2 . More particularly, advantageously and according to the invention, the ferrous metal deposition of each catalyst grain extends superficially with an average apparent surface area of between 10 ⁇ m and 1.5 ⁇ 10 5 ⁇ m 2 .
  • the unoxidized ferrous metal deposition of each catalyst grain extends superficially with a global average dimension developed greater than 35 microns.
  • the overall average dimension developed is the equivalent radius of the disk circumscribing the ferrous metal deposit after having virtually developed it in a plane.
  • the unoxidized ferrous metal deposition of each catalyst grain extends superficially with an overall average developed dimension of between 200 ⁇ m and 400 ⁇ m.
  • a process according to the invention is characterized in that a supported catalyst is used in the form of grains whose shapes and size are adapted to allow the formation of a bed fluidized of these catalyst particles, in that a fluidized bed of the catalyst particles is produced in a reactor, and in that the source of carbon in the reactor is continuously delivered in contact with the catalyst particles under clean conditions; to ensure the fluidization of the bed of catalyst grains, the decomposition reaction and the formation of nanotubes.
  • a supported catalyst having a mean particle size (D50) of between 100 ⁇ m and 200 ⁇ m is used.
  • the shape of the catalyst grains may be globally substantially spherical or not.
  • the invention also applies to a process in which catalyst grains of more or less flattened form (flakes, discs, etc.) and / or elongated (cylinders, rods, ribbons, etc.) are used.
  • each grain comprises a core of alumina covered with a gangue formed of said ferrous metal deposit.
  • the ferrous metal deposit forms a metal gangue covering the entire surface of the porous alumina support and rendering its pores inaccessible.
  • each grain depends on that of the alumina core, and the conditions under which ferrous metal deposition is formed on that core.
  • the alumina has a specific surface area greater than 100 m 2 / g.
  • the supported catalyst has a specific surface area of less than 25 m 2 / g.
  • the thickness of the ferrous metal deposition may extend at least partly in the thickness of the porous alumina core and / or at least partly in the thickness relative to the porous core. It is not always easy to determine precisely and clearly the interface between the porous alumina core impregnated with ferrous metal deposition and the pure ferrous metal layer extending out of the alumina core and their relative arrangement.
  • a supported catalyst comprising more than 20% by weight, in particular of the order of 40%, of ferrous metal deposition is used.
  • the ferrous metal deposit is exclusively made of iron.
  • the ferrous metal deposition is formed of iron and at least one metal selected from nickel and cobalt. It is known in particular that it is possible to use a bi ⁇ metal catalyst Fe-Ni or Fe-Co with similar results to a catalyst of pure iron, all things being equal elsewhere.
  • the ferrous metal deposit is mainly iron.
  • the supported catalyst composition used in a process according to the invention is advantageously formed mainly of such grains, that is to say contains more than 50% of such grains, preferably more than 90% of such grains.
  • the invention extends to a process for the selective production of ordered carbon nanotubes in which a supported catalyst composition exclusively formed, with impurities, of such grains, that is to say the grains of which all comply with all or some of the characteristics defined above or below.
  • a quantity of carbon source such as the ratio of the mass of the starting carbon source - in particular of the mass of carbon introduced into the reactor per hour - on the metal mass is used.
  • the supported catalyst, in particular present in the reactor is greater than 100.
  • the carbon source is ethylene.
  • Other carbonaceous gases can be used.
  • FIG. 1 is a diagram of an example of an installation for the manufacture of a catalyst composition that can be used in a process according to the invention
  • FIG. 2 is a diagram of an example of an installation for the preparation of carbon nanotubes with a method according to the invention
  • FIG. 3 is a micrograph of the surface of a grain of a catalytic composition that can be used in a process according to the invention obtained in example 1,
  • FIGS. 4 and 5 are micrographs of the surface of the grains of a catalytic composition obtained in Example 2 that can be used in a process according to the invention
  • FIG. 6 is a graph showing the distribution of the diameters of the nanotubes obtained in example 4,
  • FIGS. 7a and 7b are microscopic photographs at two different scales representing nanotubes obtained in Example 4.
  • FIG. 1 is a diagram of an installation for implementing a method of manufacturing a divided solid catalyst composition used in a method according to the invention.
  • This installation comprises a reactor, called a deposition reactor 20 for the synthesis of the catalytic composition by chemical vapor deposition (CVD), which comprises a glass sublimator 1 into which the organometallic precursor is introduced.
  • This sublimator comprises a sintered plate and can be brought to the desired temperature by a heated bath 2.
  • the neutral carrier gas 3, for example helium, which entrains the vapors of the organometallic precursor used is stored in a bottle and admitted to the sublimator 1 using a flow regulator (not shown).
  • the sublimator 1 is connected to a lower glass compartment 4, which comprises a sintered plate, into which is introduced water vapor which serves to activate the decomposition of the organometallic precursor.
  • the presence of water makes it possible to obtain a non-oxidized metal deposit (thanks to the reaction of movement of the gas with water), free of impurity, and thus a very active catalyst.
  • the compartment 4 has a thermostatically controlled double jacket at a temperature which can be adjusted by means of a temperature controller (not shown).
  • the steam is entrained by and with a neutral carrier gas, for example nitrogen, stored in a bottle and admitted to the compartment 4 using a flow regulator (not shown).
  • a neutral carrier gas feed 6, for example nitrogen is intended to adjust the flow rates so as to be in the fluidization conditions.
  • This carrier gas 6 is stored in a bottle and admitted into compartment 4 using a flow regulator (not shown).
  • the upper part of the compartment 4 is sealingly connected to a fluidization column 7 made of glass, for example 5 cm in diameter, which is equipped at its base with a gas distributor.
  • This column 7 jacketed is thermostatically controlled at a temperature that can be adjusted by means of a temperature controller 8.
  • the upper part of the column 7 is connected to a vacuum pump 9 via a trap, to retain the decomposition gases released.
  • the implementation protocol of the examples relating to the preparation of the catalysts according to the invention by CVD is as follows.
  • a precursor mass Ma is introduced into the sublimator 1.
  • a mass Ms of alumina support grains is poured into the column 7 and a quantity of water is introduced into the compartment 4 with the aid of a syringe (for example of the order of 20 g).
  • the vacuum is made in the assembly formed of compartment 4 and column 7.
  • the temperature of the bed is brought to T1.
  • the sublimator 1 is brought to the temperature Ts and the pressure is set to the value Pa throughout the equipment by introducing the carrier gases 3, 5 and 6 (total flow Q). The deposit then begins and lasts a while.
  • the temperature is brought back to ambient temperature by slow cooling and the vacuum pump 9 is stopped.
  • the catalytic granular composition is removed from column 7 under an inert gas atmosphere (for example nitrogen): it is ready to be used for the manufacture of nanorubes in a reactor growth 30.
  • the growth reactor 30 is composed of a quartz fluidization column (for example 2.6 cm in diameter) provided at its center with a dispensing plate (sintered in quartz) 11 on which the powder is placed. catalytic granular composition.
  • the column 10 can be brought to the desired temperature by means of an oven 12 which can slide vertically vertically along the fluidization column 10.
  • the oven 12 has either a high position where it does not heat not the fluidized bed, a low position where it provides heating of the bed.
  • the gases 13 neutral gas such as helium, carbon source and hydrogen
  • the gases 13 are stored in bottles and are admitted into the fluidization column by means of flow regulators 14.
  • the fluidization column 10 is sealingly connected to a trap 15 for collecting any fine particles of catalytic granular composition or a mixture of catalytic granular composition and nanotubes.
  • the height of the column 10 is adapted to contain, in operation, the fluidized bed of the catalyst grains. In particular, it is at least 10 to 20 times the gaseous height, and must correspond to the heated zone. In the examples, a column 70 cm in height, heated to 60 cm high by oven 12, is chosen.
  • the protocol for implementing examples relating to the production of nanotubes according to the invention is as follows:
  • a mass Mc of granular supported catalyst is introduced into the fluidization column 10 under an inert gas atmosphere.
  • the furnace 12 Since the furnace 12 is in a low position relative to the catalytic bed, its temperature is brought to the desired value Tn for the synthesis of the nanotubes, either under an inert gas atmosphere or under a mixture of inert gas and hydrogen ( reactive gas).
  • the carbon source, the hydrogen and a complement of neutral gas are introduced into the column 10.
  • the total flow rate Q x provides the bed with a bubbling regime at the temperature Tn, without firing.
  • the growth of the nanotubes then begins and lasts a time ta.
  • the oven 12 is placed in the high position relative to the catalytic bed, the gas flow rates corresponding to the carbon source and to the hydrogen are stopped and the temperature is brought back to ambient temperature by slow cooling. .
  • the carbon nanotubes associated with the metal particles and attached to the support grains are extracted from the growth reactor 30 and stored without any particular precautions.
  • the amount of carbon deposited is measured by weighing and by gravimetric thermal analysis.
  • the nanotubes thus produced are analyzed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) for size and dispersion measurements and by X-ray crystallography and Raman spectroscopy to evaluate the crystallinity of the nanotubes.
  • TEM transmission electron microscopy
  • SEM scanning electron microscopy
  • a catalyst composition is prepared at 24% by weight of
  • the organometallic precursor is pentacarbonyl iron
  • the support is mesoporous alumina- ⁇ (pore volume 0.54 cm 3 g -1 ) sieved between 120 ⁇ m and 150 ⁇ m and having a specific surface area of 160 m 2 g 4 .
  • the composition obtained is formed of alumina grains covered with iron bulb clusters (the average bulb size is of the order of 20 nm), covering the surface of the alumina with a surface composition having 22% of aluminum as measured by XPS analysis (FIG. 3).
  • This example is aimed at the preparation of a catalyst composition supported at 40% by mass of iron on alumina (Al 2 O 3 ) as indicated in Example 1, but with the following operating conditions:
  • the composition obtained is formed of alumina grains completely covered with an iron matrix consisting of iron bulb clusters of 30 nm to 300 nm ( Figures 4 and 5).
  • the specific surface area of the final material is 8 m 2 g -1 and the XPS analyzes show that the aluminum is no longer present on the surface.
  • Multilayer carbon nanotubes are manufactured from the catalyst of Example 1 at 24% FeZAl 2 O 3 in an installation according to Figure 2, from ethylene gas as a carbon source.
  • Multilayer carbon nanotubes are manufactured from the catalyst of Example 2 at 40% FeZAl 2 O 3 in an installation according to Figure 2, from ethylene gas as a carbon source.
  • the operating conditions are as follows:
  • FIG. 6 also shows that the diameter of the nanotubes obtained in Example 4 is in the majority of the order of 10 nm to 25 nm, whereas the grains of the composition have a diameter of the order of 150 ⁇ m and the bulbs iron sizes from 30 to 300 nm. Again, this result is surprising, inexplicable and goes against all previous teachings.
  • FIGS. 7a and 7b show the high selectivity of the nanotubes produced in Example 4, which are thus directly usable, particularly in view of the small proportion of residual porous support in the nanotubes that had to be eliminated in the previous processes. known.
  • Multilayer carbon nanotubes are manufactured from a 5% FeZAl 2 O 3 catalyst obtained as indicated in Example 1 with the operating conditions:
  • the carbon nanotubes are prepared in a plant according to Figure 2, from ethylene gas as a carbon source.
  • a 20% by weight FeZAl 2 O 3 catalyst composition is prepared by the fluidized bed CVD method described above.
  • the carrier gas is nitrogen.
  • the organometallic precursor is pentacarbonyl iron
  • the support is non-porous ⁇ -alumina (specific surface area (BET method) of 2 m 2 / g).
  • the resulting composition is formed of gangue-coated alumina particles formed of iron bulb clusters completely covering the surface of the alumina with a surface composition where aluminum is absent as measured by XPS analysis.
  • Multilayer carbon nanotubes are manufactured from this iron catalyst on non-porous alumina in an installation according to FIG. 2, from ethylene gas as a carbon source.

Abstract

The invention relates to a method for selectively producing nanotubes made of carbon ordered by decomposing a gaseous carbon source in contact with at least one solid catalyst in the form of catalyst grains which are made of an alumina porous support provided with a metallic ferrous non-oxidised deposit and whose mean grain-size ranges from 25 νm to 2.5 mm and on which said metallic ferrous deposit covers more than 75 % of the surface of the microscopic alumina support and is embodied in the form of at least one cluster formed by a plurality of metallic agglutinated bulbs.

Description

PROCEDE DE FABRICATION SELECTIVE DE NANOTUBES DE CARBONE PROCESS FOR THE SELECTIVE MANUFACTURE OF CARBON NANOTUBES
ORDONNEORDERED
L'invention concerne la fabrication de nanotubes de carbone ordonné.The invention relates to the production of ordered carbon nanotubes.
Les nanotubes de carbone ordonné au sens de la présente invention présentent une structure tabulaire de diamètre compris entre 0,4nm et 30 nm et de longueur supérieure à 100 fois leur diamètre, notamment comprise entre 1000 et 100 000 fois leur diamètre. Ils peuvent se présenter soit associés à des particules de catalyseur métallique, soit exempts de ces particules (suite à une purification). Les nanotubes de carbone ont été décrits depuis longtemps (S. Iijima « Helical nanotubes of graphitic carbon » Nature, 354, 56 (1991)), mais ne font pas encore l'objet d'une exploitation à l'échelle industrielle. Ils pourraient néanmoins faire l'objet de nombreuses applications, et notamment être grandement utiles et avantageux dans la fabrication de matériaux composites, d'écrans plats, de pointes pour microscopes à force atomique, le stockage d'hydrogène ou d'autres gaz, à titre de supports catalytiques...Ordered carbon nanotubes in the sense of the present invention have a tabular structure with a diameter of between 0.4 nm and 30 nm and a length greater than 100 times their diameter, in particular between 1000 and 100,000 times their diameter. They may be associated with metal catalyst particles or free of these particles (following purification). Carbon nanotubes have been described for a long time (S. Iijima "Helical nanotubes of graphitic carbon" Nature, 354, 56 (1991)), but are not yet exploited on an industrial scale. They could nonetheless be the subject of numerous applications, and in particular be greatly useful and advantageous in the manufacture of composite materials, flat screens, spikes for atomic force microscopes, storage of hydrogen or other gases, as catalytic supports ...
WO-03002456 décrit un procédé de fabrication sélective de nanotubes de carbone ordonné en lit fluidisé en présence d'un catalyseur supporté formé de fer sur alumine comprenant de 1% à 5% en poids de fer atomique fortement dispersé par CVD en lit fluidisé sur des grains d'alumine d'environ 120 μm ou 150 μm. Les particules de fer déposées sont dispersées et présentent une dimension de l'ordre de 3 à 6nm. Ce procédé permet d'obtenir une bonne sélectivité et un bon rendement (supérieur à 90%) par rapport à la source de carbone. On considère en particulier dans le cas des métaux non oxydés utilisés pour catalyser la formation de nanotubes de carbone par décomposition thermique en phase gazeuse d'une source de carbone, qu'il est nécessaire de prévoir une multiplicité de sites catalytiques métalliques discontinus dispersés au maximum sur des grains d'un support, la taille des sites métalliques dispersés correspondant au diamètre des nanotubes à former. De très nombreuses recherches ont été effectuées en ce sens. Une autre solution serait d'utiliser des particules catalytiques isolées de taille équivalente au diamètre des nanotubes à former. En effet, une particule métallique est entraînée à l'extrémité de chaque nariotube.WO-03002456 discloses a method for selectively producing ordered fluidized bed carbon nanotubes in the presence of a supported iron-on-alumina catalyst comprising from 1% to 5% by weight of highly fluidized CVD-dispersed atomic iron on alumina grains of about 120 μm or 150 μm. The deposited iron particles are dispersed and have a size of the order of 3 to 6 nm. This method makes it possible to obtain a good selectivity and a good yield (greater than 90%) with respect to the carbon source. In particular, in the case of unoxidized metals used to catalyze the formation of carbon nanotubes by thermal decomposition in the gas phase of a carbon source, it is necessary to provide a multiplicity of discontinuous metallic catalytic sites dispersed at most. on grains of a support, the size of the dispersed metal sites corresponding to the diameter of the nanotubes to be formed. A great deal of research has been done in this direction. Another solution would be to use catalytic particles isolated from size equivalent to the diameter of the nanotubes to be formed. Indeed, a metal particle is driven to the end of each nariotube.
Les catalyseurs fortement dispersés et peu chargés en métal permettent d'obtenir une bonne activité catalytique métallique A* (grammes de nanotubes formés par gramme de métal et par heure) et une activité catalytique AThe highly dispersed catalysts with low metal loading make it possible to obtain good metallic catalytic activity A * (grams of nanotubes formed per gram of metal per hour) and catalytic activity.
(grammes de nanotubes formés par gramme de composition catalytique et par heure) assez moyenne. Néanmoins, cette bonne activité est obtenue au détriment d'une faible productivité (grammes de nanotubes formés par gramme de composition catalytique). Par exemple le procédé décrit par WO-03002456 permet d'obtenir au mieux une activité A* de 13,1, et une activité A de 0,46 pour une productivité de 0,46.(grams of nanotubes formed per gram of catalytic composition and per hour) fairly average. Nevertheless, this good activity is obtained to the detriment of a low productivity (grams of nanotubes formed per gram of catalytic composition). For example, the process described in WO-03002456 makes it possible to obtain at best an activity A * of 13.1, and an activity A of 0.46 for a productivity of 0.46.
Or, du point de vue économique et industriel, il est souhaitable non seulement que la réaction soit sélective en nanotubes (par rapport aux autres formes de carbone pouvant être produites : suie, fibres, ...), que l'activité soit élevée pour que la réaction soit rapide, et que sa productivité soit également élevée pour éviter la nécessité des étapes de purification pour séparer le catalyseur des nanotubes et les frais afférents.However, from the economic and industrial point of view, it is desirable not only that the reaction be selective in nanotubes (compared to other forms of carbon that can be produced: soot, fibers, ...), that the activity is high for that the reaction is rapid, and that its productivity is also high to avoid the need for purification steps to separate the catalyst nanotubes and related costs.
Certains auteurs (« Iron-containing catalysts of méthane décomposition : accumulation of filamentous carbon » Lyudmila B. Avdeeva et al., Applied Catalysis A : General 228 (2002) 53-63) ont récemment proposé d'utiliser des catalyseurs à forte teneur en fer ou en fer-cobalt sur alumine réalisés par précipitation ou coprécipitation ou imprégnation. Les meilleurs résultats annoncés avec un catalyseur Fe/Co/Al2O3 contenant 50% en poids de fer et 6% en poids de cobalt permettent d'obtenir après 40 heures une productivité de 52,4 pour une activité A de 1,31, une activité A* de 2,34 et avec un matériau produit contenant à la fois des nanotubes de carbone et d'autres structures fibreuses (mauvaise sélectivité).Some authors ("Iron-containing catalysts of methane decomposition: accumulation of filamentous carbon" Lyudmila B. Avdeeva et al., Applied Catalysis A: General 228 (2002) 53-63) have recently proposed to use catalysts with a high iron or iron cobalt on alumina made by precipitation or coprecipitation or impregnation. The best results announced with a Fe / Co / Al 2 O 3 catalyst containing 50% by weight of iron and 6% by weight of cobalt make it possible to obtain, after 40 hours, a productivity of 52.4 for an activity A of 1.31 , A * activity of 2.34 and with a product material containing both carbon nanotubes and other fibrous structures (poor selectivity).
Ainsi, on peut penser qu'une forte proportion de métal sur un catalyseur réalisé par imprégnation ou précipitation permet d'augmenter la productivité, mais au détriment de l'activité et/ou de la sélectivité en nanotubes produits. II reste que les mécanismes qui président à la catalyse de la formation de nanotubes de carbone sont encore pour une large part inexpliquée, mal maîtrisés et que les procédés et catalyseurs envisagés sont définis de façon essentiellement empirique. L'invention vise donc à pallier ces inconvénients en proposant un procédé utilisant un catalyseur de performances étonnamment élevées. Plus particulièrement, l'invention vise à proposer un procédé permettant d'obtenir simultanément une productivité élevée -notamment de l'ordre de ou supérieure à 25-, une activité élevée -notamment de l'ordre de ou supérieure à 10- et une sélectivité très élevée -notamment supérieure à 90%, voire proche de 100%- en nanotubes de carbone produits -notamment en nanotubes multiparois-.Thus, it may be expected that a high proportion of metal on a catalyst produced by impregnation or precipitation makes it possible to increase the productivity, but to the detriment of the activity and / or the selectivity in nanotubes produced. It remains the case that the mechanisms governing the catalysis of the formation of carbon nanotubes are still largely unexplained, poorly controlled and that the processes and catalysts envisaged are defined essentially empirically. The invention therefore aims to overcome these disadvantages by proposing a method using a surprisingly high performance catalyst. More particularly, the object of the invention is to propose a process which makes it possible simultaneously to obtain a high productivity, in particular of the order of or greater than 25%, a high activity, in particular of the order of or greater than 10%, and a selectivity. very high - especially greater than 90%, or even close to 100% - in carbon nanotubes produced - especially in multiwall nanotubes -.
L'invention vise plus particulièrement à proposer un procédé de fabrication de nanotubes de carbone ordonné -notamment de nanotubes multiparois- présentant une cinétique et un rendement compatibles avec les contraintes d'une exploitation à l'échelle industrielle.The object of the invention is more particularly to provide a method for producing ordered carbon nanotubes-in particular multiwall nanotubes-having a kinetics and a performance compatible with the constraints of an industrial scale operation.
Pour ce faire, l'invention concerne un procédé de fabrication sélective de nanotubes de carbone ordonné par décomposition d'une source de carbone à l'état gazeux mise en contact d'au moins un catalyseur solide supporté sous forme de grains, dits grains de catalyseur, de support d'alumine poreuse portant un dépôt métallique, dit ferreux, non oxydé d'au moins un métal de transition dont le fer caractérisé en ce qu'on utilise un catalyseur supporté principalement formé de grains de catalyseur :To this end, the invention relates to a process for the selective production of ordered carbon nanotubes by decomposition of a source of carbon in the gaseous state brought into contact with at least one solid catalyst supported in the form of grains, called catalyst, porous alumina support carrying a so-called ferrous, non-oxidized metal deposition of at least one transition metal whose iron characterized in that a supported catalyst mainly formed of catalyst grains is used:
- de granulométrie moyenne comprise entre 25 μm et 2,5 mm,of average particle size between 25 μm and 2.5 mm,
- sur lesquels le dépôt métallique ferreux couvre plus de 75% de la surface de la forme macroscopique (sans prendre en considération la porosité) du support d'alumine.- on which the ferrous metal deposition covers more than 75% of the surface of the macroscopic form (without taking into account the porosity) of the alumina support.
Avantageusement et selon l'invention, le dépôt métallique ferreux se présente sous la forme d'au moins un amas formé d'une pluralité de bulbes métalliques agglutinés. Avantageusement et selon l'invention, le dépôt métallique ferreux forme une couche superficielle métallique ferreuse continue homogène formée de bulbes métalliques. Chaque amas -notamment la couche métallique ferreuse- est formé de bulbes, c'est à dire de renflements arrondis et globuleux agglutinés les uns aux autres.Advantageously and according to the invention, the ferrous metal deposit is in the form of at least one cluster formed of a plurality of agglutinated metal bulbs. Advantageously and according to the invention, the ferrous metal deposit forms a homogeneous continuous ferrous metal surface layer. formed of metal bulbs. Each cluster-in particular the ferrous metal layer-is formed of bulbs, that is to say of rounded and globular swellings agglutinated to each other.
De façon inexpliquée et en complète contradiction avec l'enseignement de l'état de la technique, les inventeurs ont en effet constaté que le catalyseur spécifique que constitue un dépôt métallique ferreux non oxydé - notamment réalisé sous forme d'amas, ou d'une couche continue, de bulbes - couvrant plus de 75% du support d'alumine, présente des performances très supérieures aux catalyseurs connus, et notamment permet simultanément d'obtenir une activité et une productivité élevées avec une sélectivité en nanotubes de carbone proche de 100%.Unexplained and in complete contradiction with the teaching of the state of the art, the inventors have indeed found that the specific catalyst that constitutes a non-oxidized ferrous metal deposition - in particular made in the form of clusters, or a continuous layer of bulbs - covering more than 75% of the alumina support, has a much higher performance than the known catalysts, and in particular simultaneously makes it possible to obtain high activity and productivity with carbon nanotube selectivity close to 100% .
Avantageusement et selon l'invention, le dépôt métallique ferreux est adapté pour couvrir le support d'alumine de telle sorte que ses pores soient rendus inaccessibles. Il est à noter que le fait que ces pores (mésopores dans le cas d'une alumine mésoporeuse) soient rendus inaccessibles par le dépôt métallique peut être aisément vérifié par une simple mesure de la variation de l'aire spécifique due à la présence du dépôt métallique ferreux et/ou par le calcul du volume de mésopores et/ou de micropores résiduels et/ou par analyse XPS permettant de démontrer que les éléments chimiques constitutifs du support d'alumine ne sont plus accessibles en surface. Ainsi, en particulier, la composition selon l'invention présente une aire spécifique correspondant à celle de grains dont les pores sont inaccessibles.Advantageously and according to the invention, the ferrous metal deposition is adapted to cover the alumina support so that its pores are rendered inaccessible. It should be noted that the fact that these pores (mesopores in the case of a mesoporous alumina) are made inaccessible by the metal deposition can be easily verified by a simple measurement of the variation of the specific surface area due to the presence of the deposit. ferrous metal and / or by the calculation of the volume of mesopores and / or residual micropores and / or XPS analysis to demonstrate that the constituent chemical elements of the alumina support are no longer accessible on the surface. Thus, in particular, the composition according to the invention has a specific surface area corresponding to that of grains whose pores are inaccessible.
Avantageusement et selon l'invention, chaque grain de catalyseur présente un dépôt métallique ferreux non oxydé formant une couche superficielle continue homogène s'étendant selon au moins une portion d'une surface fermée autour d'un cœur d'alumine poreuse.Advantageously and according to the invention, each catalyst grain has a non-oxidized ferrous metal deposit forming a homogeneous continuous surface layer extending in at least a portion of a closed surface around a porous alumina core.
Par couche « continue », on désigne le fait qu'il est possible de parcourir continûment toute la surface de cette couche, sans avoir à traverser une portion d'une autre nature (notamment une portion exempte de dépôt métallique ferreux non oxydé). Ainsi, le dépôt métallique ferreux n'est pas dispersé à la surface de chaque grain d'alumine, mais forme au contraire une couche continue d'aire apparente correspondant sensiblement à celle des grains. Cette couche est de surcroît « homogène » en ce sens qu'elle est formée de fer ou d'une pluralité de métaux dont le fer, et présente une composition solide identique dans tout son volume. L'expression « surface fermée » est utilisée au sens topologique du terme, c'est-à-dire désigne une surface qui délimite et entoure un espace fini interne qui est le cœur du grain, et qui peut prendre diverses formes (sphère, polyèdre, prisme, tore, cylindre, cône...)."Continuous" layer means that it is possible to travel continuously throughout the surface of this layer, without having to cross a portion of another kind (including a portion free of non-oxidized ferrous metal deposition). Thus, the ferrous metal deposit is not dispersed on the surface of each grain of alumina, but instead forms a continuous layer of area apparently corresponding to that of the grains. This layer is moreover "homogeneous" in that it is formed of iron or a plurality of metals including iron, and has a solid composition identical in all its volume. The expression "closed surface" is used in the topological sense of the term, that is to say a surface that delimits and surrounds an internal finite space which is the heart of the grain, and which can take various forms (sphere, polyhedron). , prism, torus, cylinder, cone ...).
Le dépôt métallique ferreux forme la couche extérieure des grains de catalyseur, immédiatement après sa fabrication et si la composition de catalyseur n'est pas mise en présence d'un milieu oxydant. Si la composition de catalyseur est mise à l'air atmosphérique, une couche d'oxyde peut se former en périphérie. Cette couche d'oxyde peut si nécessaire être supprimée par une étape deThe ferrous metal deposition forms the outer layer of the catalyst grains immediately after its manufacture and if the catalyst composition is not brought into contact with an oxidizing medium. If the catalyst composition is vented to atmosphere, an oxide layer may form at the periphery. This oxide layer can, if necessary, be removed by a step of
- réduction, avant utilisation des grains de catalyseur. Avantageusement et selon l'invention, le dépôt métallique ferreux est issu d'un dépôt métallique élémentaire (c'est-à-dire dans lequel un (ou plusieurs) métal(aux) est(sont) déposé(s) à l'état d'élément(s), c'est-à-dire sous forme atomique ou ionique) réalisé en une seule étape sur le support d'alumine.reduction, before use of the catalyst grains. Advantageously and according to the invention, the ferrous metal deposit is derived from an elemental metal deposit (that is to say in which one (or more) metal (s) is (are) deposited (s) in the state element (s), that is to say in atomic or ionic form) made in a single step on the alumina support.
Ainsi, la couche métallique ferreuse fait partie d'un dépôt métallique ferreux élémentaire réalisé en une seule étape sur le support d'alumine solide. Un tel dépôt métallique élémentaire en une seule étape peut résulter notamment d'un dépôt par évaporation sous vide (PVD), ou d'un dépôt chimique en phase vapeur (CVD), ou d'un dépôt électrochimique.Thus, the ferrous metal layer is part of an elemental ferrous metal deposit made in a single step on the solid alumina support. Such a single-stage elemental metal deposit can result in particular from a vacuum evaporation deposition (PVD), or a chemical vapor deposition (CVD), or an electrochemical deposition.
Au contraire, il ne peut pas résulter d'un procédé mis en œuvre en plusieurs étapes en phase liquide -notamment par précipitation ou imprégnation-, ou dépôt à l'état fondu et solidification, ou par dépôt d'oxyde(s) métallique(s) suivi d'une étape de réduction. La composition de catalyseur utilisée dans un procédé selon l'invention se distingue en particulier d'une composition obtenue par broyage de pièces de métal pur fabriquées par voie métallurgique. Un dépôt métallique élémentaire en une seule étape est formé de microdomaines cristallins du(des) métal(aux). Un tel dépôt métallique élémentaire est formé de bulbes (renflements arrondis et globuleux) métalliques agglutinés les uns aux autres.On the contrary, it can not result from a process carried out in several stages in the liquid phase - in particular by precipitation or impregnation -, or deposition in the molten state and solidification, or by deposition of metal oxide (s) ( s) followed by a reduction step. The catalyst composition used in a process according to the invention differs in particular from a composition obtained by grinding metallurgically manufactured pure metal parts. A single-stage elemental metal deposit is formed of crystalline microdomains of the metal (s). Such a metal deposit elementary is formed of bulbs (rounded and globular bulges) metallic agglutinated to each other.
En outre, avantageusement et selon l'invention, les bulbes ont une dimension moyenne comprise entre 10 nm et lμm -notamment entre 30 nm et 100 nm-.In addition, advantageously and according to the invention, the bulbs have an average size of between 10 nm and 1 μm, in particular between 30 nm and 100 nm.
Avantageusement et selon l'invention, le dépôt métallique ferreux couvre de 90% à 100% de la surface de la forme macroscopique (surface enveloppe considérée sans prise en compte de la porosité) des grains qui est elle- même une surface fermée. Cette proportion de couverture de la surface du support d'alumine par le dépôt métallique ferreux peut être déterminée par une analyse XPS. Le dépôt métallique ferreux s'étend ainsi selon 90% à 100% d'une surface fermée.Advantageously and according to the invention, the ferrous metal deposition covers from 90% to 100% of the surface of the macroscopic form (envelope surface considered without taking into account the porosity) of the grains, which is itself a closed surface. This proportion of coverage of the alumina support surface by ferrous metal deposition can be determined by XPS analysis. The ferrous metal deposit thus extends 90% to 100% of a closed surface.
Avantageusement et selon l'invention, le dépôt métallique ferreux s'étend sur une épaisseur supérieure à 0,5 μm -notamment de l'ordre de 2 à 20 μm-. En outre, avantageusement et selon l'invention, le dépôt métallique ferreux de chaque grain de catalyseur s'étend superficiellement avec une aire apparente moyenne (en surface extérieure du grain) supérieure à 2.103 μm2. Plus particulièrement, avantageusement et selon l'invention, le dépôt métallique ferreux de chaque grain de catalyseur s'étend superficiellement avec une aire apparente moyenne comprise entre 10 μm et 1,5.105 μm2.Advantageously and according to the invention, the ferrous metal deposition extends over a thickness greater than 0.5 μm, in particular of the order of 2 to 20 μm. In addition, advantageously and according to the invention, the ferrous metal deposition of each catalyst grain extends superficially with an average apparent surface area (on the outside surface of the grain) greater than 2.10 3 μm 2 . More particularly, advantageously and according to the invention, the ferrous metal deposition of each catalyst grain extends superficially with an average apparent surface area of between 10 μm and 1.5 × 10 5 μm 2 .
En outre, avantageusement et selon l'invention, le dépôt métallique ferreux non oxydé de chaque grain de catalyseur s'étend superficiellement avec une dimension moyenne globale développée supérieure à 35 μm. La dimension moyenne globale développée est le rayon équivalent du disque circonscrivant le dépôt métallique ferreux après l'avoir virtuellement développé dans un plan. Avantageusement et selon l'invention, le dépôt métallique ferreux non oxydé de chaque grain de catalyseur s'étend superficiellement avec une dimension moyenne globale développée comprise entre 200 μm et 400 μm.In addition, advantageously and according to the invention, the unoxidized ferrous metal deposition of each catalyst grain extends superficially with a global average dimension developed greater than 35 microns. The overall average dimension developed is the equivalent radius of the disk circumscribing the ferrous metal deposit after having virtually developed it in a plane. Advantageously and according to the invention, the unoxidized ferrous metal deposition of each catalyst grain extends superficially with an overall average developed dimension of between 200 μm and 400 μm.
Avantageusement, un procédé selon l'invention est caractérisé en ce qu'on utilise un catalyseur supporté se présentant sous forme de grains dont les formes et la dimension sont adaptées pour permettre la formation d'un lit fluidisé de ces grains de catalyseur, en ce qu'on réalise un lit fluidisé des grains de catalyseur dans un réacteur, et en ce qu'on délivre en continu la source de carbone dans le réacteur au contact des grains de catalyseur dans des conditions propres à assurer la fluidisation du lit de grains de catalyseur, la réaction de décomposition et la formation de nanotubes.Advantageously, a process according to the invention is characterized in that a supported catalyst is used in the form of grains whose shapes and size are adapted to allow the formation of a bed fluidized of these catalyst particles, in that a fluidized bed of the catalyst particles is produced in a reactor, and in that the source of carbon in the reactor is continuously delivered in contact with the catalyst particles under clean conditions; to ensure the fluidization of the bed of catalyst grains, the decomposition reaction and the formation of nanotubes.
Plus particulièrement, avantageusement et selon l'invention, on utilise un catalyseur supporté présentant une granulométrie moyenne (D50) comprise entre 100 μm et 200 μm. La forme des grains de catalyseur peut être globalement sensiblement sphérique ou non. L'invention s'applique aussi à un procédé dans lequel on utilise des grains de catalyseur de forme plus ou moins aplatie (flocons, disques...) et/ou allongée (cylindres, bâtonnets, rubans...).More particularly, advantageously and according to the invention, a supported catalyst having a mean particle size (D50) of between 100 μm and 200 μm is used. The shape of the catalyst grains may be globally substantially spherical or not. The invention also applies to a process in which catalyst grains of more or less flattened form (flakes, discs, etc.) and / or elongated (cylinders, rods, ribbons, etc.) are used.
Avantageusement et selon l'invention, chaque grain comprend un cœur d'alumine couvert d'une gangue formée dudit dépôt métallique ferreux.Advantageously and according to the invention, each grain comprises a core of alumina covered with a gangue formed of said ferrous metal deposit.
Ainsi, avantageusement et selon l'invention, le dépôt métallique ferreux forme une gangue métallique couvrant la totalité de la surface du support d'alumine poreuse et rendant ses pores inaccessibles.Thus, advantageously and according to the invention, the ferrous metal deposit forms a metal gangue covering the entire surface of the porous alumina support and rendering its pores inaccessible.
La forme de chaque grain dépend de celle du cœur d'alumine, et des conditions dans lesquelles le dépôt métallique ferreux est formé sur ce cœur.The shape of each grain depends on that of the alumina core, and the conditions under which ferrous metal deposition is formed on that core.
Avantageusement et selon l'invention, l'alumine présente une aire spécifique supérieure à 100 m2/g. Mais, le catalyseur supporté présente une aire spécifique inférieure à 25 m2/g.Advantageously and according to the invention, the alumina has a specific surface area greater than 100 m 2 / g. However, the supported catalyst has a specific surface area of less than 25 m 2 / g.
Il est à noter que l'épaisseur du dépôt métallique ferreux peut s'étendre au moins pour partie dans l'épaisseur du cœur poreux d'alumine et/ou au moins pour partie en surépaisseur par rapport au cœur poreux. Il n'est d'ailleurs pas toujours aisé de déterminer précisément et clairement l'interface entre le cœur d'alumine poreuse imprégnée du dépôt métallique ferreux et la couche métallique ferreuse pure s 'étendant hors du cœur d'alumine et leur disposition relative.It should be noted that the thickness of the ferrous metal deposition may extend at least partly in the thickness of the porous alumina core and / or at least partly in the thickness relative to the porous core. It is not always easy to determine precisely and clearly the interface between the porous alumina core impregnated with ferrous metal deposition and the pure ferrous metal layer extending out of the alumina core and their relative arrangement.
En outre, avantageusement et selon l'invention, on utilise un catalyseur supporté comprenant plus de 20% en poids -notamment de l'ordre de 40%- de dépôt métallique ferreux. Avantageusement et selon l'invention, le dépôt métallique ferreux est exclusivement constitué de fer.In addition, advantageously and according to the invention, a supported catalyst comprising more than 20% by weight, in particular of the order of 40%, of ferrous metal deposition is used. Advantageously and according to the invention, the ferrous metal deposit is exclusively made of iron.
En variante, avantageusement et selon l'invention, le dépôt métallique ferreux est formé de fer et d'au moins un métal choisi parmi le nickel et le cobalt. On sait en effet en particulier qu'il est possible d'utiliser un catalyseur bi¬ métallique Fe-Ni ou Fe-Co avec des résultats similaires à un catalyseur de fer pur, toutes choses étant égales par ailleurs. De préférence, le dépôt métallique ferreux est principalement constitué de fer.Alternatively, advantageously and according to the invention, the ferrous metal deposition is formed of iron and at least one metal selected from nickel and cobalt. It is known in particular that it is possible to use a bi¬ metal catalyst Fe-Ni or Fe-Co with similar results to a catalyst of pure iron, all things being equal elsewhere. Preferably, the ferrous metal deposit is mainly iron.
La composition de catalyseur supporté utilisée dans un procédé selon l'invention est avantageusement formée principalement de tels grains, c'est-à-dire contient plus de 50% de tels grains, de préférence plus de 90% de tels grains.The supported catalyst composition used in a process according to the invention is advantageously formed mainly of such grains, that is to say contains more than 50% of such grains, preferably more than 90% of such grains.
L'invention s'étend à un procédé de fabrication sélective de nanotubes carbone ordonné dans lequel on utilise une composition de catalyseur supporté exclusivement formée, aux impuretés près, de tels grains, c'est-à-dire dont les grains sont tous conformes à tout ou partie des caractéristiques définies ci- dessus ou ci-après.The invention extends to a process for the selective production of ordered carbon nanotubes in which a supported catalyst composition exclusively formed, with impurities, of such grains, that is to say the grains of which all comply with all or some of the characteristics defined above or below.
L'emploi d'un tel catalyseur supporté performant permet en particulier d'augmenter considérablement la quantité de la source de carbone de départ.The use of such a high performance supported catalyst makes it possible in particular to considerably increase the amount of the starting carbon source.
Ainsi, dans un procédé selon l'invention, on utilise une quantité de source de carbone telle que le rapport de la masse de la source de carbone de départ -notamment de la masse de carbone introduite dans le réacteur par heure- sur la masse métallique du catalyseur supporté -notamment présente dans le réacteur- est supérieur à 100. Avantageusement et selon l'invention, la source de carbone est Péthylène. D'autres gaz carbonés peuvent être utilisés.Thus, in a process according to the invention, a quantity of carbon source such as the ratio of the mass of the starting carbon source - in particular of the mass of carbon introduced into the reactor per hour - on the metal mass is used. the supported catalyst, in particular present in the reactor, is greater than 100. Advantageously and according to the invention, the carbon source is ethylene. Other carbonaceous gases can be used.
D'autres buts, caractéristiques et avantages de l'invention apparaissent à la lecture de la description suivante de ses exemples de réalisation qui se réfère aux figures annexées dans lesquelles : - la figure 1 est un schéma d'un exemple d'installation pour la fabrication d'une composition de catalyseur pouvant être utilisée dans un procédé selon l'invention,Other objects, features and advantages of the invention appear on reading the following description of its exemplary embodiments which refers to the appended figures in which: FIG. 1 is a diagram of an example of an installation for the manufacture of a catalyst composition that can be used in a process according to the invention,
- la figure 2 est un schéma d'un exemple d'installation pour la préparation de nanotubes de carbone avec un procédé selon l'invention,FIG. 2 is a diagram of an example of an installation for the preparation of carbon nanotubes with a method according to the invention,
- la figure 3 est un micrographe de la surface d'un grain d'une composition catalytique pouvant être utilisée dans un procédé selon l'invention obtenue à l'exemple 1,FIG. 3 is a micrograph of the surface of a grain of a catalytic composition that can be used in a process according to the invention obtained in example 1,
- les figures 4 et 5 sont des micrographes de la surface des grains d'une composition catalytique obtenue à l'exemple 2 pouvant être utilisée dans un procédé selon l'invention,FIGS. 4 and 5 are micrographs of the surface of the grains of a catalytic composition obtained in Example 2 that can be used in a process according to the invention,
- la figure 6 est un graphe représentant la répartition des diamètres des nanotubes obtenus à l'exemple 4,FIG. 6 is a graph showing the distribution of the diameters of the nanotubes obtained in example 4,
- les figures 7a et 7b sont des photographies microscopiques à deux échelles différentes représentant des nanotubes obtenus à l'exemple 4.FIGS. 7a and 7b are microscopic photographs at two different scales representing nanotubes obtained in Example 4.
La figure 1 est un schéma d'une installation permettant la mise en œuvre d'un procédé de fabrication d'une composition catalytique solide divisée utilisée dans un procédé selon l'invention. Cette installation comprend un réacteur, dit réacteur de dépôt 20 pour la synthèse de la composition catalytique par dépôt chimique en phase vapeur (CVD), qui comporte un sublimateur en verre 1 dans lequel est introduit le précurseur organométallique. Ce sublimateur comprend une plaque frittée et peut être porté à la température désirée par un bain chauffé 2.Figure 1 is a diagram of an installation for implementing a method of manufacturing a divided solid catalyst composition used in a method according to the invention. This installation comprises a reactor, called a deposition reactor 20 for the synthesis of the catalytic composition by chemical vapor deposition (CVD), which comprises a glass sublimator 1 into which the organometallic precursor is introduced. This sublimator comprises a sintered plate and can be brought to the desired temperature by a heated bath 2.
Le gaz vecteur 3 neutre, par exemple de l'hélium, qui entraîne les vapeurs du précurseur organométallique utilisé est stocké dans une bouteille et admis dans le sublimateur 1 à l'aide d'un régulateur de débit (non représenté).The neutral carrier gas 3, for example helium, which entrains the vapors of the organometallic precursor used is stored in a bottle and admitted to the sublimator 1 using a flow regulator (not shown).
Le sublimateur 1 est relié à un compartiment en verre 4 inférieur, qui comprend une plaque frittée, dans lequel est introduite de la vapeur d'eau qui sert à activer la décomposition du précurseur organométallique. La présence d'eau permet d'obtenir un dépôt métallique non oxydé (grâce à la réaction de déplacement du gaz à l'eau), exempt d'impureté, et ainsi un catalyseur très actif. Le compartiment 4 présente une double enveloppe thermostatée à une température qui peut être ajustée au moyen d'un régulateur de température (non représenté). La vapeur d'eau est entraînée par et avec un gaz vecteur 5 neutre, par exemple de l'azote, stocké dans une bouteille et admis dans le compartiment 4 à l'aide d'un régulateur de débit (non représenté). Une alimentation en gaz vecteur 6 neutre, par exemple de l'azote, est destinée à ajuster les débits de façon à se trouver dans les conditions de fluidisation. Ce gaz vecteur 6 est stocké dans une bouteille et admis dans le compartiment 4 à l'aide d'un régulateur de débit (non représenté).The sublimator 1 is connected to a lower glass compartment 4, which comprises a sintered plate, into which is introduced water vapor which serves to activate the decomposition of the organometallic precursor. The presence of water makes it possible to obtain a non-oxidized metal deposit (thanks to the reaction of movement of the gas with water), free of impurity, and thus a very active catalyst. The compartment 4 has a thermostatically controlled double jacket at a temperature which can be adjusted by means of a temperature controller (not shown). The steam is entrained by and with a neutral carrier gas, for example nitrogen, stored in a bottle and admitted to the compartment 4 using a flow regulator (not shown). A neutral carrier gas feed 6, for example nitrogen, is intended to adjust the flow rates so as to be in the fluidization conditions. This carrier gas 6 is stored in a bottle and admitted into compartment 4 using a flow regulator (not shown).
La partie haute du compartiment 4 est raccordée de façon étanche à une colonne de fluidisation 7 en verre, par exemple de 5cm de diamètre, qui est dotée à sa base d'un distributeur de gaz. Cette colonne 7 à double enveloppe est thermostatée à une température qui peut être ajustée au moyen d'un régulateur de température 8.The upper part of the compartment 4 is sealingly connected to a fluidization column 7 made of glass, for example 5 cm in diameter, which is equipped at its base with a gas distributor. This column 7 jacketed is thermostatically controlled at a temperature that can be adjusted by means of a temperature controller 8.
La partie haute de la colonne 7 est reliée à une pompe à vide 9 par l'intermédiaire d'un piège, pour retenir les gaz de décomposition libérés. Le protocole de mise en œuvre des exemples concernant la préparation des catalyseurs selon l'invention par CVD est le suivant.The upper part of the column 7 is connected to a vacuum pump 9 via a trap, to retain the decomposition gases released. The implementation protocol of the examples relating to the preparation of the catalysts according to the invention by CVD is as follows.
Une masse Ma de précurseur est introduite dans le sublimateur 1.A precursor mass Ma is introduced into the sublimator 1.
Une masse Ms de grains de support d'alumine est versée dans la colonne 7 et une quantité d'eau est introduite dans le compartiment 4 à l'aide d'une seringue (par exemple de l'ordre de 20g). Le vide est fait dans l'ensemble formé du compartiment 4 et de la colonne 7. La température du lit est portée à Tl.A mass Ms of alumina support grains is poured into the column 7 and a quantity of water is introduced into the compartment 4 with the aid of a syringe (for example of the order of 20 g). The vacuum is made in the assembly formed of compartment 4 and column 7. The temperature of the bed is brought to T1.
Le sublimateur 1 est porté à la température Ts et la pression est fixée à la valeur Pa dans l'ensemble de l'appareillage par introduction des gaz vecteurs 3, 5 et 6 (débit total Q). Le dépôt commence alors et dure un temps te.The sublimator 1 is brought to the temperature Ts and the pressure is set to the value Pa throughout the equipment by introducing the carrier gases 3, 5 and 6 (total flow Q). The deposit then begins and lasts a while.
En fin de dépôt, la température est ramenée à la température ambiante par lent refroidissement et la pompe à vide 9 est arrêtée. Une fois le système revenu à température ambiante et pression atmosphérique, la composition granulaire catalytique est sortie de la colonne 7 sous atmosphère de gaz inerte (par exemple de l'azote) : elle est prête à être utilisé pour la fabrication des nanorubes dans un réacteur de croissance 30. Le réacteur de croissance 30 est composé d'une colonne 10 de fluidisation en quartz (par exemple de 2,6 cm de diamètre) 10 dotée en son milieu d'une plaque distributrice (frittée en quartz) 11 sur laquelle on place la poudre de composition granulaire catalytique. La colonne 10 peut être portée à la température désirée à l'aide d'un four 12 extérieur qui peut coulisser verticalement le long de la colonne de fluidisation 10. Dans le protocole utilisé, ce four 12 a soit une position haute où il ne chauffe pas le lit fluidisé, soit une position basse où il assure le chauffage du lit. Les gaz 13 (gaz neutre tel que l'hélium, source de carbone et hydrogène) sont stockés dans des bouteilles et sont admis dans la colonne de fluidisation à l'aide de régulateurs de débit 14.At the end of the deposition, the temperature is brought back to ambient temperature by slow cooling and the vacuum pump 9 is stopped. Once the system has returned to ambient temperature and atmospheric pressure, the catalytic granular composition is removed from column 7 under an inert gas atmosphere (for example nitrogen): it is ready to be used for the manufacture of nanorubes in a reactor growth 30. The growth reactor 30 is composed of a quartz fluidization column (for example 2.6 cm in diameter) provided at its center with a dispensing plate (sintered in quartz) 11 on which the powder is placed. catalytic granular composition. The column 10 can be brought to the desired temperature by means of an oven 12 which can slide vertically vertically along the fluidization column 10. In the protocol used, the oven 12 has either a high position where it does not heat not the fluidized bed, a low position where it provides heating of the bed. The gases 13 (neutral gas such as helium, carbon source and hydrogen) are stored in bottles and are admitted into the fluidization column by means of flow regulators 14.
En partie, haute, la colonne de fluidisation 10 est raccordée de façon étanche à un piège 15 destiné à collecter d'éventuelles particules fines de composition granulaire catalytique ou d'un mélange de composition granulaire catalytique et de nanotubes. La hauteur de la colonne 10 est adaptée pour contenir, en fonctionnement, le lit fluidisé des grains du catalyseur. En particulier, elle est au moins égale à 10 à 20 fois la hauteur gazeuse, et doit correspondre à la zone chauffée. Dans les exemples, on choisit une colonne 10 de 70 cm de hauteur totale, chauffée sur 60 cm de hauteur par le four 12. Le protocole de mise en œuvre des exemples concernant la fabrication de nanotubes selon l'invention est le suivant :In part, high, the fluidization column 10 is sealingly connected to a trap 15 for collecting any fine particles of catalytic granular composition or a mixture of catalytic granular composition and nanotubes. The height of the column 10 is adapted to contain, in operation, the fluidized bed of the catalyst grains. In particular, it is at least 10 to 20 times the gaseous height, and must correspond to the heated zone. In the examples, a column 70 cm in height, heated to 60 cm high by oven 12, is chosen. The protocol for implementing examples relating to the production of nanotubes according to the invention is as follows:
Une masse Mc de catalyseur supporté granulaire est introduite dans la colonne de fluidisation 10 sous atmosphère de gaz inerte.A mass Mc of granular supported catalyst is introduced into the fluidization column 10 under an inert gas atmosphere.
Le four 12 étant en position basse par rapport au lit catalytique, sa température est portée à la valeur désirée Tn pour la synthèse des nanotubes, soit sous atmosphère de gaz inerte, soit sous atmosphère d'un mélange de gaz inerte et d'hydrogène (gaz réactif).Since the furnace 12 is in a low position relative to the catalytic bed, its temperature is brought to the desired value Tn for the synthesis of the nanotubes, either under an inert gas atmosphere or under a mixture of inert gas and hydrogen ( reactive gas).
Lorsque cette température est atteinte, la source de carbone, l'hydrogène et un complément de gaz neutre sont introduits dans la colonne 10. Le débit total Qx assure au lit un régime de bullage à la température Tn, sans renardage. La croissance des nanotubes commence alors et dure un temps ta.When this temperature is reached, the carbon source, the hydrogen and a complement of neutral gas are introduced into the column 10. The total flow rate Q x provides the bed with a bubbling regime at the temperature Tn, without firing. The growth of the nanotubes then begins and lasts a time ta.
A la fin de la croissance, le four 12 est placé en position haute par rapport au lit catalytique, les débits de gaz correspondant à la source de carbone et à l'hydrogène sont arrêtés et la température est ramenée à la température ambiante par lent refroidissement.At the end of the growth, the oven 12 is placed in the high position relative to the catalytic bed, the gas flow rates corresponding to the carbon source and to the hydrogen are stopped and the temperature is brought back to ambient temperature by slow cooling. .
Les nanotubes de carbone associés aux particules métalliques et accrochés aux grains de support sont extraits du réacteur de croissance 30 et stockés sans précaution particulière. La quantité de carbone déposée est mesurée par pesée et par analyse thermique gravimétrique.The carbon nanotubes associated with the metal particles and attached to the support grains are extracted from the growth reactor 30 and stored without any particular precautions. The amount of carbon deposited is measured by weighing and by gravimetric thermal analysis.
Les nanotubes ainsi fabriqués sont analysés par microscopie électronique à transmission (MET) et microscopie électronique à balayage (MEB) pour les mesures de taille et dispersion et par cristallographie aux rayons X et spectroscopie Raman pour évaluer la cristallinité des nanotubes.The nanotubes thus produced are analyzed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) for size and dispersion measurements and by X-ray crystallography and Raman spectroscopy to evaluate the crystallinity of the nanotubes.
EXEMPLES Exemple 1 :EXAMPLES Example 1
On prépare une composition de catalyseur à 24% massique deA catalyst composition is prepared at 24% by weight of
Fe/Al2θ3 par la technique CVD en lit fluidisé décrite ci-dessus. Le gaz vecteur est de l'azote. Le précurseur organométallique est le fer pentacarbonyle, le support est de l'alumine-γ mésoporeuse (volume poreux 0,54 cm3g"1) ayant subi un tamisage entre 120 μm et 150 μm et présentant une aire spécifique de 160 m2g4.Fe / Al 2 θ 3 by the fluidized bed CVD technique described above. The carrier gas is nitrogen. The organometallic precursor is pentacarbonyl iron, the support is mesoporous alumina-γ (pore volume 0.54 cm 3 g -1 ) sieved between 120 μm and 150 μm and having a specific surface area of 160 m 2 g 4 .
Les conditions opératoires sont les suivantes : Ms - 50 g Ma = 15,8 gThe operating conditions are as follows: Ms - 50 g Ma = 15.8 g
Tl = 2200C Pa ≈ 40 Torr Ts = 35°C Q = 250 cm3/min te = 95 min La composition obtenue est formée de grains d'alumine recouverts d'amas de bulbes de fer (la taille moyenne des bulbes est de l'ordre de 20 nm), couvrant la surface de l'alumine avec une composition de surface présentant 22% d'aluminium tel que mesuré par analyse XPS (figure 3). Exemple 2 :Tl = 220 0 C Pa ≈ 40 Torr Ts = 35 ° CQ = 250 cm 3 / min te = 95 min The composition obtained is formed of alumina grains covered with iron bulb clusters (the average bulb size is of the order of 20 nm), covering the surface of the alumina with a surface composition having 22% of aluminum as measured by XPS analysis (FIG. 3). Example 2
Cet exemple vise la préparation d'une composition de catalyseur supporté à 40% massique de fer sur alumine (Al2O3) comme indiqué à l'exemple 1, mais avec les conditions opératoires suivantes :This example is aimed at the preparation of a catalyst composition supported at 40% by mass of iron on alumina (Al 2 O 3 ) as indicated in Example 1, but with the following operating conditions:
Ms = 25 g Ma= 58,5 gMs = 25 g Ma = 58.5 g
Tl = 22O0C Pa = 40 Torr Ts = 35°C Q = 250 cmVmin te = 200 minTl = 22O 0 C Pa = 40 Torr Ts = 35 ° CQ = 250 cmVmin te = 200 min
La composition obtenue est formée de grains d'alumine complètement recouverts d'une gangue de fer constituée d'amas de bulbes de fer de 30 nm à 300 nm (figures 4 et 5). L'aire spécifique du matériau final est de 8 m2g"! et les analyses XPS montrent que l'aluminium n'est plus présent en surface. Exemple 3 :The composition obtained is formed of alumina grains completely covered with an iron matrix consisting of iron bulb clusters of 30 nm to 300 nm (Figures 4 and 5). The specific surface area of the final material is 8 m 2 g -1 and the XPS analyzes show that the aluminum is no longer present on the surface.
On fabrique des nanotubes de carbone multiparois à partir du catalyseur de l'exemple 1 à 24% de FeZAl2O3 dans une installation selon la figure 2, à partir d'éthylène gazeux à titre de source de carbone.Multilayer carbon nanotubes are manufactured from the catalyst of Example 1 at 24% FeZAl 2 O 3 in an installation according to Figure 2, from ethylene gas as a carbon source.
Les conditions opératoires sont les suivantes : Mc = 0,100 gThe operating conditions are as follows: Mc = 0.100 g
Tn = 6500C Q(H2) = 100 cmVmin Q(C2H4) = 200 cnrVminTn = 650 0 CQ (H 2 ) = 100 cmVmin Q (C 2 H 4 ) = 200 cnrVmin
Z = 500 (rapport de la masse de carbone introduite par heure sur la masse de fer présente dans le réacteur)Z = 500 (ratio of the mass of carbon introduced per hour on the mass of iron present in the reactor)
Pour tn = 120 min, on obtient : A = 13,4 (activité exprimée en grammes de nanotubes produits par gramme de composition catalytique et par heure) P = 26,8 (productivité exprimée en grammes de nanotubes produits par gramme de composition catalytique). La sélectivité est proche de 100% en nanotubes multiparois.For tn = 120 min, we obtain: A = 13.4 (activity expressed in grams of nanotubes produced per gram of catalytic composition and per hour) P = 26.8 (productivity expressed in grams of nanotubes produced per gram of catalyst composition). The selectivity is close to 100% in multiwall nanotubes.
Exemple 4 :Example 4
On fabrique des nanotubes de carbone multiparois à partir du catalyseur de l'exemple 2 à 40% de FeZAl2O3 dans une installation selon la figure 2, à partir d'éthylène gazeux à titre de source de carbone. Les conditions opératoires sont les suivantes :Multilayer carbon nanotubes are manufactured from the catalyst of Example 2 at 40% FeZAl 2 O 3 in an installation according to Figure 2, from ethylene gas as a carbon source. The operating conditions are as follows:
Mc = O3IOO g Tn = 6500C Q(H2) = 100 cm3/min Q(C2H4) = 200 cm3/min Z = 300Mw = O 3 100 g Tn = 650 0 CQ (H 2 ) = 100 cm 3 / min Q (C 2 H 4 ) = 200 cm 3 / min Z = 300
Pour tn = 120 min, on obtient A = 15,6 et P = 30,3 Pour tn = 240 min, on obtient A = 9,9 et P = 39,6 Dans tous les cas, la sélectivité est proche de 100% en nanotubes multiparois. On obtient ainsi à la fois une activité catalytique A (exprimée en grammes de nanotubes produits par gramme de composition catalytique et par heure) élevée -de l'ordre de ou supérieure à 10- et simultanément une productivité P (exprimée en grammes de nanotubes produits par gramme de composition catalytique) également élevée -de l'ordre de ou supérieure à 25-, et ce avec une sélectivité proche de 100% en nanotubes.For tn = 120 min, we obtain A = 15.6 and P = 30.3 For tn = 240 min, we obtain A = 9.9 and P = 39.6 In all cases, the selectivity is close to 100% in multiwall nanotubes. This gives both a catalytic activity A (expressed in grams of nanotubes produced per gram of catalytic composition and per hour) high - of the order of or greater than 10 - and simultaneously a productivity P (expressed in grams of nanotubes produced per gram of catalytic composition) is also high, on the order of or greater than 25, with a selectivity close to 100% in nanotubes.
Le résultat est extrêmement surprenant dans la mesure où avec tous les catalyseurs connus, on obtient soit une bonne activité A* au détriment d'une faible productivité (cas de catalyseurs ayant une faible proportion de métal sur le support), soit au contraire une forte productivité au détriment d'une faible activité (cas de catalyseurs ayant une forte proportion de métal). Or, ces paramètres sont tous importants dans le cadre d'une production industrielle. La productivité associée à la sélectivité permet d'éviter les étapes de purification ultérieures. Une bonne activité permet de minimiser la durée de réaction.The result is extremely surprising insofar as with all the known catalysts, a good activity A * is obtained at the expense of low productivity (in the case of catalysts having a low proportion of metal on the support), or on the contrary a strong productivity at the expense of low activity (the case of catalysts with a high proportion of metal). These parameters are all important in the context of industrial production. The productivity associated with selectivity avoids subsequent purification steps. Good activity minimizes the reaction time.
La figure 6 montre aussi que le diamètre des nanotubes obtenus à l'exemple 4 est en majorité de l'ordre de 10 nm à 25 nm, alors que les grains de la composition avaient un diamètre de l'ordre de 150 μm et les bulbes de fer des tailles de 30 à 300 nm. Là encore, ce résultat est surprenant, inexplicable et va à l'encontre de tous les enseignements antérieurs.FIG. 6 also shows that the diameter of the nanotubes obtained in Example 4 is in the majority of the order of 10 nm to 25 nm, whereas the grains of the composition have a diameter of the order of 150 μm and the bulbs iron sizes from 30 to 300 nm. Again, this result is surprising, inexplicable and goes against all previous teachings.
Les figures 7a et 7b montrent la forte sélectivité en nanotubes produits à l'exemple 4, qui sont ainsi directement utilisables, notamment compte tenu de la faible proportion de support poreux résiduelle dans les nanotubes qu'il était nécessaire d'éliminer dans les procédés antérieurs connus.FIGS. 7a and 7b show the high selectivity of the nanotubes produced in Example 4, which are thus directly usable, particularly in view of the small proportion of residual porous support in the nanotubes that had to be eliminated in the previous processes. known.
Exemple comparatif 5 :Comparative Example 5
On fabrique des nanotubes de carbone multiparois à partir d'un catalyseur à 5% de FeZAl2O3 obtenu comme indiqué à l'exemple 1 avec les conditions opératoires :Multilayer carbon nanotubes are manufactured from a 5% FeZAl 2 O 3 catalyst obtained as indicated in Example 1 with the operating conditions:
Ms = 100 g Ma = 18,45 g te = 21 minMs = 100 g Ma = 18.45 g te = 21 min
Les nanotubes de carbone sont préparés dans une installation selon la figure 2, à partir d'éthylène gazeux à titre de source de carbone.The carbon nanotubes are prepared in a plant according to Figure 2, from ethylene gas as a carbon source.
Les conditions opératoires de la fabrication des nanotubes sont les suivantes :The operating conditions for the manufacture of nanotubes are as follows:
Mc = O3IOO g Tn = 6500C Q(H2) = 100 cmVminMc = O 3 100 g Tn = 650 0 CQ (H 2 ) = 100 cmVmin
Q(C2H4) = 200 cm3/mm Z = 2400Q (C 2 H 4 ) = 200 cm 3 / mm Z = 2400
Pour tn = 30 min, on obtient A = 1,6 et P = 0,8. Comme on peut le remarquer en utilisant un catalyseur moins chargé ne couvrant pas 75% de la surface des grains, tout en gardant une sélectivité proche à 100% en nanotubes, il est impossible d'obtenir des valeurs élevées de A et de P.For tn = 30 min, A = 1.6 and P = 0.8 are obtained. As can be noticed by using a less charged catalyst not covering 75% of the grain surface, while keeping a selectivity close to 100% in nanotubes, it is impossible to obtain high values of A and P.
Exemple comparatif 6 :Comparative Example 6
On prépare une composition de catalyseur à 20% massique de FeZAl2O3 par la technique CVD en lit fluidisé décrite ci-dessus. Le gaz vecteur est de l'azote. Le précurseur organométallique est le fer pentacarbonyle, le support est de l'alumine-α non poreuse (aire spécifique (méthode BET) de 2 m2/g).A 20% by weight FeZAl 2 O 3 catalyst composition is prepared by the fluidized bed CVD method described above. The carrier gas is nitrogen. The organometallic precursor is pentacarbonyl iron, the support is non-porous α-alumina (specific surface area (BET method) of 2 m 2 / g).
Les conditions opératoires sont les suivantes : Ms = 50 g Ma = 14 gThe operating conditions are as follows: Ms = 50 g Ma = 14 g
Tl = 22O0C Pa = 40 Torr Ts = 35°C Q = 250 cm3/min te = 15 minTl = 22O 0 C Pa = 40 Torr Ts = 35 ° CQ = 250 cm 3 / min te = 15 min
La composition obtenue est formée de particules d'alumine recouvertes d'une gangue formée d'amas de bulbes de fer couvrant entièrement la surface de l'alumine avec une composition de surface où l'aluminium est absent tel que mesuré par analyse XPS. On fabrique des nanotubes de carbone multiparois à partir de ce catalyseur de fer sur alumine non poreuse dans une installation selon la figure 2, à partir d'éthylène gazeux à titre de source de carbone.The resulting composition is formed of gangue-coated alumina particles formed of iron bulb clusters completely covering the surface of the alumina with a surface composition where aluminum is absent as measured by XPS analysis. Multilayer carbon nanotubes are manufactured from this iron catalyst on non-porous alumina in an installation according to FIG. 2, from ethylene gas as a carbon source.
Les conditions opératoires sont les suivantes : Mc = O5IOO g Tn = 6500CThe operating conditions are the following: Mc = 0 5 100 g Tn = 650 ° C.
Q(H2) = 100 cm3/min Q(C2H4) = 200 cnrVmin Z = 500Q (H 2 ) = 100 cm 3 / min Q (C 2 H 4 ) = 200 cnrVmin Z = 500
Pour ta = 60 min, on obtient A = 0,9 et P = 0,2 Ces résultats sont 30 fois inférieurs par rapport à ceux obtenus conformément à l'invention pour un catalyseur conforme à l'invention (exemple 1) et dans les mêmes conditions opératoires. De plus la sélectivité obtenue telle qu'évaluée par microscopie électronique à transmission et analyse thermogravimétrique est mauvaise.For t a = 60 min, A = 0.9 and P = 0.2 are obtained. These results are 30 times lower than those obtained according to the invention for a catalyst according to the invention (Example 1). and under the same operating conditions. In addition, the selectivity obtained as evaluated by transmission electron microscopy and thermogravimetric analysis is poor.
Ces résultats ne s'expliquent pas dans la mesure où la seule différence entre les deux compositions catalytiques tient dans la nature poreuse ou non poreuse du coeur, qui n'est pas accessible en surface compte tenu de la gangue métallique.These results can not be explained insofar as the only difference between the two catalytic compositions lies in the porous or non-porous nature of the core, which is not accessible on the surface in view of the metal matrix.
L'invention peut faire l'objet de nombreuses variantes de réalisation et autres applications par rapport aux exemples mentionnés ci-dessus. The invention can be the subject of numerous alternative embodiments and other applications with respect to the examples mentioned above.

Claims

REVENDICATIONS
1/ - Procédé de fabrication sélective de nanotubes de carbone ordonné par décomposition d'une source de carbone à l'état gazeux mise en contact d'au moins un catalyseur solide supporté sous forme de grains, dits grains de catalyseur, de support d'alumine poreuse portant un dépôt métallique, dit ferreux, non oxydé d'au moins un métal de transition dont le fer caractérisé en ce qu'on utilise un catalyseur supporté principalement formé de grains de catalyseur :1 / - Process for the selective production of ordered carbon nanotubes by decomposition of a gaseous carbon source brought into contact with at least one supported solid catalyst in the form of grains, called catalyst grains, carrier porous alumina bearing a so-called ferrous, unoxidized metallic deposit of at least one transition metal whose iron is characterized by the use of a supported catalyst mainly formed of catalyst grains:
- de granulométrie moyenne comprise entre 25 μm et- average particle size between 25 μm and
2,5 mm, - sur lesquels le dépôt métallique ferreux couvre plus de2.5 mm, - on which the ferrous metal deposit covers more than
75% de la surface de la forme macroscopique du support d'alumine.75% of the surface of the macroscopic form of the alumina support.
2/ - Procédé selon la revendication 1, caractérisé en ce que le dépôt métallique ferreux se présente sous la forme d'au moins un amas formé d'une pluralité de bulbes métalliques agglutinés.2 / - The method of claim 1, characterized in that the ferrous metal deposition is in the form of at least one cluster formed of a plurality of agglutinated metal bulbs.
3/ - Procédé selon l'une des revendications 1 ou 2, caractérisé en ce que le dépôt métallique ferreux forme une couche superficielle métallique ferreuse continue homogène formée de bulbes métalliques.3 / - Method according to one of claims 1 or 2, characterized in that the ferrous metal deposition forms a homogeneous continuous ferrous metal surface layer formed of metal bulbs.
Al - Procédé selon l'une des revendications 1 à 3, caractérisé en ce que le dépôt métallique ferreux est adapté pour couvrir le support d'alumine de telle sorte que ses pores soient rendus inaccessibles.Al - Method according to one of claims 1 to 3, characterized in that the ferrous metal deposition is adapted to cover the alumina support so that its pores are rendered inaccessible.
51 - Procédé selon l'une des revendications 1 à 4, caractérisé en ce que le dépôt métallique ferreux est issu d'un dépôt métallique élémentaire réalisé en une seule étape sur le support d'alumine. 61 - Procédé selon l'une des revendications 1 à 5, caractérisé en ce que les bulbes ont une dimension moyenne comprise entre 10 nm et lμm -notamment entre 30 nm et 100 nm-.51 - Method according to one of claims 1 to 4, characterized in that the ferrous metal deposition is derived from an elemental metal deposition made in a single step on the alumina support. 61 - Method according to one of claims 1 to 5, characterized in that the bulbs have a mean size of between 10 nm and 1 μm -notamment between 30 nm and 100 nm-.
Il - Procédé selon l'une des revendications 1 à 6, caractérisé en ce que le dépôt métallique ferreux non oxydé de chaque grain de catalyseur s'étend superficiellement avec une dimension moyenne globale développée supérieure à 35 μm. 8/ - Procédé selon la revendication 7, caractérisé en ce que le dépôt métallique ferreux non oxydé de chaque grain de catalyseur s'étend superficiellement avec une dimension moyenne globale développée comprise entre 200 μm et 400 μm. 91 - Procédé selon l'une des revendications 1 à 8, caractérisé en ce que le dépôt métallique ferreux de chaque grain de catalyseur s'étend superficiellement avec une aire apparente moyenne supérieure à 2.103 μm2 de chaque grain de catalyseur.II - Process according to one of claims 1 to 6, characterized in that the unoxidized ferrous metal deposition of each catalyst grain extends superficially with a global average dimension developed greater than 35 microns. 8 / - Method according to claim 7, characterized in that the unoxidized ferrous metal deposition of each catalyst grain extends superficially with an overall average dimension developed between 200 microns and 400 microns. 91 - Method according to one of claims 1 to 8, characterized in that the ferrous metal deposition of each catalyst grain extends superficially with an average apparent surface greater than 2.10 3 microns 2 of each catalyst grain.
10/ - Procédé selon la revendication 9, caractérisé en ce que le dépôt métallique ferreux de chaque grain de catalyseur s'étend superficiellement avec une aire apparente moyenne comprise entre 10 μm2 et 1,5 105 μm2.10 / - Method according to claim 9, characterized in that the ferrous metal deposit of each catalyst particle extends superficially with a mean apparent area of between 10 .mu.m and 2 1.5 10 2 5 .mu.m.
11/ - Procédé selon l'une des revendications 1 à 10, caractérisé en ce qu'on utilise un catalyseur supporté se présentant sous forme de grains dont les formes et la dimension sont adaptées pour permettre la formation d'un lit fluidisé de ces grains de catalyseur, en ce qu'on réalise un lit fluidisé des grains de catalyseur dans un réacteur, et en ce qu'on délivre en continu la source de carbone dans le réacteur au contact des grains de catalyseur dans des conditions propres à assurer la fluidisation du lit de grains de catalyseur, la réaction de décomposition et la formation de nanotubes.11 / - Method according to one of claims 1 to 10, characterized in that a supported catalyst is in the form of grains whose shapes and size are adapted to allow the formation of a fluidized bed of these grains of catalyst, in that a fluidized bed of the catalyst particles is produced in a reactor, and in that the carbon source is continuously delivered into the reactor in contact with the catalyst grains under conditions suitable for fluidization. of the catalyst seed bed, the decomposition reaction and the formation of nanotubes.
12/ - Procédé selon l'une des revendications 1 à 11, caractérisé en ce qu'on utilise un catalyseur supporté présentant une granulométrie moyenne comprise entre 100 μm et 200 μm.12 / - Method according to one of claims 1 to 11, characterized in that a supported catalyst having a mean particle size of between 100 microns and 200 microns.
13/ - Procédé selon l'une des revendications 1 à 12, caractérisé en ce que le dépôt métallique ferreux couvre de 90% à 100% de la surface des grains.13 / - Method according to one of claims 1 to 12, characterized in that the ferrous metal deposition covers from 90% to 100% of the surface of the grains.
14/ - Procédé selon l'une des revendications 1 à 13, caractérisé en ce que le dépôt métallique ferreux forme une gangue métallique couvrant la totalité de la surface du support d'alumine poreuse et rendant ses pores inaccessibles. 15/ - Procédé selon l'une des revendications 1 à 14, caractérisé en ce que le dépôt métallique ferreux s'étend sur une épaisseur supérieure à 0,5 μm -notamment de l'ordre de 2 à 20 μm-.14 / - Method according to one of claims 1 to 13, characterized in that the ferrous metal deposition forms a metal gangue covering the entire surface of the porous alumina support and making its pores inaccessible. 15 / - Method according to one of claims 1 to 14, characterized in that the ferrous metal deposition extends over a thickness greater than 0.5 microns -notamment of the order of 2 to 20 microns-.
16/ - Procédé selon l'une des revendications 1 à 15, caractérisé en ce que le cœur d'alumine présente une aire spécifique supérieure à 100 m2/g, et en ce que le catalyseur supporté présente une aire spécifique inférieure à 25 m2/g.16 / - Method according to one of claims 1 to 15, characterized in that the alumina core has a specific surface area greater than 100 m 2 / g, and in that the supported catalyst has a specific surface area of less than 25 m 2 / g.
17/ - Procédé selon l'une des revendications 1 à 16, caractérisé en ce qu'on utilise un catalyseur supporté comprenant plus de 20% en poids de dépôt métallique ferreux non oxydé.17 / - Method according to one of claims 1 to 16, characterized in that a supported catalyst comprising more than 20% by weight of non-oxidized ferrous metal deposit.
18/ - Procédé selon l'une des revendications 1 à 17, caractérisé en ce que le dépôt métallique ferreux est principalement constitué de fer.18 / - Method according to one of claims 1 to 17, characterized in that the ferrous metal deposition is mainly made of iron.
19/ - Procédé selon l'une des revendications 1 à 18, caractérisé en ce que le dépôt métallique ferreux est exclusivement constitué de fer. 20/ - Procédé selon l'un des revendications 1 à 19, caractérisé en ce que le dépôt métallique ferreux est formé de fer et d'au moins un métal choisi parmi le nickel et le cobalt.19 / - Method according to one of claims 1 to 18, characterized in that the ferrous metal deposit is exclusively made of iron. 20 / - Method according to one of claims 1 to 19, characterized in that the ferrous metal deposition is formed of iron and at least one metal selected from nickel and cobalt.
21/ - Procédé selon l'une des revendications 1 à 20, caractérisé en ce qu'on utilise une quantité de source de carbone telle que le rapport de la masse de carbone de la source de carbone de départ et par heure, sur la masse métallique du catalyseur supporté est supérieur à 100.21 / - Method according to one of claims 1 to 20, characterized in that a quantity of carbon source is used such as the ratio of the carbon mass of the starting carbon source and hourly, on the mass metal of the supported catalyst is greater than 100.
22/ - Procédé selon l'une des revendications 1 à 21, caractérisé en ce que la source de carbone est l'éthylène. 22 / - Method according to one of claims 1 to 21, characterized in that the carbon source is ethylene.
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