GB1603463A - Process for preparing spheroidal alumina particles - Google Patents

Description

. r '1 1 -

PATENT SPECIFICATION ( 11) 1 603 463

Mv' ( 21) Application No 29047/80 ( 22) Filed 23 March 1978 ( 62) Divided out of No 1603461 ( 31) Convention Application No 781379 C 1 ( 32) Filed 25 March 1977 ( 31) Convention Application No 781393 ( 32) Filed 25 March 1977 in ( 33) United States of America (US) ( 44) Complete Specification published 25 Nov 1981 ( 51) TNT CL 3 COJF 7/34 ( 52) Index at acceptance CIA 519 N 4 VB ( 54) PROCESS FOR PREPARING SPHEROIDAL ALUMINA PARTICLES ( 71) We, W R GRACE & CO, a Corporation organized and existing under the laws of the State of Connecticut, United States of America, of Grace Plaza, 1114 Avenue of the Americas, New York, New York 10036, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly 5 described in and by the following statement:-

This invention relates to a process for preparing spheroidal alumina particles useful for making catalysts.

A common form of catalyst consists of a solid support and a catalytic material carried on the support; the solid support is then usually particles of a porous 10 material-e g alumnina The particles are typically of a size equal to spherical particles I mm in diameter up to 15 mm in diameter The porous material-e g.

alumina-may need to be shaped into particle form-e g spheres, spheroids, pills, cylinders-and we will refer to the material before it is shaped as support material" and after it is shaped as -formed support" The novel alumina 15 monohydrate of this invention and its admixture with amorphous alumina are in this sense a support material; the microspheroidal particles, whether made from the support material of this invention or from a similar material, are in this sense a formed support; and these microspheroids when loaded with a catalytic agent are a catalyst 20 The activity, efficiency, stability, and durability of a catalyst in a reaction depend upon the chemical, physical, and structural properties of the catalyst precursors, i e, the support material and the formed support particles, and the nature and distribution of the catalytic material on the formed support Minor variations in these properties may produce substantial differences in the 25 performance of the catalyst Desirably, the properties of the support material that enhance catalytic activity are retained by the formed support particles In general, the formed support and catalyst comprising small amounts of the catalytic material on the support have essentially the same physical and structural properties with slight differences due to the effects of the thermal activation of the catalyst 30 The internal porous structure of the catalyst particles and their precursors determines the extent and accessibility of surface area available for contact of the catalytic materials and the reactants Increased pore size results in greater diffusion rates for reactants and p roducts in and out of the catalyst particles and this often results in improved catalyst activity However, the extent to which pore size can be 35 advantageously increased is limited As the pore size is increased, there is a decrease in the surface area where the reactions take place A good catalyst should have a balanced combination of high specific surface area, cumulative pore volume, and macroporosity High macroporosity means a pore size distribution with a relatively high proportion of pores having a diameter greater than 1000 A 40 Further, alumnina and formed alumina with a low density, and consequent low thermal inertia will produce a catalyst that will reach reaction temperatures sooner.

Catalyst support material is frequently a porous refractory inorganic oxide, such as silica, alumina, magnesia, zirconia, titania, and combinations thereof.

Alumina is a particularly desirable support material since it inherently has a high 45 degree of porosity and will maintain a comparatively high surface area over the 2 1,603,463 2 temperature range normally encountered in many catalytic reactions However, when used under high temperature conditions for long periods of time, overheating of the alumina may cause sintering and change in the crystalline phase of the alumina which reduce catalytic activity, for example, due to loss of surface area available for catalysis Alumina is used as a catalyst support in the form of a finely 5 divided powder or of macrosize particles formed from a powder.

Since the physical and chemical properties of alumina are highly dependent on the procedures followed in its preparation, many preparation processes have been developed in attempts to optimize its properties for use as a catalyst support material Alumina is frequently precipitated by combining a water-soluble, acidic 10 aluminum compound which may be an aluminum salt such as aluminum sulfate.

aluminum nitrate, or aluminum chloride, and an alkali metal aluminate such as sodium or potassium aluminate However, the properties of the resultant compositions after washing and drying have generally been deficient in one or more of the properties of high surface area, macroporosity, phase stability, and 1 ' low density.

Typical methods of making alumina with some of the characteristics desired of a support material are disclosed in U S Patents 2,988,520, 3,520,654, 3, 032,514 and 3,124,418 U S Patent 3,864,461 is particularly interesting as it discloses the production of a crystalline alumina of low bulk density which is identified by its x 2 C ray bands as identical to pseudoboehmite, in some cases in admixture with a small amount of bayerite.

In addition to retaining the surface area, porosity, and density characteristics of the starting alumina material, a process for the formation of macrosize alumina particles should produce formed alumina with low shrinkage and high attrition 25 resistance and crush strength Conventional low density supports are generally deficient in structural integrity Unless stabilized, an alumina particle will undergo considerable shrinkage of its geometric volume when exposed to high temperatures during use Excessive shrinkage produces unoccupied channels in the catalyst bed through which reactants pass without contact with the catalyst 3 C High attrition resistance provides structural integrity and retention of activity under conditions of mechanical stress During transfer, loading into the reaction zone, and prolonged use, the catalyst particles are subjected to many collisions which result in loss of material from the outer layers Attrition of the catalytically active layer present in the outer volume of the particles affects catalytic 3 ' performance and also results in a decrease of the volume of the material in the reaction zone.

Volume loss by shrinkage and/or attrition of the highly compacted, tightly held particles in a fixed catalyst bed tends to loosen them and allow for increased motion and collisions during vibration Once a packed bed becomes loose, attrition tends 4 ( to increase During storage, the catalyst is often packed in large tall containers awaiting loading In order to withstand the forces generated by the weight of the particles above them, the catalyst must exhibit high crush strength.

The size, size distribution, and shape of the particles affect both structural integrity and catalytic activity These properties determine the volume of catalyst 4:

that can be packed in a fixed bed, the pressure drop across the bed, and the outer surface area available for contact with the reactants Finely divided alumina may be pelletized, tabletized, molded or extruded into macrosize particles of the desired size and shape Typically, the macrosize particles are cylinders of diameter about 1/32 to 1/4 inch and a length to diameter ratio of about 1:1 to 3:1 Other shapes 5 ( include spheroidal, polylobal, figure-eight, clover leaf, dumbbell and the like.

Spheroids offer numerous advantages as a catalyst support over particles having angular shaped surfaces with salients or irregularities, such as extruded cylinders Spheroidally shaped particles permit a more uniform packing of the catalyst bed, thereby reducing variations in the pressure drop through the bed and 5:

in turn reducing channelling which would result in a portion of the bed being bypassed Another advantage in using particles of this shape is that the spheroids exhibit no sharp edges which will attrit during processing, transfer, or use.

One of the most described methods for producing spheroidal alumina particles is the oil-drop method in which drops of an aqueous acidic alumina material gel to 6 ( spheroids in falling through a water-immiscible liquid and coagulate under basic p H conditions A wide variety of oil-drop techniques have been developed in attempts to provide structural and mechanical properties that would enhance the activity and durability of alumina-supported catalysts The density, surface area, porosity and uniformity of the spheroidal product vary greatly with the nature of 6 ' , '11 -1 1; 1 1 1 1 1 1 '1 1, A_"' -z ' 1 -, ' (J; 1 f_ the alumina feed and, along with crush strength and attrition resistance, are dependent on the conditions used in the preparation of the feed and the coagulation and gelation steps, as well as subsequent drying and calcination steps.

Internal gelation, i e gelation of the alumina by a weak base, such as hexamethylenetetramine, that is added to the feed before drop formation and that 5 releases ammonia in the heated immiscible liquid, is the most common oildrop method.

United States Patent No 3,558,508 to Keith et al describes an oil-drop method employing an external gelation technique in which gaseous ammonia is introduced into the bottom of a column containing the water-immiscible liquid and coagulates 10 the droplets by contacting their external surfaces The Keith et al process is based lo a considerable extent on the use of specific alumina feed prepared by acidic hydrolysis of finely divided aluminum Spherical alumina particles may also be formed by the hydrocarbon/ammonia process described in Olechowska et al, "Preparation of Spherically Shaped Alumina Oxide", International Chemical I 55 Engineering, Volume 14, No 1, pages 90-93, January, 1974 In this process, droplets of a slurry of nitric acid and dehydrated aluminum hydroxide fall through air into a column containing hydrocarbon and ammonia phases The droplets assume spheroidal shapes in passing through the water-immiscible liquid and then are coagulated to firm spheroidal beads or pellets in the coagulating medium 20 Similar processes utilizing pseudosol feeds and hydrochloric acid are described in:

I Katsobashvili et al, "Formation of Spherical Alumina and Aluminum Oxide Catalysts by the Hydrocarbon-Ammonia Process-I The Role of Electrolytes in the Formation Process)), Kolloidnyi Zhurnal, Vol 28, No I, pp 46-50, JanuaryFebruary, 1966; 25 2 Katsobashvili et al, "Preparation of Mechanically Strong Alumina and Aluminum Oxide Catalysts in the Form of Spherical Granules by the HydrocarbonAmmonia Forming Method", Zhurnal Prikladnoi Khimii, Vol 39, No II 1, pp.

2424-2429, November, 1966; and 3 Katsobashvili et al, "Formation of Spherical Alumina and Aluminum 30 Oxide Catalysts by the Hydrocarbon-Ammonia Process-Coagulational Structure Formation During the Forming Process", Kolloidnyi Zhurnal, Vol 29, No 4, pp.

503-508, July-August, 1967.

Catalysts are used to convert pollutants in automotive exhaust gases to less objectionable materials Novel metals may be used as the principal catalytic 35 components or may be present in small amounts to promote the activity of base metal systems United States Patents Nos 3,189,563 to Hauel and 3,932,309 to Graham et al show the use of noble metal catalysts for the control of automotive exhaust emissions United States Patent No 3,455,843 to Briggs et al is typical of a base metal catalyst system promoted with noble metal Unpromoted base metal 40 catalysts have been described in United States Patent No 3,322,491 by Barrett et al.

The activity and durability of an automotive exhaust catalyst is in part dependent on the location and distribution of noble metals on the support Since the use of noble metal is controlled to a great extent by cost, small amounts of 45 noble metals should be placed on the support in a manner that achieves the best overall performance over the life of the catalyst.

Several competing phenomena are involved in the surface treatment.

Impregnating the maximum amount of the support particle provides the greatest amount of impregnated surface area However, since gas velocities are high and 50 contact times are short in an automotive exhaust system, the rate of oxidation of carbon monoxide and hydrocarbons and the reduction of nitrogen oxides are diffusion controlled Thus, the depth of impregnation should not exceed the distance that reactants can effectively diffuse into the pore structure of the particle.

A balance of impregnated surface area coupled with proper dispersion and 55 acesbility should be achieved to formulate a practical catalyst.

Catalytic metal accessibility and dispersion will provide initial high catalytic activity, once the catalyst reaches operating temperature However, since significantly high amounts of hydrocarbons, carbon monoxide, and other partially combusted materials are produced in exhaust gases during the initial moments of 60 the engine start, the catalyst should have low thermal inertia in order to operate efficiently when the reaction zone is at a relatively low temperature.

A common deficiency of exhaust catalysts is decreased activity when exposed to high temperatures, mechanical vibration and poisons present in the exhaust such as lead, phosphorus, sulfur compounds, etc, for long periods of use of up to 50,000 65 1,603,463 miles or so An effective catalyst will retain its activity through resistance to noble metal crystallite growth, poisons, crystalline phase changes and physical degradation.

An optimum high temperature alumina catalyst support has low density and high macroporosity while retaining substantial surface area and crush strength and 5 attrition resistance Furthermore, it is stable in crystalline phases and geometric volume occupied Difficulties have been encountered in achieving the proper balance of these interrelated and sometimes competing properties and in combining an alumina support and metal impregnation techniques to provide a catalytic converter capable of decreasing automotive exhaust emissions to the 10 levels required by present and future goverment standards.

We provide, according to the present invention, a process of preparing a formed catalyst support from alumina, by what may be called an external gelation process.

Substantially uniform spheroidal alumina particles having an unexpected 15 combination of low density and high surface area, macroporosity, phase stability, and mechanical strength can be prepared, from the wet or dried boehmitepseudoboehmite intermediate, by the improved external gelation process of this invention A slurry of alumina is prepared in an acidic aqueous medium and droplets of the slurry are passed through air into a column containing an upper 20 body of a water-immiscible liquid and ammonia and a lower body of aqueous alkaline coagulating agent The resulting spheroidal particles are aged in aqueous ammonia to the desired hardness The aged particles are dried and calcined.

It has also been discovered that a catalyst comprising a catalytically active metal or metal compound impregnated on the spheroidal alumina particles made 25 by the external gelation process of this invention has excellent activity and durability in many catalytic systems It is especially suited for eliminating pollutants in automotive exhaust streams because of its quick light off and sustained activity under high temperatures and mechanical vibrations present in exhaust systems.

The catalyst support, made by our "external gelation" process, is in the form 30 of spheroidal particles and is preferably characterised by (i) a pore volume of about 0 I to about 0 4 cubic centimeters per gram in pores of 1000 to 10,000 A in diameter; (ii) a surface area of about 80 to about 135 square meters per gram; (iii) an attrition loss of less than about 5 ', preferably less than about 2 %,; and 35 (iv) a compacted bulk density of about 20 to about 36 pounds per cubic foot; and may be further characterised by (v) a total pore volume of about 0 8 to about 1 7 cubic centimeters per gram; (vi) a pore volume of about 0 5 to about 1 0 cubic centrimeters per gram in pores of 100 to 1000 A in diameter; and 40 (vii) a pore volume of 0 to about 0 06 cubic centimeters per gram in pores of less than 100 A in diameter and further characterised by (viii) a volume shrinkage of less than about 6 ', preferably less than about 4 O;, upon exposure to a temperature of 18000 F for 24 hours; and (ix) a crush strength of at least about 5 pounds, preferably greater than about 7 45 pounds.

These supports are described and claimed in our Application No 80 29046 (Serial No 1,603,462).

Throughout this specification the -nitrogen pore volume" refers to the pore volume as measured by the techniques described in the article by S Brunauer, P.

Emmett, and E Teller J Am Chem Soc, Vol 60, p 309 ( 1938) This method depends on the condensation of nitrogen into the pores, and is effective for measuring pores with pore diameters in the range of 10 to 600 A.

The surface areas referred to throughout this specification are the nitrogen

BET surface areas determined by the method also described in the Brunauer 5 ' Emmett, and Teller article The volume of nitrogen adsorbed is related to the surface area per unit weight of the support.

Dried alumina powders or washed alumina filter cake with the proper crystalline character as prepared by the process described and claimed in our Application No 11808/78 (Serial No 1,603,461) and the alumina composition 6 C described and clained in our Application No 80 29154 (Serial No 1,603,464) , are preferably used in preparing the feed for the oil-drop forming process However, other suitable starting alumina compositions as described hereinafter may also be used to form spheroidal alumina particles in our improved process The process of Application No 11808/78, (Serial No 1,603,461), comprises the following steps: 65 _ <t V't; ef' d xd"L'2 os';'' ';'' '''' I 1,603,463 1,603,463 1 An aqueous solution of an aluminium salt, generally of a strong mineral acid, preferably aluminium sulfate, having an A 12,0 concentration of 5 to 9 weight percent and at a temperature of 130 to 16001 F, is added to water at a temperature of to 1700 F; the amount of aluminium salt added is sufficient to adjust the p H of -5 the mixture to 2 to 5; 2 An aqueous solution of sodium aluminate (or other alkali metal aluminate) having an A 1203 concentration in excess of 16, generally 18 to 22, weight percent and a temperature of 130 to 160 'F and a further amount of aqueous aluminium sulfate (or other aluminium salt) solution are simultaneously (but separately) added to the mixture-this precipitates alumina to form an alumina slurry Addition of alkali metal aluminate raises the p H of the mixture to a value in the approximate region p H 7 to p H 8, and the p H of the slurry is maintained during the precipitation from 7 to 8 and the temperature is kept at from 140 to 18001 F, and a rate of addition of the solutions is maintained during the precipitation to form intermediate IS boehmite-pseudoboehmite alumina; 3 The p H of the slurry is then adjusted to 9 5 to 10 5 The slurry may then, optionally, be aged and the slurry is then filtered and the filter take washed to provide a substantially pure alumina.

The alumina composition of Application No 80 29154, (Serial No 1,603,464), comprises a boehmite-pseudoboehmite intermediate, said composition having a l 0201 d-spacing of about 6 2 to about 6 5 A and a mid-point width of Xray diffraction peak l 0201 d of about 1 65 to about 1 85 A and requiring from about 130 to 180 milliequivalents of sulfuric acid per mole of alumina to change the p H of a water slurry of the composition from about 8 3 to about 4 0.

The alumina and an acidic aqueous medium, such as an aqueous solution of an acid or acid salt, are commingled to provide a slurry Preferably, an aqueous solution of a monobasic mineral acid is commingled with water and the alumina to provide the slurry Use of a monobasic acid provides a homogeneous, plastic slurry with the desired viscosity Hydrochloric acid and other strong monobasic acids may be used and the support washed free of these electrolytes Aluminum nitrate may be used Nitric acid is preferred because it is decomposed and removed from the spheroids by heating later in the process so that washing the spheres is not necessary In order to minimize the nitrogen oxides produced in the later states as noxious emissions, a decomposable monobasic organic acid such as acetic acid, (hereinafter represented symbolically as CH 3 COOH), formic acid, or mixtures thereof, preferably replaces a major portion of the nitric acid For example, a mixture of organic acid and nitric acid in a molar ratio of about 0 5 to 5 may be employed.

Bulk density and crush strength of the spheroid product depend upon feed composition Increasing alumina and/or acid content of the feed increases these physical properties Too high a concentration of alumina and/or acid may result in spheroid fracture upon drying and too low a concentration in weak, powdery spheroids Because of the gel content of the alumina powder used in preparing the feed, a minor amount of acid is sufficient to form a plastic slurry The slurry may contain about I to about 12 weight percent of a monobasic acid or mixtures thereof and the slurry generally contains about 10 to about 40, preferably about 24 to about 32 weight percent of alumina and has a molar ratio of acid to alumina of about 0 05 to about 0 50 The quantity of water is sufficient to yield a slurry with these acid and alumina contents Normalizing the system in relation to one mole of alumina, the inorganic acid molar ratio may vary between 0 5 to 0 03, preferably 0 06, and the organic acid molar ratio from 0 to 0 3, preferably 0 12, and the water molar ratio may be about 5 to about 50, preferably about 10 to about 20 An especially preferred slurry has a molar composition of (A 1203)1 (CH 3 COOH)Q 2 (HNO 3)0 6 (HO)140 s+, The slurry may be prepared from a single alumina composition or a blend of alumina compositions Blends are used to take advantage of some specific properties of the individual components of the blend For example, alumina filter cake may be acidified with acetic acid, to about p H 6 0, prior to spray drying to reduce carbon dioxide absorption A high carbonate content in the powders may result in sphere cracking during drying Thus, 20 parts of this low carbonate alumina may be combined with 80 parts of untreated dried powder to give a blend with an acceptable carbonate level Preferably, the alumina powder and acidic aqueous medium are commingled in stages by adding portions of the powder to the , N , 1,.

I.'11 ':

medium to acidify the alumina and reduce the level of CO 2 that may be present in the spray dried alumina powder For example, 80 percent of the alumina required for a given batch of product may be mixed in water which contains the desired quantities of acid After a period of mixing, the remaining 20 percent of the powder is then added to the batch In addition, recycled, calcined product fines in an 5 amount of up to about 15 percent of total alumina may be added This decreases the tendency of the product to shrink to about 2 to about 3 volume percent It also makes the process more economical in that scrap product such as fines, etc, can be recycled.

Agitation and aging of the slurry provide a uniform material with a viscosity 10 that permits proper formation of the droplets from which the spheroids with low shrinkage can be made Agitation of the slurry can be accomplished by a variety of means ranging from simple hand stirring to mechanical high shear mixing Slurry aging can range from a few minutes to many days The aging time is inversely related to the energy input during mixing Thus, the alumina powder can be stirred, 15 by hand, into the acid and water mix for 10 minutes and aged overnight to reach the proper consistency for droplet formation For example, in a specific preferred method using about 10 Ibs of powder, 60 percent of the powder is mixed with all of the acid and water and blended vigorously with a 1/2 H P Cowles dissolver turning a 3 inch blade at about 3500 RPM For about 2 to about 30 minutes or preferably 2 C about 15 to about 20 minutes The remaining 40 percent of the powder is then added and stirring recommenced for about 5 to about 60 minutes and preferably about 30 to about 40 minutes After agitation, the slurry is aged for about I to about hours to reach the proper consistency During mixing, the p H rises and a final p H of generally about 4 0 to about 4 8, preferably about 4 3 to about 4 4, is achieved 25 The viscosity of the slurry, measured immediately after the preferred blending technique, may vary between about 60 and about 300 centipoises (cps) For optimum droplet formation, slurry viscosities of about 20 to about 1600 cps, preferably about 800 to about 1200 cps are desirable Viscosites as high as 2000 cps may be used but the slurries are difficult to pump 30 Under actual operating conditions in a plant, there might be occasions in which a slurry may have to wait for long periods of time prior to further processing.

Under these conditions, the viscosity of the system may climb above the pumpable range Such a thickened slurry need not be wasted It still can be used by following any of the following two procedures: 35 The thick slurry may be diluted with controlled amounts of water and strongly agitated for short periods of time This will result in a sharp decrease of the viscosity and will bring the system into the pumpable range.

The thick slurry may be mixed with a freshly prepared slurry which will exhibit a low viscosity between about 60 and about 300 cps The resulting mixture 4 C will have a viscosity in the pumpable range and can be used in the process.

Both of these remedial steps can be practiced without adversely affecting the properties of the finish product nor the subsequent processing steps.

The viscosity of slurries referred to in these specifications, examples and claims, is the viscosity as measured with a Brookfield viscometer 45

The spheroidal particles are formed by gelation in an organic phase and an aqueous phase Droplets of the aged slurry are formed in air above a column which contains an upper body of water-immiscible liquid and ammonia and a lower body of an aqueous alkaline coagulating agent The drops assume spheroidal shapes in passing through the upper phase and then are coagulated into firm spheroidal 50 particles in the lower phase The ammonia in the upper phase gels the droplet exterior layers sufficiently to allow the spheroidal shape to be retained as the droplets cross the liquid interface and enter the lower phase Excessive interfacial tension between the phases may result in retention of the droplets in the organic phase and possibly their deformation In such cases, a small quantity of surfactant, 55 for example, about 0 05 to about 0 5, preferably 0 1 to about 0 2 volume percent of the upper body, is placed at the interface and permits the spheres to penetrate it easily Liquinox ), a detergent sold by, Alconox, Inc, New York, N Y, and other such surfactants may be employed ' The water-immiscible liquid will have a specific gravity lower than water, 60 preferably lower than about 0 95, and can be, for example, any of the mineral oils or their mixtures The organic liquid should not permit the droplets to fall too rapidly which may inhibit proper sphere formation Furthermore, it should not exhibit high interface surface tension which may hold up and deform the particles.

Examples of suitable mineral oils, include kerosene, toluene, heavy naphtha, light 65h ': ' l _ %-', A I 1,603,463 7 1,603,463 7 gas oil, paraffin oil, and other lubricating oils, coal tar oils, and the like Kerosene is preferred because it is inexpensive, commercially available, non-toxic and has a relatively high flash point.

The organic liquid should be capable of dissolving small amounts of anhydrous gaseous ammonia or be capable of forming suspensions containing trace amounts 5 of water which contain dissolved ammonia An essential requirement of the process is that the organic phase contain sufficient, but small, amounts of ammonia, in order to be able to effect the partial neutralization and gelation of the outer layers of the falling droplets The rate of introduction of ammonia into the organic liquid should be sufficient to reach an operating concentration in which firm particles will 10 be formed in the short time span of fall However, the ammonia concentration should not be so high as to cause essentially instantaneous gelation of the slurry droplets as they enter the organic liquid Under these conditions, the droplets will gel into misformed particles since they have not had sufficient time of fall to allow their surface tension to spheroidize the droplet Furthermore, high concentrations 15 of ammonia in the upper regions of the organic liquid will cause evaporation of gaseous ammonia into the air pocket where the nozzles are located Excessive ammonia concentration in this region may cause premature gelation of the droplets prior to the point of separation from the nozzle This is very undesirable because premature gelation in the nozzle will cause plugging and malfunction of the 20 delivery system Ammonia produces good spheroids, exhibits a convenient solubility, and may be conveniently introduced into the lower portion of the organic liquid In a preferred embodiment, the organic liquid is contacted with anhydrous gaseous ammonia in a separate apparatus called the ammoniator, and circulated through the column In such an event, the organic liquid from the 25 ammoniator is introduced in the lower portion of the organic phase in the column and it flows upwardly through the column establishing a counter current flow with the falling droplets The organic liquid is removed at the top of the column and returned to the ammoniator for replenishing with added ammonia.

Under steady state conditions, an ammonia concentration gradient develops 30 within the organic phase of the column The gradient is caused by the reaction of the falling acidic alumina slurry droplets with the ascending ammonia carried by the organic phase Because of the lower ammonia concentration in the upper portions of the column, the droplets have time to shape into spheroids before they gradually gel as they descend The ammonia concentration in the organic liquid 35 may be determined by titration with hydrochloric acid to a bromthymol blue endpoint and may be maintained between about 0 01 to about 1 0, preferably about 0.04 to about 0 07, weight percent Lower concentrations generally result in flattened spheroids, and higher concentrations in deformations such as tail formation 40 The length of the column can vary widely and will usually be from about 3 to feet in height The organic phase may generally comprise about 1/3 to about 2/3 of the column length and the coagulation phase the remainder.

The aqueous medium may contain any substance capable of inducing gelation and having an appropriate specific gravity, i e lower than the specific gravity of the 45 slurry droplets This permits the spheres to pass through it Alkaline aqueous solutions such as sodium hydroxide, sodium carbonate, or ammonia can be used as the coagulating medium The preferred medium is an aqueous solution of ammonia, because it and its neutralization products are easily removed from the so spheroids in later processing steps Washing is not necessary to remove the 50 ammonium residue as it would be to remove a sodium residue The ammonia concentration in the aqueous phase may be about 0 5 to 28 4 weight percent preferably about 1 0 to about 4 0 weight percent During prolonged use, ammonium nitrate and acetate may be formed and build up to steady state levels in the aqueous phase These are products of the neutralization reaction occurring 55 during sphere gelation Their steady state concentration will be dependent upon the concentrations of the acids in the alumina slurry feed In the development of this invention ammonium acetate and ammonium nitrate were added to the aqueous ammonia phase to simulate the effects of eventual steady state values of these salts For the preferred slurry composition, the concentrations used were 60 typically about 1 3 and about 0 8 weight percent respectively.

Under continuous operation, ammonia must also be constantly added to the aqueous phase to replace that used in gelation of the spheres In a preferred embodiment of this invention, the aqueous phase is circulated between the column and an ammoniator tank This tank also serves as a reservoir with a batch collection 65 , system to take up aqueous ammonia solution displaced from the column as spheres fill up the collection vessel The aqueous phase is removed from the column to maintain a constant interface level In a continuous sphere take-off system, the reservoir feature of the aqueous phase ammoniator would not be needed Either type of collection system can be used 5 The cross sectional area of the column is dependent upon the number of droplet nozzles used For one nozzle, a one inch diameter column provides approximately 5 cm 2 of cross sectional area, which is sufficient to keep the uncoagulated droplets from hitting the column walls and smearing and sticking on the walls A four inch diameter column provides enough cross sectional area for up 10 to about 16 to 20 nozzles to permit the droplets to fall independently through the column without contacting each other or the walls.

In one embodiment of a suitable column, the aged slurry is pumped into a pressurized multiple orifice feed distributor that is located at the top of the oil column and contains a multiplicity of nozzles position about 1/2 inch above the 15 organic liquid The pressure of the feed distributor is dependent upon the slurry viscosity Pressures of about 0 1 to about 15 psig are normally used The feed distributor pressure regulates the droplet formation rate The latter varies from about 10 to about 250 droplets per minute with a preferred rate being about 140 to about 180 drops per minute A distributor pressure of about 1 5 to about 2 5 psig 20 gives the desired droplet rate when the slurry viscosity is in the range of about 800 to about 1200 cps The nozzles employed can vary in diameter to give spheroidal particles of the desired size For example, a 0 11 inch internal diameter nozzle will produce spheroids of a diameter of about 1/8 inch Preferably, an air flow is provided around the nozzles to keep ammonia vapor from prematurely gelling the 25 droplets the droplets of slurry are formed in air at the nozzle tips and fall through air into the body of water-immiscible liquid When the drops of slurry initially contact the immiscible liquid, they are usually lens-shaped As the drops fall through ammonia-treated organic liquid, they gradually become spheroidal particles which are set into this shape by the coagulating ammonia and harden 30 further in the lower aqueous ammonia phase.

The particles are then aged in aqueous ammonia with a concentration of about 0.5 to 28 4 weight percent, preferably the same concentration as in the column The particles develop additional hardness so that they are not deformed during subsequent transfer and processing steps In general, the particles may be aged 35 from about 30 minutes to about 48 hours, preferably about I to 3 hours.

The particles are then drained and dried Forced draft drying to about 210 to about 4000 F for about 2 to 4 hours may be advantageously employed although other drying methods may also be used In a preferred drying method, the drying is done in a period of under 3 hours by programming the temperature to climb 40 gradually and uniformly to about 3000 F The amount of air used may normally vary between about 400 and 600 standard cubic feet per pound of A 1203 contained in the wet spheroids Under certain circumstances, some of the air may be recirculated in order to control the humidity of the drying medium The spheres are usually spread over a retaining perforated surface or screen at thicknesses ranging from I to 6 45 inches preferably 2 to 4 inches A slight shrinkage usually occurs during drying but the spheroids retain their shape and integrity.

Deviations from the prescribed conditions of preparation of starting raw materials may often result in significant changes in the products obtained.

Excessive powder particle size, crystallinity, or level of impurities may result in 50 cracking and fracturing during drying On the other hand excessive levels of gel in the powder, or pseudoboehmite may result in excessive shrinkage and densification upon drying which can also lead to cracking Alumina compositions other than the product of our invention which are suitable for spheroid formation will generally have a boehmite or psuedoboehmite crystalline structure, preferably 55 microcrystalline, a nitrogen pore volume of 0 4 to 0 6 cm 3/g, surface areas in excess of 50 m 2/g and will contain amorphous gel.

The dried spheroid product is then treated at high temperatures to convert the crystalline alumina hydrate and amorphous gel components to a transition alumina This may be done by batch or continuous calcination by contacting the 60 product with hot gases which may be either indirectly heated gases or the combustion products of ordinary fuels with air Regardless of the particular method used, the product is calcined at specific temperature ranges depending on the particular transition alumina desired.

For example, to obtain a gamma type alumina, the product may be 65 I 1,603,463 9 1,603,463 9 conveniently calcined at temperatures of about 1000 F to about 1500 F For applications which require high temperature stability while retaining high surface area and porosity, the target material may be theta alumina A predominantly theta alumina product may be obtained by calcination at about 1750 to about 1950 F preferably about 1800 to about 1900 F for periods of from about 30 minutes to about 3 hours, preferably from about 1 hour to about 2 hours For automotive exhaust catalysts, the high temperature treatment step is often called stabilization.

The catalyst support that comprises the spheroidal alumina particles and that is obtained after stabilization generally has the following range of properties:

Property Surface area (m 2/g) Compacted bulk density (lbs/ft 3) Total pore volume (cm 3/g) Pore size distribution (cm 3/g) Below 1 OOA 1 000 A 1000 10,000 A Above 10,000 A Crust strength (lbs-force) Volume shrinkage (%) Attrition loss (%) Mesh size Approximate General Range 80-135 20-36 0.8-1 7 0 0 06 0.5-1 O 0.1-0 4 0-0 4 5-15 0-6 0-5 -4 + 10 However, when the preferred starting raw materials are used under the preferred conditions of preparation, the property ranges become:

Property Surface area (m 2/g) Compacted bulk density (lbs/ft 3) Total pore volume (cm 3/g) Pore size distribution (cm 3/g) Below 100 A 100-1000 A 1000-10,000 A Above 10,000 A Crush strength (lbs-force) Volume shrinkage (%) Attrition loss (%) Mesh size Typical Range 90-120 26-32 0.9-1 2 0-0 4 0.6-0 9 0.2-0 3 0-0 3 7-12 2-4 0-2 -5 + 7 The surface areas are nitrogen BET surface areas and the other above specified properties were determined by the following methods These methods may be also applied to the finished catalysts.

Compacted Bulk Density A given weight of activated spheroids is placed in a graduated cylinder sufficient to contain same within its graduated volume "Activated" as used herein means treated at 320 F in a forced draft oven for 16 hours prior to the testing This activation insures that all materials are tested under the same conditions The cylinder is then vibrated until all settling ceases and a constant volume is obtained.

The weight of sample occupying a unit volume is then calculated.

Total Specific Pore Volume A given weight of activated spheroids is placed in a small container (for example, a vial) using a micropipette filled with water, the said sample is titrated with water until all of the pores are filled and the endpoint of titration occurs at incipient wetness of the surface These measurements are consistent with total porosities calculated from the equation:

f I D p in which:

blo W er -,, 1 1 1 1 1 1,603,463 w 1 ' c ' 1 1 11 i 1,603,463 10 P=total specific porosity (cm 3/g) f=volume packing fraction (for spheroids typically 0 64 0 04) D=compacted bulk density (g/cm 3) p=crystal density of skeleton alumina (g/cm 3) (typically between 3 0 and 3 3 ;-'4,;''; 5 g/cm 3 for transition aluminas) 5 Mercury Pore Size Distribution The pore size distribution within the activated spheroidal particle is determined by mercury porosimetry The mercury intrusion technique is based on the principle that the smaller a given pore the greater will be the mercury pressure required to force mercury into that pore Thus, if an evacuated sample is exposed 10 to mercury and pressure is applied incrementally with the reading of the mercury volume disappearance at each increment, the pore size distribution can be determined The relationship between the pressure and the smallest pore through which mercury will pass at the pressure is given by the equation:

-2 u Cos 0 r 2 oos O 15 Up where r=the pore radius u=surface tension o=contact angle P=pressure 20 Using pressures up to 60,000 psig and a contact angle of 1400, the range of pore diameters encompassed is 35-10,000 A.

Average Crush Strength Crush strength is determined by placing the spheroidal particle between two parallel plates of a testing machine such as the Pfizer Hardness Tester Model 25 TMI 41-33, manufactured by Charles Pfizer and Co, Inc, 630 Flushing Avenue, Brooklyn, New York The plates are slowly brought together by hand pressure The amount of force required to crush the particle is registered in a dial which has been calibrated in pounds force A sufficient number (for example, 50) of particles is crushed in order to get a statistically significant estimate for the total population 30 The average is calculated from the individual results.

Shrinkage A given amount of particles is placed in a graduated cylinder and vibrated until no further settling occurs, as is done in predetermining Compacted Bulk Density.

This sample is then placed in a muffle furnace at 18000 F for 24 hours At the end of 35 this exposure, its volume is again measured after vibration until no further settling occurs The loss in volume after heating is calculated, based on the original volume, and reported as percent shrinkage.

Attrition Loss A set volume ( 60 cc) of material to be tested is placed in an inverted 40 Erlenmeyer flask of special construction which is connected to a metal orifice inlet.

A large (one inch) outlet covered with 14-mesh screening is located on the flat side (bottom) of the flask High velocity dry nitrogen gas is passed through the inlet orifice causing the particles to: (I) circulate over one another thus causing attrition, and ( 2) impact themselves in the top section of the flask thus breaking 45 down as a function of strength The material is tested for five minutes and the remaining particles are weighed The loss in weight after testing expressed as percent of the initial charge is designated the attrition loss.

The nitrogen flow will be in the range of about 3 5 and 4 0 cubic feet per minute, depending upon the density of the material The flow rate must be 50 sufficient for the particles to strike the top section of the flask The fines produced by attrition are carried out of the flask by the nitrogen flow thus causing a loss in weight of the original material charged.

The alumina and sphere formation conditions of the present invention provide spheroidal alumina particles with a highly unexpected and uniquely desirable 55 combination of properties The spheroids generally have a total pore volume ranging from about O 8 to about 1 7 cm 3/g While this is a high total pore volume, in itself it is not exceptional What makes this pore volume exceptional is the size distribution y 11 1,603,463 1 l of the pores which make up this volume and high temperature stability of this volume A large fraction of the volume is made up of macropores (> 1000 A) Most of the rest of the pores are in the 100-1000 A range There are very few micropores (< 100 A) This type of distribution is important for catalytic activity and stability In a heterogeneous process, catalytic activity is highly dependent 5 upon the rate of diffusion of reactants to the catalyst sites and of reaction products away from the sites Thus, reaction processes in a catalyst containing a large amount of macroporosity are less diffusion dependent However, the macropores account for only a small fraction of the sample surface area The intermediate size pores provide the surface area required for catalytic activity This surface area has 10 two components; namely, that required by the catalytically active clusters themselves and that required to keep the clusters separated If the clusters are allowed to fuse together, their catalytic surface area and consequently the catalyst activity will decrease Microporosity of course, provides a very large surface area, but, this does not necessarily provide good catalytic activity Diffusion of reactants 15 and/or products may be the rate controlling factor Micropores can be closed over by sintering occurring during catalyst operation or by deposition of poisons such as lead compounds in an auto exhaust system In either case, the activity of the catalyst in the closed micropores would be lost.

The surface area of the product spheroids is high, but is not unusually high 20 Surface areas generally range from about 350 m 2/g to about 500 m 2/g for spheroids heated to 10000 F and drop to about 80 M 2/g to about 135 m 2/g for thermally stabilized spheroids at 1800-19000 F What is important, however, is that most of the surface area is associated with intermediate size pores and not with micropores.

This preferred porosity distribution and its pore volume stability are a direct 25 result of the unique combination of properties in the alumina powder used to make the spheroids In particular, its purity and high ratio of crystalline material to amorphous gel aid in minimizing microporosity.

These properties also help to account for the high temperature stability of the spheroids The spheroids exhibit low volume shrinkage, preferably less than about 30 4 % O They retain the transition alumina structure Alpha alumina is not detected even at temperatures of 19500 F It is well known that impurities act as sintering aids Thus, high impurity levels can promote shrinkage and alpha alumina formation A high gel content also leads to alpha alumina formation at high temperatures A high microporosity can result in high volume shrinkage as 35 micropores are closed off during sintering.

The spheroids also have an uncommon combination of low bulk density and relatively high crush strength Low bulk density is essential for quick light off, i e.

high initial catalytic activity The crystallinity of the alumina compositions is a contributing factor to both the low bulk density and high crush strength 40 The low attrition loss exhibited by the spheroids is a direct consequence of their shape and strong structure the smooth surface will not attrit as readily as irregular surfaces which exhibit corners and/or edges Also, the gelation process produces a coherent uniform particle rather than a layered particle which results from some mechanical balling processes A mechanically formed particle may 45 delaminate during an attrition process.

Another feature of this invention is the close control of the spheroid size In a given batch, greater than 95 ,' of the spheres can be within one mesh size, such as -5 + 6 or -5 + 7 Measurement with a micrometer shows that the spheroids can be even more closely sized There is only about a 0 015 inch variation in the major or 50 minor axis of the spheroids Thus, a controlled distribution of sphere sizes can be obtained by using the proper distribution of nozzle sizes This can aid in controlling the pressure differential across a packed catalyst bed which is an important factor in auto emissions catalyst devices.

That is, 95 of the spheres pass a sieve with an aperture of 4 mm but are 55 retained on a sieve with an aperture of 3 55 mm.

The properties of the spheroid product, when taken in toto define a unique particle which makes a superior catalyst support.

A catalyst comprising the support prepared by the process of this invention impregnated with a catalytically effective amount of at least one catalytically active 60 metal or metal compound is highly effective in many catalytic systems particularly those that operate at high temperatures Although the alumina itself may be active as a catalyst, it is usually impregnated with a suitable catalytic material and , ' , ' t ' Z 1 1 C 1 1 1 1 Z 1 activated to promote its activity The selection of the catalytic material, its amount, and the impregnation and activation procedures will depend on the nature of the reaction the catalyst is employed in Preferably, the catalytically active metal is platinum group metal selected from the group consisting of platinum, palladium, ruthenium, iridium, rhodium, osmium, and combinations thereof 5 The following Examples further illustrate the present invention Examples I to 7 are included to illustrate the preparation of preferred starting materials.

EXAMPLE I

This example illustrates the preparation of an alumina composition.

Alumina trihydrate was completely dissolved in sodium hydroxide to provide a 10 sodium aluminate solution containing 20 percent A 1203 and having a Na 2/0 A 1203 mole ratio of 1 40 495 grams of water were added to a reaction vessel and then 631 milliliters of 50 percent sodium hydroxide solution were added This volume of sodium hydroxide solution corresponded to 966 grams at the specific gravity of the solution of 1 53 g/cm 3 The mixture was stirred gently and heated to 2000 F A total 15 of 672 grams of alumina trihydrate was added gradually over a period of 30 minutes During the addition of the alumina trihydrate, the mixture was heated to a gentle boiling and stirred slowly Gentle boiling and stirring were then continued for another 60 minutes or until all the trihydrate was dissolved Heating was stopped and the mixture cooled with stirring to 1400 F 20 The specific gravity and temperature of the sodium aluminate solution were adjusted to 1 428 g/cm 3 and 1300 F respectively by adding 290 grams of water at a tem perature of 1400 F and stirring the mixture 2016 grams of the solution were used for the preparation of the alumina.

2286 grams of an aluminum sulfate solution containing 7 percent A 1203 and 25 having a specific gravity of 1 27 g/cm 3 at 250 C and a SO 4 =/A 1203 mole ratio of 3 01 were prepared by dissolving 1373 grams of aluminum sulfate crystals in 1963 grams of water.

The sodium aluminate solution and the aluminum sulfate solution were heated to 1450 F A heel of 3160 grams of water was placed in a strike tank, the agitator was 30 started, and the heel heated to 1550 F.

The heel was acidified to a p H of 3 5 by the addition of 6 milliliters of aluminum sulfate at an addition rate of 36 ml/minute and aged for 5 minutes At the conclusion of the aging period, the flow of sodium aluminate was started at a rate of

28 ml/minute Within 5 seconds, the flow of aluminum sulfate was resumed at 36 35 ml/minute and maintained constant through the 50 minute strike phase The flow of sodium aluminate was adjusted as needed to maintain the p H of the reaction mixture at 7 4 The strike temperature was maintained at 1630 F by heating the strike tank.

In 50 minutes, all of the aluminum sulfate solution had been added and 317 40 grams of sodium aluminate remained.

At the conclusion of the strike, the p H of the reaction mixture was increased to 10 0 by adding 29 more grams of sodium aluminate solution The final molar ratio of Na 20 to SO-4 was 1 00 The solution was stabilized by aging for 30 minutes at a constant tem perature of 1630 F 45 After aging, the reaction mixture was filtered and washed For every gram of alumina in the mixture, 50 grams of wash water were used A standard filtrationwash test was defined as follows Reaction slurry ( 600 ml) was filtered in an 8 inch diameter crock using Retel filter cloth, material no 80, at 10 inches of vacuum It was washed with 2 5 liters of water The filtration time was 2 1 minutes and the 50 filter cake was 7 mm thick.

The filter cake was reslurried at 15 O solids and spray-dried at an outlet temperature of 2500 F to a powder having a total volatiles (T V) content of 275 , as measured by loss on ignition at 1850 'F The dried powder was calcined at 1850 OF for I hour 55 The properties of the dry product and the calcined product are shown in Table 1.

TABLE I

Dry Powder Wt% O Na O, 002 60 Wt o SO 0 20 Wt R, T V 27 5 Agglomerate size 215 u Jo,-, ,;-,,;,;;.

I 1,603,463 Bulk density X-ray phases = 1 i Calcined Powder at 1850 F for 1 N 2 surface area N 2 pore volume, < 600 A Total X-ray phases Pore size distribution 1,603,463 TABLE 1 (cont) 24.1 lbs/ft 3 (boehmite-pseudoboehmite intermediate -no alpha or beta trihydrate phases present peak for l 0201 crystallographic plane falls at d spacing of 6 37 A Hour 136 m 2/g 0.72 cm 3/g 0.95 cm 3/g theta alumina, no alpha alumina present a nitrogen PSD measurement showed that all the pores were greater than 100 A diameter and that 50 % of the pores were in the 100-200 A diameter range.

EXAMPLE 2

Given below in Table 2 is a summary of results conditions described in Example I.

Properties No of runs Wt A 12 O/run (lbs) Stroke ratio-Na 2 O/SO O Standard filtration test (min) Average Spray Dried Powder Wt% Na 2 O Wt% SO; Wt% T V.

Bulk density (lbs/ft 3) N 2 surface area at 750 F for 30 minutes (m 2/g) N 2 pore volume at 750 F for 30 minutes (cm 3/g) < 600 A X-ray Calcined Powder at 1850 O F for I Hour Surface area (m 2/g) Pore volume (cm 3/g) Total < 600 A X-ray 0.03 0.19 27.9 24.0 420 0.82 intermediate boehmitepseudoboehmite 131 1.01 0.73 theta alumina, no alpha alumina present EXAMPLE 3

Given below in Table 3 is a summary showing the results for the blended products of six large scale runs The process was the same as in Example I except that 195 lbs of alumina (dry basis) were made per run Equipment size and amounts of material were scaled up proportionately The results were the same as in laboratory scale runs showing that the process could be readily scaled up.

TABLE 3

Spray Dried Powder Wt% Na 2 O Wt% SO; Wt% CO 2 Wt% T V.

Bulk density (Ibs/ft 3) 0.059 0.31 1.37 29.6 30.0 -.1,.

K of 13 runs using the process TABLE 2

13 l 0.93 2.4 1 25 1 '1 : _ W J ' 1 1,603,463 TABLE 3 (cont) N 2 Surface Area at 750 F (m 2/g) N 2 pore volume at 750 F (cm 3/g) < 600 A X-ray phases Calcined Powder-1850 F/I Hr N 2 surface area (m 2/g) N 2 pore volume (cm 3/g) Total < 600 A X-ray phases 413 0.77 intermediate boehmitepseudoboehmite 131 0.97 0.70 theta alumina, no alpha alumina present EXAMPLE 4

The process conditions shown in Example I were important to obtain an easily filterable, pure product In runs where the process conditions of Example I were employed except that the reaction temperature and time were varied, the following results were obtained.

Reaction temperature Reaction time TABLE 4 F min Standard filtration time test (min) Wt% SO= 2.8 9.5 1200 F min 9.0 0.19 163 F min (Example I)

2.1 0.20 Thus, a decrease in process temperature led to an increase in sulfate content.

A decrease in process time leads to an increase in filtration time.

EXAMPLE 5

This example illustrates the treatment of a washed alumina filter cakeprepared in accordance with the procedure of Example 3 with acetic acid before spray drying The acetic acid has the effect of decreasing the absorption of carbon dioxide during spray drying In each run glacial acetic acid was added to the filter cake to a p H of 6 0 and the mixture agitated The spray dried product contained 3 8 percent acetic acid and 64 5 percent alumina This represents 0 I moles of acetate ion for each mole of alumina.

The properties of the alumina products of Example 3 and this Example are shown in Table 7 The carbon dioxide content is 0 76 % compared to 1 377 O present in the alumina of Example 3.

Spray Dried Powder Wt% Na 2 O Wt% SO 4 Wt% solids (A 1203) Wto CO, X-ray Calcined Powder 1850 F/I Hr N 2 surface area (m 2/g) N 2 pore volume (cm 3/g) < 600 A X-ray TABLE 5

Example 3

0.059 0.31 63.8 1.37 Intermediate boehmitepseudoboehmite 131 0.70 Theta alumina, no alpha alumina present Example 5

0.053 0.50 64.5 0.76 Intermediate boehmite pseudoboehmite 118 Theta alumina, no alpha alumina present EXAMPLE 6

In order to illustrate the relative proportions of crystalline material and amorphous material in the alumina, samples of the alumina of Example I and aluminas A and B that exhibit lower and higher degrees of crystallinity respectively ."'?; -?';,À''-%,i:?,, ' o;'q? ',;-,,3"-"- '-;,''À::3':v, 's ', -:, r:,', ', 'ú ', À'?-;;s':'' 2À-:-,-;,À'-,,&, , i:' lS-, is WE'g ': M: a: S,, W <;@'9;,,; S,; 2 1 1 1 1 ' 1 1 1 1 1 1 4 C G 4 ' _ 1,603,463 15 were slurried with deionized water at A 1203 concentration of 100 g A 1203 (dry basis) in one liter of water Potentiometric titrations of each slurry were slowly conducted - - at a rate of addition of 1 IN sulfuric acid of 1 ml/minute over the p H range of 8 3 to : 4 0 in which alumina is insoluble.

TABLE 6 5

Volume of l IN H 2 SO 4 Solution Required to Reach Indicated p H Example I A B d 1020 l Spacing 6 37 A 6 56 A,6 1 I A Midpoint Width 1 78 A 1 98 A 0 18 A of Peak l 020 l 10 p H 8.3 0 00 7.0 36 47 14 6.0 90 120 25 5 0 117 156 36 15 4.0 150 193 47 The results show that the preferred alumina compositions required intermediate amounts of acid to effect the same p H change and thus had a gel content intermediate between A and B. EXAMPLE 7 20

The degree of crystallinity of the alumina compositions of this invention was further demonstrated by X-ray diffraction measurements of the development of beta alumina trihydrate on alkaline aging and heating 100 gram samples (dry basis) of alumina A as shown in Table 6 and the alumina prepared in Example 3 as shown in Table 3 were slurried in 250 milliliters of deionized water and brought to p H 10 25 by the addition of IN Na OH solution The time and temperatures of aging and the height of the high and low intensity X-ray peaks of alumina A for beta trihydrate are shown in Table 7 No detectable beta trihydrate was present in the alumina composition of Example 3 under the same conditions of aging and heating as alumina A 30 TABLE 7

4.72 A Peak 4 35 A Peak Time/Temperature Height (mm) Height (mm) 18 hrs/50 C 8 8 24 hrs/50 C I 1 8 35 41 hrs/50 C 10 12 4 hrs/90 C 12 14 21 hrs/90 C 18 14 The ease of formation of beta trihydrate under alkaline conditions of Sample 40 A indicated a higher gel content than in the alumina of Example 3 40 EXAMPLE 8

In a series of runs, five cubic feet of spheroidal alumina particles with an average bulk density of 28 pounds per cubic foot were prepared using a mixture of (I) a blend of the products of the runs of Example 3 and ( 2) the acetic acid treated alumina of Example 5 An 80/20 mix of plain alumina to acetate alumina was used 45 and slurried in nitric acid, acetic acid, and water The composition of the mixture was:

Example 3 alumina ( 63 8 wt%/ A 1203) 1919 g Example 5 alumina ( 64 5 Wt% A 1203 3 8 wt ' H 3 CCOOH) 475 g 0 5 M HNO 3 600 ml 50 1.5 M CH 3 COOH 1000 ml Water 1780 ml Nominal composition of above mix.

(A 1203), oo(CH 3 COOH)o,2 (HNO 3)o o B(H 20),s 34 The liquids were mixed together in a five gallon bucket and blended with the 55 alumina of Example 3 using a Cowles Dissolver with a three inch diameter blade À _ D l ":;"' ":' i;: ':;:-:;-''2 ?''-':", -:: ":?:,:'" -" 16 1,603,463 16 turning at 3500 RPM A 20 minute blending was used The acetate alumina was then added and the slurry was blended for another 20 minutes Viscosity of the slurry immediately after blending was 78 cps as measured with a Brookfield viscometer The initial viscosity varied between 60 to 100 cps The slurry was aged to a viscosity of 500 to 1000 cps before being used for sphere forming After aging, 5 the p H's of the slurry varied between 4 1 and 4 5 in the runs.

After aging, the alumina slurry was pumped to a pressurized feed tank that was inches in diameter and 4 inches high The slurry was continuously circulated between the feed tank and a reservoir tank to maintain the viscosity of the slurry.

The alumina slurry feed flowed under air pressure of 0 5 to 1 5 psig from the feed 10 tank to the nozzle holder the droplet formation rate varied between 140 and 170 drops/minute The nozzle holder could hold up to nineteen 2 7 mm internal diameter nozzles in a regular array 7 to 14 nozzles were used per run and the extra openings in the nozzle holder were used as spares in case any of the original nozzles clogged The nozzle holder contained air channels to provide a linear air flow of 100 15 cm/minute around the nozzle tips and prevent ammonia vapor from premature gelling the alumina droplets.

The 2 7 mm internal diameter of the droplet nozzle was selected to give about 1/8 inch diameter (minor axis) calcined spheres The lip thickness was 0 6 mm The 3 3 mm nozzle holes opened to 1/2 inch diameter, 1/2 inch long cylindrical holes cut 20 in the bottom of the holder The ends of the stainless steel nozzles were recessed 1/8 inch from the bottom of the holder and the bottom of the nozzle holder was 1/4 inch above the organic phase of the column.

With a slurry viscosity of 700 cps and a feed pressure of 1/2 psig a droplet rate of 170 drops per nozzle per minute could be maintained using seven nozzles It took 25 1-1/4 hours to form the slurry batch into droplets.

A glass sphere-forming column was employed The column was 9 feet high and 4 inches in diameter The column was filled with kerosine (no I grade) and 28 % aqueous ammonia The top six feet of the column contained the kerosene The remainder of the column was filled with the aqueous ammonia The aqueous 30 ammonia was mixed with 1 3 wt% ammonium acetate and 083 wt% ammonium nitrate as measured under steady state operating conditions The kerosene was ammoniated to a concentration range of 0 03-0 08 wt C ammonia The kerosene also contained 0 2 volume% Liquinox.

A glass column 4 feet high by 3 inches diameter was used to ammoniate the 35 kerosene The column was half filled with ceramic saddles Kerosene was pumped from the top of the sphere forming column at a rate of approximately one liter per minute to the top of the ammoniating column Ammonia gas flowed into the bottom of this column The ceramic saddles broke up the stream of ammonia bubbles permitting a more efficient ammoniation of the kersosene Ammoniated 40 kerosene was pumped from the bottom of the ammoniator column to the bottom of the kerosene layer in the spheroid forming column An ammonia concentration gradient existed within the kerosene phase of the spheroid forming column The top of the kerosene phase had the least ammonia The ammonia concentration at the top of the kerosene phase was maintained between 0 03 and 0 08 wi> The 45 concentration was determined by titration with HCI to a bromothymol blue endpoint.

A batch collection system was used An 8 liter bottle was connected to the bottom of the spheroid forming column by detachable clamps A one inch diameter ball valve was used to seal off the bottom of the column when the collection bottle 50 was detached The collection bottle was filled with 28 C aqueous ammonia An overflow reservoir was connected to the collection bottle to catch the aqueous ammonia displaced by the spheroids When the collection bottle was full the spheroids were poured into a plastic basin where they were aged in contact with 28 % aqueous ammonia for one hour prior to drying 55 A forced air drying oven was used The spheroids were dried in nesting baskets with a 20 mesh stainless steel screen bottom The top of each gasket was open to the bottom of the basket above it The top basket was covered The bottom basket contained a charge of previously formed spheroids saturated with water Because the sides of the baskets were solid the flow of water vapor during drying was down 60 and out through the bottom of the stack of baskets A humid drying atmosphere was maintained in this manner to prevent spheroid cracking Drying temperature was 2600 F A 30 ft long, gas fired tunnel kiln with a 14 inch square opening was used to calcine the spheroids at 19000 F for one hour.

or; S, e_ __A summary of the run conditions and properties of the calcined spheroids for this example are given in Table 8.

A summary of the properties of the approximately three cubic foot blend of calcined spheroids formed in a series of runs by the conditions of this example are shown in Table 9 The spheroid bulk density and average crush strength were relatively uniform Attrition and shrinkage were low.

TABLE 8 r ''' q':'S:'::'.

Slurry Wt% A 1203; Nominal Actual Blend time (min) p H Aging before run (hours) Run viscosity; Initial (cps) 1900 F Calcination Bulk density (lbs/ft 3) Crush strength (Ibs) Range-High -Low Major axis (mils) Minor axis (mils) Major/minor axis ratio Water was evaporated during the mixing process.

26.5 27.6 + 20 4.39 4.5 700 28.2 9.0 11.5 7.5 148 1.14 Weight (Ibs) Volume (ft 3) Bulk density (lbs/ft 3) Average crush strength (Ibs) % Attrition % Shrinkage Sphericity (Major axis/minor axis) Average diameter (mils) N 2 surface area (m 2/g) X-ray TABLE 9

78.7 2.74 28.7 10.5 0.5 3.5 1.13 107 Theta alumina, no alpha alumina EXAMPLE 9

In Table 10, the slurry and spheroid forming properties of three conventional alumina powders are compared with those of three different powders produced by the powder formation process of Example 3 The process described in Example 8 was used to produce the slurries and spheroids 40 With both C and D alpha alumina monohydrate powders, it was necessary to use a lower solids content in the slurry With a higher solids content than those used, the slurries set solid in a few minutes Also, with the C alumina, it was necessary to use a higher alumina-acid ratio At the standard ratio, the slurry set up while blending 45 The C and D aluminas resulted in high bulk density spheroids Although the same size nozzles were used in all cases, these two aluminas formed spheroids - which were much smaller than the spheroids formed by the alumina compositions of this invention.

A crystalline alpha alumina monohydrate E was made by heating Alcoa C-30 D 50 alpha alumina trihydrate to 300 F for 4 hours A slurry made at the standard alumina-acid ratio had a p H of 3 2 The solids settled out immediately after blending When the alumina-acid ratio was doubled (to 1/0 09) the p H was 3 9, but the solids still settled out immediately after blending.

.,,,q - 7,faJ'#'7 '# 7 r 4,',,, f t _J 1->g::et'-e,;v'" t>X,' 1 '1', 1f' ' ' ', ',; ',, 1 1 1 1 j 'I ' ' f '11 1 1,603463 Powder Powder Properties % Total volatiles Crystallographic form as is Crystallographic form, 1900 F for I hour N 2 surface area, 1900 F for I hour(m 2/g) N 2 pore volume, < 600 A, (cm 3/g) at 1900 F for 1 hour Slurry Forming % Solids Mole ratio; A 12 O Jacids Slurry p H Initial viscosity, (cps) Time to reach 1000 cps Sphere Properties After 1900 F Calcination Crystallographic form N 2 surface area (m 2/g) N 2 pore volume, < 600 A (cm 3/g) Bulk density Average crush strength (Ibs) Major axis diameter (mils) Minor axis diameter (mils) TABLE 10

Example 3 Powders 25.6 0.70 27.6 1/0 18 4.4 84 4 hours 123 0.59 28.2 9.0 148 24.2 122 0.67 27.5 1/0 18 4.5 320 I hour 0.60 28.7 10.0 141 118 24.4 25 1 Alpha Alumina Monohydrate Theta Alumina 133 0.63 32.0 1/0 18 4.1 400 2 hours Theta Alumina 104 0.61 28.1 13.4 121 0.40 19.1 1/0 09 4.5 400 min 103 0.39 55.6 18.9 102 C' A Co E 21.3 D 21.5 124 0.54 23.4 1/0 18 4.5 220 1 hour Kappa Alumina 0.1 1/0 18 3.2 Settled out 108 0.53 52.4 21.3 116 00 j-1 -h t o G 1 r : -c :''I j 1 t i,': ' '1 'I : 1 1 '1 ' 19 1,603,463 19 EXAMPLE 10

An alumina slurry feed was made from an alumina powder which had the v-' " S following characteristics:

:'::, N ": " ' ' '; 0 08 wt% Na 2 O 0 43 wt% SO; 0.095 wt% Ca O 0.022 wt% Mg O 29.4 wt% total volatiles 0.85 cm 3/g N 2 pore volume 300 m 2/g N 2 surface area at 1000 F 10 X-ray diffraction shows alpha alumina monohydrate with the l 020 l reflection occurring at 6 6 A.

The slurry had the following composition:

17.5 wt% alumina 4 2 wt% nitric acid ( 0 38 moles HNO/mole A 1203) 15 The slurry was formed by hand stirring It was aged for 2 days Spheroids were formed in a l-inch diameter column Kerosene was the water immiscible phase.

The aqueous phase contained about 28 weight percent ammonia Three 175 g batches were made and combined The samples were calcined at 1000 F for 3 hours The properties of the spheroids were: 20 Bulk density 28 6 cf Crush strength 13 2 lbs Water pore volume 1 08 cm 3/g Size -6 + 7 mesh EXAMPLE 11 25

The spheroids discussed in Example 8 were measured for nitrogen pore size and surface area distributions The technique used is described by E V Ballou and O K Doolen in their article, Automatic Apparatus for Determination of Nitrogen Adsorption and Desorption Isotherms, published in Analytical Chemistry, Volume 32, pp 532-536 (April, 1960) The equipment used for this determination was an 30 Aminco Adsorptomat manufactured by American Instrument Company of Silver Spring, Maryland.

The nitrogen BET surface area of this material was 120 m 2/g with the following distribution:

Approximate % of Cumulative 35 Pore Diameter Nitrogen Surface Area to (A) Indicated Diameter 600 1 3 % 500 1 6 % 400 2 3 % 40 300 5 O % 16 3 % 46 4 % about 100 % It is obvious from these data that the vast majority of the pores were in the 45 intermediate range of 100-1000 A More specifically, over 80 % of the pores were between 100 and 200 A, and that no surface area was detected by this technique below pores of 100 A in diameter.

Claims (4)

WHAT WE CLAIM IS:- I A process for preparing spheroidal alumina particles which comprises: 50 (a) commingling alumina and an acidic aqueous medium to provide a slurry; (b) forming droplets of the slurry; (c) passing the droplets downwardly through air into an upper body of waterimmiscible liquid and ammonia and into a lower body comprising aqueous ammonia to form spheroidul particles; 55 (d) aging the particles in aqueous ammonia; and (e) drying and calcining the aged particles.

1,603,463 20

2 A process according to Claim I in which the alumina is a precipitated alumina.

3 A process according to Claim 2 in which the alumina is prepared by a precipitation in which aqueous solutions of sodium aluminate and aluminum sulfate are reacted so that the ratio of sodium expressed as moles of Na 2 O to sulfate 5 ion expressed as moles of equivalent H 2 SO 4 is in excess of 0 80 but below 0 97.

4, W ffi-,9: S,,; t / A-< =E, bs SSwee ';tv I' ' 1 1 1 1.603463

4 A process according to Claim 3 in which the said ratio is in excess of 0 88 but below 0 97.

A process according to any one of Claims I to 4 in which the alumina also comprises calcined alumina fines in an amount of up to about 15 percent 10 6 A process according to Claim I in which the alumina is a washed alumina filter cake.

7 A process according to any one of Claims I to 6 in which the alumina comprises a microcrystalline boehmite-pseudoboehmite intermediate having from about 70 to about 85 weight percent of the total amount of A 1203 present in 15 crystalline form.

8 A process according to Claim I in which the alumina is one claimed in any of Claims I to 8 of Application No 80 29154 (Serial No 1,603,464).

9 A process according to Claim I in which the alumina is one claimed in Claim 22 of Application No 11808/78, (Serial No 1,603,401) 20 A process according to any one of Claims I to 9 in which the slurry has a p H of about 4 0 to about 4 8 and a viscosity of about 200 to about 1600 cps.

1 1 A process according to Claim 10 in which the slurry contains about 24 to about 32 weight percent of alumina and has a viscosity of about 800 to about 1200 cps 25 12 A process according to any one of Claims I to 11 in which the acidic aqueous medium comprises an aqueous solution of an acid salt, a monobasic acid, or a mixture of monobasic acids.

13 A process according to Claim 12 in which the acidic aqueous medium is nitric acid, hydrochloric acid, acetic acid, formic acid, aluminum nitrate or a 30 mixture thereof.

14 A process according to Claim 13 in which the acidic aqueous medium comprises an aqueous solution of nitric acid and a decomposable monobasic organic acid.

15 A process according to Claim 13 in which the acidic aqueous medium 35 comprises an aqueous solution of aluminum nitrate.

16 A process according to any one of Claims 13 to 15 in which the slurry contains from about 10 to about 40 weight percent alumina and about I to about 12 weight percent acid.

17 A process according to Claim 16 in which the slurry has an acid to alumina 40 molar ratio of about 005 to about 0 50.

18 A process according to any one of Claims I to 17 in which the alumina and acidic aqueous medium are commingled by adding portions of the alumina to the acidic aqueous medium to acidify the alumina.

19 A process according to any one of Claims I to 18 in which the ammonia 45 concentration in the water-immiscible liquid is about 0 01 to about 1 0 weight percent.

A process according to Claim 19 in which the ammonia concentration in the water-immiscible liquid is about 0 04 to about 0 07 weight percent.

21 A process according to any one of Claims I to 20 in which the water 50 immiscible liquid and ammonia are introduced into the lower portion of the upper body, flow upwardly through the body in countercurrent flow with the droplets, and are removed at the top of the upper body.

22 A process according to any one of Claims I to 21 in which the spheroidal alumina particles are calcined at about 1750 to about 1950 'F for a period of from 55 about 30 minutes to about 3 hours.

23 A process according to Claim 22 in which the spheroidal alumina particles are calcined at about 1800 to about 19000 F.

24 A process according to Claim 22 or 23 in which the particles are calcined for a period of from about 1 hour to about 2 hours 60 a - -$; :-,its,_e C-x A process according to Claim I substantially as described in any one of Examples 8, 9 and 10.

26 Spheroidal alumina particles whenever prepared by a process as claimed in any one of Claims I to 25.

J A KEMP & CO, Chartered Patent Agents, 14 South Square, Gray's Inn, London WCIR 5 EU.

1 1 ' .,S.

Printed for Her Majesty's Stationery Office, by the Courier Press, Leamington Spa, 1981 Published by The Patent Office, 25 Southampton Buildings, London, WC 2 A IAY, from which copies may be obtained.