High pore volume and pore diameter aluminium phosphate

Abstract: Aluminum phosphate compositions are provided which are characterized simultaneously by high porosity and phosphorous-to-aluminum ratios of approximately 1.0. The high porosity of these compositions is a function of high pore volume coupled with low surface area, resulting in high average pore diameter. These materials have excellent properties as catalysts and catalyst supports. Methods of making the compositions are also provided.

Description: BACKGROUND OF THE INVENTION This invention is for a process for preparing aluminum phosphate compositions which are characterized by having both high porosity and phosphorus-to-aluminum (hereinafter "P/Al") ratios near unity. The high porosity of these compositions is characterized by a combination of high pore volume and low surface area, resulting in high average pore diameter. These compositions are useful as cracking catalysts, supports for ethylene polymerization catalysts, flatting agents, carriers, adsorbents and thickeners. Synthetic aluminum phosphates are known and the utility and properties of various compositions have been discussed extensively in the literature. For example, Kearby, 2nd Int'l Congress and Catalysis, "New AlPO 4 Gels As Acid Catalysts," pp. 2567-79 (1960, Paris) and Moffat, Catal. Rev. - Sci. Eng., "Phosphates As Catalysts," Vol. 19, pp. 199-258 (1978) discuss the properties of various aluminum phosphates, reporting surface areas of about 200.0 to 500.0 m 2 /g and pore volumes (hereinafter "PV") of about 0.45 to 0.78 cm 3 /g . Aluminum phosphate-containing compositions also have been described, as in U.S. 3,904,550 (Pine) which discloses a catalyst support comprised of alumina and aluminum phosphate with P/Al = 0.54 and PV = 1.34 cm 3 /g ; U.S. 4,210,560 (Kehl) which discloses magnesia-alumina-AlPO 4 catalyst supports with P/Al = 0.21 and PV = 1.11 cm 3 /g or with P/Al = 0.69 and PV = 0.72 cm 3 /g ; and Marcelin et al., J. of Catal., "Alumina-Aluminum Phosphate As Large-Pore Support and Its Application to Liquid Phase Hydrogenation," Vol. 83, pp. 42-49 (1983) which discloses alumina-aluminum phosphate supports with P/Al = 1.0 and PV = 0.32 cm 3 /g or with P/Al = 0.5 and PV = 0.64 cm 3 /g . U.S. 4,364,842 and 4,444,965 (McDaniel et al.) disclose aluminum phosphate-containing catalyst bases in which P/Al = 0.7-0.9 and in which the highest PV disclosed was 0.84 cm 3 /g (for P/Al = 0.80). Many of the prior art compositions share the same limitation. As the P/Al approaches unity, the pore volume of the prior art compositions decreases. Typically, aluminum phosphate compositions were not prepared with both these characteristics: a P/Al near unity and a high pore volume (i.e., PV of at least 1.0 cm 3 /g ). High pore volume is very desirable for aluminum phosphate compositions used as polymerization catalysts due to their polymerization characteristics. U.S. 3,342,750 (Kearby) discloses aluminum phosphate gels with PV of 1.39-1.56 cm 3 /g and surface area (hereinafter "SA") of 427-523 m 2 /g , resulting in average pore diameters of 65-114 Angstroms (6.5-11.4 nm). Kearby teaches a high PV composition which also has a P/Al near unity, but it can be seen that the high PV is achieved at the expense of pore diameter, which is low. It is taught, in U.S. 4,769,429 (Furtek), that high average pore diameter is a very desirable characteristic for polymerization catalysts. EP-A-0 215 336 discloses aluminum phosphate compositions in which phosphorous and aluminum are present in a ratio of close to unity and wherein the total pore volume of the composition is at least 1.0 cm 3 /g. The aluminum phosphates are prepared by by dissolving the selected salts in a P/Al ratio of approximately 1.0 in water and heating to form an acidic aqueous solution of aluminum and phosphate ions, cooling the solution thereafter and partially neutralizing the solution to 90-100% using ammonium hydroxide. Since ammonium hydroxide is not a strong base, the production of the aged hydrogel requires relatively large time periods. The resulting hydrogel, which may be cut into chunks or pieces, is then subjected to a second neutralization by soaking in an aqueous basic solution. The washed hydrogel is then exchanged with alcohol, acetone or ethyl acetate in several drain steps. The obtained hydrogel is dried to the desired volatile content. In providing catalyst supports with high PV and low SA, the compositions of the invention achieve this combination of properties and provide aluminum phosphate catalyst supports having high average pore diameters. Moreover, these unique characteristics of the present catalyst supports dramatically affect the characteristics of the reaction products (e.g., polyethylene). Use of the catalyst supports of this invention yields polyethylene products having different and advantageous properties, such as melt index (MI) and high load melt index (HLMI), as compared with products made using the prior art catalyst supports. For example, EP 56 164 (Phillips Petroleum) (McDaniel et al.), teaches in Table 1 that MI is 0 and HLMI is far below 1 unless an additive such as triethyl borane or hydrogen is used. SUMMARY OF THE INVENTION The primary object of this invention is to provide an improved process for preparing the described aluminum phosphates. Therefore the invention provides a process as defined in claim 1. The compositions obtained by the instant process are aluminum phosphate compounds with a unique combination of properties. These aluminum phosphates are characterized by high porosity. The compositions combine high pore volumes of at least 1.0, preferably at least 1.3 cm 3 /g, with low surface areas of 200-400 m 2 /g, preferably 200-300 m 2 /g, resulting in high average pore diameters of at least 125 Angstroms (12.5 nm), preferably at least 150 Angstroms (15.0 nm). At the same time, the ratio of phosphorus to aluminum in the compositions is close to unity. It is an additional object of this invention to provide stoichiometric aluminum phosphates with high porosity. Compositions of this description find particular utility when used as cracking catalysts or as supports for polymerization catalysts. A related object is to provide polymerization catalysts in which the catalytically active ingredients either are incorporated into the aluminum phosphate support of this invention by cogelling or by post-impregnation. It is also an object to provide high pore volume and high average pore diameter aluminum phosphates which are useful as flatting agents, flavor carriers, adsorbents and thickeners. DETAILED DESCRIPTION OF THE INVENTION High porosity stoichiometric aluminum phosphate compositions are described herein. The process of this invention provides aluminum phosphate in which phosphorus and aluminum are present in a ratio of close to unity. For purposes of this description, close to unity shall mean that the ratio is at least 0.8, preferably at least 0.9, and most preferably closer to 1.0. If the ratio of a given composition is not precisely 1.0, aluminum should predominate over phosphorus. The aluminum phosphates are further characterized by high pore volume and low surface area, resulting in high average pore diameter. This combination of characteristics is referred to herein as "high porosity." Pore volume is at least 1.0, preferably at least about 1.3 cm 3 /g , and surface area is between about 200 and about 400, preferably between 200 and 300 m 2 /g. The compositions are thermostable up to at least 700°C and are further characterized by a lack of crystallinity, that is, they will remain amorphous, even at temperatures in that vicinity. These properties make the aluminum phosphates provided by the process of this invention ideal for catalyst applications. The aluminum phosphates are conveniently prepared by the following method, although variations may be suitable. The compositions are made by neutralization of an acidic aqueous solution of aluminum and phosphate ions. Suitable solutions may be formed from aluminum salts and phosphate salts. The aluminum salts may be aluminum nitrate (Al(NO 3 ) 3 .9H 2 0), aluminum chloride hydrate (AlCl 3 .6H 2 0), aluminum bromide (AlBr 3 .6H 2 0), aluminum bromate (Al(Br0 3 ) 3 .9H 2 0), aluminum chlorate (Al(Cl0 3 ) 3 .6H 2 0), or aluminum iodide hydrate (AlI 3 .6H 2 0). The phosphate salts may be orthophosphoric acid (H 3 PO 4 ), ammonium phosphate (NH 4 H 2 PO 4 ), ammonium phosphate, dibasic ((NH 4 ) 2 HPO 4 ) or other soluble alkali phosphates. The preferred salts are aluminum nitrate and ammonium phosphate. Stoichiometric amounts of the aluminum and phosphate salts are preferred, as described above. Use of P/Al ratios of about 0.9:1 to 1:1 is significant in that the resulting solution yields a single phase, clear (i.e., homogeneous), bulk hydrogel upon neutralization. This contrasts with prior art aluminum phosphate compositions such as disclosed in U.S. 4,364,842 (McDaniels) in which the lower P/Al results in a white gelatinous precipitate, which is considered to be a two-phase system of precipitate and hydrogel. The selected salts (one or more, each, of aluminum and phosphate) are dissolved in water, in a P/Al of approximately 1.0, to form an acidic aqueous solution, pH about 2.0. It may be necessary to heat the water slightly to form a solution. The solution is then cooled. For reasons of economy, ambient temperatures are preferred for the preparation of the hydrogel, but the composition may be kept slightly warmer or cooler if desired. Alternatively, an aqueous aluminum nitrate solution may be used (for example a solution which contains about 60 wt% of the hydrated salt). A hydrogel is prepared by partially neutralizing the acidic aqueous solution and then allowing the partially neutralized composition to gel. Neutralization to about 60 to 70% is preferred. The pH of the partially neutralized composition is not critical but it should be kept low enough to avoid precipitation. The quantity of base used in this step is calculated from the stoichiometry of the reaction. One hundred percent neutralization refers to conversion of all nitrate to NH 4 NO 3 , which has a pH of 3.5 to 4.5 in water. Thus, at 100% neutralization, the pH will be about 4.0. Ammonia as NH 3 gas is used for neutralization. The ammonia gas is added to the aqueous aluminum phosphate solution with mixing sufficient to obtain uniform mixing of the reactants. The ammonia gas may be bubbled or injected into the solution as rapidly as the gas will be taken up by the liquid (i.e., will not simply bubble to the surface or displace the liquid). The actual rate of addition will depend on the system and equipment used; it is within the knowledge and ability of persons of ordinary skill in the art to determine the rate. As an example, it has been found that about 60-70 liters of ammonia gas can be added to about one liter of the solution at a rate of about 5-6 liters per minute, with the bubbles disappearing into the liquid at this rate of addition. The mixture will gel at about two-thirds neutralization. The partially neutralized solution, now a viscous mass, forms a clear, homogeneous hydrogel which is firm enough to be handled in the subsequent processing steps. A large amount of heat is generated by the neutralization reaction, which will raise the temperature of the gel (e.g., to about 80°C in a non-insulated vessel). The gelled mass is a semi-solid which fractures like glass upon application of mild shear, but which flows like a plastic fluid upon application of higher shear. The degree of plasticity is variable. The resulting aluminum phosphate hydrogel is subjected to a second neutralization. The hydrogel, which may be cut into chunks or pieces for ease in handling, is soaked in an aqueous basic solution. The basic solution must be of sufficient volume to cover the hydrogel and of sufficient strength to yield an end pH of about 8.0 to 9.0. Ammonium hydroxide is preferred, although sodium hydroxide also may be used. Where sodium hydroxide is used, care should be taken to ensure that residual sodium is washed out. The hydrogel preferably is soaked in concentrated base, such as ammonium hydroxide. Soaking allows for neutralization while keeping the hydrogel intact. It is preferred to use concentrated ammonium hydroxide (pH 10.0) at about 60.0 to 90.0°C, preferably about 80.0°C. For example, in a preferred process, the following materials and proportions may be used: for each mass unit of gel, 1.0 mass unit of de-ionized water is heated to about 80°C (for acceleration of the process) and mixed with about 0.09 mass units of concentrated ammonium hydroxide solution (about 29 wt%). A solution with lower ammonia content may be used, but it is preferred to have an excess of ammonia beyond that required for neutralization. Typically, little agitation will be required for this second neutralization step, provided temperatures of about 60 to 90°C, preferably about 80 to 85°C, are achieved and the gel is adequately exposed to the base. For example, sparging, fluidizing or mechanical turning will be adequate. The hydrogel should be soaked for at least about 2.0 hours, preferably at least about 4.0 hours. The hot base wash strengthens the hydrogel structure and maximizes the porosity of the aluminum phosphate compositions during water removal. Thus, this method of hydrogel preparation results in a homogeneous bulk hydrogel with good pore volume in the initial gel structure and in which the potential pore volume is essentially preserved by the hot base soaking step. A water wash step is used to wash out residual ammonium nitrate salt by-product. Preferably, de-ionized water, pH-adjusted to about 10 with ammonium hydroxide, is used, but pH adjustment may not be required. This step may be done in either a batch or continuous wash operation. Preferably, mixing is limited to reduce generation of particle fines. The water-washed hydrogel is exchanged with any alcohol soluble in water, or with acetone or ethyl acetate, to preserve the porosity developed in the second neutralization step. The alcohol exchange may be conducted in several soak/drain steps, for example, about 6-8 soak/drain repetitions, or by countercurrent contacting. Alternatively, the washed hydrogel may be exchanged with heavier alcohols, such as n-hexanol, followed by azeotropic distillation. The hydrogel is then dried to the desired total volatiles (TV) content, which will depend on the particular use intended for the aluminum phosphate composition. A calcination step is preferred to rid the solid aluminum phosphate composition of residual alcohol and ammonium nitrate. Removal of these residual materials is believed to maximize pore volume in the material. The aluminum phosphate composition prepared from the method of the first embodiment may be calcined, if desired. For example, it is suggested below that the compositions be calcined prior to use as cracking catalysts. Where calcination is conducted, the time and temperature should be selected to be sufficient to remove residual nitrates. For example, the composition may be calcined for about one hour at 1000.0°F (538.0°C), although other times and temperatures may be used. The composition then may be sized as desired. Aluminum phosphate compositions prepared in this manner can be expected to have the following unique combination of characteristics: The total pore volume (PV) will be at least 1.0 cm 3 /g, and preferably about 1.3 to 1.6 cm 3 /g. The surface area (SA), measured by the nitrogen Brunauer-Emmett-Teller (BET) surface area method described in Brunauer et al., J. Am. Chem. Soc., Vol. 60, p.309 (1938), may range from about 200.0 to 400.0 m 2 /g, preferably about 200 to less than 300 m 2 /g. The indicated combination of high PV and low SA necessarily results in the compositions' porosity being contained in pores such that the average pore diameter (hereinafter "APD") is high. The APD is calculated in the followingmanner, based on measured PV and SA: APD (Å) = 4 x PV (cm 3 /g ) x 10 4 SA (m 2 /g ) . (1Å = 0.1 nm) This formula provides a convenient method of predicting APD. The calculated APD values are verifiable by nitrogen desorption isotherm measurements. The relationship between PV and SA in this respect can be seen. In the compositions of this invention, having high measured pore volume and low measured surface area, the calculated (or measured) average pore diameter will be high. The high porosity of these compositions is thus based both on high pore volume and on pore volume contained in large diameter pores. The compositions have PV and SA values such that the combination of these two values yield a calculated APD of at least 125Å (12.5 nm). More preferably, the calculated APD is at least about 150Å (15.0 nm). Other characteristics of these compositions are typical of aluminum phosphates in general. It is expected that the improved aluminum phosphate compositions of this invention will find utility where conventional aluminum phosphates are used, with the added advantages of their high porosity. For example, the compositions may be used as cracking catalysts after sizing to an average of about 80.0 to 100.0 µm, then heating to about 1000.0°F (538.0°C) to remove all ammonia. For use as flatting agents, carriers or thickeners, the compositions are sized to about 1.0 to 20.0 µm, as desired, and typically are used at about 10.0% TV. The compositions also are useful as supports for polymerization catalysts. Where the compositions are used as supports for polymerization catalysts, the catalytically active agent, i.e., chromium, may be added either by incorporation into the aluminum phosphate gel or by impregnation on the formed support composition. In addition to chromium, other promoters such as boron, silicon or titanium may be present. The active agent or agents may be added initially to the aqueous solution of aluminum and phosphate ions in order to form a cogel with the aluminum phosphate or may be added to the aluminum phosphate material by post-impregnation. For post-impregnation of the catalytically active agent, the aluminum phosphate supports may be prepared as described above and then impregnated with the desired agent or agents. For example, the dried aluminum phosphate support material may be soaked in a solution of catalyst material (i.e., an isopropanol solution of Cr(NO 3 ) 3 .9H 2 0) and then dried. Typically, about l.0 to about 5.0% chromium on a total solids basis is used. Any convenient soluble chromium salt may be used, provided that the pH of the solution should not be low enough (i.e., pH less than about 3.0) to dissolve aluminum from the aluminum phosphate composition. In addition, it may be desired to add boron, silicon or titanium. Alternatively, the catalytically active agent or agents may be incorporated into the aluminum phosphate material itself by cogelling. In this embodiment, the agent is added to the initial solution containing aluminum and phosphate ions. For example, chromic nitrate (Cr(NO 3 ) 3 .9H 2 0) may be dissolved in the initial aqueous solution. The catalytically active aluminum phosphate cogel is then prepared according to the procedures described above. The examples which follow are given for illustrative purposes and are not meant to limit the invention described herein. The following abbreviations have been used throughout in describing the invention: AlPO 4 = aluminum phosphate Å = Angstroms (1Å = 0.1 nm) APD = average pore diameter BET = Brunauer-Emmett-Teller °C = degrees Centigrade cm 3 = cubic centimeter(s) conc = concentrated D.I. = de-ionized gal. = gallon(s) (1 gal. = 3.78 liters) g = gram(s) hr = hour(s) m 2 = square meter(s) min = minute(s) P/Al = phosphorus-to-aluminium ratio psig = pounds per square inch gauge (1 psig = 6.89·10 3 Pa g) PV = pore volume % = percent SA = surface area SLPM = standard liters per minute TV = total volatiles vol = volume wt = weight EXAMPLE I (comparative) The following ingredients were added to a beaker and heated to about 80°C: 1,237.5 g Al(NO 3 ) 3 .9H 2 0 and 198.0 g H 2 0. After forming a complete solution, the mixture was stirred and 342.0 g NH 4 H 2 PO 4 were dissolved in it. The solution was allowed to cool to ambient temperature. The calculated P/Al ratio was 0.90. First Neutralization - Next, 538.6 g of the cooled solution were added to a Waring blender and 127.0 cm 3 of concentrated NH 4 OH (30% NH 3 ) were added slowly (over 39.0 min) with vigorous agitation. The resulting viscous mass was transferred to a beaker and allowed to stand overnight to gel. The calculated percent neutralization (to NH 4 NO 3 ) was 96.0%, and the calculated final solids content as AlPO 4 +Al 2 0 3 was 17.6%. Second Neutralization - The aluminum phosphate hydrogel was cut into chunks (about 25.4 mm, 1.0 inch) and 514.5 g of chunks were transferred to another beaker, covered with a water solution containing 65.0 cm 3 concentrated NH 4 OH and allowed to stand overnight. The soak solution (final pH of 8.5) was decanted and the hydrogel transferred to another container for washing. Washing - The hydrogel was washed in a continuous flow-through system with 85°C dilute NH 4 OH (pH 10.0) for 19 hours. The washed hydrogel was then exchanged with acetone in seven soak/drain steps, and dried overnight in a vacuum oven at 145°C. The final product was found to have the following properties: TV (at 1750°F) = 12.3% PV = 1.43 cm 3 /g BET SA = 380.0 m 2 /g APD = 151Å (15.1 nm) EXAMPLE II (comparative) A solution of the following was prepared according to the procedures described below: 9,626.4 g A1(NO 3 ) 3 .9H 2 O 2,898.0 g NH 4 H 2 PO 4 1,134.0 g D.I. H 2 O 13,658.4 g Total In a covered container, the aluminum nitrate and water were mixed and heated to 80°C to form a clear solution. The ammonium phosphate was added and the solution heated back up to 80°C, then cooled to room temperature. The prepared solution was pumped (at a flow rate of 250.0 g /min), with ammonium hydroxide (29.0%) (at a flow rate of 47.7 g /min), into a 200 cm 3 reactor with two inlet streams and extremely turbulent mixing. High aluminum nitrate/ammonium phosphate concentration and low ammonium hydroxide concentration were used to prevent precipitation. The run-off pH was 2.10. The reactor was cooled to 53-55°C and held at that temperature during the run. Run-off from the reactor appeared very slightly white, translucent and with few small white particles floating in it. Correct sol began setting within five minutes. The gel was aged for approximately 18 hours, then cut into one-inch chunks and soaked in an ammonium hydroxide solution prepared according to the following: 12,000.0 g "as-is" gel 1,700.0 g 29.0% ammonium-hydroxide 37.8 liters (10.0 gal.) D.I. H 2 O The gel was soaked for 18-24 hours with occasional agitation. The pH of the liquid after soaking was 8.7-9.0. The liquid was drained and the hydrogel washed with ammonium hydroxide (pH 10) at 85°C for 29 hours. The wash flow rate for 12,000.0 g gel was 550-600 cm 3 /min. After washing, the liquid was drained and the gel allowed to cool in a covered tank. The hydrogel was then exchanged with ethanol by pouring 10.0 liters of ethanol over 12,000.0 g gel and agitating occasionally. The ethanol was drained after 2-3 hours. This ethanol exchange step was repeated eight times. The seventh exchange was allowed to set overnight. After eight exchanges, the gel was drained completely and put into a hot vacuum oven (150°C). After two hours, the temperature was increased to 200°C. After drying overnight, the gel was removed from the oven and sized so the final product would pass through an 80 mesh screen, staying on a 270 mesh screen. The final product was found to have the following properties: TV (at 1750°F) = 14.3% PV = 1.42 cm 3 /g BET SA = 267.0 m 2 /g APD = 213Å (21.3 nm) P/Al = 0.82 EXAMPLE III Following the procedures of the invention, 273.0 kg Al(NO 3 ) 3 .9H 2 O solution were added to a stainless steel tank, agitated and heated with steam on the jacketed tank. At about 35-40°C, 50.0 kg NH 4 H 2 PO 4 crystals were added over a 10 minute period. Agitation was continued, with heating to 60°C. The solution was held at that temperature for 30 minutes and then cooled to ambient temperature. The calculated P/Al ratio was .94. First Neutralization - Next, 85.05 liters (22.5 gal.) of the cooled solution were charged to a 151.2 liters (40 gallon) jacketed kettle equipped with a portable Lightning mixer and a sparge ring fixed at the bottom of the vessel, through which nitrogen or anhydrous ammonia gas could be sparged. The solution was agitated and sparged with N 2 . The NH 3 flow was started at 29-30 SLPM and the N 2 flow cut off. Agitation was continued and cooling water applied to the vessel jacket. About 6800 liters NH 3 were required for 100% neutralization, taking about 3 hours 50 min. for gelation. At gelation, the solution viscosity increased rapidly, stopping the mixer. NH 3 flow was continued. The mixer was removed and the gel manually broken up and mixed for about 5 min. to allow further contact between the gel and the sparging NH 3 . The NH 3 flow was then cut off and the gel allowed to set for one hour to harden. Second Neutralization - The aluminum phosphate hydrogel was added to a tank containing aqueous ammonium hydroxide solution at 80°C, gently agitated for 3-5 min., and held at that temperature for 4 hours. The solution was agitated for 5-10 seconds every half hour. Ammonia fumes were vented. The liquid was then carefully decanted to minimize entrained solids. Washing/Drying - The hydrogel was washed by adding 170.1 liters (45 gal.) D.I. water and heating to 45°C. Next, 2 liters 30% aqueous NH 4 OH were added and agitated for about 5 min. Heating was continued to 80°C and the wash was held for about 30 min. The liquid was decanted and the gel dewatered by filtering. The wet gel was slurried with 161.0 kg (355 lb.) isopropanol and dried in a Torusdisc® drier (B e pex Corporation). The dried gel was calcined in an electrically heated rotary calciner for 45 min. at 624°C (1155°F). The final product was found to have the following properties: TV (at 1750°F) = 3.0% N 2 PV = 1.24 cm 3 /g Hg PV = 1.42 cm 3 /g BET SA = 233.0 m 2 /g APD = 214Å (21.4 nm) P/Al = 1.03

Claims: A process for preparing high pore volume homogeneous aluminum phosphate compositions comprising: (a) forming an acidic aqueous solution of one or more aluminum salts and one or more phosphate salts, said solution having a P/Al ratio of about 0.9:1 to about 1:1, (b) partially neutralizing the acidic aqueous solution by the rapid addition of ammonia gas, with mixing, until gelation occurs, (c) neutralizing the hydrogel formed in step (b) by soaking for at least about 2 hours in a concentrated aqueous basic solution at a temperature of about 60.0 to 90.0 °C, (d) washing the neutralized hydrogel in water, (e) exchanging the washed hydrogel with alcohol, acetone or ethyl acetate, and (f) drying the exchanged hydrogel to obtain the composition. Process according to claim 1, in which the formed acidic aqueous solution comprises aluminum nitrate, aluminum chloride hydrate, aluminum bromide, aluminum bromate, aluminum chlorate or aluminum iodide hydrate, and orthophosphoric acid, ammonium phosphate or ammonium phosphate, dibasic. The process of claim 1 or 2 in which the dried hydrogel composition is calcined.

Inventors: GLEMZA RIMANTAS, PARENT YVES OVILA, GLEMZA, RIMANTAS, PARENT, YVES OVILA
Applicants: GRACE W R & CO, W.R. GRACE & CO.-CONN.
Application year: 1992
Main classification: C01B25
IPC codes: B01J35, C08F4, B01J27, C01B25