WIDE PORE ALUMINA SUPPORTS

Abstract: A process for preparing a high surface area, wide-pore-containing, porous alumina material which comprises: a) preparing a first alumina hydrogel by precipitating an aqueous solution of aluminium nitrate with an aqueous solution of an alkali metal or ammonium carbonate or bicarbonate, then washing said first hydrogel, b) separately preparing a second alumina hydrogel by precipitating an aqueous solution of sodium aluminate with an aqueous solution of a strong inorganic acid, then washing said second hydrogel, c) co-mulling the washed first and second hydrogels in the presence of a peptizing agent, wherein the weight percentage of the alumina provided by the first hydrogel ranges from 10 to 30 percent by weight, basis alumina (Al₂O₃), of the total and, adjusting, as needed the water content of the mulled material to provide an extrudable mixture, d) extruding the product of c), e) drying the product of d), and f) calcining the product of e) at a temperature ranging from 500 to 700 °C.

Description: This invention relates to a process for preparing high surface area, wide-pore-containing alumina materials useful as catalyst supports in the hydrotreating area. In certain petrochemical reactions the use of supported catalysts having most of their pores in diameters less than about 10 nanometres can present many problems. Diffusional limitations can occur when reactions take place in very small pores. Many petrochemical feedstocks contain various metal impurities such as nickel, vanadium or iron which can deposit out and poison small pore sized materials. Thus, catalysts having large average pore diameters, particularly catalysts having average pore diameters above about 10 nanometres, have been found to have greater metals capacity than catalysts having substantially only relatively small pores. Methods for creating controlled pore sizes in aluminas are hence quite useful. Various means have been utilized in the art to prepare supports with controlled pore sizes. Carbonaceous materials have been incorporated in aluminous material which, upon burn-out, produce selected pore sizes. Another means utilized has incorporated various fine solid particles, such as recycle catalyst fines into the processing of the alumina. Detergents have been added to hydrogels, which upon extrusion resulted in wide pores. Furthermore GB-A-1347 106 discloses a process of making an alumina support material by concurrently reacting aqueous solutions of an aluminium salt and an aluminate. This invention relates to a process for preparing a high surface area, wide-pore-containing, porous alumina material which comprises: a) preparing a first alumina hydrogel by precipitating an aqueous solution of aluminium nitrate with an aqueous solution of an alkali metal or ammonium carbonate or bicarbonate, then washing said first hydrogel, b) separately preparing a second alumina hydrogel by precipitating an aqueous solution of sodium aluminate with an aqueous solution of a strong inorganic acid, then washing said second hydrogel, c) co-mulling the washed first and second hydrogels in the presence of a peptizing agent, wherein the weight percentage of the alumina provided by the first hydrogel ranges from 10 to 30 percent by weight, basis alumina (Al₂O₃), of the total and, adjusting, as needed the water content of the mulled material to provide an extrudable mixture, d) extruding the product of c), e) drying the product of d), and f) calcining the product of e) at a temperature ranging from 500 to 700 °C. Materials prepared in this fashion have high surface areas, greater than 200 m²/g; high crush strengths, greater than 46 N; and a substantial portion, greater than 25 per cent, of its pores in the range greater than 35 nm. These materials are quite useful for preparing hydrotreating and hydrodemetallization catalysts. The instant invention then provides another means for tailor-making a catalyst (support) having both narrow and wide pores. The instant invention utilizes the addition of minor amounts (less than 50% by weight) of an aluminium nitrate derived alumina hydrogel to a hydrogel derived from sodium aluminate, which, upon calcining results in a high surface alumina catalyst (support) having a significant portion of its pores in the 35 nm and greater range in addition to the pores that would have been present in the 5-12,5 nm range had not the nitrate-derived gel been utilized. The alumina hydrogel prepared from the sodium aluminate is prepared in a routine fashion. This basically comprises precipitating an aqueous solution of sodium aluminate with a strong inorganic acid such as, for example, sulphuric acid, nitric acid, or hydrochloric acid. The precipitation can be carried out by adding an aqueous solution of sodium aluminate to a solution containing a strong acid until a pH of 7.5 to 8.5 is reached in the reacting medium, or the procedure can be reversed by adding the strong acid to the solution containing the sodium aluminate until a pH of 7.5 to 8.5 is obtained (referred to as "sequential precipitation"). Preferably, the precipitation is obtained by simultaneously mixing the aqueous solution of sodium aluminate and the aqueous acid solution in a separate container at a pH of 7.5 to 8.5 (referred to as "simultaneous precipitation"). The gel is frequently aged after precipitation, say at a pH ranging from 9.5 to 10.5 for 0.1 to 10 hours. After precipitation, the gel is washed to remove most of the by-products salts. After the washing, the gel is partially dried, but not to the extent that the gel structure is completely destroyed. The nitrate-derived alumina hydrogel to be admixed with the sodium aluminate-derived alumina hydrogel is prepared by precipitating an aqueous solution of aluminium nitrate with an aqueous solution of an alkali metal or ammonium carbonate or bicarbonate. The precipitation can be carried out by adding an aqueous solution of the alkali metal or ammonium carbonate or bicarbonate to an aqueous solution of the aluminate nitrate salt until a pH of 6 to 8 is reached in the precipitating medium, or the procedure can be reversed by adding the solution of the aluminium nitrate salt to the solution of the alkali metal or ammonium carbonate or bicarbonate salt until a pH of 6 to 8 is obtained (referred to as "sequential precipitation"). Preferably, the precipitation is obtained by simultaneously mixing the aluminium nitrate solution and the alkali metal or ammonium carbonate/bicarbonate solution in a separate container at a pH of 6 to 8 (referred to as "simultaneous precipitation"). The gel is frequently aged after precipitation, say at a pH of 6 to 8 and for a time of 0.1 to 10 hours. After precipitation, the gel is washed to remove most of the by-products salts. The gel may be partially dried, but not to the extent that the gel structure is completely destroyed. After preparation of the individual gels, from 10 to 30 per cent by weight of the nitrate-derived gel is added to the sodium aluminate-derived gel and the two gels are mulled together in the presence of a peptizing agent for a sufficient period of time to obtain a homogeneous mixture. Times of mulling will be dependent upon the type and efficiency of the mulling apparatus. Times ranging from 0.1 to 10 hours are generally suitable. Suitable peptizing agents utilized are acids, such as acetic acid or nitric acid, and are added in an amount to adjust the pH of mixture between 3 and 6.5. The water content of the mulled mixture should be set as to provide an extrudable mix. This can be accomplished in several means. It can be accomplished by precisely adjusting the water contents of the individual gels prior to mixing. If the water content of the individual gels is not correct to provide the desired extrudable mix, then the water content of the mulled mixture can be adjusted by adding water during the mulling process, or by removing water during the mulling process by suitable application of vacuum. After mulling, the mixture is extruded, dried and calcined. Drying temperatures are not critical and are typically 50-150 °C. Drying times depend on drying temperatures and typically range from 1 to 30 hours. Drying atmosphere is not critical. Drying is combined with a calcining step. Calcining is carried out at temperatures ranging from 500 to up to 700 °C. Calcining times are dependent on calcining temperatures and will typically range from ½ to 20 hours. Calcining atmosphere is not critical; although, if organic binders and/or lubricants are utilized to facilitate extrusion, calcining should be carried out in an oxidizing atmosphere. Air is a preferred calcining atmosphere. The calcined materials are found to have surface areas (BET) greater than 200 m²/g, pore volumes (mercury intrusion at 207 bar) ranging from 0.7 to 1.3 ml/g and with at least 25 per cent of their pore volume in pores having diameters greater than 35 nm. Pore diameters are also measured by mercury intrusion. Crush strengths (measured by flat plate crush test) are greater than 46 N. A critical aspect of the instant invention is the amount of nitrate-derived alumina hydrogel that is added to the sodium aluminate-derived hydrogel. It has been found that the amount of aluminium nitrate-derived hydrogel to be added must fall within the range of 10 per cent to 30 per cent than by weight, basis alumina of the total final material. If lesser amounts of nitrate-derived gel are added to the sodium aluminate-derived gel, then the amount of pore volume found in pores greater than 35 nm drops significantly. If the amount of aluminium nitrate-derived gel added to the sodium aluminate-derived gel exceed 30 per cent, then the crush strength of the final sintered material falls significantly, considerably below 46 N. The calcined alumina is most suitable for use as a catalyst in those processes catalyzed by alumina or for use as a catalyst support. It is particularly suitable as a support for preparing hydrotreating or hydrofining catalysts, for example, those utilizing Group VIIIB alone or in combination with Group VIB metals. Such catalysts can be suitably applied to hydrocarbon conversion processes such as catalytic cracking, hydrocracking, hydrotreating, reforming, isomerization, hydrogenation, dehydrogenation, oligomerization, alkylation, dealkylation, demetallization and the like. The instant porous alumina materials, when utilized to support molybdenum, vanadium and cobalt as catalytically active metals, are very suitable for demetallization reaction involving crude feedstocks. The larger pores of the instant materials are not quickly plugged up by the depositing metals, and hence, provide very long life. In a typical demetallization reaction a crude feedstock is contacted with the instant catalyst at a temperature ranging from 350 to 450 °C and at a pressure ranging from 35 to 350 bar. Example 1 Aluminate Nitrate-Derived Gel The alumina nitrate-derived hydrogel was prepared by pumping two solutions into a stirred reaction vessel at ambient temperature. One solution was 375 g (1 mole) of aluminium nitrate in 400 ml of water and the other solution was two molar ammonium carbonate. The addition time of 13 minutes at a constant pH of 7 was followed by an ageing step of 30 minutes at the same pH. The precipitate was filtered and washed with a total of 6 litres of water. The gel was then divided into equal portions and one portion was dried at 90 °C to a weight of 48 g. Sodium Aluminate-Derived Gel The sodium aluminate-derived hydrogel was prepared by pumping two solutions into a stirred reaction vessel containing 750 ml of water at 65 °C. One solution was prepared by dissolving 440 g (two moles) of sodium aluminate in 1100 ml of water containing 11 g of sodium hydroxide at ambient temperature and heating it to 65 °C. The other solution was a one molar solution of sulphuric acid at 65 °C. The addition time was 20 minutes at a constant pH of 8, followed by an ageing step at a pH of 10 for about 15 minutes. The adjustment in pH was done with 2 molar sodium hydroxide. The precipitate was filtered and washed with a total of 12 litres of water. This gel was divided into equal portions and one was dried at 90 °C to 266 g. Mixed Gel Preparation The 48 g sample of the nitrate-derived gel was combined with the 266 g sample of the aluminate-derived gel in a "Brabender Prep Mixer" and mixed for 30 minutes with 2 ml of acetic acid. The calculated loss on ignition was 62%. The material that was extruded through a die with 1.6 mm holes and dried in an oven overnight at 120 °C. The extrudate was broken into short lengths with a roller and sieved to remove fines. The material was calcined at 600 °C for 6 hours. The crush strength by flat plate crush test was 54 N. The physical characteristics of this material are given in Table I. Comparative Example A In this example the other sample of the sodium aluminate-derived gel was extruded and calcined as described above. The crush strength by flat plate crushed test was 92 N. Physical properties are given in Table I. Comparative Example B In this example the aluminium nitrate-derived gel sample from above was extruded and calcined as described in the preparation of the mixed gel material. Crush strength by flat plate crushed test was less than 28 N. Physical properties are given in Table I.

Claims: A process for preparing a high surface area, wide-pore-containing, porous alumina material which comprises: a) preparing a first alumina hydrogel by precipitating an aqueous solution of aluminium nitrate with an aqueous solution of an alkali metal or ammonium carbonate or bicarbonate, then washing said first hydrogel, b) separately preparing a second alumina hydrogel by precipitating an aqueous solution of sodium aluminate with an aqueous solution of a strong inorganic acid, then washing said second hydrogel, c) co-mulling the washed first and second hydrogels in the presence of a peptizing agent, wherein the weight percentage of the alumina provided by the first hydrogel ranges from 10 to 30 percent by weight, basis alumina (Al₂O₃), of the total and, adjusting, as needed the water content of the mulled material to provide an extrudable mixture, d) extruding the product of c), e) drying the product of d), and f) calcining the product of e) at a temperature ranging from 500 to 700 °C. A process as claimed in claim 1, wherein the precipitation in step a) is carried out using ammonium carbonate. A process as claimed in claim 1 or 2, wherein the precipitation in step b) is carried out using sulphuric acid. A process as claimed in any one of the claims 1-3, wherein the peptizing agent in step c) is an acid. A process as claimed in claim 4, wherein the acid is acetic acid or nitric acid. A process as claimed in claim 1, wherein the precipitation of steps a) and b) are effected individually by simultaneous co-mixing of the reactants.

Inventors: SCHOENTHAL, GALEON WAYNE, SLAUGH, LYNN HENRY
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1986
Main classification: C01F7
IPC codes: C04B38, C01F7, C04B35