PROCESS FOR PREPARING WIDE PORE ALUMINA SUPPORTS

Abstract: A process for preparing a high surface area, wide-pore containing, porous alumina which comprises: a) mulling an alpha alumina monohydrate with water and a peptizing agent, b) separately preparing an alumina hydrogel by precipitating an aqueous solution of an acidic aluminium salt excepting aluminium sulphate with a basic precipitating agent, c) mulling together the hydrogel of step b) and the mulled alumina of step a) wherein the amount of hydrogel calculated as Al₂O₃, ranges from 1 to 50% by weight on the total amount of Al₂O₃. d) extruding the mixture of c), e) drying the extrudate, and f) calcining 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 substantially all of their pores in diameters less than 5-8 nm can present many problems. Diffusional limitations can occur when reactions take place in very small pores. Many petro-chemical 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 8 nm, 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. This invention relates to a process for preparing a high-surface area, wide-pore-containing alumina which comprises: (a) mulling an alpha alumina monohydrate with water and a peptizing agent, (b) separately preparing an alumina hydrogel by precipitating an aqueous solution of an acidic aluminium salt excepting aluminium sulphate with a basic precipitating agent, (c) mulling together the hydrogel and the mulled alumina, wherein the amount of hydrogel calculated as Al₂O₃ ranges from 1 to 50% by weight on the total amount of Al₂O₃, (d) extruding the mixture of (c), drying the extrudate and calcining at a temperature ranging from 500 to 700°C. The resulting material has a surface area greater than 200 m²/g, a crush strength greater than 40 N, and a substantial portion greater than 20%, of its pores in the range of 10-35 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 of alumina hydrogel to a mulled alpha-alumina monohydrate, which, upon calcining results in a high surface area alumina catalyst (support) having a significant portion of its pores in the range of 10-35 nm in addition to the pores that would have been present in the 10 nm and lower range had not the hydrogel addition been utilized. The alpha alumina monohydrates utilized in the instant invention are readily obtainable commercially. The alpha alumina monohydrate has the boehmite or pseudoboehmite structure and is utilized in finely divided form. Coarse aggregates can be ground prior to use. The alpha alumina monohydrate is mulled with water and a peptizing agent. The amount of water used must be sufficient to allow the alumina to be thoroughly mixed. Generally, the amount of water used will be close to that required to provide an extrudable mix, although additional water will be added with the later addition of the gel in addition to any supplemental water needed to provide an extrudable mix. A peptizing agent is added to the material to be mulled. Such peptizing agent is an acid, such as acetic acid or nitric acid, the former being preferred, and is added in an amount to adjust the pH of the mixture between 3 and 6.5. The mixture is mulled for sufficient period to obtain a homogeneous mixture. Times of mulling will be dependent upon the type and efficiency of the mulling apparatus. Times ranging from about 0.1 to about 10 hours are generally suitable. The alumina hydrogel which is to be added to the mulled alpha alumina monohydrate is prepared by precipitating an acid aluminium salt, excepting, however, aluminium sulphate, in aqueous solution with a basic precipitating medium. Suitable acidic aluminium salts include aluminium nitrate and aluminium chloride. Aluminium sulphate has been found to be not suitable, making supports with insufficiently large pores. A preferred species is aluminium nitrate. The basic precipitating salts comprise ammonium or an alkali metal carbonate or bicarbonate. The precipitation can be carried out by adding an aqueous solution of the basic precipitating salt to an aqueous solution of the acidic aluminium salt until a pH of about 6-8 is reached in the precipitating medium, or the procedure can be reversed by adding the solution of the acidic aluminium salt to the solution of the basic precipitating salt until a pH of 6-8 is obtained. Preferably, the precipitation is obtained by simultaneously mixing the acidic aluminium salt solution and the basic precipitation salt solution in a separate container at a pH of about 6-8 (referred to as "simultaneous precipitation"). The gel is frequently aged after precipitation, say from about 0.1-10 hours. After precipitation, the gel is washed to remove most of the by-product salts. The gel may be partially dried, but not to the extent that the gel structure is completely destroyed. The above-prepared hydrogel is added to the mulled alpha alumina monohydrate and the resultant material is further mulled to obtain homogeneity. Additional water may be added to provide a consistency suitable for extrusion. Small amounts of binders and lubricants may be added at this point if desired. The amount of hydrogel added to the alpha alumina monohydrate, calculated on the basis of Al₂O₃ present in each, will range from 1 to 50%wt, preferably from 5 to 25%wt total Al₂O₃. Mulling time will vary depending on equipment but will generally range from 0.05 to 5 hours. After mulling, the mixture is extruded, dried and calcined. Drying temperatures are not critical and are typically about 50-150°C. Drying temperatures are not critical and are typically about 50-150°C. Drying times depend on drying temperatures and typically range from 1 to 30 hours. Drying atmosphere is not critical. Frequently, drying is combined with the calcining step. Calcining is carried out at temperatures ranging from up to 500°C to up to 700°C. Calcining times are dependent on calcining temperatures and with typically range from 1 2 to 20 hours. Calcining atmosphere is not critical; although, if organic binders and/or lubricants are utilized to faciliate 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 about 200 m²/g, pore volumes (Hg intrusion 220 kg/cm²) ranging from 0.7 to 1.0 cm³/g and with at least 20% of its pore volume in pores having diameters ranging from 10 to 35 nm. Pore diameters are also measured by mercury intrusion. Crush strengths (measured by flat plate crush test) are greater than 40 N. The calcined alumina is most suitable for use as a catalyst in those processes catalyzed by alumina or as use as a catalyst support. It is particularly suitable as a support for preparing hydrotreating or hydrofining catalysts, for example, those utilizing Group VIIIA alone or in combination with Group VIA 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 reactions 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 360 kg/cm². Example 1 An alumina gel was prepared by pumping two solutions into a stirred reaction vessel containing 600 ml water at 55°C. One solution was 750 g (2 mole) aluminium nitrate in 800 ml water at 65°C and the other solution was 2 molar ammonium carbonate at 45°C. The addition time of 25 min at a constant pH of 7 was followed by an aging step of 30 min. The precipitate was filtered and washed with a total of 14 litres of water. The filtered gel weighed 1039 g and was reduced to 516 g in an oven at 80°C. Alpha alumina monohydrate (700 grams calculated as Al₂O₃) was placed in a mulling machine. A mixture of 21 g acetic acid and 342 g of water was added over a 2 minute period. After 9 minutes of mixing another 50 ml water was added, and after 20 minutes the 516 g of alumina gel as prepared above was added. This was mixed for 10 minutes. Water was added to get loss on ignition (LOI) to 61.5% and mixing for an additional 5 minutes was carried out. The material was then extruded through a die with 1.6 mm holes and dried in a 120°C oven overnight. The extrudate was broken into short lengths with a roller and sieved to remove fines. The material was calcined for 2 hours at 600°C. Properties are shown in Table 1. Example 2 The above example was repeated except that the simultaneous precipitation was carried out at ambient temperature (about 20°C) and sufficient gel was used to constitute about 20% by weight, basis Al₂O₃ of the total material. The properties of the resultant material are shown in Table 1. Example 3 Example was repeated except that sufficient gel was used to constitute about 7% by weight, basis Al₂O₃, of the total material. The properties of the resultant material are shown in Table 1. Example 4 Example 1 was repeated except that aluminium chloride was used instead of aluminium nitrate. Comparative Example A In this example, only alpha aluminium monohydrate was mulled with acetic acid, extruded, dried and calcined as in Example 1. The properties are shown in Table 1.

Claims: 1. A process for preparing a high surface area, wide-pore containing, porous alumina which comprises: a) mulling an alpha alumina monohydrate with water and a peptizing agent, b) separately preparing an alumina hydrogel by precipitating an aqueous solution of an acidic aluminium salt excepting aluminium sulphate with a basic precipitating agent, c) mulling together the hydrogel of step b) and the mulled alumina of step a) wherein the amount of hydrogel calculated as Al₂O₃, ranges from 1 to 50% by weight on the total amount of Al₂O₃ d) extruding the mixture of c), e) drying the extrudate, and f) calcining at a temperature ranging from 500 to 700°C. 2. A process according to claim 1 wherein the basic precipitating agent is ammonium carbonate, ammonium bicarbonate, an alkali metal carbonate, or an alkali metal bicarbonate. 3. A process according to claim 1 wherein the peptizing agent is acetic acid or nitric acid. 4. A process according to any one of the claims 1-3 wherein the amount of hydrogel ranges from 5 to 25% by weight. 5. A process according to any one of the claims 1-4 wherein the hydrogel is prepared by simultaneously adding the acidic aluminium salt-containing solution to the basic precipitating agent. 6. A process according to any one of the claims 1-5 wherein the acidic aluminium salt is aluminium nitrate or aluminium chloride. 7. A process according to any one of the claims 1-6 wherein the hydrogel is added to the mulled alumina.

Inventors: SCHOENTHAL, GALEON WAYNE, SLAUGH, LYNN HENRY
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1986
Main classification: B01J21
IPC codes: B01J35, B01J21, C01F7