SYNTHESIS OF AN AMORPHOUS MAGNESIA-ALUMINA-ALUMINUM PHOSPHATE SUPPORT FOR USE IN RESID UPGRADING CATALYST

Abstract: A method for preparing an amorphous magnesia-alumina-­ aluminum phosphate catalyst support comprises the steps of: (a) forming an aqueous solution containing magnesium and aluminum ions and phosphoric acid; (b) precipitating amorphous magnesia-alumina-aluminum phosphate from said solution in the presence of a source of organic cation having a size equal to or larger than 2 Angstrom; and (c) separating the precipitate.

Description: Background of the Invention This invention relates to the synthesis of a magnesia-alumina-aluminum phosphate support for use in resid upgrading catalyst. It is well known that many, if not most, petroleum based stocks contain contaminants as for example, sulfur, nitrogen and metals. It is desirable, particularly if these feedstocks are to be further processed, that the contaminants be removed. This is an operation usually requiring use of a catalyst. It has been conventional in the art to effect contaminant removal, such as sulfur removal from hydrocarbon stocks, by subjecting them to treatment with hydrogen at elevated temperature and pressure while in contact with a catalyst containing hydrogenating components. Typically the hydrogenating components of such known catalysts are Group VIB or VIII metals, or other oxides or sulfides. These hydrogenating components may be supported on a variety of well known carriers, for example, alumina, kiselguhr, zeolitic molecular sieves and other materials having high surface areas. For example, U.S. Patent No. 3,546,103 teaches hydrodesulfurization with a catalyst of cobalt and molybdenum on an alumina base. The use of amorphous magnesia-alumina-aluminum phosphates (hereinafter abbreviated as MAAP) as supports for cracking and hydrocracking catalysts has been described in U.S. Patent Nos. 4,179,358 and 4,210,560. Typically, these materials are prepared by mixing together aqueous solutions of magnesium nitrate, aluminum nitrate and phosphoric acid and precipitating with ammonium hydroxide at a pH at about 9.0. In addition, U.S. Patent No. 4,376,067 discloses substitution of a Group IIB component, consisting of zinc or cadmium, for magnesium in an MAAP-type support for a cracking or hydrotreating catalyst. The present invention is predicated on the discovery that by substituting some or all of the ammonium hydroxide, used in the prior art processes for making MAAP catalyst supports, with organic cations, e.g. protonated alkyl amines or quarternary alkyl ammonium hydroxides, the pore size distribution of these supports can be advantageously shifted to be more effective for catalytic use. The pore size distribution of the organically modified support is distinctly different from known MAAP materials. These materials have also been found to have advantageous hydrodemetallization characteristics when used in the hydrotreatment of atmospheric and vacuum resids. Accordingly, the invention resides in a method of preparing an amorphous magnesia-alumina-aluminum phosphate catalyst support comprising the steps of: (a) forming an aqueous solution containing magnesium and aluminum ions and phosphoric acid; (b) precipitating amorphous magnesia-alumina-aluminum phosphate from the solution in the presence of source of organic cation having a size equal to or larger than 2 x 10⁻¹⁰m (Angstrom); and (c) separating the precipitate. After calcination, the catalyst support prepared by the method of the invention is magnesia-alumina-aluminum phosphate matrix of the formula: MgO-Al₂O₃-AlPO₄ Normally, the magnesia-alumina-aluminum phosphate constituents are in a mole percent ratio range of from 10:80:10 to 25:10:65, preferably from 10:55:35 to 20:35:45. The magnesia-alumina-aluminum phosohate matrix is characterized, after calcination at 500°C for 10 hours, as amorphous and having an average pore radius of from 10 to 200 x 10⁻¹⁰m (A), preferably from 75 to 150 x 10⁻¹⁰m (A); a surface area ranging from 100 m²/g to 350 m²/g, preferably from 125 m²/g to 250 m²/g and a pore volume of from 0.3 cm³/g to 1.5 cm³/g, preferably from 0.7 cm³/g to 1.2 cm³/g. Moreover the matrix is found to retain at least 90% of its surface area when the matrix is additionally calcined at a temperature up to about 750°C for about 10 hours. The magnesia-alumina-aluminum phosphate catalyst support is typically prepared by admixing together an aqueous solution of aluminum nitrate with an aqueous solution of magnesium nitrate and 85% phosphoric acid. The magnesia-alumina-aluminum phosphate catalyst support is then precipitated from the resultant solution by the addition of an alkylamine or a quaternary alkyl-ammonium hydroxide whose cation has a size equal to or greater than 2 x 10⁻¹⁰m (A) with or without ammonium hydroxide. The organic hydroxide compound can be an amine derivative, dialkylammonium, trialkylammonium, a tetra alkylquaternary ammonium compound, for example, tetramethylammonium hydroxide, tetraethyammonium hydroxide, tetrapropylammonium hydroxide or tetrabutylammonium hydroxide. Analogous phosphonium compounds can also he utilized, for example, tetramethylphosphonium hydroxide, tetraethylphosphonium hydroxide, tetrapropylphosphonium hydroxide or tetrabutylphosphonium hydroxide. Not only can the anion be a hydroxide, but it can also be a halide such as chlorine or bromine anion as well as other suitable anions. Thus, a general formula for the organic compound is R₄NOH or R₄NX where X is a hydroxide or halide anion or other suitable anion and R is hydrogen or an alkyl group. Normally, the solution pH is maintained at or about 9.0, although the pH can be initially about 7.5 and slowly raised to pH 9.5 as the reaction proceeds. After the magnesia-alumina-aluminum phosphate matrix has been precipitated, it is filtered from the solution, dried at about 120°C and calcined at about 500°C for about 10 hours using conventional apparatus. The resulting matrix after calcination is amorphous. The resultant magnesia-alumina-aluminum phosphate is intended for use as a support for one or more catalyst metal components, which can be incorporated with the support in any manner known to those skilled in the art. For example, CoHo and Mo magnesia-alumina-aluminum phosphates can be prepared by room temperature impregnation of the support with soluble cobalt and molybdenum salts followed by drying and air calcination at 427°C (800°F) for three hours. It is also possible to include metals by co-precipitation. The metal components are preferably Co, Mo, Ni or W or mixtures thereof. Generally, any of the Group VIII metals of the Periodic Table of Elements can be used. The use of organic cations during the precipitation step provides a method of introducing a unique and desirable pore size distribution into the catalyst supports of the invention. As will become apparent from the ensuing Examples the resultant materials are useful for preparation of catalyst for hydrodemetallization of resids. The catalyst support products of the present process can be composited with known zeolitic-type material using conventional extrusion and tabletting procedures or by precipitation of magnesia-alumina-aluminum phosphates in a suspension of zeolites from 2 to 75 weight percent. Resid hydroprocessing using a catalyst containing a support prepared by the process of the invention is conveniently performed at a hydrogen partial pressure in excess of 400 psig (2860 kPa), a temperature of 675-850°F (357-812°C) and LHSV of 0:1-10. Examples 1-9 A base preparation of MgO-Al₂O₃-AlPO₄ amorphous support was carried out. Aqueous solutions of aluminum nitrate and magnesium nitrate were combined with a solution of phosphoric acid. Separately, a basic aqueous solution of ammonia and a quaternary ammonium hydroxide or just a basic amine was prepared. The two solutions were simultaneously added to a beaker containing distilled water as a reacting medium and neutralized at a constant pH of 9.0 by careful control of the rates of addition. The precipitate obtained was filtered, washed, dried and then calcined at 538°C for up to 6 hours. In Table 1, the results of eight preparations are compared demonstrating that the organic amine or organic ammonium ion profoundly affects pore size distribution. The above results show that the subject technique can be used to tailor or control pore size distribution, which is a valuable technique in the preparation of catalytic materials. The amorphous MgO-Al₂O₃-AlPO₄ support materials of Examples 3, 5 and 8 were then converted into resid hydrotreating catalysts by impregnation with various combinations of Mo, Co, Ni, and W oxides. The properties of the resultant catalysts are given in Table 2 below: Examples 10-15 The catalysts listed in Table 2 and a conventional CoMo/Al₂O₃ resid hydrotreating catalyst having the properties set out in Table 3 below: were then evaluated for metals, sulfur, CCR (Conradson Carbon Residue), and asphaltene removal on shaker bomb experiments with a Arab Light vacuum resid having the properties set in Table 4: Shaker bomb testing has been shown to very closely simulate the resid upgrading activities observed in continuous downflow units. See S.M. Oleck and H.S. Sherry, Fresh Water Manganese Nodules As A Catalyst For Demetallizing and Desulfurizing Petroleum Residua, Ind. Eng. Chem., Process Des. Dev., 16 (4) 525 (1977) which is hereby incorporated by reference. Properties of these catalysts are shown in Table 2 while properties of the Arab Light vacuum resid are shown in Table 3. The catalysts were contacted with the oil in a conventional shaker bomb apparatus at the following conditions: Oil:Catalyst (wt:wt) 20 Temperature, °C 400 H₂ Pressure, psig (kPa) 2000 (13890) Reaction Time, min 80 A conventional apparatus is shown in J. W. Payne, C. W. Streed, and E. R. Kent, The Shaker Bomb - A New Laboratory Tool For Studying Thermal Processes, Ind. Eng. Chem., 50 (1), 47 (1958). Following each run, the catalyst and the oil were separated and both components were analyzed. Thermal contributions were determined from a blank run at identical reaction conditions but with no catalyst present. Table 5 presents the results of the shaker bomb experiments with the catalysts listed in Table 2, the conventional CoMo/Al₂O₃ catalyst and a further catalyst comprising the support of Example 9 impregnated with molybdenum oxide. From Table 5, it will be seen that the supported metal amorphous MAAP catalysts exhibited superior demetallization activity to that of the CoMo/Al₂O₃ catalyst. Moreover, it can be seen that the CoMo/amorphous MAAP catalyst was also superior to the CoMo/Al₂O₃ catalyst in asphaltene removal and sulfur removal (40% vs. 36%). Thus these MAAP catalyst were consistently superior to the conventional Al₂O₃ catalyst for upgrading resids. Examples 16-23 Further resid upgrading lists were performing using to conditions employed in Examples 10-15 and the results are listed in Table 6. Comparing the results of Examples 18 and 20 in Table 6, it will be seen that the demetallization activities of the catalysts are similar (62 and 58% vanadium removal, respectively). However, the particle size of the catalyst prepared from the organically-modified support (Example 20) is much larger than the base case (Example 18) and therefore is a superior catalyst based upon the known particle size effect. This is demonstrated by Table 7 which shows the vanadium removal activity of a CoMo/Al₂O₃ catalyst increases with decreasing particle size. Furthermore, the superiority of an organically modified MAAP compared to one prepared using NH₄OH as the precipitating medium is easily seen when Examples 18 and 23 are compared with Example 19. The catalysts prepared with MAAP without organics remove 62% and 35% vanadium compared to 75% for the organically modified material. Because of the high pressures required for resid hydroprocessing, it is desirable from an economic standpoint to minimize reactor volume. Use of these amorphous MAAP catalysts for upgrading resids will allow a refiner to attain degree of metals, sulfur and coke precursor removal with less catalyst and therefore in a smaller reactor. Alternatively, using these MAAP catalysts in existing reactors will allow the refiner to run at lower reaction severities or to attain process resids with improved quality. The subject process is particularly attractive for FCC feed pre-treatment. Also, the present process allows the pore size distribution of the catalyst support to be varied, while the large pore volume (greater than 0.8cm³ per gram) of the resultant support permits high metals capacity thereby increasing catalyst life.

Claims: A method for preparing an amorphous magnesia-alumina-aluminum phosphate catalyst support comprising the steps of: (a) forming an aqueous solution containing magnesium and aluminium ions and phosphoric acid; (b) precipitating amorphous magnesia-alumina-aluminum phosphate from said solution in the presence of a source of organic cation having a size equal to or larger than 210⁻¹⁰m(Angstrom); and (c) separating the precipitate. The method of Claim 1 wherein the organic cation is an organonitrogen cation or an organophosphoric cation. The method of Claim 2 wherein the organonitrogen cation is provided by addition to the solution of a quaternary ammonium hydroxide or an amine. The method of any preceding claim wherein said solution has a pH of 7.5-9.5 during the precipitation step. The method of any preceding claim and including the further step of calcining the precipitate. The method of any preceding claim and including the further step of incorporating a catalytically active metal or metal oxide on the support. The method of Claim 6 wherein the metal is a metal of Group VIII of the Periodic Table.

Inventors: ANGEVINE, PHILIP JAY, CHU, POCHEN, DEGNAN, THOMAS FRANCIS, JR., KIRKER, GARRY WAYNE
Applicants: MOBIL OIL CORPORATION
Application year: 1987
Main classification: B01J27
IPC codes: B01J27, B01J35, C10G47, C10G45, B01J32, B01J37