HYDROTREATING CATALYSTS FROM HYDROGELS, PROCESS FOR THEIR PREPARATION AND USE

Abstract: Process for preparing highly active hydrotreating catalysts by incorporating a compound selected from the group consisting of nickel, cobalt and mixtures thereof, a heavy metal selected from the group consisting of molybdenum, tungsten and mixtures thereof, and a stabilizing amount of phosphorus into an alumina hydrogel. The final calcined catalysts have surface areas of at least 300 m²/g, at least 20% of the pore volume in pores having diameters greater than 35 nm and at least 20% of the pore volume in pores having diameters less than 7 nm.

Description: The present invention relates to a process for preparing highly active alumina hydrogel-derived catalysts. In the catalytic processing of petroleum feedstocks, it is often desirable to alter the pore structure of the catalyst in order to accommodate different types of feeds. For example, when processing feedstocks with no metals or with a low metals content, it may be technically and economically desirable to use narrow-pore catalysts. On the other hand, when processing feedstocks of high metals content, the metals tend to deposit rapidly on the catalyst surface and plug the pores of conventional hydroprocessing catalysts, resulting in a loss of catalytic activity for sulphur and nitrogen removal. In order to maintain hydrotreating activity, it is necessary that the catalyst be high in surface area. To facilitate the diffusion of large components into and out of the catalysts and to prevent surface deposits of coke and metals, large pore diameters are required. These criteria necessitate the use of bimodal catalysts which have high surface areas and a significant fraction of pore volume in large pores. The large pores allow enhanced diffusion of large molecules into the catalyst while the smaller pores, providing most of the surface area, allow for hydroprocessing of the feed. Catalysts of this type can be used as hydrotreating catalysts, especially for residue/demetallization applications. The present invention relates to a process for preparing highly active hydrotreating catalysts having surface areas of at least 300 m²/g, at least 20% of the pore volume in pores having diameters greater than 35 nm and at least 20% of the pore volume in pores having diameters less than 7 nm which comprises: (a) precipitating an aqueous solution of one or more aluminium salts by adjusting the pH of said solution to a range between 5.5 and 10 at a temperature in the range between 20°C and 90°C for at least 20 minutes thereby forming a precipitate, (b) ageing the precipitate at a temperature ranging from 20°C to 90°C for at least 15 minutes at a pH ranging from 8.0 to 12.0, (c) washing the precipitate, (d) mixing the precipitate with an element selected from the group consisting of nickel, cobalt, and mixtures thereof, a heavy metal selected from the group consisting of molybdenum, tungsten, and mixtures thereof, and a phosphorus-containing compound in an amount of from 0.2 to 1.5 moles of phosphorus per mole of heavy metal, at a pH in the range between 4.0 and 9.0 and a temperature in the range between 25°C and 100°C until adsorption of the metal compounds onto the gel is sufficient to yield a final catalyst having from 1%w to 5%w cobalt and/or nickel and from 8%w to 32%w heavy metal, (e) homogenizing the product of step (d), (f) extruding the product of step (e), and (g) drying and calcining the product of step (f) at a temperature ranging from 300°C to 900°C. It has been found that hydrogel-derived catalysts prepared according to the process according to the present invention have activities equal to or better than catalysts prepared by conventional techniques when compared on a metals efficiency basis while having densities significantly lower than conventionally prepared catalysts. Two of the major advantages of the hydrogel route are higher metals utilization and lower cost of catalyst manufacture relative to conventionally prepared catalysts. The catalysts prepared according to the process according to the present invention have high surface areas, at least 300 m²/g; at least 20% of the pore volume in pores having diameters greater than 35 nm; and at least 20% of the pore volume in pores having diameters less than 7 nm. These catalysts are particularly suitable for residue/demetallization applications. The present invention also relates to the use of catalysts prepared in accordance with the invention in hydrotreating hydrocarbon feedstocks. In the process according to the present invention, highly active hydrotreating catalysts are suitably prepared by incorporating an element selected from the group consisting of nickel, cobalt and mixtures thereof, a heavy metal selected from the group consisting of molybdenum, tungsten and mixtures thereof, and a phosphorus-containing compound into an alumina hydrogel-derived support prepared by titrating an aqueous solution of an acid aluminium compound and an aqueous solution of a basic aluminium compound. The alumina hydrogel can be prepared by titrating an aqueous solution of one or more aluminium salt(s) with an appropriate acidic or basic material or solution to cause precipitation of the alumina gel. One skilled in the art will recognize that the alumina gel can be prepared by titrating an acidic aluminium salt such as, for example, aluminium sulphate, aluminium nitrate, or aluminium chloride, in aqueous solution with a basic precipitating medium such as, for example, sodium hydroxide or ammonium hydroxide, or, by titrating an alkali metal aluminate such as, for example, sodium aluminate or potassium aluminate, in aqueous solution with an acidic precipitating medium such as, for example, hydrochloric acid or nitric acid. One skilled in the art will recognize that the adjustment of the pH of an aluminium-containing solution to between 5.5 and 10.0 will result in precipitation of the aluminium moiety as aluminium hydroxide or hydrated aluminium oxide. In a preferred embodiment, the alumina hydrogel is prepared by titrating an aqueous solution of an alkali metal aluminate and an aqueous solution of an acidic aluminium salt to cause precipitation of the alumina gel. Suitable acidic aluminium salts include aluminium sulphate, aluminium nitrate and aluminium chloride. A preferred species is aluminium sulphate. Suitable alkali metal aluminates are sodium aluminate and potassium aluminate. The precipitation can be carried out by adding an aqueous solution of the basic aluminium species to an aqueous solution of the acidic aluminium species or the procedure can be reversed by adding an aqueous solution of the acidic aluminium species to an aqueous solution of the basic aluminium species (referred to as "sequential precipitation"). Preferably, the precipitation in the process according to the present invention is carried out by simultaneously adding the acidic aluminium species and the basic aluminium species to cause precipitation of the hydrogel (referred to as "simultaneous precipitation"). The temperature and pH of the precipitation are important variables in the preparation of the aluminas into which metals can be incorporated to form catalysts with desirable physical qualities. One skilled in the art would recognize that changes in precipitation temperatures and pHs result in changes in porosities. The optimal temperatures and pHs for the precipitation of the aluminas can be determined with a minimal amount of routine experimentation. In the process according to the present invention, a precipitation temperature typically ranges from 20°C to 90°C, preferably from 50°C to 85°C, more preferably from 55°C to 65°C, and a precipitation pH typically ranges between 5.5 and 10.0, preferably between 5.5 and 8.0, and more preferably between 6.0 and 7.5. The length of time required for the precipitation step appears to be critical to the formation of a catalyst having the desired bimodal pore size distribution. The length of time required for the precipitation step is at least 20 minutes, preferably at least 30 minutes, more preferably at least 40 minutes. The upper limit on the period of time required for the precipitation step is not critical, but is governed by economical considerations. After precipitation has taken place, the pH of the slurry is adjusted to a pH in the range from 8.0 to 12.0, preferably 9.0 to 11.0, more preferably 9.5 to 10.5, and the resulting mass is aged at a temperature in the range from 20°C to 90°C, preferably 50°C to 85°C for at least 15 minutes. An upper limit on the length of time for ageing is not critical and is normally determined by economical considerations. Ageing times will typically range from 0.1 to 10 hours, preferably from 0.25 to 5 hours, and more preferably from 0.25 to 1 hour. In general, aluminas with acceptable properties are produced by holding the ageing temperature substantially equal to the precipitation temperature. After ageing, the slurry is washed and filtered in routine fashion to remove substantially all of the removable water-soluble salts formed during the precipitation of the hydrogel. The preferred solvent for washing is water although other solvents such as lower alkanols may be utilized. After washing, the metal compounds are incorporated into the hydrogel. One method for adding the metal compounds to the hydrogel is a reslurry step in which the hydrogel is reslurried with a solution containing solubilized salts of an element selected from the group consisting of nickel, cobalt and mixtures thereof, and a heavy metal selected from the group consisting of molybdenum, tungsten and mixtures thereof, and a phosphorus-containing compound sufficient to deposit on the final catalyst from 1%w to 5%w nickel and/or cobalt and from 8%w to 18%w molybdenum or 10%w to 32%w tungsten. When mixtures of molybdenum and tungsten are utilized, the final catalyst normally contains from 8%w to 32%w molybdenum and tungsten. The solution may, however, contain amounts of nickel and/or cobalt and molybdenum or tungsten in excess of that required to deposit the aforesaid amounts of metals, which excess may be removed by washing or other techniques following the reslurry step. A typical metal compounds containing solution can be prepared by combining a molybdenum and/or tungsten containing solution with a nickel and/or cobalt containing solution. The metals containing solution also contains a stabilizing amount of phosphorus. Typically, the metals containing solution contains a phosphorus-containing compound in an amount of from 0.2 to 1.5 moles of phosphorus per mole of molybdenum or tungsten. As used herein, the term "a phosphorus-containing compound" is generic and refers to one phosphorus-containing compound as well as to more than one phosphorus-containing compound. Suitable phosphorus-containing compounds comprise the acids of phosphorus and their salts. Typical acids of phosphorus include phosphoric acids, phosphonic acids, phosphinic acids and phosphorous acids. The phosphorus-containing compound is generally selected from the group consisting of phosphoric acid, a phosphate salt and mixtures thereof. Suitable phosphate salts include alkali metal phosphates, alkali metal hydrogen phosphates, ammonium phosphate and ammonium hydrogen phosphate. The molybdenum solution comprises a water-soluble source of molybdenum oxide such as ammonium heptamolybdate or ammonium dimolybdate dissolved in water and optionally, a phosphorus-containing compound. Hydrogen peroxide may also be used to aid in solution preparation in some cases. A preferred method for preparing the molybdenum solution comprises adding hydrogen peroxide to the solution in an amount ranging from 0.1 to 1.0 mole of hydrogen peroxide per mole of molybdenum. Optionally, a suitable soluble amine compound such as monoethanolamine, propanolamine or ethylenediamine may be added to the molybdenum containing solution in order to aid in stabilization of the solution. The tungsten containing solution typically comprises ammonium metatungstate dissolved in water and optionally, a phosphorus-containing compound. A preferred method for preparing a tungsten containing solution comprises adding hydrogen peroxide to the solution in an amount ranging from 0.1 to 1.0 mole of hydrogen peroxide per mole of tungsten. In addition, a suitable soluble amine compound such as monoethanolamine, propanolamine or ethylenediamine may be added to the tungsten containing solution in order to aid in stabilization of the solution. The nickel containing solution comprises nickel salts dissolved in water and optionally, a phosphorus-containing compound. A wide range of nickel compounds are suitable, such as nickel nitrate, nickel acetate, nickel formate, nickel sulphate, nickel oxide, nickel phosphate, nickel carbonate, nickel chloride, and nickel hydroxide. Two compounds that are especially useful are nickel nitrate and nickel carbonate. The cobalt containing solution comprises cobalt salts dissolved in water and optionally, a phosphorus-containing compound. A wide range of cobalt compounds are suitable, such as cobalt nitrate, cobalt hydroxide, cobalt acetate, cobalt oxalate, or cobalt oxide. The preferred cobalt compound is cobalt nitrate. An alternative method for incorporating the metal compounds into the hydrogel comprises adding dry, water-soluble metal compounds of an element selected from the group consisting of nickel, cobalt and mixtures thereof, dry, water-soluble compounds of a heavy metal selected from the group consisting of molybdenum, tungsten and mixtures thereof, and a phosphorus-containing compound to the hydrogel and mix until dissolution and adsorption of the metal compounds and phosphorus onto the gel is substantially complete. The metal compounds of nickel and/or cobalt and molybdenum and/or tungsten are added to the hydrogel in amounts sufficient to incorporate into the final catalyst from 1%w to 5%w cobalt and from 8%w to 18%w molybdenum or 10%w to 32%w tungsten. When mixtures of molybdenum and tungsten are utilized, the final catalyst contains 8%w to 32%w molybdenum and tungsten. Molybdenum is generally added to the hydrogel as a dry, water-soluble source of molybdenum such as ammonium heptamolybdate or ammonium dimolybdate. Tungsten is typically added to the hydrogel as ammonium metatungstate. Nickel is preferably added to the hydrogel in the form of dry, water-soluble nickel nitrate, nickel acetate, nickel formate, nickel sulphate, nickel oxide, nickel phosphate, nickel carbonate, nickel chloride or nickel hydroxide, with nickel nitrate and nickel carbonate being preferred. Cobalt is typically added to the hydrogel in the form of dry, water-soluble cobalt nitrate, cobalt hydroxide, cobalt acetate, cobalt oxalate or cobalt oxide, with cobalt nitrate being preferred. The phosphorus-containing compound is typically added, either wet or dry, to the hydrogel in an amount ranging from 0.2 to 1.5 moles of phosphorus per mole of molybdenum or tungsten. The phosphorus-containing compound is preferably added directly to the hydrogel as phosphoric acid, a phosphate salt or mixtures thereof. Suitable phosphate salts include alkali metal phosphate, alkali metal hydrogen phosphate, ammonium phosphate and ammonium hydrogen phosphate. Alternatively, the phosphorus-containing compound and the dry nickel and/or cobalt salt can be mixed prior to addition to the hydrogel. A preferred method of mixing the dry metal salts of nickel and/or cobalt and molybdenum and/or tungsten with the hydrogel comprises adding hydrogen peroxide to the mixture of dry metal salts and hydrogel in an amount ranging from 0.1 to 1.0 mole of hydrogen peroxide per mole of molybdenum and/or tungsten. Optionally, a suitable amine compound such a monoethanolamine, propanolamine or ethylenediamine may be added to the mixture of dry metal salts and hydrogel in order to aid in stabilization of the mixture of the metal salts and the hydrogel. The dry metal salts of nickel and/or cobalt, molybdenum and/or tungsten and the phosphorus-containing compound (if added dry) are typically added to the hydrogel in the form of finely divided particles which are generally 0.15 mm or less in size. While particle size is not critical and larger particle sizes may be utilized, it is economically advantageous to use particles which are 0.15 mm or less in size. It is also within the scope of this invention to combine the two methods described above for adding the metals to the hydrogel. For example, one metal may be added to the hydrogel as a dry salt and another added in the form of a solution. Various permutations of this combination of dry salts additions and metals solutions additions would be obvious to one skilled in the art. The temperature and pH of the step in which the metal containing solutions and/or the dry metal salts are mixed with the hydrogel are important variables in the preparation of hydrogel-derived catalysts which have acceptable densities and porosities. In general, higher temperatures yield lower density catalysts. The mixing of the hydrogel with the metal containing solutions or the dry metal salts is carried out at a pH in the range between 4.0 and 9.0, preferably between 4.0 and 8.0, and at a temperature in the range between 25°C and 100°C, preferably between 25°C and 80°C, until incorporation of the metal compounds into the gel is sufficient to yield a final calcined catalyst having from 1%w to 5%w nickel and/or cobalt and from 8%w to 32%w heavy metal selected from the group consisting of molybdenum, tungsten and mixtures thereof. Typically, the times for mixing the hydrogel and the metal compounds will range from 0.5 to 2 hours. Optionally, the resulting material can be washed to remove unadsorbed metals and filtered in routine fashion. Following the addition of the metal compounds to the hydrogel, the resulting material is subjected to shearing in order to produce a stiffened hydrogel composition. The shearing of the hydrogel particles is accomplished by passing the hydrogel through a homogenizer such as, for example, a spring-loaded homogenization valve. The extent of shearing can be defined numerically by passing the hydrogel through a spring-loaded homogenization valve. A suitable degree to shear will normally be produced by a pressure drop in the range of from 34 to 550 bar, preferably from 138 to 482 bar, on an ordinary spring-loaded homogenizer such as, for example, a Gaulin 57 litres per hour, 550 bar Laboratory homogenizer. Shearing can also be effected by other means such as, for example, by use of a high-speed blender, but a homogenizer is preferred for continuous processing. The proper degree of shear in any event is that amount which produces an extrudate of the hydrogel which will not deform substantially under its own weight as formed. Thus, the extrudate formed prior to drying and calcining will retain its shape and enable the drying and calcining steps to be carried out without substantial change in shape. After subjecting the hydrogel to shearing, the resulting material can then be readily extruded through an orifice ranging from 12.7 to 127 mm in diameter. It is generally preferable to extrude the discharge from the homogenizer directly through the orifice using the back pressure of the homogenizer as the driving force for extrusion. Where other means are used to effect shearing, suitable pumping means can be utilized to extrude the material through an extrusion header. After extrusion, the extrudates are dried and calcined. Although it is possible to dry the extrudates in a single stage, it is preferred that the extrudates be dried in multiple stages. In multiple stages, a first drying step, called "skin drying" is carried out to remove a substantial amount of the water and to form a dried skin on the surface of the extrudate. Skin drying is suitably carried out at a temperature in the range from 100°C to 300°C, preferably from 120°C to 200°C. These skin-dried extrudates may be handled and/or stored, if desired, without serious break-up of their structure before the final drying step. Final drying is accomplished by conventional means. It may be carried out by forced draft drying, vacuum drying, air drying or similar means. Drying temperatures are not critical and depend upon the particular means utilized for drying. Drying temperatures will typically range from 50°C to 200°C. After drying, the material is calcined to produce the finished catalyst. The material may be calcined in an oxidizing or neutral atmosphere, although air is preferred. However, if binders and/or lubricants are used the material is heated in an oxygen-containing atmosphere, preferably air, in order to burn out the binders and lubricants. Calcining temperatures will typically range from 300°C to 900°C. Drying, calcining and burn-out may be combined in one or two steps. Most frequently the calcining and/or burn-out steps are combined using an oxygen-containing atmosphere. The final catalysts are found to have surface areas greater than 300 m²/g, nitrogen pore volumes ranging from 0.4 to 1.2 ml/g and with at least 20% of their mercury pore volume in pores having diameters greater than 35 nm and at least 20%, preferably 35%, of their mercury pore volume in pores having diameters less than 7 nm. In general, the metals contents of the final catalysts range from 1%w to 5%w nickel and/or cobalt, preferably from 2.5%w to 4%w nickel and/or cobalt, and from 8%w to 18%w, preferably from 10%w to 14%w molybdenum or 10%w to 32%w, preferably from 18%w to 26%w tungsten. The catalysts prepared in accordance with the present invention can be suitably applied to hydrocarbon conversion processes such as hydrocracking, hydrotreating, isomerization, hydrogenation, dehydrogenation, oligomerization, alkylation, dealkylation and the like. The catalysts prepared in accordance with the present invention are most commonly employed in hydrotreating and/or hydrocracking feedstocks ranging in volatilities from naphthas to petroleum residues, including materials derived from tar sands, shale oils and the like. Reaction temperatures will typically range from 150°C to 480°C, preferably from 260°C to 455°C. Reaction pressures are generally within the range from 14 to 240 bar, preferably from 40 to 175 bar. Reactions are normally conducted at liquid hourly space velocities within the range of 0.05 to 15 reciprocal hour. Multiple uses of these feedstocks after treating with the catalysts prepared in accordance with the present invention are possible. Depending on the particular feedstocks treated, suitable uses can include conversion unit feedstocks such as thermal cracking and hydrocracking, or finished products such as gasoline, diesel, airline turbine fuel, furnace oils, solvents, fuel oils and asphalts. The process for preparing the catalysts in accordance with the present invention will be further described below by the following Examples which are provided for illustration and which are not to be construed as limiting the invention. EXAMPLE 1 99.0 kilograms of aluminium sulphate solution were prepared by solubilizing 11.3 kilograms of gibbsite (alpha-alumina trihydrate, 34% LOI) in 87.7 kilograms of 27% sulphuric acid at a temperature slightly above 100°C. The solution was allowed to cool to 60°C prior to use. 76.4 kilograms of sodium aluminate solution were prepared by solubilizing 28.2 kilograms of gibbsite (alpha-alumina trihydrate, 34% LOI) in 48.2 kilograms of 36% sodium hydroxide at a temperature slightly above 115°C. This solution was also allowed to cool to 60°C prior to use. These two solutions were metered under computer control into a precipitation vessel containing a deionized water heel (140 kilograms) held at 60°C, maintaining a constant pH of 7.0 and a temperature of 60°C. The precipitation duration was fixed at 45 minutes. After the precipitation step was complete excess sodium aluminate solution (13.5 kilograms) was added to the slurry to raise the pH to the desired ageing pH of 10.3. Total solution quantities used: acid ― 66.7 kilograms, base ― 54.9 kilograms. The slurry was aged for one hour at the elevated pH. The slurry was then filtered in a single step on a horizontal belt vacuum filter (0.3 × 3 m) and washed with deionized water. The resulting alumina hydrogel generally had a water content between 75% and 90%, basis dry weight of alumina. Into a vessel equipped with a high speed stirrer were added a portion of alumina hydrogel prepared during a 45 minute precipitation (2500 g, 84.0% LOI ― 400 g dry weight basis), water (360 g), cobalt nitrate hexahydrate (99.92 g), 85% phosphoric acid (100.73 g), ammonium heptamolybdate (161.78 g), 30% hydrogen peroxide (48 ml) and monoethanolamine (27.1 g). The pH was adjusted to pH 6.5 using NH₄OH. The mixture was stirred vigorously to "liquefy" the hydrogel. After reaction for 2 hours at 25°C the catalyst hydrogel slurry was passed through a Gaulin Model 15M Lab Homogenizer using a pressure drop of 413 bar. The stiffened material from this homogenization step was extruded using a small, hand-held extruder. Drying of the extrudate at 120°C was followed by calcination at 510°C for two hours. The properties of the catalyst are listed in Tables I and II. EXAMPLE 2 99.0 kilograms of aluminium sulphate solution were prepared by solubilizing 11.3 kilograms of gibbsite (alpha-alumina trihydrate, 34% LOI) in 87.7 kilograms of 27% sulphuric acid at a temperature slightly above 100°C. The solution was allowed to cool to 60°C prior to use. 76.4 kilograms of sodium aluminate solution were prepared by solubilizing 28.2 kilograms of gibbsite (alpha-alumina trihydrate, 34% LOI) in 48.2 kilograms of 36% sodium hydroxide at a temperature slightly above 115°C. This solution was also allowed to cool to 60°C prior to use. These two solutions were metered under computer control into a precipitation vessel containing a deionized water heel (140 kilograms) held at 60°C, maintaining a constant pH of 7.0 and a temperature of 60°C. The precipitation duration was fixed at 45 minutes. After the precipitation step was complete excess sodium aluminate solution (7.1 kilograms) was added to the slurry to raise the pH to the desired ageing pH of 9.9. Total solution quantities used: acid ― 71.0 kilograms, base ― 50.9 kilograms. The slurry was aged for one hour at the elevated pH. The slurry was then filtered in a single step on a horizontal belt vacuum filter (0.3 × 3 m) and washed with deionized water. The resulting alumina hydrogel generally had a water content between 75% and 90%, basis dry weight of alumina. Into a vessel equipped with a high speed stirrer were added a portion of alumina hydrogel prepared during a 45 minute precipitation (4000 g, 80.77% LOI ― 769 g dry weight basis), water (100 g), nickel nitrate hexahydrate (133.76 g), 85% phosphoric acid (120.57 g), ammonium heptamolybdate (238.49 g), 30% hydrogen peroxide (76 ml) and monoethanolamine (43.23 g). The pH of the mixture was 5.9. The mixture was stirred vigorously to "liquefy" the hydrogel. After reaction for 2 hours at 25°C the catalyst hydrogel slurry was passed through a Mantin Gaulin Model 15M Lab Homogenizer using a pressure drop of 413 bar. The stiffened material from this homogenization step was extruded using a small manifold and nozzle system designed in-house for the homogenizer. Drying of the extrudate at 120°C was followed by calcination at 510°C for two hours. The properties of the catalyst are listed in Tables I and II. COMPARATIVE EXAMPLE A 99.0 kilograms of aluminium sulphate solution were prepared by solubilizing 11.3 kilograms of gibbsite (alpha-alumina trihydrate, 34% LOI) in 87.7 kilograms of 27% sulphuric acid at a temperature slightly above 100°C. The solution was allowed to cool to 60°C prior to use. 76.4 kilograms of sodium aluminate solution were prepared by solubilizing 28.2 kilograms of gibbsite (alpha-alumina trihydrate, 34% LOI) in 48.2 kilograms of 36% sodium hydroxide at a temperature slightly above 115°C. This solution was also allowed to cool to 60°C prior to use. These two solutions were metered under computer control into a precipitation vessel containing a deionized water heel (121 kilograms) held at 60°C, maintaining a constant pH of 7.0 and a temperature of 60°C. The precipitation duration was fixed at 15 minutes. After the precipitation step was complete excess sodium aluminate solution (13.5 kilograms) was added to the slurry to raise the pH to the desired ageing pH of 10.3. Total solution quantities used: acid ― 45.0 kilograms, base ― 33.7 kilograms. The slurry was aged for one hour at the elevated pH. The slurry was then filtered in a single step on a horizontal belt vacuum filter (0.3 × 3 m) and washed with deionized water. The resulting alumina hydrogel generally had a water content between 75% and 90%, basis dry weight of alumina. Into a vessel equipped with a high speed stirrer were added a portion of alumina hydrogel prepared during a 15 minute precipitation (4000 g, 84.98% LOI ― 600 g dry weight basis), cobalt nitrate hexahydrate (103.12 g), 85% phosphoric acid (93.05 g), ammonium heptamolybdate (176.67 g), 30% hydrogen peroxide (59 ml) and monoethanolamine (33.4 g). The pH was adjusted to pH 7.3 using NH₄OH. The mixture was stirred vigorously to "liquefy" the hydrogel. After reaction for 2 hours at 25°C the catalyst hydrogel slurry was passed through a Gaulin Model 15M Lab Homogenizer using a pressure drop of 413 bar. The stiffened material from this homogenization step was then extruded using a small manifold and nozzle system designed in-house for the homogenizer. Drying of the extrudate at 120°C was followed by calcination at 510°C for two hours. The properties of the catalyst are listed in Tables I and II. COMPARATIVE EXAMPLE B 99.0 kilograms of aluminium sulphate solution were prepared by solubilizing 11.3 kilograms of gibbsite (alpha-alumina trihydrate, 34% LOI) in 87.7 kilograms of 27% sulphuric acid at a temperature slightly above100°C. The solution was allowed to cool to 60°C prior to use. 76.4 kilograms of sodium aluminate solution were prepared by solubilizing 28.2 kilograms of gibbsite (alpha-alumina trihydrate, 34% LOI) in 48.2 kilograms of 36% sodium hydroxide at a temperature slightly above 115°C. This solution was also allowed to cool to 60°C prior to use. These two solutions were metered under computer control into a precipitation vessel containing a deionized water heel (121 kilograms) held at 60°C, maintaining a constant pH of 7.0 and a temperature of 60°C. The precipitation duration was fixed at 15 minutes. After the precipitation step was complete excess sodium aluminate solution (8.2 kilograms) was added to the slurry to raise the pH to the desired ageing pH of 10.0. Total solution quantities used: acid ― 47.5 kilograms, base ― 33.7 kilograms. The slurry was aged for one hour at the elevated pH. The slurry was then filtered in a single step on a horizontal belt vacuum filter (0.3 × 3 m) and washed with deionized water. The resulting alumina hydrogel generally had a water content between 75% and 90%, basis dry weight of alumina. Into a vessel equipped with a high speed stirrer were added a portion of alumina hydrogel prepared during a 15 minute precipitation (4000 g, 85.34% LOI ― 586 g dry weight basis), nickel nitrate hexahydrate (126.27 g), 85% phosphoric acid (94.60 g), ammonium heptamolybdate (203.10 g) and monoethanolamine (33.98 g). The pH was adjusted to pH 6.3 using NH₄OH. The mixture was stirred vigorously to "liquefy" the hydrogel. After reaction for 1.5 hours at 25°C the catalyst hydrogel slurry was passed through a Gaulin Model 15M Lab Homogenizer using a pressure drop of 413 bar. The stiffened material from this homogenization step was then extruded using a small manifold and nozzle system designed in-house for the homogenizer. Drying of the extrudate at 120°C was followed by calcination at 510°C for two hours. The properties of the catalyst are listed in Tables I and II. A comparison of the above catalyst preparations shows that the catalyst preparation techniques described in Examples 1 and 2 are very similar to the catalyst preparation techniques described in Comparative Examples A and B, except that the duration of the precipitation steps in Examples 1 and 2 was 45 minutes, whereas the duration of the precipitation steps in Comparative Examples A and B was 15 minutes. As stated previously, the duration of the precipitation step is critical to the formation of a catalyst having at least 20% of its pore volume in pores having diameters greater than 35 nm and at least 20% of its pore volume in pores having diameters less than 7 nm. This is evidenced by the pore size distributions listed in Table II. As can be seen in Table II, the catalysts prepared as described in Examples 1 and 2 have at least 20% of their pore volume in pores having diameters greater than 35 nm and at least 20% of their pore volume in pores having diameters less than 7 nm, i.e., a bimodal pore size distribution, whereas the catalysts prepared as described in Comparative Examples A and B have 80% of their pore volume in pores having diameters less than 7 nm, i.e., a unimodal pore size distribution. COMPARATIVE EXAMPLE C A catalyst was prepared utilizing a non-hydrogel technique. The properties of the commercially available catalyst are listed in Tables I and II. CATALYST TESTING Catalyst samples were used to hydrotreat a catalytically-cracked heavy gas oil (CCHGO) in a trickle-flow reactor. Ten ml of the appropriate extruded catalyst were crushed and sieved to 0.3-1 mm (16-45 mesh), diluted with silicon carbide, and loaded into a typical trickle-flow reactor tube. The catalyst was presulphided with a 5% H₂S/H₂ (v/v) gas mixture at 371°C for 2 hours prior to testing. A CCHGO was passed over the catalyst at 357°C and a partial hydrogen pressure of 58.6 bar with a H₂/oil ratio equal to 4.0. Measured rate constants include hydrogenation, denitrification and desulphurization and are reported relative to the non-hydrogel catalyst (Comparative Example C) and are calculated basis the total metals contents of the catalyst. Specific catalyst performance characteristics are presented in Table III. a) Time during which the acidic and basic reagents were mixed. b) Measured using an Orion 231 pH meter and Orion electrodes. c) 209 ml volume fully settled in a gradulated cup and weighed. d) Measured using an Orion 231 pH meter and Orion electrodes. e) BET (Brunauer, S., Emmet, P.Y. and Teller, E., J. Am. Chem. Soc. , 60 , 309-316 (1938)), by nitrogen adsorption/desorption, Micromeritics Digisorb 2500 Instrument. f) By nitrogen adsorption, Micromeritics Digisorb 2500 Instrument. g) Weight percent determined by neutron activation analysis or atomic absorption spectroscopy. h) Weight percent determined by neutron activation analysis or atomic absorption spectroscopy. i) Weight percent determined by neutron activation analysis or atomic absorption spectroscopy. j) Determined by mercury intrusion, to 4136 bar using a Micromeritics Autopore 9210, using a 130° contact angle and 0.473 N/m surface tension of mercury. Numbers listed are percent pore volume.

Claims: 1. A process for preparing highly active hydrotreating catalysts having surface areas of at least 300 m²/g, at least 20% of the pore volume in pores having diameters greater than 35 nm and at least 20% of the pore volume in pores having diameters less than 7 nm, which process comprises: (a) precipitating an aqueous solution of one or more aluminium salts by adjusting the pH of said solution to a range between 5.5 and 10.0 at a temperature between 20°C and 90°C for at least 20 minutes, thereby forming a precipitate, (b) ageing the precipitate at a temperature ranging from 20°C to 90°C for at least 15 minutes at a pH ranging from 8.0 to 12.0 (c) washing the precipitate, (d) mixing the precipitate with an element selected from the group consisting of nickel, cobalt, and mixtures thereof, and a heavy metal selected from the group consisting of molybdenum, tungsten, and mixtures thereof, and a phosphorus-containing compound in an amount of from 0.2 to 1.5 moles of phosphorus per mole of heavy metal at a pH in the range between 4.0 and 9.0 and a temperature in the range between 25°C and 100°C until adsorption of the metal compounds onto the gel is sufficient to yield a final catalyst having from 1%w to 5%w cobalt and/or nickel and from 8%w to 32%w heavy metal, (e) homogenizing the product of step (d), (f) extruding the product of step (e), and (g) drying and calcining the product of step (f) at a temperature ranging from 300°C to 900°C. 2. A process according to claim 1, wherein step (a) comprises titrating an aqueous solution of one or more aluminium salts with a titrating agent for at least 20 minutes, thereby forming a precipitate. 3. A process according to claim 1, wherein step (a) comprises titrating an aqueous solution of an acidic aluminium salt with an aqueous solution of a basic aluminium compound at a pH in the range between 5.5 and 10.0 and a temperature in the range between 20°C and 90°C for at least 20 minutes, thereby forming a precipitate, and wherein step (d) comprises mixing the precipitate with one or more solutions containing solubilized salts of a heavy metal selected from the group consisting of molybdenum, tungsten and mixtures thereof, and an element selected from the group consisting of nickel, cobalt and mixtures thereof, and a phosphorus-containing compound in an amount of from 0.2 to 1.5 moles of phosphorus per mole of heavy metal at a pH in the range between 4.0 and 9.0 and a temperature in the range between 25°C and 100°C until adsorption of the metal salts onto the gel is sufficient to yield a final catalyst having from 1%w to 5%w nickel and/or cobalt and from 8%w to 32%w heavy metal. 4. A process according to claim 3, wherein step (d) comprises mixing the precipitate with dry, water-soluble salts of an element selected from the group consisting of nickel, cobalt and mixtures thereof, a heavy metal selected from the group consisting of molybdenum, tungsten and mixtures thereof, and a phosphorus-containing compound in an amount of from 0.2 to 1.5 moles of phosphorus per mole of heavy metal at a pH in the range between 4.0 and 9.0 and a temperature in the range between 25°C and 100°C to yield a final catalyst having from 1%w to 5%w nickel and/or cobalt and from 8%w to 32%w heavy metal. 5. A process according to claim 3, wherein step (d) comprises mixing a dry, water-soluble salt of a heavy metal selected from the group consisting of molybdenum, tungsten and mixtures thereof, and a mixture of a dry, water-soluble salt selected from the group consisting of nickel, cobalt and mixtures thereof and a phosphorus-containing compound in an amount of from 0.2 to 1.5 moles of phosphorus per mole of heavy metal with the precipitate at a pH in the range between 4.0 and 9.0 and a temperature in the range between 25°C and 100°C to yield a final catalyst having from 1%w to 5%w nickel and/or cobalt and from 8%w to 32%w heavy metal. 6. A process according to claim 2, wherein step (a) comprises titrating an aqueous solution of an acidic aluminium salt selected from the group consisting of aluminium sulphate, aluminium nitrate and aluminium chloride, with an aqueous solution of a basic aluminium compound selected from the group consisting of sodium aluminate and potassium aluminate, at a pH in the range between 5.5 and 8.0 and a temperature in the range between 20°C and 90°C for at least 30 minutes, thereby forming a precipitate, and wherein step (d) comprises mixing the precipitate with one or more solution(s) containing solubilized molybdate or dimolybdate salts and nickel or cobalt salts, and phosphoric acid in an amount of from 0.2 to 1.5 moles of phosphorus per mole of molybdenum at a pH in the range between 4.0 and 8.0 and a temperature in the range between 25°C and 100°C until adsorption of the metal salts onto the gel is sufficient to yield a final catalyst having from 2.5%w to 4%w nickel or cobalt and from 10%w to 14%w molybdenum. 7. A process according to claim 6, wherein step (d) comprises mixing the precipitate with dry, water-soluble nickel or cobalt salts and molybdate or dimolybdate salts, and phosphoric acid in an amount of from 0.2 to 1.5 moles of phosphorus per mole of molybdenum, at a pH in the range between 4.0 and 8.0 and a temperature in the range between 25°C and 100°C to yield a final catalyst having from 2.5%w to 4%w nickel or cobalt and from 10%w to 14%w molybdenum. 8. A process according to claim 6, wherein step (d) comprises mixing a dry, water-soluble molybdate or dimolybdate salt and a mixture of a dry, water-soluble nickel or cobalt salt and phosphoric acid in an amount of from 0.2 to 1.5 moles of phosphorus per mole of molybdenum with the precipitate at a pH in the range between 4.0 and 8.0 and a temperature in the range between 25°C and 100°C to yield a final catalyst having from 2.5%w to 4%w nickel or cobalt and from 10%w to 14%w molybdenum. 9. A process according to claim 1, wherein step (d) comprises mixing the precipitate with dry, water-soluble salts of an element selected from the group consisting of nickel, cobalt and mixtures thereof, a heavy metal selected from the group consisting of molybdenum, tungsten and mixtures thereof, and a phosphorus-containing compound in an amount of from 0.2 to 1.5 moles of phosphorus per mole of heavy metal, at a pH in the range between 4.0 and 9.0 and a temperature in the range between 25°C and 100°C to yield a final catalyst having from 1%w to 5%w nickel and/or cobalt and from 8%w to 32%w heavy metal. 10. A process according to claim 1, wherein step (d) comprises mixing a dry, water-soluble salt of a heavy metal selected from the group consisting of molybdenum, tungsten and mixtures thereof, and a mixture of a dry, water-soluble salt selected from the group consisting of nickel, cobalt and mixtures thereof, and a phosphorus-containing compound in an amount of from 0.2 to 1.5 moles of phosphorus per mole of heavy metal with the precipitate at a pH in the range between 4.0 and 9.0 and a temperature in the range between 25°C and 100°C to yield a final catalyst having from 1%w to 5%w nickel and/or cobalt and from 8%w to 32%w heavy metal. 11. A process according to claim 1, wherein step (a) comprises precipitating an aqueous solution of an acidic aluminium salt selected from the group consisting of aluminium sulphate, aluminium nitrate and aluminium chloride, with an aqueous solution of a base at a pH in the range between 5.5 and 8.0 and a temperature in the range between 20°C and 90°C for at least 30 minutes, thereby forming a precipitate, and wherein step (d) comprises mixing the precipitate with one or more solution(s) containing solubilized molybdate or dimolybdate salts and nickel or cobalt salts, and phosphoric acid in an amount of from 0.2 to 1.5 moles of phosphorus per mole of molybdenum at a pH in the range between 4.0 and 8.0 and a temperature in the range between 25°C and 100°C until adsorption of the metal salts onto the gel is sufficient to yield a final catalyst having from 2.5%w to 4%w nickel or cobalt and from 10%w to 14%w molybdenum. 12. A process according to claim 11, wherein step (d) comprises mixing the precipitate with dry, water-soluble nickel or cobalt salts and molybdate or dimolybdate salts, and phosphoric acid in an amount of from 0.2 to 1.5 moles of phosphorus per mole of molybdenum, at a pH in the range between 4.0 and 8.0 and a temperature in the range between 25°C and 100°C to yield a final catalyst having from 2.5%w to 4%w nickel or cobalt and from 10%w to 14%w molybdenum. 13. A process according to claim 11, wherein step (d) comprises mixing a dry, water-soluble molybdate or dimolybdate salt and a mixture of a dry, water-soluble nickel or cobalt salt and phosphoric acid in an amount of from 0.2 to 1.5 moles of phosphorus per mole of molybdenum with the precipitate at a pH in the range between 4.0 and 8.0 and a temperature in the range between 25°C and 100°C to yield a final catalyst having from 2.5%w to 4%w nickel or cobalt and from 10%w to 14%w molybdenum. 14. A process according to claim 1, wherein step (a) comprises titrating an aqueous solution of an acid with an aqueous solution of a basic aluminium compound selected from the group consisting of sodium aluminate and potassium aluminate at a pH in the range between 5.5 and 8.0 at a temperature in the range between 20°C and 90°C for at least 30 minutes, thereby forming a precipitate, and wherein step (d) comprises mixing the precipitate with one or more solution(s) containing solubilized molybdate or dimolybdate salts and nickel or cobalt salts, and phosphoric acid in an amount of from 0.2 to 1.5 moles of phosphorus per mole of molybdenum at a pH in the range between 4.0 and 8.0 and a temperature in the range between 25°C and 100°C until adsorption of the metal salts onto the gel is sufficient to yield a final catalyst having from 2.5%w to 4%w nickel or cobalt and from 10%w to 14%w molybdenum. 15. A process according to claim 14, wherein step (d) comprises mixing the precipitate with dry, water-soluble nickel or cobalt salts and molybdate or dimolybdate salts, and phosphoric acid in an amount of from 0.2 to 1.5 moles of phosphorus per mole of molybdenum, at a pH in the range between 4.0 and 8.0 and a temperature in the range between 25°C and 100°C to yield a final catalyst having from 2.5%w to 4%w nickel or cobalt and from 10%w to 14%w molybdenum. 16. A process according to claim 1, wherein step (a) comprises precipitating an aqueous solution of an acid with an aqueous solution of a basic aluminium compound selected from the group consisting of sodium aluminate and potassium aluminate, at a pH in the range between 5.5 and 8.0 at a temperature in the range between 20°C and 90°C for at least 30 minutes, thereby forming a precipitate, and wherein step (d) comprises mixing a dry, water-soluble molybdate or dimolybdate salt and a mixture of a dry, water-soluble nickel or cobalt salt and phosphoric acid in an amount of from 0.2 to 1.5 moles of phosphorus per mole of molybdenum with the precipitate at a pH in the range between 4.0 and 8.0 and a temperature in the range between 25°C and 100°C to yield a final catalyst having from 2.5%w to 4%w nickel or cobalt and from 10%w to 14%w molybdenum. 17. A process according to one or more of claims 1-16 wherein the precipitation is carried out at a pH in the range between 5.5 and 8.0. 18. A process according to one or more of claims 1-17 wherein the precipitation is carried out at a temperature between 50°C and 85°C. 19. A process according to one or more of claims 1-18 wherein the precipitate is aged at a pH in the range between 9.0 and 11.0. 20. A catalyst which comprises a catalytically effective amount of cobalt or nickel and a catalytically effective amount of a heavy metal selected from the group consisting of molybdenum, tungsten or mixtures thereof and a phosphorus compound, on an alumina support, said catalyst having a surface area of at least 300 m²/g, at least 20% of the pore volume in pores having diameters greater than 35 nm and at least 20% of the pore volume in pores having diameters less than 7 nm and wherein said catalyst has been prepared by a process according to one or more of claims 1-19. 21. A process for hydrotreating hydrocarbons-containing feeds wherein a catalyst is used which has been prepared by a process according to one or more of claims 1-19.

Inventors: KEMP, RICHARD ALAN
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1988
Main classification: B01J27
IPC codes: B01J23, C10G45, B01J35, B01J37, B01J27