HYDROCRACKING CATALYST FOR MIDDLE DISTILLATES

Abstract: A novel catalyst for recovering middle distillates comprising silica/titanium compound impregnated on an alumina and promoted with nickel and molybdenum.

Description: This invention relates to a catalyst composition suitable for the cracking of middle distillates. Strong continuing need and demand for middle distillate oil is being felt in the industry. Heavy distillate oil has been and remains a desirable source of middle distillate oil. However, heavy oils are, in large part, diverted to fuel oils because of the lack of an effective method for converting them to lower boiling products. These oils usually contain significant amounts of nitrogenous hydrocarbon impurities. Thus in addition to hydrocracking, their conversion involves nitrogen removal. Catalysts normally selected for converting middle distillates to gasoline produce large amounts of dry gases, butanes and gasoline when used with heavy distillate feedstocks. Catalysts known in the prior art when used to produce middle distillates either provide good conversion with poor selectivity or good selectivity with poor conversion. The object of this invention is to provide an effective and improved process for producing middle distillates from heavy distillate oil. Another object of this invention is to provide a catalyst composition that will have good conversion and selectivity to middle distillates. Other objects will become clear from the description and examples herein. According to the instant invention a silica/titania catalyst which has been impregnated onto alumina and then promoted with nickel, molybdenum and phosphorus has shown good conversion and good selectivity for middle distillates. Accordingly, the invention relates to a catalyst composition suitable for cracking middle distillates comprising silica/titania on alumina having nickel, molybdenum and phosphorus impregnated thereon. Furthermore, the invention relates to a process for producing a catalyst composition, which process is characterized by (1) impregnating onto a dried alumina a solution of a silicon alkoxide and a titanium alkoxide mixed with an organic diluent, (2) hydrolyzing the product obtained in step (1), (3) impregnating the product obtained in step (2) with a solution of nickel molybdenum and phosphorus, (4) calcining the product obtained in step (3) and, optionally (5) sulfiding the product obtained in step (4). Furthermore, the invention relates to the use of the aforesaid catalyst composition for producing middle distillates. The first step in the instant invention is to form a silicon/titanium solution. To prepare the silicon/titanium solution a silicon alkoxide and a titanium alkoxide are mixed with an organic diluent. The alkoxide constituent of the titanium alkoxide and of the silicon alkoxide can be any alkoxide constituent which contains from 1 to 20, preferably from 2 to 4 carbon atoms and which is soluble in the liquid reaction medium. Suitable alkoxides include n-butoxide, secondary butoxide, isobutoxide, isopropoxide, n-propoxide, ethoxide and methoxide. The methyl or ethyl esters (alkoxides) of silicon and the isopropyl or butyl esters (alkoxides) of titanium are preferred. The organic diluent which is mixed with the titanium alkoxide and the silicon alkoxide can be any aromatic compound such as benzene, toluene, and xylene or paraffins such as hexane, heptane and cyclohexane; a halogenated hydrocarbon such as tetrachloroethylene; ether such as diethyl ether; ketones such as methyl/ethyl ketone or acetone. Preferably the organic solvent which exhibits mutual solubility for the titanium and silicon alkoxides and for water is used as the diluent. More preferably the diluent is an alcohol, most preferably a C1-C4 alcohol, such as methanol, ethanol, normal and isopropanol, normal and isobutanol. The molar ratio of silicon alkoxide to titanium alkoxide that are mixed together will depend upon the desired ratio of titanium alkoxide and silicon alkoxide in the final composition. Thus the molar ratio silicon alkoxide to titanium alkoxide may range from 10:1 to 0.05:1. The preferred molar ratio is 1:1. The organic diluent mixed with the alkoxides is added in a range from 0 to 90 volume percent based on the total mixture. The mixture is prepared at room temperature and atmospheric pressure. The thus formed silicon and titanium solution is then mixed with a dried alumina and impregnated onto the alumina. Once the silicon/titanium solution has been completely absorbed onto the alumina the mixture is then treated with moist air to hydrolyse the silicon and titanium compounds. This process takes place over a period ranging from 4 to 24 hours with the contacting preferably taking place by bubbling the air through water and then through the impregnated bed of alumina. After the hydrolysis of the silicon/titanium solution, the mixture is then dried in the presence of some gas flowing at a rate sufficient to dry the bed in a reasonable length of time at a temperature ranging from 38 to 93°C (100 to 200°F). The dried mixture, which may still contain some moieties which have not hydrolyzed, is then calcined. This is preferably done in the presence of an oxidizing gas so as to burn off the remaining unhydrolyzed material. However, care should be taken that the material being calcined does not "ignite", resulting in rapid oxidation and high temperatures in some localized area of the bed of silica/titania alumina. This can be prevented by restricting the flow of oxidizing gas into the bed, and/or diluting the oxidizing gas with an inert gas, and/or raising the temperature of the bed slowly. For example, air may be diluted with nitrogen in a nitrogen:air ratio ranging from 0 to about 5. The calcining temperature can be increased at from 0.06 to 2.78°C (0.1 to 5°F) per minute. The final temperature can range from 427 to 816°C (800 to 1500°F). Alternatively, excessive temperatures can be avoided during this calcination by using extremely shallow beds of silica/titania alumina. The thus prepared silica/titania on alumina compound is then promoted utilizing nickel and molybdenum oxide and phosphorus. A solution containing nickel, molybdenum and phosphorus is impregnated on the silica/titania/alumina product. This mixture is then calcined at a temperature ranging from 260 to 816°C (500 to 1500°F) for 1 to 20 hours. Generally when promoting with nickel and molybdenum the nickel will be present in the amount of 0.1 to 5 weight percent based on the weight of the catalyst and the molybdenum will be present in an amount of 1 to 15 weight percent. In one embodiment, the calcined catalyst composition of this invention is presulfided by the additional step of contacting the calcined catalyst composition with a suitable sulfur compound under such conditions as to at least partially convert the transition metal compounds contained in the calcined catalyst composition to sulfides. This can be accomplished by passing a sulfur-containing gas oil or a solution of COS or mercaptans or organic sulfides, e.g., in a hydrocarbon solvent, over the catalyst composition at an elevated temperature e.g., at 149 to 343°C (300-650°F), generally in the process of hydrogen gas. Or a gaseous mixture of hydrogen and hydrogen sulfide (e.g., at a volume ratio of about 10:1) can be passed over the catalyst composition at an elevated temperature, preferably 1-15 hours at about 204°C (400°F) and then 1-15 hours at about 371°C (700°F). This presulfiding step is particularly desirable when the catalyst composition of this invention is used for hydrotreating or hydrocracking of liquid hydrocarbon containing feed stream sulfur. The thus formed catalyst is suitable for use in the recovery of middle distillates after presulfiding the catalyst. One method of recovering middle distillates is to use a vacuum gas oil treatment. The vacuum gas oil treatment, which is utilized to recover distillates with a boiling point ranging from 149 to 371°C (300 to 700°F), generally takes place at conditions ranging from 343 to 482°C (650 to 900°F), at a pressure ranging from 3.45 to 20.7 MPa (500 to 3,000 psi), with a liquid hourly space velocity ranging from 0.1 to 5. It is generally understood that in this novel catalyst the silica and titania materials provide the acidity for the catalyst where the alumina provides the surface area and pore distribution. Generally, this catalyst will have pore diameter ranging from 500 to 3000nm (50 to 300A °), with a pore volume ranging from 0.3 to 1.5 ml per gram and a surface area ranging from 50 to 300 m²/g. After use this catalyst can be regenerated by burning off the "coke" in an oxidizing atmosphere using conventional methods. The following examples demonstrate the usefulness of this invention, but are not intended to limit the scope of the invention. Example I This example illustrates the preparation of various promoted hydrocracking catalyst compositions. Control Catalyst A was a silica/titania catalyst that was promoted with nickel and molybdenum. This catalyst was prepared as follows. First, 16.4 grams of NiCO₃, 51.0 grams of MoO₃ and 9.8 grams of 85 weight-% H₃PO₄ were mixed with about 80 ml of water. This mixture was stirred and heated under reflux conditions for about 4 hours. 168 grams of a clear, green solution were obtained. 1 gram of this solution contained 0.203 grams (0.0021 g-atoms) of Mo, 0.048 grams (0.0008 g-atoms) of Ni and 0.0219 grams (0.0007 g-atoms) of P. The silica/titania support material of Catalyst A was prepared substantially in accordance with Preparation "A" described in U.S. Patent 4,176,089. A mixture of 72 ml H₂O and 928 ml of isopropanol was placed in a 4-liter flask equipped with stirring bar, thermocouple, condenser and separatory funnel. This mixture was heated to 60-65°C. A second mixture containing 104 grams of Si(OC₂H₅)₄, 170 grams of Ti(C₄H₉O)₄ and 500 ml of isopropanol was slowly added through the separatory funnel into the 4-liter flask. This addition of the silicon and titanium compounds required about 3 hours. The entire mixture in the 4-liter flask was heated for one more hour at about 65°C and then filtered. The filter cake was dried under a 250 watt heat lamp for about 3 days, and then calcined at about 538°C (1000°F) for about 16 hours. The powdery material was compacted to 3.2 mm to (1/8") pills, which were crushed into 2/0.84 mm (10/20 mesh) granules. The surface area of the support material was 266 m²/g (determined in accordance with the BET/N₂ method, ASTM D3037). 9.35 grams of the above-described Ni/Mo/P solution was diluted with water to a total volume of 9.7 ml. This diluted solution was added to 15.64 grams of the above-described silica/titania material under vacuum conditions. The Ni/Mo-impregnated SiO₂/TiO₂ catalyst composition was dried under a 250 watt heat lamp for several hours and calcined for 2 hours at 204°C (400°F), for 1 hour at 260°C (500°F) and for 3 hours at 427°C (800°F) in a stream of air. The calcined Catalyst A contained 3.0 weight-% Ni, 12.7 weight-% Mo and 1.0 weight-% P. Catalyst was presulfided using H₂/H₂S. Catalyst A was presulfided before use as follows. A heated tube reactor was filled with a 6.4 cm (2½ inch) high bottom layer of Alundum (α-alumina having a surface area of less than 1 m²/g), an 28 cm (11 inch) high middle layer of a 70 ml mixture containing 12.5 ml of the catalyst and the balance 36 grit Alundum, and a 12.7 cm (5 inch) top layer of Alundum. The reactor was purged with nitrogen and the catalyst was heated for one hour in a hydrogen stream to about 204°C (400°F), the catalyst was exposed to a mixture of nitrogen (10 1/hr), hydrogen (10 1/hr) and hydrogen sulfide (1.4 1/hr) for about 14 hours. The catalyst was then heated for about one hour in the mixture of hydrogen and hydrogen sulfide to a temperature of about 371°C (700°F) and then exposed for about 14 hours while the catalyst continued to be exposed to the mixture of hydrogen and hydrogen sulfide. The catalyst was then allowed to cool to ambient temperature conditions in the mixture of hydrogen and hydrogen sulfide and was finally purged with nitrogen. Control Catalyst B was a Ni/Mo/P mixture of alumina and coprecipitated SiO₂/TiO₂. 40 grams of alumina (surface area: 293 m²/g; pore volume: 0.78 ml/g; dried for 16 hours at 350°C), 7.7 grams of dried silica/titania support material (described above; used for Catalyst A) and some water were mixed with mortar and pestle. Dilute nitric acid was dropwise added to the above wet mixture of Al₂O₃ and SiO₂/TiO₂ until a pH of 3.0 was attained. Grinding with mortar and pestle was continued about 2 hours. Then the mixture was partially dried with a hot air gun while being continuously stirred and ground. The thick paste of the mixture of alumina and silica/titania was dried under a 250 watt heat lamp for several days. The dry mixture was calcined at 538°C (1000°F) for about 6 hours under a stream of air. The calcined mixture of alumina and SiO₂/TiO₂ was impregnated under vacuum with the Ni/Mo-containing impregnating solution, dried, calcined and presulfided essentially in accordance with the procedure described for Catalyst A. Calcined Catalyst B contained 1.0 weight-% P, 3.1 weight-% Ni and 13 weight-% Mo. Invention Catalyst C₁ was prepared as follows. 9.4 grams of Si(C₂H₅O)₄ and 14.2 grams of Ti(C₄H₉O)₄ were mixed and then poured over 40.0 grams of alumina powder (dried at 300°C for 16 hours). The mixture was thoroughly stirred in a sealed flask. A stream of air, 113 l/h (4.0 scf/h) was bubbled through water and then passed over the above Si/Ti-impregnated alumina material for 16 hours. The Si/Ti-impregnated alumina was calcined in a 1:1 air/nitrogen gas stream for 2 hours at 204°C (400°F), 1 hour at 260°C (500°F), 3 hours at 427°C (800°F) and 1 hour at 538°C at (1000°F). 25.6 grams of a Ni/Mo impregnating solution, which was essentially the same as the one described in the procedure for making Catalyst A but containing 0.267 g Mo, 0.064 g Ni, 0.021 g P per gram of solution, was diluted with water to a total of 24 ml. The calcined Si/Ti-impregnated alumina was impregnated with this impregnating solution, dried, calcined and presulfided in accordance with the procedure described for Catalyst A. Calcined Catalyst C contained 2.1 weight-% Si, 3.4 weight-% Ti, 2.7 weight-% Ni, 11.4 weight-% Mo, 0.9 weight-% P. Invention Catalyst C₂ was prepared substantially in accordance with the procedure described for Catalyst C₁, with the exception that 21.9 grams of Ti(C₄H₉O)₄ were used (in lieu of 14.2 g). In addition, the calcined catalyst C₂ was presulfided by heating at 204°C in a nitrogen stream that was saturated with 2-mercaptoethanol vapor. Catalyst C₂ contained 2.0 weight-% Si, 5.1 weight-% Ti, 2.6 weight-% Ni, 11.0 weight-% Mo and 0.9 weight-% P. Invention Catalyst C₃ was substantially the same as Catalyst C₁ except that it contained more Si and Ti. Calcined Catalyst C₃ comprised 4.3 weight-% Si, 7.6 weight-% Ti, 2.4 weight-% Ni, 9.9 weight-% Mo and 0.8 weight-% P. Example II This example illustrates processes for hydrocracking of a heavy hydrocarbon feedstock. The feed was a vacuum gas oil having an API 60 gravity of 24.8 containing 0.5 weight-% S and 0.08 weight-% N, and boiling at atmospheric pressure conditions in the range of 343 to 593°C (650-1100°F). The oil feed and hydrogen gas 623m²H₂/m³ (3500 scf H₂ per barrel oil) were passed through a 1.9cm (3/4") I.D., 56cm (22") long reactor filled with a mixture of 25 ml of one of the catalysts described in Example I and 45 ml of 0.84/0.42mm (20/40 mesh) inert Alundum alumina (surface area: less than 1 m²/g). The liquid hourly space velocity of the feed was about 0.5 ml/ml hour, the reactor temperature ranged from about 700 to 800°C; the reaction pressure was maintained at about 9.7 MPa (1400 psig). Reactor effluent streams were cooled. analyzed and fractionated under atmospheric pressure conditions. Pertinent operating parameters and results are summarized in Table I. Data in Table I show that hydrocracking runs employing invention Catalysts C₁, C₂ and C₃ produced more of the valuable 66-343°C (330-650°F) boiling product, especially at the commercially more feasible temperature range of 399-427°C (750-800°F). Also, the total conversion of the feed and the conversion of the feed to the 166-343°C (330-650°F) fraction was higher in runs employing invention catalysts C₁, C₂ and C₃, especially at 399-427°C (750-800°F).

Claims: A catalyst composition suitable for cracking middle distillates comprising silica/titania on alumina having nickel, molybedenum and phosphorus impregnated thereon. The catalyst composition of claim 1 characterized in that the molar ratio of silica to titania ranges from 10:1 to 0.05:1. The catalyst composition of claim 1 or 2 characterized in that said nickel is present in an amount ranging from 0.1 to 5 weight percent and said molydenum is present in an amount ranging from 1 to 15 weight percent, each based on the weight of said composition. The catalyst composition of any of claims 1 to 3 characterized in that said composition has been sulfided. A process for producing a catalyst composition, characterized by (1) impregnating onto a dried alumina a solution of a silicon alkoxide and a titanium alkoxide mixed with an organic diluent, (2) hydrolyzing the product obtained in step (1), (3) impregnating the product obtained in step (2) with a solution of nickel molybdenum and phosphorus, (4) calcining the product obtained in step (3) and, optionally, (5) sulfiding the product obtained in step (4). The process of claim 5 characterized in that said alkoxide contains from 1 to 20 carbon atoms. The process of claim 5 or 6 characterized in that the impregnation of said dried alumina comprises contacting the silica and titania solution with the alumina followed by treating the mixture with a hydrolyzing atmosphere for a time period ranging from 4 to 24 hours. The process of claim 7 characterized in that said mixture is dried in the presence of a gas flowing in a rate sufficient to dry said mixture with a temperature ranging from 38 to 93°C. The use of the catalyst composition as defined in any of claims 1 to 8 for producing middle distillates. The use of claim 9 characterized in that a vacuumed gas oil treatment takes place at a temperature ranging from 343 to 482°C, at a pressure ranging from 3.45 to 20.7 MPa, and a liquid hourly spaced velocity ranging from 0.1 to 5.

Inventors: PARROTT, STEPHEN LAURENT
Applicants: PHILLIPS PETROLEUM COMPANY
Application year: 1986
Main classification: B01J23
IPC codes: B01J37, B01J23, C10G47