GB2073770A - Two-stage Catalytic Hydroprocessing of Heavy Hydrocarbon Feedstocks - Google Patents

Abstract

Heavy hydrocarbon feedstocks are hydroprocessed using a synergistic two-stage catalyst combination. The first stage catalyst comprises at least one Group VIb or Group VIII metal, metal oxide, or metal sulfide on a refractory porous support and has an average pore diameter of 60-150 ANGSTROM . The second stage catalyst comprises at least one Group VIb or VIII metal, metal oxide, or metal sulfide on a refractory porous catalyst support and has an average pore diameter of 30- 70 ANGSTROM and smaller than that of the first stage catalyst. Preferably the first stage catalyst has at least 40% pore volume present as pores having diameters greater than 80 ANGSTROM and the second stage catalyst has at least 50% pore volume present as pores having diameters smaller than 80 ANGSTROM .

Description

SPECIFICATION Two-stage Catalytic Hydroprocessing of Heavy Hydrocarbon Feedstocks This invention relates to catalytic hydroprocessing of heavy hydrocarbon feedstocks such as crude oil, topped crude, reduced crude, atmospheric residual oil, vacuum residual oil, deasphalted atmospheric or vacuum residua, vacuum gas oil, coal liquefaction product fractions such as solvent refined coal (SRC) and liquid solvent refined coal (SRC II), shale oil, oil from tar sands, and other heavy hydrocarbonaceous materials. Heavy hydrocarbon feedstocks suitable for processing according to this invention include those feedstocks containing significant quantities, e.g. at least about 95% by weight, of materials boiling above 2000C and particularly those feedstocks containing at least 25%, 50%, or 75% of material boiling above 3000C or above 4500C.The hydroprocessing process of the present invention may be used to perform hydrodemetalation, hydrodesulfurization, hydrodenitrification, hydrocracking, and/or hydrogenation of olefinic and aromatic hydrocarbons. The process is particularly useful for the hydrocracking of heavy feedstocks containing nitrogen and sulfur prior to fluid catalytic cracking.

A number of workers have described hydroprocessing of heavy hydrocarbons by sequential catalytic steps. Some catalyst arrangements provide high metals capacity in a first catalyst bed to reduce fouling of subsequent catalysts. Other systems employ successive catalytic zones individually optimized for demetalation, desulfurization and denitrification. U.S. Patents 4,019,976 and 3,159,568 describe the use of two catalyst beds wherein the second bed contains a more active catalyst than the first. U.S. Patent 3,437,588 describes the use of a mixture of hydrogenation catalysts on supports having 20-100 A pores. U.S.Patents 3,977,961 and 3,977,962 describe two-stage catalyst systems containing 100--275 A pores in the first stage and 100--200 A pores in the second stage. U.S.

Patent 3,696,027 describes hydrodesulfurization using a catalyst having graded macroporosity (pores greater than 500 A). The graded catalyst is packed in a downflow reactor with pore volume varying from greater than 30% macropores in the upper section to less than 5% macropores in the lower sections. U.S. Patents 3,254,017 and 3,535,225 describe two-stage hydrocracking using a first stage large pore catalyst and second stage zeolites. U.S. Patent 3,385,781 suggests two-stage hydrocracking using a large pore zeolite having 10 to 13 A pores in the first stage and a small pore zeolite having 4 to 6 A pores in the second stage. Two-stage catalyst beds wherein the pores of the second stage catalyst are larger than those of the first stage catalyst are depicted in U.S. Patents 3,730,879, 3,766,058 and 4,048,060.

It is an object of this invention to provide a process employing a two-stage catalyst system capable of effectively hydrocracking, hydrodenitrifying and hydrosulfurizing heavy hydrocarbon feedstocks and capable of being used in a single reactor under hydroprocessing conditions without the need for separation of reaction products between catalyst stages.

According to the invention, there is provided process for hydroprocessing a heavy hydrocarbon feedstock comprising the steps of: (a) contacting said hydrocarbon feedstock with hydrogen under hydroprocessing conditions in the presence of a first hydroprocessing catalyst comprising refractory support material and at least one metal, metal oxide or metal sulfide of a Group Vlb or VIII element, said first hydroprocessing catalyst having an average pore diameter in the range from 60-1 50 ;; and (b) contacting at least a portion of the hydrocarbon product from said step (a) under hydroprocessing conditions with a second hydroprocessing catalyst comprising refractory support material and at least one metal, metal oxide or metal sulfide of a Group Vlb or VIII element, said second hydroprocessing catalyst having an average pore diameter in the range from 30-70 A and smaller than the average pore diameter of said first hydroprocessing catalyst, said first and second hydroprocessing catalysts constituting a synergistic hydroprocessing combination.

Preferably the first stage catalyst has at least 40% and more preferably at least 50% pore volume in pores > 80 . The second stage catalyst preferably has at least 50% and more preferably at least 90% pore volume present as pores having diameters smaller than 80 . The feed to the second contacting step can be the entire liquid hydrocarbon product of the first contacting step, or the entire product of the first contacting step, including reaction products of hydrodesulfurization (e.g. H2S) or hydrodenitrification (e.g. NH3). The process of this invention is particularly applicable to hydroprocessing heavy hydrocarbon feedstocks containing above about 1 weight percent sulfur and about 0.1 weight percent nitrogen.The first catalyst refractory support material preferably consists essentially of alumina, the second catalyst refractory support material preferably consists essentially of alumina and 10 to 70 weight % silica. It is preferred that the hydrocarbonaceous feed contain less than about 5 weight % asphaltenes such as a deasphalted atmospheric residuum, deasphalted vacuum residuum, vacuum gas oil, or mixtures thereof.

In the accompanying drawings, Fig. 1 is a graphical representation of the hydrocracking activity of the catalyst combination employed in the invention compared to single catalysts; Fig. 2 is a graphical representation of the hydrodesulfurization activity of the catalyst combination employed in this invention compared to single catalysts; and Fig. 3 is a graphical representation of the hydrodenitrification activities of the catalyst combination employed in this invention compared to single catalysts.

According to this invention, the heavy hydrocarbon feedstock is contacted under hydroprocessing conditions with at least two catalyst beds to cause hydrodesulfurization, hydrodenitrification and/or hydrocracking of the feedstock. The precise hydroprocessing conditions depend primarily upon the extent of reaction needed.Hydroprocessing conditions include temperatures in the range of 250 to 6000C, preferably 350 to 500 C and most preferably 400 to 4500C; total pressures in the range of 30 to 200 atmospheres, preferably 100 to 1 70 atmospheres and more preferably 120 to 1 50 atmospheres; hydrogen partial pressures in the range of 25 to 1 90 atmospheres, preferably 90 to 1 60 atmospheres and most preferably 110 to 140 atmospheres, and space velocities (LHSV) of 0.1 to 10, preferably 0.3 to 5 and most preferably 0.5 to 3 hours. The catalyst of each stage is comprised of a refractory ceramic support material such as alumina, silica, magnesia, zirconia, or mixtures thereof.The catalysts contain as a hydrogenation component one or more metals, metal oxides or metal sulfides, selected from elements of group Vlb and group VIII of the Periodic Table of the Elements as set forth in Handbook of Chemistry and Physics, 45th Ed. Chemical Rubber Company, Cleveland, Ohio, 1964. It is preferred that each catalyst contain at least one metal, metal oxide, or metal sulfide from group Vlb and one metal, metal oxide or metal sulfide from group VEIL, for example, Co/Mo, Ni/Mo, NiAW, etc. The metals should typically be present in quantities of 5 to 25 weight % of group Vlb and 1 to 20 weight % of group VIII, as metals, based upon total weight of catalyst, as is typical for hydroprocessing catalysts.

Promoters, such as phosphorus or titanium as metals, oxides or sulfides, can be added, if desired. The hydrogenation and promoter metals or metal compounds can be included in the catalyst by any of the weil known methods of impregnation of a refractory shaped support, coprecipitating comulling, cogelling, etc.

The catalyst supports of the first and second stage differ in the pore size distribution. Catalyst for the first bed, i.e., the bed which first encounters the heavy hydrocarbon feedstock, has an average pore diameter within the range of 60-1 50, preferably 80-120 . The pore volume distribution is such that at least 40%, preferably at least 45%, and most preferably at least 50% of its pore volume is present in pores having diameters larger than 80 A.The catalyst for the second bed is characterized by an average pore diameter within the range of 30-70, and preferably 40-60 . The pore volume distribution is such that at least 50%, preferably at least 75% and most preferably at least 90% of its pore volume is present in pores smaller than 80 A in diameter. It has been found that a combination of hydroprocessing catalysts having such pore structures illustrates excellent hydrocracking, hydrodenitrification and hydrodesulfurization activities as well as enhanced fouling resistance relative to either catalyst alone. Consequently, the two-bed catalyst configuration of this invention can provide synergistic hydrodenitrification, hydrodesulfurization, and/or hydrocracking activities.

When heavy feeds are hydroprocessed in order to produce lighter components, i.e. hydrocracking, the second stage catalyst should have higher acidity, hence increased hydrocracking activity, than the first stage catalyst. The first stage catalyst reduces the nitrogen content of the feedstock before it contacts the second stage catalyst thereby preserving the acidity of the second stage. For example, the first stage catalyst support material can be alumina and the second stage catalyst support material can be alumina containing 10 to 70 weight % silica, more preferably 40-60 weight % silica. Activated forms of alumina such as beta, gamma, etc. can be used in either stage if desired. Either catalyst can contain zeolitic components; however, little improvement in hydrocracking is obtained unless temperatures above about 4300C are used.Consequently, the process of this invention operates satisfactorily when one or both the first and second stage catalysts are free of zeolitic components.

The hydroprocessing conditions of the first and second catalyst beds can be the same or different.

For particularly heavy feedstocks, hydrogenation conditions should be more severe in the first catalyst bed. It is believed that the first catalyst bed results in some hydrocracking of heavy materials to molecules more able to diffuse into the second stage catalyst pores.

The first and second catalyst stages can be operated as fluidized beds, moving beds, or fixed beds. When both beds are operated as fixed beds, they can be disposed in fluid communication in a single reactor or reaction zone. No other group Vlb or VIII metal-containing catalytic material need be present between the two catalyst stages, e.g. the stages can be unseparated or separated only by porous support material or reactor internals. It may be desirable, however, to include inexpensive support catalysts between the beds, such as alumina impregnated with less than 10 weight percent total metals, as metals.

The catalysts in the fixed beds can be irregular particulates or any of the other conventional catalyst shapes and sizes. The catalysts are preferably in the form of extrudate, spheres, pellets, trilobes, etc. having diameters of 1/8 inch or less.

In order to preserve the catalytic activity of the catalyst beds, the feedstock entering the first catalyst bed should contain no more than about 25 ppmw, total V, Ni, and Fe as metals. Inexpensive guard catalysts such as red mud, etc. can be employed to demetalize the feed to the required metals level. Due to the small pore size of the first stage catalyst, the feedstock should be substantially free of large asphaitene molecules. The feed preferably contains less than 5 weight % asphaltenes, more preferably less than 0.02 weight % asphaltenes. Asphaltenes are defined as hydrocarbonaceous materials which are soluble in benzene but not in n-heptane.Examples of such low asphaltene feedstocks are solvent (e.g. liquefied propane) deasphalted atmospheric or vacuum residual oils, and vacuum gas oils, etc. from the fractionation of crude oil, shale oil, oil from tar sand, dissolved coal or other coal liquefaction products. The relative amounts of first and second stage catalyst in the process can range from 1:10 to 10:1, depending upon the feedstock. Feedstocks higher in metals and heavy components generally require a greater proportion of first stage catalyst.

Catalysts useful in the first and second stages according to this invention can be obtained commercially, either as supports which can be impregnated or as catalysts containing the desired level of metals, metal oxides, or metal sulfides. Catalysts suitable for use in the first stage and second stage reactors can be prepared in the following manner. All percentages are by weight.

First Stage Catalyst Preparation Hydrated Kaiser alumina is peptized with concentrated HNO3. The resulting solution is backtitrated with concentrated NH40H to a pH of 5. The mixture is extruded at a consistency of about 50% volatiles. The extrudate is surface-dried at 1 200C for 2 hours and at 2000C for 2 hours. The dried extrudates are calcined at 7500C for one hour in dry air. An impregnant is prepared by mixing 50 ml of crude phosphomolybdic acid (a mixture of 20 parts MoO3, 2 parts H3PO4 and 48 parts water and containing 2.5 weight % and 20.1 weight % Mo) with 0.8 ml of 85% H3PO4, followed by heating to 450C. 7 ml of an aqueous NiCO3, containing 62.8% NiO is added.After the solution becomes clear, it is cooled to 250C and diluted with water to a volume of 55 cc per 100 grams of catalyst to be produced.

The resulting impregnant solution is sprayed onto the extrudate under vacuum. The sprayed extrudate is allowed to stand at room temperatures for one hour and is then surface-dried at 1 200C for one hour.

The dried catalyst is then calcined in 570 liters/hr of dry air for 6 hours at 950C, 4 hours at 2300C, 4 hours at 4000C and 4 hours at 51 00C and allowed to cool. The pore diameter can be varied, if desired, by conventional techniques, such as varying the back titration of the extrusion mix as described in U.S.

Patent 4,082,697, incorporated herein by reference.

Second Stage Catalyst Preparation (100 Gram Basis) A first solution is prepared by combining 407 cc of H2O,66 grams of a 21.5% aqueous AICI3 solution, 57 grams of 30.7% aqueous NiCl2solution and 369 grams of an aqueous solution containing 5.15% TiCI4,81.3% AiCI3, and 13.5% acetic acid. The heat of solvation produces a final temperature of about 400C for the first solution. A second solution is prepared by mixing 94 grams of a 28.7% aqueous SiO2 with 283 cc H2O. The second solution is added slowly to the first solution, with mixing.

The pH is increased to 4.5 with aqueous NH40H (8.0%) whereupon a gel is formed. After a pH of 4.5 is obtained, 281 grams aqueous ammonium paratungstate [(NH4)6W,O24 - 6 H20] solution, containing 6.97% W, is added and the pH is raised to 7.5 by adding 8.0% NH40H, whereupon gellation is completed and coprecipitation occurs. If an aluminosilicate zeolite (e.g. ultrastable Y-type) component is desired, the necessary amount of a 25% aqueous zeolite slurry is added. The catalyst gel is aged at 75"C for one hour and filtered. The filter cake is surface-dried and twice extruded.The extrudates are washed and calcined in air for 4 hours at 2000C and 5 hours at 51 00C. Those familiar with the art of preparing cogelled catalyst supports can vary the pore size distribution, if desired, using conventional techniques such as adding a detergent as described in U.S. Patent 3,657,151.

Experimental Several catalyst configurations were tested in a fixed bed pilot plant reactor. The feed was a mixture of Alaskan North Slope solvent deasphalted vacuum residuum and vacuum gas oil (3:2 vol.

ratio). The properties of the feed are shown in Table I.

Table I Specific Gravity 0.95 S,wt.% 1.6 N, wt. % 0.4 Ni/V/Fe, ppmw 8/7/4 Ramsbotton carbon, wt. % 3.0 Distillation, ASTM D1160 Start 2580C 10 401 30 471 50 521 70 585 End Point 590 % Recovery 73 The feed was passed through the pilot plant reactor containing fixed beds of catalysts. The liquid hourly space velocity was 1.0, total pressure was 135 atmospheres and hydrogen pressure was 110 atmospheres. The temperature was varied in order to measure the reaction constant. The hydroprocessing reactor atmosphere was provided by recycle gas from the reactor at 890 cubic meters per cubic meter of feedstock.

The properties of catalysts tested are shown in Table II. Catalyst C contained an ultrastable Y zeolite component.

Table 2 A B C D E Type Impregnated Cogelled Cogelled Cogelled Comulled Support Al2O3 SiO2/AI203 SiO2/Al2O3 AI2Os SiO2/AI203 Wt % Ni (NiO) 3.1 8.6 7.0 8.7 5.4 Mo (MoO3) 12.9 19.7 16.4 W (WO3) 21.5 16.8 P (P2O6) 2.4 3.0 Ti (TiO2) 4.6 4.0 4.9 SiO2/A120 - 25.7/28.6 32.7/30.5 - 24.0/44.6 Skeletal Density (g/cc) 3.41 3.43 3.42 3.14 Bulk Density (g/cc reactor) 0.92 0.98 0.82 0.84 Table 3 sets forth the pore size distribution of the catalysts. The pore distribution was obtained by nitrogen adsorption technique, using a Digisorb 2500, Micrometrics Instrument Corporation.The average pore diameter, as used herein, is obtained by dividing the measured pore volume, in cc/gm by the measured surface area, in m2/gm and multiplying the result by 40,000.

Table 3 Catalyst A B C D E Pore Volume, cc/gm .40 .38 .40 .49 .40 Avg. pore diameter, 107 .45 48 86 60 % volume present as pores having diameters, < 30 - - - - - 30-60 10 appr.100 98 15 85 60-80 40 - appr. 2 50 15 80-90 25 - - 20 - 90-100 15 - - appr.12 - 100--150 10 - - appr. 3 The catalysts were tested individually and in beds containing various combinations of two catalysts in equal volumes, with a layer of the first catalyst directly over a layer of the second catalyst.

Reaction constants KHCR (hydrocracking), KHDS (hydrodesulfurization) and KHDN (hydrodenitrification) were computed for the plant runs. These reaction constants are plotted as a function of catalyst temperature for single catalyst and 50/50 volume catalyst mixtures in Figures 1, 2 and 3.

1-X0 KHCR is equal to LHSV 1 1-x where x=liquid volume percent of product boiling below 343 OC and XO=liquid volume percent of feed material boiling below 343 OC

where S% sulfur in the feedstock and Sp=% sulfur in the product

where Nf=% nitrogen in the feedstocle and Np=% nitrogen in the product.

Because the ordinate has a logarithmic scale, the slope of the straight lines is equal to dlog lVdT, which is a measure of the activation energy for the reaction. Figs. 1, 2 and 3 demonstrate that the combinations of catalysts A and B and A and C are synergistic in that the combinations have greater activation energies (greater slopes) than either of the catalysts alone. Because the reaction constants for the combined catalysts increase more rapidly with temperature than do the reaction constants of either catalyst alone, there will necessarily be a temperature above which the combination catalyst is more active for the particular reaction than either catalyst alone. This corresponds to the intersection of the appropriate lines connecting the calculated K values.Consequently, catalyst combinations for which the slope of 1 n K vs. T, for at least one of hydrocracking, hydrodesulfurization, and hydrodenitrification, is greater than for either catalyst component alone are defined as synergistic hydroprocessing combinations. Fig. 1 demonstrates that at temperatures above about 41 00C, the combination catalysts A/B and A/C have greater hydrocracking activity than catalysts A or B alone.

Catalyst D/C would demonstrate greater activity than catalyst D above about 4270C. Fig. 2 shows that above about 41 6GC and 421 OC catalysts A/B and A/C, respectively, have greater desulfurization activity than either catalyst A or B. Catalyst D/C, on the other hand, will not surpass catalyst D in hydrodesulfurization temperature until much higher temperatures are employed.

Fig. 3 shows that above about 41 0i0C and 41 cataiysts A/B andA/Chave higher hydrodenitrification activities than either catalysts A or B alone. Again, much higher temperatures will be required before catalyst D/C becomes more active than catalyst D. In order to best achieve the objects of this invention, the catalyst components of the two-stage catalyst should be selected so that enhanced hydrocracking, hydrodesulfurization, and/or hydrodenitrification activities are achieved at the desired hydroprocessing temperature, e.g. most preferably in the 350 to 5000C range. Table 4 sets forth the product distribution and the precise reaction conditions of the various runs.As seen, the combination of catalysts A and B and C and D produce significantly higher naphtha (C5-2050C) and diesel (205 to 3430C) fractions than do the individual catalyst components.

Additional pilot plant runs were made to determine the fouling rate of the combination bed of this invention relative to larger pored catalyst, which would ordinarily be expected to be the more resistant to fouling. The feedstock was an Alaskan North Slope deasphalted oil having the composition set forth in Table 5. In each case the feed was passed downwardly through a bed having an impregnated At203 guard catalyst comprising 40% of the bed volume and situated above the catalyst sample tested. The guard catalyst was a commercially low density catalyst containing about 2% Co and 4% Mo present as oxides, and having a pore volume of 0.67 cc/gm and an average pore diameter of 80-100 A.

Table 4 Catalyst A B D E A/B A/C D/C Catalyst Temp., OC 428 427 427 427 428 422 428 LHSV 1.00 1.01 0.99 0.99 0.99 0.99 0.99 Tot. Pres., atmosphere, gauge 136.0 135.9 135.8 136.1 136.2 136.1 136.1 2 Pres., atmospheres 101.4 111.4 113.7 113.9 102.9 102.4 107.8 Total gas, m3/m3 841.7 888.4 126.5 878.8 941.3 870.9 864.9 Recycle gas, m3/m3 686.6 706.2 1070 650.1 761.9 703.7 695.3 Gross H2 consumption, m3/m3 155.1 182.2 194.7 225.1 179.4 167.2 169.6 Product Yields wt. % wt. % wt. % wt. % wt. % wt. % wit % (no loss basis) C1 0.54 0.47 0.667 0.60 0.38 0.56 0.57 C2 0.50 0.76 0.63 0.57 0.61 0.56 0.57 C3 0.62 1.08 0.76 0.72 0.87 0.74 0.88 Iso-C4 0.14 0.31 0.17 0.22 0.25 0.19 0.33 n-C4 0.45 0.84 0.59 0.61 0.68 0.55 0.76 C5-2040C 7.83 10.80 7.94 8.42 12.56 10.28 11.32 2040-3430C 22.26 22.16 24.53 24.07 26.08 21.85 22.10 3430C+ 66.85 62.97 64.26 64.25 58.02 64.56 62.77 Total C5+ 96.95 95.94 96.73 96.75 96.61 96.71 96.20 Table 5 Specific Gravity .955 S,wt.% 1.4 N,wt% 0.5 Ni/V/Fe, ppmw 10/5/8 Ramsbottom carbon, wt. % 3.8 Distillation, ASTM D1160 Start 3850C 5 442 10 491 30 547 50 581 End Point 591 % Recovery 55 Table 6 sets forth the results of these fouling tests.The hydrocracking fouling of the combination catalyst charge proceeded at about the same rate as the single charge, while the hydrodesulfurization and hydrodenitrification fouling rates of the combination catalyst A/B were approximately half the fouling rates of catalyst A alone.

Table 6 Fouling Test 4270C 1.0 LHSV 105 atmospheres H2 Catalyst Charge, Vol. % 40% Guard Al2O3 40% Guard Al2O3 60% A 30% A 30% B KHCR (hurl) SOR 0.25, 22 LV% < 3430C 0.25, 22 LV% < 3430C 1600 Hr 0.19,17 LV% < 3430C 0.20,18 LV% < 3430C HCR Fouling Rate ( C/Hr) 0.003 0.003 KHDS (hurl) SOR1 4.5, 150 ppm S 4.5, 150 ppm S 1600 Hr 3.2, 560 ppm S 3.7, 340 ppm S HDS Fouling Rate ( C/Hr) 0.0077 0.0044 KHDN (Hr-1) SOR' 1.9,700ppmN 1.8,780ppmN 1600 Hr 1.0,1730ppmN 1.3,1280ppmN HDN Fouling Rate ( F/Hr) 0.023 0.011 1Start of Run Example A solvent-deasphalted vacuum gas oil having characteristics as shown in Table 5 is introduced with a hydrogen-containing gas into the upper portion of a downflow, fixed bed catalytic reactor having at least 3 layers of catalyst material.The first, or upper, layer is a bed of guard catalyst such as alumina particles about 5 mm in diameter having a pore volume of about 0.7 cc/gram and an average pore diameter of about 80 to 100 . The second catalyst layer is comprised of 2.5 mm particles of alumina impregnated with nickel, molybdenum, and phosphorous compounds and calcined to provide a catalyst containing about 2-5 wt. % Ni as NiO,8--15 wt. % Mo as MoO3 and 1-4 wt. % P as P205. The catalyst of the second layer has a pore volume of about 0.4 cc/gram, an average pore diameter of 80 T20 Â, and at least 50% pore volume in pores of 80 to 150 A diameter.The third catalyst layer is comprised of 1/1 0 inch particles of cogelled SiO2/AI203 particles having a SiO2/AI203 ratio of about one-to-one and containing about 6-9 wt. % Ni as Ni0, 14-25 wt. % W as WO3 and about 4 wt. % Ti as TiO2. The third stage catalyst has a pore volume of about 0.4 cc/g and at least 90% pore volume in pores of 30 to 80 . The first catalyst occupies about 40% of the volume of the beds in the reactor. The second and third beds are of equal volume. Additional catalyst such as alumina containing no more than about 5--10% group Vlb or VIII metals as metals can be used as support catalysts between the beds or elsewhere in the reactor The reactor is operated at a liquid hourly space velocity, based on the second and third bed volumes of 1.7. The total pressure is 140 atmospheres with a 1 00-atmosphere H2 pressure. The H2 flow rate is 140,000 liters/min and the reactor temperature is 4250C. The product leaves the reactor below the third catalyst layer and is fractionated at atmospheric pressures. H2 is recovered from the vapor fraction and recycled to the reactor. Intermediate cuts of naphtha (C6-2000C) and diesel (200-3500C), are recovered. The 3500C+ bottom fraction, having significantly reduced nitrogen and sulfur contents, is passed as feed to a conventional fluid catalytic cracking unit.

Claims (14)

Claims

1. A process for the catalytic hydroprocessing of a heavy hydrocarbon feedstock comprising the steps of: (a) contacting said hydrocarbon feedstock with hydrogen under hydroprocessing conditions in the presence of a first hydroprocessing catalyst comprising refractory support material and at least one metal, metal oxide, or metal sulfide of a Group Vlb or VIII element, said first hydroprocessing catalyst having an average pore diameter within the range from 60-1 50 , and (b) contacting at least a portion of the hydrocarbon product from said step (a) under hydroprocessing conditions with a second hydroprocessing catalyst comprising refractory support material and at least one metal, metal oxide, or metal sulfide of a Group Vlb or VIII element, said second hydroprocessing catalyst having an average pore diameter within the range from 30-70 A and smaller than the average pore diameter of said first hydroprocessing catalyst, said first and second hydroprocessing catalysts constituting a synergistic hydroprocessing combination.

2. A process according to claim 1, wherein said first hydroprocessing catalyst has at least 40% pore volume present as pores having diameters greater than 80 A and said second hydroprocessing catalyst has at least 50% pore volume present as pores having diameters smaller than 80 .

3. A process according to claim 2, wherein said first hydroprocessing catalyst has at least 50% pore volume present as pores having diameters greater than 80 A and said second hydroprocessing catalyst has at least 90% pore volume present as pores having diameters smaller than 80 .

4. A process according to claim 1, 2 or 3, wherein substantially the entire hydrocarbon product of step (a) is fed to step (b).

5. A process according to claim 1, 2, 3 or 4, wherein said heavy hydrocarbon feedstock contains at least 1 weight percent sulfur, at least 0.1 weight percent nitrogen, less than 25 ppmw total V, Ni and Fe, as metals, and less than 5 weight percent asphaltenes.

6. A process according to any preceding claim, wherein the refractory support material in said first hydroprocessing catalyst comprises substantially alumina.

7. A process according to claim 6, wherein the refractory support material in said second hydroprocessing catalyst comprises substantially alumina and 1 0-70 weight percent silica.

8. A process according to any preceding claim, wherein steps (a) and (b) are conducted in a single reaction zone containing a fixed bed of said first hydroprocessing catalyst and a fixed bed of said second hyd roprocessing catalyst.

9. A process according to any preceding claim, wherein said hydroprocessing conditions include a temperature of from 350 to 5000 C, a hydrogen pressure of from 90 to 170 atmospheres and a liquid hourly space velocity of from 0.3 to 5 hours-1.

1 0. A process according to any preceding claim, wherein said heavy hydrocarbon feedstock is a deasphalted vacuum residuum, a vacuum gas oil, or a mixture thereof.

11. A process according to any preceding claim and further comprising, prior to said contacting step (a), contacting heavy hydrocarbon feedstock with a bed of guard catalyst to reduce the total V, Ni and Fe content of said hydrocarbon feedstock to not more than 25 ppmw as metals.

1 2. A process according to any preceding claim, wherein said first hydroprocessing catalyst comprises Ni and Mo as metals, oxides, or sulfides and refractory support material consisting of alumina and said second hydroprocessing catalyst comprises Ni, W, and Ti as metals, oxides or sulfides and refractory support material consisting of alumina and 10 to 70 weight percent silica.

1 3. A process according to claim 12, wherein the first hydroprocessing catalyst contains 1 to 20 weight percent as metal Ni and 5 to 25 weight percent as metal Mo, as metals, oxides or sulfides, and the second hydroprocessing catalyst contains 1 to 20 weight percent as metal Ni and 5 to 25 weight percent as metal W, as metals, oxides, or sulfides.

14. A process according to any preceding claim, wherein said hydroprocessing conditions include a temperature at which at least one of the hydrocracking activity, the hydrodesulfurization activity and the hydrodenitrification activity of said synergistic hydroprocessing combination exceeds the corresponding activity of said first hydroprocessing catalyst and said second hydroprocessing catalyst alone.

1 5. A process according to any preceding claim, wherein said contacting steps (a) and (b) are carried out under the same hydroprocessing conditions.

1 6. A process for the catalytic hydroprocessing of a heavy hydrocarbon feedstock, substantially as described in the foregoing Example.