Catalytic Cracking

Abstract

A process for the production of high octane motor gasoline stocks by catalytic cracking in which a distillate charge stock boiling above about 400.degree. F is subjected to catalytic cracking in a catalytic cracking unit at limited per pass conversion not exceeding 80 volume percent of the charge stock, 430.degree. F + gas oil product of the catalytic cracking operation is subjected to hydrogen treatment to lower its polycyclic aromatic content, as indicated by ultraviolet absorption to a concentration approximating that of the fresh charge stock to the catalytic cracking unit, and liquid effluent of the hydrogen treatment step is passed to the catalytic cracking unit as part of the feed thereto, producing exceptionally high yields of high octane naphtha suitable as motor gasoline blending stock.

Parent Case Text

This application is a continuation-in-part of our copending U. S. Pat. application, Ser. No. 687,283, filed December 1, 1967 now abandoned.

Description

CATALYTIC CRACKING

(D#70,282-Cl)

This invention relates to an improved process for the production of motor fuel gasoline from catalytic cracking feed-stocks. The process is particularly applicable to the production of maximum yields of motor gasolines from catalytic cracking unit feedstocks without hydrocracking. The process is applicable to existing catalytic cracking units.

When combined with conversion of C.sub.3 -C.sub.4 hydrocarbons to gasoline blending components, e.g. by alkylation, the process of this invention is capable of producing a quantity of debutanized gasoline stock substantially equal to that of the feedstock charged to a catalytic cracking unit. For example, by combination of catalytic cracking, hydrogen treatment, and alkylation, catalytic cracking feestocks, e.g., virgin gas oil boiling above about 430.degree. F, may be made to yield 95 to 110 volume percent debutanized gasoline (basis fresh feed charge).

The process of this invention consists essentially of (1) catalytic cracking of feedstock boiling above about 430.degree. F, (2) subjecting at least a portion of the 430.degree. F+ gas oil product of the catalytic cracking unit to hydrogen treatment for significant reduction of its polycyclic aromatic content, and (3) recycling normally liquid effluent of the hydrogen treatment, also referred to herein as a hydrotreater, to the catalytic cracking unit together with the fresh feedstock. Debutanized naphtha from the catalytic cracking unit is a primary product of the process. In a preferred embodiment, all or a substantial portion of the C.sub.3 -C.sub.4 olefins from the catllytic cracking unit are subjected to alkylation and the resulting alkylate blended with the naphtha fraction from the catalytic cracking unit to give yields of high octane gasoline in the vicinity of 100 volume percent, basis the fresh feed charged to the catalytic cracking unit. This process permits substantially complete conversion of catalytic cracking unit feedstocks to gas and motor gasoline products.

It has been proposed heretofore to subject catalytic cracking feedstocks to hydrogen treatment as a means for improving the yields and quality of motor gasolines. It has also been known for some time that hydrocracking operations, as distinguished from hydrogen treatment, will produce nearly 100 percent yields of gasoline from virgin gas oil feestocks. Many existing refinery facilities, however, do not have sufficient hydrogen for hydrocracking processes and, in addition, have already existing large facilities for catalytic cracking. Such catalytic cracking units are not suitable for hydrocracking operations.

The term "hydrotreating" or "hydrogen treatment," as used herein, refers to treatment with hydrogen under conditions which result in little or no cracking of the hydrocarbons supplied to the hydrogen treating unit and little or no production of lower boiling range products. "Hydrocracking," on the other hand, refers to cracking the hydrocarbons in the presence of hydrogen to produce lower boiling range products.

It is an object of this invention to provide an improved process for converting catalytic cracking unit charge-stocks to gasoline motor fuel components. Still another object of this invention is to provide an improved process for the production of motor fuel gasolines of high octane value from the catalytic cracking feestocks boiling in the range of about 430.degree. F and higher.

The FIGURE is a schematic flow diagram illustrating the process of this invention with reference to various petroleum refinery process units.

With reference to the flow diagram of the FIGURE, fresh catalytic cracking unit feedstock, e.g. virgin gas oil havin a boiling range above about 400.degree. F, e.g. 450.degree. to 850.degree. F, from a suitable source is supplied to the process through line 5, blended with hydrogen treated mixed hydrocarbons as described hereinafter, and passed through line 6 to a catalytic cracking unit 7. The catalytic cracking unit 7 may comrrise either a fluidized catalyst or moving bed type catalytic cracking unit, both of which are well known. Fluidized catalyst units may be of either bed type or riser type.

Effluent from the catalytic cracking unit 7 is passed via line 8 to a fractionation system 9 where it is separated into a plurality of fractions. As illustrated in the specific embodiment illustrated in the FIGURE, the catalytic cracking unit product is separated into a fraction boiling below about 430.degree. F at atmospheric pressure, e.g. hydrogen to 430.degree. F, which is discharged through line 11; a light gas oil fraction, e.g. one having a 50 percent point of about 530.degree. F, which is discharged through line 12; an intermediate gas oil fraction, e.g. one having a 50 percent point of about 650.degree. F which is discharged through line 13; and a heavy gas oil fraction, e.g. one having a 50 percent point of about 680.degree. F, which is discharged through line 14.

The naphtha and lighter fraction from line 11 is passed to a recovery section 16 where it is separated into various fractions, for example, a fuel gas fraction discharged through lien 17; a C.sub.3 -C.sub.4 fraction discharged through line 18; and a debutanized naphtha fraction discharged through line 19. The debutanized naphtha fraction from line 19 is the principal product of the process and is useful as base blending stock for motor gasoline.

The C.sub.3 -C.sub.4 fraction discharged through line 18 contains C.sub.3 and C.sub.4 olefins and isobutane. This stream is passed to an alkylation unit 20 wherein the olefins are alkylated with isobutane to high octane gasoline blending components or alkylate which is discharged from unit 20 to line 21 for blending into gasoline product. Those C.sub.3 -C.sub.4 olefins in excess of isobutane available in the C.sub.3 -C.sub.4 fraction may be discharged through line 22 to a suitable use, for example, as feed for petrochemical operations. Alternatively, isobutane may be supplied from a suitable source through line 23 to alkylation unit 20 for conversion to alkylate blending components for motor fuel gasoline.

The various gas oil fractions discharged from the fractionator through lines 12, 13 and 14 may be passed through line 13 to hydrogen treater unit 26. Light gas oil may be supplied to line 13 by way of a line 27 as controlled by valve 28. Similarly, heavy gas oil withdrawn from fractionator 9 through line 14 may be supplied via lines 29 and 31 as controlled by valve 32 to line 13 as feed to hydrogen treater unit 26. Part or all of the light gas oil may be taken from line 12 as product, or part or all may be passed through line 33 as controlled by valve 34 to line 35 for recycle to catalytic cracking unit without hydrogen treatment. Similarly, part or all of the heavy gas oil may be withdrawn as product through line 14 or passed through line 36 as controlled by valve 37 to line 35 for the recycle directly to catalytic cracking unit 7. Provision is also made for return of part of the intermediate gas oil fraction, if desired, to the catalytic cracking unit via lines 38 and 35 as controlled by valve 39. Fresh feedstock may be supplied from line 5 through line 41, if desired, as controlled by valve 42, to line 13 as feed to the hydrogen treater unit 26.

The effluent from the hydrogen treater unit is discharged through line 43 to a separation unit 44 in which gaseous components are separated from normally liquid components. A gaseous fraction consisting primarily of hydrogen is discharged from separator 44 through line 46 and returned to hydrogen treater 26 through line 47. Make-up hydrogen from a suitable source is supplied to line 47 from line 48. Normally liquid product of hydrotreater 26, including naphtha fractions, is discharged from separator 44 to line 35, mixed with fresh feedstock from line 5, and supplied to the catalytic cracking unit 7 through line 6.

Preferably, and for highest gasoline yields, the cracking catalyst comprises a molecular sieve or crystalline alumino-silicate base carrying catalytic metal additives, for example, rare earth metals, particularly cerium and lanthanum, their oxides or sulfides. Preferred catalysts are molecular sieve cracking catalysts of the well known commercial varieties, e.g. Davison XZ-25, Aerocat Triple S-4, Nalcat KSF, Houdry HZ-1, etc. These catalysts are made up of a silica-alumina-zeolite base in particle sizes suitable for fluidization or formed into beads or pellets, usually of a size range of 1/32 to 3/8 inch, suitably 1/16 to 1/8 inch, and containing rare earth metal oxides. Fluid catalysts usually have particle sizes of 50 to -325 mesh U. S. Standard Sieve Series.

Typical compositions of preferred catalysts are the following: Davison XZ-25, a product of Davison Chemical Company, is a mixed silica-alumina-zeolite cracking catalyst containing about 30-35 weight percent alumina, 18 weight percent zeolite X, and about 2 weight percent cerium and 1 weight percent lanthanum. Aerocat Triple S-4, a product of American Cyanamid Company, is a silica-alumina-zeolite cracking catalyst containing about 32 weight percent alumina, 3 weight percent zeolite Y, 0.5 weight percent cerium and 0.1 weight percent lanthanum. Nalcat KSF, a product of Nalco Chemical Co., is a silica-alumina-zeolite cracking catalyst containing about 31-35 weight percent alumina, 11 percent zeolite X, about 1 percent cerium and 0.3 percent lanthanum.

The catalytic cracking unit is operated at a temperature in the range of 800.degree. to 1,100.degree. F, preferably 850.degree. to 1,000.degree. F, with a space velocity, basis the total feed to the catalytic cracking unit, of 0.2 to 300 pound of hydrocarbon feedstock per hour per pound of catalyst at a reactor pressure within the range of 0 to 200 psig, preferably of the order of 25 psig. The variable reaction conditions, i.e., temperature and sapce velocity, are controlled to produce a per pass conversion of 30 to 80 volume percent. The relatively wide space velocity range indicated is subject to considerable variation and depends upon the particular reactor design under consideration, e.g., whether a riser type or bed type catalytic cracking unit is employed. The important consideration is the controlled per pass conversion which preferably is in the range of 30 to 65 volume percent to obtain maximum gasoline yield. Optimum conditions of space velocity and per pass conversion may be established for any given commercial unit by known test methods and economic evaluation.

To realize the full benefits of this invention, the catalytic cracking unit should be operated near 100 percent ultimate conversion of the feedstock to lighter products. Thus it is generally desirable to convert all of the 430.degree. F+ product from the catalytic cracking unit to naphtha and lighter products. Preferably all of the heavy gas oil and a substantial portion or all of the intermediate gas oil and of the light gas oil should be hydrogen treated and recycled to the catalytic cracking unit.

Determination of the feed stream supplied to the hydrogen treater is based on two factors. The first is that the composite recycle stream returned to the catalytic cracking unit 7 through line 35 and admixed with fresh feed from line 5 is processed so that its cracking characteristics are similar to those of the fresh feedstock supplied through line 5. Hydrogen treatment of all of the gas oils, i.e., all of the 430.degree. F gas oil from the catalytic cracking unit results in the highest yield of motor gasoline. The second factor is the market demand for catalytic cracking unit gas oils. It is recognized that it may not always be desirable to recycle all of the various gas oil fractions to extinction, depending upon available market for gas oils, usually for the heavy gas oil fraction and for the light gas oil fraction.

Since the heavy gas oil has the greatest polycyclic aromatic content, in some cases it may be desirable to hydrogen treat only the heavier fractions to reduce the hydrotreating requirements of the system. In other instances it may be desirable to recycle some of the heavy gas oil from line 29 directly to the catalytic cracking unit via lines 35 and 36 to maintain the proper reactor-regenerator heat balance in the catalytic cracking unit.

The hydrotreater design is based on providing the catalytic cracker recycle charge stock with a feed having a polycyclic aromatics content approaching that of the fresh feed (normally below 20 weight percent polycyclic aromatics). Total liquid product from the hydrotreater, including the gasoline produced is supplied to the catalytic cracking unit as part of the feedstock therefor.

Hydrogen used in the process of the present invention may be obtained from any suitable source. The term hydrogen as used in the present specification and claims includes dilute hydrogen. The hydrogen need not be pure but preferably a gas containing at least about 70 percent hydrogen is used. Suitable sources of hydrogen are catalytic reformer by-product gas and hydrogen produced by steam reforming of hydrocarbons or by partial oxidation of carbonaceous material followed by shift conversion and removal of carbon dioxide. Since the efficiency of hydrogen treatment depends to some extent on the partial pressure of the hydrogen, it is generally advantageous to employ hydrogen rich gas of relatively high hydrogen content for the hydrogen treatment.

Preferred catalysts for the hydrogen treatment are alumina base hydrogenation catalysts in the form of pellets or extrudates of a size range of 1/32 to 3/8 inch, suitably 1/16 to 1/8 inch. Oxides of boron, cobalt, molybdenum, nickel and tungsten, and their resulting sulfides formed prior to or during the use of the catalyst, are effective hydrogen treatment catalysts when deployed on suitable base supports, e.g. on high purity eta aluminas. Suitable catalysts are well known, for example, commercial catalysts Aero HDS-3, Harshaw Ni-4303, Harshaw Ni-4305 and Harshaw Ni-4309. Aero HDS-3, produced by American Cyanamid Company, is a nickel oxide-molybdenum oxide on alumina hydrogenation catalyst containing about 10 weight percent molybdenum and about 2 weight percent nickel, reported as the metals. Harshaw Ni-4303, produced by Harshaw Chemical Company, is a nickel tungsten catalyst on an alumina base comprising about 6 weight percent nickel and about 20 weight percent tungsten reported as the metals. Harshaw Ni-4305 and Ni-4309 are nickel-tungsten catalysts on boria-alumina base, Harshaw Ni-4305 contains about 5 weight percent nickel and 10 weight percent tungsten, reported as metals, and about 10 weight percent boria (B.sub.2 O.sub.3). Harshaw Ni-4309 contains about 5 weight percent nickel, about 10 weight percent tungsten, reported as metals, and about 10 weight percent boria.

The hydrotreating zone is maintained at between about 500.degree. and 800.degree. F. and 400 and 3,000 psig. Preferred conditions are 650.degree.-725.degree. F. and 500-2,000 psig. The weight hourly space velocity of the hydrocarbon feed may range betwen about 0.2 and 20 preferably 0.5 to 10 and the hydrogen rate between about 1,000 and 15,000 SCFB preferably 3,000 to 10,000 SCFB. The reaction conditions particularly temperature, pressure and space velocity are selected within the above ranges to effect reduction in the polycyclic aromatic content while minimizing the reduction in total aromatic content. The data in the following table are illustrative.

AROMATIC REDUCTION

Charge: Light Cycle Gas Oil Catalyst: Nickel-Tungsten on Alumina Operating Conditions Pressure, psig. 2000 500 Space velocity 1.0 1.0 Temperature, .degree.F. 700 700 Hydrogen rate, SCFB 6000 6000 Charge and Product Quality Charge API gravity 24.8 36.1 28.2 Total aromatics, vol. % 59.7 11.7 57.9 Polycyclic aromatics, wt. % 35.4 0.3 1.6 Olefins, vol. % 5.3 1.3 1.6 Percent Reduction Total aromatics 80 3 Polycyclic aromatics 99 95 Olefins 75 70

The same effect can be obtained by other combinations of temperature, pressure and space velocity as indicated above.

Conventional procedures are used in the alkylation step.

SPECIFIC EXAMPLES

The following specific examples demonstrate the ability of the process of this invention to produce abnormally high octane gasoline by the combination of catalytic cracking hydrotreating and alkylation.

A number of trial runs were made using virgin gas oil charge stock having the following characteristics:

Fresh Charge Stock

Gravity, .degree.API 30.9 UV Absorbance at 285 mu 4.9 Polycyclic Aromatics, wt. %.sup.1 15.2 Aromatics, Wt. % 32.5 X-Ray Sulfur, Wt. % 0.53 Conradson Carbon Residue, Wt. % 0.05 Refractive Index at 25.degree.C 1.4824 ASTM Distillation, .degree.F. IBP 453 10 528 30 579 50 625 90 747 EP 760+ .sup.1 Polycyclic aromatics (PCA) calculated by formula: PCA, Wt. % = UV Absorbance at 285 mu/0.323

Catalyst used in the fluidized bed catalytic cracking pilot unit for these tests was simulated equilibrium Davison XZ-25 catalyst. Aging of the catalyst was simulated for the runs by heat treating fresh Davison XZ-25 at 1,480.degree. F. for 17 hours and blending the heat treated catalyst with an equal weight of Davison High Alumina cracking catalyst which had been heat treated 17 hours at 1,700.degree. F. Davison High Alumina cracking catalyst, a product of Davison Chemical Company, is a silica-alumina catalyst comprising about 25 weight percent alumina and about 75 weight percent silica. Properties of the cracking catalyst are indicated in the following table.

FCCU Test Cracking Catalyst

50% XZ-25.sup.1 and Catalyst 50% high alumina.sup.1 Composition, wt. % Silica 69.3 Alumina 29.2 Cerium 1.0 Lanthanum 0.5 Zeolite content, wt. % 5 Apparent Bulk Density Settled, lb./cu. ft. 31.8 Packed, lb./cu. ft. 38.5 Particle Size Distribution, wt. % 0-20 microns 2 20-40 microns 15 40-80 microns 57 80+ microns 26 .sup.1 Products of Davison Chemical Co. Davison High Alumina catalyst is a silica-alumin a cracking catalyst containing 25 weight percent alumina and 75 weight percent silica.

EFFECT OF PER PASS CONVERSION LEVEL

The effect of per pass conversion in the fluid catalytic cracking unit (FCCU) on the volume of 430.degree. F+ gas oils from the unit charged to the hydrogen treater unit (HTU) for 100 percent conversion of catalytic cracking unit feedstock to motor fuel (430.degree. F endpoint) and lighter products and on the polycyclic aromatics content of the total 430.degree. F+ fractions are indicated in the following table.

Per pass conversion, Vol. % 40 60 70 Total charge to HTU, basis fresh feed to FCCU, Vol. % 150 66.7 42.8 Polycyclic aromatic content of 430.degree.F+ fractions from FCCU, wt. % 26.6 37.5 49.0

Effect of Polycyclic Aromatics

The effect of the polycyclic aromatics content of charge stock to the fluid catalytic cracking unit on the yield of debutanized naphtha produced by the unit at a conversion level of 60 volume percent per pass with the above blend of catalysts is shown in the following table.

Polycyclic aromatics, wt. % 7.0 15.0 29.3 44.3 Debutanized naphtha yield, vol. % 39.5 38.4 31.5 27.6

EXAMPLES 1 AND 2

In the following runs, virgin gas oil having the above characteristics was charged to a fluid catalytic cracking unit under conditions indicated below to give conversion levels of about 55 volume percent (Example 1) and about 65 volume percent (Example 2).

Example No. 1 2 Conversion Level 54.3 66.6 Reactor Temperature, Ave., .degree.F 919 918 Pressure Atm.+ Atm.+ Space Velocity lbs./hr./lb. catalyst 6.72 3.88 Catalyst/Oil, Wt. ratio 1.45 2.54 Feed Preheat Temp., .degree.F, Ave. 809 830 Regenerator Regenerator Outlet Temp. .degree.F 1060 1064 Stripper, Ave. Temp. .degree.F 928 938 Carbon on Catalyst To Regenerator, Wt. % 1.02 1.19 To Reactor, Wt. % 0.10 0.09 Yields, basis total feed Coke, Wt. % 1.2 2.3 Dry Gas, Wt. %.sup.1 5.1 6.0 Isobutane, Vol. %.sup.2 4.6 (45.5) 8.3 (50) Normal Butane, Vol. %.sup.2 0.9 (9) 2.1 (13) Butylenes, Vol. %.sup.2 4.6 (45.5) 6.2 (37) Total C.sub.4 's, Vol. % 10.1 16.6 C.sub.5 Hydrocarbons, Vol. % 6.4 12.2 Depentanized Naphtha, Vol. % 39.8 41.5 Product Quality Tests Light Gasoline (115.degree.-250.degree.F) Gravity, .degree.API 66.4 67.1 ASTM Octane RON, Clear, +3cc TEL 88.0,97.9 85.8,96.8 MON, Clear, +3cc TEL 76.5,86.8 76.8,87.1 Heavy Gasoline (250.degree.-430.degree.F) Gravity, .degree.API 41.6 41.5 ASTM Octane RON, Clear, +3cc TEL 86.1,92.0 87.5,93.9 MON, Clear, +3cc TEL 74.6,82.2 77.8,84.4 Gas Oil (430.degree.F+) Gravity, .degree.API 28.1 25.1 UV Absorption at 285 mu 11.8 14.4 Polycyclic Aromatics, Wt. %.sup.3 36.5 44.6 .sup.1 Includes H.sub.2 and C.sub.1 -C.sub.3 hydrocarbons .sup.2 Numbers shown in parentheses are individual C.sub.4 hydrocarbon as a percentage of total C.sub.4 's. .sup.3 Calculated form UV absorbance at 285 mu

EXAMPLES 3 AND 4

Two 430.degree.F+ gas oils from catalytic cracking test runs comparable to those of Examples 1 and 2 were subjected to hydrogen treatment. The hydrogen treatment catalyst was Aero HDS-3 in the form of 1/8 inch pellets. The hydrotreater catalyst was sulfided to about 5 weight percent sulfur prior to use by charging gas oil containing sufficient added carbon disulfide to give a total sulfur content of about 2 weight percent over the catalyst at 400.degree. F for 3 hours and at 600.degree. F for an additional 3 hours to a hydrogen sulfide level in the reactor off-gas of at least 500 grains per 100 cubic feet. Operating conditions for and results of the hydrogenation treatment are shown in the following table in which the charge stock for Example 3 was a 430.degree. F gas oil obtained from catalytic cracking of virgin gas oil having the characteristics indicated above at 51.5 volume percent conversion and the charge stock for Example 4 was a 430.degree. F gas oil obtained from catalytic cracking of the virgin gas oil at 63.0 volume percent conversion.

Hydrogen Treatment Unit

Example 3 4 Reactor Temperature, .degree.F. 706 680 Pressure, psig 1000 1000 Space Velocity Wo/Hr/Wc 1.96 1.25 Hydrogen/Hydrocarbon Ratio 7.63 6.91 Total Reactor Feed Gas, SCF/Bb1 4120 3914 Vol. % H.sub.2 in Reactor Feed Gas 97.7 98.4 Hydrogen Consumption, SCF/Bb1 750 1464 Charge to HTU Gravity, .degree.API 28.8 25.2 UV Absorbance at 285 mu 11.13 15.25 Polycyclic Aromatics, Wt. %.sup.1 34.5 47.2 Aromatics, Wt. % 41.2 51.8 X-Ray Sulfur, Wt. % 0.51 0.60 Conradson Carbon Residue, Wt. % 0.17 0.11 Refractive Index at 25.degree.C 1.5002 1.5304 ASTM Distillation, .degree.F IBP 440 10 481 30 516 50 549 90 EP HTU Product Gravity, .degree.API 33.0 30.8 UV Absonce at 285 mu 3.32 4.64 Polycyclic Aromatics, Wt. %.sup.1 10.3 14.4 Aromatics, Wt. % 32.9 X-Ray Sulfur, Wt. % 0.029 0.039 Conradson Carbon Residue, Wt. % 0.02 0.03 Refractive Index at 25.degree.C 1.4768 1.4894 ASTM Distillation, .degree.F IBP 382 180 10 467 465 30 504 500 50 539 528 90 636 642 EP 720 721 .sup.1 Calculated from UV absorbance at 285 mu

EXAMPLES 5 AND 6

Hydrogen treated product from Examples 3 and 4 were blended with virgin gas oil of the characteristics listed above to produce a blend of 51.5 volume percent virgin gas oil and 48.5 volume percent of HTU product from Example 3 as charge stock to the fluid catalytic cracking pilot unit (Example 5), and to produce a blend of 63.0 volume percent virgin gas oil and 37.0 volume percent of the HTU product of Example 4 as charge stock for the fluid catalytic cracking pilot unit (Example 6) to simulate commercial conditions and illustrate the benefits of the method of this invention.

Catalytic Cracking Unit

Example 5 6 Charge to FCCU Gravity, .degree.API 31.8 30.7 UV Absorbance at 285 mu 4.68 4.72 Polycyclic Aromatics, Wt. %.sup.1 14.5 14.6 Aromatics, Wt. % 32.7.sup.2 28.3 X-Ray Sulfur, Wt. % 0.32 0.39 Conradson Carbon Residue, Wt. % 0.06 0.10 Refractive Index at 25.degree.C 1.4798 1.4834 ASTM Distillation, .degree.F IBP 410 422 10 490 494 30 534 540 50 578 584 90 724 732 EP 760+ 760+ Products from FCCU Yields, basis total feed Coke, wt. % 1.3 2.1 Dry Gas, Wt. %.sup.3 4.1 5.5 Propylenes, Vol. % 3.9 4.8 Isobutane, Vol. %.sup.4 6.6 (47) 7.5 (50) Normal Butane, Vol. %.sup.4 1.5 (11) 2.1 (14) Butylenes, Vol. %.sup.4 5.9 (42) 5.3 (36) C.sub.4 's, Vol. % 14.0 14.9 C.sub.5 's, Vol. % 8.2 11.7 Depentanized Naphtha, Vol. % 37.8 41.5 Tests Light Gasoline (115.degree.-250.degree.F) 66.9 66.4 Gravity, .degree.API ASTM Octane RON, Clear, +3 cc TEL 86.2,96.7 81.6,95.3 MON,Clear, +3 cc TEL 76.5,87.2 75.0,87.6 Heavy Gasoline (250.degree.-430.degree.F) Gravity, .degree.API 40.9 38.0 ASTM Octane RON, Clear, +3 cc TEL 86.4,92.3 89.0,95.8 MON, Clear, +3 cc TEL 76.3,84.0 78.7,84.2 Gas Oil (430.degree.F+) Gravity, .degree.API 27.8 24.2 UV Absorbance at 285 mu 13.4 15.0 Polycyclic Aromatics, Wt. %.sup.1 41.5 46.4 .sup.1 Calculated from UV Absorbance at 285 mu .sup.2 Calculated .sup.3 Includes H.sub.2, C.sub.1, C.sub.2 =, C.sub.2, C.sub.3 =, C.sub.3 .sup.4 Numbers shown in parenteses are individual butanes as a percentage of total butanes.

Overall Yield Data

Yields, basis fresh feedstock charged to the fluid catalytic cracking unit with all of the charge stock ultimately converted to debutanized naphtha and lighter are shown in the following table.

Yields Basis Fresh Feed to FCCU (100% Ultimate Conversion) Coke, Wt. % 2.3 3.2 Dry Gas, Wt. % 7.3 8.5 H.sub.2 Consumption, SCF/Bb1 Fresh Feedstock 706 860 Propylenes, Vol. % 7.0 7.4 Isobutane, Vol. % 11.8 11.6 Normal Butane, Vol. % 2.7 3.2 Butylenes, Vol. % 10.5 8.2 Debutanized Naphtha, Vol. % 82.3 81.9 Research Octane, +3 cc TEL 95.9 96.5 Motor Octane, +3 cc TEL 87.9 88.4 Road Octane Index, +3 cc TEL 95.7 96.3 With Alkylation Debutanized Naphtha & Alkylate (No excess isobutane), Vol. % 98.3 97.7 Research Octane, +3 cc TEL 97.4 97.9 Motor Octane, +3 cc TEL 90.6 91.0 Road Octane Index, +3 cc TEL 97.8 98.2 Debutanized Naphtha + Alkylate (Excess isobutane), Vol. % 111.1 107.5 Research Octane, +3 cc TEL 98.4 98.6 Motor Octane, +3 cc TEL 92.2 92.2 Road Octane Index, +3 cc TEL 99.0 99.1 Excess isobutane required, Vol. % 9.2 7.0

The foregoing examples illustrate the high yields of high octane motor fuels which may be produced by the method of this invention.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

Claims

We claim:

1. A process for the conversion of a gas oil feed stock boiling above about 430.degree. F. and containing polycyclic aromatic compounds to gasoline in a yield of at least 80 volume per cent which comprises subjecting said gas oil feed stock to catalytic cracking under conditions to effect a conversion of between 30 and 80 volume per cent, separating the effluent from the catalytic cracking zone into a cracked naptha and lighter fraction having an end point of about 430.degree. F. and a cracked 430.degree. F+ gas oil fraction having a higher polycyclic aromatic compound content than said gas oil feed stock, recovering from said cracked naphtha and lighter fraction as product of the process a catalytically cracked gasoline having a boiling range of about 115.degree.-430.degree. F., subjecting at least a portion of said cracked 430.degree.F.+ gas oil fraction to hydrogen treatment under conditions to reduce the polycyclic content thereof to a concentration not appreciably greater than that of said gas oil feed stock, said portion having an initial boiling point of about 430.degree. F., separating the effluent from the hydrogenation zone into a normally gaseous portion and a normally liquid portion and introducing substantially all of said normally liquid portion with fresh gas oil feed stock into said catalytic cracking zone.

2. The process of claim 1 in which the catalytic cracking conversion is between 40 and 80 volume per cent.

3. The process of claim 1 in which a debutanized naphtha is recovered from said naphtha and lighter fraction, the C.sub.3 -C.sub.4 olefins of said naphtha and lighter fraction are subjected to alkylation with isobutane and the resulting alkylate combined with said debutanized naphtha to form a high anti-knock motor fuel.

4. The process of claim 1 in which the catalytic cracking is carried out in the presence of a catalyst comprising a hydrogen-exchanged zeolite, a silica-alumina base and a rare earth metal.

5. The process of claim 1 in which the hydrogenation of monocyclic aromatic compounds is minimized.

6. The process of claim 3 in which the yield of gasoline is at least 90 volume per cent basis gas oil feed stock.

7. The process of claim 1 in which the hydrogenation product has a polycyclic aromatic content of less than 20 weight per cent.

8. The process of claim 1 in which the total aromatic content of the hydrogenation product is at least 75 percent of the total aromatic content of the cracked 430.degree. F+ gas oil fraction.