GB1570682A - Hydrocarbon catalytic cracking process - Google Patents

Description

(54) AN IMPROVED HYDROCARBON CATALYTIC CRACKING PROCESS (71) We, GULF RESEARCH & DEVELOPMENT COMPANY, a corporation organised and existing under the laws of the State of Delaware, U.S.A., of P.O. Box 2038, Pittsburgh, Pennsylvania 15230, U.S.A., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an improved hydrocarbon catalytic cracking process.

Feed stocks to conventional catalytic cracking processes operated so as to obtain a high yield of gasoline and other low boiling fractions must contain very low concentrations of metals, normally less than 1.5 parts per million (ppm) and preferably no greater than 1 ppm, since the metals in the feed accumulate on the catalyst, substantially reducing its activity with resultant low conversion of the feed to the lower boiling range products.

The metals present in the petroleum charge stocks to the catalytic cracking processes are generally in an organometallo form, such as in a porphyrin or as a naphthenate. These metals tend to be deposited in a relatively non-volatile form onto the catalyst during the cracking process, and the regeneration of the catalyst to remove coke therefrom does not remove these contaminant metals. Metals foumd to be present in hydrocarbon feeds to catalytic processes which are deposited on to the catalyst as metal contaminants include nickel, vanadium, copper, chromium, and iron.

When the accumulation of metal contaminants on the catalyst totals about 1500 ppm nickel equivalents (ppm nickel + 0.2 ppm vanadium), it is necessary to replace the catalyst. The replacement is expensive and a number of methods have been investigated for the purpose of lowering this high replacement cost. A suggested method is to reduce the concentration of metals in the feed stock to the catalytic cracking process. For example, it has been suggested that the contaminated feed be pretreated to lower the concentration of metals to below about 1 ppm or to exclude by fractionation the heavier gas oils and residual fractions where the major concentration of metal contaminants occur. These methods have been only partially successful and as the necessity for increasing the conversion of the heavier feed stocks to lower boiling product fractions to satisfy the demands of the market place for gasoline products becomes more important, it is evident that improved catalytic cracking processes which permit the charging of feedstocks containing relatively high concentrations of metals are needed.

The present invention provides an improved hydrocarbon cracking process which includes providing a catalytic component selected from silica, silica and alumina, and natural and synthetic zeolites said component containing less than 100 ppm nickel equivalents of metal contaminants, incorporating into said catalytic component at least 1000 ppm of antimony as an improver to form a hydrocarbon cracking catalyst composition, contacting the antimonycontaining catalyst composition with a metalcontaminated hydrocarbon feedstock under cracking conditions so as to crack the feedstock and to deposit contaminants from the feedstock on to the catalyst composition, and continuing the cracking process until more than 1500 ppm nickel equivalents of metal contaminants deposit from the feedstock on to the catalyst composition.

The catalytic component may be a zeolite containing catalyst, and from 0.25 to 2.5 weight percent of antimony may be incorporated therein.

Also, the catalytic component can be a nonzeolitic silica-alumina catalyst, and from 0.1 to 2.0 weight percent of antimony may be incorporated therein.

By the present invention a process for the catalytic cracking of feedstocks is provided which produces a high yield of gasoline while producing relatively low yields of hydrogen and coke.

The hydrocarbon cracking catalystic component used in this invention is a catalyst containing silica or silica and alumina, such materials frequently being associated with zeolitic materials. These zeolitic materials can be natural occurring or can be produced by conventional ion exchange methods so as to provide metallic ions which improve the acti- vity of the catalyst. Although not to be limited thereto, preferred cracking catalysts are those which comprise a crystalline aluminosilicate dispersed in a refractory metal oxide matrix such as disclosed in U. S. Letters Patent 3,140,249 and 3,140,253 to C. J. Plank and E. J. Rosinski. Suitable matrix materials comprise inorganic oxides such as amorphous and semi-crystalline silica-aluminas, silica-magnesias, silica-alumina-magnesia, alumina, titania, zirconia, and mixtures thereof.

Zeolites or molecular sieves having cracking activity and suitable in the preparation of the catalyst composition used in this invention are crystalline, three-dimensional stable structures containing a large number of uniform openings or cavities interconnected by smaller, relatively uniform holes or channels. The formula for the zeolites can be represented as follows: xM2/nO:AI203 :1.5-6.5 SiO2 :yH2O where M is a metal cation and n its valence; x varies from 0 to 1; and y is a function of the degree of dehydration and varies from 0 to 9.

M is preferably a rare earth metal cation such as lanthanum, cerium, praseodymium, neodymium or mixtures thereof.

Zeolites which can be employed in the practice of this invention include both natural and synthetic zeolites. These natural occurring zeolites include gmelinite, chabazite, dachiardite, clinoptilolite, faujasite, heulandite, analcite, levynite, erionite, sodalite, cancrinite, nepheline lazurite, scolecite, natrolite, offretite, mesolite, mordenite, brewsterite, and ferrierite. Suitable synthetic zeolites which can be employed in the invention process includes zeolites X, Y, A, L, ZK4, B, E, F, H, J, M, Q, T,W, Z, alpha and beta, ZSM-types and omega.

The effective pore size of synthetic zeolites are suitable between 6 and 15 A in diameter.

The term "zeolites" as used herein contemplates not only aluminosilicates but substances in which the aluminium are replaced by gallium and substances in which the silicon is replaced by germanium. The preferred zeolites are the synthetic faujasices of the types Y and X or mixtures thereof.

It is also well known in the art that to obtain good cracking activity the zeolites must be in good cracking form. In most cases this involves reducing the alkali metal content of the zeolite to as low a level as possible as a high alkali metal content reduces the thermal structural stability, and the effective lifetime of the catalyst is impaired. Procedures for removing alkali metals and putting the zeolite in the proper form are well known in the art and are as described in U. S. Letters Patent 3,534,816.

Conventional methods can'bye employed to form the cracking catalyst used in this invention. For example, finely divided zeolite can be admixed with the finely divided matrix material, and the mixture spray dried to form the catalyst composite. Other suitable methods of dispersing the zeolite materials in the matrix materials are described in U. S. Patents 3,271,418;3,717,587;3,657,154;and 3,676, 330.

In addition to the zeolitic and non-zeolitic, silica-containing cracking catalyst compositions heretofore described, other materials useful in preparing the antimony-containing catalyst composition used in this invention also include the laminar 2:1 layer-lattice aluminosilicate materials described in U. S. 3,852,405. The preparation of such materials is described in said patent. Preferably, when employed in the preparation of the catalysts used in this invention, such laminar 2:1 layer-lattice alumina silicate minerals are combined with a zeolite composition.

The improved cracking catalyst compositions prepared for use in this invention comprise a hydrocarbon cracking catalyst to which has been added a concentration of antimony of at least 1000 ppm. For those non-zeolite cracking catalysts, the concentration of antimony in the catalyst composition will normally range from 0.1 to 2.0 weight percent. For zeolitecontaining cracking catalysts, the concentration of antimony in the catalyst composition will normally range from 0.25 to 2.3 weight percent.

The antimony can be added to the fresh cracking catalyst containing less than 100 ppm nickel equivalent metal contaminants (i.e. substantially free of metal contaminants) by impregnation, employing an antimony compound which is either the oxide or which is convertible to the oxide upon subjecting the catalyst composite to a calcination step. For example, a compound selected from the group consisting of antimony lactate, antimony acetate, antimony trioxide, and antimony trichloride can be added to a hydrocarbon solvent such as benzene and the catalyst composition contacted with the hydrocarbon solvent containing the selected antimony compound so as to prepare, after drying and calcination, a final catalyst composition containing a concentration of antimony as defined above.

Another method of adding the antimony to the catalyst is by the addition of antimony to an inorganic oxide gel. The preparation of plural gels is well known in the art and generally involves either separate precipitation or coprecipitation in which a suitable salt of the antimony oxide is added to an alkali metal silicate and acid or base, as required, is added to precipitate the corresponding oxide. The inorganic oxide gel as prepared and containing the antimony can then be combined with the aluminosilicate by methods well known in the art.

The catalyst compositions used in this invention are employed in the cracking of charge stocks to produce gasoline and light distillate fractions from heavier hydrocarbon feed stocks.

The charge stocks generally are those having an average boiling temperature above 6000F (316"C) and include materials such as gas oils, cycle oils and residuums. As previously described, conventional catalytic cracking charge stocks contain less than 1.5 ppm nickel equivalents as metal contaminants.

The charge stocks employed in the process of this invention can contain significantly higher concentrations of metal contaminants as the antimony-containing catalyst composition are effective in catalytic cracking processes operated at metal contaminant levels exceeding 1500 ppm nickel equivalents. As hereafter described, the process employing the antimonycontaining catalyst composition is effective at metal contaminant levels exceeding 2500 ppm nickel equivalents and even exceeding 5000 ppm nickel equivalents. Thus, the charge stocks to the catalytic cracking process of this invention can contain metal contaminants in the range up to 3.5 ppm and higher nickel equivalents.

Although not to be limited thereto, a preferred method of employing the catalyst composition in the performance of this invention is by fluid catalytic cracking using riser outlet temperatures between 900 to 1 1000F. (482 to 593 C.). The invention will hereafter be described as it relates to a fluid catalytic cracking process although those skilled in the art will readily recognize that the invention is equally applicable to those catalytic cracking processes employing a fixed catalyst bed.

Under fluid catalytic cracking conditions the cracking occurs in the presence of a fluidized catalyst composition in an elongate reactor tube commonly referred to as a riser.

Generally, the riser has a length to diameter ratio of about 20. The charge stock is passed through a preheater which heats the feed to a temperature of about 600"F. (316"C.) and the heated feed is then charged into the bottom of the riser.

In operation, a contact time (based on feed) of up to 15 seconds and catalyst composition to oil weight ratios of about 4:1 to about 15:1 are employed. Steam can be introduced into the oil inlet line to the riser arid/or introduced independently to the bottom of the riser so as to assist in carrying regenerated catalyst composition upwardly through the riser.

Regenerated catalyst composition at temperatures generally between 1100 and 13500F.

(593 to 7320 C.) is introduced into the bottom of the riser.

The riser system at a pressure in the range of about 5 to about 50 psig. (.35 to 3.50.

kg/cm2) is normally operated with catalyst composition and hydrocarbon feed flowing concurrently into and upwardly into the riserat about the same flow velocity, thereby avoiding any significant slippage of catalyst composition relative to hydrocarbon in the riser and avoiding formation of a catalyst bed in the reaction flow steam. In this manner the catalyst composition to oil ratio thus increases significantly from the riser inlet along the reaction flow steam.

The riser temperature drops along the riser length due to heating and vaporization of the feed by the slightly endothermic nature of the cracking reaction and heat loss to the atmosphere. As nearly all the cracking occurs within one or two seconds, it is necessary that feed vaporization occurs nearly instantaneously upor contact of feed and regenerated catalyst composition at the bottom of the riser. Therefore, at the riser inlet, the hot, regenerated catalyst composition and preheated feed, generally together with a mixing agent such as steam, (as hereto described) nitrogen, methane, ethane or other light gas, are intimately admixed to achieve an equilibrium temperature nearly instantaneously.

The catalyst composition containing carbon and metal contaminants gathered from the feedstock is separated from the hydrocarbon product effluent withdrawn from the reactor and passed to a regenerator. In the regenerator the catalyst composition is heated to a temperature in the range of from 800 to about 1600"F. (427 to 871:C.), preferably 1160 to 1260 F. (627 to 682 C.), for a period of time ranging from three to thirty minutes in the presence of a free-oxygen-containing gas. This burning step is conducted so as to reduce the concentration of the carbon on the catalyst to less than 0.3 weight percent by conversion of the carbon to carbon monoxide and carbon dioxide.

Cracking processes can operate with conventional catalysts can tolerate contaminated metals concentrations greater than 1000 ppm nickel equivalents, but at a substantial loss of product distribution and conversion. Further, under such conditions undesirably high concentrations of coke, hydrogen and light gas are produced. By employing the defined catalyst composition of this invention, the contaminant metals level on the catalyst can exceed 2500 ppm nickel equivalents while still obtaining a conversion and gasoline yield normally only obtainable from conventional catalysts which contain only 500 ppm nickel equivalent metal contaminants.

Yields of gasoline and carbon are unaffected significantly up to metal contaminant levels of 5000 ppm nickel equivalents. Although hydrogen yields increase with increasing metals contamination above 3000 ppm, the rate of increase is substantially less than that normally obtained in hydrocarbon cracking processes with conventional catalysts. Thus, by this invention the cracking process can be operated efficiently with a metal contaminant concentration on the catalyst up to at least 5000 ppm nickel equivalents.

As previously indicated, the process of this invention has a significant advantage over conventional catalytic cracking processes by providing an economically attractive method of using higher metals-containing gas oils as a feed to the catalytic cracking process. Because of the loss of selectivity to high value products (loss of conversion and yield of gasoline, and gain in coke and light gases) with the increase in metals contamination on conventional cracking catalysts, most refiners attempt to maintain a low metals level on the cracking catalyst - less than 1000 ppm. An unsatisfactory method of controlling metals contamination in addition to those previously discussed is to increase the catalyst makeup rate to a level higher than that required to inaintain activity or to satisfy unit losses.

The following examples are presented to illustrate objects and advantages of the invention.

EXAMPLE I In each of the catalytic cracking runs of this Example a Kuwait gas oil feed stock having a boiling range of 260"C. to 427 C. was employed. The cracking catalyst employed in each of the runs, was a crystalline aluminosilicate dispersed in a refractory oxide matrix.

The physical characteristics and chemical composition of the catalyst, after the catalyst had been heated for 3 hours at a temperature of 1025"F. (552"C.) and before addition of the antimony, were as follows: Physical Characteristics Surface Area: M2/G 181.1 Pore Volume (Nitrogen Adsorption): CC/G 0.210 Apparent Bulk Density: G/CC 0.700 Particle Size Distribution 0-20 Microns 2.0 2040 Microns 14.7 40-80 Microns 46.4 > -80 36.9 > -80/ < 40u 2.20 Chemical Composition: Weight % Iron(Fe203) 0.529 Nickel 0.005 Vanadium 0.012 Sodium 0.56 Alumina (A1203) 42.34 Cerium 0.20 Lanthanum 1.20 Titanium 0.52 In each of Runs 2, 3, and 4, antimony was added to the catalyst by impregnating the fresh catalyst with triphenyl antimony to provide the concentration of antimony indicated below in Table I Run 1, the antimony free catalyst, is indicated for comparison. In each of Runs 14, the catalyst was contaminated with metal contaminants from metalcontaminated feedstock to the level of 2570 ppm nickel equivalents.

The catalytic cracking runs were conducted employing a fixed catalyst bed, a temperature of 482 C., a liquid weight hourly space velocity of 15, and a contact time of 80.5 seconds. The results obtained are as shown in Table I.

A comparison of the results obtained demonstrates the effectiveness of the antimonycontaing catalyst compositions to obtain sig- nificant improvement in the conversion and in C5 + gasoline produced when operating with metal contaminants on the catalyst equal to 2570 ppm nickel equivalents. Also, the effectiveness of the antimony catalyst to reduce significantly the production of carbon and hydrogen is demonstrated.

EXAMPLE H In this Example, the effectiveness of employing a cracking catalyst composition containing antimony with a different charge stock to improve conversion and C5 + gasoline production and to reduce the production of coke and hydrogen when operating at a catalyst metals contaminant level of 2500 ppm nickel equivalents is demonstrated. The catalyst of Run No. 3 of Example I (0.63 weight percent antimony) was employed in Run 6 of this example. In Run No. 5, the catalyst composition of Run 1 of Example I was employed. The hydrocarbon charge to each of the cracking runs of this Example was characterized as follows: Gravity,OAPI 25.0 Sulfur, wt. O/o 0.31 Nitrogen, wt. O/o 0.12 Carbon Residue, Rams, ASTM D525, wt. % 0.77 Aniline Point, ASTM D6l1,0F. 199 (93"C) Viscosity, SUS, ASTM D2161, 2l00F. (990C) 49.8 Pour Point, ASTM D97, F. +90 (+32"C) Nickel, ppm 1.2 Vanadium, ppm 0.4 Vacuum Distillation ASTM D1160 "F.

10% at 760 mm 622 (328 C) 30% 716 (380 C) 50% 797 (425C) 70% 885 (474 C) 90% 1,055 (568 C) In each of the runs the metals contaminants level on the catalyst was 2500 ppm nickel equivalents. In each run the hydrocarbon charge was passed to a riser cracker operated at an outlet temperature of 980"F. (527"C.).

The hydrocarbon and catalyst mixture with a catalyst to oil ratio of 8.2 was charged to the riser inlet together with a hydrocarbon recycle comprising 7.5 volume percent of the fresh hydrocarbon feed. The contact time during the cracking operation was 4.5 seconds. The product yields for each of the runs were as shown below in Table II: TABLE I Cos + Carbon Hydrogen Antimony, Conversion, Gasoline, Produced, Produced, Run Wt % of Vol % of Vol % of Wt % of Wt % of No. Catalyst Feed Feed Feed Feed 1 0 56.2 36.0 5.42 0.44 2 0.23 61.0 41.5 4.47 0.23 3 0.63 64.1 43.3 3.77 0.15 4 1.0 64.0 43.9 4.40 0.16 TABLE II Run No. 5 Run No. 6 Yields: vol% Conversion: vol% 77.0 82.9 Debutanized Gasoline 57.8 63.3 Butane-Butenes 13.8 18.3 Butenes 9.4 10.4 Propane-Propylene 10.2 10A Propylene 8.0 8.1 Furnace Oil 17.8 13.9 Decanted Oil 5.2 3.2 Total C3 + Liquid Recovery 104.8 109.1 Yields: wt% Coke 9.4 8.6 C2 and Lighter 3.6 2.7 Ethane-Ethylene 1.66 1.4 Methane 1.2 1.0 Hydrogen 0.64 0.20 A comparison of Runs 5 and 6 demonstrates that the antimony-containing catalyst composition improves conversion by 5.9 percent, improves debutanized gasoline production by 5.5 volume percent, reduces coke production from 9.4 to 8.6 weight percent and reduces hydrogen production from 0.64 to 0.20 weight percent.

EXAMPLE II In the run (Run No. 7) of this Example the criticality of compositing the antimony with the fresh catalyst when compared with the addition of antimony to a catalyst previously contaminated with metals is demonstrated.

The hydrocarbon charge of Example II was employed in the cracking run of this example.

The catalyst composition of Example II was also employed in the run of this Example with the exception that the catalyst was contaminated with metals to a level of 2580 ppm nickel equivalents prior to the addition of 0.62 weight percent antimony, added to the catalyst by introducing triphenyl antimony into the hydrocarbon feed to the cracking zone.

The same operating conditions employed in Runs No. 5 and 6 of Example II were used. The product yields for Run No. 7 together with the product yields for Run No. 6 of Example II (repeated here for comparison purposes) are shown below in Table III.

TABLE III Run No. 6 Run No.7 Yields: vol% Conversion 82.9 80.2 Debutanized Gasoline 63.3 61.9 Butane-Butenes 18.3 16.6 Butenes 10.4 10.1 Propane-Propylene 10.4 11.5 TABLE III (Con't.) Run No. 6 Run No. 7 Propylene 8.1 9.5 Furnace Oil 13.9 16.0 Decanted Oil 3.2 3.8 Total C3 + Liquid Recovery 109.1 109.8 Yields: wt% Coke 8.6 7.6 C2 and Lighter 2.7 2.75 Ethane-Ethylene 1.4 1.4 Methane 1.0 1.1 Hydrogen 0.20 0.15 From the above it can be seen that antimony added to the fresh catalyst resulted in a 2.7% increase in conversion and a 1.4% increase in the production of debutanized gasoline.

EXAMPLE IV In this Example the effectiveness of antimony when added to a non-zeolitic silicaalumina cracking catalyst is demonstrated. The catalyst in each of Runs 8 and 9 was comprised of 75.0 weight percent silica and 25.0 weight percent alumina. In addition to the silica and alumina, the catalyst contained as trace impurities 0.03 weight percent chlorine, 0.01 weight percent sodium, 0.38 weight percent sulfur and less than 0.1 weight percent iron.

The catalyst composition was further characterized as having a surface area of 507.7 square meters per gram, a pore volume (nitrogen adsorption) of 0.831 cc per gram, and an average pore diameter of 65 A.

The catalytic cracking process in each of Runs 8 and 9 was conducted by passing the hydrocarbon feed of Example II through a fixed catalyst bed at a temperature of 9000 F.

(482 C.) and at a weight hourly space velocity of 14.0. The contact time between the hydrocarbon feed and the catalyst composition was 80 seconds. Run No. 8 was conducted after the catalyst had been contaminated with metals to the level of 2570 nickel equivalents.

In Run No.9 0.63 weight percent antimony in the form of triphenyl antimony was added to the fresh catalyst by impregnation and the fresh catalyst thereafter contaminated with metals to the level of 2570 nickel equivalents.

The results obtained in each of the runs is shown below in Table W.

TABLE IV Run No.8 Run No.9 Conversion, vol% of feed 39A9 41.02 Cs + gasoline, vol% of feed 18.74 20A9 Carbon produced, wt% of feed 6.74 4.67 Hydrogen produced, wtO/o of feed 0.738 0A00 A comparison of the results obtained in Runs 8 and 9 demonstrates the effectiveness of antimony-impregnated catalyst composition to increase conversion, increase gasoline production, lower carbon production, and lower hydrogen production when employed in the catalytic cracking process of this invention.

WHAT WE CLAIM IS: 1. A hydrocarbon catalytic cracking process which includes providing a catalytic component selected from silica, silica and alumina, and natural and synthetic zeolites said component containing less than 100 ppm nickel equivalents of metal contaminants, incorporating into said catalytic component at least 1000 ppm of antimony as an improver to form a hydrocarbon cracking catalyst composition, contacting the antimony-containing catalyst composition with a metal-contaminated hydrocarbon feedstock under cracking conditions so as to crack the feedstock and to deposits contaminants from the feedstock on to the catalyst composition, and continuing the cracking process until more than 1500 ppm nickel equivalents of metal contaminants deposit from the feedstock on to the catalyst composition.

2. A process according to Claim 1, in which the concentration of metal contaminants on the composition exceeds 2500 ppm nickel equivalents.

3. A process according to Claim 1 or 2, in which the catalytic component is a zeolite and the concentration of antimony is from 0.25 to 2.5 weight percent.

4. A method according to Claim 1 or 2, in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. TABLE III (Con't.) Run No. 6 Run No. 7 Propylene 8.1 9.5 Furnace Oil 13.9 16.0 Decanted Oil 3.2 3.8 Total C3 + Liquid Recovery 109.1 109.8 Yields: wt% Coke 8.6 7.6 C2 and Lighter 2.7 2.75 Ethane-Ethylene 1.4 1.4 Methane 1.0 1.1 Hydrogen 0.20 0.15 From the above it can be seen that antimony added to the fresh catalyst resulted in a 2.7% increase in conversion and a 1.4% increase in the production of debutanized gasoline. EXAMPLE IV In this Example the effectiveness of antimony when added to a non-zeolitic silicaalumina cracking catalyst is demonstrated. The catalyst in each of Runs 8 and 9 was comprised of 75.0 weight percent silica and 25.0 weight percent alumina. In addition to the silica and alumina, the catalyst contained as trace impurities 0.03 weight percent chlorine, 0.01 weight percent sodium, 0.38 weight percent sulfur and less than 0.1 weight percent iron. The catalyst composition was further characterized as having a surface area of 507.7 square meters per gram, a pore volume (nitrogen adsorption) of 0.831 cc per gram, and an average pore diameter of 65 A. The catalytic cracking process in each of Runs 8 and 9 was conducted by passing the hydrocarbon feed of Example II through a fixed catalyst bed at a temperature of 9000 F. (482 C.) and at a weight hourly space velocity of 14.0. The contact time between the hydrocarbon feed and the catalyst composition was 80 seconds. Run No. 8 was conducted after the catalyst had been contaminated with metals to the level of 2570 nickel equivalents. In Run No.9 0.63 weight percent antimony in the form of triphenyl antimony was added to the fresh catalyst by impregnation and the fresh catalyst thereafter contaminated with metals to the level of 2570 nickel equivalents. The results obtained in each of the runs is shown below in Table W. TABLE IV Run No.8 Run No.9 Conversion, vol% of feed 39A9 41.02 Cs + gasoline, vol% of feed 18.74 20A9 Carbon produced, wt% of feed 6.74 4.67 Hydrogen produced, wtO/o of feed 0.738 0A00 A comparison of the results obtained in Runs 8 and 9 demonstrates the effectiveness of antimony-impregnated catalyst composition to increase conversion, increase gasoline production, lower carbon production, and lower hydrogen production when employed in the catalytic cracking process of this invention. WHAT WE CLAIM IS:

1. A hydrocarbon catalytic cracking process which includes providing a catalytic component selected from silica, silica and alumina, and natural and synthetic zeolites said component containing less than 100 ppm nickel equivalents of metal contaminants, incorporating into said catalytic component at least 1000 ppm of antimony as an improver to form a hydrocarbon cracking catalyst composition, contacting the antimony-containing catalyst composition with a metal-contaminated hydrocarbon feedstock under cracking conditions so as to crack the feedstock and to deposits contaminants from the feedstock on to the catalyst composition, and continuing the cracking process until more than 1500 ppm nickel equivalents of metal contaminants deposit from the feedstock on to the catalyst composition.

2. A process according to Claim 1, in which the concentration of metal contaminants on the composition exceeds 2500 ppm nickel equivalents.

3. A process according to Claim 1 or 2, in which the catalytic component is a zeolite and the concentration of antimony is from 0.25 to 2.5 weight percent.

4. A method according to Claim 1 or 2, in

which the catalytic component is a non-zeolitic, silica-alumina cracking catalyst and the concentration of antimony is from 0.1 to 2.0 weight percent.

5. A process according to any one of Claims 1 to 4, wherein the hydrocarbon feedstock contains nickel as contaminant.

6. A hydrocarbon catalytic cracking process according to Claim 1, substantially as described in Example I to IV hereinbefore.

7. Cracked hydrocarbons whenever produced by the process claimed in any one of Claims 1 to 6.