CA1088912A - Hydrocarbon catalytic cracking process - Google Patents

Abstract

HYDROCARBON CATALYTIC CRACKING PROCESS

ABSTRACT OF THE DISCLOSURE
An improved hydrocarbon catalytic cracking process conducted in the presence of a catalyst containing a high con-centration of metals contaminants is obtained by employing a catalyst containing a significant concentration of antimony.

Description

BACKGROUND OF THE INVENTION
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. The metals in the process feed are accumu-lated on the catalyst, substantially reducing the activity of the catalyst 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 contami-nant metals. Metals found to be present in hydrocarbon feeds to catalytic processes which are deposited onto the cataly~t as metal contaminants include nickel, vanadium, copper, chromium, and iron.

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When the accumulation of metal contaminants on the catalyst total~ 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 pre-treated 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 t~e heavier feed stocks to lower boiling product fractions to satisfy ~he demands of the market place for gasoline products becomes more important, it is evident that improved catalytic cracking processes which permit the charging o~ feed stocks containing relatively high concentrations of metals are needed.

By the invention a process for the catalytic cracking of feed stocks containing relatively high concentrations of metal contaminants is provided whereby the process is operated continuously until the concentration of contaminant metals on an antimony-containing catalyst exceeds 1500 ppm nickel equivalents, obtaining a high yield of gasoline while producing relatively low yields of hydrogen and coke.
The present invention provides a cracking catalyst composition for cracking of hydrocarbons, the composition being substantially free of metal contamination and having an antimony content of at least 1000 ppm of said composition.

' . ' , ' ' ' ' ' ' ,''''. ' ' . , , 1~g8912 .. _ The cracking catalyst~ oi. this invention are tho~e catalysts generally containing silica or silica-alumina, such materials frequently being associated with zeolitic materials.
These zeolitic materials can be nat:ural occurring or can be produced by conventional ion exchange methods so as to provide metallic ions which improve the activity of the catalyst.
Although not to be limited thereto, preferred cracking catalyst compositions are those which comprise a crystalline alumino-silicate dispersed in a refractory metal oxide matrix such asdisclosed in U. S. Letters Patent 3,140,249 and 3,140,253 to C. J. Plank and E. J. Rosinski. Suitable matrix materials com-prise 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 cxacking activity and suitable in the preparation of the catalysts of 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:

M2/nO:A12O3:1.5-6.5 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.

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108~9~2 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, brewsl:erite, ferrierite, and the like. Suitable synthetic zeolites which can be employed in the inventive process include zeolites X, Y, A, L, ZK-4, 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 aluminum are replaced by gallium and substances in which the silicon is replaced by germanium. The preferred zeolites are the synthetic faujasites 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 20 the zeolite to as low a level as possible as a high alkali metal content reduces the thermal structural stability, and the effec-tiYe lifetime of the catalyst is impaired. Procedures for remov-ing alkali metals and putting the zeolite in the proper form are well known in the art and are as described in V. S. Letters Patent 3,534,816.
Conventional methods can be employed to form the catalyst composite. 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 30 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 E~ 4 -, , - ~8~391Z
In addition to the zeolitic and non-zeolitic, silica-containing cracking catalyst compositions heretofore described, other materials useful in preparing the antimony-containing catalyst of this invention also include the laminar

2:1 layer-lat~ice 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 of this invention, such laminar 2:1 layer-lattice aluminosilicate minerals are combined with a zeolitic composition.
The cracking catalyst compositions of this invention also contain a concentration of antimony of at least 1000 ppm.
For those non-zeolitic cracking catalyst compositions, the concentration of antimony in the catalyst composite will normally range from 0.1 to 2.0 weight percent. For zeolitic-containing cracking catalyst compositions, the concentration of antimony in the catalyst composite will normally range from 0.25 to 2.5 weight percent.
The antimony can be added to the fresh cracking catalyst containing less than 100 ppm nickel equivalent metal contaminants (substantially free of metal contaminants) by impregnation, employing an antimony compound which is either the oxide or which is convertible to the oxide upon su~jecting 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 a~
defined above.

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1~8~912 Another method of adding the antimony to the catalyst composite 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 ~eparate precipitation or coprecipita-tion in which a suitable salt of the antimony oxide is added to ;
an alkali metal silicate and an 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 of 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 600F. (316C.) and include materials such as gas oils, cycle oils, residuums and the like. 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 signiicantly higher concentrations of metal contaminants as the antimony-containing catalysts are effective in catalytic cracking processes operated at metal contaminant levels exceeding 1500 ppm nickel equivalents. As hereater described, the process employing the antimony-containing catalysts is effective at metal contaminant levels exceeding 2500 ppm niakel equivalents and even exceeding 5000 ppm nickel equivalents. Thus~ the charge stocks to the aatalytic cracking process of this invention can contain metal aontaminants in the range up to 3.5 ppm and higher nickel equivalents.

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Although not to be limited thereto, a preferred method of employing the catalysts of this invention is by fluid catalytic cracking using riser outlet temperatures between about 900 to 1100F. (482 to 593C.). 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 composited catalyst in an elongated 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 600F. (316C.) and the heated feed is then charged into the bottom of the riser.
In operation, a contact time (based on feed) of up to lS seconds and catalyst 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 and/or introduced independently to ~he bottom of the riser so as to assist in carrying regenerated catalyst upwardly through the riser. Regenerated catalyst at temperatures generally between about 1100 and 1350F. (593 to 732C.) 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 and hydrocarbon feed flowing concurrently into and up-wardly into the riser at about the sama flow velocity, thereby avoiding any significant slippage of catalyst relative to hydro-carbon in the riser and avoiding formation of a catalyst bed in the reaction flow qtream. In this manner the catalyst to oil ratio thus increases significantly from the riser inlet along the raaction flow stream.

The riser temperature drops along the riser length due to heating and vaporization of the ~eed 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 upon contact of feed and regenerated catalyst at the bottom of the riser. Therefore, at the riser inlet, the hot, regenerated catalyst 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 containing metal contaminants and carbon is separated from the hydrocarbon product effluent withdrawn from the reactor and passed to a regenerator. In the regenerator the catalyst is heated to a temperature in the range of about 800 to about 1600F. (427 to 871C.), preferably 1160 to 1260F. (627 to 682C.), 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.
Conventional processes can operate with catalysts con-taining contaminated metals concentrations greater than 1000 ppm nickel equivalents but at a substantial loss of product distribu-tion and conversion. Further r under such conditions undesirably high concentrations of coke, hydrogen and light gas are produced.
By employing the defined catalyst in the manner of this invention, the contaminant metals level on the catalyst can exceed 2500 ppm nickel equivalents while obtaining a conversion and gasoline yield normally effected by conventional catalysts containing only 500 ppm nickel equivalent metal contaminants.

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Yields of gasoline and carb~n are uneffected signifi-cantly 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 conventional hydrocarbon cracking processes. Thus, by this invention the cracking process can be operated efficiently with a metal con-taminant 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 to include 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 contami-nation on conventional cracking ~atalysts, most refiners attempt to maintain a low metals level on the cracking catalyst -- less than 1000 ppm. An unsatisfactory method of controlling metals con-tamination in addition to those previously discussed is to increase the catalyst makeup rate to a level higher than that required to maintain activity or to satisfy unit losses.
The following examples are presented to illustrate objects and advantages of the invention. However, it is not intended that the invention should be limited to the specific embodiments presented therein.

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EXAMPLE I

In each of the catalytic cracking runs of this Example a Kuwait gas oil feed stock having a boiling range of 260C. to 427C. was employed. The catalyst employed in each of the runs, prior to the addition of the antimony thereto, 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 1025F. (552C.) 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 20-40 Microns 14.7 40-80 Microns 46.4 > 80 Microns 36.9 > 80/ ~ 40u 2.20 Chemical Composition: Weight %
Iron (Fe2O3) 0.529 Nickel 0.005 Vanadium 0.012 Sodium 0.56 Alumina (A12O3) 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.
In each of Runs 1-4, the catalyst was contaminated with metal contaminants to the level of 2570 ppm nickel equivalents.

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

TABLE I

C5+ 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 A comparison of the results obtained demonstrates the effectiveness of the catalyst composition containing antimony to obtain significant 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 significantly reduce ~0 the production of carbon and hydrogen is demonstrated.

EXAMPLE II

In this Example, the efectiveness of employing a cracking catalyst 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 i8 demonstrated. The catalyst of Run No. 3 of Example I (0.63 weight percent antimony) was employed in Run 6 of this example.

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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 charac~erized as follows:

Gravity, ~PI 25.0 Sulfur, wt. %i 0.31 Nitrogen, wt. % 0.12 Carbon Residue, Rams, ASTM D52S, wt. % 0.77 Aniline Point, ASTM
D611, F. 199 t93C) Viscosity, SUS, ASTM :
D2161, 210F. (99C) 49.8 Pour Point, ASTM D97, F. +90 (~32C) Nickel, ppm 1.2 Vanadium, ppm 0.4 Vacuum Distillation ASTM Dll60 F.
10% at 760 mm 622 (328C) 30~ 716 (380C) 50% 797 (425C) - -70% 885 (474C) :~
90~ 1,055 (568C) In each of the runs the metals contaminantis 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~. ~527C.). The hydrocarbon and aatalyst mixture with a catalyst to oil ratio of 8.2 wa~ charged to the riser inlet together with a hydrocarbon recycle comprising ., . . . . i . . . .
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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 II

Run No. 5 Run No. 6 Yields: vol%
Conversion: vol% 77.0 82.9 Debutanized Gasoline57.8 63.3 Butane-Butenes 13.8 18.3 Butenes 9.4 10.4 Propane-Propylene 10.2 10.4 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 catalyst 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.

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EXAMPLE III
-In the run (Run No. 7) of this Example the criticality of compositing the antimony with the i-resh catalyst when compared with the addition o antimony to a mel:als contaminated catalyst is demonstrated. The hydrocarbon charge of Example II was employed in the cracking run of this example. The catalyst com-position 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 or Run No. 6 of Example II
kepeated here for comparison purposes) are shown below in Table III.
TABLE III
Run No. 6 Run No. 7 20 Yields: vol%
Conversion 82.9 80.2 Debutanized Gasoline63.3 61.9 Butane-Butenes 18.3 16.6 Butenes 10.4 10.1 Propane-Propylene 10.4 11.5 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 :

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Run No. 6 Run No. 7 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 ef~ectiveness of antimony when added to a non-zeolitic silica-alumina 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 o~ 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 o Runs 8 and 9 was conducted by passing the hydrocarbon feed of Example II
through a fixed catalyst bed at a temperature of 900F. (482C.) and at a weight hourly space velocity of 14Ø The contact time between the hydrocarbon feed and the catalyst was 80 seconds.

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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 IV.

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T~BLE IV
Run No. 8 Run No. 9 10 Conversion, vol% of eed 39.49 41.02 C5 + gasoline, vol% of feed 18.74 20.49 Carbon produced, wt%
of feed 6.74 4.67 Hydrogen produced, wt%
of feed 0.738 0.400 A comparison of the results obtained in Runs 8 and 9 demonstrates the effectiveness of antimony-impregnated catalyst to increase conversion, increase gasoline productionl lower carbon production, and lower hydrogen production when employed in the catalytic cracking process of this invention.
Although the invention has been described with reference to speciic embodiments, references, and details, various modifications and changes will be apparent to one skilled in the art and are contemplated to be embraced in this invention.

Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A cracking catalyst composition for cracking of hydro-carbons, the composition being substantially free of metal contamination and having an antimony content of at least 1000 ppm of said composition.

2. A cracking zeolitic-containing catalyst composition for cracking of hydrocarbons, the composition being substantially free of metal contaminants, and having an antimony content of from 0.25 to 2.5 weight percent of said composition.

3. A non-zeolitic, silica-alumina cracking catalyst for cracking of hydrocarbons, the composition being substantially free of metal contaminants, and having an antimony content of from 0.1 to 2.0 weight percent of said composition.

4. A hydrocarbon cracking process which comprises contacting a hydrocarbon feed with a cracking catalyst composition under cracking conditions until the concentration of metal contaminants on said catalyst exceeds 1500 ppm nickel equivalents, at least 1000 parts per million antimony having been deposited on said cracking catalyst during its preparation.

5. The process of claim 4 wherein the concentration of metal contaminants on said catalyst exceed 2500 ppm nickel equivalents.

6. The process of claim 4 wherein said cracking catalyst composition is a zeolitic-containing catalyst composition which has an antimony content of from 0.25 to 2.5 weight percent.

7. The process of claim 4 wherein said cracking catalyst composition comprises a silica-alumina composition having an antimony content of from 0.1 to 2.0 weight percent.