US2887450A - Catalyst and hydrocarbon conversion therewith - Google Patents

Description

United States Patent CATALYST AND HYDROCARBON CONVERSION THEREWITH Alfred E. Hirschler, Springfield, and Edward J. Janoski,

Philadelphia, Pa., assignors to Sun Oil Company, Philadelphia, Pa, a corporation of New Jersey No Drawing. Application December 29, 1954 Serial No. 478,531

4 Claims. (Cl. 208-120) reaction conditions, has been described. Such heretofore described processes, however, are not suitable for converting the hydrocarbon fraction boiling substantially within the range of from about 375 F. to 500 F. to high octane gasoline in a single stage. Instead of achieving a good yield of high octane gasoline, there is produced gasoline hydrocarbons of relatively low octane ratingusually in low yields, the production of normally gaseous hydrocarbons, such as propanes and butanes, is excessive, and the reduction of catalyst activity is rapid. It has heretofore been necessary to employ at least two stages to convert a petroleum hydrocarbon fraction boilmg above the gasoline range, especially a fraction boiling within the range of from about 375 F. to 500 F., to high octane gasoline. Such processes usually involve a cracking stage wherein a portion of the hydrocarbons are converted to hydrocarbons boiling in the gasoline range, and a reforming, or hydroforming, stage to upgrade the octane rating of the gasoline. In the upgrading stage, the use of two catalysts in separate reactors with a hydrocarbon separation step between the reactors, or the use of two catalysts in a single reactor, has heretofore commonly been required.

An object of this invention is to provide a new and improved catalytic composition effective for converting hydrocarbons.

Another object is to provide a process for converting a hydrocarbon fraction boiling within the range of from about 375 F. to 500 F. to high octane gasoline in a single stage and in good yield.

A still further object is to provide a process for the 7 preparation of a new and improved catalyst.

Other objects and their achievement, in accordance with the invention will be apparent from the following specification.

GENERAL A new catalytic composition has been discovered which gives improved results in converting hydrocarbons. The new catalytic composition contains cerium oxide, chromia, silica and alumina in defined quantities, as hereinafter discussed. It has been found that this new catalytic composition is especially effective in converting relatively high boiling petroleum fractions e.g. a fraction boiling within the range of from about 375 F. to 500 F., to gasoline hydrocarbons of high octane number, and that the normally gaseous hydrocarbons produced in the process are remarkably high in olefinic content, so that such normally gaseous hydrocarbons are especially suitable for subsequent processing in reactions such as polymerization and alkylation.

The reactions involved in the process of the invention are primarily the cracking of the relatively high molecular weight hydrocarbons to hydrocarbons boiling in the gasoline range, and the dehydrogenation of hydrocarbons to produce hydrocarbons of higher octane number, such as the dehydrogenation of naphthenes to produce aromatic hydrocarbons. Hence, the process of the present invention is conveniently designated herein as dehydrocracking. Other reactions, however, are involved and assist in producing the high octane hydrocarbons prepared by the process, such as the isomerization of paraffins to produce more highly branched chain paraflins of relatively high octane number, and cyclization followed by dehydrogenation to produce aromatics from paraflins.

The new catalyst of the invention may be prepared by a variety of means, the general techniques of which are known in the art. It is of primary importance that the limits on the ranges of components of the catalytic composition be observed as hereinafter discussed.

THE CATALYST As above stated, the catalytic composition of the present invention contains cerium oxide, chromia, alumina and silica. It is important that the weight percent, based on the final composition, of each component be within the following ranges: cerium oxide=0.1 to 6, chromia=1 to 12, alumina=6 to 20, silica=62 to 92.

When the quantity of cerium oxide in the catalytic composition is below 0.1% by weight, a substantial loss of octane rating of the gasoline hydrocarbons is observed, whereas in quantities above 6% by weight, excessive coke formation on the catalyst is observed. When the quantity of chromia is below 1% by weight, a substantial loss in octane number of the gasoline product is observed, whereas at concentrations above 12% by weight, conversion of higher boiling hydrocarbons to hydrocarbons boiling within the gasoline range is low. If the quantities of alumina or silica are varied from the stated ranges, the conversion of the high molecular weight hydrocarbons to hydrocarbons boiling in the gasoline range is adversely effected. Accordingly, it is of primary importance that the components of the catalytic composition be within the stated ranges.

PREPARATION OF CATALYST Although the catalytic composition of the present invention may be prepared by various means, it is preferred to first prepare a synthetic silica-alumina composition, and to deposit the remaining components thereon. Synthetic silica-alumina compositions are well known as cracking catalysts, and heretofore described methods for their preparation may be employed in preparing the silicaalumina portion of the present catalyst. For example, the silica-alumina portion of the catalyst may be prepared by impregnating silica with aluminum salts, by directly combining precipitated hydrated alumina and silica, or by joint precipitation of alumina and silica from aqueous solutions of their salts, and by washing, drying, and heating the resulting composition.

The remaining components in the catalytic composition may be deposited on the silica-alumina composition by means known to the art. Impregnation may be accom plished by using solutions of soluble compounds of the metals and is advantageously performed by using aqueous solutions of water soluble salts of the materials. Impregnation may be with the cerium followed by the chromium salt, by the chromium salt followed by the cerium salt, or simultaneously with the same acqueous solution. It is preferred to impregnate silica-alumina with an aqueous solution of both 'a 'ceriumJsalt and a chromium salt, and to dry and calcine the.impregnatedrsilica-alumina to prepare the final composition, since this procedure yields a catalyst of exceptionally high activity in producing gasoline hydrocarbons of .high octane :rating :from higher boiling hydrocarbons. The drying can be performed by any convenient means such as .by heating by .infrared radiation win an oven. Calcinining is performed with the catalyst in contract with an oxidizing gas, such as air, at a temperature .of from about 500 C. to 750 C.

DEHYDROCRACKING The reactions involved in the'presentprocess for converting relatively high boiling petroleum hydrocarbons to gasoline hydrocarbons ofhigh octane rating are primarily dehydrogenation and cracking, and hence the overall process is conveniently designated as dehydrocracking. The gasoline product preferably contains only hydrocarbons having a molecular weight lower than the hydrocarbons of the charge stock, and hence includes only the hydrocarbons which have been cracked in the process.

As above stated, the new catalytic composition of the invention is especially suitable for dehydrocracking hydrocarbon fractions boiling in the range offrom 375 F. to 500 F. to gasoline hydrocarbons of high octane rating, heretofore described processes being unsuitable for this conversion. Accordingly, the use of the present catalyst will be described in terms of this preferred embodiment.

Especially suitable charge stocks are straight-run fractions having a naphthene content .of at least and preferably above 30%, say from about 30% to 75% by volume. Other fractions such as those obtained from catalytic cracking, andrecycle gas oils .in general, .may he used.

In the process, temperatures within'the range of from 450 C. to 540 C. give good results and with the preferred hydrocarbon charge stock .must be observed in .order to obtain suitable conversion without excessive coke formation. The pressure .is preferably maintained at about atmospheric pressure, but super atmospheric pressure up to about 100 p.s.i.g. can be used if desired. The space velocity must be maintained within the range of from about 0.5 to 3. his preferred to employ a'space velocity of from 0.8 to 1.5 since within this range there is obtained a high gasoline yield of high octane number. By space velocity, as used herein, is meant the liquid hourly space velocity, which is the liquid volume of hydrocarbons charged per volume of catalyst per hour.

In carrying out the process of the invention, it is preferred to pass the hydrocarbon charge through a bed of catalyst under the above conditions. By such operation the activity of the catalyst is gradually decreased, principally due to the deposition of carbonaceous materials thereon. Periodic regeneration of the catalyst, such as by discontinuing the operation, flushing the catalyst bed with an inert gas such as steam, flue gas, nitrogen, or the like, and burning off the carbonaceous materials by passing an oxygen containing gas, such as air, through the hot catalyst bed, is advantageously employed. Regeneration is generally advantageously employed at intervals of from about 10 minutes to 2 hours, depending upon the particular operation and reaction variables being used.

Hydrogen is preferably not employed in the process, but a small partial pressure thereof is not deleterious. In some other uses of the present catalyst, however, an atmosphere of hydrogen is advantageous, especially where operation is at superatrnospheric pressure, as hereinafter described.

Example In order to illustrate a preferred catalytic composition of the invention and its use in dehydrocracking, a catalytic composition, in accordance with the invention, was prepared as follows, in which parts" refers to parts by weight:

364 parts of a synthetic silica-alumina cracking catalyst, containing about 13% by weight alumina prepared by coprecipitation and having a cracking activity of about 46, was impregnated with an aqueous solution containing about 7.15 parts of cerous 'nitrate hexahydrate and about 33 parts of ammonium dichromate. A small amount of excess liquid was drained and the impregnated composition dried at about 200 C. for several hours. The dried impregnated composition was then calcined at a temperature of about 650 C. for about 2 hours, a stream of air being passed through the catalyst during the calcination. The resulting composition constitutes a preferred catalytic composition in accordance with the invention and contained in parts by weight, 0.7 part ceric oxide, 4.8 parts chromia, 12.3 parts alumina and 82.2 parts silica. The quantity of the cerium oxide is herein calculated as ceric oxide, but it is realized that a portion of thisoxide may be in the form of cerous oxide.

In order to illustrate the efiicacy of this new catalytic composition for converting hydrocarbon fractions boiling in the range of from 375 F. to 500 F. to high octane gasoline hydrocarbons, a straight-run petroleum hydrocarbon fraction boiling in the range of from about 375 F. to 460 F. was contacted therewith. The following conditions were employed during the contacting: temperature of catalyst=506 C., space velocity=l.0, pressure=atmospheric. The catalyst bed was regenerated after operation for 20 minutes 'by burning carbonaceous materials therefrom with a stream of air as above described. Products were collected over 12 cycles of operation and regeneration.

A yield of gasoline hydrocarbons, i.e., hydrocarbons .from'pentane to those boiling at 350 F. of 25.6% by volume was obtained. There was also obtained 13.7% by volume of hydrocarbons having 4 carbon atoms and 3.34% by weight of hydrocarbons having 3 carbon atoms. The bottoms fractions, i.e., hydrocarbons boiling over 350 F. constituted 50.5% by volume of the charge. Where desired, a .gasoline fraction having a higher end point can be separated from the reaction mixture thereby increasing the observed yield of gasoline. However, it is preferred to maintain the boiling range of the gasoline product below the boiling range of the charge stock.

The gasoline fraction had an octane rating of 99 (ASTM Method D908-53) and an aromatic content of 57% by volume. The hydrocarbons having 3 carbon atoms contained 68% by weight propylene and the hydrocarbons containing 4 carbon atoms contained 45% by weight olefins, principally isobutylene.

If the above example is repeated using, as the catalyst, the silica-alumina composition on which was deposited cerium oxide and chromia in the above example, the octane number of the gasoline product is substantially lower and the olefinic content of the normally gaseous hydrocarbons is lower. For example, in a comparable procedure using the silica-alumina composition as the catalyst, the olefinic content of the butane fraction was found to be only 30.5% by weight, as compared to 45% by weight obtained in the above example.

The foregoing example illustrates a preferred embodiment of the invention, including a preferred catalytic composition and its preferred use in hydrocracking a refractory, relatively high boiling hydrocarbon fraction to gasoline having a remarkably high octane number. The catalyst is also effective to dehydrocrack other relatively high boiling fractions, such as gas oils boiling from about 400 F. to 750 F. or higher, to gasoline.

When other catalytic compositions within the scope of the present invention are employed, substantially equivalent results are obtained, and when other operating conditions are employed within the ranges herein described, substantially equivalent results are obtained. The process may also be operated batchwise or as a moving bed or fluidized process by maintaining the reaction conditions equivalent to those herein described.

The catalyst of the invention can be used in other reactions involving the conversion of hydrocarbons, such as destructive hydrogenation using elevated pressures in an atmosphere of hydrogen, reforming, and the like, in which catalytic conversion conditions known to be effective in such processes give good results.

The invention claimed is:

1. A catalyst for use in the cracking of hydrocarbons consisting of a synthetic silica-alumina composition impregnated with from 1 to 12% by weight, based on the final composition, of chromia and from 0.1 to 6% by weight, based on the final composition, of cerium oxide, wherein the quantity of silica is from 62 to 92% by weight, based on the final composition, and the alumina is from 6 to 20% by weight, based on the final composition.

2. Process for cracking a relatively high boiling petroleum hydrocarbon fraction which comprises contacting said fraction with a catalyst consisting of from 62 to 92% silica, from 6 to 20% alumina, from 1 to 12% chrornia and from 0.1 to 6% cerium oxide under catalytic conversion conditions in the absence of added hydrogen, whereby said hydrocarbon fraction is converted to gasoline of high octane rating.

3. Process according to claim 2 wherein said petroleum hydrocarbon fraction boils within the range of from 375 F. to 500 F.

4. Process of cracking which comprises contacting a petroleum hydrocarbon fraction boiling in the range of from about 375 F. to 500 F. with a catalyst consisting of from 62 to 92% silica, from 6 to 20% alumina, from 1 to 12% chromia and from 0.1 to 6% cerium oxide at a temperature Within the range of from 450 C. to 540 C., a space velocity of from 0.5 to 3, and at substantially atmospheric pressure in the absence of added hydrogen, and recovering gasoline of high octane rating from the reaction mixture.

References Cited in the file of this patent UNITED STATES PATENTS 2,281,919 Connolly May 5, 1942 2,372,165 Arveson Mar. 20, 1945 2,385,326 Bailey Sept. 25, 1945 2,708,180 Fuener et al. May 10, 1955

Claims (1)

1. A CATALYST FOR USE IN THE CRACKING OF HYDROCARBONS CONSISTING OF A SYNTHETIC SILICA-ALUMINUM COMPOSITON IMPREGNATED WITH FROM 1 TO 12% BY WEIGHT, BASED ON THE FINAL COMPOSITION, OF CHROMIA AND FROM 0.1 TO 6% BY WEIGHT, BASED ON THE FINAL COMPOSITION, OF CERIUM OXIDE, WHEREIN THE QUANTITY OF SILICA IS FROM 62 TO 92% BY WEIGHT, BASED ON THE FINAL COMPOSITION, AND THE ALUMINA IS FROM 6 TO 20% BY WEIGHT, BASED ON THE FINAL COMPOSITION.