US2867578A - Cracking a hydrocarbon oil with a silica-alumina-chromium oxide-be-ryllium oxide catalyst composite - Google Patents

Description

United States Patent CRACKING A HYDROCARBON OIL WITH A SILICA ALUMINA CHROMIUM OXIDE-BE- RYLLIUM OXIDE CATALYST COMPOSITE Alfred E. Hirschler, Springfield, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey No Drawing. Application December 29, 1954 Serial No. 478,530

' l'Claim. (Cl. 208120) This invention relates to a catalytic composition effective in catalytic processes for converting hydrocarbons. More particularly, this invention relates to new and improved catalytic compositions, their preparation, and to a process for converting hydrocarbons employing the new catalyst wherein a specific hydrocarbon ,fraction, boiling above the gasoline range, is converted to gasoline of high octane rating.

The conversion of various petroleum hydrocarbon fractions by processes such as cracking, reforming, hydroforming, and the like, using a variety of catalysts and. reaction conditions, has been described. Such heretofore described processes, however, are not suitable for converting the hydrocarbon fraction boiling substantially Withinthe 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 rating usually 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 boiling 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 improvedcatalytic composition effective for converting hydrocarbonsp v Another object is to provide a process for converting a hydrocarbonfraction 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 preparationof a new and improved catalyst.

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

General I Alnew catalytic composition has been discovered which gives improved results inconverting hydrocarbon's, The new catalytic composition contains beryllium 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 fromabout 375 F. to 5001F., to gasoline hydrocarbons of high 2,867,578 Patented Jan. 6, i 1959 carbons 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 octane number, and that the normally gaseous hydrothe 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 parafiins to produce more highly branched chain parafiins 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. However, a new method has been discovered which gives an especially effective catalyst. This new method of preparation is described hereinafter.

It is of primary importance that the limits on the ranges of components of the catalytic composition be observed as hereinafter discussed.

The catalyst based on the final composition, of each component be Within the following ranges: beryllium oxide=0.2 to 7, chromia=1 to 12, alumina=6 to 20, silica=61 to 93.

When the quantity of beryllium oxide in the catalytic composition is below 0.2% by Weight, a substantial loss of octane rating of the gasoline hydrocarbons is observed, whereas in quantities above 7% 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 eifecteda 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 maybe 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 pre paring the silica-alumina portion of the present catalyst.

For example, the silica-alumina portion of the catalyst near, '78

determined by a method described by Alexander, Proceedings Am. Pet. Inst. 27 (III) 51 (November 1947).

The remaining components in the catalytic composition may be deposited on the silica-alumina composition by meansknown 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. Impregnation may be with the beryllium salt followed by the chromium salt, by the chromium salt followed by the beryllium salt, or simultaneously with the same aqueous solution. It is preferred to first impregnate silica-alumina with an aqueous' solution of a water soluble beryllium salt, calcine the impregnated composition in contact with an oxidizing gas at atemperature of from about 500 C. to about 750 C., impregnate the calcined composition with an aqueous solution of a water soluble chromium compound, andagain calcine, in contact with an oxidizing gas, the impregnated composition at a temperature of from about 500 C; to about 750 0,, to prepare the final composition, since this procedure yields a catalyst of exceptionally high activity in producing asoline hydrocarbons of high octane rating from higher boiling hydrocarbons.

Dehydrocracking The reactions involved in the present process for convertmg relatively high boiling petroleum. hydrocarbons to gasoline hydrocarbons of high 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 I invention is especially suitable for dehydrocracking hydrocarbonfractions boiling in the range of from 375 F. to 500 F. Accordingly, the use of the present catalyst will be described in terms of this preferred embodiment.

Especially suitable charge stocks are straight-run fractionshaving 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, and recycle gasoils ingeneral, may be used. In the process, temperatures within the range of from 450 C. to 540 C. give good results and with the. pre-l ferred hydrocarbon charge stock must beobserved in order to obtain suitable conversion without excessive coke formation. The pressure is; preferablyymaintained at about atmospheric pressure, but superatrnospheric 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. 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 operatron 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 11130;! the particular operation and reactr'ion variables being use It is preferred to employ a space,

Hydrogen preferably is 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 superatmospheric, pressure.

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:

355 parts of a synthetic silica-alumina cracking catalyst prepared by coprecipitation containing about 13% by weight alumina and having an activity index of about 46, was impregnated Withan aqueous solution containing about 92.3 parts of beryllium nitrate trihydratc. A small amount of excess liquid was drained from the composition. The hnpregnating composition was dried for about 16 hours at 97 C, and calcined at about 504 C. for 2 hours. The calcined composition was cooled and impregnatedwith an aqueous solution containing about 25.8 parts of ammoniumdichromate. A small amount of excess liquid was drained from the composition. The impregnated composition was again dried, as described above, and calcined at a temperature of about 650 C. for about 1 hour, 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, 2.6 parts beryllium oxide, 3.7 parts chromia, 12.2 parts alumina and 81.5 parts silica.

In order to illustrate the etficacy of this new catalytic composition for converting hydrocarbonfractions boiling in the range of from 375 F. to 500 F..to high octane gasoline hydrocarbons, a straight-run petroleum hydrocarbon fraction boiling in therange ofgfrom about 375 F. to 460 F., and having an aromatic content of about 13% by volume and a naphthene content of about 50% by volume, was contacted therewith. The following conditions were employed during the contacting: temperature of catalyst=520 0., space velocity=0;9,7, -pressure=atmospheric. The catalyst bed wasgregenerated after operation for 20minutes by burning carbonaceous materials therefrom with a stream of air-as above described. Products were collected over, 14 cycles of operation and regeneration.

A yield of gasoline-hydrocarbons; i. e;, hydrocarbons from pentane to those boiling at350 F. of 23.8% by volume was obtained. There were also obtained'6.2% by volume percent hydrocarbons-having 4 "carbon atoms and 2.15% by weight of hydrocarbons having 3 carbon atoms. The bottoms fractions, i. e., hydrocarbons boiling over 350 F. constituted 61.9% 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 octanenumber of 99 (ASTM Method D90853) and an aromatic :content of 60% by volume. The hydrocarbons having 3v carbon atoms contained 78.2% by weight propylene andthe hydrocarbons containing 4 carbon atoms contained 55.3% by weight olefins, principally isobutylene.

If the above example is repeated using, as the catalyst, silica-alumina composition on which was deposited beryllium 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, theolefinic content of the butane fraction was found to be only 30.5% by weight, as compared to 57.9% 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 dehydrocracking a refractory, relatively high boiling hydrocarbon fraction to gasoline having a remarkably high octane number in good yield. 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 efiective in such processes give good results.

The invention claimed is:

Process of cracking which comprises contacting a straight run petroleum hydrocarbon fraction boiling in the range of from 375 F. to 500 F. with a catalyst consisting essentially of from 61 to 93% by weight silica, from 6 to 20% by weight alumina, from 1 to 12% by weight chromium oxide and from 0.2 to 7% by Weight beryllium oxide at a temperature within the range of 450 C. to 540 C., a space velocity of from 0.5 to 3 and at substantially atmospheric pressure, and recovering gasoline of high octane rating from the reaction mixture.

References Cited in the file of this patent UNITED STATES PATENTS 2,347,231 Stoewener Apr. 25, 1944 2,375,757 Bates May 15, 1945 2,417,054 Bond Mar. 11, 1947 2,463,508 Bates Mar. 8, 1949 2,518,714 Parker et al. Aug. 15, 1950 2,647,860 Plank et al. Aug. 4, 1953