US2865843A - Silica-alumina-chromia-manganese oxide catalyst and hydrocarbon conversion therewith - Google Patents

Description

SILICA ALUMINA- crrRo r MANGANESE OXIDE-CATALYST AND HYDROCARB'ON CON- VERSION rnnnnwrrn Alfred E} Hirschler, spriitg nmai'a Edward J. Janeen, Philadelphia, Pal, assignors to Slim Oil Company, Philadelphia, Pal, a corporation of New Jersey No Drawing. Application January 20', 1955 Serial No. 483,178

6 been. or. 208-120) This invention relates to a catalytic composition efiective in catalytic'p'rocesses 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 describedprocesses, 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 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 boilingabove 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 hydroformin 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 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 manganese 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 fractionbofiing within the range of from about 375 F. to' 500 F., to gasoline hydrocarbons of high octane number, and that the formation of normally gaseous States Patent .thedeliyd'rogenationof naphthenes to produce aromatic hydrocarbons; Hence, the processor the present inven tion is conveniently designated herein as dehydrocracking. Other reactions, however, are involved andassist in producing the high octane hydrocarbons prepared by the process, such as the isomerization ofpa raflins to prdduce more'highly branched chain paraffins of relative- 1y high octane number, and cyclization followed by dehydrogenation to produce aromatics from paraflins'.

The new catalyst of, th'eqin'vention may b'e prepared by a variety of means the general techniques of which are known inthe art. However, a: new method hasbeendiscovered which gives an' espccially etfective catalyst. This new method o fpreparation' is described hereinafter.

It is of primaryimportance that the' limits on the rangeso f components of the catalytic composition be observed as hereinafter discussed.

The catalyst As above stated; the catalyticcomposition of the present" invention contains nranganese oxide, chromia, alumina and silica. It is important that the weightpercent, based on the final composition; or ea-ehcomponent be within the following ranges: manganese oxide=0.5 to 8; chromia=0.5 to' 8; alumina6 to 20; and silica=64 to 93. I The values herein reported for manganese oxide have been calculated for the dioxide (MnO )',-but it is realized that other oxides of manganese may be present. As used herein, manganeseoxide is intended to include the various oxides of manganese and mixtures thereof.

1 When the quantity of manganese oxide in the catalytic composition is below 0.5% by weight, a substantialloss of octane rating of the gasoline hydrocarbons and a decrease in the olefinic content of the normally gaseous hydrocarbons are observed, whereas in quantities above 8% byweight, excessive coke formation on the catalyst is observed. When the quantity of chromia is below 0.5% by weight, a substantial loss in octane number of the gasoline product is observed, whereas at concentrations above 8% 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 component 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 alumiuum salts, by di rectly 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 resulting silica-alumina composition should have an activity index of at least 30, and preferably from 40 to 50. Activity index, as used herein, is a measure of the efiiciency of a catalyst for cracking hydrocarbons and is determined by a method described by Alexander, Proceedings Am. Pet. Inst., 27 (Ill), 51 (November 1947).

Although the remaining components of the catalytic compositions may be deposited on the silica-alumina composition by a variety of means, such as by using solutions of soluble compounds of the metals, the preferred method which gives an especially efiective catalyst is as follows: a synthetic silica-alumina composition is impregnated with an aqueous solution containing a water soluble compound of manganese and a water soluble compound of chromium. The resulting composition is dried such as by heating at a relatively low temperature, say from about 100 C. to 200 C. for from about 1 to hours. The dried composition is then calcined in contact with an oxidizing gas, such as air, at a temperature of from about 500 C. to about 750 C. for several hours, say from about 1 to 6 hours, to form the catalytic composition of the invention. The quantities of the water soluble compounds of manganese and chromium present in the aqueous impregnating solution should be such that the final composition contains the oxides thereof in quantities within the stated ranges.

Other methods of preparation may be employed, such as by first depositing chromia on silica-alumina followed by deposition of manganese oxide, or by first depositing manganese oxide on silica-alumina followed by deposition of chromia.

The foregoing procedure, as has been found, yields a catalyst of exceptionally high activity in producing gasoline hydrocarbons at a high octane rating from higher boiling hydrocarbons.

Dehydrocracking The reactions involved in the present process for converting 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 by drocarbons 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 of from 375 F. to 500 F. to gasoline hydrocarbons of high octane rating, heretofore described processes and catalysts 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 10%, and preferably above say from about 30% to 75% by volume. Other fractions such as those obtained from catalytic cracking, and recycle gas oils in general, may be 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 superatmospheric pres sure 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. It is 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 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, 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:

355 parts of a synthetic silica-alumina cracking catalyst prepared by coprecipitation and containing about 13% by weight alumina and having an activity index of about 46 was impregnated with an aqueous solution containing about 49.3 parts of manganous nitrate and about 16.2 parts of ammonium dichromate in about 264 parts of water. A small amount of excess liquid was drained and the impregnated composition was dried by heating at about C. for about 16 hours. The dried composition was then calcined by heating at about 650 C. for about 2 hours in contact with air.

The resulting composition constitutes a preferred catalytic composition prepared in accordance with the invention and contained in percent by weight, 2.3% manganese oxide, 2.3% chromia, 12.4% alumina, and 83.0% silica.

In order to illustrate the efficacy of this new catalytic composition for converting hydrocarbon fractions boiling in the range of from 375 F. to 500 to high octane gasoline hydrocarbons, a straight-run petroleum hydrocarbon fraction boiling in the range of from about 375 F. to 460 F., 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=492 C., space velocity=0.96, 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 14 cycles of operation and regeneration.

A yield of gasoline hydrocarbons, i. e., hydrocarbons from pentane to those boiling at 350 F., of 30.9% by volume was obtained. There were also obtained 12.4% by volume of hydrocarbons having 4 carbon atoms, which had an olefinic content of 43% by weight consisting principally of isobutylene, and 2.07% by weight of hydrocarbons having 3 carbon atoms. The bottoms fraction, i. e., hydrocarbons boiling over 350 F., constituted 50.6% 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 number of 92.7 (AST M Method D908-53) and an aromatic content of 49% by volume.

If the above example is repeated, using as the catalyst the silica-alumina composition on which was deposited manganese oxide and chromia in the above example, the quantity of hydrocarbons having 4 carbon atoms formed is above 20% by volume, the olefinic content of which is only about 30.5% by weight.

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. The catalyst is also eifective 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 eflfective in such processes give good results.

The invention claimed is:

1. A catalyst for the conversion of hydrocarbons consisting essentially in percent by weight of from 64 to 93% silica, from 6 to 20% alumina, from 0.5 to 8% chromia and from 0.5 to 8% manganese oxide.

2. A catalyst for the conversion of hydrocarbons consisting essentially of a synthetic silica-alumina composition impregnated with fro-m 0.5 to 8% by weight, based on the final composition, of chromia and from 0.5 to 8% by weight, based on the final composition, of manganese oxide, wherein the quantity of silica is from 64 to 93% by weight, based on the final composition, and the alumina is from 6 to 20% by weight, based on the final composition.

3. Process for the preparation of a catalyst for use in the conversion of hydrocarbons which comprises impregnating a synthetic silica-alumina composition having an activity index of from 30 to with an aqueous solution of manganous nitrate and ammonium dichromate, drying the resulting composition and calcining the dried composition in contact with air at a temperature of from about 500 C. to about 750 C., wherein the concentration of manganous nitrate in said aqueous solution is sufficient to give a concentration of manganese oxide of from 0.5 to 8% by weight in the final composition and wherein the concentration of ammonium dichromate in said aqueous solution is suflicient to give a concentration of chromia of from 0.5 to 8% by weight in the final composition.

4. Process for converting a hydrocarbon fraction boiling above the gasoline range which comprises contacting said fraction with a catalyst consisting essentially of from 64 to 93% silica, from 6 to 20% by weight alumina, from 0.5 to 8% by weight chromia and from 0.5 to 8% by weight manganese oxide under catalytic conversion conditions whereby said hydrocarbon fraction is converted to gasoline of high octane rating.

5. Process according to claim 4 wherein said hydrocarbon fraction boiling above the gasoline range boils within the range of from 375 F. to 500 F.

6. Process of dehydrocracking which comprises contacting a petroleum hydrocarbon fraction boiling in the range of from 375 F. to 500 F. with a catalyst consisting essentially of from 64 to 93% by weight silica, from 6 to 20% by weight alumina, from 0.5 to 8% by weight chromia and from 0.5 to 8% by weight manganese 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 2,078,951 Houdl'y May 4, 1937 2,325,287 Thomas July 27, 1943 2,351,793 Voorhees June 20, 1944 2,385,326 Bailey Sept. 25, 1945 2,401,246 Hull May 28, 1946 2,463,508 Bates Mar. 8, 1949 2,647,860 Plank et a1. Aug. 4, 1953

Claims (2)

1. A CATALYST FOR THE CONVERSION OF HYDROCARBONS CONSISTING ESSENTIALLY IN PERCENT BY WEIGHT OF FROM 64 TO 93% SILICA, FROM 6 TO 20% ALUMINA, FROM 0.5 TO 8% CHROMIA AND FROM 0.5 TO 8% MANGANESE OXIDE.

4. PROCESS FOR CONVERTING A HYDROCARBON FRACTION BOILING ABOVE THE GASOLINE RANGE WHICH COMPRISES CONTACTING SAID FRACTION WITH A CATALYST CONSISTING ESSENTIALLY OF FROM 64 TO 93% SILICA, FROM 6 TO 20% BY WEIGHT ALUMINA, FROM 0.5 TO 8% BY WEIGHT CHROMIA AND FROM 0.5 TO 8% BY WEIGHT MANAGANESE OXIDE UNDER CATALYTIC CONVERSION CONDITIONS WHEREBY SAID HYDROCARBON FRACTION IS CONVERTED TO GASOLINE OF HIGH OCTANE RATING.