US2865842A - Cracking of a hydrocarbon oil with a silica-alumina-tungsten phosphate catalyst composite - Google Patents

Description

Alfred E. Hirschler, Springfield, and Edward J. Janoski,

Philadelphia, Pa., assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application December 29, 1954 Serial No. 478,510

1 Claim. (Cl. 208-114) No Drawing.

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 convertinghydrocarbons 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 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 propane 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 improved catalytic compositioneffective 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 tungsten phosphate, 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 therange of from about 375 F. to

500 F., to gasoline hydrocarbons of high octane number,

that the formation of normally gaseous hydrocarbons is nited States Patent ice '2 substantially reduced as compared to heretofore described processes, and that the normally gaseous hydrocarbons produced have a remarkably high olefinic content so that they are especially valuable in processes such as alkylation and polymerization.

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 parafiins of rela- .tively high octane number, and cyclization followed by T catalyst As above stated, the catalytic composition of the present invention contains tungsten phosphate, alumina and silica. It is important that the weight percent, based on the final composition, of each component be within the following ranges: tungsten phosphate=0.5 to 10%, alumina=6 to 20% and silica=70 to 94%. The values herein reported for tungsten phosphate have been calculated for the complex P O -24WO but it is realized that the material so calculated probably exists in the present catalytic composition as a mixture of the designated complex with other complexes between oxides of tungsten and oxides of phosphorus, and that an oxide or oxides of tungsten, as such, may be present in minor quantities. As used herein, tungsten phosphate is used for convenience in designating such compounds, complexes, and mixtures thereof, and includes materials consisting essentially of tungsten, phosphorus and oxygen.

When the quantity of tungsten phosphate in the catalytic composition is below 0.5% by weight, a decrease in the olefinic content of the normally gaseous hydrocarbons is observed, whereas in quantities above 6% by weight, excessive coke formation on the catalyst and excessive .formation. of normally gaseous hydrocarbons are observed. If the quantities of alumina or silica are varied from'the stated ranges, the conversion of the high 'catalyticcomposition' be within the stated ranges.

Preparation of catalyst,

Although the catalyticiccmposition of the present invention may be prepared by various means, it is preferred to first prepare a synthetic silica-alumina composition,

and to depositqthe tungsten phosphate thereon. -Syn thetic"silica-alumina compositions are 'well kno'wnas cracking-catalysts, and heretofore described methods for their preparation'may be employed in preparing the silica alumina portion of the present catalyst. For example,

the silica-alumina portion of the catalyst may bejp repared by impregnating silica with aluminum saltsf 'by directly combining precipitated hydrated alumina' 'aiidi-f silica, or by joint precipitationof' alumina and silicafrorn' 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 efficiency of a catalyst for cracking hydrocarbons and is determined by a method described by Alexander, Proceedings Am. Pet. Inst. 27 (III), 51 (November 1947).

Tungsten phosphate is advantageously incorporated with the silica-alumina composition by impregnating the silica-alumina with an aqueous solution containing a water soluble compound of tungsten and a phosphate. It is preferred to use acids of tungsten and of phosphorus, tungstic acid and orthophosphoric acid being preferred. The impregnating liquid is advantageously made by preparing a mixture of tungstic acid, orthophosphoric acid and water, and heating the mixture, if necessary, to obtain a solution. The solution is then neutralized, preferably with aqueous ammonium hydroxide, and again heated, if necessary, to obtain a solution. On cooling, any insoluble material is removed such as by filtering or centrifuging. An additional quantity of orthophosphoric acid is added to the solution to give a final concentration of the phosphate, as desired, within the hereindefined limits.

After impregnation, any excess liquid is removed and the impregnated silica-alumina composition dried by heating to from about 80 C. to 200 C. for from about 1 to 20 hours and calcined by heating to from about 500 C. to 750 C. for from about minutes to 4 hours in contact with an oxidizing gas such as air. Free acids of phosphorus should not be present in the final composition, and if necessary, the calcined composition should be washed to insure their absence.

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 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 of from 375 F.

to 500 F. to gasoline hydrocarbons of high octane rating, heretofore describedprocesses and catalysts being unsuitable for this conversion. Accordingly, the use of the present catalyst will be described in terms of this.

coke formation. The pressure is preferably maintained at about atmospheric pressure, but superatmospheric pressure up to about 100 p. s. i. g. can be used if desired;

'The space velocity must be maintainedwithin 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 by drocarbons 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:

397 parts of a synthetic silica-alumina cracking catalyst prepared by coprecipitation, and containing about 13% by weight alumina and about 19% water, and having an activity index of about 46, was impregnated with an aqueous solution prepared as follows: a mixture of 436 parts water, 21 parts tungstic acid and 1.8 parts of orthophosphoric acid was heated to the boiling temperature of the liquid and then cooled and neutralized with 28% aqueous ammonium hydroxide. The neutralized liquid was heated to its boiling temperature, cooled, and insoluble material filtered. About 23.8 parts of 85% orthophosphoric acid was added. The resulting solution was used to impregnate the solid silica-alumina composition, after which the impregnated silica-alumina was dried by heating to about C. for about 16 hours and calcined by heating to 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, 4% tungsten phosphate, 12.5% alumina and 83.5% silica. it is important that free acids of phosphorus be absent from the final composition.

In order to illustrate the etficacy 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 fromabout 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=5l2 C., space velocity=l.06, 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 10 cycles of operation and regeneration.

A yield of gasoline hydrocarbons, i. e., hydrocarbons from pentane to those boiling at 350 F., of 26.2% by volume was obtained. There were also obtained 15.2% by volume of hydrocarbons having 4 carbon atoms which contained 40.2% by weight olefins, principally isobutylone. The bottoms fraction, i. e., hydrocarbons boiling over 350 F., constituted 54.6% 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 of the gasoline charge stock.

The gasoline fraction had an octane number of 96.9 (ASTM Method D90853) and an aromatic content of 50% by volume.

If the above example is repeated, using as the catalyst the silica-alumina composition on which was deposited tungsten phosphate in the above example, the quantity of hydrocarbons having 4 carbon atoms produced substantially above 20% by volume, and the olefinic conpreferred to maintain the boiling range product below the boiling range of the tent thereof is only about 30% by weight.

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 efiective 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:

Process of cracking which comprises contacting a straight run petroleum fraction boiling in the range of from 375 F. to 500 F. with a catalyst consisting essentially of, in percent by weight, 70 to 94% silica, 6 to 20% alumina and 0.5 to 6% tungsten phosphate and essentially free of free acids of phosphorus at a temperature within the range of from 450 C. to 540 C., a space velocity of from 0.5 to 3 and a pressure of about atmospheric, and recovering gasoline of high octane rating from the reaction mixture.

References Cited in the file of this patent UNITED STATES PATENTS 2,336,600 Fawcett Dec. 14, 1943 2,378,209 Fuller et al. June 12, 1945 2,463,508 Bates Mar. 8, 1949 2,470,190 Schmerling May 17, 1949 2,496,621 Deery n. Feb. 7, 1950 2,500,197 Michael et al. Mar. 14, 1950 OTHER REFERENCES Ser. No. 390,534, Pier et al. (A. P. C.), published May 18, 1943.