US2206921A - Process for desulphurization of hydrocarbons - Google Patents

Description

y 9, 1940- w. A. SCHULZE I 2,206,921

PROCESS FOR DESULPHURIZATION OF HYDROCARBONS Original Filed Oci. 6, 1936 HEATED v DESULFURIZED GASOLINE GASOLINE VAPORS TO STORAGE u- N CATALYST CHEMICAL TOWER TREATIN 6 UNIT on FRACTIONATING UNIT INVENTOR. w. A. SCHU LZE BYLLM-M m A TTORNEYS.

Patented July 9, 1940 UNITED STATES,

PROCESS FOR DESULPHURIZATION OF HYDROCARBONS Walter A. Schulze, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation oi. Delaware Application October 6,

1936, Serial No. 104,304

Renewed July 1, 1939 3 Claims.

This invention relates to the treatment of hydrocarbons and relates more particularly to catalytic methods of treating petroleum fluids such as straight run and cracked gasolines, pressure 5 distillates, naphthas, polymerized gasolines and natural gasolines, such petroleum fluids being referred to hereafter as gasoline stock.

Applicants co-pending application Serial No. 104,303 relates to reducing poisoning of catalysts, and Serial No. 104,306 relates to catalytic treatment of oils with a bauxite catalyst.

In a more specific sense an object of this invention is a process for treating such potential motor fuel components in the vapor form over a catalytic material to remove the organic sulphur compounds which are so deleterious to the octane number and lead response of such fuels.

Another object of the invention is a process for treating gasoline stock in the vapor form over a catalytic material to reduce its sulphur content and simultaneously increase its octane number, improve its antiknock characteristics and otherwise produce desirable refining effects.

A further object of this invention is the marked improvement in quality of the gasoline stock with only a small decrease in volume of product boiling within the same range as the untreated oil. This is in contradistinction to the large losses which occur in such conventional operations as thermal reforming of such oils.

A still further object of the invention is the production under certain conditions of a gasoline stock with both a higher specific gravity and a higher octane rating than the untreated stock, whereas cracking of oils in the established manner produces higher octane products but of lower specific gravity.

Another object of the invention is the production under certain conditions of a by-product gas 40 relatively rich in hydrogen, such gas being quite useful in hydrogenation processes as well as for many other purposes.

It is well known that motor fuel specifications call for much higher octane ratings now than 45 formerly, and gasoline stocks are being subjected to extensive refining and reforming operations in order to meet these more rigid specifications. Since the advent of Q" gasoline several years ago, large quantities of tetraethyl lead, also, have 50 been added to gasolines to raise them to 70 octane number, the rating of the average house-brand gasoline at the present time. All of these practices are quite expensive.

More recently certain results showing the 55 deleterious efiects of impurities of the sulphur type on the octane number and lead response of motor fuels were published in an article by Schulze and Buell (Oil and Gas Journal, vol. 34, No. 21, p. 22 (1935)). Organic sulphur compounds of dif- 60 ferent types exist in varying percentages in all gasoline stocksand are present in unusually large amounts in those from West Texas and certain other regions. The form of combination of the sulphur also varies, e. g., mercaptans, alkyl sulphides, thiophenes and thiophanes. Some of these compounds are much more deleterious than others to the octane number and lead response of the motor fuels; hence the magnitude of the reduction in sulphur content may or may not be a criterion of the improvement. in antiknock characteristics.

Schulze and Buell in an application, Serial No. 756,142, filed December 5, 1934, describe certain catalytic processes for removing these impurities from sulphur bearing petroleum oils, thereby obtaining marked improvement in octane number and lead response of such products as natural gasoline and refinery straight run, cracked and vapor recovery gasolines.

I have now discovered a rather superior catalytic material for efiecting the decomposition of the deleterious organic sulphur compounds in hydrocarbon oils and gases. Solid adsorbent catalytic material consisting of zirconium oxide either alone or in admixture with alumina causes rapid decomposition of mercaptans, organic sulphides and the like to hydrogen sulphide when hydrocarbon vapors containing such impurities are passed over these contact masses. The zirconium oxide may be synthetically prepared or the naturally occurring minerals may be used, the latter not being quite as eiiective as the former. The zirconium oxide gel may, if desired, be mixed with other metallic oxides or impregnated with solutions of salts which may be subsequently reduced to the oxide form.

A typical process for simple desulphurization of gasoline stock consists in contacting the gasoline stock in vapor form at a temperature in the range of about 500 to 800 F. which eliminates a part or all of the sulphur from mercaptans, alkyl sulphides, etc., as hydrogen sulphide. The hydrocarbons are then freed of hydrogen sulphide by a caustic wash or other suitable means. Completely sweetened products can be obtained in this manner. The following example is given as merely illustrative of the results obtained by this invention and shall in no sense be interpreted as a limitation of. the invention.

Composite cracked gasoline from Panhandle topped crude was contacted with zirconium oxide catalyst at a temperature of 735 F. and a flow rate of about three liquid volumes per hour per volume of catalyst. For comparative purposes, another portion of the gasoline was treated under similar conditions with bauxite. A considerable improvement in lead response resulted with the bauxite treatment but the zirconia gave even a greater one. The decomposed impurities were removed in each instance prior to determination of octane ratings.

One form of apparatus in which my desulphurization process may be carried out is illustrated in the drawing, Figure 1. In this drawing the catalyst tower l containing the mass of catalyst receives the heated raw gasoline vapors from a vaporizing and heating device not shown. After passage through the catalyst the treated vapors may be sent to the chemical treating unit 2. (2 may instead be a fractionating unit for in either case the function of this part of apparatus is the removal of hydrogen sulphide formed in the desulphurization reaction.)

I have discovered also that still greater improvement in antiknock characteristics can be obtained when the gasoline stocks are treated under the conditions specified below. In addition to the removal of the organic sulphur impurities which are so deleterious to the octane number and lead response of the gasoline stock, or the motor fuel made therefrom, certain reactions which involve still other deleterious impurities and/or low octane number compounds are made to take place while in contact with catalysts comprising zirconia; therefore, the treated product has an octane number considerably higher than that produced merely by the removal of the organic sulphur.

In one specific embodiment of this process which yields the combined advantages noted above, the gasoline stock is passed in the vapor form over a well dehydrated zirconium oxide catalyst at a temperature in the range of about 900 F. to 1200 F. and at a flow rate of 1 to 100 liquid volumes per hour per volume of catalyst. For example, at a temperature of 1000" F. to 1025 F. the preferred flow rate is of the order of 1 to 10 liquid volumes per hour per volume of catalyst. At higher temperatures shorter contact times are sufficient; therefore, flow rates as high as 100 liquid volumes per hour per volume of catalyst may be employed.

I have discovered that in treating gasoline stocks in the vapor form over zirconia catalyst there are specific temperature ranges for the reactions involving the decomposition of those compounds responsible for the low octane rating of the gasoline. As stated above, at temperatures of 500 to 800 F. the organic sulphur compounds such as mercaptans, alkyl sulphides, etc., are decomposed into hydrogen sulphide without any substantial decomposition of the hydrocarbon constituents, at temperatures in the range of 800 to 900 F. there is little or no additional improvement in octane number over that obtained in the simple desulphurization treatment, but at temperatures above 900 F. a second series of reactions takes place as evidenced by the formation of large quantities of hydrogen gas and by the marked increase in octane number of the treated gasoline stock.

This marked improvement in octane number which results from the treatment at temperatures above 900 F. is not due to cracking in the usual sense of the word, since in the absence of the zirconia catalyst and under otherwise similar conditions of temperature and contact time there is no appreciable change in the characteristics of the gasoline stock. Furthermore, the improvement which results from the treatment with zirconia catalysts under the conditions mentioned is not due to an accelerated reforming similar to that occasioned by the presence of adsorbent porous material sometimes referred to as material of the clay type. For example, when the same gasoline stock is contacted at these temperatures above 900 F. with fullers earth under identical conditions of temperature, pressure and contact time the improvement is almost nil as compared with that obtained with the zirconia catalysts.

In the operation of this process high pressures are not needed, extremely good results being obtained in the range of atmospheric to 100 pounds. Higher or lower pressures may of course, be employed wherever economic conditions warrant them. In practice it is usually desirable to use pressures somewhat above atmospheric so that the vapors can be conducted directly to a fractionator or to treating tanks for final processing.

Following the treatment of the vapors over the catalyst the decomposed impurities and light gas fraction are separated from the gasoline hydrocarbons by fractional condensation or any other conventional means. If desired, the uncondensed light gas fraction may be passed through a vapor recovery plant of the absorption or other conventional type whereby the hydrocarbons other than methane may be recovered and made useful for other purposes. Also the decomposed impurities may be removed by chemical means in a step apart from that of removal of the hydrogen and low boiling hydrocarbons from the gasoline hydrocarbons.

A typical example of the operation of this process above 900 F. is given as illustrative of the results which have been obtained in the treatment of various gasoline stocks, but this example is in no sense to be interpreted as limiting the invention.

Refinery high end-point straight run gasoline from Panhandle crude oil was contacted in the vapor form with dehydrated zirconia catalyst maintained at a temperature of 1000 F. and a flow rate of about 2 volumes of liquid gasoline per hour per volume of catalyst. After removal of the decomposed impurities and the light gas fraction by fractionation or any other conventional means the following remarkable improvement was noted.

Before After treatment treatment A. S. T. M. octane number (0 cc. TEL). 46.8 57.3

A. B. T. M.octane number with 1.0 cc. TEL. 55. 7 67.9

A. S. T. M. octane number with 2.0 cc. TEL- 60. 9 73. 7

A. S. T. M. octane number with 3.0 cc. TEL 65. l 76. 8

Reid vapor pressur 7. 80 9. 75

Unsaturation-... .mol percent. 0. 2 6. 4 Engler distillation:

10% evaporated F. 156 151 50% evaporated F. 255 246 95% evaporated .F. 394 395 The fixed gas formed during the treatment of this gasoline amounted to 235 cu. ft. (S. T. P)

cent. The hydrogen amounted to i68cubic feet per barrel of gasoline and the methane to 34 cubic feet, a hydrogen to methane ratio of 4.9. The gas loss calculated as weight per cent of the The total loss in volume of gasoline boiling within the same range as the untreated was about 3 per cent. By this treatment the gasoline was made into a 70 octane numbermotor fuel merely by adding 1.33 cc. of tetraethyl lead (TEL) per gallon whereas the untreated gasoline made only a 65 octane number motor fuel with the addition of 3 cc. tetraethyl lead (TEL) per gallon.

I have found that in the treatment of gasoline stocks in the vapor form over zirconia catalysts in the temperature range of 900 to 1200 F., as

shown in the example given above, considerable dehydrogenation of the hydrocarbons occurs. There is only a very slight amount of cracking, as evidenced by the small proportion of methane in the gas, providing, of course, the temperature and contact time are properly chosen, since it is obvious that substantially long contact times at temperatures of 1100 F. and above will produce cracking. With proper choice of the temperature and contact time, however, it is possible by means of this invention to substantially avoid the formation of methane and other products of cracking. Hydrogen to'methane ratios as high as 30 to 1, and sometimes higher, can readily be obtained.

I have found that although dehydrogenation of certain of the hydrocarbons occurs during the treatment of gasoline stocks with zirconia catalysts at temperatures above 900 F., this dehydrogenation is only one of several reactions taking place. It is evident from the results such as those given above that 'an improvement of 19.5 octane numbers could not have resulted merely by the conversion of 6.5 per cent of saturated aliphatic hydrocarbons to simple unsaturated hydrocarbons of the olefin type. Neither can it be accounted for on the basis of the amount of hydrogen formed. While I am not certain of the exact changes which occur during this treatment of gasoline stocks over a catalyst of the peculiar nature of zirconium oxide, I believe the remarkable improvement in octane number results from several concurrent reactions, namely, (1) decomposition of deleterious organic sulphur compounds to hydrogen sulphide'which may .be removed, (2) decomposition and subsequent removal of impurities other than the sulphur type, (3) dehydrogenation of hydrocarbon constituents, and (4) changes in molecular structure of certain of the hydrocarbons. The extent of the improvement from each of these sources varies,

of course, with the gasoline stock being treated.

In the practice of the present invention the zirconium oxide or the zirconialike material is crushed to a suitable size, usually to 30 mesh. If desired it may be diluted with active or inactive substances. Particularly active catalytic masses may be prepared from intimate mixtures of zirconia and alumina gels. Either one of these gels impregnated with a salt solution of the other gives on drying and on conversion of the salt to the oxide form a very' satisfactory catalyst. Bauxite impregnated with a solution of am- 3 conium salt. usually convertedto the oxide in a subsequent step. has high activity.

synthetic zirconium hydroxide gel usually contains a large proportion of water which is driven oil by heating at elevated temperatures. In the practice of my process for the treatment of gasoline stocks to obtain desulphurization, dehydrogenation and the like concurrently, best results are obtained with rather thoroughly dehydrated zirconia catalysts. The first step in this process usually conslstsptherefore, in dehydrating the zirconia, preferably in situ, by raising the temperature gradually to the temperature of operation or higher while a slow stream of air or hy-' drocarbon gas is passed over it. Vacuum drying may be done, if desired. This step of passing air or hydrocarbon gas over the catalyst can obviously be omitted in practice, and the gasoline vapors started immediately over the zirconia. Much of the improvement in the gasoline stock will be lost, of course, during the first few hours of operation in this manner, or until the workingtemperature has been reached and the catalyst has been dehydrated.

It has been found that the zirconia catalysts gradually lose their catalytic activity with use but they may be reactivated indefinitely by burning out the carbonaceous residues in situ with steam and air, or an oxidizing gas, or by recycled through the system by adding such gas,

or a, portion of it, to the gasoline vapors prior to passage over the catalyst. Such hydrogen gas should, of course. not be allowed to pyramid too much or the reactions may be unfavorably influenced. Also in processing gasoline stocks containing appreciable quantities of sulphur compounds, the hydrogen sulphide should be removed" from the gas prior to recycling.

Obviously the hydrogen gas produced as a by-product in my process has considerable economic value. A gas containing up to 95 per cent hydrogen and the balance methane can be readily obtained by applying simple extraction methods for the removal of the small amount of hydrocarbons higher than methane. Concentrations of hydrogen higher than 95 per cent can be obtained by more elaborate extraction methods. In any event hydrogen for hydrogenation and/or other purposes can be obtained in this treatment of gasoline stocks over zirconia catalysts at extremely low cost. A very distinct advantage of my process is the formation of relatively large quantities of hydrogen from such hydrocarbons as those of the aliphatic series with methane being the only impurity in appreciable amount. Obviously this gas can be utilized for many purposes where the more common mixture of hydrogen and carbon monoxide cannot be tolerated at any cost.

If desired, the gasoline stock vapors may be given two or more successive treatments with the zirconia catalytic material in a series of catalyst towers, or the vapors or any fraction thereof may be recycled with the fresh vapors through the catalyst tower. Some additional heat, also, may be supplied to the vapors prior to the second and/or successive catalytic treatments.

The gasoline stocks after treatment at desulphurizing temperatures of 500 to 800 F. may or may not need a subsequent treatment to remove colored and gum forming constituents. At temmake them suitable as motor fuel.

it is of generally wide application and the number of examples oi. results obtainable by its use might be multiplied greatly neither is to be construed as imposing limitations upon the scope of the invention. The term gasoline stocks as used herein includes natural gasolines, refinery straight run, cracked and vapor recovery gasolines, polymerized gasolines, naphthas, pressure distillates,

and/or mixtures or blends of any two or more of these or of similar hydrocarbon mixtures. Light gases associated with such stocks may be treated along with the hydrocarbons boiling within the gasoline range, or, ii desired, such gases may be treated alone.

I claim as my ivention:

l. The process or desulphurizing a gasoline stock containing organic sulphur compounds as impurities, comprising contacting the said gasoline stock in the vapor form at a pressure between atmospheric and pounds per square inch with a zirconium oxide catalyst at a temperature in the range of 500 to 800 F. and a flow rate equivalent to about three liquid volumes of gasoline stock per hour per volume of catalyst, whereby a substantial proportion of the organic sulphur compounds are decomposed into hydrogen sulphide without any substantial decomposition of the hydrocarbon constituents, separating the hydrogen sulphide from the gasoline stock, and thereby obtaining a gasoline stock with a lowered sulphur content and improved response to tetraethyl lead.

2. The process of sweetening a gasoline stock containing organic sulphur compounds of the mercaptan type, comprising contacting the said gasoline stock in the vapor form at a pressure between atmospheric and 100 pounds per square inch with a zirconium oxide catalyst at a temperature in the range of about 500 to 800 1". and a flow rateequivalent to about three liquid volumes 0! gasoline stock per hour per volume of catalyst, whereby the mercaptans are converted into hydrogen sulphide, separating the hydrogen sulphide from the gasoline stock, and thereby obtaining a sweetened gasoline stock.

3. The process of desulphurizing a gasoline stock containing organic sulphur compounds as impurities, comprising contacting the said gasoline stock in the vapor form at a pressure between atmospheric and 100 pounds per square inch with zirconium oxide catalyst at a temperature in the range oi. about 500 to 800 F. for a period of time sufficient to cause decomposition of a substantial proportion of the organic sulphur compounds into hydrogensulphide but insuillcient time to cause any substantial decomposition of hydrocarbon constituents, separating the hydrogen sulphide from the gasoline stock, and thereby obtaining a gasoline stock with reduced sulphur content and improved response to tetraethyl lead.

WALTER A. SCHULZE.

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