US2336736A - Conversion of hydrocarbons - Google Patents

Description

Patented Dec. 14, 1943 UNITED STATES PATENT OFFICE CONVERSION OF HYDROCARBONS Elmer R. Kanhofer. Chicago, Ill., ass gnor to Universal Oil Products Company, Chicago, 111., a corporation of Delaware No Drawing. Application August12, 1939,

Serial No. 289,775

8 Claims.

properties and suscept bility to tetraethyl lead,

from gasoline produced by the catalytic cracking of hydrocarbon oils under conditions which yield a product of high olefin content.

Practically all motor fuels, and particularly those produced by the thermal non-catalytic, or catalytic cracking of hydrocarbon oils require some form of treatment to render them of usable quality. Among the methods which have been employed are treatment with various chemicals including sulfuric acid, salts of metals, adsorbents, etc., under varying conditions of temperature and pressure whereby certain desirable properties of the gasoline are improved. The properties aifected by such treatment usually comprise color, color stability, storage stability, gum content and odor. When manufacturing gasolines for use in the automobile industry, the above enumerated refining steps supplemented or supplanted by the use of inhibitors have been found adequate in so far as producing a stable marketable gasoline is concerned.

The use of cracked gasolines in the aviation industry, however, has been generally regarded with disfavor because of the presence in cracked gasolines of monoand di-olefins and similar readily oxidizable substances which, in contact with air, may tend to develop gums. For this reason, the specifications of aviation motor fuels have included tests. such as the acid heat test (A. S. T. M. D481-38T) and the accelerated aging tests with oxygen (U. S. Aeronautical Specifications F-2C), which cannot be met by gasolines containing substantial amounts of olefinic hydrocarbons.

As a consequence, the major source of base fuel for airplane engines has been straight-run gasolines with or without blending agents added thereto. The octane number of these fuels is usually increased by the addition of various quantitles of tetraethyl lead since few gasolines as produced are of sufliciently high octane number to meet aviation requirements.

It is with methods of treating cracked gasolines to produce high yields of motor fuels suitable for use as aviation base gasoline that the present invention is concerned. Such gasolines may be produced by catalytic cracking processes, or by thermal non-catalytic cracking of high boiling hydrocarbon fractions, particularly of petroleum origin. the latter processes being well developed and well-known in the petroleum industry.

One source of low-boiling distillate suitable for treatment according to the present invention is the s'o-called catalytic cracking process, wherein gasoline of high anti-knock value and containing relatively'high percentages of olefinic hydrocarbons may be obtained by, contacting petroleum fractions with a catalytic mass capable of selectively promoting the conversion of high boiling distillates into substantial yields of motor fuel and readily polymerizable olefinic gases. Gasolines produced by catalytic cracking are of particular interest in the present invention, because they usually have higher octane number than gasolines produced by the conventional noncatalytic thermal cracking of hydrocarbon oils, and also the yields of gasoline from catalytic cracking are usually greater than for the noncatalytic process, and their oleflnic content may be higher. a

In one specific embodiment the present invention comprises a process for converting cracked gasoline, and more particularly gasoline produced by the catalytic cracking of hydrocarbon oils, into substantially saturated motor fuel of good antiknock properties and improved stability, by separating said gasoline into a low-boiling fraction having an end-point within the range of approximately 200-250 F., and a higher boiling fraction having an end-point between approximately 300 and 400 F., mixing said low-boiling fraction with hydrogen or hydrogen-containing gas, contacting the mixture withhydrogenating catalysts such as nickel, nickel-copper, copper, chromium, cobalt, iron, molybdenum oxide or nickel thiomolybdate under conditions adequate to effect substantial hydrogenation of the olefins contained in said low-boiling fraction, separately contacting the higher boiling fraction with sulfuricacid' of more than concentration, recovering the separately treated fractions and blending them to produce a finished motor fuel having a low acid heat test and animproved susceptibility to tetraethyl lead.

The gasoline intended for treatment according to the present invention may be obtained by the cracking of hydrocarbon fractions such as kerosene, gas oil, etc., in the presence of a suitable catalytic mass at a temperature within the range of approximately 500-1200 F. and a pressure of substantially atmospheric or slightly uperatmosp erc. say of the order of 50-100 pounds per square inch. Non-catalytically cracked gasolines may also be treated by this method, such gasolines being produced by the cracking of heavy hydrocarbon oil or the reforming of straight-run gasoline or naphtha at a temperature within the range of 800-1100 F. and a pressure of approximately 100-2000 pounds per squar inch. The process differs from ordinary acid treatment in that a reduction of olefin content to a definite limit is desired, while in the usual acid treatment the limit of olefins is higher, since losses are to be avoided as much as possible.

The cracked gasoline is separated into lower and higher boiling fractions prior to treatment according to the present process. The lower boiling fraction which may boil within the range beginning at approximately 90 F. and having an end-point of approximately 200-250 F., contains a relatively large percentage of olefinic hydrocarbons, some paraiiinic hydrocarbons including both straight chain and. cyclic structure, and a relatively minor quantity of aromatic hydrocarbons. The sulfur content of this lower boiling fraction is generally relatively small so that washing with a solution of sodium hydroxide or some other alkali metal hydroxide is usually adequate to remove dissolved hydrogen sulfide, mercaptans, etc., and is the only treatment required to reduce the sulfur content to a low figure. The low-boiling fraction, after treatment to remove sulfur is hydrogenated by mixing it with hydrogen or hydrogen-containing gas, heating to a temperature of approximately 200-450 F., and contacting the mixture with a suitable hydrogenation catalyst, preferably reduced nickel or a mixed copper-nickel catalyst, whereby the olefins present in the fraction are hydrogenated to the corresponding parafiln hydrocarbons without substantially affecting other types of hydrocarbons which may be present. In addition to nickel or copper-nickel, copper, cobalt, iron or chromium as well as molybdenum oxide or nickel thiomolybdate may be used. Since the hydrocarbon fraction is usually low in sulfur content, the life of the hydrogenation catalyst is relatively long because there is not enough sulfur present to poison the catalytic mass until after a reasonably large amount of gasoline has been hydrogenated.

The higher boiling fraction of cracked gasoline contains a relatively smaller amount of olefin hydrocarbons, and a considerably greater amount. of aromatic hydrocarbons than is present in the low boiling fraction. The proportion in which these compounds are present depends on the conditions of cracking, the stock from which it is produced, and the exact boiling range of the fraction. The higher boiling fraction generally contains relatively larger amounts of sulfur-compounds than the lower boiling fraction, and moreover, these sulfur compounds are not as readily removed as those from the lower boiling fraction. It is not, therefore, generally feasible from the standpoint of the quality of the product and the life of the catalytic mass employed to refine and desulfurize the higher boiling fraction by hydrogenation.

When the higher boiling fraction of cracked gasolines are to be used in aviation gasoline, however, it is necessary to remove a part or all of the olefin hydrocarbons present and according to the present invention, this is accomplished by treating the higher boiling fraction of gasoline with a sufficient quantity of relatively concentrated sulfuric acid to effect a substantial reduction in the olefin content thereof. Although concentrations of -100% sulfuric acid or more may be used, the preferred range i of the order of approximately JO-100%. Any suitable method of contacting the gasoline with the acid may be used, and since such methods are well-known, there is no need to describe them in detail.

Contact is preferably carried out at a reduced temperature, for example, within the range of from approximately 0 F.- F., although temperatures below 60 F. are preferred because of undesirable econdary reactions which take place at higher temperatures. The exact amount of acid required will depend to a certain extent upon the amount of unsaturated hydrocarbons present in the fraction and to a certain extent upon the conditions employed in the treating step.

After the contacting is complete, the acid and hydrocarbon mixture are separated and the gasoline fraction is usually neutralized by washing with an alkaline reagent such as sodium hydroxide solution or its equivalent. This treatment may or may not be followed by steam distillation. The reaction involved in the acid treating step are not known with any degree of certainty, becaus of their complexity. The olefin removal may possibly be accomplished by a num ber of ways including solution in the sulfuric acid, polymerization to higher boiling range hydrocarbons, or by alkylation of the aromatics and/or paraflins with the olefins.

The sulfuric acid may be recovered by wellknown methods and reused where this is eco nomical.

The, hydrogenated low-boiling hydrocarbon fraction and the acid-treated higher boiling fraction are blended together to form a substantially olefin-free gasoline of high antiknock value and improved susceptibility to tetraethyl lead. It has been found that this method of treatment has some depreciating effect on the original octane number of the gasoline but the susceptibility to tetraethyl 1ead is markedly improved.

The following example is given to illustrate the usefulness of the invention, but should not be construed as limiting it to the exact conditions or compounds used therein:

'A Mid-Continent gas oil of 355 A. P. I. gravity was contacted in vaporous form with a catalytic mass comprising a major portion of precipitated silica having deposited thereon approximately 10 weight per cent of alumina and 5 weight per cent of zirconia, said mass having been washed substantially free of alkali metal compounds, dried, formed into pellets, and calcined at a temperature of 1500 F. for one hour prior to use as a cracking catalyst. The gas oil was passed over the catalytic mass at a temperature of 950 F. and a pressure of approximately 50 pounds per square inch gage. The gasoline was separated into a fraction boiling within the limits of -200 F. and a fraction boiling at approximately 200300 F. The lower boiling fraction was contacted with 10% by volume of 15 B. sodium hydroxide solution whereby the small amounts of hydrogen sulfide and mercaptan sulfur present were removed. The fraction was then mixed with a hydrogen-containing gas and passed over a hydrogenation catalyst comprising reduced nickel supported on kieselguhr at a temperature of 400 F. and a pressure substantially atmospheric. The fraction was found to be substantially saturated after this treatment as evidenced by the fact that its bromine number had been reduced from approximately 103 to 1.

The high boiling fraction was contacted at a temperature of 20 F. with 10 pounds per barrel of 98% sulfuric acid. The acid sludge was separated and the gasoline fraction was washed with a small amount of water followed by by volume of sodium hydroxide solution. The fraction was combined with the hydrogenated low boiling fraction to produce a gasoline having an octane number of 74 which was increased to 93 by the addition of 6 cc. of tetraethyl lead per gallon. The original catalytically cracked gasoline prior to the treatment of this invention had an octane number of 79.5, which was increased to 87 by the addition of 6 cc. of tetraethyl lead. The olefin content of the final blend was less than 1% of the gasoline, which permitted its meeting specifications as an aviation fuel.

I claim as my invention:

1. A process for treating cracked gasoline which comprises separating said gasoline into a lower boiling fraction having an end-point within the range of approximately 200-250 F. and a higher boiling fraction having an endpoint between approximately 300 and 400 F., the lower boiling fraction being richer in olefins than the higher boiling fraction, mixing said lower boiling fraction with a hydrogen-containing gas, contacting the mixture with a hydrogenating catalyst, under conditions adequate to efiect substantial hydrogenation of olefins contained therein, recovering the hydrogenated fraction; contacting the higher boiling fraction of said cracked gasoline with sulfuric acid in amount and under conditions adequate to effect substantial reduction of the olefin content thereof, recovering the so treated fraction, and blending said hydrogenated low boiling fraction and acid-treated high boiling fractionto produce a substantially saturated motor fuel of high antiknock value.

2. A process for manufacturing motor fuel of high antiknock value and improved susceptibility to tetraethyl lead from cracked gasoline which comprises separating said cracked gasoline into a lower boiling fraction having an end-point within the range of approximately 200-250 F. and. a higher boiling fraction having an endpoint between approximately 300 and 400 F.,

the lower boiling fraction being richer in olefins than the higher boiling fraction, mixing said lower boiling fraction with a hydrogen-containing gas; contacting the mixture with a hydrogenating catalyst under conditions adequate to i effect substantial hydrogenation of the olefins contained in the fraction, recovering the hydro.- genated fraction, treating the higher boiling fraction of said cracked gasoline with relatively concentrated sulfuric acid in amount and under fraction; contacting the higher boiling fraction-- of said olefin-containing distillate with sulfuric acid having a concentration of approximately -100% at a temperature of approximately 0-60 F., the acid being in-sufficient amount to effect substantial reduction in the olefin content of said higher boiling fraction, separating the treated fraction and blending it with the hydrogenated lower-boiling, fraction from the previous step.

6. A process for the catalytic conversion of hydrocarbon oil which comprises contacting said hydrocarbon oil with a catalytic mass comprising essentially a major portion of precipitated silicahaving added thereto a minor portion of a compound selected from the group consisting of alumina, zirconia, and alumina-zirconia, said mass being substantially free of alkali metal compounds, separating the reaction products comprising cracked gasoline, separating the cracked gasoline into a lower boiling fraction of about 200-250 F. end point and a higher boiling fraction of about BOO-400 F. end point, washing said lower boiling fraction of gasoline with a solution of an alkali metal hydroxide, mixing the washed fraction with a hydrogen-containing gas, contacting the mixture with a hydrogenating catalyst under conditions adequate to efiect substantial hydrogenation of the olefins contained therein, recovering the hydrogenated fraction; contacting the higher boiling fraction of said catalytically cracked gasoline with relatively concentrated sulfuric acid under conditions adequate to effect substantial desulfurization and reduction in the olefin content thereof, recovering the treated fraction and blending it with the hydrogenated lower-boiling fraction from the previous step.

7. The process of claim 1 wherein the lower boiling fraction is hydrogenated at a temperature within the range of approximately ZOO-450 F.

8, A process for increasing the stability of cracked gasoline which comprises separating the gasoline into a light fraction of about 200250 F. end-point and of relatively high olefin content and a heavier fraction of about 300-400 F. endpoint and of lower olefin content than the firstnamed fraction, subjecting the light fraction to hydrogenation under conditions adequate to effect substantial saturation of its olefin content,

treating said heavier fraction with sufficient concentrated sulfuric acid to remove a substantial portion at least of the olefins contained therein, and blending the acid-treated heavier fraction with the hydrogenated light fraction.

ELMER R. KANHOFER.