US3546098A - Making a lube oil by hydrocracking and solvent extraction - Google Patents

Description

United States Patent O 3,546,098 MAKING A LUBE OIL BY HYDROCRACKING AND SOLVENT EXTRACTION Byron G. Spars, Mill Valley,'Calif., assiguor to Chevron Research Company, San Francisco, Calif., a corporation of Delaware No Drawing. Filed July 24, 1968, Ser. No. 747,101

Int. Cl. Cq 37/00 U.S. Cl. 208-96 11 Claims ABSTRACT OF THE DISCLOSURE A process for the production of lubricating oil which is stable in ultraviolet light, which comprises hydrocracking a heavy oil under specified conditions to produce a lubricating oil fraction and then treating the fraction with anhydrous or aqueous N,N-dimethylformamide or dimethylsulfoxide to produce an ultraviolet-light-stable lubricating oil. Treating conditions are specified. High yields of stable oil are obtained.

BACKGROUND OF THE INVENTION This invention relates to processes for the production of lubricating oils. More particularly, it relates to processes for the production of stable lubricating oils by hydrocracking and treating with selective extractants.

Lubricating oils, which can be defined in general as those hydrocarbon materials which boil above 600 F., are presently produced by two principal methods. The first, which produces straight-run lubricating oils, may include steps of distillation of a crude oil, solvent refining, solvent dewaxing, acid treating and clay contacting. Solvent refining is generally employed to separate the lubricating oil components from the other components of the distilled oil.

The second method is somewhat similar to the first but substitutes mild hydrofining or hydrofinishing for one or more of the steps of solvent refining, acid treating or clay contacting. Hydrofining or hydrofinishing is a process wherein the contaminants in the crude distillate are converted, by contacting with hydrogen in the presence of a hydrogenating catalyst, to easily removable or harmless species. Only minimal cracking occurs during hydrofining.

Recently it has been discovered that lubricating oils may also be produced by hydrocracking. In this process, a heavy petroleum oil is contacted with hydrogen at elevated temperature and pressure in the presence of a hydrocracking catalyst; and the hydrocracked product (which is often termed the hydrocrackate) is separated, usually by distillation, into materials boiling in different temperature ranges. One or more of these materials will boil within the lubricating oil boiling range.

It has now been found that lubricating oils produced by hydrocracking, although having many desirable properties not otherwise obtainable by straight-run processing, also possess to a significant degree one undesirable property which had previously been noted only to an insignificant degree with straight-run lube oils. This undesirable property is the instability of hydrocracked oils when exposed to ultraviolet light in the presence of air. This instability is evidenced by the formation of a precipitate in the oil after a short period of exposure to ultraviolet light. Such a precipitate is undesirable, not only because it may prove detrimental to the lubrication function which the oil is designed to perform, particularly in high-performance oils such as turbine oils, but also because it reduces the esthetic value of what would otherwise be a clear, premium-quality oil. The latter is not a trivial consideration; refiners have learned through experience that consumers will not buy lubricating oils which contain visible precipitates even though those precipitates might have no adverse effect on the performance qualities of the lubricating oil.

In the past, it has been known that certain types of lubricating oil instability, such as oxidation instability, could be prevented by treating the oil with any of a number of polar solvents, such as phenol, furfural and sulfuric acid. The acid treating of straight-run oils referred to above is such a treating process. While this treatment tends to remove the ultraviolet instability-causing components, it is unselective, i.e., it has the disadvantage that it also removes a considerable portion of the desirable lubricating oil components along with the undesirable components. Such indiscriminate removal occurs by either or both solvent extraction or chemical reaction with certain components of the oil (e.g., when sulfuric acid treating results in sulfonation of some oil components). Until now, it has been believed that treatment of any oil with any of the polar solvents produced approximately equivalent results; i.e., low yield of a moderately stable oil. Further, since ultraviolet instability was an insignificant problem with straight-run oils, solvent treating was only sparingly used in order to avoid the problem of resulting low yields. Such a solution is not satisfactory, however, for hydrocracked oils where the problem of ultraviolet instability is a very significant one.

It has been known for some time that N,N-dimethy1- formamide (hereinafter referred to as DMF) and dimethylsulfoxide (hereinafter referred to as DMSO) were useful as extractives to remove aromatic compounds from mixtures of aromatics and paraflins. This extraactive ability has heretofore been believed to be restricted to the ability to make only gross discriminations between aromatics and parafiins. Consequently, since it is thought that ultraviolet light instability is due to the presence in the oil of only certain species of aromatics, it has been believed that DMF and DMSO suffer from the same disadvantage as the other polar solvents mentioned above.

SUMMARY OF THE INVENTION I have now unexpectedly discovered that under the conditions found in the process of this invention DMF and DMSO exhibit selective extractive ability and remove essentially all the instability-causing compounds, leaving a high yield of ultraviolet light stable oil. Broadly stated, this invention comprises contacting in a hydrocracking zone a liquid hydrocarbon feedstock containing a substantial portion of components boiling above 750 F. with hydrogen in the presence of a hydrocracking catalyst at an elevated temperature and pressure in order to convert at least 15 weight percent of said feedstock components boiling above 750 F. to materials boiling below 750 F., recovering from the effluent of said hydrocracking zone a lubricating oil fraction boiling above 600 F., contacting said lubricating oil fraction in contacting apparatus with a treating agent comprising a selective ex tractant selected from the group consisting of N,N-dimethylformamide, dimethylsulfoxide, aqueous solutions of N,N-dimethylformamide, and aqueous solutions of dirnethylsulfoxide, and recovering from the effiuent of said contacting apparatus a lubricating oil with an improved ultraviolet light stability. 7

Treating is conducted at temperatures of 0250 F, and pressures of about atmospheric up to about 10 atmospheres. Room temperature and pressure of about 0-100 p.s.i.g. are preferred. Treating may be single stage or multistage. Solvent-to-oil ratios are 0.255.0 volumes of solvent per volume of feed. Use of this treating step allows production of highly stable oil in yields of or greater.

3 DETAILED DESCRIPTION OF THE INVENTION The process of this invention is a process for producing hydrocracked lube oils which are stable in the presence of ultraviolet light. Any hydrocarbon oil having a substantial portion boiling above 750 F. may be hydrocracked in this process and converted to lubricating oil. Preferred feeds are lubricating oil stocks boiling above 900 F., although crude oils, reduced crudes, residual oils, deasphalted oils, and the like, may also be used.

The hydrocracking step in this process is operated at a pressure in the range of from about 500 to about 5,000 p.s.i.g., a temperature in the range of 720850 F., a liquid hourly space velocity (LHSV) in the range of from about 0.2 to about 10.0 and a hydrogen throughput rate in the range of from about 1,000 to about 20,000 s.c.f./ bbl. More preferred conditions, which produce a higher yield of lubricating oils, are a pressure of l,5003,000 p.s.i.g., a temperature of 750-830 R, an LHSV of 0.5 2.0 and a hydrogen throughput rate of 5,000-l0,000 s.c.f./bbl. I

A critical element in the invention is the conversion of at least weight percent of the materials boiling above 750 F. to materials boiling below 750 F. by hydrocracking at elevated temperatures in the range of 720-850 F., and preferably 750-830 F. If the temperature is below 750 F., the effect of DMF and DMSO treating is lessened. This is believed due to the nature of the instability-causing components which appear to be certain polynuclear aromatic compounds. At the lower temperatures, one or more rings of each of the polynuclear aromatic molecules will become saturated; and it is believed that in this partially or fully saturated form the compounds are less susceptible to extraction by DMF and DMSO. Conversely, if the temperature of conversion is above 850 F., catalytic hydrocracking is minimized and the predominant reaction is thermal cracking. The actual operating temperature will depend on the type of feed processed and its viscosity index, the viscosity index of the lubricating oil product desired, and the degree of conversion required to produce the desired viscosity index increase. It is usually found that feedstocks which contain higher proportions of aromatics require higher degrees of conversion which may be accomplished by hydrocracking at a high temperature, low space velocity, or any combination of relatively more severe conditions within the acceptable ranges described above.

Hydrocracking may be accomplished in a single hydrocracking reactor, particularly when the feed to be treated requires only a small amount of conversion to produce a lube oil suitable for DMF and DMSO treating. However, many of the common high boiling oil feeds require a large amount of hydrocracking to produce acceptable lube oils. Consequently, when a high degree of conversion (e.g., more than 60 percent) is desired, it is preferred to use two or more hydrocracking reactors in series. This permits the hydrocracking process to be operated with considerable flexibility, for each reactor can be operated at somewhat below its maximum conversion potential, thus avoiding severe conditions of temperature, pressure and space velocity which put an unnecessary strain on the process equipment and shorten the useful life of the hydrocracking catalyst.

The catalyst used in the hydrocracking reactors may be of the sulfactive hydrogenation type commonly used for desulfurization and denitrification. Suitable catalysts include combinations of the Group VI and Group VIII metals, oxides or sulfides associated with porous refractory oxide carriers. The most suitable metal are nickel or cobalt in combination with molybdenum or tungsten as sulfides. The refractory oxide may be alumina; but usually, to provide more hydrocracking activity, there is employed a combination of alumina with silica, magnesia, titania and other like materials or combinations of such other oxides-for example, silica-magnesia. Such catalysts can be prepared in a number of ways, including preparing the porous carrier first and then impregnating it with solutions of the metal compounds which are later converted to metal oxides by calcining. Particularly good catalysts for use in the hydrocracking step can be prepared by coprecipitation or cogelation techniques wherein all of the components are initially supplied as dissolved compounds in aqueous solutions and coprecipitated together. Zeolitic-supported hydrocracking catalysts may also be used.

As noted earlier, ultraviolet light instability is evidenced by the formation of a visible precipitate in the oil. The degree of stability possessed is determined by the relative amount of time required for the precipitate to form. One obvious way to measure this degree of stability is to expose the oil to the ultraviolet light in sunlight and observe the number of days required for the precipitate to form. This, however, is an unsatisfactory procedure for two related reasons; First, natural ultraviolet light is not concentrated, so the oils usually require several weeks or months of exposure before any precipitate forms. Secondly, over this period of time, the daily exposure is not uniform, for the daily amount of sunlight varies with the time of year and the weather on any particular day. Consequently, in order to measure ultraviolet stability rapidly and reliably, the following test has been developed: A 5 ml. sample of the oil in a clear glass container is exposed to a 450 watt mercury vapor ultraviolet light (type L) placed in a closed cabinet with the oil sample and with a distance of 2 inches between the oil sample and the light source. Light neutral oils which form a precipitate in less than four hours exposure are considered to be too unstable to be commercially acceptable. Oils which form precipitates in more than four but less than ten hours are considered reasonably stable and marginally acceptable, although inferior, while those which require more than ten hours exposure before precipitation are considered of premium quality.

The contacting of the oil and treating agent occurs in what, for convenience, will herein be termed the stabilization step. The stabilization step, as defined in this process, may be a single contacting step or a plurality of contacting steps in series. In general, the single step procedure is preferred. The treating agent, as defined in the claims, comprises an extractive selected from the group consisting of N,N-dimethylformamide, dimethylsulfoxide, aqueous solutions of N,N-dimethylformamide, and aqueous solutions of dimethylsulfoxide. It is preferred that if aqueous solutions are used the concentration of the DMF or DMSO in the solution not be less than 70 volume percent, and a volume percent minimum is more preferred. The presence of water improves the yield of product oil, but at higher amounts of water the selectivity of the aqueous solution for extraction of the instability-causing components is decreased. If desired, small amounts of other materials may be present during contacting if they are restricted to minor portions and do not adversely affect the extractive power of the chosen extractant.

Any conventional liquid-liquid contacting apparatus is suitable for use in this process if it provides for substantially complete contacting of the oil and the treating agent. Satisfactory methods of providing adequate contacting are well known in the art. The contacting apparatus used in the stabilization step should be operated at a temperature in the range of from about 0 F. to about 250 F. It is most convenient to operate in the range of 60-l50 F. Pressure must be sufficiently high to maintain substantially all of each component in the liquid phase. In many cases, atmospheric pressure will be sufiicient to accomplish this objective. The suitable operating pressure range is from about atmospheric pressure to about 30 atmospheres gauge pressure. The most convenient operating pressures are those in the range of 0-300 p.s.i.g. The ratio of solvent to oil is 0.255.0 volumes of solvent per volume of oil. It is most convenient to use ratios of 0.5-2.0 volumes of solvent per volume of oil. Where the oil is relatively heavy and viscous, it is desirable to add a hydrocarbon diluent to thin the oil and improve the degree of contacting. Suitable diluents are the C -C paraflins, particularly butane or pentane. Of these two, butane is preferred, because it is more easily separated from the treated oil and recovered. Further, excess butane is more often available in oil refineries than is excess pentane. Use of this diluent should not be confused with the provision stated above that minor portions of other materials may be present in the treating agent. The diluent is an essentially inert material used only to reduce the viscosity of the oil to be stabilized and it may be present in any amount required to provide adequate viscosity reduction.

As stated above, it is known in the prior art that DMF and DMSO can be used as aromatic extractives. Thus they can be used to extract'the aromatics from oils boiling over a wide boiling range and not merely restricted to those produced byhydrocracking under the conditions stated in this process. However, the extractive power of DMF and DMSO under conditions other than those described in the process of this invention is not selective for particular aromatics; and thus a substantial portion of the aromatic content of an oil will be removed by DMF or DMSO treatment under those conditions. In most cases this will result in a stable oil because the instability-causing aromatic compounds will have been removed. However, the yield of stable oil will be unnecessarily low be cause many additional aromatic compounds which play no part in the ultraviolet light instability problem will also have been removed. The stabilization process may be considered satisfactory only when oil yield is at least 95 percent of feed and stability of the oil product is at least 10 hours. The following Table I illustrates that under the conditions required in the process of this invention only DMF and DMSO provide this degree of stability and yield while other extractants fail to provide either or both a high yield of oil or a sufficiently stable oil. Data for this table were derived from experiments in which a hydrocracked oil was solvent treated at room temperature and atmospheric pressure with the volume of treating agent shown, and then subjected to ultraviolent light in the standard test described above.

It is apparent from the above Table I that if treating agents other than DMF and DMSO are used, yield must be sacrificed if a stable product is to be obtained, or, conversely, a high yield can be obtained only by accepting an unstable and inferior product. Only DMF and DMSO' produce stable products in high yield.

Typical results of treating hydrocracked lubricating oil stocks with DMF and DMSO, pure and in aqueous solution, are illustrated in the following Table II. In each of the runs shown, the oil treated was a 700-1050 F. lubricating oil which had been produced by catalytically hydrocracking high boiling gas oil to 65 percent conversion at about 780 F. and 2700 p.s.i.g. The oil was mixed with one volume of pentane diluent and 1.4 volumes of treating agent at room temperature and atmospheric pressure.

These data clearly illustrate that a high yield of high quality oil is obtained from the process of this invention.

A small amount of DMF or DMSO may remain in the treated oil following the contacting and subsequent separation of the oil and treating agent. This is not harmful to the oil as long as the residue of DMF or DMSO is not too high. For instance, an oil with 100 p.p.m. residual DMF had 10 hours of ultraviolet light stability prior to precipitation, while one with 500 p.p.m. had 12 hours stability.

When the hydrocracked oil contains waxy components, these may be removed by conventional dewaxing procedures, such as solvent dewaxing. Dewaxing may occur before or after the stabilization step described in this specification.

The preceding examples and descriptions are given for illustrative purposes only. It is apparent that there are many embodiments of the process of this invention, and it is not intended that it be limited other than as described in the appended claims.

I claim:

1. A process for the production of a high yield of lubricating oil which is stable in the presence of ultraviolet light, which comprises:

(A) In a hydrocracking zone contacting a liquid hydrocarbon feedstock containing a substantial portion of components boiling above 750 F. with hydrogen in the presence of a hydrocracking catalyst at an elevated temperature and pressure in order to convert at least 15 weight percent of said feedstock components boiling about 750 F. to materials boiling below 750 F.;

(B) recovering from the effluent of said hydrocracking zone a lubricating oil fraction boiling above 600 F.;

(C) contacting said lubricating oil fraction in contacting apparatus with a treating agent comprising a selective extractant selected from the group consisting of N,N-dimethylformamide, aqueous solutions of N,N-dimethylformamide, and aqueous solutions of dimethylsulfoxide; and

(D) recovering from the efliuent of said contacting apparatus a lubricating oil with improved ultraviolet light stability.

2. The process of claim 1 wherein said improved stability of said oil is such that no visible precipitate forms n the oil during 10 hours exposure of the oil in an ultraviolet light test.

3. The process of claim 2 wherein said treating agent consists essentially of a selective extractant selected from the group consisting of N,N-dirnethylformamide, aqueous solutions of N,N-dimethylformamide, and aqueous solutions of dimethylsulfoxide.

4. The process of claim 3 wherein said aqueous solutions of N,N-dimethylformamide and dimethylsulfoxide contain at least 70 volume percent of N,N-dimethylforn'tamide and dimethylsulfoxide, respectively.

5. The process of claim 3 wherein said aqueous solutions of N,N-dimethylformamide and dimethylsulfoxide contain at least volume percent of N,N-dimethylformamide and dimethylsulfoxide, respectively.

6. The process of claim 2 wherein the ratio of said treating agent to said lubricating oil fraction is 0.255.0.

7. The process of claim 2 wherein said contacting apparatus is operated at a temperature in the range of 250 F. and a pressure of 0-300 p.s.i.g.

8. in a process for the production of a high yield of lubricating oil, which is stable in the presence of ultraviolet light, by contacting in a hydrocracking zone a liquid hydrocarbon feedstock containing a substantial portion of components boiling above 750 F. with hydrogen in the presence of a hydrocracking catalyst at an elevated temperature and pressure in order to convert at least 15 weight percent of said feedstock components boil ing above 750 F. to materials boiling below 750 F., and recovering from the efiluent of said hydrocracking zone a lubricating oil fraction boiling above 600 F.; the improvement which comprises:

contacting said lubricating oil fraction in contacting apparatus with a treating agent comprising a selective extractant selected from the group consisting of N,N-dimethylformamide, aqueous solutions of N,N- dimethylformamide, and aqueous solutions of dimethylsulfoxide, and recovering from the efiiuent of said contacting apparatus a lubricating oil with improved ultraviolet light stability.

9. A process for the production of a high yield of lubricating oil with an ultraviolet light stability of at least 10 hours, which comprises hydrocracking in a hydrocracking zone at elevated temperature and pressure, in the presence of hydrogen and a hydrocracking catalyst, a hydrocarbon feedstock containing a substantial portion of materials boiling above 750 F., at a conversion of at least 15 weight percent of said materials boiling above 750 F. to materials boiling below 750 F., recovering from the efiiuent from said hydrocracking zone a lubricating oil fraction boiling above 600 F., contacting said lubricating oil fraction in contacting apparatus with a treating agent comprising dimethylsulfoxide, and recovering from said contacting apparatus a lubricating oil product in a yield of at least weight percent, based on said lubricating oil fraction, said lubricating oil product having an ultraviolet light stability of at least 10 hours.

10. A process as in claim 9, wherein said treating agent comprising dimethylsulfoxide is dimethylsulfoxide.

11. A process as in claim 9, wherein said treating agent comprising dimethylsulfoxide is an aqueous solution of dimethylsulfoxide.

References Cited UNITED STATES PATENTS 2,615,057 10/1952 Wolff et al. 208322 3,005,032 10/1961 Makin 208322 3,077,733 2/1963 Axe et al 20896 3,308,055 3/1967 Kozlowski 20818 3,414,506 12/1968 Campagne 20818 HERBERT LEVINE, Primary Examiner US. Cl. X.R.

PO-IWJ UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,5 46 ,098 Dated December 8 1970 Inventor(s) BYRON G. SPARS It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col 6 5th line of Table II a DMF (aqueous)" should ree ---95% DH? (aque0us)- Col 6 6th line of Table II "0% DMF (aqueous)" should rea --90% DMF (aqueous)- Signed and sealed this 20th day of July 1971 (SEAL) Attest:

EDWARD M.FLETCHER,J'R. WILLIAM E. SCHUYLER,

Attesting Officer Commissioner of Pate: