US3012963A

US3012963A - Hydrogenation of lubricating oils to remove sulfur and saturate aromatics

Info

Publication number: US3012963A
Application number: US791074A
Authority: US
Inventors: Raymond C Archibald
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1959-02-04
Filing date: 1959-02-04
Publication date: 1961-12-12
Anticipated expiration: 1978-12-12
Also published as: GB897240A; DE1470615A1; FR1246671A; NL125742C; NL248007A

Description

Dec. 12, 1961 W. OF TOTAL REACTANTS R. c. ARCHIBALD 3,012,963 HYDROGENATION OF LUBRICATING OILS TO REMOVE SULFUR AND SATURATE AROMATICS Filed Feb. 4, 1959 LOW MOL.. WT. HYDROCRAC'KING PRODUCTS O 20 4O 6O 80 I00 DECAHYDRONAPHTHALEN ES] W. CONVERSION OF 2"METHYL NAPHTHALENE SELECTIVE HYDROGENATION OF Z-METHYL NAPHTHALENE INVENTORI RAYMOND C. ARCHIBALD HIS ATTORNEY ce I Patented Dec. 12, 3551 3,512,963 1 DRGGENATTGN F LUBRTCATHIG GILS T0 ht TOW SULFUR AND SATURATE ARQMATICS Raymond C. Archibald, Kensington, Calif., assignor to Sheli Oil Company, a corporation of Delaware Filed Feb. 4, 1959, Ser. No. 7%,074 tllaims. ((Jl. 2ti8--217) This invention relates to the hydrotreatment of lubricating oils. More particularly, it relates to the quality improvement of lubricating oils containing polycyclic aroma-tics.

The conventional refining of lubricating oils involves several steps, each of which is directed to the removal of certain undesirable components. Some refining methods are chemical but most are merely physical separations of the undesirable components. Among these are distillation, adsorption, solvent extraction, crystallization and solvent precipitation. Of the chemical methods for re fining lubricating oils, sulfuric acid treatment ha v heretofore been the most common. All or merely part of these unit operations may be used in processing a given lllbIleating oil stock, depending upon the end use of the finished oil.

Distillation is most commonly employed to remove low molecular weight components which would unduly reduce the viscosity and flash point of the oil, and to separate the high molecular weight components which would have an adverse effect upon the color, carbon residue, and sludging characteristics of the oil. Residual lubricating oils are usually deasphalted by means of solvent precipitation. The lubricating oil to be deasphalted is mixed with a light liquefied paraffinic hydrocarbon, such as propane. The oil and any wax in it remain dissolved in the propane while the higher molecular Weight resins and asphalt are precipitated in the form of a viscous liquid, which is readily separated. The oil from which the asphalt has been removed is then suitable for further treatment to produce residual lubricating oils, i.e., bright stocks.

Most lubricating oil stocks contain wax, which if left in the oil, would interfere with the flow of the finished lubricant at low temperatures. Wax in the finished oil can therefore be tolerated only in low concentrations unless the oil is to be used only under conditions in which low temperatures are not encountered. The most widely used process for dewaxing lubricating oil stocks is solvent dewaxing in which the waxy oil is diluted with a solvent having a low solvency for wax and a high solvency for oil. The mixture of solvent, wax, and oil is then chilled to bring about a phase separation, and the precipitated wax is removed by filtration. The pour point of the dewaxed oil is then determined by the extent to which the wax is removed. Especially in the manufacture of motor oils, it is preferred to have a fiat viscosity-temperature relationship (i.e., a high viscosity index). Therefore, since the removed waxes usually have a higher viscosity index (VI) than the dewaxed oil, the oil is dewaxed only to the depth necessary to obtain the maximum pour point con sistent with the intended service of the finished oil.

Even after resins, asphalt, and wax are removed from the oil, most petroleum crude oils contain significant quantities of aromatics within the lubricating oil range which cause excessive sludging and also adversely affect the viscosity-temperature slope. There are usually removed by solvent extraction with an appropriate polar solvent. Liquid sulfur dioxide, furfural, nitrobenzene, phenol, and mixed cresols with propane are solvents which are particularly suited for the extraction of lubricating oils.

Treatment with sulfuric acid may also be used to remove the same components as solvent extraction. Unlike the aforementioned processes which are purely physical separations, treatment with sulfuric acid is also chemical in nature in that part of the undesirable components are converted to insoluble sulfonates which are removed With the acid sludge. However, similarly to the purely physical separations, the undesriable components, whether chemically converted or not, are removed from the oil.

in addition to the foregoing treatment, most lubricating oilsmust also be treated with clay to improve the clarity and color of the finished oil, and in some cases their oxidation stability. The primary result of clay treatment is to remove suspended solids, Water droplets, and dissolved polar ingredients such as naphthenic acid, phenols, soaps, etc.

All of the above processes are extractive in nature, i.e., the undesirable components are removed from the Oil. As a result, the yields of finished oil are usually quite small. In the case of some highly refined oils such as turbine oils, insulating oils and some bright stocks, the net yield of finished oil may be as small as 40% by volume or even less, based on the starting material. Since the undesirable components removed from lubricating oils have only relatively small by-product value, a large part of the cost of manufacturing lubricants is due to the loss in Volume incurred during the necessarily complex series of processing steps. The amount of loss in the foregoing process is dependent upon the nature of the crude petroleum used. However, in all cases, except for the most paraflinic crude such as Pennsylvania crude oil, up to 50% of the loss in volume results from the removal of the aromatic constituents by sulfuric acid and/or solvent extractions.

A very desirable method by which lubricating oil processing losses may be reduced is to convert the undesirable aromatic hydrocarbon components to more desirable napthenic hydrocarbon by means of hydrogenation. By this means, the processing loss during the viscosity-index improving step may be substantially reduced. The hydrogenation of lubricating oils is, of course, well known; for example see Zuidema, The Performance of Lubricating Oils, Reinhold Publishing Company (1952, page 164). However, hydrogenation of lubricating oils has been practiced only to a limited extent despite the fact it has long been known. This has been due in part to the relatively high cost of hydrogenation and in part to the lack of flexibility of prior hy'drotreating methods to obtain good quality lubricants from a wide range of lubricating oil stocks.

It is therefore an object of this invention to provide an improved process for hydrogena-ting lubricating oils. It is a particular object of the invention to provide an improved method of hydrogenating lubricating oils to irnpart to them superior lubricating oil properties. It is also an object of the invention to provide a process for manufacturing lubricating oils whereby the processing losses are reduced without a sacrifice in product quality.

These and other objects will be apparent from the detailed description of the invention which is an improved process for the manufacture of lubricating oils wherein the aromatics contained in the oil are converted to more desirable materials, without substantial loss in yield, by selective hydrogenation with a nickel and sulfur-containing catalyst.

Most lubricating oil crudes and the resulting fractions contain substantial amounts of polycyclic aromatics,-par ticularly condensed ring polycyclic aromatics. These polyaromatics generally have low viscosity indices. Howi ever, by hydrogenating them selectively to monoaromatics, their viscosity indices are substantially raised. By selective hydrogenation as referred to herein, it is meant that sulfur compounds are substantially removed and the polycyclic aromatics are selectively converted to partially hydrogenated products containing one aromatic ring without substantial cracking of the oil. This type of selective senses hydrogenation is illustrated by the hydrogenation of 2- methylnaphthalene, which typifies the reaction of the polycyclic aromatics contained in lubricating oils when hydrogenated according to the invention.

This type of selectivity may be more readily understood by reference to the attached drawing which is a graphical representation of the variations in the composition of the reactant mixture during conversion of Z-methylnaphthalene by selective hydrogenation according to the method of the invention. It will be observed that by use of the process of this invention, over 90% of the Z-methylnaphthalene was converted to the monoaromatic methyltetrahydronaphthalene with but little conversion to the completely saturated methyldecahydronaphthalene, and almost no hydrocracking.

A particular sulfur-containing nickel catalyst is used for the selective hydrogenation. Nickel sulfide catalysts have long been well known as hydrogenation catalysts. Their use has been disclosed, inter alia, for the hydrogenation of cracked petroleum residues, phenols, and simple sulfur compounds, and for the cracking of waxes and other hydrocarbons. However, in a large degree because of their high hydrocracking activity under ordinary hydrotreating conditions, the use of nickel sulfides as hydrotreating catalysts has been restricted to mixtures thereof with other catalytically active metals, especially tungsten.

According to the present invention, however, it has been found that nickel sulfide may, under proper operating conditions and within a certain range of atomic ratios of nickel to sulfur, be used for the hydrogenation of lubricating oils without excessive hydrocracking. With unsulfided or slightly sulfided nickel catalyst, there is very little selectivity for the conversion of polyarornatics to monoaromatics, i.e., complete saturation of the polyaromatics takes place to an excessive degree, and hydrocracking activity is excessive. Therefore, in order to attain the aforementioned selectivity, it is necessary that the ratio of nickel to sulfur be kept low. However, it has also been found that if the degree of sulfiding is too high, i.e., the

nickel-sulfur ratio too low, the activity of the catalyst is impaired. From this, it is apparent that the degree of sulfiding has a pronounced effect on both the activity and selectivity of the catalyst. The reasons for this are not known with certainty. However, it is known that within the practicable operating limits of hydrogenation reactions, and in a hydrogen-hydrogen sulfide environment, the nickel catalyst may exist in the solid state in several stable forms. The following molecular formulae have been reported: NiS NiS, Ni S Ni S and Ni. Since the selectivity of the catalyst decreases with less sulfiding of the metallic nickel and further, since it has been found that activity decreases with additional sulfiding, itis believed that the Ni S form of the catalyst is the most active form to attain the desired selectivity for this invention. It is therefore preferred that the catalyst contain a major amount of nickel in the form of Ni S Since the presence of nickel in the Ni S form cannot be readily determined, it is necessary to maintain the degree of sulfiding within narrow limits. It has thus been found that the catalyst may be maintained at a satisfactory de 'gree of activity and selectivity if the average atomic ratio of nickel to sulfur is from about 1.3 to about 3.0. At these ratios, the amount of Ni S will generally not be lower than about 30%. However, to obtain both optimum activity and selectivity, it is preferred that the atomic ratio of nickel to sulfur be from about 1.4 to 1.8.

1 Nickel sulfides maybe prepared in a number of ways from finely divided metallic nickel. Nickel can be sulfided with hydrogen sulfide gas to form nickel sulfide and hydrogen. In a like manner, the catalyst may be prepared by reacting carbon bisulfide with finely divided metallic nickel to form nickel sulfides and carbon. A method of preparing the catalyst is the hydrogenation of finely divided higher nickel sulfides prepared as above to the Ni S form, in which case hydrogen sulfide gas is liberated.

The stable existence of a particular sulfide in a hydrogenation system such as that encountered in the instant process depends upon the temperature and the composition of the vaporous phase surrounding the sulfide. Thus, at a constant temperature, the molecular state of the stable sulfide depends on the ratio of hydrogen sulfide to hydrogen.

To maintain the nickel-to-sulfur atomic ratio of the catalyst at from 1.3 to 3.0 the H szH molar ratio of the hydrogen-containing gas must be adjusted to at least about 0.0002 but not more than about 0.02 within the useful temperature range of the process.

Within the foregoing H S:H limits, the catalyst is stable in the Ni S form up to a temperature of about 850 F. However, to avoid excessive hydrocracking of the lubricating oil being treated, the temperature sh uld not be greater than about 800 F. The lower temperature limit of the invention is governed largely by the desired reaction rate, which is related directly to the temperature of the process. Though a temperature as low as 600 F. may be used, at least 650 F. is preferred. From the standpoint of both hydrogenation rate and freedom from hydrocracking, a temperature of from about 650 to about 750 F. is preferred.

Since catalytic hydrogenation reactions are reversible, it is necessary to use a hydrogen pressure high enough to shift the hydrogenation-dehydrogenation equilibrium to favor hydrogenation. Moreover, the higher the pressure which is used the greater the temperature which also may be employed, thus increasing the reaction rate. The invention can therefore be practiced at a pressure of from about 500 to 3,000 psi. or greater. It is preferred, however, to operate within the pressure range of from about 1,200 to 2,200 p.s.i.

Hydrocracking during the practice of the invention is, of course, largely to be avoided. Furthermore, since cracking is a direct function of time as well as temperature, it is preferred not to employ excessive contacting times at the high temperature beforernentioned. For this reason a liquid hourly space velocity (LHSV) of from 0.1 to 5 volumes of oil per volume of catalyst per hour is preferred. To obtain even more complete conversion while minimizing cracking, an LHSV of 0.2 to 1.0 is particularly preferred.

In performing the selective hydrotreating of the invention, only relatively small amounts of hydrogen are consumed. The amount varies materially with the particular lubricating oil stock being treated, viz, with its content of sulfur and polyaromatics. However, the hydrogen uptake of the treated oil is preferably from to about 500 standard cubic feet per barrel of liquid feed. It is important that the degree of hydrogenation not exceed about 500 s.c.f. per barrel hydrogen uptake since the treated oil may lose much of is lubricating properties. It is even further preferred that the hydrogen uptake of the treated oil not exceed 300 s.c.f. per barrel.

Both distillate and residual lubricating oil fractions may be processed according to the invention. The treatment of lubricating oils is most advantageous, however, with respect to lubricant fractions containing a major proportion of polycyclic aromatics. Such aromaticscontaining fractions are normally obtained from naphthenic-and intermediate base lubricating oil crudes having a U0? characterization factor of from about 11.0 to 12.1. Typical of such crudes which are found in the United States are those from the Gulf Coastal Area, East Texas, West Texas, New Mexico, Mid Continent, and the Four Corners Area. Certain polyaromatics-containing gas oils such as catalytically cracked cycle oil and heavy gas oils may also yield useful lubricant materials when processed according to the invention. The lubricant stock to be treated by the process may be completely unrefined, partially refined, or even completely refined as defined by prior processing schemes. However, the greatest benefit is derived therefrom in the use of unrefined or only partiallymefined oils. In the case of residual lubricating oils,

it is, however, preferred that the oil be deasphalted since the highly condensed asphaltic portions therein tend to deposit coke on the catalyst and tend also to promote excessive hydrocracking. Deasphalted oil, as used here, refers to an oil from which the asphalt and tars have been essentially completely removed. Asphalt and tars, as used here, are defined as in 3. Ph. Pfeiffer, The Properties of Asphaltic Bitumen (1950), page 5. The asphaltic constituents are additionally detrimental in that they contain large amounts of metallic contaminants which poison the catalyst. However, the oil need not be dewaxed or otherwise treated prior to the selective hydrogenation step of the invention.

The process of the invention may be more readily understood from the following illustrative examples:

Example I A propane-dewaxed (DW) naphthenic lubricating oil distillate (West Texas Ellenburger) having a viscosity of about 250 Saybolt Universal Seconds (S.U.S.) at 100 F. and is viscosity index [Dean and Davis, Chemical and Metallurgical Engineering, vol. 36, p. 618-9 (1929)] of 91 was selectively hydrogenated over a supported nickel sulfide catalyst having the average composition Ni S The catalyst was supported on alumina. The operating conditions of the hydrogenation reaction were 734 F. and 1500 p.s.i.g. pressure. The oil feed was contacted with the catalyst at a space velocity (LHSV) of about 0.4, and a hydrogen-to-oil mole ratio of 30 to 1 was maintained throughout. Gas was continuously bled from the reaction system and fresh hydrogen added in order to maintain the molar ratio of H 8 to H at 0.001. The VI of the hydrotreated oil was 104, and the net yield was 90% by weight. The aromatics content of the treated and untreated oil were as follows:

Untreated Selectively DW250 Hydrotreated Distillate Distillate Percent Aromatic Typo Reduction m (Aromatics Content, millimoles/100 grams) Tetraaromatics 12 5 58. 4 Triaromatics l4 6 57. 2 Diaromaticsbh 18 12 33. 3 Monoarornatics. 57 67 17. 5 Total 101 90 ll 0 Between 240 and 300 s.c.f. of hydrogen were consumed per barrel of oil. Upon stripping of the light ends from the hydrotreated oil, the color, clarity, and stability of the oil were such that no further treatment was required.

Example II Another portion of the same dewaxed naphthenic lubricating oil distillate as was used in Example I was extracted in a conventional Duosol solvent extraction system, employing propane and mixed cresols as the duosolvents, to a depth such that the VI of the extracted etfiuent oil was 103. The net yield of raflinate was 79% by The extracted oil was of good color but possessed considerable haze and had poor stability and thus required clay contacting before the oil had satisfactory properties. The oil was therefore contacted with 18 pounds per barrel of clay at a temperature of 450 F. A 3% volume loss was incurred during the contacting step and the net yield of finished oil was 76.5% by Weight, based on the dewaxed starting material.

' Example III A propane-deasphalted (DA) and dewaxed (DW) residual lubricating oil (New Mexico-Ellenburger) having a VI of B5 was selectively hydrogenated over a. supported nickel sulfide catalyst having the same average composition as in Example I. The temperature of the hydrotreatrnent was 707 F. and the pressure was 1500 p.s.i. The oil feed was contacted with the catalyst at a space velocity of 0.4 and a hydrogen-to-oil mole ratio of 30 to 1 was maintained throughout. Gas was continuously bled from the reaction system and fresh hydrogen added in order to maintain the molar ratio of H 8 to H at 0.001. The VI of the hydrotreated oil was and the net yield was 90% by weight. The aromatics content of the untreated and treated oil were as follows:

Approximately 200 s.c.f. of hydrogen were consumed per barrel of oil.

Example IV The same dewaxed residual lubricating oil as in Exam: ple III was extracted in a conventional Duosol solvent extraction system, employing propane and mixed cresols as the duo-solvents, to a depth such that the VI of the extracted rafiinate oil was 96. The yield of rafiinate was only 66% by weight.

From the foregoing examples, it is clear that the inven tion has great value in providing a method by which satisfactory lubricating oil may be made in larger yields. However, the advantage of the selective hydrogenation of lubricating oils in the manner of the invention is not limited thereto. For it has been found that the lubricating oils produced according to the invention have certain properties superior to those of conventionally treated lubricating oils. These oils are particularly susceptible to the addition of VI improving agents, as may be seen in the following example:

Example V A waxy naphthenic lubricating oil distillate from the Four Corners district of Utah having a viscosity of about 250 S.U.S. at F. was hydrotreated over a Ni S on-alumina catalyst in accordance with the invention. The operating conditions were as follows:

Reactor temperature 725 F.

Space velocity (LHSV) 2.0.

Pressure 1,500 p.s.i.a. Hydrogen-to-oil ratio 5,000 s.c.f./ bbl. of feed.

The hydrogen consumption was about 250 sci/barrel of feed and the product contained 94.0% by volume of Waxy hydrogenated lubricating oil distillate having a VI'of 85. The V1 improver susceptibility of this relatively low VI oil was then compared with that of a deeply extracted raflinate produced by extraction of the same waxy distillate starting material with furfural to a VI of 100.

Various amounts of two commercially available VI improvers were added to samples of both the hydro- 7 treated and'deeply'extractedoil, a'n'dthe VI of each determined. The results were as follows:

Add-1: Oopolyruerpf type referred to in 11.8. 2,737,496 (Copolymer of 2-1nethyl-5-vinyl pyridine and lauryl, stearyl, and methyl methacry- 35%1-2: Acryloid 966 (N-vinylpyrrolldone-lauryl methacrylate copoly- From the foregoing, it is clear that the oil which had been selectively hydrogenated according to the invention was almost twice as susceptible to additive VI improvement as the conventionally refined oil. A noteworthy aspect of this unexpected benefit is that it is present not only when the VI of the hydrotreated oil is below that of the extracted oil but also when the VI of the additive containing oil is greater than the extracted oil.

Thus, because of the higher susceptibility of the oils of the invention to V1 improvement, high viscosity index oils may be made in high yields from relatively low VI lubricating oil starting materials.

A particularly desirable method of preparing the catalyst is illustrated by the following example:

Example VI A commercially available pelleted catalyst comprising 40% by Weight of nickel in the form of nickel carbonate, composited with granulated kieselguhr, was ground to pass through a 6-8 mesh standard screen. Twohundredninety-three grams of the ground catalyst were then placed in a cylindrical pressure vessel, having appropriate inlet, outlet, and support means, to form a fixed foraminous bed of granulated nickel catalyst. At operating condi tions of 707 F., 1500 psi. pressure, and a liquid hourly space velocity, (LHSV) of one volume of liquid per volume of catalyst per hour, the following three steps were performed:

(1) One-half gallon of a medium, sour (0.25% w. sulfur) West Texas lubricating oil distillate having a viscosity of about 250 Universal seconds at 100 PK, and to which had been added 23 grams of carbon disulfide, was passed through thecatalyst bed. The total sulfur content of the treating oil was 1.4% by weight. The atomic ratio of .nickel to sulfur was 2.7.

(2) A second one-half gallon of the same distillate, to which 8 grams'of carbon disulfide had been added, was passed through the catalyst bed, after which the atomic ratio of nickel to sulfur was 2.0.

(3) A third one-half gallon of the same lubricating oil distillate was passed through the bed without prior addition of sulfur; The resultant sulfided catalyst had a Ni:S atomic ratio of 1.71 corresponding to the empirical formula of Ni3S1 75. The foregoing stepwise sulfiding procedure is particularly advantageous in that precise control over the final degree of sulfidingis possible. Moreover, it is readily adaptable to commercial scale operations.

The sulfided nickel catalysts used in the invention have sutficient mechanical strength that they may be used in the granular or pelleted form in a fixed bed Without a support. The catalyst can be prepared by impregnating or admixing suitable supporting materials with various reducible nickel salts, followed by conventional drying and/ or pelleting procedures. When the catalyst is in the form of such salts, it can be reduced to the metallic form prior to sulfiding if desired. Materials which are suitable as catalyst supports for this invention include various refractory oxides,'which arees's'entially nonreactive with hydrogen sulfide, such as alumina, silica, thoria, zirconia, and titania. Silica and alumina are particularly preferred to be used as catalyst supports in the practice of this invention. Alumina clays of the montmorillonitic type are also useful as supports for the catalyst of the process.

The present invention may be used to supplant conventional lubricat'ing oil solvent extraction facilities and in many cases clay contacting facilities as well. .On the other hand, the invention may be also used advantageously in cooperation with such conventional refining facilities, eitherin series or in parallel with, leg, solvent extraction and/ or acid treating processes. In either case, high viscosity index lubricating oils may be produced at higher yields than were heretofore possible at equivalent quality levels.

The invention is equally advantageous whether it is used for treating narrow viscosity range lubricating oil stocks or broad viscosity range stocks. Moreover, the entire lubricating oil fraction of a given crude oil may be processed according to this process without prior separation into narrow viscosity ranges. However, as pointed out hereinbefore, it is preferred to separate and deasphalt the residual lubricating oil portion prior to the selective hydrogenation. After such separation, however, the deasphalted residue and separated distillate may be recombined if desired.

It is characteristic of the process that the viscosity of the oil undergoes some decrease because of the presence of lower viscosity materials resulting from hydrocracking, which can not be eliminated entirely, and from oxygen and sulfur atom removal, as well as the natural lowering due to conversion of polyaromatics to naphtheno-monoaromatics. This is particularly true with respect to high boiling lubricating oils. The viscosity of the treated oil may be raised substantially by stripping out the light ends under reduced pressure with, for example, steam, nitrogen, or other inert gas. However, some lubricating oils processed in this manner contain small amounts of higher boil ling non-strippable low viscosity materials. Such higher boiling lowviscosity materials are produced during the hydrotreatment by isomerization and also by hydrocracking of short alkyl side chains. These may best be removed by distillation. It should be noted, however, the lower viscosity, higher-boiling materials removed accordingly are frequently good lubricants and may have viscosity indices as great as or even greater than the bulk of the treated oil. Such oils may advantageously be used as blending agents for higher viscosity oils. The degree of viscosity decrease depends of course on the particular character of each lubricating oil crude from which the oil is derived. Therefore, in some instances where a particular viscosity range is desired it may be preferred to employ a slightly higher viscosity oil as a starting material than would be used for conventional viscosity index-improving refining processes.

It has long been the custom of lubricating oil refiners to process the lubricating oils in the form of narrow boiling and viscosity range fractions. Frequently, these fractions were chosen on the basis of obtaining greater operating efficiencies during the various treating steps. This use of narrow boiling fractions is particularly advantageous in the solvent extractionstep. However, when the present invention is used in place of extraction, it is not necessary to employ such fractions. It is, in fact, preferred tohydrotreat the full lubricating oil range to obtain maximum yields with greater economy. By thusly hydrotreating the full range oil, the light ends can be removed in a single stripping operation. Moreover, when the full range product is subsequently fractionally distilled into conventional narrow fractions, there are no off-specification fractions to be reblended according to viscosity.

As mentioned hereinbefore, the lubricating oil to be hydrotreated according to the invention need notbe dcwaxed prior to hydrogenation. Moreover, it is a preferred aspect of the invention that the oil not be dewaxed since even greater overall lubricating oil yields may be obtained. The mechanism by which this further advantage is obtained appears to be that the molecular configurations of the treated oil components are more varied after selective hydrogenation according to the invention because of a small amount of isomerization and mild hydrocracking which take place noncurrently with the hydrogenation. The greater variety in molecular configuration thus creates a higher degree of crystalline heterogeneity which depresses the pour point of the hydrogenated oil. Because of the lower pour point, less wax need be removed during the dewaxing step to reach a given pour point. Though this same effect may also be observed in hydrotreating dewaxed lubricating oils, its magnitude is greater when waxy oils are used since the waxes undergo a greater amount of isomerization during hydrotreating.

An additional advantage of lubricating oils produced according to the invention is that they have higher peptizing power, which, by maintaining potential sludge-forming materials in solution, contributes to superior oxidation stability.

It is recognized that the process is capable of other modifications and applications in the processing of lubricating oils, particularly with respect to the state of refinement of the oil to be treated.

I claim as my invention:

1. A process for the treatment of essentially asphalt-free petroleum lubricating oils containing polycyclic aromatics to reduce the sulfur content thereof and to convert selectively polycyclic aromatics to incompletely saturated compounds having one aromatic ring per molecule without substantial cracking of the oils which comprises contacting said oils at a temperature of from about 600 to about 800 F. and at a pressure of from about 500 to about 3,000 pounds per square inch with a nickel sulfide catalyst in the presence of a treating gas containing hydrogen sulfide and hydrogen in a ratio of from 0.0002 to 0.02 moles of hydrogen sulfide per mole of hydrogen, the average atomic ratio of nickel to sulfur in said nickel sulfide catalyst being at least 1.3:1 but not more than 3:1, and the consumption of hydrogen being not less than but not more than about 500 standard cubic feet per barrel of lubricating oil treated.

2. The process of claim 1 in which the lubricating oil is an undewaxed wax-containing oil.

3. The process of claim 1 in which the lubricating oil is a full-range lubricating oil.

4. The process of claim 1 in which the hydrogen uptake of the hydrogenation reaction is not less than 100 but not more than about 300 standard cubic feet per barrel of lubricating oil treated.

5. The process of claim 1 in which the lubricating oil is deasphalted residual lubricating oil.

References Cited in the file of this patent UNITED STATES PATENTS 2,673,175 Stratford et a1 Mar. 23, 1954 2,706,167 Harper et a1. Apr. 12, 1955 2,779,711 La Goretta Jan. 29, 1957 2,779,713 Cole et a1. Jan. 29, 1957 2,879,223 'Cole et a1. Mar. 24, 1959 2,914,470 Johnson et a1. Nov. 24, 1959

Claims

1. A PROCESS FOR THE TREATMENT OF ESSENTIALLY ASPHALT-FREE PETROLEUM LUBRICATING OILS CONTAINING POLYCYCLIC AROMATICS TO REDUCE THE SULFUR CONTENT THEREOF AND TO CONVERT SELECTIVELY POLYCYCLIC AROMATICS TO INCOMPLETELY SATURATED COMPOUNDS HAVING ONE AROMATIC RING PER MOLECULE WITHOUT SUBSTANTIAL CRACKING OF THE OILS WHICH COMPRISES CONTACTING SAID OILS AT A TEMPERATURE OF FROM ABOUT 600* TO ABOUT 800*F. AND AT A PRESSURE OF FROM ABOUT 500 TO ABOUT 3,000 POUNDS PER SQUARE INCH WITH A NICKEL SULFIDE CATALYST IN THE PRESENCE OF A TREATING GAS CONTAINING HYDROGEN SULFIDE AND HYDROGEN IN A RATIO OF FROM 0.0002 TO 0.02