Two-stage Hydrocracking-hydrotreating Process To Make Lube Oil

Abstract

A high-viscosity-index mineral lubricating oil is produced by treating, for instance, a deasphalted residuum or a raw, heavy lubricating distillate oil in a two-stage process. The feedstock is first catalytically hydrocracked, then catalytically hydrogenated and can be fractionated and dewaxed to produce a finished product. Catalysts such as nickel-tungstate on boria-alumina and nickel-molybdate on alumina are employed in the two stages, respectively. The catalysts are preferably used in sulfided form.

Description

The present invention relates to a process for the production of high quality mineral lubricating oils from feedstocks that are not normally used in present commercial processes to make such products. In addition to mineral lube oil distillates and deasphalted residuums of relatively high quality, stocks containing high percentages of sulfur, nitrogen and carbon residue, such as sour oils and more highly contaminated deasphalted oils, may be employed as feeds. Moreover, a wide range of products is possible. Lubricating oils with viscosity indexes up to about 150 or more (ASTM Designation: D-2270) with partial or even complete aromatic saturation are possible. The present process is also more economical than present methods for the production of high viscosity index oils involving solvent treatment, dewaxing and finishing. The invention produces such oils by hydrocracking the mineral oil feed while in contact with a catalyst containing nickel, and tungsten or molybdenum along with boria on an alumina support, followed by hydrogenation of resulting hydrocracked materials of lubricating viscosity over a hydrogenation catalyst whereby a high viscosity index oil is produced.

Many of the present day refining techniques employed to produce high quality mineral lubricating oils having high viscosity indexes possess certain undesirable features. For example, the production of finished oils having a viscosity index of 95 by known methods of fractionation and solvent extraction of vacuum distillates or deasphalted residuums followed by dewaxing and finishing with acid, clay or hydrogen, normally results in yields of about 50 to 65 volume percent. The present invention, however, can produce 95 VI oils in yields of about 60 to 80 volume percent on a dewaxed basis and yields of about 40 volume percent or more on a dewaxed basis of oils having viscosity indexes of about 120 and higher.

The mineral lubricating oils treated by the process of the present invention are of lubricating viscosity at 210.degree. F. and are principally stocks having at least about 90 weight percent boiling above about 600.degree. F.; preferably the feed is a residuum at least about 90 weight percent of which boils above about 1,000.degree. F. The feeds are usually oils of at least about 50 VI, e.g., about 50 to 80, or even about 70 to 80 VI, and can be derived from paraffinic or mixed base crude oils. The total or full range oil of lubricating viscosity obtained by the method of the present invention has a viscosity index in the range of at least about 90, say up to about 150 or more, with the increase in the viscosity index of the product being at least about 20, preferably at least about 30, over that of the feed. Both the initial hydrocarbon feedstock and the product of lubricating viscosity from the hydrogenation reaction boil over a considerable temperature range, e.g., over a range of at least about 100.degree. F., often at least about 200.degree. F. The hydrocarbon feedstock preferably has a specific dispersion (ASTM Designation: D-1218) in the range of about 105-165 while the specific dispersion of the product of lubricating viscosity is preferably in the range of about 100-110. The method of the present invention is particularly suitable for treating feedstocks having a specific dispersion in the range of about 135-165, such stocks being the highly contaminated stocks, containing larger amounts of aromatics and frequently having been subjected only to fractionation and deasphalting. Thus the present method can utilize these economically cheaper feedstocks to produce high quality lubricating oils in high yields.

Hydrocracking of the feedstock which includes ring opening and usually desulfurization and denitrogenation, is carried out in contact with a catalyst containing nickel and one or both of molybdenum or tungsten supported, along with boria, on a catalytically active alumina base. The metals of the catalyst may be present in the form of free metals or in combined form such as the oxides and sulfides, the sulfides being the preferred form. Examples of such mixtures or compounds are nickel molybdate or tungstate (or thiomolybdate or thiotungstate). These catalytic ingredients, along with boria, are employed while disposed on a catalytically-active alumina. The catalyst is composed of minor, catalytically effective amounts of nickel, tungsten and/or molybdenum and boria on the alumina base. Nickel may often comprise about 1-40 weight percent of the catalyst, preferably about 2-10 percent, with the total amount of tungsten and molybdenum being about 5-30 weight percent, preferably about 10-20 percent, of the catalyst on a metal oxide basis. Preferably the boria is present in an amount of about 2 to 10 weight percent, based on the total weight of the catalyst while the alumina is the major component of the catalyst, e.g., the essential balance of the composition.

The catalyst composition used in the hydrocracking stage of the present invention can be prepared by adding the nickel, tungsten, molybdenum and boria components to the alumina by the various methods known to the art, for example by impregnation or precipitation and coprecipitation using suitable compounds of the metals and boron. For example, alumina particles containing boria or a material which upon heating yields boria, can be mixed with aqueous ammonia solutions containing nickel and tungsten, and/or molybdenum, or other aqueous solutions of water-soluble compounds of nickel and tungsten and/or molybdenum, so that the metal components are absorbed on the base. Alternatively, the promoting materials can be precipitated on the boria-containing alumina base through suitable reaction of an aqueous slurry of the support containing water-insoluble salts of the promoting metals. The boria-containing particles can be formed into macrosize either before or after being mixed with the nickel and tungsten and/or molybdenum components. The catalyst can be dried and calcined, e.g., at temperatures of about 800 to 1,200.degree. F. or somewhat more. Prior to use the catalyst is preferably sulfided at elevated temperature.

The hydrocracking step is carried out under conditions designed to selectively crack the feed so that opening of aromatic and naphthenic rings is favored, rather than the splitting of chains into lower molecular weight compounds. Such conditions include a temperature of about 725.degree.to 875.degree. F., preferably about 750.degree.to 850.degree. F. The other reaction conditions often include a hydrogen partial pressure of about 1,000 to 5,000 p.s.i.g., preferably about 1,500 to 3,000 p.s.i.g. In the production of 95 VI oils by the method of this invention, cracking may take place to the extent that from about 5 to 10 percent by volume of the product of the hydrocracking stage is material boiling below about 600.degree. F. In the production of 120 VI oils, about 30 to 40 percent by volume of the product of the hydrocracking stage may be comprised of such materials. The amount of free hydrogen employed during hydrocracking can be generally about 1,000 to 5,000 standard cubic feet per barrel of hydrocarbon feed, preferably about 1,500 to 3,000 standard cubic feet per barrel. The weight hourly space velocity (WHSV), weight units of feed introduced into the reaction zone per weight unit of catalyst per hour, will often be in the range of about 0.3 to 3, preferably about 0.5 to 2. The reactor effluent from the first or hydrocracking stage can be flashed to prevent hydrogen sulfide and ammonia from going to the hydrogenation stage, but this is not necessary, especially if nonprecious metal hydrogenation catalysts are used in the hydrogenation stage. Also, if desired any light hydrocarbons can be removed from the feed to the hydrogenation stage.

Lubricating oil from the hydrocracking stage is subjected to a hydrogenation operation which involves contacting lubricating oil, preferably the essentially full range lube oil, from the hydrocracking stage in the presence of hydrogen with a solid hydrogenation catalyst at a temperature of about 550.degree.to 825.degree. F., preferably about 600.degree. to 800.degree. F. It is preferred that the temperature employed in the second stage be at least about 50.degree. F. less than the temperature of the first stage for optimum decolorization and saturation. The other reaction conditions often include pressures of about 1,000 to 5,000 p.s.i.g., preferably about 1,500 to 3,000 p.s.i.g.; space velocities (WHSV) of about 0.3 to 5, preferably about 0.5 to 3; and molecular hydrogen to feed ratios of about 500 to 3,500 standard cubic feet of hydrogen per barrel of hydrocarbon feed, preferably about 1,500 to 2,500 standard cubic feet of hydrogen per barrel of hydrocarbon feed.

The solid catalyst employed in the hydrogenation operation is preferably a sulfur-resistant, nonprecious metal hydrogenation catalyst, such as those conventionally employed in the hydrogenation of heavy petroleum oils. Examples of suitable catalytic ingredients are tin, vanadium, members of Group VIB in the periodic table, i.e., chromium, molybdenum and tungsten and metals of the iron group, i.e., iron, cobalt and nickel. These metals are present in minor, catalytically effective amounts, for instances, about 2 to 30 weight percent of the catalyst, and may be present in the elemental form or in combined form such as the oxides or sulfides, the sulfide form being preferred. Mixtures of these materials or compounds of two or more of the oxides or sulfides can be employed, for example, mixtures or compounds of the iron group metal oxides or sulfides with the oxides or sulfides of Group VIB constitute very satisfactory catalysts. Examples of such mixtures or compounds are nickel molybdate, tungstate or chromate (or thiomolybdate, thio-tungstate or thiochromate) or mixtures of nickel or cobalt oxides with molybdenum, tungsten or chromium oxides. As the art is aware and as the specific examples below illustrate, these catalytic ingredients are generally employed while disposed upon a suitable carrier of the solid oxide refractory type, e.g., a predominantly calcined or activated alumina. To avoid undue cracking the catalyst base and other components have little, if any, hydrocarbon cracking activity. Usually not more than about 5 volume percent, preferably not more than about 2 volume percent, of the feed is cracked in the second or hydrogenation stage to produce materials boiling below about 600.degree. F. Commonly employed catalysts have about 1 to 10 weight percent of an iron group metal and about 5 to 25 percent of a Group VIB metal (calculated as the oxide). Advantageously, the catalyst is nickel molybdate or cobalt molybdate, supported on alumina. Such preferred catalysts can be prepared by the method described in U.S. Pat. No. 2,938,002.

Other suitable hydrogenation catalysts which can be employed in the method of this invention include the platinum group metal types. Such catalysts often have a minor catalytically effective amount, say about 0.05 to 2 weight percent, preferably about 0.1 to 1 weight percent of one or more platinum group metals carried on a solid support, especially an active alumina. Suitable platinum group metals include platinum, rhodium and ruthenium with platinum being preferred.

The catalysts employed in both the hydrocracking and hydrogenation stages of the method of this invention are preferably disposed in the reaction zones as fixed beds. Such fixed bed catalysts are usually particles of macrosize, e.g., about one sixty-fourth to one-fourth inch, preferably about one-sixteenth to one-eighth inch, in diameter, and, about one sixty-fourth to 1 inch or more, preferably about one-eighth to one-half inch in length. These catalysts can be made by extrusion, tableting or other suitable procedures.

The hydrogenation operation provides additional aromatic saturation, color improvement and stability towards oxidation and corrosion. Additional color improvement can be provided by subjecting the effluent from the hydrogenation operation to treatment with ultraviolet light. The treatment was found to lighten considerably the color of the darker oils, a surprising result since such treatment usually produces the opposite effect. The reactor effluent from the hydrogenation stage may be flashed to recover hydrogen for possible recycle and fed to a steam stripper to remove excess light hydrogenated components. The oil can then be fractionated and the lube fractions dewaxed. This dewaxing step can be carried out, for example, by pressing or by solvent dewaxing using methyl ethyl ketone and toluene as the solvent system. Dewaxing may be carried out prior to the initial hydrocracking step but it is preferred to conduct dewaxing after hydrogenation has been completed. No additional finishing is required. Yields of about 60 to 80 volume percent, based on the raw stock, of 95 VI oils are not uncommon and finished base oils having viscosity indexes of 120 and higher are obtained in economical yields, e.g., in the range of about 40 volume percent and higher.

The following example is illustrative of the method of this invention:

Deasphalted petroleum residuum was fed to an isothermal reactor unit having a nickel-tungstate on boria-aluminia catalyst in the first or hydrocracking stage and nickel-molybdate on alumina catalyst in the second or hydrogenation stage. The catalysts were macrosize and presulfided. The feedstock employed had the following specifications:

VI (D-2270) (dewaxed basis) 76 Gravity, .degree.API 23.1 Flash, .degree.F. 555 Viscosity, SUS/210.degree.F. 154.4 Pour, .degree.F. 120+ ASTM color Dark Carbon residue (Con.), wt.% 1.58 10% boiling point >1,000.degree.F.

table I lists operating conditions and dewaxed oil inspections for nominal 100 and 130 VI operations. --------------------------------------------------------------------------- TABLE I

Operation 100 VI 130 VI __________________________________________________________________________ Pressure, p.s.i.g., (1st & 2nd stages) 2,500 2,500 Temperature (1st stage),.degree.F. 775 815 (2nd stage),.degree.F. 700 700 WHSV (1st stage) 1.0 1.0 (2nd stage) 1.5 th 1.5 H.sub.2 Rate, SCF/bbl.(1st & 2nd stages) 2,500 2,500 Second-Stage Product Oil Inspection (dewaxed basis) Yield, vol. % 61 50 Gravity, .degree.API 28.7 33.2 Flash, .degree.F. 405 375 Viscosity, SUS/100.degree.F. 605.8 180.9 Viscosity, SUS/210.degree.F. 70.17 47.27 VI (D-2270) 100 128 Pour, .degree.F. +5 +10 ASTM Color L2.0 L1.5 Carbon Residue (Con.) 0.026 0.004 Specific Dispersion 102.4 101.5 __________________________________________________________________________

The catalysts employed in the successive stages analyzed as follows: --------------------------------------------------------------------------- TABLE II

NiW on NiMo on Boria-Alumina Alumina __________________________________________________________________________ Nickel, wt.% 5.35 2.30 Tungsten Oxide, wt.% 12.15 -- Molybdenum Oxide, wt.% -- 15.60 Silicon Dioxide, wt.% 0.29 -- Boria, wt.% 5.06 -- Volatile matter at 1,200.degree. F. 3.98 (at 1,000.degree. F.) 0.86 Apparent Density, g./ml. 0.75 0.765 __________________________________________________________________________

Claims

It is claimed:

1. A process of preparing a mineral hydrocarbon lubricating oil having a viscosity index of at least about 90 on a dewaxed basis which comprises:

a. Contacting a mineral hydrocarbon oil feedstock of lubricating viscosity at 210.degree. F., at least about 90 weight percent of which boils above about 600.degree. F. and having a viscosity index of about 50 to 80, with molecular hydrogen under hydrocracking conditions including a temperature of about 725 to 875.degree. F., in the presence of a catalyst having minor, catalytically effective amounts of each of nickel, a member selected from the group consisting of tungsten and molybdenum, and boria on an active alumina support; and

b. Contacting hydrocarbon oil of lubricating viscosity from step (a) with molecular hydrogen under hydrogenation conditions including a temperature of about 550.degree. to 825.degree. F. in the presence of a solid hydrogenation catalyst at a hydrotreating severity such that not more than about 5 volume percent of the feed to step (b) boiling above 600.degree. F. is cracked to material boiling below about 600.degree. F. to produce oil of lubricating viscosity having a viscosity index of at least about 90 and at least about 20 viscosity index number greater than the hydrocarbon oil feedstock passing to step (a).

2. The process of claim 1 wherein said hydrocracking conditions include a hydrogen partial pressure of about 1,000 to 5,000 p.s.i.g., a weight hourly space velocity of about 0.3 to 3 WHSV and a molecular hydrogen to hydrocarbon feed ratio of about 1,000 to 5,000 standard cubic feet per barrel of feed.

3. The process of claim 2 wherein the catalysts are in sulfide form.

4. The process of claim 3 wherein the hydrocracking catalyst contains about 2 to 10 weight percent nickel, about 10 to 20 percent of the member selected from the group consisting of tungsten and molybdenum on an oxide basis, and about 2 to 10 percent boria.

5. The process of claim 4 wherein the selected member of the catalyst employed in the hydrocracking stage is tungsten.

6. The process of claim 2 wherein said hydrogenation conditions include a temperature of about 550.degree.to 825.degree. F., a hydrogen partial pressure of about 1,000 to 5,000 p.s.i.g., a weight hourly space velocity of about 0.3 to 5 WHSV and a molecular hydrogen to hydrocarbon feed ratio of about 500 to 3,500 standard cubic feet per barrel of feed.

7. The process of claim 6 wherein the catalyst employed in the hydrogenation stage contains minor, catalytically-effective amounts of a member selected from the group consisting of nickel and cobalt, and molybdenum on alumina.

8. The process of claim 7 wherein the catalyst is in sulfide form.

9. The process of claim 8 wherein the hydrocracking catalyst contains about 2 to 10 weight percent nickel, about 10 to 20 percent of the member selected from the group consisting of tungsten and molybdenum on an oxide basis, and about 2 to 10 percent boria.

10. A process of preparing a mineral hydrocarbon lubricating oil having a viscosity index of at least about 90 on a dewaxed basis which comprises:

a. Contacting a mineral hydrocarbon oil feedstock of lubricating viscosity at 210.degree. F., at least 90 weight percent of which boils above about 1,000.degree. F. and having a viscosity index of about 50 to 80, with molecular hydrogen under hydrocracking conditions including a temperature of about 750.degree. to 850.degree. F., a hydrogen partial pressure of about 1,500 to 3,000 p.s.i.g., a weight hourly space velocity of about 0.5 to 2 WHSV and a molecular hydrogen to hydrocarbon feed ratio of about 1,500 to 3,000 standard cubic feet per barrel of feed, in the presence of a catalyst containing about 2 to 10 weight percent nickel, about 10 to 20 percent tungsten on an oxide basis and about 2 to 10 percent boria on an active alumina support, the metals of the catalyst being present in the sulfide form; and

b. Contacting hydrocarbon oil of lubricating viscosity from step (a) with molecular hydrogen under hydrogenation conditions, including a temperature of about 600.degree. to 800.degree. F., a hydrogen partial pressure of about 1,500 to 3,000 p.s.i.g., a weight hourly space velocity of about 0.5 to 3 WHSV and a molecular hydrogen to hydrocarbon feed ratio of about 1,500 to 2,500 standard cubic feet per barrel of feed in the presence of a solid hydrogenation catalyst containing minor, catalytically effective amounts of a member selected from the group consisting of nickel and cobalt, and molybdenum on alumina, the metals of the catalyst being present in the sulfide form, to produce oil of lubricating viscosity having a viscosity index of at least about 90 and at least about 30 viscosity index numbers greater than the hydrocarbon oil feedstock passing to step (a).

11. The process of claim 1 wherein the product from step (b) is fractionated to separate oil of lubricating viscosity and the lubricating oil fraction is dewaxed.

12. The process of claim 10 wherein the product from step (b) is fractionated to separate oil of lubricating viscosity and the lubricating oil fraction is dewaxed.