Process for the preparation of lubricating oils

Abstract

A process for the preparation of lubricating oils of enhanced stability comprising hydrocracking a hydrocarbon oil the predominant portion of which exhibits an initial boiling point above about 650.degree.F. over a hydrocracking catalyst, fractionating the resulting hydrocrackate to form at least two lubricating oil fractions, and hydrogenating each of said fractions over a hydrogenation catalyst.

Description

This invention relates to an improved process for the preparation of lubricating oils. More particularly, this invention relates to an improved process for hydrogenating hydrocracked lubricating oils.

Lubricating oils are susceptible to decomposition caused by contact with light, especially ultraviolet light and oxygen.

Lubricating oils derived from hydrocracked vacuum distillates and/or deasphalted oils have been found deficient as compared to conventional solvent-refined lubricating oils in that they are more unstable to daylight and air, and are rapidly degraded to sludge. Attempts to overcome this deficiency via hydrogenation have proved unsatisfactory. Generally, hydrogenation of the hydrocrackate yields, after subsequent fractionation and de-waxing, lubricating oils of improved color, but only slightly improved stability.

Accordingly, it is an object of the present invention to provide an improved process for the preparation of lubricating oils.

It is another object of the present invention to provide an improved process for hydrogenating hydrocracked lubricating oils whereby lubricating oils of significantly improved color and stability are obtained.

These as well as other objects are accomplished by the present invention which provides a process for the preparation of lubricating oils of enhanced stability comprising:

I. hydrocracking a liquid hydrocarbon oil the predominant portion of which exhibits an initial boiling point above about 650.degree.F. over a hydrocracking catalyst;

Ii. fractionating the resulting hydrocrackate to form at least two lubricating oil fractions; and

Iii. hydrogenating each of said fractions over a hydro-genation catalyst.

The process of the present invention will become more completely understood from the drawings, wherein:

FIGS. 1 to 3 are schematic arrangements illustrating, the process of the present invention and showing a de-waxing treatment at various stages in the processing.

The liquid hydrocarbon oil feedstocks that are suitable for use in the process of the present invention include hydrocarbons, mixtures of hydrocarbons and particularly hydrocarbon fractions, the predominant portions of which exhibit inital boiling points above about 650.degree.F. Unless otherwise indicated, boiling points are taken at atmospheric pressure. Nonlimiting examples of useful process feedstocks include: crude oil vacuum distillates from paraffinic or naphthenic crudes, deasphalted residual oils, the heaviest fractions of catalytic cracking cycle oils, coker distillates and flash or thermally cracked oils and the like. These fractions may be derived from petroleum crude oils, shale oils, tar sand oils, coal hydrogenation products and the like. Preferred feedstocks include: deasphalted petroleum oils that exhibit initial boiling points in the range of from about 850.degree.-1050.degree.F. and a conradson carbon residue number less than about 3 and heavy gas oils that boil predominantly between about 650.degree. and 1050.degree.F. and exhibit viscosities ranging from about 35-200, preferably 40-100 S.U.S. at 210.degree.F. In the embodiments illustrated in each of the figures, the feedstock is charged via line 2 into a catalytic hydrocracker 10 containing one or more beds of hydrocracking catalyst wherein it is contacted with hydrogen which is charged to the hydrocracking unit via line 4 to effect both hydrotreating and conversion of the feedstock in one operation.

Useful hydrocracking catalysts include (a) metal compounds contained on a porous non-zeolitic support, and (b) zeolite-containing catalysts having exchanged or deposited catalytic metals. Suitable catalyst materials falling within the first category are the oxides and/or sulfides of Group VIB metals, such as molybdenum and/or tungsten, preferably composited with a Group VIII metal oxide and/or sulfide such as the oxides or sulfides of nickel and/or cobalt. Preferred catalysts of this type comprise sulfided composites of molybdenum oxide and nickel oxide supported on a porous, relatively non-cracking carrier such as activated alumina, silica-alumina or other difficultly reducible refractory oxides. When alumina or silica-alumina are employed as supports, they may be promoted with phosphorous or phosphorous-containing compound such as phosphoric acid. The most preferred catalyst materials of this general type contain about 2-6 weight percent nickel and about 5-25 weight percent molybdenum.

As described above, zeolite-containing materials can also be employed as the process catalyst. These catalysts comprise a crystalline aluminosilicate (sieve component) and a porous, relatively inert, thermally stable inorganic adjuvant (amorphous component). The porous adjuvant is preferably alumina, silica and mixtures thereof. The crystalline aluminosilicates employed in the preparation of these catalysts can comprise one or more natural or synthetic zeolites. Representative examples of particularly preferred zeolites are zeolite X, zeolite Y, zeolite L, faujasite and mordenite. Synthetic zeolites have been generally described in U.S. Pat. Nos. 2,882,244, 3,130,007 and 3,216,789, the disclosures of which are incorporated herein by reference.

The silica/alumina mole ratio of useful aluminosilicates is greater than 2.5 and preferably ranges from about 2.5 to 10. Most preferably this ratio ranges between about 3 and 6. These materials are essentially the dehydrated forms of crystalline hydrous siliceous zeolites containing varying quantities of alkali metal and aluminum with or without other metals. The alkali metal atoms, silicon, aluminum and oxygen in the zeolites are arranged in the form of an aluminosilicate salt in a definite and consistent crystalline structure. The structure contains a large number of small cavities, interconnected by a number of still smaller holes or channels. These cavities and channels are uniform in size. The pore diameter size of the crystalline aluminosilicate can range from 5 to 15 A and preferably from 5 to 10 A.

The aluminosilicate component may comprise a sieve of one specific pore diameter size or, alternatively, mixtures of sieves of varying pore diameter size. Thus, for example, mixtures of 5 A and 13 A sieves may be employed as the aluminosilicate component. Synthetic zeolites such as type-Y faujasites are preferred and are prepared by well-known methods such as those described in U.S. Pat. No. 3,130,007.

The aluminosilicate can be in the hydrogen form, in the polyvalent metal form or in the mixed hydrogen-polyvalent metal form. The polyvalent metal or hydrogen form of the aluminosilicate component can be prepared by any of the well-known methods described in the literature. Representative of such methods is ion-exchange of the alkali metal cations contained in the aluminosilicate with ammonium ions or other easily decomposable cations such as methyl-substituted quaternary ammonium ions. The exchanged aluminosilicate is then heated at elevated temperatures of about 300.degree.-600.degree.C. to drive off ammonia, thereby producing the hydrogen form of the material. The degree of polyvalent-metal or hydrogen exchange should be at least about 20%, and preferably at least about 40% of the maximum theoretically possible. In any event, the crystalline aluminosilicate composition should contain less than about 6.0 wt. % of the alkali metal oxide based on the final aluminosilicate composition and, preferably, less than 2.0 wt %, i.e. about 0.3 wt. % to 0.5 wt. % or less.

The resulting hydrogen aluminosilicates can be employed as such, or can be subjected to a steam treatment at elevated temperatures, i.e. 427.degree. to 704.degree.C. for example, to effect stabilization, thereof, against hydrothermal degradation. The steam treatment, in many cases, also appears to effect a desirable alteration in crystal structures resulting in improved selectivity.

The mixed hydrogen-polyvalent metal forms of the aluminosilicates are also contemplated. In one embodiment the metal form of the aluminosilicate is ion-exchanged with ammonium cations and then partially back-exchanged with solutions of the desired metal salts until the desired degree of exchange is acheived. The remaining ammonium ions are decomposed later to hydrogen ions during thermal activation. Here again, it is preferred that at least about 40% of the monovalent metal cations be replaced with hydrogen and polyvalent metal ions.

Suitably, the exchanged polyvalent metals are transition metals and are preferably selected from Groups VIB and VIII of the Periodic Table. Preferred metals include nickel, molybdenum, tungsten and the like. The most preferred metal is nickel. The amount of nickel (or other metal) present in the aluminosilicate (as ion-exchanged metal) can range from about 0.1 to 20% by weight based on the final aluminosilicate composition.

In addition to the ion-exchanged polyvalent metals, the aluminosilicate may contain as non-exchanged constituents one or more hydrogenation components comprising the transitional metals, preferably selected from Groups VIB and VIII of the Periodic Table and their oxides and sulfides. Such hydrogenation components may be combined with the aluminosilicate by any method which gives a suitably intimate admixture, such as by impregnation. Examples of suitable hydrogenation metals, for use herein, include nickel, tungsten, molybdenum, platinum, palladium and the like, and/or the oxides and/or sulfides thereof. Mixtures of any two or more of such components may also be employed. Particularly preferred metals are tungsten and nickel. Most preferably, the metals are used in the form of their oxides. The total amount of hydrogenation components present in the final aluminosilicate composition can range from about 0.05 to 50 wt. %, preferably from 0.1 to 25 wt. % based on the final aluminosilicate composition. The final weight % composition of the crystalline component of the total catalyst will range from about 10 to 70 wt. % and preferably from about 10 to 30 wt. %, i.e. 20 wt. % based on total catalyst. The final weight % composition of the amorphous component will range from about 30 to 90 wt. % and preferably from about 70 to 90 wt. %, i.e. 80 wt. % based on total catalyst.

The amorphous component and the crystalline aluminosilicate component of the catalyst may be brought together by any suitable method, such as by mechanical mixing of the particles thereby producing a particle form composite that is subsequently dried and calcined. The catalyst may also be prepared by extrusion of wet plastic mixtures of the powdered components following by drying and calcination. Preferably the complete catalyst is prepared by mixing the metal-exchanged zeolite component with alumina or silica-stabilized alumina and extruding the mixture to form catalyst pellets. The pellets are thereafter impregnated with an aqueous solution of nickel and molybdenum or tungsten materials to form the final catalyst. The preferred catalyst species are a nickel exchanged hydrogen faujasite admixed with a major amount of alumina, the final catalyst also containing deposited thereon a minor amount of a transition metal hydrogenation component, such as nickel and/or tungsten and/or molybdenum metal or their oxides or sulfides.

The temperature within the hydrocracking unit can range from about 550.degree. to about 850.degree.F. and preferably ranges from about 650.degree. to about 800.degree.F. Pressure within the unit can range from about 500 to about 4000 psig. and preferably ranges from about 1,000 to about 3,000 psig. The liquid hourly space velocity (LHSV) can range from about 0.2 to 10 and preferably ranges from about 0.5 to about 5. The hydrogen to hydrocarbon ratio ranges from about 1 to about 15 M.s.c.f./b. and preferably ranges from about 2 to about 6 M.s.c.f./b.

The total effluent from the reactor 10 is passed into a heat exchanger or suitable cooling device 12. In the heat exchanger 12, the effluent is cooled to temperatures at which gaseous hydrogen can be separated from the liquid phase. The thus cooled effluent is passed into a high pressure separator 14. The gaseous phase containing substantial amounts of hydrogen is removed and can be recycled to hydrocracker 10 through line 16. A liquid product from the high pressure separator 14 is then passed through a depressurizing zone 18.

In cocnducting the process of the present invention, it may be necessary to de-wax the liquid product at some stage in the processing. The exact stage in the process sequence for performing the de-waxing operation is not critical and is normally dictated by economics and the local refining situation with regard to the availability of equipment, materials, etc. For example, the de-waxing can be performed: before fractionation, as illustrated in FIG. 1; after fractionation but before hydrogenation, as illustrated in FIG. 2; of after hydrogenation, as illustrated in FIG. 3.

According to the embodiment illustrated in FIG. 1, the liquid product from depressurizing zone 18 is charged to a suitable de-waxing unit 20, wherein the wax is separated and removed through conduit 22 as a result of precipitation in the presence of a solvent introduced to the unit through line 24. The solvent and oil mixture from the de-waxing unit 20 is charged to stripper 26 wherein the solvent is removed by steam stripping. The mixture of steam and solvent is removed via line 28 and sent to a solvent recovery system (not shown).

The de-waxed liquid product effluent is then charged to a suitable fractionating tower 30 via line 32. In the fractionator 30, the de-waxed liquid product is fractionated into two or more lubricating oil cuts.

It has been found in the present invention that by initially fractionating the liquid product, before or after de-waxing, from the hydrocracking unit into two or more lubricating oil fractions and separately hydrogenating each of these fractions, lube oils are produced which exhibit unusual stability to daylight and air. Surprisingly, it has been found that hydrogenation of the total liquid product does not produce a lube oil product characterized by stability to the formation of sludge under the influence of daylight or air oxidation. However, fractionation of the total liquid product into a number of fractions and the separate hydrogenation of each of these fractions unexpectedly does produce a lube oil having the desired stability characteristics. Thus, as shown in the illustration, the respective hydrocracked, de-waxed lube oil fractions are subjected to individual hydrogenation treatments. The effluent streams from conduits 34, 36 and 38 are respectively admixed with hydrogen and heated to about reaction temperature in heaters 58, 60 and 62. The heated mixtures are respectively charged to hydrogenation reactors 64, 66 and 68 each containing one or more beds of hydrogenation catalyst. The reaction products are removed via lines 70, 72 and 74 and flow into high pressure separators 76, 78 and 80 wherein the hydrogen is separated and recycled via lines 82, 84 and 86. The lube oils then flow respectively into low pressure separators 88, 90 and 92 wherein any small amount of light gases present are removed through conduits 94, 96 and 98. The finished lube oil products are then respectively removed through conduits 100, 102, and 104.

The embodiment illustrated schematically in FIG. 2 is similar to that of FIG. 1, differing only in that the dewaxing treatment is performed after fractionation of the total liquid product. According to this embodiment, each of the fractionator effluent streams 34, 36 and 38 are charged, respectively, to de-waxing units shown generally as 40, 42 and 44 and are dewaxed therein in the manner described with reference to FIG. 1. The de-waxed liquid effluent streams 46, 48 and 50 are then hydrogenated as in the embodiment illustrated in FIG. 1.

The embodiment illustrated schematically in FIG. 3 is similar to that to FIGS. 1 and 2, differing only in that the de-waxing treatment is performed after hydrogenation. According to this embodiment the total liquid effluent from the hydrocracker is fractionated into three narrow boiling range lubricating oil fractions which are separately hydrogenated. The hydrogenated product effluents 100, 102 and 104 are then passed through de-waxing units shown generally as 106, 108 and 110 and are de-waxed therein in the manner described with reference to FIG. 1. The finished lube oil products are then removed through conduits 112, 114 and 116 respectively.

In each instance, hydrogenation is conducted at temperatures ranging from about 350.degree. to about 600.degree.F., at pressures from about 400 to about 3000 psig. at space veolicities (LHSV) between about 0.1 and 2. The hydrogenation catalyst employed must be active enough not only to hydrogenate the olefins, diolefins and color bodies within the lube oil fractions, but also to reduce the aromatic content of these fractions to a value of below about 1% by weight. Suitable hydrogenation catalysts include conventional metallic hydrogenation catalysts, particularly the Group VIII metals such as cobalt, nickel, palladium, platinum and the like, associated with suitable carriers such as bauxite, alumina, silica gel, silica-alumina composites, crystalline aluminosilicate zeolites, and the like. Nickel is a particularly preferred hydrogenation catalyst. If desired, Group VIII metals associated with molybdates can also be suitably employed. It has been found that the sulfided forms of these metals are not particularly suitable for use in accordance with the present invention.

The following examples further define, describe and compare methods of preparing lubricating oils of enhanced stability in accordance with the present invention. Parts and percentages are by weight unless otherwise indicated.

Comparative example 1

lubricating oils are prepared by hydrocracking a feedstock over a catalyst at a temperature of 760.degree.F., a pressure of 2,500 psig and a space velocity of 0.5V/V/hr. with 5000 SCF/B pure hydrogen. The catalyst is used in the form of a 1/16 in. extrudate and comprises 4.5 wt. % NiO, 13.0 wt. % MoO.sub.3, 15 wt. % SiO.sub.2 and the remainder alumina. The feedstock is a blend of 40 LV% of a heavy vacuum distillate boiling between about 850.degree. and 1,050.degree.F from a West Texas crude and 60LV% of a blend of deasphalted vacuum residua from West Texas and other crudes. The hydrocrackate is fractionated to separate low boiling fuel products and to recover three lubricating oil fractions having respective boiling ranges of 700.degree. - 925.degree. F., 925.degree. - 1050.degree.F. and 1050.degree.F. plus. These lubricating oil fractions are then de-waxed. These lubricating oils are exposed to daylight and air and are found to rapidly form a heavy brown sludge. The results obtained are summarized in Table I below:

TABLE I ______________________________________ Days Exposed to Lubricating Oil Tag Robinson Light and Air to Fractions (.degree.F) Color Form Sludge ______________________________________ 700 - 925 11 2 925 - 1050 5 2 1050 + 1 2 ______________________________________

It can be seen that lubricating oils prepared in this manner exhibit both poor color and stability to daylight and air as manifested by the rapid formation and deposition of a heavy brown sludge upon exposure to daylight and air.

Comparative example 2

a liquid hydrocrackate obtained in the manner described in Comparative Example 1 is hydrogenated by contacting said hydrocrackate with 5000 SCF/B pure hydrogen over a catalyst comprising 58 wt. % nickel on a kieselguhr support at 500.degree.F., 2,500 psig., and a space velocity of 0.5 V/V/hr. Thereafter, the hydrogenated product is fractionated and de-waxed to provide lubricating oils of improved color as compared to those obtained in Comparative Example 1; however, only slight improvement is obtained with respect to stability to daylight and air. The results obtained are shown in Table II below:

TABLE II ______________________________________ Days Exposed to Lubricating Oil Tag Robinson Light and Air to Fractions (.degree.F) Color Form Sludge ______________________________________ 700 - 925 171/2 3 925 - 1050 9 4 1050 + 7 4 ______________________________________

It can be seen that although hydrogenating of the hydrocrackate aids in improving color, it is of little effect in improving stability to light and air.

EXAMPLE 1

A hydrocrackate obtained in the identical manner described in Comparative Example 1 is fractionated into three lubricating oil cuts and these narrow boiling range materials are de-waxed and then hydrogenated separately employing a catalyst having the same composition as that in Comparative Example 2, above. Hydrogenation is conducted at 500.degree.F. at 2000 psig., at space velocities of at least about 2 V/V/hr. with 5,000 SCF/B of pure hydrogen. Lube oils obtained in this manner exhibit excellent color, are extremely stable to daylight and air. The results obtained are summarized in Table III below:

TABLE III ______________________________________ Lubricating Space Tag Days Exposed to Oil Velocity Robinson Light and Air to Fractions (.degree.F) (V/V/hr.) Color Form Sludge ______________________________________ 700 - 925 2 +34.sup.(1) >14 925 - 1050 3 18 >50 1050 + 5 16 >50 ______________________________________ .sup.(1) Saybolt Color

It can be seen from Table III that both color and stability are significantly improved in the process of the present invention as compared to the results obtained by hydrogenating the total liquid product from hydrocracking as shown in Comparative Example 2, or by simply hydrocracking as shown in Comparative Example 1. The process of the present invention is also more economical than that wherein the total liquid hydrocrackate is hydrogenated due to the much higher space velocity which can be employed. This enables higher through puts or lower reactor pressures to be used.

Claims

What is claimed is:

1. A process for the preparation of lubricating oils of enhanced stability comprising:

i. hydrocracking a liquid hydrocarbon oil feedstock, the predominant portion of which exhibits an initial boiling point above about 650.degree.F. over a hydrocracking catalyst under hydrocracking conditions to produce a hydrocrackate;

ii. fractionating said resulting hydrocrackate to form at least two lubricating oil fractions; and

iii. hydrogenating each of said fractions over a hydrogenation catalyst consisting of Group VIII metals, said Group VIII metals being supported on a carrier, said hydrogenating being carried out under conditions so as to obtain a product having an aromatics content of below about 1% by weight.

2. Process as defined in claim 1 wherein the hydrocrackate is de-waxed prior to fractionation.

3. Process as defined in claim 1 wherein the lubricating oil fractions are each de-waxed prior to hydrogenation.

4. Process as defined in claim 1 wherein the lubricating oil fractions are de-waxed after hydrogenation.

5. Process as defined in claim 1 wherein the hydrocracking catalyst comprises oxides and/or sulfides of molybdenum and/or tungsten on a porous non-zeolitic support.

6. Process as defined in claim 1 wherein said Group VIII metal is nickel.

7. Process as defined in claim 1 wherein the hydrocracking catalyst comprises (1) from 10 to 70 wt. % of a crystalline aluminosilicate having a silica/alumina mole ratio greater than about 2.5, upon which is deposited or base exchanged, from about 0.05 to 50 wt. % based on the aluminosilicate, of a transition metal hydrogenation component; and (2) from 30 to 90 wt. % of a porous, substantially inert, thermally stable inorganic adjuvant upon which is deposited a minor proportion of a transition metal hydrogenation component.

8. Process as defined in claim 1 wherein the hydrocracking catalyst compress (1) from 10 to 30 wt. % of a crystalline aluminosilicate having a silica/alumina ratio of from 3 to 6, upon which is deposited or base exchanged from 0.1 to 25 wt. % based on the aluminosilicate, of a transition metal hydrogenation component; and (2 ) from 70 to 90 wt. % of a porous, substantially inert, thermally stable inorganic adjuvant upon which is deposited a minor proportion of a transition metal hydrogenation component.

9. Process as defined in claim 1 wherein hydrocracking is conducted at temperatures varying from about 550.degree. to about 850.degree.F.; pressures varying from about 500 to about 4,000 psig.; liquid hourly space velocities varying from about 0.2 to 10 and hydrogen/hydrocarbon ratios varying from about 1 to about 15 M.s.c.f./b.

10. Process as defined in claim 1 wherein the hydrogenation is conducted at temperatures varying from about 350.degree. to about 600.degree.F.; pressures varying from about 400 to about 3,000 psig.; and liquid hourly space velocities varying between about 0.1 and 2.

11. A process for the preparation of lubricating oils of enhanced stability comprising:

i. hydrocracking a liquid hydrocarbon oil feedstock the predominant portion of which exhibits an initial boiling point above about 650.degree.F. over a hydrocracking catalyst comprising (1) from 10 to 30 weight % of a crystalline aluminosilicate having a silica/alumina ratio of from 3 to 6, upon which is deposited or base exchanged from 0.1 to 25 weight %, based on aluminosilicate, of a transition metal hydrogenation catalyst, and (2) from 70 to 90 weight % of a porous, substantially inert, thermally stable inorganic adjuvant upon which is deposited a minor proportion of a transition metal hydrogenation component to produce a hydrocrackate;

ii. fractionating said resulting hydrocrackate to form at least two lubricating oil fractions;

iii. dewaxing each of said lubricating oil fractions; and

iv. hydrogenating each of said dewaxed lubricating oil fractions over a hydrogenation catalyst consisting of nickel on a kieselguhr support at a temperature ranging from about 350.degree. to about 600.degree.F., at a pressure from about 400 to about 3,000 psig and a space velocity of between about 0.1 and 2 so as to reduce the aromatics content of each of said fractions to below about 1% by weight.