US3746635A

US3746635A - Lubricating oil refining process

Info

Publication number: US3746635A
Application number: US00101708A
Authority: US
Inventors: R Woodle
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1970-12-28
Filing date: 1970-12-28
Publication date: 1973-07-17
Anticipated expiration: 1990-07-17
Also published as: DE2164871A1; AU3745671A; JPS5243844B1; AU449859B2; DE2164871B2; IT944396B; CA956584A; GB1311400A; ES398381A1

Abstract

A PROCESS FOR THE REFINING OF LUBRICATING OILS BY SOLVENT EXTRACTION OF A LUBRICATING OIL FRACTION FROM PARAFFIN BASE CRUDE TO FORM AN INTERMEDIATE VISCOSITY INDEX LUBRICATING OIL STOCK, DEWAXING THE INTERMEDIATE VISCOSITY INDEX LUBRICATING OIL STOCK AND SOLVENT FRACTIONATING THE DEWAXED STOCK TO PRODUCE A HIGH VISCOSITY INDEX LUBRICATING OIL STOCK AND A LOW VISCOSITY INDEX LUBRICATING OIL STOCK. THE INTERMEDIATE VISCOSITY INDEX LUBRICATING OIL STOCK MAY BE FINISHED PRIOR TO SOLVENT FRACTIONATION BY ACID TREATING, CLAY CONTACTING OR HYDROTREATING. THE SOLVENT EMPLOYED IN THE SOLVENT REFINING STEP MAY BE FURFURAL AND THE SOLVENT EMPLOYED IN THE SOLVENT FRACTIONATION STEP MAY BE NMETHYL-2-PYRROLIDONE.

Description

July 17, 1973 R. A. WOODLE LUBRICATING OIL REFINING PROCESS IVI United States Patent U.S. Cl. 20S- 36 2 Claims ABSTRACT F THE DISCLOSURE A process for the refining of lubricating oils by solvent extraction of a lubricating oil fraction from paraffin base crude to form an intermediate viscosity index lubricating oil stock, dewaxing the intermediate viscosity index lubricating oil stock and solvent fractionating the dewaxed stock to produce a high viscosity index lubricating oil stock and a low viscosity index lubricating oil stock. The intermediate viscosity index lubricating oil stock may be finished prior to solvent fractionation by acid treating, clay contacting or hydrotreating. The solvent employed in the solvent refining step may be furfural and the solvent employed in the solvent fractionation step may be N- methyl-Z-pyrrolidone.

BACKGROUND OF THE INVENTION In the manufacture of lubricating oils from crude petroleum a number of processing steps are required to incorporate the desired characteristics in the finished lubricating oil products. These characteristics inlude a selected viscosity range, and depending upon the quality level, high viscosity index, low pour point, light color, stability, and resistance to oxidation. Stocks for lubricating oil manufacture are separated from crude petroleum by vacuum distillation. Typically, several fractions of different boiling range are produced thereby providing fractions of different viscosity ranges. The vacuum distillate is then treated by solvent extraction to produce a lubricating oil stock of improved viscosity index, i.e., to produce an oil which exhibits relatively little change in Viscosity with change in temperature. The vacuum distillates and solvent refined distillates have a relatively high pour point due to the presence of wax. Typically, wax is removed to produce low pour point lubricating oil stocks by the solvent dewaxing process. Improved color, stability, and resistance to oxidation are imparted by finishing treatments which may include such Well known process steps as acid treating, clay contacting, or mild hydrogenation or a combination of such finishing treatments. The solvent refining process also improves the stability of the lubricating oil stock by virtue of the separation of polar compounds and polynaphthenic type materials.

In the solvent extraction process, the oil to be treated is contacted with a selective solvent which exhibits the desired selectivity for at least one component of the hydrocarbon charge and the solvent is at least partially irnmiscible under the conditions of contact in the contacting zone with the hydrocarbon mixture. Solvents which may be employed, for example, include furfural, N-methyl-Z- pyrrolidone, nitrobenzene, liquid propane, liquid sulfur dioxide, beta-beta-dichloroether, phenols, and other various well known organic and inorganic selective solvents.

In the solvent dewaxing process, the wax bearing oil is mixed with a solvent having substantially complete solvent action upon the oil component of the wax bearing oil charge and substantially no solvent action upon the wax contained therein at dewaxing temperatures of about l0 to -30 F. Such a solvent comprises, for example, a mixture of aliphatic ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and an aromatic hydrocarbon such as benzene, toluene, or a mixture of benzene and toluene. A number of other solvents are known which are useful for effecting separation between a hydrocarbon oil and wax including hydrocarbons less viscous than the oil, for example, naphtha, gasoline, pentanes, butanes, propanes, or mixtures thereof and certain hydrocarbon derivatives such as dichloromethane, methylene chloride, chloroform, and ethers.

In the use of mild hydrogenation as a lubricating oil finishing step, it is preferred to employ a catalyst such as nickel sulfide-tungsten sulfide, molybdenum sulfide, and cobalt molybdate. The hydrogenation step is conducted at temperatures within the range of about 400 to 750 F. and preferably within the range of about 500 to k650 F. Pressures of about 100 to 100G p.s.i.g. are employed, preferably of about 200 to 600 p.s.i.g. Liquid hourly space velocities of about 0.1 to 3.0 volumes of oil per volume of catalyst are employed and preferably about 0.5 to 2.0 v./v./hr. A hydrogen consumption of about 50 to 200 cubic feet per barrel of charge stock is employed. Suitably recycle hydrogen rates vary within the range of about 100 to 1000 standard cubic feet per barrel of charge and rates of about 100 to 500 s.c.f./ bbl. are preferred.

In modern petroleum refining technology, high viscosity index products are manufactured from high viscosity index base oils from parafiinic crude oils plus the addition of Viscosity index improvers. These viscosity index improvers are organic polymers, and they are inherently shear unstable. Desirably in the manufacture of premium high viscosity index products having high Shear stability, it is preferred to use a relatively high viscosity index base oil with a minimum amount of viscosity index improver. However, the refiner also has a demand for products, of a high viscosity index but not requiring maximum shear stability. Accordingly, the refiner needs a process to provide flexibility in the manufacture of high viscosity index lubricating oils some of which have high shear stability whereas others do not require this characteristic. Accordingly, it is an objective of this invention to provide a method of manufacturing a plurality of viscosity index grades of lubricating oil. It is a further objective of this invention to manufacture a plurality of grades of lubrieating oil in high yields in the simplest and most economical way.

SUMMARY OF THE INVENTION In accordance with the process of this invention, a Wax distillate such as is produced by the vacuum distillation of a paraffin base crude oil is treated by a process in sequence comprising solvent rening, dewaxing, and solvent fractionation. The solvent fractionation is a second step of solvent extraction in which both the raffinate and extract are finished lubricating oil stocks. When employing acid treating, clay contacting, or mild hydrogenation, steps usually referred to as finishing steps, the finishing step is applied to the dewaxed primary refined oil product prior to fractionation in the second solvent extraction step. An intermediate VI grade product may also be produced by withdrawal of a portion of the primary refined oil as such product.

In the primary extraction step, any of the solvents referred to above may be employed. However, it is preferred to employ furfural or N-methyl-Z-pyrrolidone. Op-

erating conditions are selected to produce a primary raffinate having a dewaxed viscosity index of about to and preferably about 90 to 96. When employing furfural as a solvent, extraction temperatures within the range of about to 225 F. and preferably about 170 to 200 F. are employed. Solvent dosages within the range of about 150 to 600 percent are employed in order to provide the desired VI level. When N-methyl-2-pyrrolidone is employed as solvent, solvent extraction temperatures within the range of 140 to 210 F. are employed and preferably within the range of 150 to 200 F. with solvent dosages within the range of 100 to 500 percent and preferably 150 to 400 percent.

The primary ra'inate is dewaxed to produce a lubricating oil fraction having the desired pour point. If desired, the dewaxed oil may be subjected to a linishing treatment for color and stability improvement as described above. The intermediate viscosity index stock is then subjected to a secondary solvent extraction or solvent fractionation to separate two lubricating oil fractions, the secondary ratiinate having a viscosity index of at least 100 and preferably about 105 to 125 and the secondary extract having a viscosity index of about 70 to 95. In the secondary extraction process it is preferred to employ N-methyl-Z-pyrrolidone as solvent since this solvent is capable of splitting the' charge into two -inished lubricating oil fractions without degrading the color or stability of the extract fraction. Since the oil charged to the reextraction step is already a dewaxed and finished oil, the separation effected in the re-extraction step may be carried out at high temperature, low dosage and at low selectivity conditions. The ability to use much higher temperatures than are usual with N-methyl-Z-pyrrolidone comes about because refined oil charged to the re-extraction step is much less miscible with the solvent than the wax distillates from which they are derived. The higher temperatures in turn allow lower solvent dosages to be used. Generally, the extraction temperatures in the reextraction step are not less than F. nor more than 40 F. below the temperature at which the mixture of 6 volumes of N-methyl-Z-pyrrolidone and 4 volumes of the charge oil became completely miscible. A preferred extraction temperature is about to 30 F. below the above detined miscibility temperature. At these temperatures, the solvent dosage may be varied to produce the desired final high VI level over a range of yields. The solvent dosage in general is in the range of about 100 to 800 volume percent with dosages in the range of 200 to 500 volume percent being preferred.

lDESCRIPTION OF THE DRAWING Oil charge, for example, a vacuum distillate from paratiin base crude oil is passed through line 11 to primary solvent contactor 2. In primary solvent contactor 2, oil is contacted in countercurrent flow with a selective solvent, for example, furfural introduced into contactor 2 through line 3. Contactor 2 may be any countercurrent liquid-liquid contacting apparatus such as a column packed with Raschig rings or a rotating disc contactor which effects multistage countercurrent contacting. The solvent and constituents extracted from the oil charge pass downwardly through the tower and are withdrawn as extract through line 4. Treated oil rising through contactor 2 containing some dissolved solvent is withdrawn from the top of the tower as rainate through line 5. Extract in line 4 is passed to solvent stripper 7 wherein the solvent is stripped from the dissolved constituents of the oil charge. Extract free of solvent is withdrawn through line 8 and recovered solvent is returned to solvent contactor 2 through line 3. Rainate in line 5 contains some sol` vent dissolved therein and is passed to solvent stripper 9 for recovery of the dissolved solvent. Recovered solvent is withdrawn through line 10 and combined with the solvent in line 3 to supply the solvent passed to solvent con;- tactor 2.

Treated oil free of solvent is withdrawn through line 11 and passed to dewaxing step 12. Lubricating oil stocks produced from wax distillates have relatively high pour points due to the presence of wax. Accordingly, in dewaxing step 12 wax is separated from the remaining lubricating oil stock by a process such as solvent dewaxing. In solvent dewaxing the wax bearing oil is admixed with a solvent which has substantially complete solvent action upon the oil component of the waxy oil charge and substantially no solvent action upon the wax contained therein at a dewaxing temperature of about +10 to -30 F. Such a solvent comprises, for example, a mixture of 50 percent methylethyl ketone and 50 percent toluene. Wax separated from dewaxing step 12 is withdrawn through line 13. Dewaxed oil having a pour point of -20 to +20 F. is withdrawn through line 14. The viscosity index of the dewaxed oil in line 14 is within the range of about 85 to and preferably within the range of about 90 to 96.

Dewaxed lubricating oil stock in line 14 is then passed to Afinishing step 17 if processing is required to improve the color, stability, or oxidation resistance of the lubricating oil stock. Finishing step 17 may comprise clay contacting, acid treating, or mild hydrogenation. Treated oil from finishing step 17 is discharged through line 18. Since the oil in line 18 is an intermediate viscosity index lubricating oil which has been finished, it is suitable for use in blending some grade of lubricating oil and a portion may be withdrawn for such use through line 19.

At least a portion of the oil in line 18 is passed to secondary solvent contractor 20. Solvent contractor 20 may be the same type and operated in a manner similar to that described in connection with contractor 2. The function of solvent contractor 20 is to fractionate the lubricating oil stock into a high viscosity lubricating oil fraction and a low viscosity index lubricating oil fraction. This fractionation is done by a solvent extraction technique. However, since both the extract and rainate fractions are intended for use in lubricating oil products, it is necessary that the solvent selected be a highly eiicient solvent to achieve sharp fractionation and it must also effect fraction without degrading the quality of either the rainate or extract fractions. Accordingly, it is preferred to use N-methyl-Z-pyrrolidone as solvent in the secondary sol-vent contactor. Solvent is introduced into contactor 20 through line 21. Extract is withdrawn through line 22 and passed to solvent stripper 23. In solvent stripper 23, the solvent is recovered as distillate through line 24 and returned through line 21 to contactor 20. Low VI lubricating oil having a VI within the range of about 65 to 95 and preferably 78 to 92 and a pour point within the range of about -10 to +20 F. is removed from the bottom of stripper 23 through line 25 and is discharged as product. Rainate from contactor 20 containing a small amount of dissolved solvent is discharged through line 27 and passed to solvent stripper 28. In solvent stripper 28, the small amount of dissolved solvent is withdrawn through line 29 and solvent free high VI lubricating oil fraction is withdrawn from stripper 28 through line 30. The high VI 1ubricating oil has a viscosity index in excess of 100 and preferably within the range of about to 125 and a pour point of about -10 to +20.

In the process illustrated in the figure, only a single iinishing step is needed. Optionally finishing step 17 may follow fractionation in secondary solvent contactor 20. In this case, it is necessary to separately treat each of the high VI, low VI and intermediate VI products in separate finishing steps or to treat each of the fractions as separate batches in the finishing facilities.

DESCRIPTION `OF THE PREFERRED EMBODIMENTS In an example of the process of this invention, a wax distillate is solvent extracted with furfural using a dosage of 230 volume percent and an extraction temperature of F. to produce an SAE 20 grade lubricating oil stock. The furfural refined oil is then dewaxed using methylethyl ketone-toluene as a solvent at a filtration temperature of 0 F. to produce an oil having a pour point of +5 F. The dewaxed-furfural refined oil is then decolorized by hydrogen treatment at 200 p.s.i.g. and 550 F. in the presence of a cobalt-molybdenum catalyst. The resulting intermediate viscosity index lubricating oil has the following tests:

Gravity, API 30.4 Flash, COC F. 435 viscosity, SUS at 210 F. 54.4 5 VI 90 Color, Lovibond (6 inch cell) 45 Pour, F +5 The intermediate viscosity index lubricating oil stock is 10 then fractionated by countercurrent contact with N-methyl-Z-pyrrolidone using a dosage of 200 volume percent solvent and a contacting temperature of 220 F.

The raliinate from the N-methyl-2-pyrrolidone fractionation comprises a high VI oil and the extract comprises a low VI lubricating oil stock. Tests and yields of the two fractions are as follows:

High vI Low v1 lubricating lubricating oil stock oil stock Gravity, API 32.0 26. 0 Flash, Coo, F 435 435 Viscosity SUS at 210 F 52.0 55.0 V 10a 75 Color, Lovibond (6 cell) 45 75 Pour, F +10 +5 25 Yield, vol. percent basis, intermediate VI The high VI lubricating oil stock is suitable for manufacture of premium lubricating oils having high shear stability. The low VI lubricating oil stock is suitable for inclusion in those products normally made from unextracted oils Where the change in viscosity with temperature is not critical to performance.

EXAMPLE II In this example, the intermediate VI oil of Example I is fractionated with N-methyl-Z-pyrrolidone employing a solvent dosage of 300 volume percent and a contacting temperature of 220 F. The following lubricating oil stocks are produced:

High VI Low VI lubricating lubricating oil stock oil stock Gravity, API 31.8 30.1 Flash, C00, F. 430 435 VI 115 e7 Pour F +10 +5 Yield, vol. percent basis, intermediate VI oil- 10. 0 90. 0

EXAMPLE III In the example, a light solvent neutral oil having a Viscosity equivalent to an SAE 7 grade oil is made by furfural refining, solvent dewaxing, and finishing. The neutral oil is then re-extracted using N-methyl-Z-pyrrolidone at 200 F. and 315 percent solvent dosage. The in- 55 termediate VI lubricating oil fraction from furfural refining and the high and low VI lubricating oil fractions produced by fractionation with N-methyl-Z-pyrrolidone have the following tests and yields:

Intermediate VI High VI Low VI lubricating lubricating lubricating oil stock oil stock oil stock Gravity, API 31. 5 33. 8 27. 9 Viscosity, SUS 210 F 42. 8 42. 5 43. 0 V 9e 111 87 Yield vol. percent basis, intermediate VI oil 100 38 62 6 EXAMPLE 1v In this exam-ple, a Wax distillate 40 useful in the manufacture of SAE 40 grade lubricating oils is extracted with furfural at a solvent dosage of 450 volume percent and a temperature of 210 F. to produce a 60 volume percent yield of a lubricating oil fraction having a dewaxed VI of 90. The resulting VI lubricating oil fraction is then fractionated using N-methyl-Z-pyrrolidone at a solvent dosage of 400 percent and at a refining temperature of 200 F. to produce a yield of 33 percent raffinate having a VI of to 66 percent yield of extract having a VI of 85.

EXAMPLE V In this example, the charge stock of Example IV is treated with N-methyl-2-pyrrolidone at a solvent dosage of 270 percent and a temperature of 200 F. to produce a yield of 40 percent of a 95 dewaxed VI intermediate grade lubricating oil. The resulting intermediate grade lubricating oil is then fractionated with N-methyl-2-pyrrolidone at a solvent dosage of 400 and a refining temperature of 200 F. to produce a 50 percent yield of raffinate having a VI of 100 and 50 percent yield of extract having a VI of 90.

I claim:

1. A process for the production of lubricating oils of improved properties which comprises treating a vacuum distillate derived from a parafiin base crude oil with a selective solvent in a first extraction zone forming a first rafiinate and a rst extract, dewaxing said first rafiinate forming a first lubricating oil stock having a pour point of -10 to +20 F. and a viscosity index of 85 to 100, hydronishing said first lubrication oil and treating at least a portion of said first hydrofinished lubricating oil stock with N-methyl-Z-pyrrolidone in a second extraction zone forming a second raflinate comprising a second lubricating oil stock having a pour point within the range of about -10 to +20 F. and a viscosity index in excess of 100 and a second extract comprising a third lubricating oil stock having a pour point within the range of -10 to +20o F. and a viscosity index within the range of about `65 to '95, the temperature in the second extraction zone being between 10 F. and 40 F. below the temperature at which a mixture of six volumes of N-niethyl-Z-pyrrolidone and four volumes of charge oil become completely miscible.

2. The process of claim 1 in which the second extraction zone temperature is between 15 F. and 30 F. below the miscibility temperature.

References Cited UNITED STATES PATENTS 2,952,610 9/1960 Fear 208-36 3,520,796 7/1970 Murphy et al. 2108-18 3,488,283 1/ 1970 Button et al. 208-36 3,472,757 10/ 1969 Morris et al. 208-36 2,967,147 1/ 1961 Cole 208-144 HERBERT LEVINE, Primary Examiner U.S. Cl. X.R. 208-18