US3470089A - Separation of solvent from raffinate phase in the solvent refining of lubricating oil stocks with n-methyl-2-pyrrolidone - Google Patents

Description

Sept. 30, 1969 H, c. MORRIS ET Ax.

SEPARATION OF SOLVENT FROM RAFFINATE PHASE IN THE SOLVENT REFINING OF LUBRICA'I'ING OIL STOCKS WITH N-METHYL-Z -PYRROLAIDONE Filed June 20, 1967 United States Patent Oihce 3,470,089 Patented sept. 3o, 1969 U.S. Cl. 208-326 9 Claims ABSTRACT OF THE DISCLOSURE In the solvent refining of a lubricating oil charge stock for the removal of constituents having a low viscosity index and poor stability, said lubricating oil charge stock is contacted with a solvent comprising N-methyl-Z-pyrrolidone effecting separation of a ranate-mix comprising a major portion of oil with a minor portion of said solvent dissolved therein and an extract-mix comprising a major portion of said solvent with said constituents having a low viscosity index and poor stability dissolved therein. Solvent is separated from rainate-mix by adding water in an amount of at least 2.0 weight percent of the N-methyl- Z-pyrrolidone dissolved therein effecting separation of an oil phase and a wet solvent phase comprising at least 2.0 weight percent water. Refined oil is separated by distilling remaining solvent therefrom. Wet solvent is recycled with solvent of lower water content to comprise at least a part of the solvent charged in contact with said lubricating oil charge stock.

BACKGROUND OF THE INVENTION Field of the invention In the manufacture of lubricating oils from crude petroleum, one or more fractions containing the lubricating oil constituents are separated by distillation, usually by vacuum distillation. The raw lubricating oil fractions contain unstable naturally occurring materials which tend to form deposits or become corrosive in operating equipment as a result of heating or oxidation or both. Additionally, in the case of paraffinic oils, it is often desirable to increase the viscosity index by removing the more aromatic lower viscosity index constituents from the oil. To accomplish this it is necessary to remove or destroy a significant amount of material present in the raw stock, typically ranging from 10 to 60 percent depending on the qualities desired in the product oil. The most common way to do this is by extraction with a solvent having selectivity for the more unstable molecules which are predominantly aromatic and non-hydrocarbon materials. Prior to the advent of solvent extraction, severe treatment with concentrated sulfuric acid was commonly used to destroy these undesirable materials.

In the treatment of oils to remove unstable, corrosive, and low viscosity index constituents of oil, a substantial amount of material isA removed from the charge stock, that is, an amount in excess of about l0 volume percent. This is distinctly different from decolorizing treatment in lubricating oil manufacture where only trace amounts of coloring material are removed, typically less than 1.0 percent. Here, handling losses are usually greater than the amount of material removed. Common methods us'ed for color improvement are, for example, clay treating, mild acid treating and hy-finishing (mild hydrogenation). Such color improvement steps are often used after solvent reiining. A raw stock that is only treated for color improvement is usually unsatisfactory as regards thermal and oxidating stability or viscosity index.

This invention is directed to the solvent refining of lubricating oil charge stocks with N-methyl-Z-pyrrolidone hereinafter referred to as NMP. In the solvent refining process, the lubricating oil charge stock is contacted with a solvent stream comprising NMP and not more than about 1.0 Weight percent water forming a railinate-mix comprising a major portion of oil with a minor portion of NMP dissolved therein. An extract-mix is also separated comprising a major portion of solvent with the extract constituents dissolved therein. This invention relates to an improved method of separating the NMP dissolved in the raffinate-mix.

Description of the prior art Heretofore, NMP has been known as a solvent for the separation of olelins, dioleiins, and aromatic hydrocarbons. The usual method of separation of solvent from the resulting extract and rainate-mix has been by simple distillation. Disadvantages of simple distillation are that the entire raffinate-mix must be subjected to distillation thereby subjecting the refined oil to an additional distillation step and requiring relatively large distillation facilities.

SUMMARY OF THE INVENTION It has now been found that a major portion of the solvent may be separated from the raffinate-mix by the addition of a small amount of water thereby reducing the solubility of the NMP in the oil and separating a wet solvent phase. The remaining NMP dissolved in the rafnate-mix is readily separated by a stripping distillation for example by steam stripping or vacuum steam stripping. The wet NMP phase separated from the rainate-mix by water dilution, although a major portion of the NMP dissolved in the railinate-mix, is a minor portion of the total solvent employed in the extraction system. This small stream of wet solvent may be combined with other solvent streams containing less water, for example, solvent separated from the extract-mix, and the combined stream having a water content less than about 1.0 weight percent water recycled to the extraction zone.

Solvent extraction with NMP may be applied to parain base oils for example, oils used in the manufacture of crankcase lubricants for internal combustion engines, and naphtenic oils for example, oils used in the manufacture of turbine lubricating oils. In the case of paraffin base oils, an extraction temperature within the range of about to 250 F. and preferably within the range of about to 180 F. is employed and a solvent dosage within the range of about 50 to 450 percent and preferably about 100 to 340 percent is employed. The corresponding extraction temperatures and dosages when relining naphthene oils are within the range of about 50 to 200 F., preferably within the range of about 75 to 150 F. and about 50 to 300 percent, and preferably about 75 to 200 percent respectively. Significantly the dosage of solvent employed is only about half that employed with furfural, a widely used selective solvent. Typically the viscosity index of parain base lubricating oil charge stocks is within the range of about 40 to 105 and the viscosity index of the refined lubricating oil stock is at least ten units higher.

In accordance with this invention water in an amount within the range of about 2 to 20 weight percent and preferably about 5.0 weight percent of the NMP in the raflinate-mix is added thereto to effect separation of a wet solvent phase. The effect of water addition to a rainate-mix containing 30 weight percent NMP produced in the treatment of a wax distillate at F. is shown in the following Table I.

Y TABLE I Water Added, Wt. basis NMP 5. 10. 0 20. 0 Oil layer:

Yield, wt. percent 76. 4 75.0 70. 8 NMP, Wt. percent..- 10. 6 8.0 6.0 Water, wt. percent.-. 0.4 2. 0 2. 7 Oil, wt. percent 89. 0 90.0 91. 3 RI at 71 C. of stripped oil 1. 4564 1. 4565 1. 4565 Wet solvent layer:

Yield, wt. percent. 23. 6 25.0 29. 2 N MP, wt. percent. 90.8 92. 82. 5 Water, wt. percent 5. 0 5. 9 12. 7 Oil, wt. percent. 4. 2 1. 6 4. 8 RI at 71 C. of stripped oil 1. 4638 1. 4786 1. 4641 Wt. percent N MP rejected from raffinate-mix 65 7 3 80 The amount of wet solvent layer separated may be increased by cooling the diluted rafiinate-mix to a temperature below the treating temperature. The degree of sepation of wet solvent from the refined oil phase is a function of the boiling range of the charge stock, the temperature of the raffinate-mix leaving the extractor, the amount of water added, and the degree of cooling. Generally, the lower the boiling range of the charge stock and the higher the raffinate-mix temperature leaving the extractor, the greater is the amount of solvent soluble in the oil phase. The greater the amount of water added and the lower the separation temperature, the greater is the volume of solvent removed in the separator. For a given charge stock, operating with the lowest possible raffinate-mix outlet temperature necessary to obtain the desired quality and the lowest practical wet solvent separation temperature minimizes the volume of solvent remaining in the oil phase and permits the separation of the desired amount of wet solvent with a minimum of water. The use of a minimum amount of dilution water permits the use of the largest volume of wet solvent from other processing steps while controlling the water content to 1.0 weight percent maximum. The volume of aromatic oil contained in the wet solvent is less than 0.3 weight percent of the recycled solvent which does not have any significant effect on the solvent power of the solvent recycled in the extraction step. The aromatic oil dissolved in the wet solvent is similar to the extract oil and does not build up in the recycle solvent since it is, in effect, displaced into the extract oil.

Dissolved water has a substantial effect upon the solvent refining characteristics of NMP. The effect is shown in a series of tests wherein a vacuum distillate :from crude distillation referred to as a Wax Distillate 7 and having a refractive index at 70 of 1.4741 is solvent refined with NMP at constant conditions of solvent dosage and extract outlet temperature with varying amounts of water dissolved in the NMP solvent. Results of this series of ltests are shown in Table II following:

TABLE II Extraction conditions:

Solvent dosage, volume percent 200 200 200 200 200 Extraction temperature,

F 154 154 154 154 154 Solvent composition:

NMP, weight percent 100. 0 99. 5 99. 0 98.0 95. 0 Water, weight percent 0 0. 5 1. 0 2. 0 5. 0 Yields:

Refined oil, weight percent- 76. 0 78. 0 78. 5 84. 6 89. 4 Extract oil, weight percent.- 24. 0 22.0 21. 5 15. 4 10. 6 Product Tests:

Refined oil RI at 71 0--..- 1.4605 1.4605 1.4608 1.4620 1.4630 Extract oil RI at 70 0-...- 1.5030 1.5072 1.5077 1.5194 1.5349 Solvent in raffinate-mix: Volume percent 16. 8 13. 8 10. 6 `Solvent in extractmix:Vo1

ume percent 89. 0 89. 6 90. 0 92. 5 95. 1

It will be noted that as water is added to the NMP solvent, the amount of oil extracted decreases. The effect of this reduced extraction of undesired constituents however, does not affect the refined oil quality until the amount of water in the solvent exceeds about 1.0 percent. The solvents efficiency in producing a refined oil of high quality is then significantly affected as shown by the higher refractive index of the refined oil at solvent water levels of 2.0 and above. It will also be noted that at 0.5 percent water, a higher yield of refined oil is obtained having the same quality as the product obtained with water-free solvent as indicated by the fined oil refractive index.

A series of tests is made to show the effect of water addition and cooling on the separation of solvent from the rafiinate-mix. The raffinate mix is produced by refining a Vacuuml Distillate 20 with NMP at a solvent dosage of volume percent, .an extract-mix outlet temperature of F. and a raffinate-mix outlet temperature of 190 F. The resulting raffinate-mix comprises 19.3 weight percent oil which upon stripping produces a stripped oil having a refractive index at 70 C. of 1.4605. Other portions of said raffinate-mix are treated by water addition, Water addition with cooling, or by cooling alone to effect separation of two phases, an upper oil layer containing dissolved solvent and water and .a bottom solvent layer containing dissolved oil and water. The yields and cornpositions of the resulting layers are shown in Table III following:

TABLE III Raflinate-mix treatment:

Water added, basis Wt. percent NMP in raffinate-mix.. 5. 0 5. 0 Nono Cooling from F to. 160 130 130 Separate oil phase:

Yield, Wt. percent 93. 1 86.5 85.7 8S. 4 Oil, wt. percent 85. 1 91. 6 92. 8 89. 0 Solvent, Wt. percent. 14. 1 8. 2 6. 9 11.0 Water, wt. percent 0.8 U. 2 0. 3 None Stripped oil, RI at 70 C 1.4600 1. 4602 1. 4600 1. 4605 Separated solvent phase:

Yield, wt. percent 6. 9 13. 5 14. 3 11. 6 Oil, wt. percent 0.5 5. 5 3. 2 4. 8 Solvent, wt. percent 87. 5 88. 7 91. 8 95. 2 Water, Wt. percent 12.0 5. 8 5. 0 None Stripped oil, RI at 70 C. 1, 4730 l, 4745 l, 4710 TABLE IV Solvent composition, volume percent:

NMP 100. 0 98. 0 100.0 95. 0

Water 0 2. 0 0 5. 0 Solvent refining condition:

Solvent dosage, volume percent charge 200 414 107 411 Extraction temperature, F 200 200 200 200 Refined oil yield, volume percent... 45. 2 50. 5 60. 0 66. 2 Refined oil quality: RI at 70 C 1, 4622 1, 4620 1, 4665 1,4667

Reference to Table IV shows that the solvent efficiency of NMP is significantly reduced by the presence of Water levels of 2.0 and 5.0 volume percent. This is clearly shown by the substantial increase in solvent dosage which is necessary to maintain the same refined oil refractive index which is a criterion of the quality of the refined oil. It will be noted that when 2.0 volume percent water is present, about twice as much solvent must be used to maintain the same refractive index, and when 5.0 volume percent water is present, about 4 times the amount of solvent is necessary to maintain the same refined oil refractive index.

BRIEF DESCRIPTION OF THE DRAWING The accompanying figure is a flow diagram of a solvent refining system employing the process of this invention. Although the figure illustrates particular arrangements of apparatus in which the invention may be pracdisc contactor, and it may include mechanical means to improve contacting such as sonic generators or pulsing means. Solvent is introduced in the top of extractor 2 through line 26. The charge oil constituents soluble in the solvent leave the extractor as extract-mix through into the rainate-mix and controlling the temperature to which this phase is cooled in balance with the amount of atmospheric ash tower overhead split to the recycle stream. y

Atmospheric flash tower bottoms of reduced solvent line 3 at a temperature of about 185 F. with the bulk 5 content is withdrawn through line 41, through heating of the solvent. The charge stock constituents insoluble coil 42 in furnace 43 where it is heated to about 538 in the solvent leave the extractor through line 4 at a F. and discharged through line 44 to pressure hash tower temperature of about 190 F. as ra'inate-mix containing 45 at a top tower pressure of about 55 pounds per square some dissolved solvent. Water in an amount of about 5 10 inch absolute. About 90 percent of the solvent remaining weight percent of the dissolved solvent in line 5 in inin the extract-mix is removed as dry distillate through jected into the raffinate-mix .and the mixture passed to line 46. This stream is passed through heat exchanger 32 cooler 7. Cooled, diluted raffinate-mix at about 130 F. and line 47 to comprise the dry solvent combined with is passed through line 8 to separator 9. Separator 9 is the wet solvent in line 25. Extract oil with a small amount divided into two compartments by wier 10. Wet solvent of remaining solvent is Withdrawn through line 50 and phase having an upper level 11 is separated in the compassed at about 523 F. to vacuum flash tower 51 which partmcnt behind wier 10 and is withdrawn through line is operated at a top tower pressure of about 2 pounds per 12, and recycled with dry solvent through lines and square inch absolute so that about 95 percent of the re- 26 to extractor 2. Separated oil phase, having an upper maining solvent is flashed overhead through line 52. Since level 13, rises above interface 11, overflows wier 10 and 20 this S01V11t iS 2180 dry, it iS paSSed through line 53 and collects in the outlet compartment of separator 9. Sepacombined with the dry solvent in line 47. The extract oil rated oil phase is withdrawn through line 1S, heated in containing the remaining solvent is withdrawn from the exchanger 16 to about 350 F. and passed through line bottom of vacuum flash tower 51 through line 55 and 17 to vacuum steam stripper 18. Steam is introduced passed at about 460 F. to vacuum steam stripper 56 opthrough line 17 to vacuum steam stripper 18. Steam is 25 erated at a top tower pressure of about 11 pounds per introduced through line 19 into the lower portion of square inch absolute wherein it is contacted with steam vacuum steam stripper 18 operated at a top tower presintroduced through line 57 to remove the remaining traces sure 0f about 11 pounds per square inch absolute strip- 0f SOlVent. EXtI'act Oil free 0f Solvent iS Withdrawn ping the remaining NMP from the oil. Distillate comthrough line 58 and discharged to storage. Distillate from prising NMP and steam is discharged through line 21. 30 vacuum steam stripper 56 comprising steam and solvent Reiined oil product is withdrawn from stripper 18 through is combined with the wet streams in lines 38 .and 21 and line 20, passed through line to solvent dryer 61. Solvent dryer yExtract-mix at a temperature of about F, leaving 61 is a fractional distillation tower which is operated at extractor 2 through line 3 is passed through exchanger a OP OWCI PreSSure 0f about 18 Pounds per Square inch 30, line 31, exchanger 32 and line 33 to atmospheric Hash 35 absolute to remove water as distillate which is discharged tower 34 operated at a top tower pressure of about 20 through line 62. Dry solvent is withdrawn from the botpounds per square inch absolute, Heat supplied by extoni of solvent dryer 61 through line 63 .and is recycled changers 30 and 32 raises the extract-mix temperature to i0 eXraCOl' 2 through lines 53 and 26 With the dry solabout 418 F. and effects vaporization of about 40 per- Vent from lines 52 and47. cent of the solvent present in the extract-mix which is 40 DESCRIPTION 0F THE PREFERRED removed together with dissolved water as distillate EMBODIMENTS through hhe 35' Thls dlshhate Stream 1S, used to supply In an embodiment of this invention, a vacuum distillate heat to exchanger 30 1s Passed through hhe 36 to Supply from crude distillation is rened with NMP in the appaheat tf exehehger 16 and 1S 'heh passed throhgh 37' ratus and at the conditions described in connection with The distillate in line 37 comprising solvent and dissolved 45 FIGURE l, NMP Solvent containing 1.0 weight percent Water 1S f heh, Spht betWeeh the Solvent recycled to eX water is employed at a solvent dosage of 151 volume perh'aetor z 1h hhe 2 5 and fed to the s olveht drylhg :tower cent. A yield of refined oil of 68.9 weight percent is ob- 1r1 1111@ 38 1n afatlo Controlled t0 mamfam the maXlmum tained which refined sii has a gravity API of 31.1, and a WaCI desired 111 the recycled Solvent AS 'die Wafer COH- viscosity index before dewaxing of 105.0. A material baltent and volume of the stream in line 12 is increased, 50 ance Showing the distribution of NM1), Water, and Oil less of the atmospheric flash tower distillate in line 37 fractions in the refining of 10,000 barrels per day of the is included in the recycled solvent passed through line Wax Distillate 20 charge stock is shown in Table V, 25. Recovery is optimized by injecting a volume of water following.

TABLE V.-MATERIAL BALANCE [Thousands of pounds per day] Charge oil Oil charge 3,164 Rairiate-mix Water injected into ralnat Extract-mix NMP charge Separator solvent phase. Separator oil phase Refined oil stripper overhead Rened oil product Steam to refined oil stripper Eilrltt atmospheric flash tower ov id. Split to treating tower it to solvent dryer Eitract atmospheric flash tower b OIDS Extract pressure Hash tower overhea Extract pressure flash tower bottoms Extract vacuum flash tower overhead Extract vacuum flash tower bottoms Extract vacuum steam stripper overhead Extract vaeuum steam stripper bottoms Steam to extractvacuum steam stripper. Wet solvent charge to solvent dryer Solvent dryer overhead Solvent dryer bottoms id. Sp1

We claim: 1. In the solvent refining of a lubricating oil charge stock produced by vacuum distillation of the crude oil for the removal of constituents having a low viscosity index and poor stability wherein said lubricating oil charge stock is contacted with a solvent stream comprising N- methyl-Z-pyrrolidone and not more than about 1.0 weight percent water afectin g separation of a rafinate-mix comprising a major portion of oil with a minor portion of said solvent dissolved therein and an extract-mix comprising a major portion of said solvent with said constituents having a low viscosity index and poor stability dissolved therein, the improvement which comprises:

adding water to said raffinate-mix in an amount of at least about 2.0 weight percent of the N-methyl-Z- pyrrolidone dissolved therein effecting separation of an oil phase and a wet solvent phase comprising at least 2.0 weight percent Water, distilling said oil phase effecting separation of remaining solvent as distillate from bottoms comprising refined oil, recycling at least a portion of said wet solvent in admixture with solvent of lower water content to comprise at least a part of said solvent stream comprising N methyl 2 pyrrolidone and not more than about 1.0 weight percent water, and distilling said extract mix to effect separation of a distillate comprising solvent containing less than 1.0 weight percent water and recycling said distillate as at least a part of said solvent of lower water content.

2. The method of claim 1 wherein said lubricating oil charge stock is contacted with said solvent stream at a solvent dosage within the range of about to 450 percent of said lubricating oil stock.

3. The method of claim 1 wherein said lubricating oil charge stock is contacted with said solvent at a temperature within the range of about 5 0` to 250 F.

4. The method of claim 1 wherein said lubricating oil charge stock is a parafiinic base oil having a viscosity index within the range of about 40 to 105 and the viscosity index of said refined oil is at least l0 units higher than said lubricating oil charge stock.

5. The method of claim 1 wherein said lubricating oil charge stock is paraffin based, the solvent dosage is within the range of about to 340 volume percent and the contacting temperature is within the range of about to F.

6. The method of claim 1 wherein said lubricating oil charge stock is naphthene based, the solvent dosage is within the range of about 75 to 200 volume percent and the contacting temperature is within the range of about 75 to 150 F.

7. The method of claim 1 wherein said rainate-mix is separated at a first temperature within the range of 50 to 250 F. and said oil phase is separated from said wet solvent at a second temperature below said first temperature.

8. The method of claim 1 wherein the amount of water added to said raffinate-mix is within the range of about 2 to 20 weight percent of the N-methyl-Z-pyrrolidone dissolved therein.

9. The method of claim 1 wherein the amount of wa ter added to said rafiinate-rnx is about 5 weight percent of the N-methyl-Z-pyrrolidone dissolved therein.

References Cited UNITED STATES PATENTS 2,923,680 2/1960 Bushnell 208-321 2,963,427 12/1960 Nevitt 208-326 FOREIGN PATENTS 610,414 12/1960 Canada.

HERBERT LEVINE, Primary Examiner UNITED STATES PATENT OFFICE /f.. CERTIFICATE 0F CORRECTION rgghizo. ,u7o,o89 mud september 3o, 1969 Inventorh) grhgrp C. Mogris and John I. Nixon It is certificd that error appears in the above-identified patent and that laid Lettura Patent are hereby corrected as shown below:

I Column 3, line '7, "71C." should read 70C.;

column 3, line ll, "71C." should read 70C.; column 3,

line )45, "The" should read --This--g column 3, line 63, "71C."

should read 70C.; column 4, line 13, after "cent" insert "solvent, and 80.7 `weight percent".

SIGNED MD SEALED (SEAL) Attest:

I" WILLIAM E. soaunER. JR. dmd Gomissione `or Patents nesting Ice

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