US2673174A

US2673174A - Solvent refining process

Info

Publication number: US2673174A
Application number: US227873A
Authority: US
Inventors: Edward P King
Original assignee: Pure Oil Co
Current assignee: Pure Oil Co
Priority date: 1951-05-23
Filing date: 1951-05-23
Publication date: 1954-03-23
Anticipated expiration: 1971-03-23

Description

March 23, 1954 E. P. KING SOLI/ENT REFINING PROCESS Filed May 23 S mw llllllllll IIv III I #mm1 I I G BSE xm .E 35km 1 IIIIIIIII I I mu. IIIIIIII I 1 R. m Y In A| Nw N P m mm .ESE E.. E o V D HN N R T 3 Fm 1 m A S l] 3 n n m 2 mw. vs w u v FE 1 w w. w m. mzmq/ w .la w a 3 .I N M u d/J 7 I I I I In J w o Y s www INU..- N B w T. L M .I u r...w-- m MW 3 w.. 3 wvlw w s a I Uv v2 1 d w62 I Ui M m2 E nNu onu .vw t 7 5 8: I I I o uozmrl HMnva @M am Tn-|nI-|I|- I.||.l. I 3 m I Vv- .qEm II wv I. Il .B ra u .q I I.. nu m ov om 232mm@ n. hummm muqz Sm .B E ma Eqzh IIIII I I I I L IL fwn mtm IIIIIIIIIIIII I I L IIII I I 4mm IIIIIIIII I I L Patented Mar. 23, 1954 2,673,174 soLvENT REFINING PaooEss Edward P. King,

Beaumont, Tex., assignor to The Pure Oil Company, Chicago, Ill., a corporation of Ohio Application May 23, 1951, Serial No. 227,873 13 Claims. (Cl. 1962-1442) This invention relates to a method for increasing the emciency of solvent extraction processes utilized in the reiining of lubricating oils.

In the manufacture of lubricating oils from petroleum oil base stocks, it is frequently necessary to supplement the conventional treatments of lubricating oil stocks, such as distillation and/or clay treating processes, with various types of physical or chemical processes. The prime objective sought by the use of these supplemental processes is to free the lubricating oil stocks from all materials which have an adverse effect on the performance characteristics of the lubricating oils. In general, these undesirable materials which are contained in the base stock impart undesirable characteristics to the iinished oil, namely, low viscosity index, high carbon residue and general instability.

The processes employed to effectuate the removal of these undesirable materials are generally classied as acid treating and solvent refining. In the former process the base stock is contacted with an acid such as sulfuric acid. The acid reacts with the various impurities to remove, in the form of an acid sludge, the undesirable constituents of the crude oil distillates being treated. Although this type of process has been used with considerable success in the preparation of lubricating oils, it has been found that lubricating oils refined by the solvent refining methods are generally superior to the sulfuric acid treated oils. As a result modern refining practices demand that solvent refining processes be employed in the general refining scheme utilized to produce a wide variety of saleable products from the crude petroleum oil processed by the refinery.

Solvent refining methods, which are physical in nature, are essentially simple in their basic principles in that the essence of these processes lies in the liquid-liquid contacting of a lubricating oil base stock with a solvent material having pref erential solubility characteristics. As a result. the chemical composition of the hydrocarbon mixture treated is undisturbed. The initial contacting of the oil and solvent is carried out in `an extraction tower in which countercurrent or concurrent contacting is employed. Due to the immiscibilities of the solvent and the lubricating oil base stock being treated, there occurs in the extraction tower a phase separation which permits the oil-rich phase or rafiinate to be withdrawn from the treating tower as overhead and the solvent-rich phase or extract to be removed from the bottom of the tower. As in all contact mechanisms encountered in solid-liquid, liquidgas, or the liquid-liquid system employed in solvent extraction processes, there is frequently encountered due to the interfacial tension that exists at these various boundaries increased emulsification tendencies which result in an unfavorable eiect o`n the ease of separation of the two phases into two separate and distinct layers. If a clean phase separation does not occur there will be either a carryover of the solvent-rich phase in the raffinate or, conversely, the oil-rich phase in the extract. These diiiiculties are generally present in all solvent extraction processes. It has been found, however, that these diiculties may be alleviated by carrying out the contacting of the oil and the solvent in the presence of small, added amounts of an ammoniacal reagent.

Accordingly, it is the object of this invention to provide a method of solvent refining which obviates or mitigates the phase separation difculties encountered in solvent extraction processes.

A process ow diagram is shown in Figure 1 which schematically represents a conventional phenol extraction process.

It has been found that by carrying out the phenol solvent extraction of the undesirable constituents of a petroleum oil base stock in the presence of small, added proportions of ammonia that not only is the phase separation effectively enhanced but also the yield of the desired high viscosity index raliinate oil product is beneficially effected. Although ammonia has been employed as a rening agent in the phenol solvent extraction process, it has not been used in the manner taught by this invention and the beneficial results shown by this invention have not previously been made manifest. Hendrey in United States Patent 2,128,029 has utilized substantial amounts of anhydrous ammonia as a means for recovering the selective solvents of the phenol type. The recovery is accomplished by reacting the phenolic type solvent with the ammonia to form a compound Which will readily break down under the proper conditions to liberate the recovered phenolic type solvent and ammonia for reuse in the process. The ability of ammonia to function as a solvent modifying agent when in combination with a phenolic type compound is shown by Arveson in United States Patent 2,092,199. In this latter process substantial amounts of ammonia are added to the phenol solvent. However, it will be noted that this combination solvent produces phase separation diiculties as it is brought .outby the patentee that small quantities of Water can be used to assist in overcoming this difficulty.

In contradistincticn to the foregoing teachings, it has been found that when the petroleum oil base stock is contacted with the phenol solvent in the presence of small, added amounts of ammonia, certain beneficial results are shown which are not evident from and are contrary to the teachings ofv the .prior art.

The chemistry of surface activeagents has had considerable application in many fields related to the petroleum industry. A notable example being the use of surface active agents. inthe. de.- mulsification of oil and water emulsions encountered in the production. of. crude: petroleumv While the use of surface:v active compounds oils. has been widely investigated in aqueous media, very little attention has beenl directed tov their, use in non-aqueous media for the surface active agents are not generally prepared for. this pur:- pose. It has been found; however, that apparently surface: activechemistry has; itsapplication in increasing; thefefciency of solvent refining processes wherein. a non-aqueous mediaiis employed as a solvent. Tofacilitate a better understanding of. the invention abrief description of a typical; phenol extraction processfwill not be amiss. Referring nowto Figure 1, it will be' seen that in` general the several process streams encounteredin a phenol extraction process are four in number andiwill be'discussed separately.v Initially, the preheated petroleum oil charge stock, whichA mayf consist of a low, intermediate orv high.- viscosity lubricating oil stock' obtained as-.a sidestream fromvthe vacuum distillation ofy a: topped crude'for theY deasphalted residuum produced in-` the: vacuum distillation processis introducedxby-4 means@ ofline I0 into a` phenol absorberrtower H wherein it is countercurrentlycontacted'witha constant boiling mixture.ofphenoland` watenobtained from a hereinafter mentioned source. This initial treatment' effects the removal, of the" phenol from thisV constant boiling. mixture' thereby eliminating the necessity for; employing: a distillation process for separatingr ther constituents of this phenol-water mixture; the separationl of which would be extremely'difcult because of the closeness' of. the boiling pointsf of the distillateand the mixture from which the distillate isbeing produced.` The process'water is removed. in the vaporousV state fromitheabsorber tower II- by line I I2' which transfers the.A phenol-free water to the waste disposal systemi of. the refinery. The chargeV stock containing minor amounts of phenolk removed from thel phenolic: water isthen `passed by line I3 toi the extraction'- tower I4 e where it is countercurrentlyv contacted withthe phenol' solvent to extract Vthe undesirable constituents from the lubricating oil basestock. The phenol employed: in'Y this; operation is introduced into the topfofv the extraction tower I4- by means of line I5 which connects the extraction tower I4 with thephenol storage facility I6. Because of their immiscibility, the two liquids contacted in the extraction tower I4 separate into two phases, namely, an oil-rich or raftinate phase. whichv is withdrawn' fron-'ii the.4 top of the extraction'Y tower I4: by means of line I1, and a solvent-rich' or extract.` phase which is. withdrawn from the bottom of thetreating tower I4 by meansV of line I8. Considering first the raffinate. this overhead product is transferred from the extraction. tower I4 by means of line I1 to` the; evaporator section of' the raffinate tower I9.. While being transferred, it passes through the raffinate furnace 20 wherein it is 4 I heated to an elevated temperature sufficient to effect in the evaporator section the flash distillation of the phenol constituent of the raflinate phase. The raflinate solution containing minor amounts of phenol is then introduced into the stripping section of the raffinate tower I9 by means of line 2I.. In thisk section:y the raffinate is denuded of trace amounts of the remaining phenol by means of steam stripping. The 1inished raffinate is then removed from the bottom of. the stripping section by means of line 22. The thus treated raffinate, having distinctly improved' characteristics of viscosity index, carbon residue, andr general stability, may then be passed to subsequent processing steps such as solvent dewaxing, clay contacting or various blending operations to produce the nished lubricating oil. With regards to the extract which is withdrawn from the bottom of extraction tower I4 `by means ,of line. I Init` will, be rseenfrom Figure 1. that. this product is introduced. at an elevated temperature to an extract. dryer. 23Y whereinv all` of the water whichA is contained in theextractphase is separated therefrom. There is also effected, a partial` phenol separation at this step 1 and asr a result the water and phenol are removed byline 214 asa vaporous, constant boiling mixture of phenoland. water. The elevated temperature. required for. thisv dehydration may. be obtainedv by. passing the extract solution-in indirect heatexchange withother process streams or other suitable means. The anhydrousy extract still containing some quantities of phenol isuthenwithdrawn from` the bottom of dryer 23 and transferredvia, line.. 25,totthe extract flash tower.v ZGI-wherein mostof the remaining phenol is separated by flash distillation. This phenol. is` removed asY overhead. eluent by line 21 by meansl of .which it is returned tothe phenol storage I6. An, extract furnace 28 is employed inconjunction with the extract flash tower 26: Thisfurnace'ZB in. effect acts as a reboiler for the. extract flash` tower 23 to insure the substantial removal of most of the phenol from the anhydrous extract which is fed into the .dash tower: 25; The bottoms fromV the ash tower arethen fed by: line 29 into the extract stripper. 30. In this vessel, theremaining traces of phenol contained in theanhydrous extract are eliminated. by means of steam` stripping. The extract oil is removed from the bottom of the stripper 30- byv means ofL line 3|I. Although this extract oil contains theundesirable constituents separated from the lubricating oil base stock it is however a marketable, product which` may be blended in with fuel oils or used as a compoundingj agent in other typest of composition.

rIshe two remaining streams tol be considered ares the: phenol streams and the phenolic water streams; As ity has been pointed out above the phenol solvent initially used is introduced into the extraction towerl I-4 by means of line I5. Thephenol. solvent is then. carried from the extractiontower I4 tothe recovery section of the solvent; refining process byy the. raffinate and extract' streams. The; separationA and recovery of the phenol solvent. from these respectiyestreams is effected in the rainate tower I9, the extract dryer 23, the extract flash towerv 26, and the extract stripper 30. The anhydrous phenol which is recovered, from the evaporator section of theraflnate tower- I9-isreturned to the phenol storage I6 by line;` 32.V The. phenol; recovered from the extract flash tower 2 6. is; returned to the phenoll storage I6 by line 21.. The remaining amounts of phenol are recovered from the system in the form of mixtures of phenol and water. These phenolic water streams originate as overhead eliiuent streams from a number of locations, namely, the stripping section of raffnate tower is, the extract dryer 23, and the extract stripper 3d. The phenolic vapors (90% phenol and 10% water) recovered from the stripping section of raiinate tower is and the extract stripper 30 are condensed and transferred to a phenolic water accumulator 33' by means of lines 34 and 3&5, respectively. Phenolic water vapors from the dryer (90% water and 10% phenol) are condensed and collected in phenolic water accumulator 33H. Reflux in the form of phenolic water is withdrawn from the phenolic water accumulator 33" and returned to the extract dryer 23 by line 36. Non-condensed or excess phenolic water vapors are transferred via line 2d' or by means oi' the steam ejector 3l through line to the phenol absorber tower H wherein the phenol constituent of the phenolic water mixture is separated by contact with the preheated charge stock introduced into the tower as hereinbefore mentioned. The mixture of phenol and water obtained from extract dryer 23 is transferred to the phenol recovery system by means of line 24 which interconnects with line 38, returning the phenolic water to the phenol absorber tower il. It will be noted that not all of the phenolic water is returned to the phenol absorber tower It. In addition to that which is employed as reiiux in the extract dryer 23, quantities of the phenolic water may also be introduced into the bottom of the extraction tower ill by means cf line te', or into the tower with the oil feed via line 39H. This phenolic water is introduced near the bottom of the extraction tower lil for two purposes, rstly, to increase internal reiuxing, and secondly, to raise the immiscibility temperature of the phenol with the oil charge stock. The addition of this phenolic water changes the solvent characteristics of the phenol and the amount of phenolic water introduced into the extraction tower must be properly balanced to provide maximum eiiiciency. L

In carrying out the instant invention, in one of its embodiments, it has been found that by adding ammonia to the phenol and phenolic water Streams, it is possible to improve the opj eration of the phenol extraction process by improving the tower extraction eiiiciency. In accordance with this particular embodiment ammonia is delivered from the ammonia supply source il into the respective phenol and phenolic water lines by means of line All and the branch lines 42, d3, dit, d5 and 4&3. Although any suitable source of supply of ammonia may be employed, it has been .found liquid ammonia will provide an appropriate means for introducing the desired amounts of ammonia into the system. Line 42 is employed to introduce ammonia into the phenolic water recovered from the stripping section of the railinate tower I9. Line 43 is similarly employed to introduce ammonia into the phenolic water `overhead from extract stripper 30. Line 4.4 introduces ammonia to the extract dryer whence it is recovered in the overhead which is condensed in phenolic water accumulator 33". Line d5 is employed to introduce ammonia into the anhydrous phenol recovered as the ilash distillate from the extract :dash tower 26. Line it serves the same purpose in introducing ammonia into the phenol overhead recovered from the ash section of rafnate tower I9. Although the ammonia may be introduced into the system at any point whereby the initial extraction is carried out in the presence of ammonia, it is preferred to introduce the ammonia at 'the above points in order that advantage may also be taken of the inherent acid neutralization properties of ammonia to minimize the corrosion occurring in these lines due to the acidic nature of the phenolic streams. The main objective, however, of the instant invention is to enhance materially the eihciency of the extraction step of the solvent extraction process. This is eiectuated in one form by the addition of minor amounts of ammonia to the phenol and phenolic water streams. The effect of the invention is also illustrated by the tabular summary in Table I in which the results obtained when injecting ammonia at those points illustrated in Figure 1 are compared with conventional operations.

Table I `n E* Run No 1 2 3 Ammonia injected None None 20-25 lbs/day. Ammonia concentration in treat- None None 0.02% by wt.

ing tower. Charge, B./D 5, 315 5, 120 5, 200. Ralinate y' ,1d, Vol. percent. 06. 1 67.8 67. 0. Ralinate Gravity, oAPI 32.5 32. 4 32. 7 V. I.-Fuished Oil 101 100. 3 102. 4 Extract Gravity, API 11.1 10.3 l1 0 rhen01/oi1-vo1.nau0 1. 71 1.99 1h54 Water to treating tower (Vol.

percent of Solvent):

$0 rlpottom 7.1 N 8. 6 8.

o op 0. 6 one one Treating tower temp.;

To -F 135 131 124.

Bottom-W 117 130 123.

It is noted from Table I that when ammonia is introduced into the system as illustrated by I run No. 3, a slightly decreased yield of increased lviscosity index was obtained with a lower phenol/ oil ratio. This improvement in viscosity index is obtained in spite of a reduced treating ratio. This improvement is attributed to the enhancement in phase separation resulting from the use of ammonia injection. Run No. 1 is shown to compare the effect evidenced when water is added to the phenol entering the top of treating tower to assist in phase separation. This addition of water may be introduced into the treating tower by means ofline lil shown on the Figure l if it is so desired. It will be noted, however, that although phase separation and the carryover of the phenol-rich phase with the oilrich rainate phase is reduced by the addition of water to the top of the extraction tower iii, the yield and the viscosity index of the product obtained is lower than those shown in run No. 3 when ammonia was being injected. ln both of these instances the phenol/oil ratio was substantially the same. Run No. 2 is included to show the eiiect on viscosity index and yield when neither water nor ammonia is employed to increase the eiiiciency of the tower extraction process. From the results of run 2, it is seen that in spite of the higher phenol/oil ratio the viscosity index of the finished raiinate is lower than that obtained in runs l and 3. Although a higher yield resulted in run 2, this advantage is oiiset by the lower viscosity index of product obtained in run 2. The improvements in the properties of the raffinate oil product, however, are inoidental to the major improvement in the operation of the solvent extraction process resulting from the addition of ammonia to the system, namely, improved phase separation in the exployed must be determined experimentally.

tractiontower. From this improvement results less solvent carryover in the raffinate phase and reduced. solubility of the oil in the phenol and provides a solution for a bothersome operation problem resulting from emulsion difculties occurring in the extraction tower.

While it is seen that the introduction of ammonia into the phenol and water stream of a phenolic solvent extraction process materially improves the efficiency of phase separation in the extraction operation and provides increased yields and improved quality or products over conventional operations, the theory of operation is not clearly understood. It is thought that the improved operation results from an improvement in the interfacial tension relationships existing at the liquid-liquid boundaries that occur from tray to tray in the extraction tower. Most lubricating oil stocks contain organic acids. While the less volatile acids such as naphthenic acid are recovered in the extract, the more volatile ones such as acetic remain in the system in the circulating phenolic streams. These volatile acids may react with the ammonia to form ammonical organic salts which function as surface active agents. It is also possible that the ammonia alone or in some combination with phenol or water or both may function as a Surface active agent in the media composed of oil, phenol and water and provide the desirable result shown by this invention. However, these explanations are merely postulations and it is not intended to limit the scope of the instant invention thereby.

The optimum quantity of ammonia that is em- It is obvious that an amount less than that which would react with vSubstantial amounts or the phenol solvent to form precipitant reaction products which would clog up the process lines and vessels should be employed. It has been found that in operating a unit having a capacity of about 5200 barrels per day, and processing a petroleum oil feed stock obtained from a Mid- Continent crude, if about 20 to 25 pounds per day of ammonia are introduced into the system, after building up a concentration of between 0.01 and 0.05% by weight of material in the treating tower, the emulsication problems encountered in the extraction tower of the process are minimized. Although the amounts consumed are equivalent to between about 00012-00016 percent by weight of lubricating oil feed stock charged to the unit, the concentration existing in the phases within the treating tower is maintained at more than ten times this amount by recirculation of the `ammonia with the water and phenol in the recovery system. The distribution of ammonia between phases in the tower has not been precisely evaluated but it is known that the greater proportion of ammonia is held in the phenol extract phases. If greater concentrations are desired or needed the extraction tower may be operated under superatmospheric conditions to obviate gasication problemg that might arise through the use of increased amounts of ammonia or other similar ammoniacal compounds.

Although from the above it is seen that the ammonia has been introduced into the system by means oi' the oil-free, phenol-containing streams, it is evident that the Scope of the invention should not be so limited. Any expedient whereby ammonia is introduced into the extraction tower "in .amounts sufcient to enhance the phase separaimproved by carrying out tion resulting therein should be considered to be within the purview of the instant invention. It is to be further noted that although ammonia is the preferred reagent employed in accordance with this invention other ammoniacal compounds or compounds which will produce ammonia in the treating tower environment may be utilized. Ammonium salts are relatively unstable materials which dissociate upon being exposed to moderately elevated temperatures. Examples of such compounds which would dissociate under the ambient conditions encountered in the extraction tower include the acetate, perborate, carbamate, carbonate, citrate, fluoride, hydroxide, molybdate, nitrite and sulfide of ammonium. The use of these compounds may produce undesirable solids or corrosive products upon dissociation lwhich would deleteriously affect the treating operation or the rened product unless removed therefrom at some stage. It is for this reason that the use of ammonia per se is the preferred embodiment of the instant invention.

It is therefore seen that tower extraction efficiency of a phenol extraction unit is materially the contacting of the petroleum oil and phenol solvent in the presence of small, added amounts of ammonia. The arnmonia may be introduced into the system by the addition of ammonia to the phenol and phenolic water streams which are employed in the recovery system of the solvent rening process or any other suitable means.

What is claimed is:

l. In a solvent refining process for improving the viscosity index of a mineral oil lubricant wherein a 4petroleum oil is contacted with a phenol solvent to produce an oil-rich phase and a solvent-rich phase, the improvement comprising maintaining within the contacting zone a material selected from the group consisting of ammonia and ammoniacal compounds which decompose to liberate ammonia under the conditions of operation of said process, said material being present in small amounts up to the equiva- .lent of about 0.05 per cent by weight of ammonia based on the amount of phenol and oil in said contacting zone, but sufficient to enhance phase separation between the oil-rich and the solventrich phases.

2. A process in accordance with claim l in which the material is ammonia.

3. In a solvent reiining process for improving the viscosity index of a mineral oil lubricant wherein a petroleum oil is contacted with a phenol solvent to produce an oil-rich phase and a solvent-rich phase, the improvement comprising maintaining within the contacting zone a material selected from the group consisting of ammonia and ammoniacal compounds which decompose under the conditions of operation of said process to liberate ammonia, said material being present in an amount suicient to provide 0.01 to 0.05 per cent by weight of ammonia based on the amount of phenol and oil in said contacting zone.

e. In a solvent reiining process for improving the Viscosity index or" a mineral oil lubricant wherein a petroleum oil is contacted with a phenol solvent to produce an oil-rich phase and a solvent-rich phase, the improvement comprising maintaining within the contacting Zone of said solvent refining process a concentration of from .0l to .05 per cent by weight of ammonia 'based on the amount of phenol vand oil in said contacting zone.

5. In a phenol extraction solvent refining process for improving the viscosity index of a mineral oil lubricant wherein a raiinate phase and an extract phase are produced in the extraction zone of said process, the improvement comprising introducing into the circulating phenolcontaining effluents recovered from said raffinate and extract phases prior to recycling these eiiluents to said extraction zone from .0012 to .0016 per cent by weight of ammonia based on the amount of oil charged to said process.

6. In a solvent refining process for improving the viscosity index of a mineral lubricating oil wherein a petroleum oil is contacted with a phenol solvent to produce an oil-rich phase and a solvent-rich phase, the improvement comprising introducing into the contacting zone of said process a material selected from the group consisting of ammonia and ammoniacal compounds which decompose to liberate ammonia under the conditions of operation I" said process, said material being added in an amount suicient to supply .0012 to .0016 per cent by weight of ammonia based on the amount of oil charged to said process.

'7. In a solvent rening process for improving the viscosity index of a mineral oil lubricant wherein a petroleum oil is contacted with a phenol solvent to produce an oil-rich phase and a solvent-rich phase, the improvement comprising introducing into the contacting zone of said process from .0012 to .0016 per cent by weight of ammonia based on the amount of oil charged to said process.

8. In a solvent refining process for improving the viscosity index of a mineral oil lubricant wherein a petroleum oil is contacted with a phenol solvent to produce an oil-rich phase and a solvent-rich phase, the improvement comprising introducing into the contacting zone of said process ammonia in amounts suicient to build up within said contacting zone a concentration of .01 to .05 lper cent by Weight of ammonia based on the amount of phenol and oil in said contacting zone and thereafter introducing into said contacting zone from .0012 to .0016 per cent by weight of ammonia based on the amount of oil charged to said process.

9. A method in accordance with claim 8 in which the said petroleum oil feed stock contains volatile organic acids.

10. A method in accordance with claim 8 in which the said petroleum feed stock is prepared from a Mid-Continent crude.

l1. In a solvent rening process for improving the viscosity index of a mineral oil lubricant wherein a petroleum oil is contacted with a phenol solvent to produce a ranate phase and an extract phase, the improvement comprising building up within the contacting zone of said process a concentration of from .01 to .05 per cent by weight of ammonia based on the amount of extract phase, the improvement comprising subjecting the said raiinate phase to a flash distillation `wherein phenol vapors are recovered as overhead products, steam stripping a flash distillation residue to produce an overhead product consisting essentially of phenol and water and a bottoms product consisting of the desired high viscosity index raflnate oil, passing said extract phase to a drying zone and recovering therefrom as overhead product a constant boiling mixture of phenol and Water, Hash distilling the dried extract solution, recovering as overhead therefrom a substantial portion of the remaining phenol solvent, steam stripping the remaining extract to remove the residual traces of phenol solvent, thereby producing an overhead product consisting of phenol and water and a bottoms product consisting essentially of phenol-stripped extract containing low viscosity index constituents, introducing into the aforementioned phenolcontaining overhead products from .0012 to .0016 per cent by weight of ammonia based on the amount of oil charged to said process and recycling said ammonia-containing phenol to said extraction zone to contact additional amounts of said petroleum oil feed stock.

13. In a phenol extraction solvent refining process for improving the viscosity index of a mineral oil lubricant wherein a raffinate phase and an extract phase are produced in the extraction zone of said process, the improvement comprising introducing into the circulating phenolcontaining eiliuents recovered from said raiiinate and extract phases prior to recycling said effluents to said extraction zone a material selected from the group consisting of ammonia and ammoniacal compounds which decompose under the conditions of operation of said process to liberate ammonia, said material being added in an amount suiicient to provide from .0012 to .0016 per cent by weight of ammonia based on the amount of oil charged to said process.

EDWARD P. KING.

References Cited in the le of this patent UNITED STATES PATENTS

Claims

1. IN A SOLVENT REFINING PROCESS FOR IMPROVING THE VISCOSITY INDEX OF A MATERIAL OIL LUBRICANT WHEREIN A PETROLEUM OIL CONTACTED WITH A PHENOL SOLVENT TO PRODUCE AN OIL-RICH PHASE AND A SOLVENT-RICH PHASE, THE IMPROVEMENT COMPRISING MAINTAINING WITHIN THE CONTACTING ZONE A MATERIAL SELECTED FROM THE GROUP CONSISTING OF AMMONIA AND AMMONIACAL COMPOUNDS WHICH DECOMPOSE TO LIBERATE AMMONIA UNDER TE CONDITIONS OF OPERATION OF SAID PROCESS, SAID MATERIAL BEING PRESENTS IN SMALL PROCESS, SAID MATERIAL LENT OF ABOUT 0.05 CENT BY WEIGHT OF AMMONIA CONTACTING ZONE, BUT SUFFICIENT TO ENHANCE PHASE SEPARATION BETWEEN THE OIL-RICH AND THE SOLVENTRICH PHASES.