US2043388A - Method for producing lubricating oil - Google Patents

Description

June 9, 1936. D. R. MERRILL METHOD FOR PRODUCING LUBRICATING OIL Filed Nov. 6, 1933 f m I I INVENTORH 531 10 P. Men"!!! I, ATTORNEY Patented June 9, 1936 UNITED STATES PATENT OFFICE IVIETHOD FOR PRODUCING LUBRICATING OIL David R. Merrill, Long Beach, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California This invention relates to a process for the treatment of petroleum with selective solvents. It is a continuation in part of my copending United States patent applications Serial No. 686,176 flled August 21, 1933 and Serial No. 686,941 filed August 26, 1933.

In the production of lubricating oil for internal combustion motors it is highly desirable to obtain a product which exhibits a low temperature viscosity susceptibility, a low Conradson carbon residue value, a high stability towards sunlight and a low oxidation value. Crude lubricating oil fractions produced either as distillates or as residues are usually composed of mixtures of paraflinic, naphthenic, aromatic and olefinic hydrocarbons. The olefinic hydrocarbons are highly unsaturated and their presence in the finished lubricating oil is undesirable because of their unstable characteristics. These compounds are unstable and usually darken when exposed to sunlight. Furthermore, they have a high tendency towards polymerization with the result, after a considerable period, that these compounds are converted into resinous substances which increase the sludge value of the oil.

The aromatic and naphthenic hydrocarbons present in crude lubricating oil fractions are undesirable because these compounds exhibit too great a change in viscosity for a given change in temperature. The paraflinic hydrocarbons present in crude lubricating oil fractions are the most desirable materials to be employed as lubricants.

exhibit a low temperature viscosity susceptibility.

In other words, they exhibit a minimum change in viscosity for a given change in temperature. Furthermore, these highly saturated hydrocarbons are relatively stable to sunlight, exhibiting, little tendency toward discoloration or sludge formation. When I use the term parafllnic hydrocarbons I mean those compounds which are present in petroleum having the aforementioned characteristics and which are liquid at ordinary temperatures. This group of hydrocarbons does not include those compounds present which are usually solid or semi-solidat ordinary temperature and which are known as wax or petrolat A further indication of the purity of a lubricating oil is its viscosity gravity constant. This constant represents the parafllnicity or naphthenicity of an oil. A high value represents a high degree of naphthenicity while low values indicate relatively greater parafiinicity. Lubricating oils from natural crudes range from 0.903 viscosity gravity constant for an extreme Gulf Coast type to 0.807 6 foran extreme Pennsylvania type, or even beyond. The viscosity gravity constant referred to in this application has been determined by the method employed by Hill and Coates as set forth in the Journal of Industrial and Engineering Chemistry, 10

vol. 20, page 641 of 1928.

As a matter of convenience hereafter, I will refer to the desirable lubricating oil constituents of petroleum as the parafiinicf hydrocarbons and to the undesirable constituents, such as olefinic, 15 naphthenic and/or aromatic hydrocarbons as the non-paraflinic constituents of petroleum.

In the production of lubricating oil from crude petroleum residues or distillates, it is becoming conventional in the art to separate the desirable parafflnic hydrocarbons from the undesirable olefinic, naphthenic and/or aromatic compounds by the use of solvents which selectively dissolve the undesirable hydrocarbons present in the petroleum fraction but which exhibit only a very limited solvent power on the desirable parafiinic hydrocarbons.

A number of selective solvents have been found desirable to separate the parafllnic from the nonparafllnic hydrocarbons, for example, it has been shown that such materials as sulphur dioxide, beta beta dichlorethyl ether, chloraniline, nitrobenzene,- aniline and furfural are highly selective as the solvents for the non-parafilnic hydrocarbons. The foregoing selective solvents are relatively 35 heavy as compared to petroleum. When these relatively heavy solvents are commingled with petroleum or petroleum fractions under the proper conditions of temperature, the undesirable nonparaflinic hydrocarbons present pass into solution to a greater or less extent but the desirable paraifinic hydrocarbons remain largely undissolved. If the commingled mass is allowed to remain in a quiescent state the solution of undesirable hydrocarbons and solvent settles to the bottom of the container and forms what is known as an extract phase. The relatively light parafllnic hydrocarbons rise to the top of the vessel and form a rafllnate phase. These phases are then readily separable by ordinary decantation r means. The ramnate phase is usually found to contain a small quantity of the selective solvent and the extract phase ordinarilycontains a relatively large quantity of the solvent. These fractions may be purified by subjecting them to dis; 55

tillation whereby the solvent is distilled away from the hydrocarbon oils.

Due to the general similarity of the various hydrocarbon components of mineral oil fractions such as lubricating oils, solubilities of the undesirable, non-paraffinic fractions and the desirable parafiinic fractions in a selective solvent usually differ only in degree, and there is, therefore, a tendency for desirable, high grade parafiinic oil to becarried away with the extract resulting in a loss in the yield of paraffinic fractions obtained. In other words, in a phase separation of extract and raflinate fractions from mineral oil employing a selective solvent, an equilibrium of paraflinic components as well as non-paraffinic components is established between the phases. Consequently, some of the desirable paraffinic fraction is found in the extract instead of in the raflinate.

While some loss may occur in a primary extraction of lubricating oil with a selective solvent for the production of a low grade primary extract and a primary rafiinate, the loss of desrable paraffinic fractions in the extract is especially severe when the rafiinate produced by the primary extraction is further treated by a selective solvent to produce a high grade rafiinate and intermediate grade extracts. In the production of a low grade primary extract and a primary raflinate in the first extraction, the difierence in solubility of the respective oils is usually so great that a commercially satisfactory separation is obtainable. In some cases, however, such a process results in a substantial loss of paraifinic components in the low grade extract. The difference in solubility between the intermediate grade extracts and high grade raifinate produced by a succession of extractions is usually not so great and there is, therefore, more tendency for parafiinic oil to be carried away with the intermediate grade extracts.

It has been proposed to regulate the solvent power of the extracting agent at any stage of the treatment in accordance with the solubility of the material to be extracted and as the refining of the stock by extraction progresses in a stepwise manner, the solvent power of the treating agent may be increased.

By substantially increasing the solvent power or ease of miscibility of the treating agent, it is possible to fractionate the rafiinate obtained after extraction with the pure solvent into a further extract of lower solubility than the first extract obtained by the use of said pure solvent and a second rafiinate of consequently lower solubility than the first raflinate.

It has also been found desirable to first extract a hydrocarbon mixture with a pure selective solvent, for instance one of the solvents set forth above, and then to re-treat the rafiinate so produced with a modified solvent. As modifying agents such materials as carbon bisulphide, xylene, benzene, toluene, carbon tetrachloride, ethers or tetrachlorethane may be employed with the selective solvent.

By these processes the oil feed is divided in one general operation into three or more fractions of different viscosity-gravity constants. ously stated, the successive extractions produce a high grade raflinate and intermediate grade extracts characterized by solubilities which are not very different from each other. Consequently, in ordinary treatment of mineral oil by successive extractions, a substantial portion of the parafiinic fraction is soluble in the extract-solvent mixture As previ-' and is lost therein, resulting in a corresponding loss in yield of desirable high grade rafilnate.

It has also been proposed to regulate the solvent power of the extracting agent at any stage of the treatment by controlling the temperature at which 5 the extraction takes place. For instance, the temperature at which the primary extraction takes place may be relatively low in order to reduce correspondingly the solvent power of the solvent. The low grade extract thus produced may then contain substantially only the highly aromatic and most soluble fractions of the mineral oil. Subsequent to recovery of the primary raffinate from the low grade extract, the former may again be solvent extracted at a higher temperature than that which prevailed in the primary extraction. The extraction at higher temperature may be accomplished by the same solvent as that used in the primary extraction or a solvent of greater or less solvent power than that employed for the first extraction may be used for the second extraction. These successive extractions likewise produce a high grade raflinate and intermediate grade extracts having relatively similar solubilities and consequently substantial quantities of desirable paraffinic components are lost in the extract phases. Such loss also occurs when mineral oil is successively extracted with the same solvent at the same temperature.

It is an object of my invention to retain the desirable, high grade parafiinic fractions in the raflinate produced by solvent extraction of mineral oils.

I have found that the parafiinic fractions may be retained in the rafiinate by rectifying the 3 phases. This may be accomplished in a series of successive extractions by intermingling the extract phases with rafiinate phases of low content of parafimic constituents. The equilibrium es tablished in the phase separation of these mixtures is such that the paraifinic content of these extracts tends to be re-distributed into the ramnate phase.

It is a further object of my invention to rectify intermediate extracts produced by successive solvent extractions in order to reduce their content of valuable paraflinic components and to retain these components in the raflinate.

In my applications for patent filed August 21, 1933 bearing Serial No. 686,176 and filed August 26, 1933 bearing Serial No. 686,941, I have disclosed that an oil recovered from the extract phase by cooling may be reintroduced into the extraction system for rectification purposes. Other oils may likewise be employed; for example, the oils recovered from the extract phase of a solvent extraction by totally evaporating the solvent from a portion of such extract phase, or by removing only a part of the solvent from the extract phase, or I may use an oil from an extraneous source such as liquid propane or naphtha.

The addition of these materials to an extract phase containing fractions desired in the raidnate results in rectification because, at the appropriate temperature, the solubility of the parafiinic oil in the extract phase is exceeded and some of this parafiinic oil passes into the raflinate phase by redistribution or rectification.

By the addition of propane or naphtha to the extract containing valuable paraflinic components, as well as non-parafiinic fractions and solvent, redistribution results in at least a portion of the paraflinic fraction passing from solution to form a rafiinate phase.

However, such rectification is at the expense of using substantially more solvent because the added oil mustfalso be partially redissolved, and more solvent is necessary because the oil concentration is reduced when the extract'phase is finally removed from the system at a low temperature after being chilled for production of a ramnate to be returned to the system.

I have found that an economy of solvent can be obtained by removing the extract at a higher temperature. Also, by my rectification, the extract phase leaving the column contains more non-paraflinic fractions. Consequently less solvent need be used in my process.

Accordingly, it is another object of my invention to employ an economical amount of solvent in solvent extraction of oils.

Referring to the drawing, the figure is a diagrammatic view of one type of apparatus suitable for carrying out my invention.

In the apparatus shown in the figure, oil is introduced into extractor and rectifying column I6 via line II controlled by valve I2 by action of pump I3. Line II connects with orifice mixer it which in turn communicates'with column I6 via line I5. Stock tank I6connected with line II may containunextracted fresh feed or a rain-- nate produced by a prior solvent extraction. In the latter case fresh feed is introduced into primary extractor via line 2I controlled by valve 22 by action of pump 23. Fresh selective solvent is introduced into primary extractor 23 via lines 25 and 23 by action of pump 26. Flow through lines 25 and 23 is controlled by valves 26 and 33 respectively. In some instances, solvent from a second extraction to be described may be introduced into primary extractor 26 via lines I 16, valve 33 and line 23. In the latter case, fresh solvent may or may not be introduced via lines 25 and 23, as desired. Preferably the oil in 23 is subjected to countercurrent extraction by the selective solvent, however introduced. Low grade extract and the major proportion of the solvent are removed from the primary extractor through line 21 controlled by valve 28. Primary ramnate produced in extractor 26 is removed therefrom through line 36 and valve 31 by pump 32. Line 33 connects with storage tank I6.

I Extractor and rectifying column II) is divided into a number of sections to 31 by imperforate plates 32. Each section in turn is divided into a mixing zone 33 and asettling zone 34 by plate 35 provided with port 66. Each mixing zone may be provided with agitator 111 if necessary. Column I6 is preferably a vertical unit provided with sections 35 to M in descending order. While the feed may be introduced into any of these sections, in practicing my invention I prefer to introduce the same at some intermediate section, for instance section 31. Fresh solvent is introduced into column II) through lineifl, valve 5I, orifice mixer 52 and line 53 by action of pump 53. I prefer to introduce the fresh solvent into the uppermost section 35. High grade raffinate is removed from this section by line 55 controlled by valve 56. Extract and solvent from section 35 are removed therefrom by pump 6|] through line 61 controlled by valve 62 and are intermixed with a raifinate produced in a lower section of the tower, in a manner to be described. This mixture passes through line 63, orifice mixer 66 and line 65 into the mixing zone 43 of section 36. From the mixing zone the mineral oil mixture and solvent passes through port 46 into settling zone 44. The rafiinate from the settling zone of section 36 is removed therefrom by action of pump 16 and passes via line 11 controlled by valve 12 into contact with the solvent entering the column III via line 50.

The extract and solvent phase produced in setting zone M of section 36 is removed by pump 13 through line 16 controlled by valve 15. Line 16 connects with feed line II and the mixture of extract, solvent and feed passes through orifice mixer I3 and line I5 into mixing zone 63 of section 31 in the manner previously described. The mixture passes through port 66 into settling chamber M of section 31 and the raffinate separated therein is passed by pump 16 through line 11 controlled by valve 18. Line 11 joins with line 61 and the commingled material passes through line 63, orifice mixer 63 and line 65 into section 36 in the manner previously described.

In a similar manner the extract and solvent from section 31 and the rai finate from section 39 are removed through lines 80 and BI, valves 82 and 83 by pumps 86 and 85, respectively, and are then commingled by passage through line 86, orifice mixer 81 and line 88 prior to their entrance into section 38. Raffinate from section 38 passes through line 96 controlled by valve 31 by action of pump 92 and thence into feed line II with which line 98 is connected.

Extract and solvent from section 38 and raffinate from section 38 pass through lines 96 and 85, valves 96 and 91 by pumps 98 and 99, respectively, thenceintermingle in line I00 and orifice mixer IIlI before passage into section 33 via line I02. Extract and solvent from section 39 and rafiinate from section 61 pass through lines I65 and I06, valves I51 and I68 and pumps I09 and I I6 and intermingle in line III and orifice mixer II2 before passage into section 60 via line II3. Extract and solvent from section 36 passes through line II5, valve II6, pump II1, line IIIl, orifice mixer H9 and line 123 into section 41.

Intermediate extract phase is removed from section 6| through line I25 controlled by valve I26 by action of pump I21 and may be entirely removed from the system by passage through line I28 and valve I29. The solvent with which it is associated may be removed by any means such as by conventional distillation.

In the above described apparatus, the solvent is introduced into an upper or primary section, such as section 35, and the oil is introduced into a lower or tertiary section. Extraction takes place in both sections and the extract phase from the upper section is commingled in an intermediate or secondary section with the raffinate phase produced in the lower section. the intermediate section travels to the upper section and extract from the intermediate section passes to the lower section.

Part of the intermediate extract and solvent may be by-passed from line I25 through valve 133 and line I31 for passage through cooler I32 cooled by any appropriate means. The mixture then travels through line I33, into settler I35. Sufficient cooling should be provided in cooler I32 to reduce the solvent power of the solvent intermingled with the intermediate extract to cause substantial phase separation in settler I35. Raffinate is removed from I35 through line I36, valve I31 and pump I38. Line I36 connects with line I I1 and the raffinate from I35 flows with the extract from section 68 through line H8, orifice mixer H9 and line I26 in the manner previously described. The solvent contaminated with some extract separated in settling chamber I35 passes Raffinate from via line I 40, valve I M and pump I42 into heater I45 where thesolvent is heated to increase its solvent power prior to passage through line I45 which connects with feed lines I I and 29.

In the operation of this apparatus, fresh, unextracted oil feed may be introduced intoextractor and rectifying column Ill via line II. In certain instances it may be desirable to maintain sections 35 to 4| at successively decreasing temperatures but it is also within the purview'of my invention to maintain sections 35 to M at the same temperature or even at successively increasing temperatures.

It is also within the scope of my invention to first extract a mineral oil in primary extractor 2G and to subject the rafiinate thus obtained 'to a second extraction in column III in the manner described. The solvent employed for the second extraction may be the same as that used in the primary extraction. In that case, I usually prefer to use higher temperatures in the second extraction than in the first extraction, although in some instances the same or a lower temperature than that prevailing in the primary extraction may be used in the second extraction.

In order to exemplify the application of my invention to a solvent extraction process involving a pure solvent for the first extraction followed by a modified solvent for the second extraction, liquid sulphur dioxide introduced through lines 25 and 29 passes countercurrently in primary extractor 20 with the incoming oil introduced through line 2I. The low grade extract containing the highly aromatic fractions and the major proportion of the liquid sulphur dioxide is removed from the primary extractor 20 through line 27. The primary raifmate containing a small proportion of liquid sulphur dioxide constitutes the feed for the second extraction. The solvent employed for the second extraction may be modified by one or more of the aforementioned modifying agents; for instance, this sol" vent may comprise 70% liquid sulphur dioxide and 30% benzene. It is desirable that the high grade raflinate removed via line 55 will contain substantially all of the paraifinic fractions of low viscosity gravity constant and it is also desirable that the intermediate extract removed from the second extraction via line I28 will be substantially free of these valuable paraffinic fractions.

The raflinate in section 35 will contain a substantial proportion of the paraffinic components of the feed introduced into column I0 via line II, orifice mixer I4 and line I5. Because of the magnitude of the partition co-efficient of paraffinic constituents between the rafiinate and extract phases in section35, the presence of the highly parafiinic rafiinate therein results in substantial proportions of the paraflinic components passing into the extract phase. By intermixing the less parafiinic raffinate from section 31 with the extract and solvent from 35 containing a relatively high proportion of paraffinic materials and reextracting in section 36, at least a portion of the parafiinic fractions will pass from the extract into the rafiinate.

By contacting an extract-solvent mixture from an upper section of the tower with a railinate from a lower section, a redistribution of paraffinic fractions takes place. The extract-solvent mixture contains so large a proportion of paraffinic hydrocarbons and the rafiinate from a lower section contains relatively so small a proportion of these hydrocarbons that when said extract and said raffinate are min led in the presence I25 through cooler I32 into settler I35.

of the solvent, sufi'icient parafiinic fractions pass from the extract to the raifinate to establish equilibrium between the two phases. Also, at the same time, some of the non-paraifinic fractions pass from the raifinate to the extract, resulting in a more paraffinic rafiinate and a less paraflinic extract. Consequently after a. succession of such steps the final extract contains the least amount of paraflinic fractions and the final rafiinate contains those parafiinic fractions which are normally lost in the extract. The solvent associated with the intermediate grade extract and high grade raffinate, respectively, can be removed therefrom by distillation.

I have found that I can accomplish an economy of solvent in operation of my process by by-passing part of the intermediate extract from line The temperature of the extractnand solvent mixture is suificiently reduced in cooler I32 to cause substantial phase separation in settler I35 whereby the solvent is largely freed of oil. When the raffinate from I35 passing through line I36 is intermixed with the extract from section 40 passing through line II", an equilibrium is established in section II to which the mixture flows, whereby the parafiinic components brought into the mixture by the extract tend to migrate into the raffinate in the manner described above.

The solvent from settler I35 contaminated with a small quantity of oil has high solvent power at the proper temperature. By proper cooling it may contain less than 3% of oil. Consequently, this slightly contaminated solvent is heated in heater I45 prior to return into the system with the feed introduced through line I I. While the feed may be introduced into any other section of tower Ill, it is preferred to introduce the feed and re-cycled extract and solvent into the same section because the proper equilibrium between the paraflinic fractions in the raflinate and the nonparafilnic fractions in the solvent is a function of the proportion of the volume of mineral oil being extracted and the volume of solvent employed for said extraction. Therefore, it is desirable to submit the relatively large volume of feed directly to intermixture with the relatively large volume of slightly contaminated solvent recycled from settler I35. The return of this solvent from I35 substantially reduces the amount of fresh solvent to be introduced via line 50.

As an example of the temperature conditions which may exist in the above described process, the oil may bevintroduced into primary extractor 20 at F. for countercurrent extraction with 200 volume percent. liquid sulphur dioxide introduced via line 25 at F. The primary raflinate thus produced may enter section 31 at column III at 90 to 100 F. As the raffinate rises from section to section in II] its temperature is successively increased and the temperature in section 35 may be F. As the extract descends from section to section in I0, its temperature is successively decreased and the temperature in section 4I may be 80 F. The fresh sulphur dioxide-benzene mixture introduced via line 50, may be 250 volume percent. of the original oil feed. In order to produce adequate phase separation of the intermediate extract and solvent insettler I35 this mixture may be cooled to 20 F. The extract thus obtained together with the solvent, may be heated to 100 F. or more in heater I 45 prior to intermixture with the fresh feed to the column I 0.

In some instances I may desire to employ the same solvent in both the primary and secondary extractions, and at the same time utilize the solvent power of the contaminated solvent obtained in settler I35. Accordingly, all of the intermediate extract from column l passing through line I25 is caused to travel, together with the solvent contained therein, through cooler I32 and line H33 into settler I35 wherein phase separation occurs. As previously described, the raflinate thus produced passes from settler l35 via line I36 to intermingle with the extract from section 40 prior to introduction to section M. The solvent removed from settler i35 travels via line I 40, valve Hi and pump M2 through heater M5, line M6, valve33 and line 29 into primary extractor 20 for countercurrent extraction with incoming feed entering through line 2i.

When the same solvent is used in both extractions, the amount of solvent introduced into the system through line 50 will preferably be controlled in such manner that the primary extract issuing from extractor 20 via line 21 will have the desired predetermined viscosity gravity constant. Ordinarily, according to this operation, no additional fresh solvent is necessary for the first extraction and consequently valve 26 in line 25 will remain closed.

The temperature of the contaminated solvent from H35 may be raised sufficiently in heater I45 so that the temperature of the primary extraction is suitable for dissolving the desired amount of low grade constituents.

With 200 volume percent. of solvent comprising 30% benzene and 70% liquid sulphur dioxide, a temperature of 30 F. would frequently be suitable. With the exceptions set forth above, the sequence of steps for solvent extraction using the same solvent in both extractions is the same as that for the described method of extraction employing a different solvent in the primary extractor 20 than in the col-- with a selective solvent, separating a primary.

rafiinate insolublein said solvent from a low grade extract soluble thei in, introducing a selective solvent into a primary stage of a second extraction system, introducing said primary rafflnate into the tertiary stage of said system, introducing a parafiinic oil fraction and selective solvent in said primary and tertiary stages respectively of said second extraction system, removing a rafllnate from the primary stage andextract from the tertiary stage and at a secondary stage of said second extraction system commingling extract phase from the primary stage with rafiinate from the tertiary stage.

2. A process according'to claim 1 in which the selective solvent for the second extraction is modified selective solvent.

3. A process according to claim 1 in whichthe temperature in the primary stage of the second extraction system is higher than the temperature in-the secondary stage and the temperature in the secondary stage is higher than thetemperature in the tertiary stage.

4. A process for the separation of paraffinic and non-paramnic fractions from an oil containing the same which comprises extracting said oil with a selective solvent, separating a primary rafiinate insoluble in said solvent from a low 5 grade extract soluble therein, introducing a selective solventinto a primary stage of a second extraction system, introducing said primary raffinate into the tertiary stage of said system, removing a raffinate from the primary stage and .extract from the tertiary stage, at a secondary stage of said second extraction system commingling extract phase from the primary stage with rafiinate from the tertiary stage, separating extract phase and rafiinate at said secondary stage, introducing said last mentioned raflinate into the primary stage and said last mentioned extract phase into the tertiary stage.

5. A process according to claim 4 in which the selective solvent for the second extraction is a modified selective solvent.

6. A process for the separation of parafl'inic and non-parafiinic fractions from an oil containing the same which comprises extracting said oil with a selective solvent, separating a primary raflinate insoluble in said solvent from a low grade extract soluble therein, introducing a selective solvent into an upper stage of a second extraction system, introducing said primary raffinate'at alower stage of the system, introducing a paraffinic oil fraction and selective solvent in said upper and lower stages respectively of said second extraction system, removing a raffinate from. the upper stage and extract from the lower stage and at an intermediate stage commingling extract phase from the upper stage with rafinate from the lower stage.

'7. A process for theseparation of paraflinic and non-parafiinic fractions from an oil containing the same which comprises extracting said 40 oil with a selective solvent, separating a primary raflinate insoluble in said solvent.from a low grade extract soluble therein, introducing a selective solvent into an upper stage of a second extraction system, introducing said primary raffinate at a lower stage of the'system, removing a raflinate from the upper stage and extract from the lower stage, at an intermediate stage contacting extract phase from the upper stage with rafiinate from the lower stage, separating extract phase and raflinate at said intermediate stage, introducing said last mentioned rafiinate into the upper stage and said last mentioned extract into the lower stage.

8. A process according to claim 7 in which the temperature inthe-upper stage of said second extraction system is higher than the temperature in the intermediate stage and the temperature in the intermediate stage is higher than the temperature in the lower stage. i

9. A process for the selective solvent extraction of mineral oils at difierent temperatures which comprises extracting said oil with a selective solvent, separating a primary raflinate in-- soluble in said solvent from a low grade extract soluble therein, introducing a selective solvent into an extraction zone of relatively high temperature, introducing said primary rafiinate into an extraction zone of relatively low temperature, removing high grade raffinate from the high temperature zone and intermediate grade extract from the low temperature zone, at a zone of intermediate temperature contacting extract phase from the high temperature zone with raffinate from the low temperature zone, separating extract phase and railinate from said intermediate temperature zone, introducing said last mentioned rafilnate into the high temperature zone and said last mentioned extract phase into the low temperature zone.

10. A process for the separation of paraflinic and non-parafiinic fractions from an oil containing the same which comprises extracting said 011 with liquid sulphur dioxide, separating the raffinate insoluble therein from the extract phase, subsequently extracting said rafllnate with liquid sulphur dioxide modified by benzene, separating the rafilnate insoluble in said liquid sulphur dioxide and benzene from the extract phase comprising dissolved fractions, chilling said last mentioned extract phase to reject an insoluble fraction therefrom, separating said rejected insoluble fraction from said extract phase, and returning said rejected fraction to said second mentioned extraction for treatment with liquid sulphur dioxide modified by benzene.

DAVID R. MERRIIL.

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