US2054295A - Process for solvent extraction of hydrocarbon oils - Google Patents

Description

Sept 15, 1936. R MERR|LL 2,054,295

PROCESS FOR SOLVENT EXTRACTION OF HYDROCARBON O ILS Filed Dec. 12, 1935 3 Sheets-Sheet l r 1 60 ,63 62 6 Joli/e211 Exfra afor- INVENTOR. Dav/0 R MQZ'T'I/l BY ATTORNEY.

Sept. 15, 1936.

D. R. MERRILL PROCESS FOR SOLVENT EXTRACTION OF HYDROCARBON OILS Filed Dec. 12, 1955 S 3 Sheets-Sheet 2 coozer se arafor l 107 ffea zer INVEN TOR. David R Merrill ATTORNEY.

Sept. 15, 1936. D. R. MERRILL 2,054,295

PROCESS FOR SOLVENT EXTRACTION OF HYDROCARBON OILS Filed Dec. 12, 1955 :5 Sheets-Sheet 3 J5 60 r54 62 Solvenf L k4? 66 67 Exfracior nnn 32 30 IJUU Exfraczor INVENTOR. Dame R Merrz/Z v I 1 ATTORNEY.

Patented Sept. 15, 1936 PROCESS FOR SOLVENT EXTRACTION OF HYDRQCARBON OILS David R. Merrill, Long Beach, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application December 12, 1933, Serial No. 702,015

9 Claims.

This invention relates to a process for the treatment of petroleum with selective solvents.

In the production of lubricating oil for internal combustion motors, turbines, and other machinery, 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.

The aromatic, naphthenic and olefinic hydrocarbons present in crude lubricating oil fractions are undesirable because they do not possess these desired characteristics. The more paraflinic hydrocarbons present in crude lubricating oil fractions are the most desirable materials to be employed as lubricants. These compounds are more highly saturated hence, from a chemical standpoint, they are rather inactive and exhibit less tendency towards the formation of undesirable resinous or sludge forming constituents on contact with air at elevated temperatures. Furthermore, these compounds 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 paraflinic 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 semisolid at ordinary temperature and which are known as wax or petrolatum. As a matter of convenience hereafter, I will refer to the undesirable constituents, such as olefinic, naphthenic and/or aromatic hydrocarbons as the non-paraflinic constituents of petroleum.

A further indication of the purity of a lubricating oil is its viscosity gravity constant. This constant is an index of 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 about 0.903 viscosity gravity constant for an extreme Gulf Coast type to 0.807 for an extreme Pennsylvania type, or even beyond. The viscosity gravity constantreferred 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, vol. 20, page 641, of 1928.

In the production of lubricating oil from crude petroleum residues or distillates, it is becoming conventional in the art to separate the desirable paraflinic hydrocarbons from the undesirable olefinic, naphthenic and/or aromatic compounds by 5 the use of solvents which selectively dissolve the undersirable hydrocarbons but which exhibit only a very limited solvent power for the desirable parafllnic hydrocarbons.

A number of selective solvents for this purpose 10 have been found; for example, it has been shown that such materials as liquid sulphur dioxide, beta beta dichlorethyl ether, ortho chloraniline, nitrobenzene, aniline and furfural are highly selective as solvents for the non-paraflinic hydrocarbons. 15 When these relatively heavy solvents are commingled with petroleum or petroleum fractions under the proper conditions of temperature, the undesirable non-paraffinic hydrocarbons pass into 7 solution to a greater or less extent but the desir- 2r phase ordinarily contains a relatively large quantity of the solvent. These fractions may be purified by distillation whereby the solvent is distilled away from the hydrocarbon oils.

The quality of raflinate obtainable in a countercurrent extraction process with continuous flow depends to a very large extent upon the temperature in the stage from which the final rafflnate leaves the system. The higher this temperature is, the better is the quality of the raf- 40 finate obtained. For successful operation, however, it is necessary that the conditions in this stage (referred to for convenience as the last stage) should be such that complete miscibility does not occur, for if complete solution occurs in the settling section of this last stage no rafflnate can be produced.

The temperature of complete miscibility of all the oil with the solvent (hereinafter termed the miscibility temperature) in any stage is a function of both the average composition of the oil in the stage, including the oil in both phases, and the proportion of total solvent to total oil in the stage. In producing a high quality final rafiinate from a stock containing a limited quantity of such rafiinate, it is necessary to dissolve and carry away a large proportion of the original feed. In the case of many solvents, such as dichlorethyl ether and, to an even greater extent, liquid sulphur dioxide alone or modified with for example, 30 percent. .of benzene, the solubility of the oil in the extract phase even at temperatures within 5 F. or 10 F. of the miscibility temperature is rather limited. In conseqence. it is necessary in refining such stocks for the production of low viscosity gravity constant oils to usea large proportion of solvent to feed stock in order to remove in solution from the system the undesirable constituents of the feed.

In usual practice, all of the solvent is introduced into the last stage of the system in which the final raifinate is produced. The solvent then passes countercurrently to the flow of rafiinate through the various stages of the system until it is removed from the system, carrying with it the non-paraifinic material. The introduction of a large amount of solvent into the last stage has the undesirable effect of lowering the miscibility temperature in this stage and in adjacent stages so that the temperatures at which it is practicable to operate these end stages are materially reduced.

It is an object of my inventionto operate the last stages of extraction in which the final raffinate is produced at relatively high temperatures.

It is a further object of my invention to main tain such proportion of solvent to oil in the last stages of extraction in which final rafllnate is produced that the mixtures therein are characterized by high miscibility temperatures whereby said extraction may be accomplished at relatively high temperatures.

Referring to the drawings,

Fig. 1 is a diagrammatic view of one type of apparatus suitable for carrying out my invention;

Fig. 2 is a diagrammatic view of similar apparatus provided with means for recovering and reusing solvent; and

Fig. 3 is a diagrammatic view of similar apparatus provided with means for rectification.

In the apparatus shown in Fig. 1, oilv may be introduced into extraction column 10 from one or both of two sources. Fresh, unextracted oil may enter Ill via line H controlled by valve l2 by action of pump l3. Line ll connects with line l4 and orifice mixer l5 which in turn communicates with column l0 via line [6. If a raflinate produced by a Prior solvent extraction is to be treated in column I 0, fresh feed is introduced into primaryextractor 20 via line 2| controlled by valve 22 by action of pump 23. Fresh selec- -tive solvent is introduced into primary extractor 20 by action of pump 24 in line 25 controlled by valve 26. Preferably the oil in 20 is subjected to countercurrent extraction by the selective solvent. Low grade extract and the major proportion of the solvent is removed from the primary extractor through line 2'! controlled by valve 26. Primary rafiinate produced in extractor 26 is removed therefrom through line 30 and valve 3| by pump 32. Line 30 connects with feed line l4.

Extractor I0 is divided into a number of sections to by imperforate plates 42. Each.

section in turn is divided into a mixing zone 43 and a settling zone 44 by plate 45 provided with port 46. Each mixing zone may be provided with an agitator (not shown) if necessary. Column I0 is preferably a vertical unit provided with s csection 35 by line controlled by valve 56.

tions 35 to 46 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 the lowest section, for instance section 46. Fresh solvent from tank 50 may be introduced into each section of extractor Hi. In some instances, it is not necessary to add fresh solvent to the lower sections such as section 40. High grade raffinate is removed from uppermost Extract is removed from column ill by line 51 controlled by valve 58.

Fresh solvent for extractor I0 is pumped from tank 50 through line and valve Si by action of pump 62. That portion of solvent which is then diverted through line 63 enters sections 35, 31 and 39 of column ill by passage through valves 64 in lines 65 which communicate with orifice mixers 66 and thence by passage through lines 61 into these respective sections. That portion of solvent which is diverted through line 68 enters sections 36 and 38 by passage through valves 69 in lines 16 which communicate with orifice mixers II and thence by passage through lines 12 into these respective sections.

When both extractors l0 and 20 are-used, the solvent employed in I0 may be the same as that used in 26 or that used in i0 may be a different solvent or may be the same solvent as in 20 modified by the addition of one or more modifying agents to be described. When the same solvent is used in both extractions, valve 26 in line 25 may be closed and the solvent from tank 50 may then pass via lines 60 and 68 through valve 13 and line 14 into extractor 20 for countercurrent extraction therein. When different solvents are employed in the two extractors, valve 13 is closed and the flow of materials proceeds in the manner described above.

As previously described, a fresh supply of solvent may be introduced into each section of column III. From each section, excluding section 40, the extract phase is removed from settling zones 44 via lines 15- and valves 16 by action of pumps 11. The extract phases from sections 35 to 38 pass into the next lower section, respectively, through the orifice mixers with fresh solvent. The extract phase from-section 39 passes into section 46 commingled with oil passing through line l4.

' From each section, excluding section 35, the rafilnate is removed from settling zones 44 via lines 80 and valves 8| .by action of pumps 82.

The raflinate'is then intermingled in the next upper section respectively, with fresh solvent and with extract phase from an upper section. Raffinate from section 36 is intermingled only with fresh solvent prior to passage into section 35.

In the above described apparatus, the solvent is introduced into an upper or primary section, for example 36, an intermediate or secondary section such as 31 and a lower or tertiary section such as 38. The oil is introduced into the lower or tertiary section. Extraction takes place in all sections and the extract phase from the upper section is commingled in the intermediate or secondary section with the railinat'e produced in the lower section. Rafiinate from the intermediate section travels to the upper section and extract from the intermediate section passes to the lower section.

Due to the general similarity of the various hydrocarbon components of mineral oil fraction such as lubricating oils, solubilities of the unde- 51rable, non-paraffinic fractions and of the desirable paraflini'c fractions in a selective solvent usually diflfer only in degree and there is, therefore, a tendency for desirable, high grade parafflnic oil to be carried away with the extract resulting in a loss in the yield of parafllnic fractions obtained. In other words, in a phase separation of extract and rafflnate fractions from mineral oil employing a selective solvent, an equilibrium of parafllnic components as well as non-paraflinic components is established between the phases. Consequently, some of the desirable paraflinic fraction is found in the extract instead of in the raffinate.

Because of the magnitude of the partition coeiiicient of paraflinic constituents between the rafllnate and extract phases in section 36, the presence of the highly parailinic ramnate therein results in substantial proportions of the paraffinic components passing into the extract phase. By intermixing the less paraffinic raflinate from section 38 with the extract and solvent from 36 containing a relatively high proportion of parafflnic materials and causing phase separation in section 31, at least a portion of the paramnic fractions will pass from the extract into the raf- By contacting an extract-solvent mixture from an upper section of the tower with a raflinate from a lower section, a re-distribution of parafflnic fractions takes place, The extract-solvent mixture contains so large a proportion of parafflnic hydrocarbons and the rafiinate from a lower section relatively contains so small a proportion of these hydrocarbons that when said extract and said raffinate are mingled in the presence of the solvent, sufllcient paraflinic fractions pass from the extract to the raflinate to establish equilibrium between the two phases. Also, at the same time, some of the non-parafinic fractions pass from the rafiinate to the extract, resulting in a more parafllnic rafiinate and a less paraflinic extract. Consequently, after a succession of such steps the final extract contains the least amount of parafilni'c fractions and the final railinate contains those parafiinic fractions which are normally lost in the extract. The solvent associated with the extract and rafllnate can be removed therefrom by usual means such as by distillation.

In the operation of the apparatus shown in Fig. 1, fresh, unextracted oil may enter column l0 via lines I4, and H5 in which case extractor 20 may be disconnected from the system by closing valves 3| and 13.

When the total amount of solvent for use in column I0 is introduced into top section 35, the

introduction of this large amount of solvent into the last stage has the undesirable effect of lowering the miscibility temperature of the extract phase and raffinate phase in this stage and in adjacent stages so that the temperatures at which it is practicable to operate these end stages are materially reduced. As previously stated, the higher the temperature at which the final raflinate leaves the system, the better is the quality of the rafiinate obtained. By distributing the total amount of solvent used in column ID by separately introducing regulated quantities thereof into sections 35 to 39, the proportion of solvent to oil in the later stages is not excessive and the undesirably large reduction in miscibility temperatures in these later stages is also avoided. In some cases it may be sufiicient to introduce solvent into alternate stages or. merely into a number of the intermediate stages.

The amount of solvent introduced in the last stage, for instance section 35, is preferably that giving the highest miscibility temperature in this stage when oil of the desired quality is being produced. With constant quality of oil feed toa stage, the total proportion of solvent to oil for the maximum miscibility temperature will vary, depending upon the solvent employed but will usually be not far from the proportions of 100 to 200 volume percent. of solvent, based on the oil feed to that stage. As previously stated the introduction of the solvent is preferably distributed by separate entrance into a number of the sections. When the solvent employed in column I0 is a mixture comprising 70% liquid sulphur dioxide and 30% benzene, the temperature may successively increase from F. in section 40 to 130" F. in section 35.

In the operation of the apparatus shown in Fig. l, the 'oil which enters column |0 may be a primary raiiinate from extractor 20 in which case valve 3| is open and valve I2 is closed. When the same solvent used in column I0 is also employed in preliminary extractor 20, valve 13 is open, valve 26 is closed and oil is introduced into 20 via line 2| in the manner described above. In that case, using the above described liquid sulphurdioxide-benzene mixture, the temperature at which the low grade extract is removed via line 21 may be 20 F. while the primary rafllnate produced in the upper part of the extractor 20 may be at 40 F. The primary raflinate may enter column H) at F. The temperature in l0 may successively increase from 85 F. in section 40 to F. in section 35.

In some instances it may be desired to use a different solvent in column I!) from that employed in extractor 23 or a modified solvent may be used in l0. For example, a hydrocarbon mixture may first be extracted with one of the pure selective solvents set forth above and then the raflinate so produced may be re-treated with one of these solvents modified by carbon bisulphide, xylene, benzene, toluene, carbon tetrachloride, ethers, tetrachlor-ethane or the like. stantially increasingthe solvent power or ease of miscibility of the treating agent, it is possible to fractionate the raflinate 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.

By these operations the oil feed is divided in one general process into three or more fractions of different viscosity-gravity constants. When operating in this manner valve |3 is closed and solvent is introduced into extractor 20 via line 25. For example, when liquid sulphur dioxide is used in 20, low grade extract may be removed at 80 F. via line 21 and primary raftinate may By subbe removed'at 130 F. via line 30. This primary railinate may be introduced into tower |0 at 85 F. when the solvent used in I0 is the above described liquid sulphur dioxide-benzene mixture.

In this case, the temperature in l0 may succes-" and 0.80 for the final rafilnate issuing from I0 via line 55.

When both extractors I0 and 20 are employed, it is also possible to estimate closely the optimum proportion of solvent to be introduced into the last stage, section 35. Thus, for example, if the yield of desired quality, final rafiinate from a certain stock is known to be 30% and that the proportion of solvent to oil for maximum miscibility temperature is 150 volume percent. While the solubility of oil in the extract phase is 15%, the proportion of solvent introduced into the last stage is about 60%, based on the original feed. This is estimated from the fact that in order to obtain 30% of the original feed as final rafilnate at the last stage, about 40% of raffinate must flow into it from an adjacent stage and in order to give the desired 150 volume percent. proportion of solvent to oil, 60% of solvent must be used with the 40% of oil.

After thus establishing the optimum amount of solvent to be employed-in the last stage, the remainder of the total amount of solvent required to hold in solution those portions of the feed stock which it is necessary to remove may be distributed over the other stages of this part of the system. For example, if 30% of low grade extract is removed via line 21 and 30% of high grade raflinate is produced in the last stage, section 35, there remains 40% of material to be removed in the form of intermediate extract via line'5I. If the solubility of this intermediate extract in the solvent employed at the temperature existing in section 40 is about 13%, the total amount of solvent required in this part of the system will be about 300 volume percent, based on the original feed. If 60 volume percent. is introduced at stage 35, there remains 240 volume percent, to be distributed over the next four stages, or about 60 volume percent. per stage. It is not essential that this distribution over the intermediate stages be in equal amount as a greater distribution in either the higher or lower stages can be offset by adjustment of temperature therein. However, excessive introduction of solvent in the higher stages is to be avoided because the miscibility temperature and the practicable operating temperature in these stages is reduced, thereby interfering with the degree of refinement at these intermediate points.

With certain oils, the amount of intermediate quality fractions to be removed is very large and in consequence the amount of solvent required to hold these fractions in solution is correspondingly large. In order to reduce the total consumption of solvent when treating such oils, my invention includes the recirculation of a part of the extract phase to operate as the solvent.

In the apparatus shown in Fig. 2, contaminated solvent is recirculated for this purpose. I Parts which are alike in Figs. 1 and 2 have been similarly numbered. Fresh solvent from tank 50 may be introduced into a number of sections of column I0, for instance sections 35, 36, and .31, in order to obtain a high miscibility temperature in the upper sections as previously described.

To recover solvent for reuse, a portion of the intermediate extract phase issuing from column I0 is forced by pump I00. through line. 51 into cooler IOI wherein the solvent power of the solvent in the extract phase is reduced by cooling sufficiently to cause phase separation in separator I 03 to which the mixture passes via I02. The remaining intermediate extract is drawn off through line I09 and valve II I. An intermediate oil fraction, insoluble in the cooled mixture, is

removed via line I04 and valve I05. The recovered solvent which under preferred temperature conditions in cooler IOI may be contaminated,

with 3% or less of oil is removed from separator I03 via line I06 and valve I01 by pump I08. The stream of contaminated solvent may then be divided and part is passed via line I I 0 and valve I l I for intermixture with extract phase from section 38 and raflinate phase from section 40 prior to phase separation in section 39.

Another part of the contaminated solvent may pass into sections 38 and 40 via lines I06, H2, H3 and valve H5 and thence via line H6 and valve III, orifice'mixer II and line I2 and via line IIO cgntrolled by valve H9, orifice mixer I5 and line If desired, by opening valve I20 in line II3, the contaminated solvent may be used as the selective solvent in primary extractor 20. In this event, valve H4 in line I09 may be closed so that all the extract phase from I0 will be subjected to treatment for recovery of contaminated solvent. In extractor 20, the contaminated solvent may either be used alone or in intermixture with other solvent entering therein via line 25 in the manner above described.

Another part of the contaminated solvent may pass via lines I06 and H2 through valve I22 into heater I23 where its solvent power is increased by raising its temperature prior to passage through line I24 for intermixture with the primary raflinate issuing from extractor 20 via line 30. The combined fiow passes through line I25, orifice mixer I26 and line I21 into separator I 30 where phase separation takes place. Extract phase is removed via line I3I controlled by valve I32. Raflinate phase is forced through line I33 and valve I34 by pump I35 into line I I8 for intermixture with extract phase from section 39 of column I 0 prior to phase separation in section 40 in the above described manner. 1

As an example of the operation of the apparatus shown in Fig. 2 employing liquid sulphur dioxide in extractor 20, the low' grade extract may be removed via line 21 at F. while the primary raffinate may be drawn off at 130 F. Employing the above mentioned mixture of 70% liquid sulphur dioxide and 30% benzene in column I0, the temperature therein may successively increase from F. in section 40 to F. in section 35. Separator I03 may be maintained-at 20 F. and separator I30 may be maintained at 85 F. By operating in the above described manner, the successive, controlled introduction of solvent into each stage creates mixtures characterized by high miscibility temperatures-whereby phase separation can take place at desirable, relatively high temperatures. Also, an economy of solvent is eflected by the return of contaminated solvent.

As previously stated, the contaminated solvent recovered from extractor I0 may be used as the solvent in extractor 20. In that case, the temperature in I0 may successively increase from 80 F. in section 40 to 130 F. in section 35, using the above described liquid sulphur dioxide-benzene mixture. The temperatures in extractor 20 and separators I03 and I30 may all be about 20 F.

When employing the contaminated solvent from separator I03 as the solvent for extraction in 20, the total quantity of solvent employed is preferably restricted to that required for solution of the low grade extract from the feed stock removed via line 21. Thus, for example, if 30% of such oil is to be dissolved and the attainable concentration of this oil in the extract phase in extraction of the section 35.

, feed stock at the low temperature required to give an extract of the desired high viscosity gravity constant is the amount of solvent required would be 200 volume percent. based on the feed. As previously stated, for the production of a yield of final raiiinate, 60 volume percent. is a typical amount of solvent to be introduced into Therefore, there remains 140 volume percent. to be introduced in the other sections of column I0 and the total requirement of solvent for removal of intermediate grade extract via line 51 is made up by recirculation, for example, of 200 volume percent. of recovered solvent into the intermediate sections. The amount of recirculated solvent will normally be larger than the amount v of fresh solvent which would be required because of the presence of residual oil due to the incompleteness of rejection in separator I03 at readily attainable temperatures,

My invention may also be combined with rectification during solvent extraction, for example, in the manner shown in Fig. 3 in which parts similar to those described for Figs. 1 and 2 are given the same numbers. As previously described, solvent introduced into column I0 from tank 50 may be apportioned between sections to 38 whereby the mixtures in the last sections are characterized by high miscibility temperatures. Part of the intermediate extract issuing through line 51 is cooled in cooler IOI sufficiently to cause phase sepmation in I03. The remainder exits through line I09 and valve I. The raflinate thus produced in separator I03 passes through line I and valve I5I by action of pump I52. Part of the rafilnate may be removed from the system via line I53 controlled by valve I 54.

The remaining raftinate from I03 is mixed with extract phase from section 39 and passes via line I into orifice mixer I5 and via line I6 into rectifying section 40 wherein it becomes enriched in high grade components. Loss of such high grade components in the intermediate grade extract is thus reduced.

Part of the extract phase in separator I03 comprising solvent contaminated with oil passes through line I06 and can be removed via valve I56 while the rest travels through valve I01 and pump I00 into heater I23 where its temperature is raised sufficiently to increase its solvent power. The contaminated solvent then travels via line I and valve I6I into admixture with primary raffinate passing through line 30 from extractor 20. The mixture continues to pass through line 30 and intermingles with extract phase from section 38 and rafiinate phase from section 40 before passage into section 39.

If it is desired to use the contaminated oil as the solvent in extractor 20, part of the stream in line I60 may be diverted through line I62 and valve I63. In this event valves Ill and I56 may be closed so that all the extract phase from I0 will be subjected to treatment for recovery of contaminated solvent. In extractor 20, this contaminated solvent may be used alone or with fresh solvent entering via line 25.

As an example of the operation of Fig. 3, employing the above described liquid sulphur dioxide-benzene mixture in column I0, the temperature in section 40 may be 85 F. while the temperature in the upper part, of the column may be progressively higher, for instance from 95 F. in section 39 to 130 F. in section 35. Separator I03 may be at 20 F. When using contaminated solvent from separator I03 as solvent in extractor 20, the low grade extract may be removed via line 21 at 20 F. and the primary raiiinate may beremoved via line 30 at 40 F.

It should be understood that these. temperatures are merely by way -01 illustration and that they may be varied for other stocks and solvents. Furthermore, the number ofstages shown in the figures is to be considered merely typical for these general conditions and may be varied as described. Thus, more than one rectification stage may be employed and the number of extraction stages may be increased or decreased as is found desirable in any particular circumstance.

I claim: i

1. A process for the separation of paramnic and nonaparamnic fractions from an oil containing the same which comprises introducing only sufficient selective solvent at a primary extraction stage to produce a mixture characterized by a high miscibility temperature, introducing said oil at a tertiary extraction stage, removing'raflinate from the primary stage and extract phase from the tertiary stage and at a secondary stage com-' mingling extract phase from the primary stage, rafllnate from the tertiary stage and additional selective solvent.

2. A process for the separation of paraflinic and non-parafllnic fractions from an oil containing the same which comprises introducing only sufficient selective solvent at a primary extraction stage to produce a mixture characterized by a high miscibility temperature, introducing said oil at a tertiary extraction stage, removing raflinate from the primary stage and extract phase from the tertiary stage and at a secondary stage commingling extract phase from the primary stage,

raflinate from the tertiary stage and additional selective solvent, separating extract. phase and railinate from said secondary stage, introducing said last mentioned rafi'inate into the primary stage and said last mentioned extract phase into the tertiary stage.

3. A process as in claim 2 in which the temperature in the primary stage is higher than the temperature in the secondary stage and the temperature in the secondary stage is higher than the temperature in the tertiary stage.

4. A process for the separation of parafiinic and non-paraflinic fractions from an oil containing the same which comprises extracting said oil with a selective solvent, separating a primary raffinate insoluble in said solvent from a low grade extract soluble therein, introducing only sumcient selective solvent into a primary stage of a second extraction system to produce a mixture characterized by a high miscibility temperature, introducing said primary raflinate into the tertiary stage of said second extraction system, removing a raffinate from the primary stage and an extract from the tertiary stage, at a secondary stage of said second extraction system commingling extract phase from the primary stage, raflinate from the tertiary stage and additional solvent, separating extract phase and rafiinate at said secondary stage and introducing said last mentioned raffinate into the primary stage and said last mentioned extract into said tertiary stage.

5. A process for the separation of parafiinic and non-parafiinic fractions from an oil containing the same which comprises flowing said oil and a selective solvent countercurrently, introducing only sufficient selective solvent into that zone from which final rafiinate is removed to produce a mixture characterized by a high miscibility temperature, removing extract phase from said countercurrent extraction, cooling said extract phase to separate a ramnate insoluble therein from contaminated solvent and introducing said contaminated solvent into'said countercurrent extraction at an intermediate point.

6. A process for the separation of paraflinic and non-parafllnic fractions from an oil containing the same which comprises introducing only sutlicient selective solvent at a primary extraction stage to produce a mixture characterized by a high miscibility temperature, introducing said 011 at a tertiary extraction stage, removing raiflnate from the primary stage and extract phase from the tertiary stage, cooling said last mentioned extract phase to separate a ramnate insoluble therein from contaminated solvent and at a secondary stage commingling said contaminated solvent with extract phase from the primary stage and with raflinate from the tertiary stage.

'7. A process for the separation of paraflinic and non-paraflinic fractions from an oil containing the same which comprises introducing only suflicient selective solvent at a primary extraction stage to produce a mixture characterized by a high miscibility temperature, introducing said oil at a tertiary extraction stage, removing raflinate from the primary stage and extract phase from the tertiary stage, cooling said last mentioned extract phase to separate a raflinate insoluble therein from contaminated solvent and at a secondary stage commingling said contaminated solvent with extract phase from the primary stage and with rafiinate from the tertiary stage, separating extract phase and raffinate from said secondary stage, introducing said last mentioned raflinate into the primary stage and said last mentioned extract phase into the tertiary stage.

8. A process for the separation oi paraiiinic and non-paraflinic fractions from an oil contain: ing the same which comprises flowing said oil and a selective solvent countercurrently, introducing only sufllcient selective solvent into that zone from which final rafilnate is removed to produce a mixture characterized by a high miscibility temperature, introducing additional selective solvent at an intermediate point in said countercurrent extraction, removing extract phase from said extraction, cooling said extract phase to separate an insoluble oil fraction from contaminated solvent and returning said last mentioned insoluble oil fraction into said first mentioned countercurrent extraction.

9. A process for the separation of paraflinic and non-paraflinic fractions from an oil containing the same which comprises introducing only sutflcient selective solvent at a primary extraction stage to produce a mixture characterized by a high miscibility temperature, introducing said oil at a secondary extraction stage with additional solvent, introducing raflinate from the secondary stage into the primary stage, removing raflinate from the primary stage, introducing extract phase from the primary stage into the secondary stage, introducing extract phase from the secondarystage into a tertiary stage, introducing raflinate from said tertiary stage into said secondary stage, cooling extract from said tertiary stage to separate an insoluble oil fraction from contaminated solvent and returning said last mentioned insoluble oil fraction into said tertiary stage.

DAVID R. MERRILL.

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