US3428553A - Separating primary solvent with a secondary solvent - Google Patents

Description

Feb. 18, 1969 cHYN DUoG s'HlAH 3,428,553

SEPARATING PRIMARY soLvENT WITH A SECONDARY soLvENT Filed Feb. 5, 1966 United States Patent O 8 Claims ABSTRACT OF THE DISCLOSURE The aromatic components of hydrocarbon oil are separated from the non-aromatic components by contacting the oil with a primary solvent, preferably a solvent corr.- taining a major amount of dimethyl formamide and then contacting the thus produced extract and raffinate with a secondary solvent which is an organic hydroxy compound to remove the primary solvent. Y

This application is a continuation-in-part of copending application Ser. No. 322,577, filed on June 4, 1964, now Patent No. 3,249,532, which is a continuation-in-part of application Ser. No. 96,890, filed Mar. 20, 1961, and now abandoned.

This invention relates to a process for the separation of petroleum or petroleum products into fractions of differing chemical compositions and is more particularly concerned with a process which is applicable to petroleum distillates of all boiling ranges.

Liquid-liquid extraction is an increasingly important tool in chemical processing, especially in petroleum refining. Solvent extraction, as applied in petroleum refining, for example, serves to separate a hydrocarbon oil stock into two or more fractions of differing chemical compositions and most frequently has been applied to the separation of aromatics from other hydrocarbon types (naph-f thenes, paraflns and olens). Examples of the application of liquid-liquid extractions include:

(l) Separation of benzene, toluene and xylenes from catalytically reformed naphthas.

(2) Removal of aromatics from kerosene to improve smoke point.

(3) Removal of aromatics from light gas oils in order to make high-quality diesel fuel, jet fuel and rocket fuel.

(4) Removal of aromatics from catalytic cracking charge stocks in order to improve yields and reduce coke lay-down in catalytic cracking units.

(5) Separation of naphthalene precursors (alkyl naphthalenes) from petroleum fractions.

(6) Removal of aromatics from heavy straight-run gas oils to produce spray oils and transformer oils.

(7) Removal of aromatic-type compounds from lubricating oil distillates in order to produce high-quality lubricating oils.

Sulfur reduction of petroleum distillates (particularly light and heavy gas oils) is also a concomitant and desirable result of aromatics extraction, since most of the sulfur contained in middle distillates is either a part of an aromatic compound or is contained in a thiophene ring which usually responds to a selective solvent in the same manner as an aromatic compound.

3,428,553 Patented Feb. 18, 1969 Mice A modern refinery may employ liquid-liquid extraction in one or more of the foregoing applications.

A large number of compounds have been found to exhibit selectivity for the separation of aromatics from other hydrocarbons. Of these only a few have been employed to any significant extent on a commercial scale. These include (together with their boiling points) the following:

Boiling point at 760 mm. F.)

Liquid-sulfur dioxide 15 Furfural 323 Phenol 358 Diethylene glycol 473 Sulfolane 550 Most of the processes which have been developed involve essentially the same processing sequence. The first step in the process is counter-current contacting of the solvent and the oil. A number of contacting devices are well known in the trade and include packed columns, mechanically-agitated columns, mixer-settler combinations and centrifugal contactors. The solvent selectively absorbs the aromatic portion of the feed stock, which portion is produced from the column as an extract phase. The less soluble (non-aromatic) portion of the feed stock is produced as a raffinate phase. The solvent is contained in both the rainate and the extract phases, with most of the solvent occurring in the extract phase. The usual method of recovering the solvent from the extract and the raffinate phase is to take advantage of the difference in boiling point between the hydrocarbonsin the extract phase and the solvent by employing distillation procedures. The recovered solvent is then recycled to the extraction device to complete the process.

There is, however, no solvent-extraction process which can be used effectively and in a practical manner for the extraction of the full range of petroleum oil stocks. Furthermore, the existingprocesses employing the solvents referred to above are either relatively complicated or unduly expensive.

The customary practicein the recovery of a solvent employed in solvent extraction is by distillation, and the cost of heat required for Such solvent recovery constitutes the largest item of the operating cost of the solvent extraction process. Furthermore, conventional solvent extraction processes are generally operated at the same relatively elevated temperature level as the solvent stripper in an effort to effect maximum heat economy. In addition, by reason of the bulk of the extract and/ or raffinate which is admixed with the solventat the boiling temperature of the solvent, the chance of heat deterioration of the solvent and of the extract or railinate is increased, and the chance of possible interaction between the solvent and the oil, or between the air in the system, e.g. air dissolved in the oil and solvent, with the solvent and/ or oil, is also increased.

A major consideration which has heretofore been an obstacle to the provision of a solvent extraction process which can be applied to hydrocarbon stocks of all boiling ranges is the boiling point of the solvent. Customarily, as previously mentioned, the recovery of the solvent is effected by distillation. There must, therefore, be a certain temperature difference between the boiling point of the solvent and the boiling range of the stock extracted in order to effect efficient separation between the oil and the solvent upon distillation. In the event that the oil feed stock has a -boiling range close to that of the solvent, it is impractical to separate the two phases by distillation procedures. Hence, the above-listed solvents are limited in their applicability. For example, furfural, which has a boiling point of about 323, is commonly used lfor the extraction of hydrocarbons having an initial boiling point of approximately 400 F. and higher. It cannot, however, lbe effectively used for oil stocks boiling much lower than about 400 F. because of the difliculty of separation of the oil from the furfural. Diethylene glycol, with a boiling point of 473 F., is suitable for the extraction of naphthas (maximum boiling point about 400 F.), but has not been used for heavier distillates because of its high boiling point.

However, the boiling points of most solvents, with the exception of sulphur dioxide, all in or near the boiling range of the kerosene fraction, i.e. S80-'550 F. As a result, none of the commercial solvent extraction processes, with the exception of the sulphur dioxide process, is applicable to oils of the kerosene boiling range. Sulphur dioxide extraction plants are inherently expensive inasmuch as, the extraction takes place at low temperature, requiring the use of refrigeration; the solvent is recovered by evaporation and since it is a gas at normal temperatures and pressure, compressors must be employed to liquefy the gas; and since sulfur dioxide is highly corrosive in the presence of water, elaborate precautions are necessary to dry the feed and prevent water from entering the plant.

Therefore, a new solvent extraction process that is applicable to hydrocarbon feedstock of all boiling ranges must use other means than distillation for the recovery of the main bulk of the solvent. In many extraction applications, it is necessary to produce a high purity extract. For example, benzene, toluene and xylene specifications require a purity in excess of 99%. By contrast, where removal of the aromatic-type hydrocarbons from the charging stock is the primary objective, a lower purity is accepta-ble. For example, in the extraction of kerosene the recovered extract phase may have an aromatic content of 70-80%.

Nearly all of the pure polar solvents which have been found to be effective in aromatic separations from type l solubility `diagrams with aromatics and non-aromatics. A type 1 diagram has the following characteristics appearance when plotted by triangular coordinates:

Aromatic Non-aromatics i Solvent:

The maximum purity of the extract which .can be produced in a type l system is represented by point E, the terminus of a line starting at the solvent apex (100% pure solvent) and drawn tangent to the envelope. Typically, the extract will contain 70-80% aromatics.

Various methods have been used to increase extract purity. These include:

(l) Subjecting the extract phase to extraction distillation to remove remaining non-aromatics.

(2) Emloying extract reflux.

(3) Employing a high-boiling wash oil which will displace the undesired non-aromatics and may later be removed by distillation.

(4) 4Employing a low-boiling diluent which will displace the undesired non-aromatics and may later be removed by distillation.

(5) Adding another solvent to the primary solvent which will modify the solvency and selectivity of the primary solvent. For example, water has been used for this purpose. In general, water will increase selectivity and reduce solvency. Adding water or similar compounds to the solvent system will often permit the production of higher purity aromatics at the expense of increased solvent circulation.

A single process which is applicable to all boiling ranges of hydrocarbons (i.e., from naphtha to lubricating oil distillates) should have the following features:

(1) The primary solvent should possess high solvency and selectivity.

(2) The boiling point of the primary solvent should be high enough so that the vaporized solvent may be condensed with cooling water, but low enough so that excessive temperatures (which may lead to degradation of the materials 'being extracted) or extremely low vacuums are not required in the solvent recovery stage.

(3) The solvent should be inexpensive, non-toxic, thermal stability and should 'be non-corrosive to ordinary materials of construction, such as steel.

(4) It should ibe possible to control the selectivity and solvency of the primary solvent to provide optimum extraction conditions Ifor the particular stock being treated.

(5) It should be possible to separate and recycle the primary solvent economically from any boiling range of stock (from naphtha to vacuum gas oil).

(6) It should be possible to produce any desired purity of the extract phase (from high purity to low purity).

The foregoing features combined in a single economical plant will permit a rener to employ liquid-liquid extraction to a much greater extent than has heretofore been possible. Up to now, many small refiners have been unable to employ extraction in their processing schemes because, with the available processes, each possible application requires a separate small plant of an uneconomical size. However, with a single multi-purpose plant, a small rener can take advantage of liquid-liquid extraction for a variety of applications and can produce the same range of product as a large rener who can economically justify separate extraction plants for each type of stock.

It is, accordingly, an object of the present invention to provide a liquid-liquid extraction process which possesses the advantageous features enumerated above and can be applied to hydrocarbon stocks of all boiling ranges.

It is a further object of this invention to provide a process for the recovery of high-purity aromatics from hydrocarbon stocks of all boiling ranges.

It is a still further object of this invention to provide a process' wherein the primary solvent may be recovered without subjecting the charging stock to excessive temperature.

It is another object of this invention to provide a process which does not require the use of high pressure, low temperatures or corrosion resistant materials.

In accordance with the invention, the extraction of hydrocarbon oils is effected with two solvents dissimilar in their solvent properties. For convenience of description, one of the two components may be designated as a primary solvent and the other as a secondary solvent. The primary solvent in the process lof this invention is a solvent for aromatics. A preferred primary solvent is dimethyl formamide, but a number of other solvents possessing similar solvent properties may also be used, such as alkylamides, arylamides, and particularly dimethyl acetamide and tetrahydrofurfuryl alcohol.

A secondary solvent is chosen which effects the separation between the primary solvent and the hydrocarbon portion which has been selectively extracted. Thus, the secondary solvent is a solvent which is completely miscible with the primary solvent but immiscible with hydrocarbon oil extract.

In a preferred manner of operation, the primary solvent is introduced at one end of the primary extractor, the feed at an intermediate point and the secondary solvent at the other end of the extractor. The ratio of solvent to feed may range from about 0.2:1 to about 15:1. The

lower solvent ratios are generally applicable to lubricating oils and the higher solvent ratios to the lighter stocks such as catalytic reformates.

According to the invention, a secondary solvent is used which is miscible with the primary solvent, but essentially immiscible with said hydrocarbon oil extract. Useful solvents of this type include mono and poly alcohols such as methanol, glycerol and glycol and other lower alkyl mono and 4poly hydroxy compounds. The primary and secondary solvent pair are chosen so that a separation of primary and secondary solvent can be easily achieved. Advantageously, there should be a boiling point difference of at least 75 F. between the two solvents.

In practicing the process, the hydrocarbon oil to be extracted is introduced as feed into the lower portion of an extraction column and the extracting fluid comprising the primary solvent and up to 90% of the total volume of the uid of the secondary solvent is introduced into the upper portion of the column. The proportion of primary solvent in the extracting fluid can Vary from 100 to 50 percent of the mixture.

The raffinate stream, which leaves the top of the extraction column is a mixture of most of the parafnic hydrocarbons from the charging stock with a small amount of the extracting fluid. The extr-act stream, which leaves the bottom of the column contains most of the aromatics and olens from the feed stock and most of the extracting fluid introduced into the column. Both the raffinate and the extract stream are then washed countercurrently in separate washers by means of further quantities of the secondary solvent. Pure hydrocarbon streams issue from the washers as the light layers from each of the washing operations. The heavier layer from both of the Washing operations is -composed of mixtures of the primary solvent and of the second-ary solvent with the proportion `of secondary solvent higher than the original extraction fluid used for the extraction operation. Inasmuch as the primary solvent and the secondary solvent are selected so that their boiling points are widely spaced apart, the two are separated easily by a simple vacuum flash operation, e.g. at pressures of 2 mm. to 100 mm. Hg. A typical vacuum ash operation, carried out in a simple vacuum flash tower, is effected at a pressure of 50 mm. Hg (abs.) and at a temperature of 100 C. Su-ch conditions are particularly suitable when the solvent is dimethyl formamide and the secondary solvent is glycerol. The overhead from the vacuum ash operation is primarily the primary solvent and the bottoms from the vacuum ash tower are the secondary solvent. The overhead prmiary solvent stream is mixed with the desired quantities of secondary solvent from the bottom stream and the mixtures are used over again in the main extraction column. The minute amounts of -oil stock which may be carried over along with the primary solvent are, of course, recycled through the main extraction column. The secondary solvent used for the washing of the raffinate and extract streams from the main extraction column is obtained from the bottom stream of the vacuum flash tower. Inasmuch as the extracting fluid used in the main extraction step can be a mixture of the solvent and the secondary solvent, sharp separation in the vacuum flash operation is not necessary and generally a one-stage vacuum flash will suice. It will be understood, of course, that if sharper separation is desired, it can be achieved Without difculty by conventional techniques.

The amount of secondary solvent used in the main extraction step can vary from 0 to 90% of the extracting uid, depending upon the boiling range of the hydrocarbon oil stock to be extracted. The lighter the stock, the more secondary solvent in the fluid. For instance, in extracting a light naphtha cut, e.g. having a boiling range of 140 to 400 F., as much as 20% of the secondary solvent will be needed. On the other hand, in the extraction of heavy lubricating cuts, no secondary solvent is needed. The extraction can be carried out at a temperature of 15-200" C. and at a pressure of from 0.200 lb. per sq. in. gage, but` is preferably carried out at 25 C. and at 14.7 lbs. per sq. in gage, using a countercurrent extraction column with 2-20 theoretical plates or stages depending on the separation desired Other objects and features of the invention will be apparent from the following detailed description of illustrative embodiments thereof and from the accompanying drawings which show diagrammatically on the nature of flow sheets, apparatus systems which are particularly suitable for use in carrying `out the process of the invention.

The flow of materials in the above-described operations is readily seen from the drawing which illustrates diagrammatically a typical apparatus layout suitably used. In the drawing, the hydrocarbon oil to be treated enters the extraction column 10 through line 12 while the extracting fluid enters through line 14. The raffinate stream leaves the top of column 10 through line 16 and passes to the rainate washer 18. At the same time, the extract stream leaves the bottom of column 10 through line 20 and is conducted to the extract washer 22. In the washer 18, the raffinate stream is brought into contact with a stream of the secondary solvent which enters through line 24 and the hydrocarbon raflinate, freed from primary solvent and secondary solvent, leaves the system through line 26. In the extract washer 22, the extract stream is countercurrently washed with further quantities of the secondary solvent which enters through line 28, and the hydrocarbon extract, free from primary solvent and from secondary solvent, leaves the system through line 30. The non-hydrocarbon streams issuing from washer 18 and washer 22 pass into lines 32 and 34, respectively, which merge into line 36 which leads to the vacuum ash tower 38. In the vacuum ash tower 38, the primary solvent is separated from the secondary solvent with the former passing through ya condenser 40 into line 14, and the latter passing through a cooler 42 into line 28. The only heat supplied is from heater 44 which adds only suflicient heat to cause vaporization of the primary solvent under the pressure conditions prevailing in the vacuum liash tower 38. A branch line 46 provides communication between secondary solvent line 24 and primary solvent line 14 to permit regulation of the ratio between primary solvent and secondary solvent passing to the extracting column 10. As indicated in the drawing, the several uid lines are provided with valves to permit control of iiow, and pumps (not shown) may be provided to insure desired movement of the several Huid streams.

In practicing the process advantageously, the extraction needs to be no higher than C. At all times, contact ambient range. The primary extraction is usually carried out in a column having from 5 to 25 theoretical stages and the secondary extractions are carried out in columns having from 5 to 15 theoretical stages.

As will be apparent from the foregoing, the highest temperature encountered in the entire system is the inlet temperature to the vacuum tower 38 and this generally needs to be no higher than 150 C. At all times, contact between the hydrocarbon oil and the extracting uid occurs at a low temperature level, much below the normal boiling point of the primary solvent. The only process heat requirement is the heat of vaporization of the low boiling component of the extracting fluid, i.e. the solvent which, in the case of dimethyl formamide, is 248 B.t.u. per lb. at 760 mm. Hg, plus a small amount of sensible heat to bring the mixture of primary and secondary solvents to a boil at the pressure existing in the vacuum tower.

Preferably, and to improve the selectivity of the separation, a paraflinic hydrocarbon with a much higher or a much lower boiling point than the feed stock is suitably injected into the lower portion of the extraction column, e.g. through line 48, to serve as a counter-solvent. For

this purpose, normal butane and/or normal pentane have been found to be particularly effective.

The only important heat input in the process is the distillation to separate the primary and secondary solvents and both the aromatic hydrocarbon oil portion and the parafllnic hydrocarbon oil portion are obtained solely by treatment with solvents.

Although the invention has been described by references to particular embodiments thereof, it is obvious that many modications may be employed without departing from the spirit and scope of the invention. Hence, the invention is not to be construed as limited in any manner except by the appended claims.

EXAMPLE 1 A xylene-rich cut from a refinery stream containing 90 volume percent aromatics and having a specific gravity of 0.846 at 60 F. was countercurrently extracted in a ll x 4' glass Scheibel column containing eleven stages. The solvent, a mixture of DMF and glycerine containing vol. percent glycerine was introduced at the top of the column at a solvent/feed ratio of 3.3/1. Feed was added near the center of the column, and pentane, at a pentane/feed ratio of 1.6/ 1, was introduced at the bottom. An extract stream was recovered that contained 99.6% of the aromatic feed hydrocarbons, these hydrocarbons having an aromatics content of 99.5 vol. percent after removal of the pentane.

EXAMPLE 2 A solvent mixture was prepared by mixing parts of dimethyl formamide with 7 parts of USP grade glycerine. One part of this solvent mixture was shaken vigorously with one part of pure normal-heptane. The mixture separated into two layers immediately yand there was no change in the volume of the normal-heptane, indicating that normal-heptane was completely immiscible with the solvent mixture. One .part of this solvent mixture was shaken with one part of pure benzene. The mixture became a single homogeneous phase. Ten parts of a 1:1 mixture of benzene and normal-heptane were brought into contact with 10 parts of the solvent mixture. The mixture separated into two distinct layers. The upper layer amounted to flve parts which consisted almost entirely of normal-heptane. The lower layer represented 15 .parts and consisted of the original solvent mixture and benzene. To this mixture were added 15 parts of glycerine, whereupon 5 parts of benzene separated from the mixture as an upper layer. The lower layer was a mixture of dimethyl formamide and glycerine.

EXAMPLE 3 A 275-5857 F. kerosene cut from a 31.5 API Kuwait crude oil was extracted with dimethyl formamide counterf Raw Stock Ranate Extract SO2 extraction:

Aniline point 156 176. 3 8.3 Yield 100 84. 5 15. 5 Sulphur 0.90 0. 37 3. 32 Gravity (API) 39. 3 43. 5 19. 3

F extraction:

Aniline point 157. 4 175. 5 Yield (calculated) 100 82 18 Surphur 729 332 2. 84 Gravity (API) 40. 5 43. 3 21. 2

* Below 30.

8 EXAMPLE 4 A 430-565 F. cut from a catalytic cycle gas oil was extracted countercurrently with dimethyl formamide with a weight ratio of 1.65 dimethyl formamide tol 1.0 of oil at 92 F. and at atmospheric pressure. During the extraction, the mass velocity rwas 762 lb./hr./sq. ft. in the case of the oil feed, 1260 lb./hr./sq. ft. for the extracting lluid stream, 372 lb./hr./sq. ft. for the raffinate stream and 1650 lb./hr./sq. ft. in the case of the extract stream. The extract contained 21.3% by volume of oil and was extracted countercurrently `with 3 volumes of USP grade glycerine. The glycerine-dimethyl formamide mixture was vacuum flashed at 140 F. (13 mm. Hg abs.) and the dimethyl formamide was recovered overhead.

The raffinate contained 3.2% by volume of solvent which was removed by contact with 10% by volume of glycerine. The resulting solvent-glycerine mixture was vacuum flashed together with that from the glycerine extraction of the extract.

The net extract obtained was by volume of the feed and the raflinate `was The property changes were as follows:

It is thus seen that the separation of aromatic components from non-aromatic components according to the method of the invention is successful even when the nonaromatic components include olefins.

EXAMPLE 5 A full range platformate with a specic gravity of 0.775 at 25 C. containing 30 percent of aromatics was countercurrently extracted with a solvent mixture consisting of 87% by weight dimethyl formamide and 13% by weight of glycerine. The extraction column was a 1 glass pipe :packed with 1A raschig rings to a depth of 8 feet, which was equivalent to 4 theoretical contact stages. The flow rate for the platformate was 2350 m1. per hour and that for the extracting fluid stream was 3250 ml. per hour, i.e., the solvent to oil `ratio was 1.37 to 1 by volume. The ralnate, amounting to 1210 ml. per hour, was cxtracted countercurrently with 213 ml. per hour of glycerine in a washing column. This produced a raffinate of 1163 ml. per hour of water-white oil stock with -a specific gravity of 0.735. The extract from the main extractor column amounted to 4390 ml. per hour and was also extracted countercurrently with 2630 ml. per hour of glycerine in another washing column, yielding an oil product at the rate of 982 ml. per hour with a specific gravity of 0.804. This oil contained 71% aromatics. The glycerinedimethyl formamide solution, together with a small amount of dissolved oil from both washing columns were combined and vacuum flashed at 90 (100 mm. Hg). The overhead from the vacuum flash -was dimethyl formamide with about ml. per hour of oil. The bottom stream from the vacuum flash tower was essentially all glycerine, which was mixed with the overhead to provide the 87-13 solvent mixture, and reu-sed in the main extraction column. The balance of the vacuum flash tower bottoms stream was used :as solvent in the two secondary extraction columns.

EXAMPLE 6 A solvent mixture was prepared by mixing 75 parts by volume of tetrahydrofurfuryl alcohol with 25 parts by volume of pure glycerine. One part 'by volume of this solvent `was shaken vigorously with one part by volume of pure normal-heptane. The mixture separated into two layers immediately and there was no change in the volume of normal-heptane, which indicated that normal-heptane is completely immiscible with the solvent mixture. One part of this solvent mixture was shaken with one part of pure benzene. The mixture became one homogeneous phase, which indicated that benzene is completely miscible with the tetrahydrofurfuryl alc-ohol-glycerine mixture. To a homogeneous solution of parts by volume of benzene and 5 parts |by volume of tetrahydrofurfuryl alcohol were added 8 parts by volume of glycerine. After vigorous shaking and settling, the mixture separated into two layers. Five parts by volume of benzene separated out as an upper layer. To a homogeneous solution of 5 parts by volume of normal-heptane, 5 parts by volume of benzene and 10 parts of the above-mentioned solvent mixture were added 6 parts of glycerine. Ten parts by volume of oil separated out as an upper layer.

What I claim and desire to secure by Letters Patent is:

1. A process of treating hydrocarbon oil to separate the aromatic components from the non-'aromatic components therein, which comprises contacting said oil with a primary solvent comprising a major amount of dimethyl formamide to produce as a primary ralinate the portion of said oil rich in non-aromatic components and as a primary extract the portion of said oil rich in aromatic components, contacting said primary extract with a secondary solvent consisting of an organic hydroxy compound which is completely miscible with said primary vsolvent but immiscible with said oil to produce a hydrocarbon stream rich in aromatic components and substantially free of primary solvent and lof secondary solvent and to prod-nce a mixture of said primary solvent and said secondary solvent, contacting said raffinate stream with said secondary solvent to produce a hydrocarbon stream `rich in non-aromatic components and substantially free of primary solvent and secondary solvent and to produce a second mixture of said primary solvent and said secondlary solvent, product hydrocarbon streams thereby being produced solely by treatment with said solvents, separating said primary solvent from said secondary solvent and recycling said solvents.

2. A process according to claim 1 wherein said primary extracting solvent contains some of said secondary solvent.

3. A process according to claim 1 wherein said secondary solvent is glycerol.

4. A process according to claim 1 wherein said primary solvent is separated from said secondary solvent by ash distillation and wherein the heat necessary to separate said primary solvent from said secondary solvent is the only process heat requirement.

5. A process of treating hydrocarbon oil to separate the aromatic components -from the non-aromatic components therein which comprises contacting said oil with dimethyl formamide as ia primary extracting solvent to produce primary rainate containing the portion of said oil rich in non-aromatic components and a primary extract containing the portion of said oil rich in aromatic components, contacting said primary extract with glycerol las a secondary solvent to produce a hydrocarbon stream rich in aromatic components and substantially free of said dimethyl formamide `and of said secondary solvent and to produce a mixture of said primary solvent and said secondary solvent, contacting said ralinate stream with said secondary solvent to produce a hydrocarbon stream rich in non-aromatic components and substantially free of dimethyl formamide and of said secondary solvent and to produce a second mixture of said primary solvent and said secondary solvent, the product hydrocarbon streams thereby being produced solely by treatment with said solvents, separating said dimethyl yformamide from said secondary solvent by flash distillation and recycling said solvents.

6. A method according to claim 1, in which said nonaromatic components include olelins.

7. A method laccording to claim 5, in which said nonaromatic components include oleins.

8. A method :according to claim 5 in Which said primary extracting solvent contains some of said secondary solvent.

References Cited UNITED STATES PATENTS 2,167,632 8/1939 BroWnSCOmbe et al. 260-674 2,261,799 1l/19'4l Franklin 208-321 2,307,242 1/ 1943 Savelli et al. 208-321 2,357,344 9/1944 Morris et al. 208-240 2,646,387 7/1953 Francis 20S-39 DELBERT E. GANTZ, Primary Examiner.

H. LEVINE, Assistant Examiner.

U.S. Cl. X.R.

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