US 3883420 A
An improved process for the solvent extraction of aromatics from a mixture thereof with non-aromatics. Increased aromatic recovery and solvent purity in the lean solvent recycle to the extraction zone is afforded. The resulting non-aromatic raffinate stream is reduced in the concentration of aromatic hydrocarbons, particularly those having more than eight carbon atoms per molecule, and is suitable for use as an edible oil solvent.
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Description (OCR text may contain errors)
United States Patent Stone May 13, 1975 EDIBLE OIL SOLVENT PRODUCTION 3,436.435 4/1969 Van Tassell 208/321 3, 90,092 6 1971 U'tt' t l 2 8 32  Inventor: Richard D. Stone, Des Plaines,ll1. 5 I 1 .6 a 0 I 1  Assignee: Universal Oil Products Company, Primary Examiner-Herbert Levine D65 P1311165, Altorney, Agent, or FirmJames R. Hoatson, Jr.;  Filed: Jan. 30, 1974 Robert W. Enckson; William H. Page, II
 Appl. No.: 438,073 ABSTRACT 1521 US. Cl. 208/321; 208/325; 208/333 lmpmved pmFeSs for the emacm F matics from a mixture thereof wlth non-aromatics. In-  Int. Cl ClOg 21/28 creased aromatic recover and solvent um in the  Field of Search 208/321 Y y lean solvent recycle to the extraction zone is afforded. References Cited :The resulting non-aromatic rafiinate stream IS reduced In the concentration of aromatic hydrocarbpns, partic- UNITED STATES PATENTS ularly those having more than eight carbon atoms per 687,982 8/1954 Baumann .2 208/321 molecule, and is suitable for use as an edible Oil sol- 2,923,680 2/1960 Bushnell 208/321 vent, 3,119,767 1/1964 Scheibel 208/321 3.179.708 4/1966 Penisten 2. 208/321 8 Claims, 1 Drawing Figure /3 9 LE fine/var Warn-Wash 8 Separation Zana l9 Ergo/Legion 1/ farm/amen! Sena/am! 4 f t 30 3 f8 S/eom Gene/afar EDIBLE OIL SOLVENT PRODUCTION APPLICABILITY OF INVENTION This invention herein described is intended for utilization in the separation, and ultimate recovery of polar hydrocarbons from a mixture thereof with non-polar hydrocarbons, which separation is effected through the use of a water-soluble solvent characteristically selective for adsorbing the polar hydrocarbons. More specifically, my invention is directed toward the separation and recovery of aromatic hydrocarbons from various mixtures thereof with non-aromatic hydrocarbons.
My invention is particularly concerned with an improvement in the type of separation process wherein a mixture of aromatic and non-aromatic hydrocarbons is introduced into a solvent extraction zone. being countercurrently contacted therein with a solvent selective for the adsorption of the aromatic hydrocarbons. A raffmate phase, comprising substantially all of the nonaromatic hydrocarbons in the feed stock (at least about 90.0% by weight), is removed from one end portion of the extraction zone, and an extract phase comprising the aromatic components and the solvent is removed from the other end portion of the extraction zone, with the aromatic solute being recovered therefrom in a solvent stripping zone through the utilization of steam. The hydrocarbon-lean solvent emanating from the solvent stripping column is recycled to the extraction zone wherein it further countercurrently contacts the hydrocarbonaceous feed mixture.
My invention is applicable for utilization with any hydrocarbon feed stock having a sufficiently high aromatic concentration to justify the recovery thereof i.e., at least about 25.0% by volume. As a general rule, the overall carbon number range of suitable charge stocks is from about 6 to about 10, although both lower-hoiling and higher-boiling material is often present. These charge stocks will include, in addition to C C and C -aromatics, non-aromatics, which can predominate in C and C -paraffms, C,,-plus aromatics and naphthcnic material. Typical of various sources of suitable charge stocks constitutes the depentanized effluent from a naptha catalytic reforming unit, coke-oven by-products, resulting from the pyrolysis of naphtha to produce propylene, wash oils, etc.
My inventive concept is specifically directed toward the solvent stripping facility integrated into a solvent extraction process. The term solvent stripping" is utilized to connote the technique wherein an aromaticrich solvent stream is contacted with steam to provide a solvent concentrate substantially free from hydrocarbons, a vaporous stream comprising steam. solvent and hydrocarbons, and an aromatic concentrate having a reduced solvent content and containing steam. The present technique is particularly advantageous in that it affords additional removal of hydrocarbons, and particularly aromatic hydrocarbons having more than eight carbon atoms per molecule from the solvent concentrate. A distinct improvement is afforded when the solvent concentrate is recycled for further utilization in the solvent extraction zone. As a general rule, approximately 50.0% of the aromatic hydrocarbons contained in the recycled solvent suffer from re-cntry loss; that is, they ultimately appear in the recovered rat'finate phase. This is of significant import when the ultimate considered utilization of the raffmate phase is as a solvent for edible oils.
Within the food processing industry, it is common practice to extract edible oil from various food materials by contacting pulverized particles with a solvent and subsequently recovering the extracted oil by distillation or fractionation. Such food materials include corn, peanuts, soy beans, etc. Generally, the extracted oil is further purified by contacting with caustic soda to effect the removal of fatty acids in order to further enhance the oil for human consumption. The purified oil is commonly referred to as edible oil." Suitable solvents for use in extracting edible oils include-acetone, benzene, hexane, carbon disulfide, etc. One of the more common requirements for a satisfactory edible oil solvent is that it contains less than about 1.0% by volume of total aromatic hydrocarbons, and preferably less than 0.5% by volume, and less than about 10 ppm. by weight of the water-soluble solvent. With respect to the aromatic concentration of the edible oil solvent, it is fur ther generally required that the same contain less than about 0. l0% by volume of the heavier aromatic hydrocarbons, or those having more than eight carbon atoms per molecule. A suitable source of edible oil solvent is the non-aromatic raffinate phase recovered from a solvent extraction process, provided the aforementioned criteria are met.
PRIOR ART It must be recognized that the prior art proliferatcs in a wide spectrum of solvent extraction processes for effecting the separation of aromatic hydrocarbons from a mixture thereof with non-aromatic hydrocarbons. No attempt will be made herein to delineate exhaustively the appropriate published literature; it will suffice simply to note several examples which appear to be exemplary of prior art practices and procedures, and to which the present invention is most suitably applicable. The greater majority of solvent extraction processes indicate a distinct preference for a water-soluble solvent comprising an oxygenated organic compound. A review of the relevant prior art indicates that the preva lent solvent is either a sulfolane-type organic compound, or an alkylene glycol, preferably a poly-alkylene glycol. While most prior an processes are intended for utilization with either of these water-soluble solvents, specific techniques have been illustrated which are peculiar either to one, or the other.
Illustrations of solvent extraction processes may be typified by U.S. Pat. Nos. 3,466,346 (Cl. 260-674), 3,396,101 (Cl.208-3l3), and U.S. Pat. No. 3,520,946 (Cl. 260-674). U.S. Pat. No. 3,429,802 (Cl. 208-87) recognizes that an edible oil solvent can be produced from the raffmate stream recovered from a solvent extraction process. However, there is no recognition of the utilization of a low molecular weight paraffinic hydrocarbon in the solvent stripping zone, but rather the addition of a catalytic hydrogenation reaction system which processes the as-produced raffinate stream.
OBJECTS AND EMBODIMENTS A principal object of my invention is directed towards increased solvent purity of the lean solvent stream recovered in a stripping column integrated within a solvent extraction process. A corollary objective resides in decreasing the quantity of aromatic hydrocarbons, and particularly those having more than about eight carbon atoms per molecule, in the lean solvent stream recycled to the solvent extraction zone.
A specific object of my invention affords the production of an edible oil solvent containing less than about 0. l()% by volume of aromatic hydrocarbons having more than about eight carbon atoms per molecule.
Therefore, in one embodiment, my invention affords a process for removing aromatic hydrocarbons having more than eight carbon atoms per molecule from the extract phase from a solvent extraction zone, which process comprises contacting said extract phase, containing (i) solvent, characteristically selective for ad sorbing aromatic hydrocarbons, (ii) aromatics contain ing less than nine carbon atoms per molecule and, (iii) aromatic hydrocarbons containing more than eight carbon atoms per molecule, with a lower molecular weight paraffinic hydrocarbon, containing from about three to about seven carbon atoms per molecule, in a stripping zone, and recovering said solvent reduced in the concentration of aromatic hydrocarbons having more than eight carbon atoms per molecule.
In a specific embodiment, the present invention involves a process for preparing a substantially aromaticfree edible oil solvent which comprises the steps of: (a) contacting a mixture of aromatic and non-aromatic hydrocarbons with a water-soluble solvent, selective for the dissolving of aromatic hydrocarbons, in a solvent extraction zone, to provide (i) a first solventrich extract stream and, (ii) a solvent-lean raffinate stream; (b) contacting said first extract stream with a paraffinic hydrocarbon having from three to about seven carbon atoms per molecule, in a stripping zone; (c) recovering, from said stripping zone, (i) a first vaporous stream containing said paraffinic hydrocarbons, (ii) a vaporous, aromatic-rich stream, and, (iii) a second solventrich stream; (d) introducing said second solvent-rich stream into said solvent extraction zone, as said watersoluble solvent; and, (e) recovering said raffinate stream as said substantially aromatic-free edible oil solvent.
These, as well as other objects and embodiments of my invention, will become evident from the following detailed description thereof. Briefly, however, with respect to such other embodiments, these involve operating conditions, particular solvents, in-process separations and stream flows, preferredparaffinic hydrocarbons for utilization in the removal of aromatic hydrocarbons from the solvent stream to be recycled to the solvent extraction zone, etc. For example, preferred solvents include alkylene glycols, polyalkylene glycols and sulfolane-type organic compounds, while the preferred paraffinic hydrocarbons contain from about four to about six carbon atoms per molecule.
SUMMARY OF INVENTION Although applicable to a multitude of hydrocarbo naccous mixtures. further discussion will be limited to the separation of aromatic hydrocarbons from a mixture thereof with paraffins and/or naphthenes, and the recovery of a nonaromatic raffinate stream suitable for use as an edible oil solvent. Initially, the mixture of hydrocarbons is contacted with a water-soluble, oxygencontaining solvent particularly selective for the extraction ofthe aromatic hydrocarbons. There is recovered an extract stream containing aromatic hydrocarbons and a major proportion of the water-soluble solvent (more than about 99.0% by weight), and a raffinate stream containing non aromatic hydrocarbons and a relatively minor proportion (less than about 1.0%) of the water-soluble solvent. The raffmate stream, also containing less than about l 0% by volume of total aromatic hydrocarbons, is generally contacted, in countercurrent flow, with water to recover the selected solvent and to provide a hydrocarbon oncentrate substantially free from solvent. The extract stream is contacted with steam, in a solvent stripping zone, to recover an aromatic hydrocarbon concentrate from the water-soluble solvent. The latter is then recycled to the extraction zone for further use in extracting aromatic hydrocarbons from the charge stock.
The aromatic hydrocarbon concentrate is generally withdrawn, as a principally vaporous phase, from an intermediate portion of the solvent stripping zone. As such, it contains significant quantities of steam and solvent, as well as entrained liquid (principally solvent). This aromatic concentrate is introduced into an entrainment separator for the removal of the greater pro portion of the entrained liquid phase therefrom. The separated liquid phase is returned to the solvent stripping zone, while the balance of the extract phase is condensed and introduced into an extract receiver for separation into an aromatic-rich product stream and a water concentrate.
In an alternative embodiment. not shown in the accompanying diagrammatic illustration, rich solvent from the extraction zone initially enters an extractive distillation zone and then a solvent recovery column. In the extractive distillation zone, additional lean solvent contacts rich solvent from the extraction zone. Nonaromatics present in the rich solvent are removed via extractive distillation, in which technique, nonaromatics have a higher than normal vapor pressure in the presence of many of the aromatic selective solvents, thus permitting removal of small amounts of non-aromatics by distillation. Of course, the temperature and pressure in an extractive distillation column are too low to allow recovery of aromatics from the solvent; therefore, a second column is generally required to recover aromatic hydrocarbons from the solvent. Accordingly, in this alternative embodiment, a recovery column, operating at either a higher temperature, or lower pressure, or both, recovers aromatic hydrocarbons as an overhead vapor fraction. The recovery column is generally refluxed with condensed aromatic hydrocarbons. Lean solvent is recovered from the bottom of this column, but steam stripping is required to remove aromatics from the solvent. In this alternative embodiment i.e., extractive distillation followed by a solvent recovery column the practice of the pres ent invention helps remove the deleterious amounts of aromatic hydrocarbons which would otherwise remain in the lean solvent. In this alternative embodiment, paraffinic stripping augments steam stripping in the solvent recovery column.
In accordance with the inventive concept of the present invention, a lower molecular weight paraffinic hy drocarhon is utilized as the stripping agent in the stripping column. Preferably, the same is utilized in admixture with steam, with the mole ratio of paraffin to steam being in the range of about U. l:l.() to about l0.0:l.0. Suitable paraffinic hydrocarbons contain from about three to about seven carbon atoms per molecule, and include propane, normal butane, isobutane, normal pcntane, isopentane, neopentane, hexane, isohexane, heptane and isoheptane. Preferred paraffinic hydrocarbons contain from about four to about six carbon atoms per molecule.
Particularly preferred stripping agents are those paraffinic hydrocarbons having four carbon atoms per molecule, since lighter hydrocarbons are difficult to condense at the low pressures generally encountered in the stripping column. Stripping with hydrocarbons heavier than those containing six carbon atoms per molecule, requires additional heat input due to the greater heat of vaporization per mole, which increases the utility requirements of the unit. Also, heavier stripping agents cannot be readily separated from the extract via distillation, where separation is necessary to produce a very pure aromatic product. The reason for the peculiar effectiveness of these light paraffinic stripping agents is not fully understood. It is postulated that the effectiveness is due, at least in part, to the presence of very large amounts of aromatic-selective solvent which rejects all things paraffinic.
SOLVENTS AND OPERATING CONDITIONS Generally accepted solvents, having solubility selectivity for aromatic hydrocarbons, are water-soluble, oxygen-containing organic compounds. In order to be effective in a system of extraction, such as the process provided by the present invention, the solvent component must have a boiling point substantially greater than the boiling point of water, which is added to the solvent composition for the purpose of enhancing its selectivity; in general, the solvent must also have a boiling point substantially greater than the end boiling point of the hydrocarbon feed stock. In most instances, the solvent has a greater density than the hydrocarbon feed stock and is accordingly introduced into the uppermost portion of the solvent extraction zone, thereafter flowing downwardly, countercurrently to the rising hydrocarbon feed stock which is introduced into the extraction zone at about its mid-point.
Organic compounds, suitable as the solvent, may be selected from the relatively large groups of compounds characterized generally as oxygen-containing compounds, particularly the aliphatic and cyclic alcohols, the glycols and glycol ethers. Monoand polyalkylene glycols, in which the alkylene group contains from about two to about four carbon atoms, such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, and tripropylene glycol, constitute a particularly preferred class of organic solvents,
Another suitable class of selective solvents are those commonly referred to in the art as the sulfolane-type. This is a solvent having a five-membered ring, one atom of which is sulfur, the other four being carbon, and having two oxygen atoms bonded to the sulfur atom. Many of the solvents may be illustrated by the following formula:
R HCH-R wherein R, R R and R are independently selected from the group consisting of a hydrogen atom, an alkyl group having up to carbon atoms, and alkoxy radicals having up to eight carbon atoms and an arylalkyl radical having up to 12 carbon atoms. Other solvents preferably included are the sulfolenes such as 2- sulfolene or 3-sulfolene which have the following structures:
Still other solvents having a high selectivity for separating aromatics from non-aromatic hydrocarbons are 2- methylsulfolane, 2,4-dirnethylsulfolane, methyl 2- sulfonyl ether, and 2-sulfonyl acetate.
The aromatic selectivity of the selected solvent is further enhanced through the addition of water. Preferably, the solvent contains a small amount of water dissolved therein to increase the selectivity of the solvent phase for aromatic hydrocarbons over non-aromatic hydrocarbons, without reducing substantially the solubility of the solvent phase for aromatic hydrocarbons. The solvent composition contains from about 0.5% to about 25.0% by weight of water, and preferably from about 3.0% to about l5.0%, depending on the particular solvent utilized and the process conditions under which the extraction zone and solvent stripper are operated. By the inclusion of water in the solvent composition, the solubility of aromatic hydrocarbons in the solvent, although somewhat reduced in comparison with a non-aqueous solvent, decreases the solubility of raffinate components in the solvent and the solubility of solvent in the raffinate stream. Solvent recovery from the raffinate stream may be accomplished efficiently by countercurrently washing the raff'mate with water in a separate washing zone from which an aqueous wash effluent is recovered containing the solvent. During steady-state operations, water washing reduces the solvent concentration in the raffinate stream from about 500 ppm. by weight to less than about l0.0 ppm.
The solvent extraction zone is operated at elevated temperatures and at a sufficiently elevated pressure to maintain the hydrocarbonaceous feed stock, solvent and backwash streams in the liquid phase. Suitable temperatures are within the range F. to about 400F., and preferably an intermediate level from about l75F. to about 300F. Pressures are generally within the range of about atmospheric up to about 400 psig., and preferably from about 50 psig. to about I50 psig. Generally, the volume of backwash introduced into the lower point of the extraction zone is at least 10.0% by volume of the extract phase emanating therefrom. The solvent to hydrocarbon feed volumetric ratio is in the range of l.0:l,0. to about l5.0:l.0, and preferably from about 2.0:l.0 to about l0.0: L0.
The stripping column functions at moderate pressures and sufficiently high reboiler temperatures to drive all the backwash non-aromatic components and some of the aromatics, water and solvent overhead. Stripping pressures are from atmospheric to about psig., although the top of the stripper is generally maintained at from about 1.0 psig. up to about 20.0 psig. The reboiler temperatures dependent upon the composition of the feed stock and the solvent, and are generally in the range of from 275F. to about 360F.
Other operating conditions will be given in conjunction with the description of one embodiment of the present invention as illustrated in the accompanying drawing. Miscellaneous appurtenances, the description of which is not believed required. by those possessing the requisite expertise in the appropriate art. have been eliminated from the drawing. The use of details such as pumps. compressors. controls and instrumentation. heat-recovery circuits. valving. start-up lines and similar hardware. etc., is well within the purview of those skilled in the art. It is understood that the illustration does not limit my invention beyond the scope and spirit of the appended claims.
DESCRIPTION OF DRAWING The accompanying drawing is presented for the sole purpose of illustrating the method of integrating the present inventive concept into a solvent extraction process which is designed to separate and recover aromatic hydrocarbons from a mixture thereof with nonaromatic hydrocarbons. With reference now to the drawing. the fresh feed charge stock. for example a C plus fraction separated from the effluent of a naphtha catalytic reforming unit. is introduced via line 1 into solvent extraction zone 2. The charge stock contains about 41.0% by weight of paraffins. 4.0% naphthenes and 55.0% aromatic hydrocarbons. A solvent-rich stream. containing less than 0.l85 molv total aromatic hydrocarbons, and less than 0. l% aromatic hydrocarbons containing more than eight carbon atoms per molecule. is introduced into extraction zone 2 by way of line 3 in an amount such that the solvent to hydrocarbon feed volumetric ratio is about 5.25: l .0; this solvent stream contains approximately 6.0% by weight of water. A light hydrocarbon backwash stream. from line 4, is introduced into a lower portion of the extraction zone and serves to strip the heavier non-aromatic hydrocarbons from the solventrich extract stream withdrawn by way of line 5.
A first raffmate stream, containing about 0.09% total aromatics, and 0.05 mol.% heavier aromatics. and solvent in an amount of about 500 ppm. by weight. is withdrawn by way of line 6 and introduced thereby into a lower portion of water-wash column 7. A first water stream, containing a minor amount of both solvent and aromatic hydrocarbons, the latter being less than about 0.1%. and substantially free from non-aromatic hydrocarbons (less than about 0.01% is introduced into an upper portion of water-wash column 7 by way of line 8. A second raffinate phase, containing less than about 10 ppm. by weight of solvent. is removed from the process by way of line 9. A second water stream, containing the solvent in the first water stream and that removed from the first raffinate stream. and both dissolved and entrained non-aromatic hydrocarbons. is withdrawn by way of line 10 and introduced via line 1] into separation zone 12.
Also introduced into separation Zone 12. in admixture with the second water stream in line 10. is a substantially pure first aromatic hydrocarbon from line 28, the source of which is hereinafter set forth. A second aromatic stream. containing at least 90.0% of the non aromatic hydrocarbons in the second water stream. is withdrawn from an upper portion of separation zone 12 by way of line 13. while a third Water stream substantially free from non-aromatic hydrocarbons is withdrawn by way of line 14.
The third water stream is utilized to generate steam in steam generator 15, employing the solvent-rich first extract stream in line 5 as the heat-exchange medium. In some operations. rich solvent from the extraction zone is not hot enough to be used as a heat exchange medium. In this event. hot lean solvent from the stripping column may be used as a heat exchange medium in steam generator 15. Normal butane. in an amount such that the mole ratio of normal butane to steam. entering steam generator 15, is 50.02500. is introduced into the process by way of line 30. The cooled extract stream is introduced by way of line 17 into solvent stripping zone 18, wherein it countercurrently contacts the generated steam being introduced by way of line 16. The solvent concentrate, containing less than 0.10 mol.% of heavier aromatics, is removed by way of line 3 and recycled therethrough to solvent extraction zone 2. A principally vaporous phase. containing steam, hy drocarbons and solvent is withdrawn by way of line 19, admixed with the second aromatic stream in line 13, and introduced via line l9 into stripper receiver 20.
The second extract stream. of reduced solvent content (about 2.5% by weight), concentrated in aromatic hydrocarbons and containing steam. is withdrawn from an intermediate portion of stripping column 18 by way of line 21. The second extract stream, at a temperature of about 220F., containing entrained liquid. is introduced into separator 22, from which entrained solvent is withdrawn by way of line 23 for re-introduction thereby into stripping column 18. A third extract stream. containing about 0.5% solvent. is introduced through line 24 into condenser 25, wherein the temperature is decreased to a level of about 140F. The con densed third extract stream is passed via line 26 through extract receiver 27. from which a fourth water stream. containing substantially all the solvent in the third extract stream. is removed by way of line 8 and preferably recycled. at least in part. as the first water stream introduced into water-wash column 7. The substantially pure aromatic concentrate is withdrawn through line 28. In one embodiment. at least a portion continues through line 28 to serve as the substantially pure first aromatic stream combined with the second water stream in line 11. The aromatic concentrate product of the process is withdrawn by way of line 29.
Stripper receiver 20 serves to provide a light hydrocarbon backwash stream in line 4 which is introduced into the lower portion of extraction zone 2 as hereinbefore set forth. A fifth water stream is withdrawn by way of line 11, admixed with the second water stream in line 10, the mixture continuing through line 11 into separation Zone 12.
Without the addition of butane. via line 30, to steam generator 15, the lean solvent recycle in line 3 to extraction zone 2 contains total aromatics in an amount of 0.344 mol.% and 0159 mol.% heavier, C plus aromatics. Furthermore. the solvent concentration of the total stream is 97.25 mol.%. When the stripping vapors in line 16 are generated utilizing the 50/50 mixture of butane and steam, as hereinabove illustrated. the total aromatic hydrocarbon content is decreased to 0.l mol.7(. that of the heavier aromatics to a level of 0.098 mol."/( and the solvent content is increased to 98.7l7av Therefore. as hereinbefore set forth. since approximately onehalf of the aromatics entering the extraction zone 2 by way of line 3 suffer from reentry loss. and appear in the raffinate stream in line 6. only about 0.05 mol.7( heavier aromatics appear in the edible oil solvent produced as the raffinate stream in line 9.
The foregoing indicates the method by which the present invention is utilized to separate and recover an aromatic concentrate substantially free from both solvent and non-aromatic hydrocarbons. The resulting edible oil solvent clearly meets the contaminant level limitation as previously stated.
Alternatively, the amount of stripping steam in line 16 may be decreased with the substitution therefor of a light paraffinic stripping agent of the present invention. With reduced stripping steam, the lean solvent will contain about the same level of impurities as in typical prior art schemes, however, the stripping of heavy aromatic hydrocarbons will have been effected with lesser utility requirements than prior art processes. This is because the heat required to vaporize one mole of C or C paraffins is less than that required to vaporize one mole of water. If a refiner wants to make unleaded gasoline, he can tolerate, and frequently requires, the presence of butanes in his gasoline to satisfy octane and volatility requirements. Accordingly, butanes used as stripping agents can be left in the extract product without detrimental effect, and most important, without increasing water circulation rates in the process. This is in contrast to prior art processes where water recovered from the extract fraction contains too much expensive solvent to permit disposal, so all water has to be recycled and it is virtually impossible to increase stripping action in the stripping column without simultaneously increasing steam flow thereto.
I claim as my invention:
1. A process for removing aromatic hydrocarbons having more than eight carbon atoms per molecule from the extract phase from a solvent extraction zone. which process comprises countercurrently contacting said extract phase, containing (i) solvent, characteristically selective for dissolving aromatic hydrocarbons, (ii) aromatics containing less than nine carbon atoms per molecule and, (iii) aromatic hydrocarbons containing more than eight carbon atoms per molecule, with a mixture of steam and a lower molecular weight paraffinic hydrocarbon, containing from about three to about seven carbon atoms per molecule, the mole ratio of paraffin to steam in said mixture being in the range of about 0.1 l .0 to about 10.0: 1 .0, and recovering said solvent reduced in the concentration of aromatic hydrocarbons having more than eight carbon atoms per molecule.
2. The process of claim 1 further characterized in that said paraffinic hydrocarbon contains from four to about six carbon atoms per molecule.
3. The process of claim 1 further characterized in that said paraffinic hydrocarbon is a butane.
4. The process of claim 1 further characterized in that said paraffinic hydrocarbon is a pentane.
5. A process for preparing a substantially aromaticfree edible oil solvent which comprises the steps of:
a. contacting a mixture of aromatic and non-aromatic hydrocarbons with a water-soluble solvent, selec tive for dissolving aromatic hydrocarbons, in a solvent extraction Zone, to provide (i) a first solventrich extract stream and, (ii) a solvent-lean raffinate stream;
b. countercurrently contacting said first extract stream with a mixture of steam and a paraffinic hydrocarbon having from three to about seven carbon atoms per molecule, the mole ratio of paraffin to steam in said mixture being in the range of about 0.1:].0 to about [00:10, in a stripping zone,
c. recovering, from said stripping zone, (i) a first vaporous stream containing said paraffinic hydrocarbons, (ii) a vaporous, aromatic-rich stream and, (iii) a second solvent-rich stream;
d. introducing said second solvent-rich stream into said solvent extraction zone, as said water-soluble solvent; and
e. recovering said raffinate stream as said substantially aromatic-free edible oil solvent.
6. The process of claim 5 further characterized in that said water-soluble solvent is a polyethylene glycol.
7. The process of claim 5 further characterized in that said water-soluble solvent is a sulfolane-type compound.
8. The process of claim 5 further characterized in that said aromatic hydrocarbons comprise both aromatics having less than nine and more than eight carbon atoms per molecule.