Sept. 7, 1954 D. E. BADERTSCHER TAL 2,688,645 SOLVENT EXTRACTION Filed Sept. 10, 1952 4. Sheets-Sheet 4

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UNITED STATES PATENT OFFICE 2,688,645 SOLVENT EXTRACTION Darwin E. Badertscher, Pitman, and Alfred W. Francis, and George C. Johnson, Woodbury, N. J., assignors to Socony-Wacuum Oil Com pany, incorporated, a corporation of New York Application September 10, 1952, Serial No. 308,828 19 Claims. (CI. 260-674) 1. 2 This invention is concerned With extraction and non-aromatic hydrocarbons, with a cyclic with certain selective solvents of . Various mix Organic carbonate. Such as ethylene carbonate, tures, and particularly of hydrocarbon mixtures, C2H4CO3, which is a cyclic ester represented by to separate the mixtures into fractions having the formula: different properties. EC-O Numerous processes have been developed for N Cs-O the separation of hydrocarbons and hydrocarbon / derivatives of different molecular configuration BC-O by taking advantage of their behaviour With As a class, the cyclic organic carbonates con selective agents. For example, aromaticS Such O templated herein are represented by the general as benzene, toluene and xylenes have been Sep formulae: arated from hydrocarbon mixtures in which they occur, by adsorption on gels such as Silica-alu 'R mina composites and the like, by azeotropic dis R-6-0 tillation, and by solvent extraction. In the last 5 N mentioned field, many solvents have been pro posed, such solvents dissolving more benzene than heptane. Benzene and heptane are typical rep resentatives of aromatic and non-aromatic hy and drocarbons. 20 Saunders (Ind. Eng. Chenn., 43, 121 (1951) ) has reported his study of many Such Solvents. He C-O has rejected several because a moderate amount (C2), of aromatic hydrocarbon rendered the Solvent miscible with the hydrocarbon mixture. This 25 effect seriously limits the concentration of aro matic hydrocarbon obtainable With Such a Sol Wherein R1, R2, R3 and R4 are hydrogen or alkyl vent. Saunders has recommended several nitriles or alkenyl groups, and n is a whole number and such as beta, beta '-oxydipropionitrile for sep is usually three, or four. arating aromatics and non-aromatics. Wilkes 30 ... It is an object of this invention, therefore, to U. S. Patent No. 2,439,534 (1948)-has proposed provide an effective means for separating a mul nine solvents of the same class, i. e., nitriles. All tiplicity of fractions (or compounds) of different of these solvents are miscible with benzene, a properties from mixtures containing the same. criterion applied by SaunderS, Which, however, It is also an object of this invention to provide is unnecessary and undesirable since it limits the for the selective separation of several hydrocar concentration of aromatic which can be obtained. bon fractions of different properties from hydro Another recently developed solvent extraction carbon mixtures. An important object is the involves the use of diethylene glycol, which is not Selective separation of hydrocarbon fractions, miscible with benzene at ordinary temperatures differing in properties, from hydrocarbon mix (20-40° C.) but becomes. So at 89° C. As de 40 tures within the molecular weight range of about scribed (Chem. Eng., Nov. 1951, p. 242), the 72 to about 200. A further object is selectively extraction may be carried out at a still higher to Separate. benzene and other aromatics from temperature; and, in order to prevent miscibility mixtures containing the same. Still another ob with benzene, a small amount of water, of the ject is selectively to separate non-aromatics, par order of three to eight per cent by weight, may 45 affins and/or napthenes, from mixtures contain be added. ing the Same and aromatics. One other object is It has now been discovered that a plurality to provide more highly aromatic concentrates of fractions of, different properties can be ob from hydrocarbon fractions having a relatively tained more advantageously than With-Said prior high concentration of aromatics. solvents, by contacting a mixture of aromatic 50 Other objects and advantages of the invention 2,688,645 3 4 will be apparent from the following description. terpenes. Any concentration of aromatics is op Inasmuch as ethylene carbonate is a preferred erable. If a single pure aromatic hydrocarbon solvent herein, the invention is described below is desired, one can either distill the mixture to in detail with this particular solvent as an ex obtain a narrow boiling fraction for the extrac ample. tion, or separate the desired aromatic from the Ethylene carbonate is Superior in selectivity to mixed aromatics by distillation after extraction. diethylene glycol and to almost all of the nitriles In Order that this invention may be more referred to above. Moreover, it makes possible leadily understood, typical separation procedures a substantially better recovery of benzene than are described below with reference being made to any one of the aforementioned solvents. Corre 10 Figures 1 through 3. The processes illustrated sponding to the nitriles it is miscible With ben alre Countercurrent extractions of a hydrocarbon zene, but unlike the nitriles it is also miscible mixture with ethylene carbonate at a temperature with Water. The latter feature is an important above its melting point, which can be lowered by advantage, since by slight dilution with a dilu a diluent. ent the solvent power of ethylene carbonate for 5 Referring to Figure 1, a benzene-containing hydrocarbon mixtures can be controlled to any fraction, in line f, is introduced into extractor 2 desired extent. For example, the addition of four Wherein it is contacted countercurrently with per cent or more of water makes ethylene car ethylene carbonate added through line 3. The bonate incompletely miscible with an equal Vol Countercurrent extraction is carried out at a ten ume of benzene, so that With Such an aqueous 20 perature of about 40° C. to about 80° C., and at solvent practically pure benzene is obtainable, atmospheric pressure. Lower temperatures can instead of 95.5 per cent benzene obtained by use also be used. So also can higher temperatures of the anhydrous ester. by suitable adjustment of pressure, that is, main Certain other diluents can be used instead of taining sufficient pressure to keep the system in Water to effect the same result. Typical of Such 25 the liquid state. In the extractor, benzene and diluents are: glycerol, ethylene glycol, penta any other aromatic present in the charge are erythritol, formamide, formic acid, ethanolainines eXtracted and are removed, together with a major such as mono-, di-, and tri-ethanolamines. Cer portion of the ethylene carbonate, through line 4 tain of these diluents such as glycerol and ethyl to distillation tower 5. This extract is fed to ene glycol, are more advantageous than Water, in 30 tower 5 at an intermediate point, and benzene that long continued contact of water with ethyl Concentrate is removed as an overhead product ene carbonate can cause partial hydrolysis. Fol through line 6. If desired, a portion (e.g., twenty this reason, formic acid and bases Such as ethan to fifty per cent) of the benzene concentrate can olamines may be less efficient. When toluene is be returned, through line 1, to extractor 2 as an 35 extract reflux. the desired aromatic to be separated, a Smaller The bottoms product from still 5 comprises amount of water or other diluent can be used ethylene carbonate and a small amount of hy than when benzene is sought; and no diluent is drocarbons, predominantly aromatics. This necessary to obtain pure xylenes or higher aroma product is taken through line 8 to vacuum still tics. In general, the diluent should be immiscible 9 Wherein this Small amount of hydrocarbons is with benzene and soluble in the cyclic carbonate, removed from the solvent. Still 9 is operated such as ethylene carbonate, to the extent re Such that the maximum temperature is below quired. All of the diluents mentioned above are the boiling point of ethylene carbonate at the miscible with ethylene carbonate except glycerol, Operating pressure e.g., 10-100 mms. The over which has a solubility in the carbonate of 5.7 per head product from 9 contains hydrocarbons and cent by Weight. Mono-, di- and tri-ethanol a Small amount of solvent; this product is taken annines are substantially equivalent to ethylene through line () and is returned to still 5 via line glycol in miscibility relationships. Still other 4. Ethylene carbonate, free from hydrocarbons, diluents which can be used as diluents include: is taken from vacuum still 9 and from the system glycerol monochlorohydrin, acetamide, hydro 50 through line . It can be returned to the system quinone and resorcinol. Liquids such as diethyl through line 3. In the event that only a partial ene glycol, propylene glycol, trimethylene glycol recovery of the benzene is sought, the material in and lactic acid, all of which are miscible, would line 8 can be returned directly to stream 3 with not be disadvantageous but would also be of little out any vacuum distillation. help, except to lower the melting point of the 55 Returning now to extractor 2, the rafiinate ob Solvent, because in the quantities recommended tained therein comprises non-aromatics and some they would not render ethylene carbonate immis Solvent. The raffinate is removed from extractor cible with benzene. It is to be noted that most of 2 through line 2 to washing vessel 3. The raf the suggested diluents have a high Concentration finate is washed, in a countercurrent operation, of hydroxyl groups, and all of them are Com 60 With Water from line 4 in 3 such that raffinate pletely miscible with Water if liquids, or are ex free of Solvent is removed overhead via line 5. tremely soluble in Water if Solids. Water containing Solvent comprises the bottoms The foregoing cyclic carbonates, alone or in product in 3, and is removed through line 6 to admixture with the aforesaid diluents, are effec Still T. Water is distilled overhead through line tive for extracting benzene, toluene, xylenes and 65 A8 and solvent is recovered via line 9. higher monocyclic hydrocarbons, and also methyl The illustration given by Figure 1 applies for naphthalene, tetralin and other polycyclic aro ethylene carbonate used alone or used with such matic hydrocarbons, from mixtures in which one diluents as ethylene glycol and glycerol. or more of them are present. The hydrocarbon When ethylene carbonate is used with water as mixture extracted can be from any Source Con 70 the diluent, a modification such as shown by Fig taining aromatics, either straight run or cracked. lure 2 is followed. A charge containing aromat Typical mixtures include: aliphatic hydrocarbon iCS-for example, a benzene fraction--is led in alkylbenzene mixtures, catalytically cracked from line 2: to an intermediate section of extrac gasolines, catalytically reformed gasolines, frac tor 22. This fraction is extracted countercur tions from hydrogenated coal and aromatized 75 rently with ethylene carbonate containing water, 2,688,645 5 6 which is introduced to extractor 22 through line lation tower 41. The bottoms product in 47 is 23. Benzene and any other aromatics present in ethylene carbonate containing some hydrocar the charge are extracted and are removed from bons; this product is removed through line 48 22 through line 24 to distillation tower 25. A for further treatment (not shown) as in Fig benzene concentrate and water are distilled over ure.1 for recovery of ethylene carbonate. The head through line 26, containing condenser 27, overhead product from tower 47 comprises ben to Settler 28, wherein water forms a lower layer zene and pentane. The latter product is brought and from which it is removed through line 29. through line 49 to a second distillation tower The benzene concentrate is removed from settler 58, from which pentane is removed as an over 29 and from the System through line 30. Again, O head product via line 5 and from which ben a portion of the benzene concentrate can be used zene is removed as a bottoms product via line 52. as an extract reflux; thus, it can be returned The invention is also illustrated by experi through line 3 f to extractor 22. mental data obtained with benzene, n-heptane, The bottoms product from tower 25 is ethyl and ethylene carbonate perse or with a diluent. ene carbonate containing a small amount of wa 15 These experimental data are presented in the ter; this is removed through line 32. The sol form of charts, or more particularly ternary di Vent thus recovered by distillation of the ex agrams, identified here as Figures 4 to 6. These tract layer (from 22) is effectively stripped of diagrams can be used to determine: the suit hydrocarbons by the water and can be re-used ability of a solvent for the desired separation; in the extraction upon proper adjustment of its 20 the selectivity of the solvents; the range of com Water content to the desired percentage. position of cyclic carbonate, diluent and the Referring now to the raffinate obtained in ex mixture to be treated; the number of stages or tractor 22, the raffinate is brought through line extractions necessary to effect a separation of 33 to Washer 34. The raffinate contains a small desired degree; etc. The tie lines show com amount of dissolved ethylene carbonate, and 2 5 positions of layers in equilibrium. is washed with water, from line 35. The raf Figure 4 represents the system benzene-hep finate comprising non-aromatics, is removed tane-ethylene carbonate; Figure 5 represent a from the washer through line 38. A water so similar system in which aqueous ethylene car lution of ethylene carbonate is formed in wash bonate is used, five per cent of water being used; er 34 and is taken through line 37 to distillation 30 and Figure 6 represents a similar System in tower 38. Excess water is removed from the tow which ethylene carbonate diluted with 5.2 per er (33) through line 39 and ethylene carbonate cent of ethylene glycol is used. is recovered for re-use as a bottoms product via Figure 4, at 40° C., is of the common hyper line 4. bolic type. A straight line from the ethylene It is also contemplated that a wash oil-or, 35 carbonate corner (isologous line) through the more technically correct, a displacement solvent left ends of the tie lines indicates a concentra -be used in conjunction with ethylene carbonate tion of 93 to 95.5 per cent benzene in the ex or with ethylene carbonate and a diluent of tracts. The percentage of benzene in the raf the type described above. The displacement finates, found by a similar isologous line through Solvent, typically pentane, is a substance whose 40 the right ends of the tie lines, varies for a single Solvent properties resemble those of the impur stage according to the concentration of the ities or contaminants in the fraction being charge. Countercurrent operation will reduce treated, but which is more readily separable from this percentage to a negligible amount, the num the desired aromatic (e. g., benzene), especial ber of stages required depending on the avail ly by distillation. Pentane, boiling point 36.0° able concentration in the charge. C., is readily separated from benzene, boiling Figure 5 shows that five per cent of water per point 80.1° C.; whereas, a common impurity with mits recovery of pure benzene since, after the benzene, namely, cyclohexane has a boiling point extract reaches a gross concentration of 33 per of 80.8° C. and is difficult to separate by distil cent of benzene, the isologous line through the lation. In general, then, the displacement sol left extremity of the tie lines becomes coincident vent used herein is a non-aromatic hydrocarbon With the side line. The tie lines in this graph which can boil above or below, and preferably are somewhat steeper than in Figure 4. below, the boiling point of the desired aromatic. Figure 6, involving dilution with ethylene gly Preferably the displacement solvent is one hav col, shows similar relationships. The maximum ing a boiling point at least about 20° C. above concentration of benzene in the solvent-free ex or below the boiling point of the desired aromatic tract is about 98.5 per cent with this degree of or aromatics. Representative displacement Sol dilution. Recovery of pure benzene requires di vents used in the Separation of benzene are: n lution of ethylene carbonate With about 22.6 butane, mixed butanes, n-pentane, mixed pen per cent of ethylene glycol. The phase bound tanes, mixed pentanes-pentenes, nonanes, dec 60 ary reveals a reverse curve. The Solvent is not anes, alkylate fractions containing eight to miscible with pure benzene between 68.4 per cent twelve carbon atoms such as the heavy ends and 94 per cent benzene; but this portion of from alkylate gasoline, and turpentine. the diagram is not useful for our purpose, be Figure 3 illustrates an extraction. Wherein cause the other liquid phase is only a Small ethylene carbonate and a displacement solvent, amount of glycol precipitated by the benzene pentane, are used. A benzene fraction in line from the solvent (ethylene carbonate). Such a 4 is fed to an intermediate Section of extractor breakup of the solvent does not take place with 42, Wherein it is contacted by ethylene carbonate water, formic acid, or formamide as diluents from line 43 and by pentane from line 44. A because ethylene carbonate has much greater af rafiinate layer comprising non-aromatics, some 70 finity for these diluents than for the hydrocar ethylene carbonate and Some pentane, is re bons. In this respect, the latter diluents are moved from 42 through line 45, and is treated preferable to ethylene glycol and glycerol. (not shown) as in Figure 1 whereby a raffinate, Additional data has been obtained by extract ethylene carbonate and pentane are recovered. ing mixtures of benzene and n-heptane. All of Extract from 42 is taken through line 46 to distill 75 these were single-stage, batch operations. The 2,688,645 7 8 ratio of solvent to n-heptane was 1.67 by vol hexene carbonate and butadiene dicarbonate. ume or 3.25 by weight. The distribution of ben The homologs of ethylene carbonate have a Zene is shown in Tables I through III below. higher solvent power and, therefore, are less ap TABLE I Single eactraction stage Dith ethylene carborate at 40 C.

Benzene in Solvent Benzene in Layers Free Benzene Benzene in Recovery in Extract, HSabonarge Wt. w.fercent Eact, Ratgate, Esfact, Ragate, Percent Percent Percent Percent Percent

6.4 17.5 93 17.6 31 94 31.5 13.5 41.5 94.5 42 17.2 50 95 51 22 55.5 95.5 57 25 59 95.5 61 33 63 95 65 37 64 95 66, 5 40.5 66 95 69 42 68 94.5 71.5 54 plicable for extraction of benzene and toluene, TABLE I but are applicable for extraction of higher aro Single eactraction stage with 95% ethylene 25 matic hydrocarbons. Such as methyl naphthalene. carbonate at 30° C. The olefin carbonates, typified by ethylene car bonate, should constitute the major portion of Benzene in Layers Benzene in Solvent Free the Solvent used, for example, at least about Benzene in Eydrocarbon 30 Seventy per cent by weight. Charge, Wt. Extract, Raftinate, Extract, Rafflinate, Percent Wt. Per. Wt. Per. Wt. Per- Wt. Per We claim: cent cent cent cent 1. The process for resolving a hydrocarbon mixture containing aromatic and non-aromatic 3.2 15.5 98 15.5 hydrocarbons into fractions of different degrees 6.2 27, 5 98 27.5 of aromaticity, which comprises: contacting the 8.3 36.5 98 36.5 35 13.5 47.5 98 47.5 mixture with a Solvent comprising a cyclic or 16 53 99 53 17 56 99.5 56 ganic carbonate selected from the group consist 00 ing of allene carbonate and of carbonates rep resented by one of the general formulae: The third and fifth columns of Table II are identical 40 because the raffinate is practically free of solvent. TABLE III Single eactraction stage with 94.8% ethylene car bonate and 5.2% ethylene glycol at 30° C.

Benzene in Layers Benzene in Solvent Free and Benzene in --m-m-m- Hydrocarbon Charge, Wt. Extract, Rafiinate, Extract, Rafiinate, Percent Wt. Per- Wt. Per- Wt. Per- Wt. Per cent cent cent cent 50 7.3 22.0 95 22.0 1.6 39.5 97 39.6 16.2 49.7 98 49.8 19 55 98.5 55.2 29 62.5 98.5 62.8 wherein R1, R2, R3 and R4 are selected from hy 36 68.5 98 69 55 drogen and alkyl and alkenyl groups, and n is a whole number from 3 to 4, and effecting phase Minimum amounts of various diluents required Separation of the phases thus formed, an extract to make ethylene carbonate incompletely mis phase more aromatic than said mixture and a cible with an equal volume of benzene, and there rafiinate phase less aromatic than said mixture. fore Suitable for recovering pure benzene from a 60 2. The process defined by claim 1 in which a mixture with other non-aromatic hydrocarbons, diluent is used in combination with said solvent, are given in Table IV below. Said diluent being characterized by immiscibility TABLE IV With benzene and solubility in said carbonate. 3. The process defined by claim 1 in which a Diluent: Percentage, wt. 65 diluent having a high concentration of hydroxyl Water ------3.9 groups is used in combination with said solvent, Glycerol ------4. Said diluent being characterized by immiscibility Formamide ------17.0 with benzene and solubility in said carbonate. Ethylene glycol ------22.6 4. The process defined by claim 1 in which Formic acid ------32.6 70 aqueous ethylene carbonate is the solvent, said In addition to ethylene carbonate, other typi Solvent containing from about two to about ten cal carbonates represented by the general for per cent by weight of water. mulae set forth above, and contemplated herein 5. The process defined by claim 1 in which are: propylene carbonate, butene carbonates, al ethylene glycol is used in combination with said lene carbonate, cyclopentene carbonate, cyclo 75 Solvent. 2,688,645 9 10 6. The process defined by claim 1 in which said diluent being characterized by immiscibility glycerol is used in combination with said solvent. with benzene and solubility in said carbonate. 7. The process defined by claim 1 in which 14. The process defined by claim 11 wherein a displacement solvent is used in combination the hydrocarbon mixture is One containing ben With Said solvent. Zene and non-aromatic hydrocarbons of similar 8. The process defined by claim 1 in which boiling range. pentane is used in combination with said solvent. 15. The process defined by claim 11 wherein . The process defined by claim 1 wherein the the hydrocarbon mixture comprises aromatic, hydrocarbon mixture is one containing benzene aliphatic and cycloparaffinic hydrocarbons. and non-aromatic hydrocarbons of similar boil 10 16. The process defined by claim 11 in which ing range. ethylene glycol is used in combination with said 10. The process defined by claim 1 wherein the Solvent. hydrocarbon mixture comprises aromatic, ali 17. The process defined by claim 11 in which phatic and cycloparaffinic hydrocarbons. glycerol is used in combination with said solvent. 11. The process for resolving a hydrocarbon 5 18. The process defined by claim 11 in which mixture containing aromatic and non-aromatic a displacement solvent is used in combination hydrocarbons into fractions of different degrees With said solvent, of aromaticity, which comprises: contacting the 19. The process defined by claim 11 in which mixture with a solvent comprising ethylene car pentane is used in combination with said solvent. bonate, and effecting phase separation of the 20 phases thus formed, an extract phase more aro References Cited in the file of this patent matic than said mixture and a raffinate phase IeSS aromatic than said mixture. UNITED STATES PATENTS 12. The process defined by claim 11 in which Number Name Date a diluent is used in combination. With Said Sol 25 1917,910 Sullivan ------July 11, 1933 vent, Said diluent being characterized by in 2,582,883 Myers ------Jan. 15, 1952 miscibility with benzene and solubility in Said FOREIGN PATENTS carbonate. 13. The process defined by claim 11 in Which a Number Country Date diluent having a high concentration of hydroxyl 413,307 Great Britain ----- July 11, 1934 groups is used in combination with said solvent,