Sept. 7, 1954 D. E. BADERTSCHER TAL 2,688,645 SOLVENT EXTRACTION Filed Sept. 10, 1952 4. Sheets-Sheet 4 AewZawe Aawza NE AvAyzewa (246OWA7a AA/AWe COWA/WWG 5% W47aa Aawza NE Af//YZEAE GAgaowana Aayawa cow/A/w/WG 622 GZYaoz. Aaw/W ANÉea AZAAAA WA4WC/6 BY GAOQ6A. C. JoAVsow & & ), e.g- Patented Sept. 7, 1954 2,688,645 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.