Patented Nov. 17, 1942 2,302,608

UNITED STATES PATENT OFFICE 2,302,608 AZEOTROPIC DISTILLATION Edmund Field, Wilmington, Del, assignor to E. I. du Pont de Nemours & Company, Wilmington, Del, a corporation of Delaware No Drawing. Application August 22, 1940, Serial No. 353,673 2 Claims. (C1, 202-42) This invention relates to a method for separating TABLE substances which either boil closely together Or Distillation of cycloheacane-acetone miactures form binaries such that separation cannot be achieved by simple fractional distillation. More Per cent Percent particularly, this invention relates to the sepa Wt. per cent Cs third 3. P. ration of cyclohexane from benzene and is an im acetone substance provement upon U. S. Patent 2,212,810, which re lates to the same separation. 32.7------67.3 None 53.1°C, 0.5 It is an object of this invention to provide a 41.5------55.5 3.0 H2O 52.2 0.5 method for separating closely-boiling substances 0 or substances which form azeotropes where Sepa From the table above it will be observed that the ration by fractional distillation is difficult or in proportion of cyclohexane in the distillate is in practical. It is a further object of this invention creased Over that in the acetone binary and in to provide a method for separating cyclohexane asmuch as Water may subsequently be employed to from benzene. It is an additional object of this Separate the cyclohexane from the acetone by invention to increase the efficiency of separation extraction, the presence of water in the original of cyclohexane from benzene by altering the Com distillate adds no complicating factor and is, as position of the acetone-cyclohexane azeotrope. a matter of fact, of great advantage in increas Other objects and advantages of the invention ing the efficiency of operation. Less acetone is will be apparent from the following specification. 20 required for the distillation, thereby reducing the I have found, as described in U. S. Patent quantity necessary to be recovered. 2,212,810, that cyclohexane can be removed from Although the proportions of water to the mix a mixture containing cyclohexane and Substances ture of cyclohexane and acetone may vary over of similar boiling point, such as benzene (B. P. a considerable range, I have found that the great 25 est efficiency of operation may be obtained by 80.1° C.) (which cannot be distilled ordinarily using from 3-5% water, based upon the volume from cyclohexane, B. P. 80.8 C.) by adding ace of the cyclohexane-acetone mixture, greater tone to the mixture and distilling. As described quantities not being Soluble in the acetone-hydro in the patent previously referred to, I have found carbon System, and Smaller quantities not giving that acetone forms a binary azeotrope with Cy the maximum increase of cyclohexane content in clohexane (67.3% acetone by weight) which boils the cyclohexane azeotrope. Preferably there at a lower temperature (53.1° C) than either ace should be at least 1.3 parts of acetone per part tone or any benzene-cyclohexane mixture and a of cyclohexane, and at least 0.01 part of water weight ratio of acetone to cyclohexane of at least per part of cyclohexane. 2.0:1.0 is preferable when separating these sub The general technique described in my prior stances by distilling under a pressure of one at application Serial No. 317,531 may be followed in mosphere. the operation of the present invention, the prime According to the present invention, cyclohexane difference existing between the present invention can be removed from a mixture containing cyclo and that described in my prior application being hexane and substances of a similar boiling point in the addition of a relatively small amount of by adding acetone and water to the mixture or water to the cyclo-hexane-acetone-containing by adding acetone to a mixture containing water mixture. Thus, when treating cyclo-hexane as well as cyclohexane and distilling. By the benzene mixtures for recovery of benzene or cy maintenance of a relatively small amount of wa clohexane, or both, each in the pure form, ace ter in the acetone-cyclohexane-containing mix tone may be added to the cyclohexane-benzene ture, the ratio of acetone to cyclohexane in the mixture together with a small amount of water, distillate is changed appreciably, and advantage and the mixture thereafter distilled. The excess ously, so that a more efficient separation is pos acetone distills following the acetone-cyclo sible than when acetone alone is utilized in the hexane-water azeotrope but at a higher tempera proceSS. ture, and finally benzene in the pure form is ob The addition of water raises the cyclohexane tained. The acetone-cyclohexane-water ternary concentration and lowers the acetone concentra is then processed with Water. tion as indicated in the following table giving the This process preferably involves water-washing compositions of cyclohexane-acetone mixtures of the ternary which is carried out by conducting with and without added substances: the ternary to the bottom of a baffle tower down 2 2,802,608 which water is flowing. The counter-current flow cyclohexane mixture is then separated into its of water and binary affects solution of acetone constituents by countercurrent water extraction in water and release of the cyclohexane which such as previously outlined, or by some other rises to the top of the tower and is removed by convenient, well known device. Acetone is re decantation. The acetone dissolved in the water covered from the water solvent by simple dis may be recovered for further use by distillation tillation. The cyclohexane is dried either by a from its mixture with water. The cyclohexane Suitable drying agent or by a process of dis may be obtained chemically pure by removing the tillation which takes advantage of the conven traces of residual water by distillation or by the ient cyclohexane-water pseudo-azeotrope. use of common drying agents. () Following the removal of cyclohexane, the re The process as above described may be applied sidual mixture of acetone, isopropanol and ben to any mixture of compounds containing cyclo Zene is topped to remove acetone, and the un hexane, provided the boiling temperatures of the converted benzene and isopropanol are returned additional constituents or any azeotropic mix to the hydrogenation unit for reprocessing. ture between such constituents or between Such While I have illustrated my invention by cer constituents and acetone are sufficiently remote tain applications, I do not limit my claims to from the boiling temperature of the cyclohexane such specific cases, for there are many possible acetone water ternary. In certain cases involv problems of separation where solutions may em ing constituents, part of which are water solu ploy as a basic principle the recovery of cyclo ble, water extraction may be substituted for dis 2) hexane from mixtures by means of its azeotrope tillation. None of these preliminary treatments with acetone and water. are necessary, however, in the following illustra I clain: tive case, the technique of which I have success 1. A method for the removal of cyclohexane fully employed in conjunction with a process for from admixture with benzene which comprises the simultaneous manufacture of acetone and cy treating the cyclohexane-containing mixture clohexane by exchange of hydrogen between iso with acetone and water in the ratio of at least propanol and benzene described in Copending ap 1.3 parts of acetone per part of Cyclohexane and plication of E. P. Bartlett, Serial No. 265,932. at least 0.01 part of water per part of cyclo As a process of this type involves an equilib hexane and thereafter distilling off the resultant rium, the product is a mixture of isopropanol, 30 cyclohexane-acetone-water azeotrope. acetone, benzene and cyclohexane. Such a mix 2. A method for the removal of cyclohexane ture contains constituents for forming at least from admixture with benzene which comprises three different azeotropic mixtures, benzene treating the cyclohexane-containing mixture isopropanol (B. P. 71.9), cyclohexane-isopro with acetone and water in the ratio of at least panol (B. P. 68.6°), both of which are revealed : 1.3 parts of acetone per part of cyclohexane and in the literature, and acetone-cyclohexane (B. P. at least 0.01 part of water per part of cyclo 53.1°). From such a mixture cyclohexane can hexane and thereafter distilling off the resultant be removed quantitatively as its azeotrope with cyclohexane-acetone-water azeotrope and there acetone. The efficiency of the process is, as after removing the cyclohexane by treating the indicated above, greatly improved by the pres 40 resultant distillate with water. ence of small amounts of water. The acetone EDMUND FIELD. CERTIFICATE OF CORRECTION, Patent No. 2,502, 608. November 17, 1942. EDMUND FIED It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page l, sec ond column, lines 55 and 56, for "my prior application Serial No. 517,55l." read --U. S. Patent 2, 212,810--; lines ll and 42, for "cyclo-hexane" read -- cyclohexane--; and that the said Letters Patent should be read with this correction there in that the same may conform to the record of the case in the Patent Office. - Signed and sealed this 29th day of December, A. D. l942.

Henry Wan Arsdale, (Seal) Acting Commissioner of Patents.