Separation of Phenol-Cyclohexanone Azeotrope by Extractive Distillation With Adipic Acid Diester

This invention relates to the separation of a phenol-cyclohexanone azeotrope. In one of its aspects, it relates to an extractive distillation separation of a mixture containing phenol-cyclohexanone azeotrope. In a more specific aspect the invention relates to a process for recovering cyclohexanone on the one hand and phenol on the other form a mixture containing these compounds, for example, from a mixture resulting from cleavage of 1-phenyl-cyclohexylhydroperoxide as obtained by the oxidation of cyclohexylbenzene.

In one of its concepts the invention provides a process for the separation of a mixture containing phenol, cyclohexanone, and which may contain cyclohexylbenzene by subjecting the same to conditions of extractive distillation with a selective solvent essentially comprising a diester of adipic acid. In another of its concepts the invention relates to such a separation by extractive distillation of a mixture resulting from a cleavage of 1-phenyl-cyclohexylhydroperoxide obtained by the oxidation of cyclohexylbenzene. In a further concept of the invention the diester of adipic acid can be a dialkyl and/or a dicycloalkyl ester.

It is an object of this invention to provide a process for the separation of a mixture containing phenol and cyclohexanone. It is another object of the invention to provide a process for the extractive distillation of a mixture containing phenol and cyclohexanone which mixture may contain some cyclohexylbenzene. It is a further concept of the invention to provide a selective solvent, which may be modified by further solvents or co-solvents, for the extractive distillation separation of phenol and cyclohexanone.

Other aspects, concepts, objects, and several advantages of the invention are apparent from a study of this disclosure and the appended claims.

According to the present invention there is provided a process for the separation of a mixture containing phenol, cyclohexanone, and possibly cyclohexylbenzene which comprises subjecting said mixture to an extractive distillation operation in which an extractive solvent is employed and which essentially is a diester of adipic acid.

Solvents useful for the invention are the dialkyl and dicycloalkyl esters of an adipic acid of the general formula (CH.sub.2 CH.sub.2 CO.sub.2 R).sub.2 where R can be an alkyl or cycloalkyl group containing up to 14 carbon atoms. Examples include dimethyl dibutyl, diisobutyl, di(2-ethylhexyl), didecyl, dicyclohexyl, bis(2-cyclohexyl ethyl), and bis(4-butylcyclohexyl) adipates.

Extractive distillations according to the concept of the invention were conducted in a 3/4-inch diameter packed column 3 feet long.

A 70-30 weight percent mixture of phenol-cyclohexanone, which is an azeotropic mixture boiling at 122.degree. C at 100 mm Hg absolute pressure was fed to the column near the mid-point at a rate of 1 cc/min at a temperature of 149.degree. C. Di(2-ethylhexyl) adipate solvent was introduced near the top of the column at a rate of 1.4 cc/min at a temperature of 95.degree. C. Overhead product was taken off at an average rate of 0.3 cc/min and averaged 98 percent cyclohexanone purity with no detectable solvent. Accumulated kettle product was 89 percent phenol on a solvent-free basis.

A mixture composed of 32 percent cyclohexanone, 66 percent phenol and 2 percent cyclohexylbenzene was fed at about the mid-point of the extractive distillation column operating at 50 mm Hg absolute pressure at a rate of 1 cc/min and a temperature of 144.degree. C. Di(2-ethylhexyl) adipate solvent was introduced near the top of the column at a rate of 1.6 cc/min at a temperature of 92.degree. C. Overhead product was about 99.7 percent cyclohexanone, 0.3 percent phenol and contained no cyclohexylbenzene. Accumulated kettle product was 91 percent phenol, 6 percent cyclohexanol and 3 percent cyclohexylbenzene.

Reasonable variation and modification are possible within the scope of the foregoing disclosure and the appended claims to the invention the essence of which is that a diester of adipic acid, as disclosed, has been found to be an effective extractive distillation solvent by the extractive distillation of cyclohexanone-phenol containing mixtures.