GB975948A - Recovery and production of cyclohexanone - Google Patents

Abstract

Cyclohexanone is recovered from a mixture consisting mainly of cyclohexanol and cyclohexanone by fractionating the mixture to separate an overhead fraction consisting predominantly of cyclohexanone and a cyclohexanol-enriched bottoms fraction, dehydrogenating the bottoms fraction to produce a further amount of cyclohexanone and recycling the dehydrogenated bottoms fraction to the fractionating stage. The starting material may be the product mixture derived from the partial oxidation of cyclohexane with molecular oxygen from which unreacted cyclohexane has been separated. Preferably the fractionation takes place in two steps, in the first of which a heavy ends fraction is removed and in the second of which the mixture is separated into a cyclohexanone fraction and a cyclohexanol fraction, the latter being dehydrogenated and the product being recycled to the first step of the fractionation. The mixture is preferably treated with an aqueous alkali solution (for example as in Specification 966,546) prior to the separation into cyclohexanone and cyclohexanol fractions. The fractional distillation steps are preferably effected at sub-atmospheric pressure and the cyclohexanone fraction may be further fractionally distilled at a higher pressure than the preceding distillation, but not above atmospheric pressure, to recover substantially pure cyclohexanone. The dehydrogenation may be effected at 200 DEG C. to 550 DEG C. and 3 to 50 p.s.i. absolute using a dehydrogenation catalyst, such as zinc oxide (as described in Specification 909,227) copper or brass. The process may be batch-wise or continuous. In an example, an oil feed obtained by the oxidation of cyclohexane and augmented by the products of dehydrogenation of the cyclohexanol fraction is distilled at 16 mm. to separate a cyclohexanol-cyclohexanone mixture from heavy ends, the product is scrubbed with sodium hydroxide solution, the oil phase is fractionated at 16 mm. and the overhead is further fractionated at 60 mm. giving cyclohexanone; the bottoms comprising cyclohexanol is dehydrogenated at 420 DEG C. using zinc oxide catalyst and the dehydrogenation products, after removal of hydrogen, are recycled to mix with the oil feed. Specification 975,949 also is referred to.