(721e) A Continuous Reactive Distillation Process for the Production of Cyclohexanol from Cyclohexene

Cyclohexanol is one of the important bulk chemicals used widely in the chemical industries as an intermediate for the production of polymers (Nylon 6,6 and Nylon 6). Conventionally, cyclohexanol is produced by hydrogenation of benzene to cyclohexane and its subsequent oxidation by air to cyclohexanol/cyclohexanone. This process has a high energy demand; a further disadvantage is the risk associated with the operation of the process.

In recent years, a promising alternative process has been developed that includes hydrogenation of benzene to cyclohexene and subsequent hydration of cyclohexene to cyclohexanol. Cyclohexanol production by direct hydration of cyclohexene is a challenging task due to its low solubility with water. Asahi Chemical Co. made an attempt in this direction to improve the reaction rate using a zeolite catalyst of HZSM5 type. However, still a large amount of catalyst is required to obtain significant reaction rates. We propose a novel process scheme for the indirect hydration of cyclohexene to cyclohexanol in a reactive distillation column using formic acid as a reactive entrainer. The proposed process includes the continuous esterification of cyclohexene with formic acid in a reactive distillation column followed by hydrolysis of cyclohexyl formate in a second reactive distillation column to produce pure cyclohexanol.

In the present study, the feasibility of the first step of this process scheme (i.e. the esterification of cyclohexene with formic acid) is investigated experimentally in a continuous reactive distillation column. Pilot scale experiments were carried out in a stainless steel column (length: 2.134 m, inner diameter: 50 mm) under low pressure conditions (<0.6 bar). The column consists of a reactive and a non reactive stripping section. The reactive section is packed with the structured packing Sulzer-Katapak. The non reactive stripping section is packed with Sulzer-DX packing. The concentration and temperature profiles obtained under steady state conditions showed that high conversion (>99%) of cyclohexene can be obtained with the present column configuration.