Cyclohexene esterification--hydrogenation for green and efficient production of cyclohexanol

A novel process based on cyclohexene esterification–hydrogenation for the production of cyclohexanol, the key intermediate for the production of ε-caprolactam, was devised and validated for the first time. In this process, cyclohexene obtained from the partial hydrogenation of benzene is esterified with acetic acid to cyclohexyl acetate, followed by hydrogenation to cyclohexanol. The experimentally determined equilibrium conversion of cyclohexene for cyclohexene esterification at the stoichiometric ratio is always 68% in the temperature range of 333–373 K over the commercial Amberlyst 15 catalyst, which is substantially higher than that of cyclohexene hydration. The apparent activation energy (Ea) for the esterification of cyclohexene with acetic acid is 60.0 kJ mol–1, also lower than that of cyclohexene hydration. On the other hand, the hydrogenation of cyclohexyl acetate to cyclohexanol is not thermodynamically limited, and high conversion of 99.5% and high selectivity of 99.7% are obtained on the La-promoted Cu/ZnO/SiO2 catalyst.