Partial hydrogenation of benzene to cyclohexene

Abstract We (Asahi Chemical Industy Co., Ltd.) have developed a technology for a highly selective partial hydrogenation of benzene to cyclohexene and succeeded in the commercialization of a new production process for producing cyclohexanol from benzene through cyclohexene. The process has been considered to be difficult for a long time in the industry. Several innovative technologies made the partial hydrogenation reaction possible. A catalyst that consists of specific metallic ruthenium particles exhibited excellent high selectivity of cyclohexene. The catalyst was obtained by reducing a ruthenium compound which contains a zinc compound. The use of a zinc of strong acid as a co-catalyst exhibited a remarkable effect to enhance selectivity. Dispersing agents of metal oxides were found to extend the life of the metallic ruthenium catalyst and some dispersing agents had the effect of enhancing the selectivity in the partial hydrogenation reaction. One of the remarkable features of the reaction was the reaction field. This comprises four phases: vapor (hydrogen), oil, aqueous and solid (ruthenium catalyst). The catalyst was used in the aqueous phase, and the reactants (benzene and hydrogen) were dissolved in the aqueous phase where the reaction proceeded. Therefore the products and reactants transfer between four phases through dissolution, diffusion and extraction, rendering quick transfer was a very important factor in enhancing reaction selectivity. The catalyst system and the reaction field described above made the selectivity for cyclohexene very high, and a yield of 60% for cyclohexene was obtained.