Partial Hydrogenation of Benzene

Cyclohexene is an important chemical, as its reactive CC bond facilitates facile conversion to value-added cyclohexanol, caprolactam, and adipic acid via typical olefin reactions. The production of cyclohexene by benzene partial hydrogenation features advantages of feedstock accessibility, atomic economy, succinct reaction route, and, consequently, operational simplicity. However, benzene partial hydrogenation to cyclohexene is thermodynamically less favorable than benzene complete hydrogenation to cyclohexane. By elaborate catalyst design and careful optimization of the process conditions, though challenging for this four-phase reaction, industrially acceptable cyclohexene yield can be achieved. Herein, after an overview of the thermodynamics and reaction mechanisms for benzene partial hydrogenation, the preparation methods for the active and selective catalysts are summarized. Then, the influences of the process conditions, which are crucial for the improvement of the selectivity, are described that are important for the development of more efficient benzene partial hydrogenation process. Finally, the advantages and disadvantages of the Asahi–Kasei Chemical Co. process, i.e. benzene partial hydrogenation–cyclohexene hydration, are discussed. The basic results of the new RIPP process based on benzene partial hydrogenation–cyclohexene esterification–hydrogenation are demonstrated, which is a promising alternative to the Asahi–Kasei Chemical Co. process in terms of the high process efficiency.