Study On The Selective Hydrogenation Of Benzene And Hydration Of Cyclohexene

Assembling multistep reactions into one reactor has many advantages, such as simplifying processing, saving resources and decreasing emission. In this paper, three single reactions related to production of caprolactam from benzene are studied, including the selective hydrogenation of benzene to cyclohexene, the hydration of cyclohexene to cyclohexanol and the oxidation of cyclohexanol to cyclohexanone. Based on the above work, two integrated processes are discussed preliminarily, including selective hydrogenation of benzene with hydration of cyclohexene and hydration of cyclohexene with oxidation of cyclohexanol.The effects of operation conditions and catalysts preparation conditions on the selective hydrogenation of benzene were studied. The results show that, 4%Ru-1%Zn/nano-size SiO₂ catalyst prepared by the precipitation method has the best catalytic performance for the selective hydrogenation of benzene. Under the conditions of reaction temperature 120℃, concentration of ZnSO4 0.2 mol·L-1 and reaction time 75 min, the yield and selectivity of cyclohexene reach 22.6% and 48.9%, respectively, using the catalyst prepared at a reduction temperature of 300℃and with the molar ratio of NaOH to Ru of 6.8:1. XRD, BET surface area and pore distribution measurement, CO chemical adsorption were employed for the catalyst characterization.The reaction conditions of cyclohexene hydration were optimized. Under the most suitable conditions of reaction temperature 110℃and reaction time 4h, the highest yield of cyclohexanol is 13.5% over HZSM-5 (SiO₂/Al2O3 ratio =25) catalyst. When acetophenone is used as the solvent, the yield of cyclohexene reaches 17.7%. Atomic absorption spectra, NH3-TPD, FT-IR spectra of adsorbed pyridine were employed for the catalyst characterization.The effects of reaction temperature, reaction time and the amount of catalysts on the oxidation of cyclohexanol were studied according to the operation conditions of cyclohexene hydration. The results show that the yields of cyclohexanone are in the range of 14.8%-17.1%.The integrated process of cyclohexene hydration with the oxidation of cyclohexanol was studied. Owing to the presence of HZSM-5, hydrogen peroxide was decomposed completely during the heat-up process. Meanwhile, serious coke deposition was observed during the reaction. These resulted in the poor yield of cyclohexanone, only 0.825%. So the integrated process of cyclohexene hydration with the oxidation of cyclohexanol needs to be further researched.The integrated process of the selective hydrogenation of benzene with cyclohexene hydration was studied preliminarily. When the mechanical mixture of Ru-Zn/SiO₂ and HZSM-5 was used as the catalyst, most of the product was cyclohexane, and only little cyclohexene and cyclohexanol were produced. The effects of Ru loading, reduction temperature, calcination temperature and additive on the integrated process over Ru-Zn/HZSM-5 catalyst were studied. Only little cyclohexanol was produced. The integrated process needs to be further researched.