Studies On Selective Hydrogenation Of Benzene To Cyclohexene

Cyclohexene is an important intermediate for the production of organic chemical industrial products, which has found significant applications in the organic chemical industry. There have been various methods for the synthesis of cyclohexene, which are still problematic. Comparatively, the selective hydrogenation of benzene to cyclohexene brings a promising future for development since it enjoys the supermancy such as rich in raw material of benzene, low cost and shorter technological process. At present, there are many reports on selective hydrogenation of benzene over Ru supported catalysts, which suffer from the disadvantages like high cost and rigorous for raw materials. However there are few reports on the selective hydrogenation of benzene over non-noble metal catalysts. Thus, it is of great theoretical and realistic significance to develop non-noble metal catalysts that are more economical and environmentally friendly.In this thesis, the non-noble metal catalysts were prepared by homogeneous precipitation. The reaction process of selective hydrogenation of benzene to cyclohexene was studied in detail using the gas phase reaction processes. The main achievements are illustrated as follow:(1) Study on the thermodynamics and kinetic analysis of hydrogenation of benzene to cyclohexene were conducted. The results showed that the suitable reaction temperature was between100to200℃.And there was an appropriate pressure for the reaction. Lower pressure would lead to low conversion. While higher pressure was negative for the selectivity of cyclohexene.(2) Studies on catalysts with oxide supports:The effects of Fe, Co, Ni, Cu, etc., as the active component of the catalysts were studied. The results showed that the activity of Ni was best. Then with Ni as the active component, the supports with different acid or basic properties were investigated. It was found that best activity was obtained with acidic alumina as support. The L18(37) orthogonal experiments were arranged to optimize the reaction conditions. The reaction temperature of180℃, pressure of0.6MPa and n(H2)/n(benzene) of0.1were found to be the optimal operating conditions for5wt%Ni/acid-Al2O3catalyst. On these bases, the influences of the metal modification, the loading amount of Ni, the reduction temperature and the calcination temperature on the catalytic activity were further investigated. The optimization conversion and selectivity over5wt%Ni/acid-Al2O3were8.16%and7.93%, respectively. And the characterizations with XRD, UV-Vis, FT-IR, BET and SEM were carried out as well to study the influences.(3) Studies on catalysts with zeolite supports:The effects of zeolites with different pore sizes such as NaA, ZSM-5,13X, NaY, on the catalytic activity were studied. The zeolite4A was found to show best activity. Then, the single factor experiments were arranged to optimize the reaction conditions. The reaction temperature of180℃, pressure of0.3MPa and n(H2)/n(benzene) of0.27were found to be the optimal operating conditions for5wt%Ni/4A catalyst. On these bases, the influences of the pre-adjusted precipitation pH, the loading amount of Ni, the reduction temperature and the calcination temperature on the catalytic activity were further investigated, assisted by the characterization techniques of XRD, FT-IR, BET and SEM. The optimization conversion and selectivity over5wt%Ni/4A were3.16%and42.01%, respectively.