Study On The Selective Hydrogenation Of Benzene And Its Kinetics Over Ru Catalysts

Cyclohexene is an important raw material for chemical production. It is of great synthetic and industrial interest for selective hydrogenation of benzene to cyclohexene, by which the production cost is lowered and the production process for nylon-6 and nylon-66 is shortened. Nowadays, the key technique of this process, i.e. the efficient catalytic system, is monopolised by Asahi Chemical Industry. It is of great importance to develop the novel catalyst and technology with proprietary intellectual property rights. Therefore, in this work, the development of a novel heterogeneous catalyst for selective hydrogenation of benzene to cyclohexene was studied.Ru-Zn@SiO₂ catalyst for selective hydrogenation of benzene was prepared in a water-in-oil microemulsion. The influence of preparation method, adding way of tetraethyl orthosilicate, and hydrazine hydrate, et al,were studied. It was found that the addition of hydrazine hydrate enlarged Ru particles, but Ru size didn't change with the further increase of hydrazine hydrate amount. However, the catalytic activity changed obviously with the addition of hydrazine hydrate, even when the Ru particles sizes remained constant. This should be contributed to the formation of a kind of highly dispersed Ru species, which was in favor of the benzene conversion. On the contrary, the crystallized Ru was beneficial for increasing cyclohexene selectivity. Benzene conversion was 62.7% and cyclohexene was 47.7% under the optimal operation conditions.The effect of zinc on the Ru-Zn/SiO₂ catalyst performance was studied. It was found that there was strong interaction between some Ru and Zn atoms, which retarded the reduction of Ru. There were two kinds of adsorption sites for H₂ on the surface of the Ru-Zn/SiO₂ catalyst, and the corresponding H₂ desorption temperature is 150-170℃and 400-430℃,respectively. With increase of the zinc content, benzene conversion decreased, while cyclohexene selectivity increased.The kinetics study of liquid-phase selective hydrogenation of benzene to cyclohexene on the Ru-Zn/SiO₂ catalyst was carried out. The results indicated that based on the reaction scheme, the kinetic model of Langmuir-Hinshelwood type can well describe the experimental data. The kinetic equation is:...