Study On The Green Integrated System Of Benzene Selective Hydrogenation And Cyclohexene Hydration

Cyclohexanol is an important industrial intermediate used to produce adipic acid and caprolactam. Traditional process for producing cyclohexanol suffers from several drawbacks such as extremely large recycles, high energy consumption, poor selectivity and explosion hazards. In the 1980s, Asahi developed a commercial process for cyclohexene hydration. In this process, cyclohexene was produced through selective hydrogenation of benzene. In this paper, a novel nano-microscale catalyst with high efficiency and multi-function was designed and developed for the integration of selective hydrogenation of benzene and hydration of cyclohexene. A green integrated system for synthesizing cyclohexanol was established on this catalyst. It provided the technical basis for developing a clean and short process for synthesizing cyclohexanol.A series of Ru-Zn/SiO₂ catalysts were prepared for selective hydrogenation of benzene. The effects of particle size and pore structure of the supports on the catalytic activity were studied. The catalytic performance of the catalysts prepared by different methods was compared.The effect of ILs on the activity of benzene selective hydrogenation was studied. ILs could replace ZrO₂ as dispersant, and simplify the recovery of Ru-Zn.A new quasi-homogeneous catalyst, nano-Ru/[Bmim][BF₄] was developed by chemical reduction method. It was proved that the ionic liquid served not only as the protective agent or stabilizing agent to inhibit the aggregation of Ru nanoparticles, but also modification agent adsorbed on the Ru nanoparticles. The effect of Ru loading on catalytic performance of Ru/[Bmim][BF₄] was examined. The morphology of nano-Ru prepared by different dropping sequences was characterized.The indirect hydration of cyclohexene catalyzed by sulfuric acid was studied. The reaction conditions were optimized. The effect of organic solvents on the activity of cyclohexene hydration catalyzed by phosphorus acid was studied. The reaction conditions were optimized by orthogonal experiments with acetone as solvent. The effect of SiO₂/Al₂O₃ ratio of HZSM-5 zeolite on cyclohexene hydration was investigated. The optimum SiO₂/Al₂O₃ ratio of HZSM-5 zeolite was 25. It was proved by acidic characterization that the strong Br?nsted acid sites were the active sites of cyclohexene hydration. Under the optimum conditions, the highest cyclohexene conversion was 11.8% with 98.7% cyclohexanol selectivity. Effect of different kinds of organic solvents on cyclohexene hydration was studied, and the optimal organic solvent was selected. The reaction conditions of cyclohexene hydration with solvents were optimized. Under the most suitable conditions, the highest cyclohexene conversion was 34.5%, the cyclohexanol selectivity was 99.3%.HZSM-5 zeolite was synthesized using various templates. HZSM-5 zeolite synthesized using aluminum nitrate (Al(NO₃)₃), tetraethyl orthosilicate (TEOS), and tetrapropyl ammonium hydroxide (TPAOH) as raw materials was mainly studied. The effects of pH regulators, SiO₂/Al₂O₃ ratio, crystallization temperature and surfactants on morphology and particle size of HZSM-5 zeolite were investigated. Because the HZSM-5 zeolite with regular morphology and small particle size could provide more active sites in cyclohexene hydration, it could obtain cyclohexanol 12.3% yield. On the basis of HZSM-5 zeolite synthesis, HZSM-5 zeolite membranes were synthesized on irregular supports by in situ hydrothermal synthesis method, pre-seeding method and self-assembly seeding method. The differences of these HZSM-5 zeolite membranes synthesized by different methods were studied.A new multi-functional composite catalyst for the integration reaction was prepared with Ru-Zn catalyst or Ru-Zn/SiO₂ catalyst as core, HZSM-5 zeolite membrane as shell. The green integrated system of benzene selective hydrogenation and cyclohexene hydration in nano-scale was established on the Ru-Zn@HZSM-5 and Ru-Zn/SiO₂@HZSM-5 catalysts. The green integrated system of benzene selective hydrogenation and cyclohexene hydration in micro-scale was established on the mechanical mixed Ru-Zn+HZSM-5 catalyst. A dynamic operation by pulsed hydrogenation for the integration reaction was investigated to deal with the mismatch of reaction time. The reaction conditions of the integrated reaction were optimized. Under the most suitable conditions, the yield of cyclohexene and cyclohexanol was 18.1% and 1.9% respectively.The interaction between benzene selective hydrogenation and cyclohexene hydration was studied. The addition of HZSM-5 resulted in high conversion of benzene and low selectivity of cyclohexene. It was thought to be the result of the effect of hydrogen spillover which was closely related to the number of acid sites and particle size of HZSM-5 zeolite. The addition of ZnSO4 resulted in decreasing of cyclohexene conversion and cyclohexanol yield. It was found that the existence of Zn2+ on the surface of HZSM-5 resulted in decreasing of B acid. The competitive adsorption of benzene, cyclohexane and cyclohexene on the suface of HZSM-5 resulted in cyclohexene conversion decreasing.