The Preparation And Improvement Of ZSM-5Catalyst For Cyclohexene Hydration

Cyclohexanol is an excellent medium/high boiling point organic chemical product,which is widely used in the organic chemical industry, paint and textile industry.High-silica ZSM-5zeolite with uniform pore structure, high shape selectivity andthermal stability, is a major catalyst for the preparation of cyclohexanol. Developinginexpensive synthetic pathway of ZSM-5zeolite and appropriately modify to make itmore suitable for the hydration reaction are an important research direction.In our research, synthesis of ZSM-5catalyst for cyclohexene hydration is the mainobject. With cheap and easy of access water glass as silicon source firstly, throughimproved the traditional zeolite synthesis pathway, we have successfully synthesizedthe ZSM-5zeolite. The crystallinities and morphologies of ZSM-5zeolite werecharacterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).Through investigating the effects of reaction temperature, reaction time, pH, waterconsumption, seed crystal and stir on the crystallinities and morphologies of ZSM-5(SiO2/A12O3=50) catalyst, we obtained the optimum synthesis conditions: reactiontemperature of170℃, the reaction time of24h, pH=10, the reaction molar ratio ofn(SiO2): n(H2O)=l:40.With sodium silicate, silica sol, TEOS as the silicon source, we synthesized theZSM-5at optimum conditions. By comparing the morphologies, infrared spectro-scopy, surface acid content, thermal stability of the products, it was found that the lowmodulus sodium silicate as silicon source for template-free ZSM-5synthesis issuperior than the other silicon sources. The process conditions for hydration ofcyclohexene were optimized, then compared the catalytic activities of the ZSM-5which were from different synthesis conditions. Sodium silicate as silica source, theZSM-5synthesized from the optimum synthesis conditions has the highest catalyticactivity, the cyclohexene conversion is10.1%, and selectivity of cyclohexanol is99.8%.HMDSZ, TMCS, ECS, BDCS were used to modify the surface of ZSM-5, and thedegree of hydrophilicity of the modified catalyst surface was measured by goniometer.Triethylchlorosilane-modified ZSM-5has the biggest contact angle, which means therepellent of water is the strongest. In static condition, trimethylchlorosilane-modifiedZSM-5has the highest activity in the four modified catalysts, the cyclohexeneconversion and selectivity of cyclohexanol are3.4%and89.1%, respectively. The ZSM-5surface was modified with trimethylchlorosilane and niobate at the same timeto increase the acid amount, improve the contact between catalyst and cyclohexene.Compared with the unmodified ZSM-5, the catalytic activity oftrimethylchlorosilane-Nb-HZSM-5has increase, the cyclohexene conversion is12.9%and selectivity of cyclohexanol is99.4%.