Preparation Of Niobic Acid Modified Hydrophobic Catalyst And Their Application In Cyclohexene Hydration Reaction

Cyclohexanol is an important chemical product, which is used in the production of adipic acid, caprolactam and dye. The cyclohexene hydration conforms to the sustainable economic development by using environmentally friendly ZSM-5 catalyst.In our research, the efficient ZSM-5 zeolite was developed and modified. Firstly, the ZSM-5 was modified by trimethylchlorosilane(TMCS) and named as TMCS-ZSM-5. The proper TMCS content was 4wt%. Secondly, the ZSM-5 was modified by niobium acid and named as Nb2O5-ZSM-5. The proper Nb2O5 loading was 0.5wt.%. Finally, the ZSM-5 was modified with both niobium acid and trimethylchlorosilane at the same time to increase the acid amount as well as to improve the contact between catalyst and cyclo hexene. Compared with the unmodified ZSM-5, the catalytic activity of TMCS-Nb-ZSM-5 has significantly increased.In addition, under the condition of eliminating the diffusion, the influence of reaction pressure, reaction temperature, reaction time, catalyst content and the feed mass ratio on cyclohexene hydration over the TMCS-Nb-ZSM-5 zeolite was studied. The optimal reaction conditions were as followings: for without stirring condition, reaction temperature 403 K, reaction time 5 hours, atmospheric pressure, catalyst content 20 wt.%, feed mass ratio(oil/water) 0.4(w/w). The cyclohexene conversion was 7.3%, while the cyclohexanol selectivity was 99.9%. For stirring and pressurized conditions, reaction temperature 403 K, reaction time 2 hour, reaction pressure 0.6Mpa, catalyst content 30 wt.%, feed mass ratio(oil/water) 0.5(w/w). The cyclohexene conversion and cyclohexanol selectivity were 12.94% and 99.91%, respectively.At last,cyclohexene hydration kinetics was explored primarily and its model was obtained. The results of kinetic study showed that the kinetic models gave a satisfactory agreement with the experimental data. According to the kinetic result, it is suggested that cyclohexene hydration catalyzed by TMCS-Nb-ZSM-5 belongs to the ER mechanism. The water molecule is first adsorbed on the active sites of TMCS-Nb-ZSM-5 to form hydroxonium ion, which plays the role of the Bronsted acid site. And then the cyclohexene molecule in the aqueous phase could react with the adjacent hydroxonium ion to obtain the product cyclohexanol. For cyclohexene hydration over TMCS-Nb-ZSM-5, the obtained activation energy was 70.39kJ/mol.