Effect Of P-H₂O₂ Treatment On Catalytic Performance Of ZSM-5 Zeolite For Hydration Of Cyclohexene

Cyclohexanol is being synthesized on an industrial scale today as an intermediate in the production of adipic acid andε-caprolactam, and is also an important industrial solvent.The conventional method of cyclohexanol production is cyclohexane oxidation process, but cyclohexane is oxidized via peroxides, which are essentially associated with explosion risk. Asahi Chemical Co. has developed a more economical and safer process,and the key point of the technology is the selection of the catalyst. Compared with other catalysts, HZSM-5 zeolite shows better hydration activity, But there are still the disadvantages of low conversion and slow reaction rate. So, The modification of zeolite is an important research direction.Firstly, the effects of HZSM-5 zeolites with different SiO2/Al2O3 and crystal size on catalytic performance for hydration of cyclohexene were studied, HZSM-5 zeolites with SiO2/Al2O3 ratio 25 and more small crystal size was good catalyst. Secondly, The influence on physicochemical properties, surface acidity and catalytic activity of HZSM-5 zeolites modified by phosphorus and steam treatment for hydration of cyclohexene to cyclohexanol were investigated. XRD shows that no new crystalline phase exists in the modified samples. NH3-TPD indicates the introduction of phosphorus by impregnation of the zeolite and steam treatment decreased the acidity and the number of acid sites of HZSM-5, especially the number of strong acid sites were reduced. The IR spectra of adsorbed pyridine showed that the reduction of number of strong acid sites were mainly Br(?)nsted acid site. Furhermore, as the reduction of the number of strong acid sites, the conversion of cyclohexene and selectivity to cyclohexanol were both improved. It can be concluded that the catalytic activity of HZSM-5 zeolites for hydration of cyclohexene was closely related to the amount of acid site especially of strong acid site and the acid strength. The optimal modified condition for the HZSM-5 zeolites was as follows: phosphorus loading 0.8%(mass fraction), steam treatment temperature 570℃, steam treatment time 2 h. The conversion of cyclohexene 8.31% and selectivity to cyclohexanol of 97.73% were obtained under the optimal modification condition.At last, HZSM-5 zeolites treated with H2O2 was characterized by means of XRD,N2 adsorption,SEM,NH3-TPD and Py-FTIR. The effects of HZSM-5 zeolite treated with H2O2 were investigated on the structure and catalytic performance for hydration of cyclohexene. The results showed that particle size of HZSM-5 treated by H2O2 decrease, it only was 0.5-0.7 u m, furthermore the number of acid sites of HZSM-5 zeolite treated by H2O2 was reduction. As for the change of acid sites, the number of the Br(?)nsted acid sites and Lewis acid sites on the zeolite treated one were both decreased, what's more, the Lewis acid sites decreased significantly. The catalytic activity of treated one for hydration of cyclohexene was improved. The conversion of cyclohexene and selectivity to cyclohexanol was 8.33% and 97.80% respectively.