| Propylene oxide is an important organic raw material.The preparation of propylene oxide which has been industrialized include the chlorohydrin process,HPPO route and co-oxidation route. The chlorohydrin process has been eliminated gradually due to the production of acid waste,alkali waste and solid waste. The HPPO process is not as mature as the others and it must build near the plant of hydrogen peroxide. The co-oxidation process face a problem of coproduct sales. Using hydroperoxide cyclohexyl hydroperoxide(CHHP) as oxidant to product propylene oxide has advantages of less wastes and less investment of the recycle equipment. Meanwhile cyclohexyl hydrogen peroxide is cheaper and can be directly derived from the process of cyclohexanone cyclohexane oxidation.In this thesis, the CVD process to preparation Ti-containing mesoporousTi/SiO2 was explored firstly. The effect of space velocity,temperature and time on the catalyst structure and activity were inverstigated. The catalysts were characterized by FT-IR、UV-Vis、and low temperature N2 adsorption techniques. The results show that the catalyst surface area, pore volume decreases gradually with the increase of CVD temperature, while the pore diamter show a trend of increase with the increasing temperature. When CVD temperature reaches800℃, Ti component within the framework transfer to the channel and form the TiO2. As CVD time is longer than 1.0 h, the Si-OH of the catalyst reacted completely. The Ti content in the framework is relative to the catalyst activity. Using the co-epoxidation of propylene and CHHP as probe reaction, the optimal conditions of CVD is as follow: 10 min-1space velocity under 700 ℃ for 1.5 h.Before silylation modification of the catalysts, effect of calcination temperature and hydrothermal treatment conditions on the structure and catalytic activity of Ti/SiO2 are investigated. The catalysts were characterized by low temperature N2 adsorption 、 Raman spectroscopy、ultraviolet spectrum and element analysis techniques. The result showed that the catalyst changed when the calcination tempreature higher than 800 ℃, the components of the skeleton Ti removed to be TiO2 outside the framework.Hydrothermal treatment influence the effect of silylation while part of anatase titanium dioxide can be eliminated. The co-epoxidation of propylene and CHHP concluded that the optimum calcination temperature was 700 ℃and the optimal hydrothermal condition is 10 g/h waterunder 300℃ for 2 h.Finally, the different between gas silylation and liquid silylation and the effect of different silylation agent, silylation time, and silylation temperature on the structure and activity of the catalyst were studied. The catalysts were characterized by low temperature FT-IR,N2 adsorption,Ultraviolet spectrum,Element analysis and TG techniques. The resultsshow that the liquid silylation is more effectiveand the silane grafting reaction finish after 9hours, as a result longer silylation time cannot make silicon alkylation reaction to continue. It is also proved that with the increase of silylation temperature, more and more organic groups graft or accumulate on the catalyst surface. The organic groups eliminate from the catalyst surface when the silylation temperature is above 140℃. The result of the co-epoxidation of propylene and CHHP concluded that the optimal liquid silylation condition is HMDS as silylation reagents, under for 9 h, and the quantity ratio of HMDS to Ti/SiO2 0.5. The catalyst prepared by the above conditions exhibits excellent catalytic performance for the epoxidation of propylene with CHHP. The CHHP conversion is 92.94% and the selectivity to PO is83.16% while the selectivity of cyclohexanol and cyclohexanone reach 90.66% and 8.14%respectively. |
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