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Liquid Phase Propylene Epoxidation Over Titanium Silicalite-1 In A Fixed-bed Reactor

Posted on:2015-01-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:W P FengFull Text:PDF
GTID:1221330485491660Subject:Chemical processes
Abstract/Summary:PDF Full Text Request
Propylene oxidation(PO) is an important chemical product which is widely used in the production of polyether polyols, propylene glycol, nonionic surfactants, etc. Currently, PO is mainly produced by the cholorohydrin or hydroperoxide processes. However, the former uses chlorine and propene to produce propene chlorohydrins as intermediates and produces a large volume of waste water containing chlorine, which is not environmentally friendly; the latter uses ethyl benzene or tert-butyl hydro-peroxide to oxidize propene and is restricted by the price of by-products. The process of epoxidizing propylene with hydrogen peroxide to propylene oxide(HPPO) catalyzed by TS-1 gives high conversion of H2O2 and high selectivity to PO under mild reaction conditions.In this work, the epoxidation of propylene with H2O2 in liquid phase catalyzed by a TS-1/SiO2 catalyst in a fixed-bed reactor has been studied. Firstly, the effects of the reaction temperature, reaction pressure, composition of feed solution, and feeding methods on the catalyst stabilities were investigated. Secondly, the effect of triethylamine(TEA) treatment of TS-1 on propylene epoxidation was studied. Finally, the H2O2 decomposition under different conditions and the effect of adding 1,10-phenanthroline into reactants on the H2O2 decomposition were studied.The reaction results showed that the catalyst stability was improved with increasing the reaction temperature, reaction pressure, the mass fraction of CH3 OH in the CH3OH/H2O2/H2 O solution and H2O2 concentrations. Moreover, hydrogen peroxide from different factories and different feeding methods have appreciable impact on the catalyst stability.The characterization results showed that many irregular hollows were generated in the TS-1 crystals after TEA treatment. The TS-1 samples treated with triethylamine solution under different conditions improved in varying degrees the catalyst life for the epoxidation of propylene, which is attributed to the generation of the hollows making it easier for the reactants and products diffusing out of the zeolite channels. However, the hollow cavities are not the larger the better for the reaction. A large volume of the hollow cavities means a heavy damage to the TS-1 crystals and a considerable loss of the framework Ti species. This can explain the decrease of the catalyst life with the catalyst treated with too high TEA concentration.The experimental results showed that the H2O2 decomposition increased with increasing the reaction temperature and decreasing the hydrogen peroxide concentrations. The reaction pressure had little impact on the H2O2 decomposition. However, the H2O2 decompositions under different feeding methods were very different. The addition of 1,10-phenanthroline into the reactants could appreciably prevent the H2O2 decomposition.
Keywords/Search Tags:Titanium silicalite-1, propylene, epoxidation, propylene oxidation, catalyst stability, catalyst treatment, H2O2 decomposition
PDF Full Text Request
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