Kinetic Modeling Of Liquid-phase Epoxidation Of Propylene With H₂O₂ Over TS-1 Catalysts

H₂O₂ decomposition experiments were carried out without propylene on unmodified TS-1 and TS-1 after TPAOH treatment.A thorough investigation of kinetic behavior on HPPO process by two catalysts was conducted in fixed-bed reactor.The formation of PO and MME were studied as a function of H₂O₂ concentration（0.4mol/L¹.2mol/L）,H₂O₂ space velocity（0.023⁰.068mol/gcat·h）and molar ratio of C₃H₆ to H₂O₂（2⁸）as well as temperature（30℃-46℃）.The research shows that:1.Analyzed variety of Ti species through UV-Raman characterization.Unmodified TS-1 has framework Ti and anatase TiO₂,while modified ones has octahedral coordinated Ti besides the two Ti species.The contents of different Ti species were quantified by UV-Vis and ICP.Therein,the formation of PO and MME are attributed to framework Ti and octahedral coordinated Ti,while Ti O₂ are considered to be invalid for the two reactions.2.Rate equations were fitted on the two catalysts.The decomposition performance of two catalysts grows with temperature rising,concentration going up as well as space velocity dropping down.Unmodified TS-1 has high decomposition performance may due to high percentage of TiO₂.3.For unmodified TS-1,reaction statistics were fitted by L-H and E-R models respectively in the case of ignoring the PO ring open reaction.The E-R mechanism of H₂O₂absorbing on Ti while C₃H₆ in liquid phase has the better result.On the basis of E-R model of main reaction,three possible mechanisms for MME formation are proposed and calculated.The consequence shows that PO on active sites combined with CH₃OH in liquid phase is proved to be the best mechanism.Electron-donating property may be the cause of oxygen absorbent on framework Ti which is electron-deficient.4.Modified TS-1 has the octahedral coordinated Ti as one more active species.After obtaining kinetic parameters of framework Ti,activation energy,pre-exponential factor and equilibrium constants of octahedral coordinated Ti are calculated using modified TS-1.After TPAOH treatment,the activation energy of main reaction decreases while that of side reaction grows up,which means octahedral coordinated Ti was beneficial to conversion and selectivity of main reaction from activation energy aspects.On the other hand,the adsorption equilibrium constant percentage of H₂O₂ minor while that of PO larger.Which means,framework Ti was superior to conversion and selectivity of main reaction in this respect.