Epoxidation Of Propylene Over Titanium Silicalite-1in Fixed-bed Reactor

Titanium silicalite-1(TS-1) catalyzed epoxidation of propylene with H2O2toproduce propylene oxide can be carried out under mild conditions with highconversion and high selectivity, and it is environmentally friendly. So it has beenintensively researched in recent years. This process is hopeful to replace thetraditional processes to become the main technology for the production of propyleneoxide.In this work, TS-1was synthesized by using tetrapropylammonium hydroxide(TPAOH) as template and tetrabutyorthotitanate (TBOT) and tetraethylorthosilicate(TEOS) as Ti and Si sources, respectively. Then SiO2-supported TS-1(TS-1/SiO2)catalyst was prepared through extrudation, and tested in a fixed-bed reactor. Theexperimental results indicated that the catalyst activity declined gradually with theonline reaction time. In order to investigate the reason of the catalyst deactivation, thefresh, deactivated and regenerated catalysts were characterized by XRD, FT-IR,UV-Vis, BET and TG. The results suggested that the catalyst deactivation is not dueto the collapse of catalyst framework structure or the loss of titanium from theframework. The main reason is the blockage of the channels of the catalyst by bulkyorganic compounds formed by PO and by-products, which cover the active centers oftitanium of catalyst. The results further suggested that the deposited materials on thedeactivated catalyst can be removed by treatment with hydrogen peroxide/methanolsolution at high temperature; the higher the regeneration temperature and the higherthe H2O2concentrations in methanol, the better the catalyst regeneration effects. Twosteps regeneration is better than one step regeneration.The decomposition of H2O2was also studied in the epoxidation of propylene.The experimental results indicated that the higher the reaction temperature, the moredecomposition of H2O2. In order to decrease H2O2decomposition, trace amounts ofsome addictives were added in the reactants to prevent the decomposition of H2O2.The results suggested that trace amounts of addictives had good performance toreduce the decomposition of H2O2. However, the addition of much more addictives isnot beneficial to reduce the decomposition of H2O2.