.ag/ts-1 Catalyst Propylene Gas Epoxidation Performance

Propylene oxide (PO) is one of the most important chemical feedstocks for producing polyether polyols, and polyether polyols is further used to produce polyurethane. Commercially, PO is manufactured by either chlorohydrin or co-production (Halcon) routes. The former suffers from the bad pollution by waster-water produced in process; the later disadvantageously produces equimolar amounts of co-products, it is capital-intensive and its economics is linked to the economic values of the by-products. The invention of titanium silicate- 1 (TS-1) by Taramasso et al. opened a new route for the synthesis of PO. In the epoxidation of propylene with H2O2, high H2O2 conversion and high selectivity to PO can be obtained over TS-1. However, the cost of H2O2 is very high. In view of the ethylene epoxidation, researchers have paid more attention to the direct synthesis of PO by oxygen or air in the vapor phase. In this field, the research work is mainly focused on two aspects about silver catalyst ,one is to produce PO over modified silver catalyst ,which has been used for ethylene epoxidation, at high temperature; the other is to produce PO over silver catalyst with low loading at low temperature.In this dissertation, the epoxidation of propylene was carried out over Ag/TS-1 in the presence of hydrogen and oxygen at atmospheric pressure. The effects of the factors involved in the catalysts preparation and reaction conditions on the catalytic properties have been investigated; through the modification and treatment of Ag/TS-1 catalyst, the reaction activity is improved; at last , the titanium speices and deactivation and regeneration of the Ag/TS-1 catalyst have been preliminarily discussed; at the same time the catalysts have been characterized by TEM, XRD, UV-Vis, FT-IR, ESR, ICP and AAS. The results show that:TS-1 synthesized with TPABr as the template in the hydrothermal system is favorable as the support of Ag/TS-1. There is a synergy between Ag species and Ti species. The optimum preparation conditions of Ag/TS-1 catalyst are: Ag loading, 2wt%; precipitator, 0.07Mol/L K2CO3; (deposition-precipitation) DP preparation method; the nsi/nri of TS-1, 64; precursor was washed by 500ml H2O and the Ag/TS-1 catalysts were calcined at 450 C in air for 10h. The optimum reaction conditions are: reaction temperature, 150 C; volume gas velocity ,4000h-1; V(C3H6): V (O2): V (H2): V (N2) = 1:2:3:12. Moreover, hydrogen plays an important role in the gas-phase epoxidation of propylene. Alkali metal carbonate is favorable as the precipitator. The catalytic properties can be improved with the existence of K+. With 0.07mol/L K2CO3 as the precipitator, 1 .72% propylene conversion and 98.21% PO selectivity are obtained over 2wt%Ag/TS-l (nsi/nTi=64) catalyst, when it reacted at the optimum reaction conditions. Only the suitable size silver particles(7~12nm) with good dispersion degree can exhibit good catalytic properties; Neither big nor small silver particles favor the formation of PO. In UV-Vis spectra, the stronger the electron transition signal at 400~500nm which characterized oxidized silver ions, the higher the reaction activities; the blue shift of the absorbance wavelength of the silver species is beneficial to the formation of PO. With high temperature activation or the combination treatment of air and hydrogen of 2%Ag/TS-l catalyst before the reaction, propylene conversion increase greatly with slight decrease in PO selectivity. When the catalyst is pretreated by hydrogen pretreatment and Air pretreatment in turn, the catalyst exhibits optimum performance of a 1.98% propylene conversion and a PO selectivity of 89.59%. There is a synergy between Pd species and Ti species over 2%Ag/TS-l catalyst with Pd modification. And the addition of Mo or Ce with proper quantities is beneficial to the formation of oxidized silver species. All the three modifications can improve propylene conversion, but with slight decrease in PO selectivity. The subsequence of the addition of promoters can affect the catalytic properties directly. The frame...