Epoxidation of propylene using supported titanium silicalite catalysts

摘要

The propylene epoxidation using supported titanium silicalite TS-1 catalyst was systematically investigated in a fixed bed reactor. Different supports such as SiO_2 and Al_2O_3 were used and two molding methods were adopted to prepare the catalyst. Strip TS-1 catalyst of 1 mm X 2 mm dimensions is obtained by the extruding method. Use of SiO_2 as the support rather than Al_2O_3 is better becau7se the latter has strong acidity that promotes the side reaction of propylene oxide (PO) with the solvent. With the decrease of the amount of TS-1 in TS-1/SiO_2, the PO selectivity increases. The lamina TS-1 catalyst, the core of which is an inert ball used as the support and the shell of which is a TS-1 lamina of 0.1-0.2 mm, exhibits better performance than the strip TS-1 catalyst owing to its shorter diffusion path for reaction heat, raw material and product. The lamina TS-1 catalyst was used in the fioxed bed reactor for about 200 h. The results indicate that it is a promising catalyst in propylene epoxidation. The effect of aluminum impurity was also investigated. It has been shown adcid sites originating from framework aluinum can catalyze the side reaction and a small amount of base can inhibit it. In conclusion, diffusion and theconcentration of acid sites are the two main factors influencing the performance of titanium silicalite catalyst in propylene epoxidation.