Catalytic epoxidation of propylene glycol and its acetates

The base-catalyzed, gas-phase epoxidation of propylene glycol acetates to propylene oxide (PO) is carried out in a laboratory-scale fixed-bed reactor. Potassium salts (0.5-2.5 mmol K/g) on silica are identified as selective catalysts for the reaction. A temperature of 400 degrees C at high space velocity gives a maximum PO selectivity of 81%, while the maximum yield of 30% is achieved at the same temperature but lower space velocity. Pre- and post-reaction catalysts were characterized by N-2 adsorption, TGA, XPS, and FTIR. High temperature and high potassium loading lead to collapse of the silica pore structure, and in severe cases to obstruction of flow in the reactor. Potassium carbonate, formed via ketonization of potassium acetate generated on the support during reaction with KOH as the catalyst material, is the stable potassium species on the catalyst at high loadings ( > 1.5 mmol K/g silica). At low loadings, surface potassium silicate analogs (Si-O-K) predominate. The use of potassium on a low surface area, annealed silica support gives similar activity and PO selectivity without degradation of pore structure.