Catalytic epoxidation of propylene glycol and its acetates

[Display omitted] •The active form of potassium salt catalysts for epoxidation of propylene glycol acetates to propylene oxide is described.•K2CO3 is the active catalyst species at high loadings and surface K-O-Si is present at sub-monolayer loadings.•Selectivity to propylene oxide from propylene glycol acetates reaches 80% at optimal conditions. 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 °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 N2 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.