Enhanced phenol hydroxylation with oxygen using a ceramic membrane distributor

A CuO/TiO₂ catalyst was prepared by impregnation and characterized by X-ray diffraction, transmission electron microscopy, and temperature-programmed reduction. Two types ofdispersed species formed on the TiO₂ surface, which were possibly isolated and polymeric CuO species.The CuO catalyst interacted strongly withthe TiO₂ support.A porous ceramic membrane was used as a distributor to control the supply of oxygen in phenol hydroxylation over the CuO/TiO₂ catalyst. Compared to a direct feed of oxygen without a membrane, the yield of dihydroxybenzene (DHB) increased by 13% using a porous ceramic membrane with a pore size of 0.5 μm as an oxygen distributor. This is because the membrane distributor produced numerous small oxygen bubbles, increasing the volumetric oxygen transfer coefficient and gas-liquid mass transfer. Optimizing reaction conditions resulted in a yield of DHB of 2.5%. Scanningelectron microscope observation of the used ceramic membrane showed that it possessed excellent thermal and chemical stability.