Experimental study of porous tubular catalytic membranes for direct synthesis of hydrogen peroxide

A continuous process for safe direct synthesis of H2O2 from H2 and O2 over Pd-catalysts in a gas/liquid membrane contactor is proposed. As a prerequisite for the process a method was developed for coating of Pd based catalysts into the fine porous layer on the inside of asymmetric tubular membranes. The method reached uniform distribution and high dispersion of the Pd nano particles with ca. 11 nm size for a range of membrane geometries and lengths and a variety of membrane materials. For the selection of the best catalytic system additional experiments with supported catalysts were performed. They were prepared using the same materials and coating method as for the manufacture of the catalytic membranes. The principle of the membrane contactor was verified with 10 cm long single channel membranes with stable operation of the continuous system for more than 10 h at differential pressures up to 4.5 bar in methanol. Further, the role of key process parameters such as solvent type, system pressure and flow regime were assessed. Productivities up to 1.7 molH2O2 gpd−1 h−11.7 molH2O2 gpd−1 h−1 (6.1 molH2O2 m−2 h−16.1 molH2O2 m−2 h−1 related to the geometric surface area of the membrane) with a selectivity of 83% towards H2O2 were achieved.