Determination of the gas-to-membrane mass transfer coefficient in a catalytic membrane reactor

A novel method to determine the external mass transfer coefficient in catalytic membrane reactors (Sloot et al., 1992a, b) was presented in this study. In a catalytically active membrane reactor, in which a very fast reaction occurs, the external transfer coefficient can conveniently be measured by shifting the reaction plane (or zone) towards the membrane interface. Then the transport rate of one of the components is completely determined by its external transport rate. In a continuously operated diffusion cell with a flat membrane, mass transfer coefficients were obtained from the Claus desulphurization reaction as well as the heterogeneous oxidation of carbon monoxide over platinum. The results were compared with the determination of the mass transfer coefficient from the sublimation rate of naphthalene. In the absence of a viscous flow through the membrane, it appeared that the Claus reaction was insufficiently fast over the present catalyst to determine the external mass transfer rates of H2S in the present setup. At low mass transfer rates the heterogeneous CO-oxidation appeared to be fast enough to be initially controlled by external mass transfer.