SURFACE-DIFFUSION OF HYDROGEN-SULFIDE AND SULFUR-DIOXIDE IN ALUMINA MEMBRANES IN THE CONTINUUM REGIME

Surface diffusion of H2S and SO2 in alumina membranes with an average pore diameter of ca. 350 mm, impregnated with gamma-Al2O3, is studied as a function of pressure at temperatures between 446 and 557 K. Diffusion through the gas phase in the pores of the membrane almost entirely takes place in the continuum regime. The pressure dependence of transport by diffusion through the gas phase and by surface diffusion is different, a fact which is used for the interpretation of the steady-state diffusion measurements. It is observed that the contribution of surface diffusion to the total diffusion through the membrane can be as high as about 40%. The surface diffusion data obtained are interpreted by a theoretical surface diffusion model using two parameters to be fitted, the product of the effective surface diffusion coefficient, the concentration of the adsorption sites and the adsorption parameter as well as the adsorption parameter itself. The parameters fitted for SO2 show a remarkable change between 498 and 525 K. This probably maybe attributed to a change in the adsorbed species also reported in literature. The parameters fitted for H2S at different temperatures show a maximum; however, the product of the effective surface diffusion coefficient and the concentration of the adsorption sites increases with temperature.