GAS AND SURFACE-DIFFUSION IN MODIFIED GAMMA-ALUMINA SYSTEMS

The transport of pure gases through a microporous membrane is described. The alumina-based membrane (pores 2.5-4 nm) is suitable for Knudsen diffusion separation. In adsorption experiments, little oxygen adsorption on the silver-modified γ-alumina could be detected. The mobility of hydrogen on the surface was tested by counterdiffusion experiments, of which the theory is given. Hydrogen shows a considerable mobility on the surface at 293 K. Magnesia was introduced into the γ-alumina membrane to enhance the adsorption and mobility of CO2. It is known that 30% of the CO2 transport on non-modified γ-alumina is surface diffusion. The highest achievable magnesia load was 2.2% by weight. Introduction of magnesia into the γ-alumina surface gives more strong base sites and fewer weak base sites. This results in stronger bonding of CO2 on the surface, but the amount adsorbed is comparable with the amount of CO2 adsorbed on non-modified γ-alumina.