Permeance of pure vapours in porous γ-Al2O3/α-Al2O3 ceramic membrane

The permeances of pure vapours including water, methanol, ethanol, cyclohexanol and cyclohexanone across porous alumina ceramic membrane were measured at the temperature ranges of 200–350 °C and in the trans-membrane pressure ranges of 0.005–0.050 MPa. Water molecules adsorbed on the surface of alumina membrane through hydrogen bond and this favoured to transport of water molecules across the membrane by surface diffusion. However, alcohols adsorbed on the surface of alumina membrane through chemical adsorption and this had a disadvantage for transport of alcohol molecules across the membrane. In terms of adsorption strength, cyclohexanol adsorbed more strongly on the surface of alumina than that of methanol and ethanol. Permeance of cyclohexanol at 350 °C was higher than that at 300 °C since high temperature favoured to desorption of cyclohexanol molecules from the surface of alumina membrane, leading to reduce of blockage of absorbed cyclohexanol molecular. Only at higher temperature, when the adsorption was eliminated, the permeate behaviour of alcohols vapours was similar to that of hydrogen and nitrogen, which decreased with increase of permeate temperature. If cyclohexanol, prior to cyclohexanone, was adsorbed on the surface of the porous alumina, the adsorbed cyclohexanol molecules would form a blockage for gas-phase transport of cyclohexanone across the membrane. This greatly enhanced the permselectivity for hydrogen/cyclohexanone, which was at least 17 and was much higher than the theoretical Knudsen diffusion value of 7.

► At lower temperature, surface adsorption had an important influence on the transport of vapours across porous membrane.
► Water molecules adsorbed on the surface of alumina membrane through hydrogen bond mode and this favoured to transport of water molecules across the membrane by surface diffusion.
► However, alcohols adsorbed on the surface of alumina membrane through chemical adsorption and this had a disadvantage for transport of alcohol molecules across the membrane.
► Ceramic membrane displayed excellent properties such as thermal stability, chemical stability and high mechanical strength although the resistance for water vapour was not satisfactory.