The Study On The Wettability And Hydrogen Separation Performance Of Silica Membranes Modified By Hydrophobic Groups

Microporous silica membranes have been considered as promising candidates for gas separation due to their excellent properties such as high thermal stability, corrosion resistant, high porosity, tunable pore size in gas molecule level and so on. However, the hydrothermal stability of silica membranes still remains challenged owing to the serious deterioration of pore structure, which is caused by the reaction between the surface hydroxyl groups and the physically adsorbed water.It is possible to reduce the adsorption of water and further improve the hydrothermal stability of silica membranes by enhancing their hydrophobic property via replacing the hydrophilic surface hydroxyl groups with hydrophobic groups.In the present work, organic-inorganic silica membranes were synthesized by sol-gel technique using 1,2-bis(triethoxysilyl)ethane(BTESE) as precursor and siloxanes containing hydrophobic groups as co-precursor. The effect of the concentration of hydrophobic groups, the roughness of the supports and the carbon chain length of hydrophobic groups on the hydrophobic property of the silica membranes was investigated in detail. Methyl-modified organic-inorganic silica membranes were prepared using the relatively cheap methyltriethoxysilane(MTMS) as modified agent and the hydrophobic property, thermal stability, hydrothermal stability and hydrogen permeation and separation performance were also discussed.The results show that the hydrophobic property of the silica membranes is enhanced with increasing concentration of modified agents in the mixture, increasing roughness of the supports and increasing carbon chain length of the modified agents.Methyl-modified silica membranes are successfully deposited on the γ-Al2O3/α-Al2O3 supports by dip-coating under clean room conditions. The particle size of the sol is 4.7nm at the MTES/BTESE molar ratio of 1.0 and the water contact angle is 103.7? at such composition. The modified silica membrane is thermally stable up to 350℃ and also hydrothermally stable at humid atmosphere, without physically adsorbing any water molecules. The modified membrane demonstrates a hydrogen permeance of 1.04?10-6mol·m-2·s-1·Pa-1 at 300℃ and a H2/CO2 and H2/CO permselectivity of 5 and 4, higher than those of Knudsen diffusion 4.69 and 3.7, respectively.