Effect of physically adsorbed water molecules on the H2-selective performance of a silica membrane prepared with dimethoxydiphenylsilane and its regeneration

The effect of exposure to humid conditions at room temperature on the H2-selective performance of a dimethoxydiphenylsilane (DMDPS)-derived silica membrane was studied. Immediately after exposure to air with 20% relative humidity, the permeances of H2 and N2 decreased drastically and then kept constant values, and that of SF6 also decreased slightly. This decrease was considered to result from the physical adsorption of water molecules on the membrane surface or on the inside of the pore surfaces in the membrane, which resulted in a decrease of effective pore size for gas permeation. In addition, a regeneration procedure of the membrane was investigated. When the membrane was treated at 573 K with pressurized H2 streaming in one side while depressurizing the other side, the permeance of each gas recovered considerably. This is because the physically adsorbed water molecules detached during the regeneration process. However, the recovery of N2 permeance was not so excellent, probably because a slight amount of adsorbed water molecules was remained even after the regeneration inside the pores where N2 can originally permeate, which greatly reduced the effective pore size for N2 permeation.