Effect of physically adsorbed water molecules on the H ₂-selective performance of a silica membrane prepared with dimethoxydiphenylsilane and its regeneration

The effect of exposure to humid conditions at room temperature on the H ₂-selective performance of a dimethoxydiphenylsilane (DMDPS)-derived silica membrane was studied. Immediately after exposure to air with 20% relative humidity, the permeances of H ₂ and N ₂ decreased drastically and then kept constant values, and that of SF ₆ 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 573K with pressurized H ₂ 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 N ₂ permeance was not so excellent, probably because a slight amount of adsorbed water molecules was remained even after the regeneration inside the pores where N ₂ can originally permeate, which greatly reduced the effective pore size for N ₂ permeation.