Abstract A new pressure swing membrane permeation process that can achieve significant improvement in the selectivity of a membrane possessing opposite diffusivity and solubility characteristics toward a gas pair is proposed. By operating a membrane permeator under an unsteady state, the opposite mobility and solubility selectivities of the membrane can work synergistically to accomplish a degree of separation beyond the steady-state membrane permselectivity in the following manner: along the flow direction in the feed channel, the gas mixture is separated by the selective absorption of gases into the membrane; and simultaneously across the membrane, the gas mixture is separated by the diffusivity selectivity of the membrane. The viability of the new process is supported by the results of a theoretical and experimental study on the transient responses of a membrane permeator with a silicone rubber membrane separating a helium-methane mixture. Two different operating schemes are identified in carrying out the proposed process, depending on the mobilities and solubilities of the gas species to be separated.
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