Separation of gas mixtures in unsteady-state conditions

The prospects for the application of unsteady-state boundary conditions at the membrane inlet for increasing the selectivity of gas separation are discussed in this paper. The phenomena occurring upon passage of a concentration pulse and two-gas-component penetrant concentration waves through the membrane have been investigated. It has been shown that pulsed supply of the mixture to be separated at the membrane inlet increases the separation coefficients by a factor of several orders owing to differences in the diffusion coefficients of the gas mixture components in the membrane. Sinusoidal boundary conditions at the membrane inlet allow filtration of the amplitude of the total output oscillations from the signal of the component with a low diffusion coefficient (in this case the membrane acts as a frequency filter), which can be employed for increasing the selectivity of the sensors. The proposed techniques are exemplified by separation of the He/CO 2 gas mixture on a polymeric polyvinyltrimethylsilane (PVTMS) membrane. Introduction At present, the membrane separation of gas mixtures is performed exclusively in steady-state conditions. The effectiveness of the gas separation process in this case is determined mainly by the transport characteristics of the membrane material. The purpose of the present communication is to consider the prospects for application of unsteady-state boundary conditions for experiments (a pulsed version of the permeability method and the method of concentration waves) on membrane separation of gas mixtures. Theoretical aspects of the method are considered. Experimental testing of the method is exemplified by the separation of the He/CO 2 mixture in the process of diffusion across polyvinyltrimethylsilane (PVTMS) films