On the gas-separation properties of two-layer porous membranes

The peculiarities of the flows of binary gaseous mixtures through two-layer membranes are investigated at different orientations of the membranes with respect to the flows. The separation properties of the membranes are shown to depend on the membrane orientation and to dramatically decrease when supporting coarse layers are located before the finely disperse active layer with respect to the direction of a gaseous mixture flow through the membrane. The consecutive location of the layers with increasing average pore sizes along the flow direction appears to be more advantageous. The magnitude of the asymmetry effect significantly depends on the parameters that characterize the Knudsen and bulk diffusion and the viscous transfer of a gaseous mixture.