Anisotropic membrane materials for gas separations

To date the design of membranes for gas separations has relied on isotropic materials that control the magnitude of mass flux. However, mass flux is a vector quantity and controlling its direction is essential for complete manipulation of diffusion processes. In this article, we show how anisotropic materials enable control of mass flux direction in membranes and allow for novel mechanisms for gas separation. We present a detailed study of the design parameters that control membrane selectivities and permeances and demonstrate that this new class of membranes can provide a new avenue to obtain significant improvements with respect to isotropic materials. We also discuss how the proposed anisotropic membranes can be constructed using isotropic materials. Mass diffusion principles for gas separations in anisotropic membranes are different from those in isotropic materials and this novel strategy for the design of membranes can open new opportunities in membrane separation processes.