Membrane Gas Separation

Membrane gas separation is a widely applied, energy-saving separation process, which can provide a high separation factor and high permeation rate. This chapter surveys some important knowledge of this process focusing on permeability and mass transport rate, which determine the separation performance. It discusses the characterization of the membrane, the solution/diffusion model, based on thermodynamics, solubility, and adsorption isomers, mass transport through dense and porous membranes, as well as mass transfer rate with diluted and binary mixtures. In the latter case it takes into account the convective velocity induced by the diffusive flow of the components. Bulk convective phase transport consists of two parts. One part is induced by the diffusive fluxes of the components and the second part is generated by the transmembrane pressure difference. In special cases, both parts should be taken into account. This review also analyses the effect of pore size on the transport mechanisms of components. Finally, it defines the binary mass transfer rates in the presence of an external polarization layer in cases of homogeneous and asymmetric, two-layer membranes.