Separation of CO₂ from gas mixtures with liquid membranes

Conventional ethanolamine based CO₂ removal processes are not energy efficient. Separation by membranes may provide considerable energy savings over conventional processes. Ideally, to be economically competitive, a membrane should not only be highly permeable, it should also have higher selectivity for the component to be separated. However, permeability and selectivity of common polymeric membranes are, in general, inversely related. Mass flux as well as selectivity of permeation can be improved by employing reactive liquid films immobilized on a sheet of microporous filter as a substitute to solid polymeric membranes. Mixtures of various amines such as monoethanolamine (MEA), diethanolamine (DEA), and amino-methyl-propanol (AMP) and polyethylene glycol (PEG) were immobilized in a microporous polypropylene film and placed in a permeator. The permeabilities of CO₂ and other hydrocarbon gases through the immobilized liquid membrane were measured under low pressure differential and isothermal conditions. The permeation characteristics and trans-membrane flux show favourable separation as compared to the conventional polymeric membrane. Separation factors as high as 145 were obtained. Environmental implications of the results for gas processing industry are discussed.