New Coating Techniques for Composite Membranes

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Membrane diffusion is an inherently slow process. Consequently, membrane-based separation processes can only be economically viable if extremely thin, defect-free membranes are used. Thin-film composite membranes with a permselective layer thickness down to about 0.5 um can be made by presently available techniques. Membranes with permselective layers thinner than this would dramatically improve the economics of membrane separation. The goal of this program is to develop the technology for making industrial-scale composite membranes with permselective layer thicknesses down to 0.1 um or below. The membranes will be made by modifying the solution coating process used to apply the thin permselective layer. The coating solutions to be used will be characterized in having high viscosity at low polymer concentration. Previous experimental data indicate that the use of such solutions enables a much thinner defect-free coating to be applied than is possible with conventional techniques. If the technique can be applied to many different polymers, it will enable economically viable membrane-based separation systems to be made and applied to a broad range of gas separation problems. Membranes made by the proposed process could have a significant impact on many industrial gas separations, for example, oxygen/nitrogen separation, removal of acid gases from effluent streams, or hydrogen recovery from many sources. The process economics could be sufficiently attractive to make membrane systems competitive with conventional separation methods in these and other applications.