Reverse osmosis molecular differentiation of organic liquids using carbon molecular sieve membranes
Carbon sieving to separate the similar Separating organic molecules, particularly those with almost equal sizes and similar physical properties, can be challenging and may require energy intensive techniques such as freeze fractionation. Taking inspiration from reverse osmosis of aqueous fluids, Koh et al. describe the synthesis, characterization, and mass transport performance of carbon molecular sieve membranes for the separation of liquid phase organic molecules at room temperature. This technique is capable of separating very similar isomers, such as ortho and para xylene, on an industrial scale. Science, this issue p. 804 Carbon membranes efficiently separate similarly sized organic liquid molecules and isomers. Liquid phase separations of similarly sized organic molecules using membranes is a major challenge for energy intensive industrial separation processes. We created free standing carbon molecular sieve membranes that translate the advantages of reverse osmosis for aqueous separations to the separation of organic liquids. Polymer precursors were cross linked with a one pot technique that protected the porous morphology of the membranes from thermally induced structural rearrangement during carbonization. Permeation studies using benzene derivatives whose kinetic diameters differ by less than an angstrom show kinetically selective organic liquid reverse osmosis. Ratios of single component fluxes for para and ortho xylene exceeding 25 were observed and para and ortho liquid mixtures were efficiently separated, with an equimolar feed enriched to 81 mole para xylene, without phase change and at ambient temperature.
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