Abstract
New facilitated transport membranes which selectively permeate carbon dioxide from hydrogen and methane have been prepared and examined under a variety of conditions. Membranes consist of melts of the salt hydrates tetramethylammonium fluoride tetrahydrate, [(CH 3) 4N]F·4H 2O, or tetraethylammonium acetate tetrahydrate, [(C 2H 5) 4N]CH 3CO 2·4H 2O, immobilized in films of Celgard 3401®. Operating at 50°C, both membranes exhibited CO 2 permeabilities which increased with decreasing feed partial pressure of CO 2, characteristic of a facilitated transport membrane. Selectivities of CO 2 H 2 and of CO 2 CH 4 increased with decreasing feed pressure since H 2 and CH 4 permeances were independent of feed pressure. Selectivities of CO 2 H 2 were disappointingly low due to permeation of H 2 through the dense phase of Celgard®. With some difficulty, the microporous support was eliminated by construction of membranes consisting of liquid [(CH 3) 4N]F·4H 2O on the surface of a film of poly (trimethylsilylpropyne). Selectivities of CO 2 H 2 as high as 360 were then observed at low feed partial pressures of CO 2. Modeling of membrane properties is consistent with permeation of CO 2 by a facilitated transport mechanism with reasonable derived diffusivities for the chemically bound CO 2 carrier species.
Published Version
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