Abstract
The separation of hydrogen from synthesis gas is a major cost element in the manufacture of hydrogen from coal. Separation of these gases by membranes is an alternative technique that is still largely unexplored and that could offer substantial cost savings. The authors have been developing membranes for this application at Membrane Technology and Research, Inc. Most of this work has been supported by the U.S. Department of Energy. There are three opportunities for membrane separation in the production of hydrogen from coal: (1) The separation of hydrogen from carbon monoxide before the shift reactor. (2) The separation of hydrogen from carbon dioxide and hydrogen sulfide after the shift reactor. (3) The separation of hydrogen from nitrogen after the acid gas removal in an air-blown gasification process. After reviewing polymer permeability data available in the literature or obtained at MTR, two polymers were selected for membrane development work: (1) Poly(etherimide) for the separation of hydrogen from nitrogen and from carbon monoxide. (2) Poly(ether-ester-amide) for the separation of hydrogen sulfide and carbon dioxide from hydrogen. After characterizing the membrane properties of relatively thick (20-50 ..mu..m) films, the authors concentrated on fabricating asymmetric and composite ultrathin high-performance membranes. Asymmetric or composite ultrathin membranes in which the permselective layer is on the order of 0.5 to 1.0 ..mu..m-thick are required if usefully high membrane fluxes are to be obtained. The membranes were then tested with pure gases and gas mixtures.