Polymeric facilitated transport membranes for hydrogen purification

The most widely used method of hydrogen production, steam methane reforming, yields a product stream consisting mainly of hydrogen (H(2)) and carbon dioxide (CO(2)) Purification of this product is currently accomplished using amine-based acid gas scrubbers or pressure swing adsorption technology. Membranes are well suited to bulk CO(2) removal and offer a viable alternative to these established technologies. This review considers one type of such membranes, polymeric facilitated transport membranes. These membranes selectively permeate CO(2) by means of a reversible reaction between the gas and the membrane material. In addition, the membrane provides a barrier to H(2) permeation. The result is removal of the CO(2) contaminant and recovery of the H(2) product at high pressure, eliminating the need for recompression prior to use or storage. A wide range of polymeric materials have been investigated, including ion-exchange resins, hydrophilic polymers blended with CO(2)-reactive salts, polyelectrolytes, fixed-site carrier polymers, and biomimetic materials. This review provides a description of the reaction chemistry of facilitated transport, a summary of membrane permselective properties, and suggestions for future research efforts.