Reversible Chemisorbents for Carbon Dioxide and Their Potential Applications

Physisorbents like zeolites, activated carbons, silica, and alumina gels have been traditionally used for separation of bulk or trace carbon dioxide from a gas mixture using a pressure or a thermal swing adsorption process. These processes are generally operated at near ambient or at moderate temperatures (say < 100 degrees C) because the equilibrium sorption capacity and selectivity of sorption of CO2 on the physi-sorbents rapidly decrease at higher temperatures. Recently, a variety of reversible CO2 chemisorbents have been developed which offer decent sorption capacity and high selectivity for CO2 at relatively higher temperatures (similar to 150 to 500 degrees C). Some of these chemisorbents even exhibit high selectivity of CO2 sorption in the presence of H2O which is mechanistically impossible for a physisorbent. Consequently, these chemisorbents can be used in (a) sorption enhanced reaction (SER) concepts for production of fuel-cell grade H, from natural gas by low temperature steam-methane reformation reaction at ca. 400-500 degrees C or from synthesis gas by water-gas shift reaction at ca. 200-400 degrees C, and (b) removal and recovery of CO2 from a flue gas at a temperature of 150-200 degrees C without precooling, predrying, and precompression. A comprehensive review of this subject is presented.