A novel process and material for the separation of carbon dioxide and hydrogen sulfide gas mixtures

Carbon fiber composite molecular sieve (CFCMS) synthesis and characterization of the macro-, meso- and micropore structure are reported. CFCMS physical properties, including strength, thermal conductivity and electrical resistivity, are reported and the thermal conductivity of CFCMS compared with literature data for granular activated carbon (GAC) and packed beds of GAC. Adsorption studies, including isotherms for CO2 and CH4 at temperatures of 30, 60 and 100 degrees C on CFCMS samples activated to different burn-offs, are reported. High pressure adsorption data for CO2 and CH4 show that the CFCMS material has sufficient selectivity for CO2 over CH4 for a commercial separation. Breakthrough experiments were conducted for CO2/CH4 and H2S/H-2 gas mixtures and the selective separation of CO2 and H2S was demonstrated. The electrical conductivity of our novel monolith was exploited to effect the rapid desorption of adsorbed gases. Desorption at low applied voltage was accompanied by a heating of the CFCMS to temperatures <100 degrees C. The passage of greater electrical current (similar to 14 A at 3.25 V) caused the CFCMS temperature to exceed 300 degrees C. During desorption, the release of adsorbed gas was noted to occur prior to a rise in CFCMS bulk temperature. It is demonstrated that the heat of adsorption is responsible fbr this phenomenon. The relationship between the carbon fiber structure, electrical behavior, and the desorption characteristics of CFCMS are discussed. A preliminary design of an ''electrical swing adsorption'' (ESA) system is outlined. Potential uses of the CFCMS/ESA technology are suggested. (C) 1997 Elsevier Science Ltd.