Ion Exchange Resins as Reversible Acid Gas Absorbents

Strongly basic anion exchange resins containing quaternary ammonium functionality and fluoride or acetate anions were found to remove carbon dioxide and hydrogen sulfide from gas streams. The absorption/desorption isotherms, heats of absorption, and gas separation properties were determined for a series of such resins. The fluoride form of Amberlyst® A-26, for example, absorbed CO2 and H2S reversibly, 0.23 mol CO2/mol F− and 0.24 mol H2S/mol F− at 100 kPa and 22 and 30°C, respectively. Absorption of CO2 was fast compared to its desorption. Characterization by NMR indicated that bicarbonate was formed by reaction of CO2 with F− containing resins. Heats of CO2 absorption by F− Amberlyst® A-26 were pressure dependent and ranged from −5.0 to −3.2 kcal/mole CO2 for pressures of 50 to 1000 kPa. The fluoride and acetate containing resins were effective for removal of CO2 and H2S from gas mixtures. Passage of a gas mixture containing 1% CO2 or 5% H2S through a packed column of F− Amberlyst® A-26 at 22°C reduced the CO2 or H2S concentration to less than 25 ppm. Regeneration of the absorbents was accomplished by purging with inert gas at 50°C. Removal of CO2 from gas streams containing substantial water vapor concentrations was achieved using F− Amberlyst® A-26 resin.