CO2 capture by aqueous ammonia with hollow fiber membrane contactors: Gas phase reactions and performance stability

A critical challenge involved in developing membrane contactor technology for CO2 capture by aqueous ammonia is ensuring long-term performance stability in industrial application. When working at low temperatures and with dry inlet gas, this study demonstrates precipitation fouling due to crystallization of ammonium salts using a commercially produced composite membrane contactor (Oxyplusi). The fouling occurred on the lumen side of the membrane where the gas circulated. Experiments performed using a CO2/N-2 mixture saturated with water vapor to mimic real flue gas, interestingly, showed stable performance and no fouling. Experiments were performed at different operating temperature. Under all conditions, with and without solid salt formation leading to fiber fouling, an aqueous solution formed inside the fiber lumen. In this solution, 76% of the ammonia leaking from the shell side and 12% of CO2 feed was captured. The aqueous solution formed in the lumen can be easily separated to recover the ammonia content, which under the tested conditions, resulted in lower ammonia loss than what would be expected in a packed column.