Semi-batch absorption and regeneration studies for CO 2 capture by aqueous ammonia

Abstract

Carbon dioxide transfer capacities of aqueous ammonia solution and monoethanolamine (MEA) solution were compared. The ammonia process for CO 2 capture was simulated using a semibatch reactor, where the flow of gas is continuous. The CO 2 carrying capacity in g CO 2 per g of NH 3 solution (8 wt.%) circulated is 0.07 as compared with 0.036 g CO 2 per g MEA solution (20 wt.%). The energy requirement for liquid mass circulation of ammonia solution is approximately 50% of MEA solution for equal weight of CO 2 carried. In another comparison, the thermal energy required to regenerate CO 2 from the rich solution is substantially less as compared to the MEA process. A 3-cycle absorption–regeneration test was conducted in the semibatch reactor to simulate an approach-to-steady state in a flow system. pH values of the absorbent solution was found to oscillate between 9.6 (CO 2-lean) and 8.8 (CO 2-rich) under the test conditions. Thermodynamics study shows that ammonium bicarbonate required the least thermal energy among the ammonium compounds for CO 2 regeneration.