Studies on absorption and regeneration for CO2 capture by aqueous ammonia

To examine the characteristics of absorption and regeneration for CO2 capture by aqueous ammonia, the removal efficiency of CO2, the pH value of solution and thermal decomposition of solid product were investigated using a continuous absorption system and TGA technique. The reaction product was analyzed by XRD method. It is observed that the initial removal efficiency of CO2 can reach 90% by 10wt% concentration of aqueous ammonia. Higher concentration of aqueous ammonia from 5 to 20 wt% enables higher CO2 removal efficiency. The physical solubility of CO2 in aqueous ammonia solvent decreases, however, with increasing absorption temperature from 20 to 50 degrees C CO2 removal efficiency increased slightly due to increase the reaction rate of the dissolved CO2 with the solvent. NH4HCO3 is the main product of the CO2-NH3-H2O reaction. The regeneration results showed there was one distinct phase in the thermal decomposition of reaction product and the mass loss value during this phase was more than 95%. An improved iterative Coats-Redfern method was used to evaluate non-isothermal kinetic parameters. The reaction order model (first order) predicted accurately the main phase in the thermal decomposition of the reaction product. The values of kinetic parameters such as E and A were different for four heating rates of 5, 10, 15, and 25 K min(-1), indicating the thermal decomposition of reaction product may depend on the conditions, especially the heating rate in dynamic experiments. Based on the experimental results, system design of CO2 capture by aqueous ammonia was also discussed. (C) 2011 Elsevier Ltd. All rights reserved.