Performance analysis of ammonia solution for CO2 capture using microporous membrane contactors

• CO2 capture with ammonia solution was modeled in a hollow fiber membrane contactor.
• Ammonia solution can remove CO2 very effectively at ambient temperature.
• Effects of NH3 evaporation, liquid temperature and NH3 concentration were studied.
• Removal efficiency reduces dramatically with membrane wetting at low temperatures.
• NH3 has better performance compared to DEA at both wetted and non-wetted cases.

Aqueous ammonia solution has recently been proposed for separation of CO2 from flue gas because of the low cost of regeneration. In the present work, this promising absorbent has been applied for CO2 separation from a gas mixture in a microporous hollow fiber membrane contactor. To obtain the two-dimensional concentration profiles in the liquid, membrane and gas phases, the coupled partial differential equations were solved using a numerical technique. The proposed model was validated with the experimental data of CO2 absorption by diethanolamine solution due to lack of experimental data of CO2-ammonia system in membrane contactors. The effects of ammonia evaporation, liquid temperature and ammonia concentration were studied using the model. Evaporation of ammonia increases if a concentrated solution is used for CO2 separation, however it can be restricted effectively by controlling the absorbent temperature and concentration. The effects of gas and liquid velocities showed that the mass transfer resistance of liquid phase is negligible. It was found that ammonia solution can remove CO2 effectively even under the wetting of membrane pores. The results revealed that ammonia solution has a better performance compared to diethanolamine solution, and it is an attractive absorbent for sequestration of CO2 using membrane contactors.