Post-combustion CO2 capture using [Emim][Ac] ionic liquid, piperazine activated N-methyldiethanolamine and promoted K2CO3 in a bench scale

Abstract

Post-combustion CO2 capture requires the focus on improvement of absorbent formulations and process efficiency to capture CO2 from flue gas streams in the plants. The present work was aimed to a comparative study of CO2 absorption capacity into 1-Ethyl-3-methylimidazolium acetate ([Emim][Ac]) ionic liquid (IL) and both the aqueous solutions of activated N-methyldiethanolamine (MDEA) with 3.8wt.% piperazine (PZ) and promoted potassium carbonate with 2.5wt.% diethanolamine (DEA) in a bench scale packed bed column. The CO2 absorption tests were conducted at pressure of 4bar and temperatures of 343.15–353.15K. The inlet gas mixture has a typical composition of post-combustion processes consisting of 7.0% (v/v) CO2 diluted with N2. The influence of temperature and gas and liquid flow directions on the CO2 absorption at constant pressure and inlet CO2 concentration were examined. The results showed that the aqueous activated 38.7wt.% MDEA solution has the highest overall mass transfer coefficient followed by the aqueous 28wt.% promoted K2CO3 solution, while the [Emim][Ac] solvent showed the least overall mass transfer coefficient. The [Emim][Ac] indicated enhancement by chemical absorption, giving a value higher than 44 for enhancement factor. Additionally, as temperature raised from 343.15 to 353.15K, only small decrease in overall mass transfer coefficients of both aqueous solutions was observed, while in the case of [Emim][Ac] IL, the overall mass transfer coefficient increased significantly. It was also found that the cocurrent flow of gas and liquid for all the absorbents takes more absorption time than the countercurrent flow case. The liquid side mass transfer coefficient of the IL was lower than both the traditional activated absorbents. This can be attributed to significant impact of the IL viscosity as an important factor on mass transfer flux. At 353.15K and 4bar, the studied IL showed 29% more CO2 absorption capacity than activated MDEA solution and 16% more than promoted K2CO3 solution. Based on this study, the investigated solvents showed promising capability for removal of CO2 from post combustion flue gases emitted in industrial plants.