Comparative evaluation of CO2 capture from flue gas by [Emim][Ac] ionic liquid, aqueous potassium carbonate (without activator) and MEA solutions in a packed column

The objective of the present work is to study and compare CO2 capacity absorption into 1-Ethyl-3-methylimidazolium acetate ionic liquid, [Emim][Ac], the aqueous 15w% MEA and 28w% K2CO3 (without activator) solutions, in a packed column. The CO2 absorption experiments were conducted in an absorbing column packed with randomly placed Rraschig rings. The gas mixture stream has a typical composition of post-combustion processes consisting of CO2 (7% v/v) diluted in N2 was used to test CO2 absorption in all experiment under 4 bar at T = (343.15, 348.15, 353.15) K. In this work the effect of temperature, gas and liquid flow direction on CO2 absorption at constant pressure and inlet CO2 concentration were examined. The comparison of the used IL with both the aqueous MEA and K2CO3 solutions was done for the same absorption conditions. The results show that the aqueous MEA has the highest KOverall followed by the aqueous K2CO3 (without activator) and the [Emim][Ac] has shown the least KOverall. Experimental evidence suggests that for the same amount CO2 absorption from the gas mixture, the [Emim][Ac] needs much longer times than both the absorbents under investigation. The [Emim][Ac] shows enhancement by chemical absorption, being obtained the value of enhanced factor, EA, higher than 44. Consequently at higher temperatures the [Emim][Ac] behaves more efficiently. In case of the [Emim][Ac], the overall mass transfer increased significantly, from 2.812 to 4.187 × 10−6 ms−1 as the temperature rises. Nevertheless in cases of using the aqueous MEA and K2CO3 solutions this remains constant for the temperature interval 343.15-353.15 K. The behavior of the [Emim][Ac] was correlated with the mass transfer enhanced by the chemical reaction. The results show that liquid side mass transfer coefficient using packed bed contactor with the studied ionic liquid is lower than with both the absorbents. This can be attributed to significant impact of the viscosity of the ionic liquid as an important factor in the mass transfer and therefore in the separation in comparing with both the absorbent. At 343.15 K and 4 bar, on mass basis (kg CO2/kg absorbent), the studied IL showed 7% more CO2 absorption capacity than the aqueous MEA and 26% more than the aqueous K2CO3 (without activator) solutions.