A study of structure-activity relationships of aqueous diamine solutions with low heat of regeneration for post-combustion CO2 capture

The structure-activity relationship of eleven diamines and MEA was investigated in order to provide guidance for the selection of the potential CO2 capture absorbent. The effects of methyl, ethyl, hydroxyl groups, and distance between N groups in molecular structures were evaluated experimentally by using the rapid fast screening method and computed by Gaussian 09. Experimental results revealed that the proper number of methyl groups and ethyl groups on N atom could improve the absorption rate as well as the cyclic CO2 capacity, and the addition of a hydroxyl group actually achieved a lower energy requirement (i.e. cyclic CO2 capacity) for solvent regeneration with the decreasing stability of carbamate. In addition, the diamine with a hydroxyl group is more favorable for good stability in regeneration process, which addresses the problem of solvent loss in the application of diamines. Chain length extension from C-2 to C-3 can result in the poorer stability of the carbamate and lower energy requirement for amine regeneration. Thus, the lowest energy consumption (i.e. CO2 cyclic capacity) was then achieved by aqueous 2-((2-aminoethyl)amino)ethanol (AEEA) solution, presenting it can be considered as an alternative or a potential absorbent for post-combustion CO2 capture. Furthermore, the relative free energies of the tested diamines were computed by the Gaussian software for validating the stability of the carbamate formation, the order of which is in accordance with the order of the cyclic CO2 capacity for all tested amines, indicating the experimental conclusion can be reliable. (C) 2018 Elsevier Ltd. All rights reserved.