Enhancing CO2 capture of an aminoethylethanolamine‐based non‐aqueous absorbent by using tertiary amine as a proton‐transfer mediator: From performance to mechanism

Non-aqueous absorbents (NAAs) have attracted increasing attention for CO 2 capture because of their great energy-saving potential. Primary diamines which can provide high CO 2 absorption loading are promising candidates for formulating NAAs but suffer disadvantages in regenerability. In this study, a promising strategy that using tertiary amines (TAs) as proton-transfer mediators was proposed to enhance the regenerability of an aminoethylethanolamine (AEEA, diamine)/dimethyl sulfoxide (DMSO) (A/D) NAA. Surprisingly, some employed TAs such as N,N -diethylaminoethanol (DEEA), N,N,N',N'',N'' -pentamethyldiethylenetriamine (PMDETA), 3-dimethylamino-1-propanol (3DMA1P), and N,N -dimethylethanolamine (DMEA) enhanced not only the regenerability of the A/D NAA but also the CO 2 absorption performance. Specifically, the CO 2 absorption loading and cyclic loading were increased by about 12.7% and 15.5%–22.7%, respectively. The TA-enhanced CO 2 capture mechanism was comprehensively explored via nuclear magnetic resonance technique and quantum chemical calculations. During CO 2 absorption, the TA acted as an ultimate proton acceptor for AEEA-zwitterion and enabled more AEEA to form carbamate species (AEEACOO − ) to store CO 2 , thus enhancing CO 2 absorption. For CO 2 desorption, the TA first provided protons directly to AEEACOO − as a proton donor; moreover, it functioned as a proton carrier and facilitated the low-energy step-wise proton transfer from protonated AEEA to AEEACOO − . Consequently, the presence of TA made it easier for AEEACOO − to obtain protons to decompose, resulting in enhanced CO 2 desorption. In a word, introducing the TA as a proton-transfer mediator into the A/D NAA enhanced both the CO 2 absorption performance and the regenerability, which was an efficient way to “kill two birds with one stone”.