Evaluation of the novel biphasic solvents for CO2 capture: Performance and mechanism

Abstract

For its high potential in reducing energy penalty of power plant, the biphasic solvent for CO2 capture has recently attracted increasing attention. In this work, a novel blend of N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) and diethylenetriamine (DETA) was used to obtain a liquid-liquid phase separation solvent. The CO2 absorption loading of the PMDETA-DETA solvent (5M, 4:1) was 0.613mol CO2/mol of total amine, in which 99.7% of the capacity was contributed by the lower phase with 57% of the total volume. In addition, the PMDETA-DETA solvent maintained a high CO2 absorption capacity and good phase separation at 30–60°C. Based on the absorption results and the 13C NMR analysis, the reaction mechanism of CO2 absorption into PMDETA-DETA solvent was clarified. In the blend system, DETA played as a reactant to attack CO2 and PMDETA played as a proton acceptor to deprotonate the zwitterion. Therefore, the presence of PMDETA in the solution helped DETA to react with CO2 rather than participate in the deprotonation process of zwitterion, which ensured a high CO2 absorption capacity. The phase change mechanism indicated that, as more CO2 was absorbed into the system, the more products of carbamate and HCO3−/CO32− migrated to the lower phase while more PMDETA migrated to the upper phase, which led to the phase separation.