Nonaqueous (amine + glycol ether) solvents for energy-efficient CO2 capture: New insights into phase change behaviors and assessment of capture performance

Abstract

Nonaqueous amine-based absorbents, particularly liquid biphasic solvents, have recently received increasing attention due to the potential for reducing the energy penalty of CO2 capture. In this work, a series of glycol ethers were used as cosolvents dissolving primary and secondary alkanolamines. Phase transition behavior, CO2 absorption and desorption characteristics have been investigated for the nonaqueous 5.0 M amine blends. Different phase behaviors upon CO2 absorption were discussed and well explained by the polarity change and the solubility parameter interaction distance (SPID) of components and the reaction products. Regeneration energy requirement was also experimentally estimated and compared with the reference aqueous monoethanolamine (MEA). The species in the CO2-loaded solution play a central role in regulating phase separation behaviour and CO2 capture performance. A defined SPID value was recommended to predict the monophasic and the biphasic states. Advanced systems of 2-(methylamino)ethanol (MAE) with diethylene glycol dimethyl ether (DEGDME) as liquid biphasic solvent and MAE with ethylene glycol monomethyl ether (EGME) as single phase solvent were proposed for energy-efficient CO2 capture. Among the systems investigated, MAE/EGME has the lowest regeneration energy consumption estimated at about 1.75 MJ kg−1 CO2 captured. The ionic carbonated products of alkanolamines can trigger the phase change behaviour due to their limited solubility in the more hydrophobic and weakly polar DEGDME, resulting in two opposite phases enriched in different components. Benefiting from the high enrichment (>95 %) of CO2 captured in the lower phase and the large cyclic capacity, MAE/DEGDME biphasic solvent can reduce the energy consumption by 50–59 % compared with aqueous MEA.