Energy-efficient carbon dioxide capture using a novel low-viscous secondary amine-based nonaqueous biphasic solvent: Performance, mechanism, and thermodynamics

Biphasic solvents have been widely studied for CO2 capture due to their remarkable energy-saving potentiality. However, most existing biphasic solvents suffer from the high viscosity of their CO2-rich phase. This study proposed a novel low-viscous secondary amine-based nonaqueous biphasic solvent for CO2 capture. With dimethyl sulfoxide (DMSO) as the organic diluent and pentamethyldiethylenetriamine (PMDETA) as the phase splitting agent, the secondary amine of 2-methyl-ethynolamine (MAE) was proved to be the optimal candidate for preparing the biphasic solvent. The MAE/DMSO/PMDETA (M/D/P) biphasic solvent could realize a high CO2 loading of 0.84 mol mol−1 and the viscosity of its CO2-rich phase was only 8.87 mPa s, which was significantly lower than that of most reported biphasic solvents. The reaction mechanism analysis revealed that M/D/P absorbed CO2 to form products of protonated amines, carbamate, and carbamic acid species. Since the products were polar and showed a stronger affinity to polar DMSO, while less polar PMDETA was isolated, thereby resulting in a phase change. Thermodynamics analysis showed that the M/D/P biphasic solvent could sharply cut down the sensible heat and latent heat during CO2 desorption. Eventually, the total regeneration energy penalty of M/D/P was significantly reduced by 46.3% compared with the benchmark aqueous MEA solution.