Novel alkanolamine-based biphasic solvent for CO₂ capture with low energy consumption and phase change mechanism analysis

Biphasic solvents for CO₂ capture have received significant attention due to their potential for energy conservation. However, traditional biphasic solvents result in highly viscous CO₂ rich-phases and high amine losses. To overcome these drawbacks, we have developed a novel alkanolamine-based biphasic solvent by blending 2-(methylamino) ethanol (MAE), 3-(dimethylamino)propan-1-ol (3DMA1P), diethylene glycol dimethyl ether (DGM), and water. The aqueous MAE/3DMA1P/DGM solvent showed a cyclic capacity of 0.45 mol CO₂/mol amine, which is 1.8 times that of monoethanolamine (MEA), and a desorption rate and regeneration efficiency twice those of MEA. The viscosity of the biphasic solvents can be reduced to 13.12 mPa⋅s at 313 K, which is lower than that of reported biphasic solvents. The evaluated regeneration energy was 2.33 GJ/ton CO₂. Cation chromatography measurements revealed the tendency of MAE to accumulate in the CO₂-rich phase with increasing CO₂ absorption loading. Quantitative ¹³C NMR analyses were performed to investigate the species distribution in both phases, and DGM was found to be the major component of the CO₂-lean phase. Different solubilities of the MAE molecules and MAE carbamate in DGM resulted in phase separation. Molecular dynamics (MD) simulations on the CO₂-unloaded and CO₂-loaded solutions verified the phase separation mechanism. MAE molecules tended to cluster, and the interactions between MAE and DGM dropped significantly, with increasing DGM concentration.