Research on Alkanolamine-Based Physical-Chemical Solutions As Biphasic Solvents for CO₂ Capture

CO₂ capture using biphasic solvents is a promising technology for a significant reduction in regeneration energy. However, the existing biphasic solvents suffer significant amine loss because volatile tertiary amines with a high concentration (∼60 wt %) are used as the phase separation promoter. To address this drawback, high boiling point physical solvents were employed into aqueous alkanolamines to exploit a biphasic solvent for CO₂ capture. We utilized diethylene glycol dimethyl ether (DEGDME) and sulfolane as the phase separation promoters and developed 2-amino-2-methyl-1-propanol (AMP)/monoethanolamine (MEA) blend-based physical-chemical biphasic solvents. Distribution of CO₂ loading, amine species, physical solvents, and water in the two phases after CO₂ absorption were investigated to optimize the phase separation behavior. ¹³C NMR analysis indicated that CO₂ absorption in an AMP/MEA-based physical-chemical solution is first dominated by CO₂ reaction with MEA and then followed by the hydrolysis reaction of AMP carbamate at high CO₂ loading. The physical solvents facilitate the extraction of water and CO₂ reaction products and result in liquid phase separation. The CO₂ absorption rate in AMP/MEA-based physical-chemical solution is faster than in aqueous AMP/MEA. The optimal AMP/MEA-based physical-chemical biphasic solvent shows a 69% higher CO₂ capacity and a 36% lower regeneration energy than 30% MEA. Further, both effects of increased viscosity and the phase separation on the regeneration energy were evaluated.