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 (similar to 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-l-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. C-13 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.