A Novel Phase-Changing Nonaqueous Solution for CO₂ Capture with High Capacity, Thermostability, and Regeneration Efficiency

A novel nonaqueous solution, triethylenetetramine (TETA) blended with polyethylene glycol (PEG200), was developed for CO₂ absorption, with which a phase-changing phenomenon was observed after the absorption. A reaction mechanism for TETA-PEG200 solution and CO₂ was proposed based on ¹³C NMR analysis. It was found that PEG200 not only acts as a solvent that contributes to biphasic separation but also gets involved in the reactions, leading to an increased CO₂ absorption capacity. Results show that 1 M TETA-PEG200 solution exhibits a high CO₂ capacity of 1.63 mol/mol TETA, which is comparable to a TETA-water solution. The capacity is only slightly affected when the temperature rises up to 60 °C. Moreover, the solution demonstrates good thermostability similar to typical functionalized ionic liquids (ILs) while presenting much lower viscosity than the ILs. For regeneration processes, microwave heating was identified to be a more effective method than classic heating. The solution shows a regeneration efficiency as high as 96% after four absorption-desorption cycles.