Phase Separation Behavior of an Activated Methyldiethanolamine-Based Biphasic Solvent for CO2 Capture

A CO 2 phase change absorbent (CPCA) is of interest because it has the potential to reduce energy consumption for CO 2 capture. Controllable phase separation behavior was expected in the development and application of a CPCA. In this study, the effects of CO 2 loading under different activators and physical solvents on the phase separation behavior of an activated methyldiethanolamine (MDEA)-based CPCA were investigated. By adjustment of the CO 2 loading, controllable phase separation behavior was achieved and the absorbent comprising an activator with more −NH– groups and a physical solvent with low E T (30) was favored to exhibit phase separation. Of special interest was that, with the increasing of CO 2 loading, phase behaviors, from the liquid phase to solid–liquid phase and then to the liquid phase, were observed for CPCA comprising MDEA/piperazine (PZ)/ N -methyl-2-pyrrolidone (NMP), which was different from all of the other known CPCAs. The solid compound was identified as PZ carbamate by X-ray diffraction (XRD), Fourier transform infrared (FTIR), and elemental analysis, and the liquid-phase samples were detected by 13 C nuclear magnetic resonance (NMR). The phase change mechanism of this special phenomenon was proposed.