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A nonaqueous, phase-change absorbent of 2-amino-2-methyl-1-propanol (AMP)/piperazine (PZ) and environmentally friendly solvent dipropylene glycol dimethyl ether (DME) fixes a number of issues suffered by a solid–liquid biphasic solvent, such as high viscosity of the saturated solution and difficult separation and regeneration of the viscous solid. The solid phase occupies 43% of the total volume while attributes about 94% of the total loading (0.87 mol mol–1) of the solution. Beside the formation of AMP-carbamate and PZ-carbamate according to zwitterions mechanism, the coupling products of AMP/PZ-carbamate are also found in the crystal, which helps to reduce the desorption temperature during the regeneration. Because of low solubility, self-aggregation, and high lattice energy in DME, the CO2 products precipitate and form a white crystalline powder in the lower phase of the solution. Meanwhile, the solid precipitation helps the bulk solution to keep a lower partial pressure and higher diffusivity of CO2, conforming a perfect performance of CO2 capture into the biphasic solvent. The regeneration heat duty of the solvent (1.61 GJ t–1 CO2) was approximately 57% less than that of the benchmark monoethanolamine (MEA) because of its perfect performance on CO2 capture, such as high absorption loading, high regeneration efficiency, and low amount of rich phase required for regeneration. The novel absorbent has a great potential for green and sustainable CO2 capture.
Chen et al. (Mon,) studied this question.