Novel diamine DMAPA-sulfolane-water biphasic absorbent for equimolar CO2 absorption: Performance and mechanisms

A novel diamine-based biphasic absorbent, 3-(Dimethylamine)-1-propylamine (DMAPA)-Sulfolane-Water, was proposed for equimolar CO2 absorption with high absorption–desorption efficiency. To optimize the CO2 capture performance of the proposed DMAPA-Sulfolane-Water biphasic absorbents, the phase separation experiments and the absorption–desorption cyclic experiments were conducted. The results indicated that the DMAPA-Sulfolane-Water biphasic absorbent could realize a liquid–liquid phase separation performance after CO2 absorption with sulfolane as the phase splitter and generate a CO2-rich upper-phase and a CO2-lean lower-phase. An equimolar absorption (1.023 mol CO2 /mol DMAPA), a high initial absorption rate (0.106 mol/(L*min)), a low viscosity (10.96 mPa.s) and a high CO2 loading (3.68 mol/L) of the CO2-rich upper-phase, a high desorption efficiency (92 %), and high cyclic stability were obtained due to the interaction of the intramolecular primary and tertiary amino groups in DMAPA. The minimum volume percentage of the rich phase was as low as 32 % of the total volume. In addition, temperature was confirmed to be an essential factor in the absorption and desorption process. The species in the two phases after CO2 absorption were identified by 13C NMR, not only further identifying the CO2-rich upper-phase but also revealing the mechanism of equimolar absorption by the DMAPA-Sulfolane-Water biphasic absorbents because of the high carbon peak of carbamic acid (DMAPACOOH) in the upper-phase. The quasi-salting out effect and the improved polarity of the solvents were proved to trigger the phase separation.