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 CO 2 absorption with high absorption–desorption efficiency. To optimize the CO 2 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 CO 2 absorption with sulfolane as the phase splitter and generate a CO 2 -rich upper-phase and a CO 2 -lean lower-phase. An equimolar absorption (1.023 mol CO 2 /mol DMAPA), a high initial absorption rate (0.106 mol/(L*min)), a low viscosity (10.96 mPa . s) and a high CO 2 loading (3.68 mol/L) of the CO 2 -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 CO 2 absorption were identified by 13 C NMR, not only further identifying the CO 2 -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.