Novel water-free biphasic absorbents for efficient CO2 capture

Screening tests of a number of amines and organic diluents indicated that 30% weight blends of 2-(methylamino)ethanol (MMEA) or 2-(ethylamino)ethanol (EMEA) with bis(2-ethoxyethyl) ether (DEGDEE) split into two liquid phases upon CO2 capture, an upper CO2 lean phase (mainly DEGDEE) and a lower CO2 enriched phase (mainly amine carbamate and protonated amine). These water-free biphasic absorbents have experimental CO2 loading capacity in the range 0.52-0.54. Besides batch experiments to measure the efficiency of CO2 capture and absorbent regeneration, the biphasic absorbents were tested in continuous cycles of CO2 (15% v/v in air) absorption-desorption carried out in packed columns. CO2 capture efficiency up to 97.6% was achieved with EMEA-DEGDEE and desorption temperature of the sole EMEA carbamate at 110 °C. 13C NMR analysis was used to identify and quantify the species occurring in the different liquid phases. The features of the absorbent were compared to those of 30% weight aqueous MEA. The better performances of our absorbent were greater absorption efficiency, reduced flow rate in the desorber and avoidance of any parasitic diluent to be heated in the desorption step.