Performance and mechanism of the functional ionic liquid absorbent with the self-extraction property for CO2 capture

Abstract

Regarding the bottleneck of high regeneration consumption for the amine absorbents, it was innovatively proposed in this work to construct a novel functional ionic liquid absorbent (3-Dibutylamino-propylamine-imidazole, [DBAPAH][Im]) with the self-extraction property for CO2 capture. The solvent changed from liquid-liquid two-phase to homogeneous as absorption loading increased, and it returned to a two-phase after desorption. The absorption loading of [DBAPAH][Im]-H2O solution for CO2 capture was 1.49 mol mol−1, and its regeneration efficiency was found to be 92.09% for the first regeneration and remained at 81.34% even after six cycles with a low regeneration temperature of 98 °C. It was found that this ionic liquid featured a reversible polarity, for which the polarity of [DBAPAH][Im] was much lower than that of water before absorption. The solvent changed from liquid-liquid phase to homogeneous as absorption loading increased because the polarity of the carbamate product and the Van der Waals interaction between carbamate and water were all increased. After desorption, the ionic liquid resumed with the low polarity and was not miscible in water to form an organic extraction phase, which promoted the rapid separation of the ionic liquid from the main solution and finally achieved the purpose of low temperature regeneration. Due to the coordination between cations and ions, the desorption free energy of the products formed by [DBAPAH][Im] and CO2 was very low (7.56 kJ mol−1). Furthermore, the energy consumption was estimated as 1.83 GJ t−1 CO2, which was much lower than that of benchmark monoethanolamine (MEA; 3.8 GJ t−1 CO2), and finally achieve the purpose of low regeneration temperature and low energy consumption regeneration.