Amino acid salts have potential use as alternative absorbents to alkanolamines for post combustion CO 2 capture, because of their negligible volatility, resistance to oxidative degradation and fast absorption rates. In this work, the density and viscosity of CO 2 -free and CO 2 -loaded aqueous solutions of potassium lysinate (LysK) and potassium prolinate (ProK) were measured at temperatures from (298.15 to 348.15) K and for their concentrations from (0.2 to 3.0) mol L −1 . The data were correlated accurately ( R 2 ≥ 0.99) as a function of temperature, concentration and CO 2 loading by nonlinear regression analysis. The solubility of CO 2 in 2.5 mol L −1 amino acid salt solutions was also determined in vapor–liquid equilibrium vessels at temperatures (313 and 333) K and CO 2 partial pressures relevant to flue gas conditions. It was found that, the CO 2 absorption capacity of LysK is higher than that of industrially used monoethanolamine (MEA) and the CO 2 loadings vary as LysK > ProK > MEA at given CO 2 partial pressures. Moreover, LysK may offer higher cyclic loading than MEA for CO 2 capture.
Water-lean phase change amino acid salts (AAS) are of great interest as potential absorbents for post-combustion CO 2 capture. In this work, effect of water content in the absorbent containing potassium prolinate (ProK) and 2-butoxyethanol (EGBE) on the phase behavior and capture performance was investigated to mimic water accumulation during wet flue gas treatment. Three types of phase separation behaviors were observed for the first time after CO 2 absorption from the homogenous liquid, as increasing water content in the absorbent. Phase change mechanisms were proposed based on composition analysis of each phase, which can well explain the improved regeneration efficiency by desorbing CO 2 -rich phases for the three-phase system. Noticeably, forming liquid–liquid-solid phase change for water-lean ProK/EGBE absorbent shows a promising strategy with advantages of high energy efficiency and water balance management for CO 2 capture.
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