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Water as a solvent remains the weakest point of CO2 capture systems using aqueous chemical absorbents due to large heat capacity and latent heat of water. Water-lean absorbents including low volatile solvent have been considered as potential use for CO2 capture in terms of reducing energy consumption. In this work, we have examined the capture performance of several water-lean amino acid salts. Ethylene glycol (EG) with high boiling point and low specific heat was used to replace water. The physical properties and the absorption and desorption rate of CO2 were determined and evaluated for potassium lysinate (LysK)/​EG/​water and potassium prolinate (ProK)/​EG/water. Aqueous monoethanolamine (MEA), ProK, and LysK systems were used for comparison. The samples from the absorption test and continuous absorption–desorption cycles were analyzed by NMR spectra to provide insight into the product species and the stability of absorbent. Absorption mechanisms and degradation species were also discussed as well as the main issues such as high viscosity of CO2-free/​loaded absorbents and high desorption temperature related to these EG-based water-lean systems.

Aqueous monoethanolamine (MEA) is widely used for CO2 capture and has been demonstrated as an effective absorbent in many postcombustion capture plants. However, several disadvantages such as toxicity, high volatility, solvent degradation, and high energy consumption were reported in the practical applications. Aqueous amino acid salts, particularly potassium lysinate (LysK), are considered as attractive alternatives to MEA. A comparative study of absorbent characteristics of aqueous LysK (2.0 M and 2.5 M) and aqueous MEA (5.0 M) was conducted in this study. The absorption and cyclic capacities, absorption and desorption rate, solubility of CO2, and heat of absorption were measured using a stirred batch-type reactor and a CPA201 reaction calorimeter under similar postcombustion capture conditions. Thermal and oxidative degradation was also evaluated for aqueous 2.0 M LysK at 383 and 423 K under static N2 and O2 exposure conditions for 15 days. Samples were analyzed by total alkalinity and 13C and 1H NMR spectra to provide insight into the degradation products. The advantages of the comparable CO2 capture performance, high stability, and low solvent loss compared to the state-of-the-art solvent MEA, suggest LysK can be a potentially advantageous absorbent for industrial CO2 capture processes.

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