A study on degradation and CO2 capture performance of aqueous amino acid salts for direct air capture applications

We have previously proposed amino acid salts solutions as potential absorption liquids for direct air capture (DAC) of CO₂ from the atmosphere. However, little is known about their relevant CO₂ solubilities, CO₂ mass transfer rates, and susceptibility to oxidative and thermal degradation under conditions relevant to DAC. We report here on the overall solubility of CO₂ and CO₂ mass transfer rates into a series of amino acid salts solutions. Additionally, the robustness of various amino acid salt solutions to thermal and oxidative degradation has been assessed.

CO₂ absorption rates into the amino acid salts solutions were observed to be in the same order of magnitude as aqueous monoethanolamine (MEA), with sarcosinate and lysinate solutions providing the fastest and slowest CO₂ mass transfer rates at 25°C, respectively. Degradation data revealed that all amino acid salt solutions investigated in this study displayed elevated rates of thermal degradation at both 120 and 150°C relative to MEA. The opposite trend was observed with respect to oxidative degradation where all amino acid salt solutions showed a greater resistance to oxidative degradation than that observed for MEA under the conditions investigated here. Considering the degradation, CO₂ absorption capacity, and CO₂ mass transfer rate data, we propose the potassium salts of proline and sarcosine as the most promising amino acid salts (of those considered here) for further evaluation in DAC processes. Overall, this study provides valuable insight into the suitability of various amino acid salt solutions as absorption liquid for DAC. © 2024 The Author(s). Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.