Investigation of the CO2 capture behavior in multiple-site natural deep eutectic solvents

The sustainable development of carbon dioxide (CO2) resource requires the realization of green and efficient capture for the fossil fuel CO2. However, the high operation costs and biological toxicity have hampered the application. Natural deep eutectic solvents (NADESs) are efficient and green CO2 absorbent. In this manuscript, kinds of amino acid-based NADESs were prepared successfully to improve the absorption efficiency of CO2 capture solvent. The chemical structure of NADESs was characterized, and the thermal stability was also measured. The CO2 capture behavior of amino acid-based NADESs was investigated. With multi-reactive sites, unstable stage and more accessibility of alkyl structure on HBA (alkyl amino acids and aromatic amino acids, especial L-Ary), and less electronegativity on HBD (EG), L-Arg/EG NADESs had lower solvation effect (β value, 1.286) and reduced viscosity (48.33 mpa.s at 60 ºC). It behaved better absorption capacity. The optimized conditions by single-factor analysis and Response surface methodology were L-Arg/EG at the mole ratio of 1:5, 30 °C and 200 mL/min, and the absorption could reach 0.81 molCO2/kgNADESs. Additionally, an insight into the reaction mechanism was investigated. It was found that hydrogen-bond structure played an important role in CO2 capture. The broken of H-O···H-N formed by amino acids and ethylene glycol promoted the formation of new bonds of -(O=)C···NHR between L-Arg/EG and CO2, thus achieved higher CO2 capture. The investigated proved that the green solvent amino acid-based NADESs could be efficient absorbents for CO2 capture.