Deep eutectic solvents formed by novel metal-based amino acid salt and dihydric alcohol for highly efficient capture of CO2

Abstract

Deep eutectic solvents (DESs) are considered to be potential absorbents for CO2 capture compared to traditional amine solutions, because they have many advantages such as lower volatility and better thermal stability. In this study, a series of novel γ− and ε− m−based amino acid salts (AASs) were prepared through one-step hydrolysis reaction of accessible and cheap lactams as hydrogen bond acceptor (HBA). The chemical structures of these AASs were characterized by ESI-MS and NMR. Dihydric alcohol was selected as hydrogen bond donor (HBD) to prepare AAS-based DESs because of its low specific heat capacity and high boiling point. The physical properties of AAS-based DESs, such as density at 313.2–353.2 K, viscosity at 313.2–353.2 K, the melting temperature from 173.2 to 273.2 K, and thermal decomposition temperature from 300 to 750 K, were also determined. The gas absorption experiments were carried out on a dual-chamber at temperatures from 313.2 to 333.2 K and pressures up to 1.1 bar. It is found that K[Gaba]-EG has the largest CO2 uptake capacity with 0.12 g·g−1 at 1.0 bar and 313.2 K, better than almost all absorbent with AASs reported in literatures (0.02 g·g−1 ∼ 0.07 g·g−1). The CO2 absorption mechanisms were proved to be a combination of 2:1 and 1:1 stoichiometric reaction through thermomechanical analysis and NMR. This paper will present distinctive insights into the preparation of CO2 absorbent for effective carbon capture.