Molecular Dynamics Simulation on CO2/SO2/H2S Gas Absorption by Amine-Based Deep Eutectic Solvents

Abstract

Two deep eutectic solvents (DESs), Glycerol-EtHexam and Glycerol-EtHexen, were synthesized using glycerol as the hydrogen bond donor (HBD) and 2-ethyl-hexylamine (EtHexam) or 2-ethyl-hexylethylenediamine (EtHexen) as the hydrogen bond acceptors (HBA). These were confirmed by the measurement of the phase transition temperature, FT-IR and ¹H-NMR spectra. The molecular structures of glycerol, EtHexam, and EtHexen were optimized at the M06-2X/6-311G(d,p) level using Gaussian 09 software, and were used to investigate the absorption behavior of CO₂/SO₂/H₂S mixed gases by the Glycerol-EtHexam (with mono amine) and Glycerol-EtHexen (with two amines). The results of gas absorption efficiency, molecular spatial distribution, and interaction energy showed that absorption ability followed the order: SO₂ > CO₂ > H₂S. The absorption efficiencies (Absorbed gases / total gases) of Glycerol-EtHexam for CO₂, SO₂, and H₂S were 70.7%, 95.3%, and 54.0%, respectively, while those of Glycerol-EtHexen were 74.0%, 97.3%, and 60.7%, respectively. The results revealed that as the number of amine groups in the HBA increased, the gas absorption capacity of the DESs increased correspondingly. Furthermore, MD simulations indicated that all absorbed SO₂ molecules were concentrated within the liquid phase of the DESs, whereas CO₂ and H₂S molecules were predominantly distributed at the gas–liquid interface.

Graphical Abstract