Liquid-Liquid Extraction Experiments and Molecular Mechanism Studies Based on New Deep Eutectic Solvents for Separating Biomass Derivatives in Water

Abstract

Due to technical limitations, the process of directly synthesising γ-valerolactone (GVL) based on the biomass derivative ethyl levulinate (EL) will ultimately produce wastewater containing GVL and EL that needs to be treated. In this paper, GVL and EL aqueous solutions are used as model wastewater, and seven hydrophobic deep eutectic solvents (HDESs) prepared from three terpene compounds and two fatty acids are used as extractants to carry out liquid-liquid extraction (LLE) experiments respectively, to screen the optimal HDES and the best operating conditions for the separation of this wastewater. The ability of selected hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) to form HDESs and the affinity or repulsion of HDESs and the substances to be separated were also predicted based on the COSMO-SAC model. A combined method of quantum chemistry (QC) calculations and molecular dynamics (MD) simulations was used to analyse the microscopic mechanism of action between HDESs and the components to be separated during the LLE process of model wastewater. The influence of different extraction conditions on the separation efficiency of GVL and EL was studied in combination with the experimental results of LLE. Thy-Oct (1:1) was finally selected as the optimal HDES. Under the conditions of 25 °C and a solvent ratio of 1:1, the extraction efficiency of GVL and EL in model wastewater (3%) can reach 99.95%, almost complete separation. Both the molecular simulation results and the LLE experimental results are consistent, and can be used as a reference for the separation of similar substances.

Keywords: Recovery of biomass derivatives, Quantum chemical calculation, molecular dynamics, liquid-liquid extraction, hydrophobic deep eutectic solvents