Separation of butyl acetate and propyl acetate from wastewater by liquid-liquid extraction and molecular dynamics simulation

Pharmaceutical production processes produce ester-containing wastewater, and the concentration of esters must be reduced to a specific limit for wastewater discharge. Therefore, this study investigated a synthetic menthol eutectic solvent to separate the ester-water mixture and meet industrial discharge standards. A deep eutectic solvent (DES) composed of menthol as the hydrogen bond acceptor and lauric acid as the hydrogen bond donor in a molar ratio of 2:1 was synthesized to study the liquid–liquid extraction experiment by separating mixtures of water and propyl acetate (PA) and water and butyl acetate (BA) at 1 atm. In addition, a temperature range of 273.15–318.15 K was used to measure the influence of temperature on the experimental results within a 5 K interval. The experimental results indicated that the increase in temperature promoted the extraction efficiency of ester to some extent, but the fluctuation range was unclear. The DES had a high distribution coefficient (β) and selectivity (S) for ester, enabling a better separation of ester and water. Thereafter, molecular dynamics (MD) simulations were performed to ascertain the mechanism of the DES extraction of esters, and the molecular simulations were used to calculate the interaction energy, radial distribution function (RDF), spatial distribution function (SDF), and self-diffusion coefficient (D). The results of the MD simulations illustrated that menthol played an important role in the extraction process, and the hydrogen bond force between menthol and ester was the main force in the extraction process. Both BA and PA were effectively removed from the water by the DES. In general, the excellent extraction ability of the DES for esters was verified by experiments and simulation, which provides solid theoretical support for ester separations in other fields.