Thermodynamic and molecular insights into the separation of ethanol/ ethyl propionate by extraction using low transition temperature mixtures

Low-transition temperature mixtures (LTTMs) have been proposed as green solvents for the separation of ethanol (EtOH)/ethyl propionate (EtPa) azeotropes. COSMO-SAC model was used to screen LTTMs, and ammonium acetate, ethylammonium chloride, and choline chloride were selected as hydrogen bond acceptors to form LTTMs with ethylene glycol. Liquid-liquid phase equilibrium experiments were carried out for the screened LTTMs and the separation system to confirm the validity of the selected solvents. And the distribution coefficients of EtOH in the three LTTMs were all greater than 1.2, and the selectivity for EtOH ranged from 6 to 50. The separation mechanism at the molecular level was revealed through quantum chemical calculations and wave function analysis. The thermodynamic behavior of the EtOH/EtPa/LTTMs system and the role of hydrogen bonding interactions were systematically investigated. The results indicated that electrostatic forces are the main molecular interactions, and the stronger interaction of LTTMs with ethanol is the basis for achieving the azeotropic separation.