Liquid-Liquid Extraction of Lower Alcohols Using Menthol-Based Hydrophobic Deep Eutectic Solvent: Experiments and COSMO-SAC Predictions

The lower alcohols tend to form azeotropic solution with water which makes the separation challenging. The current work primarily focuses on the synthesis and application of a menthol-based hydrophobic deep eutectic solvent (DES) for the removal of lower alcohols from its aqueous solutions. The DES is synthesized by the addition of DL-menthol and lauric acid (dodecanoic acid) with a molar ratio of 2:1. Liquid-liquid equilibria (LLE) experiments are then performed to evaluate the performance of the synthesized DES for the extraction of lower alcohols such as ethanol, 1-propanol, and 1-butanol. LLE corresponding to the pseudo ternary systems of lower alcohols (1-butanol, ethanol, and 1-propanol) + hydrophobic DES + water are measured at T = 303.15 K and p = 1 atm. The composition of the tie lines were evaluated using H-1 NMR analysis for both extract and raffinate phases. Thereafter, the extraction efficiency of the DES is analyzed and compared by determining the solute distribution coefficients and the selectivity values. Finally, the experimental LLE data for the systems were regressed using the excess Gibbs free energy model, namely the Non Random Two Liquid (NRTL). Further the predictions of the tie lines were also confirmed through the COnductor like Screening MOdel Segment Activity Coefficients (COSMO-SAC) model. The average root-mean-square deviations (RMSD) obtained were 0.01 and 0.07 for NRTL and COSMO-SAC model, respectively.