Liquid-Liquid Extraction of Toluene from n-Heptane Using Butane-1,4-diol + 2-Methyl-pentane-2,4-diol Liquid Mixtures

In order to investigate the effect of using 2-methyl-2,4-pentanediol as a co-solvent to 1,4-butanediol in the extraction of toluene from n-heptane, liquid-liquid equilibrium (LLE) phase compositions (tie-line data) were experimentally measured and thermodynamically modeled for the system n-heptane + toluene + 1,4-butanediol + 2-methyl-2,4-pentanediol at 298.2 and 313.2 K and 0.1 MPa. The direct analytical method was used to obtain the LLE data using a double-walled glass cell. The phase equilibrium samples were quantitatively analyzed using gas chromatography. The quaternary systems were successfully correlated using the NRTL and UNIQUAC thermodynamic models. Selectivity and solvent capacity were evaluated at various concentrations of co-solvent and compared to that of using pure 1,4-butanediol. The pseudo-ternary systems studied were found to demonstrate type II or type I phase behavior depending on temperature and co-solvent concentration. The presence of 2-methyl-2,4-pentanediol was found to have significantly improved solvent capacity at the cost of reduced selectivity.