A comparative study on liquid phase equilibria of aqueous mixtures of two structurally close carboxylic acids with sec-amyl alcohols at 298.2 K

Abstract

This research reports the results of measurements on liquid-liquid equilibrium (LLE) for the four ternary systems of (water + butyric or 3-methylbutyric acids + sec-amyl alcohol) and (water + butyric or 3-methylbutyric acids + sec-isoamyl alcohol) at 298.2 K and 0.1 MPa. According to the measured solubility and tie-line data, the related phase diagrams for the studied systems were plotted. Due to the strong structural similarity of the studied system's constituents, the influence of the chemical structures of the acids and the solvents on the LLE behavior was comparatively studied. The ternary systems display two forms of LLE phase diagrams. The aqueous systems of butyric acid and the two structural isomers (sec-amyl alcohol and sec-isoamyl alcohol) exhibit type-1 phase behavior of LLE, whereas the type-2 behavior was observed for the systems containing the branched chain carboxylic acid (3-methylbutyric acid). The activity coefficients models of UNIQUAC and NRTL fit the measured tie line-data. According to the measured LLE data, the values of the models' binary interaction parameters were optimized using MATLAB Fminsearch function. Based on the experimental data, the mass distribution coefficients and selectivity were evaluated and systematically compared for the studied systems. Finally, reliability of the obtained NRTL parameters was checked using topological analysis connected to the Gibbs tangent plane test.