Prediction of Stability Limits for Binary and Ternary Systems Using the NTRL Liquid Phase Model

Abstract

Stability limits (spinodal loci) were determined for 53 binary systems and 26 ternary systems. Rigorous thermodynamic criteria for spinodal limits and criticality conditions in terms of mixture Gibbs free energy were derived from the NRTL model. The highly nonlinear coupled algebraic equations were solved using a Matlab® code employing a double precision strategy to minimize round-off errors. The generated critical temperatures and compositions were compared with literature, when available, and found in good agreement. The binary systems studied contain six groups: acetonitrile + hydrocarbons, N-formylmorpholine (NFM)+ alkanes, perfluoroalkanes + n-alkanes, sulfolane + hydrocarbons, 1,3- propanediol + ionic liquids, and N-methyl-α -pyrrolidone + n-alkanes. Additionally, the ternary systems analyzed belong to six groups; 2-propanol + water + alkanes, 2-propanone + water + alcohols, ethyl acetate + water + carboxylic acids, dibutyl ether + alcohols + water, water + ethanol + toluenes, and water + ethanol + benzene. Additionally, a ternary system consisting of limonene + linalool + 2-Aminoethanol was studied for temperatures of 298.15 K, 308.15 K, and 318.15 K. For binary systems, literature reported data for critical temperatures and compositions exists for 44 out of the 53 binary systems studied. The average difference between literature and values obtained in the study is ± 0.58 K, while 75% of the critical temperatures obtained deviated less than 1 K. The average difference in critical compositions from literature reported values is 1.8 mol%. However, critical conditions are not reported in literature for any ternary systems except limonene + linalool + 2-aminoethanol, where the maximum difference in critical composition is 0.7 mol%. The results obtained indicate the model developed in this thesis can accurately predict the stability limits. The results of the binary system were found to obey the universal exponent and follow simple power law with β of 0.3126 & 0.3623 for binodal and spinodal points, respectively. In addition, the critical exponent of susceptibility (γ) has been deduced to follow the expanded power law and the regressed value of γ is -0.8468. Search Terms: Stability, critical temperature, critical point, spinodal loci, NRTL, critical exponent, binary liquid systems, ternary liquid systems, liquid-liquid equilibrium