Identification of UNIQUAC binary interaction parameters in liquid-liquid equilibrium

• Published in: Fluid phase equilibria 2020-04, Vol.510, p.112483, Article 112483
• Main Authors: Tomassetti, Sebastiano, Di Nicola, Giovanni, Santori, Giulio
• Format: Article
• Language: English
• Subjects: Activity coefficient models; Common tangent plane; Excess gibbs free energy; Parameter regression; Stability criterion; UNIQUAC
• ISSN: 0378-3812; 1879-0224
• DOI: 10.1016/j.fluid.2020.112483

An algorithm is presented for the estimation of the UNIQUAC interaction parameters for liquid-liquid equilibrium of ternary systems. The algorithm is based on two optimization levels. In the inner level the algorithm performs the minimization of an objective function based on the isoactivity conditions. The outer level aims to minimize the error between calculated and experimental compositions. The Common Tangent Plane condition is checked at the end to guarantee a thermodynamically consistent representation of the phase behavior of ternary liquid systems. The algorithm is challenged with a historical Type 1 ternary liquid-liquid equilibrium system from the seminal study of Anderson and Prausnitz in which the authors showed the limitations of the original UNIQUAC model and justified its amendment in the modified UNIQUAC model. The present algorithm makes available single temperature and temperature-dependent interaction parameters enabling accurate and thermodynamically correct description of the experimental data with the original UNIQUAC model, therefore without the need of any model modification. This outcome does not change when the interaction parameters from the binary partially miscible constituent pair are first regressed and kept constant during the estimation of the remaining parameters on ternary equilibrium data. This investigation confirms that a model cannot be judged if the correctness of the model parameters has not been proved first. •An algorithm for UNIQUAC parameter estimation for LLE of ternary systems is presented.•The algorithm checks the Common Tangent Plane condition to ensure correct results.•The algorithm was tested on LLE of Methanol + Benzene + n-Heptane ternary system.•The derived parameters for original UNIQUAC ensured an accurate LLE description.