Chapter 4 - Classical Models Part 2: Activity Coefficient Models and Applications

Abstract

Activity coefficient models commonly used in food engineering are presented, including Margules, Redlich–Kister, van Laar, Flory–Huggins, Wilson, nonrandom two-liquid (NRTL), universal quasi-chemical (UNIQUAC), regular solution, analytical solution of groups (ASOG), UNIQUAC functional-group activity coefficients (UNIFAC), as well as UNIFAC modifications and activity models in terms of mass fractions. Application is illustrated with the determination of activity coefficients from minimal data (single data point), like azeotropic data and activity coefficients at infinite dilution, as well as from more complete data sets of vapor–liquid, solid–liquid, and liquid–liquid equilibrium. Prediction of activity coefficients by group contribution methods is also illustrated. Examples and case studies cover a variety of systems of interest in the food industry where the calculation of activity coefficients is important, namely, wine and must distillation, aroma retention/release, fatty acid fractionation, water activity in polymer solutions, solid–liquid behavior of oils and fats, and edible oil refining using solvent extraction.