Computing Liquid-Liquid Phase Equilibria: An Exercise for Understanding the Nature of False Solutions and How to Avoid Them

An exercise to compute LLE data is presented to illustrate the problems that can arise when the isoactivity equilibrium condition is used in the LLE calculations. A much more efficient condition is obtained when isoactivity is combined with the common tangent line criterion, avoiding false solutions that correspond with very low values of the activity objective function. Also, 3D figures are represented to discuss the topological aspects of the dimensionless Gibbs energy of mixture function (GM/RT).