Prediction of isobaric and isothermal vapour–liquid equilibria from limited experimental data

Malesinski's method for prediction of isobaric vapour–liquid equilibrium data using a single experimental datum on a T–x isobar has been modified and extended to a more general case where the molar entropies of vaporisation of the components are not necessarily equal and the non-ideality in the vapour phase is considered. However, it is assumed that the solution behaves like a strictly regular one over the temperature range in question, that is, the constant A in the expression for excess free energy: g^E=Ax₁x₂ is independent of temperature. The method has been illustrated for several systems and is found to be highly satisfactory for non-polar–non-polar as well as polar–non-polar systems in which the boiling points of the pure components are not much different. Incorporating temperature dependence of the constants in the Redlich–Kister equation for excess free energy, a method has been developed for predicting isothermal vapour–liquid equilibrium data at several temperature levels from equilibrium values at a single pressure. For testing the validity of this method, predicted results have been compared with the available experimental data for zeotropic as well as azeotropic systems comprising non-polar–non-polar, polar–non-polar and polar–polar mixtures, and the method has been found to be satisfactory for all systems.