MEASUREMENT AND REPRESENTATION OF TERNARY VAPOR LIQUID LIQUID EQUILIBRIA

For the design of separation processes in systems showing azeotropic behaviour and two liquid phases, VLLE data must be represented with high accuracy. The ternary system ethanol/water/cyclohexane has been investigated for model development. The static method of p(x, T) measurement was applied to evaluate VLE of this highly non-ideal system which exhibits a wide miscibility gap. The tie-lines and the LL coexistence curve were determined by analysing samples of two liquid phases in equilibrium. The vapour composition of the heterogeneous azeotrope was determined by analysis of the head product of a rectification at infinite reflux ratio. To obtain full thermodynamic information on multicomponent VLE from p(x, T) measurement, a consistent description of the excess Gibbs energy of the liquid phase is required. The experimental data were described consistently, facilitating a modification of the NRTL equation with considerably increased flexibility in the ternary region. © 1990.