A method for calculation of vapor-liquid and liquid-liquid equilibria

Abstract

A new parameter, pseudo temperature (Tp) is introduced to solve two-phase equilibrium calculations. The resulting Tp-method has a single set of equations to describe different phase regions encountered in vapor-liquid equilibrium (VLE) and liquid-liquid equilibrium (LLE). It does not require a priori the number of phases existing at equilibrium, and involves a minimization problem having a linear objective function subject to nonlinear constraints, which can be solved by a version of successive linear programming method. Tp-method is tested on typical examples for VLE and LLE, and compared with pseudo pressure (Pp) method of Bullard and Biegler [Computers and Chemical Engineering 17, 95-109 (1993)] for VLE. In each example, several operating conditions are considered to cover both single- and two-phase situations. The results show that Tp-method is successful for both VLE and LLE, and that Tp-and Pp-methods are comparable for VLE. © 1997 Elsevier Science Ltd.