Calculation of critical points and phase boundaries in the critical region

Abstract

A computationally efficient, general method is presented for calculating the critical temperature and pressure of a multicomponent mixture of specified composition. The procedure suggested also provides coefficients α T , α P and u relating changes in temperature, pressure, phase fraction β and composition in the immediate vicinity of the critical point. These variations are shown to be of the general form T − T c = α T (1 − 2β)δ P − P c = α P (1 − 2β)δ ln K i = u iz i − 1 2 δ where δ is the distance parameter of the phase-boundary expansion. Finally, an explicit first-order approximation is developed, based on derivatives of the Gibbs-energy surface, givin the phase fractions and equilibrium phase composition for a mixture under near-critical conditions.