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 αT, αP 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 − Tc = αT(1 − 2β)δ P − Pc = αP(1 − 2β)δ ln Ki = uizi− 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.