New procedures for application of the Wong-Sandler mixing rules to the prediction of phase equilibria

New procedures are developed for use with the recent Wong-Sandler mixture combining rules (WS/MCR) (Wong and Sandler, 1992) for the prediction of mixture phase equlibria from cubic equations of state. Improvements in the a priori evaluation of both the liquid-phase parameter A{dollar}sbsp{lcub}infty{rcub}{lcub}rm E{rcub}{dollar} and the gas-phase parameter B{dollar}sbsp{lcub}12{rcub}{lcub}rm EOS{rcub}{dollar} (or k{dollar}sb{lcub}12{rcub}{dollar}) are made. An important new procedure is developed where the latter parameter is found from experimental measurements of the cross second virial coefficient B{dollar}sbsp{lcub}12{rcub}{lcub}rm Exp{rcub}{dollar} in the single-phase vapor mixture at low pressures. A priori prediction of phase equilibria to high pressures and temperatures then follows when the liquid-phase parameter A{dollar}sbsp{lcub}infty{rcub}{lcub}rm E{rcub}{dollar} is estimated from a group-contribution method, such as UNIFAC. These new procedures are most promising in the prediction (not correlation) of the phase behavior of complex systems, such as CO{dollar}sb2{dollar}/H{dollar}sb2{dollar}O/oil in petroleum reservoirs undergoing CO{dollar}sb2{dollar} and/or steam flooding.; An efficient Gibbs minimization method has been used with an Equation of State (EOS) model for the prediction of phase equilibria of hydrocarbon/water binary mixtures. The method uses the plot of the derivative of the Gibbs energy of mixing, g {dollar}rm equiv Deltasb{lcub}m{rcub}G/RT{dollar}, against composition. Equilibrium exists when there is equal area about a specific value of the derivative, m{dollar}sb1{dollar}. Hence, the method is called the Equal Area Rule (EAR). The stability analysis of the system is integrated into the EAR procedure. The EOS model used was the Peng-Robinson EOS (PR/EOS) with the WS/MCR.; Non-cubic EOS are required for accurate multi-thermophysical properties of pure components. These equations often produce isotherms on a pressure-specific volume (P-V) plot with more than one van der Waals loop (more than two local extrema). A new corollary of the Maxwell Equal Area Rule (MEAR), called the Maximum Positive Area (MPA) criterion, was developed for determining the correct vapor-liquid equilibrium (VLE) of pure components regardless of the complexity of the EOS used. In the MPA criterion, the correct VLE occurs when the positive area, determined in the MEAR criterion, is maximized. Maximizing the positive area is equivalent to obtaining an equilibrium which satisfies MEAR subject to any mechanical stability test.