CRITICAL-POINTS WITH THE WONG-SANDLER MIXING RULE - II - CALCULATIONSWITH A MODIFIED PENG-ROBINSON EQUATION OF STATE

This is the second of two papers in which critical point calculations in binary systems were performed utilizing cubic equations of state (E OS) combined with excess energy models using the Wong-Sandler mixing r ule. In the first paper, a qualitative study of critical phase diagram s calculated using the simple van der Waals EOS combined with the NRTL model was made. In this paper, the Stryjek and Vera version of the Pe ng-Robinson EOS was also combined with the NRTL model and the resultin g model was used in the computation of the critical loci of real syste ms. The binary interaction parameters of the model were estimated by c orrelating vapor-liquid equilibrium (VLE) data and, for some systems, successful predictions of the critical loci were obtained even when VL E data far from the critical point were used. To estimate parameters i n systems for which the equation of state model may incorrectly predic t a false liquid-liquid split, we used a penalty function approach bas ed on the results of global stability tests. While the model studied h ere has been able to quantitatively predict the critical behavior of s ome non-ideal systems, involving compounds such as water, acetone and alkanols, only qualitatively correct behavior could be predicted for s ome highly asymmetric and non-ideal mixtures, such as water + n-dodeca ne. (C) 1997 Elsevier Science Ltd.