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Some of the most widely used commercial process simulators and property programs cannot calculate P-xy diagrams of even simple binary mixtures satisfactorily when the specified temperature is greater than the critical temperature of one of the two components because of the limitations of the methods used by them currently. In this paper, we present a new method for drawing P-xy diagrams of binary mixtures that overcomes the limitations of the present methods. In the proposed method, the density of the vapor/liquid phase is varied systematically and the saturation point calculated at each of the specified density (instead of the conventional specified concentration) to generate P-xy diagrams. Two different approaches have been presented for the calculation of saturation points at specified density. The methods presented are an extension of the density marching method presented earlier for drawing two-phase and three-phase isopleths. A number of zeotropic and azeotropic mixture examples are presented to demonstrate the methods. [ABSTRACT FROM AUTHOR]

Thereare very few automatic procedures in the literature to calculatethree-phase envelopes (VLLE boundaries). The best existing proceduresrequire selecting each step manually to complete the three-phase envelope.In this article, a density marching procedure and a saturation pointcalculation at specified density of one of the incipient phases developedrecently for drawing two-phase envelopes is extended to three-phaseenvelopes. Procedures have been presented to determine three-phasebubble and dew points reliably. Two examples are presented to demonstratethe method. The method has direct application in process simulationand thermodynamic property programs. [ABSTRACT FROM AUTHOR]