A Novel Method for Assessing the Effect of Pressure on Vapor-Liquid Equilibrium in Ternary Systems

In distillative separations, operating pressure is an important parameter influencing not only the cost of a given separation, but potentially its feasibility too. A reliable technique for assessing the effect of pressure on vapor-liquid equilibrium is thus imperative for robust distillation design. This paper presents a method that is not only reliable, but also allows a designer to creatively synthesize a column by finding areas where the phase equilibrium may be beneficial for a particular separation. By viewing global residue curve maps which incorporate theoretical negative compositions, pressure effects are easily traceable. It is shown how the NRTL model in particular is a very useful thermodynamic model for this unique assessment of pressure effects. Using this technique, significant insights are gained into the appearance and disappearance of azeotropes at certain pressures. Moreover, this paper presents a novel eigenvalue method which allows one to determine exact critical pressures where residue curve map topology is transformed.