Pinch Composition versus Reflux Ratio for a Benzene-Ethylenediamine Mixture at 1 atm

This Demonstration plots the bifurcation diagram (pinch composition versus reflux ratio) for a mixture of benzene and ethylenediamine at 1 atm. The tangent pinch is shown as a blue dot in the diagram.
For this particular binary mixture, the vapor-liquid equilibrium (VLE) relation is as follows:
, where and .
The bifurcation diagram is obtained; this is the implicit function relating the reflux ratio and the pinch point location:
, where is the reflux ratio and the distillate composition.
The tangent pinch obeys the following conditions: and .
As decreases, the curve loses its distinctive S-shape. The critical point where this transition occurs is verified by the following relations: , and .


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For more information, see:
M. F. Doherty and M. F. Malone, Conceptual Design of Distillation Systems, Boston: McGraw-Hill, 2001.
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