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

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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 .


Contributed by: Housam Binous (March 2011)
Open content licensed under CC BY-NC-SA



For more information, see:

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

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