Steady State of an Extractive Distillation Column

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Consider an extractive distillation column operating at atmospheric pressure. This column has 22 stages, a partial reboiler, and a total condenser. It is used to obtain anhydrous ethanol using ethylene glycol as an entrainer.


Pure entrainer at is fed to the column at a flow rate equal to and at stage two (counting from the top). The lower feed is composed of a mixture of ethanol and water ( ethanol and water). The lower feed, a saturated liquid, is located at stage 12 (counting from the top) and has a flow rate equal to .

The Demonstration solves the MESH equations (mass, equilibrium, summation, and heat) and displays the composition and temperature profiles for user-set values of the reflux ratio. The second degree of freedom is set by taking a distillate flow rate equal to .

Finally, a comparison of the present calculation with Aspen-HYSYS shows excellent agreement.


Contributed by: Housam Binous and Naim Faqir (July 2012)
Open content licensed under CC BY-NC-SA



The expressions for pure component vapor and liquid enthalpies were adapted from Aspen HYSYS®.

The mixture is assumed to obey the modified Raoult's law, and the activity coefficients are predicted using the Wilson model.


[1] M. F. Doherty and M. F. Malone, Conceptual Design of Distillation Systems, Boston: McGraw–Hill, 2001.

[2] E. J. Henley and J. D. Seader, Equilibrium-Stage Separation Operations in Chemical Engineering, New York: Wiley, 1981.

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