Estimating Relative Volatility from Batch Distillation Data

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Consider an equimolar binary mixture with a constant relative volatility . An initial quantity of this mixture is fed into the still of a simple batch distillation apparatus.


Assume that the batch distillation is conducted at a constant boil-up rate (i.e. the selected heating policy of the experiment). Thus the overall molar balance gives , where is the still's molar holdup. The experiment stops when the still runs dry at minutes, when .

The liquid composition in the still is related to the distillate composition by [1, 2].

A component molar balance is given by the equation , with .

Suppose you run a batch distillation experiment and gather the data indicated by the red dots in the plot. To generate such data, fix the value of the relative volatility and the level of the random noise. This Demonstration uses the governing equations to estimate the relative volatility (shown on the plot in magenta) using your "experimental" data. The quality of the theoretical predictions (shown by the blue curve) is given by the root-mean-square deviation or rmsd (reported in and in black on the plot).


Contributed by: Housam Binous, Farrukh Shehzad, and Ahmed Bellagi (January 2016)
(King Fahd University of Petroleum & Minerals, KSA; ENIM, University of Monastir, Tunisia)
Open content licensed under CC BY-NC-SA



For more information, see [1] and [2].


[1] M. F. Doherty and M. F. Malone, Conceptual Design of Distillation Systems, New York: McGraw-Hill, 2001.

[2] P. C. Wankat, Separation Process Engineering, 3rd ed., Indianapolis: Pearson, 2012.

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