Three-Stage Batch Rectification with Constant Reflux

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Consider a three-stage batch rectification column charged with 100 kg·mole of a binary mixture composed of 20% mole fraction of -hexane and 80% mole fraction of -octane. The boilup rate, , is constant and is set equal to 10 kg·mole/hr. The constant reflux ratio is equal to 1.


This Demonstration plots the equilibrium curve in blue and the straight operating line in magenta. Indeed, the slope of the operating line is the constant ratio of the liquid‐to‐vapor flow rates in the column, , which is equal to 0.5. Stages are stepped off using the operating line and the equilibrium curve for the initial and final times of the distillation operation. The staircase graphical constructions are shown by a dashed red line and a solid cyan line for the initial and final times of the distillation operation, respectively. The user has to specify the value of the final composition in the still pot, .

This Demonstration then computes the shaded area below the curve, representing versus , where is the distillate composition. The amount of material left in the still pot, expressed in kg·mol, , is given by the following relationship:

, where is the initial composition in the still pot and is the initial amount of material in the still pot. Both the final amount of material in the still pot and the distillation time required to achieve the user specified composition in the still pot, (expressed in hours), are displayed in red.


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



E. J. Henley and J. D. Seader, Equilibrium-Stage Separations in Chemical Engineering, New York: John Wiley & Sons, 1981.

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