Distillation Column Calculation Incorporating Pressure Drop Effect

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Consider a distillation column separating a quaternary mixture of benzene, toluene, -xylene, and ethylbenzene. This column has 10 stages, a total condenser, and a partial reboiler. The feed stage location is stage five counting from the top. The feed composition is 25 mole % for each of the four components. The feed quality is taken to be 1. The feed flow rate is set to 10 kmol/hr. The reboil and reflux ratios are both chosen to be 5.


This Demonstration uses a rigorous approach (solving MESH equations) and takes into account pressure drop effects in both the condenser and the reboiler as well as in the trays. You can vary these various pressure drops. The pressure at the bottom of the column is set to 151.325 kPa. The Demonstration displays the composition versus the stage for all four components (benzene in orange, toluene in blue, -xylene in green, and ethylbenzene in red), the temperature profile inside the column, as well as the vapor and liquid flow rates (magenta and blue, respectively). The results obtained are compared with Aspen HYSYS for two cases (see last two snapshots with two different sets of reboiler, condenser, and trays pressure drops).


Contributed by: Housam Binous, Naim Faqir, and Brian G. Higgins (November 2012)
Open content licensed under CC BY-NC-SA



Expressions for pure component vapor and liquid enthalpies were adapted from Aspen HYSYS.

The mixture is assumed to obey Raoult's law since it is composed of four aromatic compounds at a moderate pressure.


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

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