Batch Rectification of an Ideal Benzene/Toluene Binary Mixture

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Consider an ideal binary mixture composed of benzene and toluene. This Demonstration performs the dynamic simulation of a batch rectification of such a mixture. Temperature is plotted versus time for selected values of the initial composition, reflux ratio, and number of theoretical stages.


The still is charged with 1000 kmol of the initial mixture. The vapor rate is assumed constant and equal to 10 kmol/hr. The molar hold-up of all stages and the condenser are 5 and 20 kmol, respectively.

It is found that (1) the products that exit the column are benzene first and toluene next; and (2) if the initial composition is very rich in either benzene or toluene then the constant temperature segment at 80.1°C or 110.6°C, respectively, is quite large.

In addition, the separation is improved if you choose large reflux ratios or a large number of theoretical stages. Otherwise you get sloppy separation and neither pure benzene nor pure toluene.


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



The reflux ratio is given by:


where is the flow rate of the liquid refluxing to the column.

When the flow rate of the distillate, , is close to zero, the reflux ratio is very high; a situation commonly called near total reflux operation.

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