Consider a feed composed of benzene (), toluene (), and -xylene () at . This ternary mixture, with a thermal quality equal to 1.0 (i.e. saturated liquid), is fed to a 19-stage column with a total condenser and partial reboiler. The feed is at stage 10. The feed flow rate is set to . The initial values of the reflux and reboil ratios are and , respectively. This Demonstration computes the dynamic behavior using a rigorous approach, which takes into account both the energy and mass balances. The red, blue, and green curves, shown for both the distillate and bottom streams, correspond to benzene, toluene, and -xylene compositions versus time when the column is subject to a step in the reflux ratio at . You can change the magnitude of the step applied to the reflux ratio. It is straightforward to modify the program in order to perform simulations where a step in either the reboil ratio or the feed composition is applied. For simplicity, the molar holdups of the reboiler, the condenser, and the stages are assumed constant and equal to , , and , respectively.