Consider a distillation column with 10 stages, a partial reboiler, and a total condenser. The column is used to separate a nonideal equimolar mixture of ethanol and water. Deviation from ideal behavior is taken into account using the Wilson model. The feed, a biphasic stream with a quality equal to , enters at stage 8 with a rate equal to . The reboil ratio is constant and equal to 15. Suppose that the column is subject to a step in the reflux ratio as follows: and , where is the percent increase or decrease in the reflux ratio, . This Demonstration performs a rigorous dynamic simulation (including both material and energy balance equations) of this column and plots the behavior of both the distillate and bottom compositions versus time. Molar hold-ups of the reboiler, condenser, and plates are taken equal to , , and , respectively.