Steady-State Distillation of a Methanol-Water Mixture
Consider a distillation column separating a binary mixture of methanol and water at . This column has 10 stages, a total condenser, and a partial reboiler. Feed stage location is stage nine counting from the top. The feed composition is equimolar. The feed vapor fraction is , where is the feed quality. The feed flow rate is set to . The values of both the reboil () and the reflux () ratios are to be selected by the user. This Demonstration uses a rigorous approach (solving MESH equations) and displays the composition versus stage for both components (methanol in orange, water in blue), the temperature profile inside the column, as well as the vapor and liquid flow rates (magenta and blue, respectively). Comparisons with the results obtained with Aspen HYSYS are shown for and . Finally, the Ponchon–Savarit graphical construction is shown and several checks of external overall and partial mass balances and condenser and external energy balances are performed.
 E. J. Henley and J. D. Seader, Equilibrium-Stage Separation Operations in Chemical Engineering, New York: Wiley, 1981.
The expressions for pure component vapor and liquid enthalpies were adapted from Aspen HYSYS. Enthalpies are above and are given in .
The mixture is assumed to obey the modified Raoult's law with activity coefficients predicted by the van Laar model.