Separating a Ternary Mixture of Water, 2-Propanol, and Acetone at Atmospheric Pressure

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Consider a ternary mixture composed of water, -propanol, and acetone at . This Demonstration plots the residue curve map (RCM) for this mixture. There are two distillation regions separated by a distillation boundary (shown in red) running from pure acetone to the only azeotrope in the ternary system (i.e., the binary azeotrope between water and -propanol shown in red).

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A distillation column with 10 stages, a partial reboiler, and a total condenser is used to separate this ternary mixture. The column operates at atmospheric pressure (i.e., ). The feed used the following compositions:

Case 1: water, -propanol, and acetone.

Case 2: water, -propanol, and acetone.

The feed flow rate is and the feed location is stage , counting from the top. You can select the value of the vapor fraction of the feed stream, , where is the feed quality.

The distillation composition profile for either case is given by selecting the appropriate tab. The straight magenta line represents the overall column mass balance. The magenta dot gives the feed location. Both cases indicate that the profile is either in one region or the other of the two regions that are separated by the distillation frontier (shown in brown). As expected, no crossing of the frontier is allowed. The distillate stream is almost pure acetone (with a boiling point equal to C) and the residue (or bottom stream) is composed of essentially a mixture of a water and -propanol. For both distillation cases, the reflux and reboil ratios are and . The composition profile was checked against results from Aspen HYSYS and perfect agreement was found. This is expected since the method is rigorous and solves the MESH equations using Mathematica's built-in command FindRoot.

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Contributed by: Housam Binous and Naim Faqir (May 2012)
Open content licensed under CC BY-NC-SA


Snapshots


Details

Reference

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

Expressions for pure component vapor and liquid enthalpies were adapted from Aspen-HYSYS. Enthalpies are in .



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