Multicomponent Distillation: The Case of Pentane/Hexane/Heptane System

Consider a ternary mixture composed of pentane (component 1), hexane (component 2), and heptane (component 3) such as their relative volatilities are equal to and . This mixture is fed into a distillation column in the form of a saturated liquid with the following composition: 30% pentane, 30% hexane, and 40% heptane. The distillate composition specification is 95% pentane, 4.9% hexane, and 0.1% heptane. The bottom composition specification is 5% pentane, 39.7% hexane, and 55.3% heptane.
This Demonstration computes the rectifying and stripping profiles (blue and magenta curves) for a fixed maximum number of plates in each section equal to seven stages. You can change the reboil and reflux ratios to see if the distillation is feasible (i.e., if the stripping and rectifying profiles intersect). The number of plates needed to achieve the separation is then easily obtained by counting the stages from the bottom stage to the intersection point and the stages from the condenser stage up to the intersection point ; the number of stages is . As expected for a ternary system, the global material balance around the whole distillation column is represented by a line shown here in green.


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For more information, see:
M. F. Doherty and M. F. Malone, Conceptual Design of Distillation Systems, New York: McGraw–Hill, 2001.
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