Unit OperationsLecture 20

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7 Nov 2012

McCabe-Thiele – AZ diagrams

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Ethanol – Water Binary (1.013 bar):

Overview

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• Review rigorous methods / RADFRAC• Multicomponent systems:o Residue curveso DSTWU / RADFRAC o Rules of thumb

• Complex (Enhanced) distillation• Column internals• Batch distillation

Azeotropic Distillation

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Perry’s 8th ed.

Azeotropic Distillation

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Water with (binary system at atmospheric P):• methanol - no azeotrope• ethanol - azeotrope• propanol - azeotrope

In-class exercise:• using Aspen Plus, explore if we can use distillation to separate the binary

mixture of water and n-butanol.

Heterogeneous Azeotropic Distillation

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VLLE (NRTL)

Heterogeneous Azeotropic Distillation

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Perry’s 8th ed.

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Residue Curve Maps

Complex Multicomponent Systems

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Pressure Swing Distillation

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Pressure Swing Distillation

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Complex or Enhanced Distillation

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• Extractive Distillationo Higher boiling solvento Enters near top of columno Interacts with other components to affect volatility or activity coefficients

• Homogeneous Azeotropic Distillationo Add entrainer that forms min/max boiling point AZ w/ 1 or more of feed compdso Added near top or bottom, depending upon if AZ is min or max BP

• Heterogeneous Azeotropic Distillationo Add entrainer to form min BP heterogeneous azeotrope (EtOH-H2O + benzene)

• Pressure – Swing Distillationo For pressure sensitive azeotropes and distillation boundaries

• Salt Distillationo Alter relative volatilities of feed compds by dissolving a soluble ionic salt into

the reflux• Steam Distillation

o Steam is added to reduce temperature of distilling organic mixture• Reactive Distillation

o add reactant &/or catalyst to cause a reversible/selective reaction with one of the feed components

o Reaction and distillation occur in same vessel

Reactive Distillation

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• Esterification of acetic acid with ethanol to ethyl acetate and water

OHEAAAEtOH 2

Column Internals

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Column Internals

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