Unit Operations
Lecture 20
7 Nov 2012
1
McCabe-Thiele – AZ diagrams
Ethanol – Water Binary (1.013 bar):
2
Overview
•Review rigorous methods / RADFRAC
• Multicomponent systems:
o Residue curves
o DSTWU / RADFRAC
o Rules of thumb
• Complex (Enhanced) distillation
• Column internals
• Batch distillation
3
Azeotropic Distillation
Perry’s 8th ed.
4
Azeotropic Distillation
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.
5
Heterogeneous Azeotropic Distillation
VLLE (NRTL)
6
Heterogeneous Azeotropic Distillation
Perry’s 8th ed.
7
Residue Curve
Maps
8
Complex Multicomponent Systems
9
Pressure Swing
Distillation
10
Pressure Swing Distillation
11
Complex or Enhanced Distillation
• Extractive Distillation
o Higher boiling solvent
o Enters near top of column
o Interacts with other components to affect volatility or activity coefficients
• Homogeneous Azeotropic Distillation
o Add entrainer that forms min/max boiling point AZ w/ 1 or more of feed compds
o Added near top or bottom, depending upon if AZ is min or max BP
• Heterogeneous Azeotropic Distillation
o Add entrainer to form min BP heterogeneous azeotrope (EtOH-H2O + benzene)
• Pressure – Swing Distillation
o For pressure sensitive azeotropes and distillation boundaries
• Salt Distillation
o 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
12
Reactive Distillation
• Esterification of acetic acid with ethanol to ethyl acetate and water
EtOH  AA  EA  H 2O
13
Column Internals
14
Column Internals
15