Interpreting a Ternary LiquidLiquid Triangle Diagram
Mike Hansen
ChEn 3603, Spring 2013
University of Utah
Where are we?
• In the textbook, this is Section 5 of
Chapter 4
• In the notes, this is the set on Single Stage
Equilibrium
• Just finished flash drums
Example Problem
• We’ll do an example problem involving
water, ethylene glycol, and furfural
!
• Furfural completely dissolves ethylene
glycol, but only partially dissolves water
Solvent
We’re using furfural to separate
ethylene glycol from water
Solute
Carrier
Triangle Diagram: Basics
If you forget how to
read the compositions,
use the zero lines
PURE
1
0
Ternary
mixture
Be careful in reading back to the composition!
Binary mixture with no water
Ethylene Glycol
Binary mixture with no furfural
Water
0
PURE
1
1
Binary mixture with Furfural
no ethylene glycol
0
PURE
Triangle Diagram:
Miscibility Boundary
1 0
We need to be in the two-phase
region (extract & raffinate)
Single
Phase
Region
Miscibility Boundary
Ethylene Glycol
made by adding water to ethylene glycol & furfural mixture until there
is cloudiness (2nd phase)
Water
Two Phase Region
0
1
Furfural
0
1
Triangle Diagram:
Tie Lines & Plait Point
1 0
Plait Point
Tie lines converge to the Plait Point,
where both liquid phases (extract
and raffinate) have the same
composition
Tie lines connect equilibrium points on
the miscibility boundary
At 2-phase equilibrium,
these are our extract and
raffinate compositions!
Ethylene Glycol
Extract
Composition
(Phase 1)
0
1
Tie Lines
(Feed + Solvent)
Water
Raffinate
Composition
(Phase 2)
Mix
Furfural
0
1
Feed + Solvent --> Mix composition --> Tie Line --> Extract and Raffinate composition at two-phase equilibrium
Triangle Diagram:
Getting the Input Point
1 0
Points S and F define the line
the mix point M is found with the inverse-lever-arm rule
flow rates
F
Ethylene Glycol
M
F
SM
=
S
MF
Feed comp.
Water
Mix
0
S
1
Furfural
Solvent composition
0
1
Triangle Diagram:
Getting the Outflows
1 0
Find the tie line that point M lies on
Extend to the extract and raffinate compositions
Use the inverse-lever-arm rule again...
unknown
flow rates
R
Ethylene Glycol
M
Total mass/mole balance to complete
Water
E+R=F +S
Mix
0
E
1
E
RM
=
R
EM
Furfural
0
1
geometrically:
EM + RM = ER