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Interpreting a Ternary Liquid-

Liquid Triangle DiagramMike Hansen 

ChEn 3603, Spring 2013 

University of Utah

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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

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Example Problem

• We’ll do an example problem involving

water, ethylene glycol, and furfural 

• Furfural completely dissolves ethylene

glycol, but only partially dissolves water

We’re using furfural to separate

ethylene glycol from water

Solvent

Solute Carrier

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Triangle Diagram: Basics

Ethylene Glycol Water

Furfural

0

10

01

1PURE

PUREPURE

Binary mixture with

no water

Binary mixture with

no furfural

Binary mixture with

no ethylene glycol

Ternary 

mixture

Be careful in reading back to the composition!

If you forget how toread the compositions, 

use the zero lines

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Triangle Diagram: 

Miscibility Boundary

Ethylene Glycol

Miscibility Boundary

Two Phase Region

Single

PhaseRegion

Water

Furfural

made by adding water to

ethylene glycol & furfuralmixture until there 

is cloudiness (2nd phase)

0

1001

1

We need to be in the two-phase

region (extract & raffinate)

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Triangle Diagram: 

Tie Lines & Plait Point

Ethylene Glycol Water

Furfural

0

1001

1Plait Point

Tie lines converge to the Plait Point, 

where both liquid phases (extract and raffinate) have the same 

composition

Tie Lines

Tie lines connect equilibrium points on 

the miscibility boundary

Extract

Composition

(Phase 1)

Raffinate

Composition(Phase 2)

Mix(Feed + Solvent)

Feed + Solvent --> Mix composition --> Tie Line --> Extract and Raffinate composition at two-phase equilibrium

At 2-phase equilibrium,these are our extract and

raffinate compositions!

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Triangle Diagram: 

Getting the Input Point

Ethylene Glycol

Water

Furfural

0

1001

1

Mix

Solvent composition

Feed

comp.

S

F

Points S and F define the line

M

the mix point M is found with the inverse-lever-arm rule

F 

S   =

SM 

MF 

flow rates

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Triangle Diagram: 

Getting the Outflows

Ethylene Glycol

Water

Furfural

0

1001

1

Mix

Find the tie line that point M lies on

M

Use the inverse-lever-arm rule again...

unknown 

flow rates

E

R

Total mass/mole balance to complete

E +R = F  + S 

EM  +RM  = ER

geometrically:

Extend to the extract and raffinate compositions

E 

R  =

RM 

EM