Graphical Representation of Liquid-Liquid Phase Equilibria

Graphical Representation of
Liquid-Liquid Phase Equilibria

0 INTRODUCTION/PURPOSE
1 SCOPE
2 FIELD OF APPLICATION
3 DEFINITIONS
4 GRAPHICAL REPRESENTATIONS OF PHYSICAL
PROPERTIES
4.1 Use of Composition Diagrams
4.2 Ternary Systems with Immiscible Liquids
4.3 Graphical Design Using Ternary Diagrams

APPENDICES

A INTERPOLATION AND CORRELATION OF THE LINES

FIGURES

1 TRIANGULAR CO-ORDINATES
2 TYPE 1 SYSTEM: ONE PAIR OF PARTIALLY MISCIBLE LIQUIDS
3 TYPE 2 SYSTEM: TWO PAIR OF PARTIALLYMISCIBLE LIQUIDS
4 DESIGN OF COUNTERCURRENT EXTRACTION SYSTEM WITHOUT REFLUX – TYPE 1 SYSTEM
5 BLOCK DIAGRAM OF REFLUXED LIQUID-LIQUID EXTRACTION
6 DESIGN OF COUNTERCURRENT SYSTEM WITH REFLUX
7 CONSTRUCTION OF THE CONJUGATE LINE

1. 1 CATALYST, PROCESS TECHNOLOGY

CONSULTANCY

Process Engineering Guide:
GENE PEGMASS14

Graphical Representation of
Liquid-Liquid Phase Equilibria

2. DEFINITIONS

GRAPHICAL REPRESENTATIONS OF PHYSICAL
PROPERTIES

4.1 Use of Composition Diagrams
4.2 Ternary Systems with Immiscible Liquids
4.3 Graphical Design Using Ternary Diagrams

APPENDICES
INTERPOLATION AND CORRELATION OF THE LINES 10

3. BLOCK DIAGRAM OF REFLUXED LIQUID-LIQUID EXTRACTION 7
DESIGN OF COUNTERCURRENT SYSTEM WITH REFLUX

CONSTRUCTION OF THE CONJUC

DOCUMENTS REFERRED TO IN THIS PROC
ENGINEERING GUIDE

4. Liquid Extract
Enterprises.

1 SCOPE
This Process Engineering G

balance effects that make Liquid-Liquid Extraction possible and how these can
be represented in a graphical form.

2 FIELD OF APPLICATION

This Guide applies to the Process Engineering community in GBH Enterprises
oridwide.

3 DEFINITIONS

For the purposes of this Guide the following definitions apply:

Extract Thisis the exit stream from the process being sul
material into which the

Feed

5. nd liquid phase fed to the process into which the
Solute is transferred. The Solvent must be substantially immiscible
ith the Feed

The line joining compositions represented on a temary diagram that
can coexist in equilibrium with each other. A method of producing
this is given in Appendix À.

With the exception of terms used as proper nouns or tiles, those terms
with initial capital letters which appear in this document and are not

defined above are defined in the Glossary of Engineering Terms.

4 GRAPHICAL REPRESENTATIONS OF PHYSICAL PROPERTIES

The simplest representation used for physical properties associated with
distillation is that of the binary diagram. This is either plotted as an X-Y
diagram wih vapor compositon onthe vertical axis and quid

ntal axis or as an H-X diagram with

ntally and enthalpies shown verti
Liquid- Liquid Extraction at least three components are present for the

6. range of compositions for which two liquid phases form.

In Figure 1 the apexes of the triangle represent the pure componer
and C respectively. Any point on the side of the triangle represents a
binary mixture so point D for example represents a mixture containing
60% B and 40% A. Points inside the triangle represent mixtures of al
three components such as point E which contains 40% A, 40% B and 20%

FIGURE 1 TRIANGULAR CO-ORDINATES.

A

7. Thus all points on the line CD represent mixtures with constant rat

10 B with vary fC. The nearer the point is to point C the

richer the mixture is in component C. Any mixture on the line CD from
‘component C is subsequently removed will result in a mixture
-omposition is represented by point D.

42 Ternary Systems with immiscible Liquids
The types of system of most interest in Liquid-Liquid Extraction are given

in Figures 2 and 3.
More complex diagrams do exist but are of limited importance.

42.1 Type 1 - One Pair of Partially Miscible Liquids

xempliied by the diagram shown in Figure 2.
Two of the components Band C are only partially miscible whilst
component A is completely miscible with the other two components.

8. All mixtures of the components outside and on the curve DFPGE are
single liquid phase whereas mixtures falling within the curve will form two
liquid phases. The curve DFPGE represents the locus of saturated
solutions and is called the solubility o

‘A mixture of overall composition H will form two immiscible liquid solutions
of composition F and G. From the above, the ratio of F formed to G
formed will be in the same as the ratio of HG to HF. The straight line FHC
forms a Tie Line along which all mixtures will split to give two liquid phases

9. FIGURE 3 TYPE 2 SYSTEM: TWO PAIRS OF PARTIALLY MISCIBLE LIQUIDS

10. tree basis. Solvent $ is to be used in a countercurrent extraction
system without reflux. Figure 4 shows the ternary diagram for A, B and

represent the final Ralfinate and Extract products required from the
extraction.

FIGURE 4 DESIGN OF COUNTERCURRENT EXTRACTION SYSTEM
WITHOUT REFLUX - TYPE 1 SYSTEM

11. possible and in how many
(6) In the distilation constructions an operating line for an X-Y diagram or
an Operating Point for an H-X diagram may be const
Consideration of stage wise mass balance. A similar
possible for Liquid: Liquid Extraction. From the Feed and Extract end of
the extractor the Operating Point must lie on the line FE and from the
Raffinate and Solvent end of the extractor the Operating Point must lie
on the line ANS. Thes
lines intersect, at point

To check whether the sepat

carry out the following:

13. Raffinate is required 10 have a compostion 015% À on a |
tree basis and the Extract a composition of 95% A on a Solvent

FIGUR E 6 DESIGN OF COUNTERCURRENT SYSTEM WITH REFLUX

14. End Re
(4) Join R a

(6) Find R3 by constructing the Tie Line ASES.
(6) Join R3 to X to find E4 by mass balar

(7) Find R4 by constructing the Tie Line R4E4

(6) _ The operating line forthe section ofthe Extractor beyond th

lies atthe intersection of the lines RNS and
‘crossed the line FX with the Tie Line R4E4, the

Operating Point Y should be used. Continuing with X
towards the solution but wil be inefficient, The construction now
as bel

(1) Join R4 to Y to find ES by mass balance.
(2) Find RS ructing the Tie Line ASES.
(8) Join RS to Y to find ES by mass balance.
(4) Find RB by constructing the Tie Line ASES.
(6) Join RG to Y to find E7 by mass balance.
(6) Find AN by constructing the Tie Line RNE7.

ll make progress

15. ction of the conjugate line with the binodal curve indicate
position of the plait point.

The conjugate line being known, any Tie Line can easily be constructed. The

ymposition of the phase which coexists with an arbitrary phase N is found by
drawing consecutively NO parallel to AS and NO parallel io AB. Thus N' the
phase in equilibrium with phase N, is found. The composition of N' could
equally be found with the aid of the upper part of the conjugal

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