Download - ChE41A LLE VLLE Partitioning (Ver 2008)
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“Oil and water just don’t mix.”
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Solubility of a Liquid in a LiquidSolubility of a Liquid in a Liquid
LIQUID I
LIQUID II
T P
IIi
IIi
Ii
Ii
IIi
Ii
xx
ff
Equilibrium RelationshipIix o
ix
IIix
IN
IIN
Mole Balance
IIi
IIi
Ii
Iii
IIi
Iii
NxNxN
NNN
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T-x Diagram: 2,6-dimethyl pyridine-water systemSolubility of a Liquid in a LiquidSolubility of a Liquid in a Liquid
tie line
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T-x Diagram: methyl ethyl ketone-water systemSolubility of a Liquid in a LiquidSolubility of a Liquid in a Liquid
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T-x Diagram: perfluoro-n-heptane in various solvents
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Measurement of Liquid-Liquid Equilibrium
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Why do two liquid phases separate?Why do two liquid phases separate?CONCEPT: The equilibrium criterion for a closed system at constant T and P is that the Gibbs free energy of the system be a minimum.
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0
021
2
P,Tx
G
CONDITION FOR UPPER CONSOLUTE TEMPERATURE
CONDITION FOR LOWER CONSOLUTE TEMPERATURE
for some value of x1 at T=Tuc
for all values of x1 at T >Tuc
0
021
2
P,Tx
G for some value of x1 at T=Tlc
for all values of x1 at T <Tlc
R
ATuc 2
For a Margules mixture
02 Gd phase stability criterion
Why do two liquid phases separate?Why do two liquid phases separate?
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TERNARY SYSTEMSTERNARY SYSTEMSTriangular Diagram
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MIK-Acetone-Water System at 298.15 K
tie line
plait pointbinodal curve
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Acetone-Water-1,1,2-trichloroethane System
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TERNARY SYSTEMSTERNARY SYSTEMS Triangular Diagram
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ASSIGNMENTProblem 11.2-4
11.2-1211.2-1411.2-15
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Phases in Thermodynamic EquilibriumPhases in Thermodynamic Equilibrium
VAPOR
LIQUID
GAS
LIQUID
LIQUID
LIQUID
T TTP P P
Binary mixtures
Basis of analysis:II
ifIif
IIiGI
iG
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Computational skills you must have gained so far…Vapor-Liquid Equilibria
Compute conditions of VLE and develop x-y, T-x-y, and P-x-y diagrams for ideal mixtures and for non-ideal mixtures (using activity coefficient models).
Predict low-pressure VLE when no experimental data are available.
Do bubble point, dew point, and partial vaporization calculations for both ideal and non-ideal systems.
Solubility of a gas in a Liquid Compute the solubility of a gas in a liquid
Solubility of a liquid in a Liquid Compute the compositions when two partially miscible liquids are
mixed
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CONSIDER>>> CONSIDER>>> isobutane (1) – furfural (2) mixtureisobutane (1) – furfural (2) mixture
T = 37.8oC P = 5 bar
phase I
phase II
bar005.0C8.37Tvap2P
bar956.4C8.37Tvap1P
77.12II2030.1I
20716.0II1
x8872.0I2x
018.1II1
375.8I1
9284.0II1
x1128.0I1
x
Question>>>Question>>>Without changing the temperature, is it possible to form a vapor phase that is in equilibrium with the 2 liquid phases?
What is then the bubble-point pressure of the system and the composition of the vapor that forms?
CONCEPT: a liquid mixture will vaporize when its total vapor pressure equals the imposed pressure.
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Phase behavior of isobutane-furfural mixture at 37.8Phase behavior of isobutane-furfural mixture at 37.8ooCC
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Question>>>Question>>>Say, you are doing vapor liquid-equilibrium calculations. When should you be concerned about the possible existence of liquid-liquid equilibrium?
Answer>>>Answer>>>When results of the calculation of vapor pressure as a function of mole fraction would show an unusual maximum and local minimum, you should undertake a liquid-liquid phase equilibrium calculation.
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Phase behavior of ethanol-n-hexane system
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Phase behavior of ethanol-n-hexane system at P = 0.133 bar
heterogeneousazeotrope
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VLLE CALCULATIONS
PiyLif
IIiixL
ifI
iix
AB
Stepwise
SimultaneousTHREE-PHASE FLASH PROBLEMS
Simultaneous equations:equilibrium equations for all speciesmass balance equations
Degree of Freedom?Degree of Freedom?
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ASSIGNMENTProblem 11.3-1
11.3-211.3-411.3-511.3-16
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Partitioning of a Solute Among Two Coexisting Liquid Phases
add solvent shake solute partitionsmixture withsolute
The two liquids are completely immiscible!
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The Distribution Coefficient
IIphaseinsoluteofionconcentrat
IphaseinsoluteofionconcentratK
I1
II1
II1x
I1x
xK
COMPLICATIONS1. presence of undissolved solute2. the two liquids are partially miscible
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Experimental Determination of K
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Octanol-Water partition Coefficient for Species Octanol-Water partition Coefficient for Species ii
phaserichWiniofionconcentrat
phaserichOiniofionconcentratK
Oi
WC
Wi
OC
WiC
OiC
i,OWK
Sometimes used as a measure of hydrophobicity.
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ASSIGNMENTProblem 11.4-1
11.4-211.4-4