“Oil and water just don’t mix.”

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

T-x Diagram: 2,6-dimethyl pyridine-water systemSolubility of a Liquid in a LiquidSolubility of a Liquid in a Liquid

tie line

T-x Diagram: methyl ethyl ketone-water systemSolubility of a Liquid in a LiquidSolubility of a Liquid in a Liquid

T-x Diagram: perfluoro-n-heptane in various solvents

Measurement of Liquid-Liquid Equilibrium

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.

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?

TERNARY SYSTEMSTERNARY SYSTEMSTriangular Diagram

MIK-Acetone-Water System at 298.15 K

tie line

plait pointbinodal curve

Acetone-Water-1,1,2-trichloroethane System

TERNARY SYSTEMSTERNARY SYSTEMS Triangular Diagram

ASSIGNMENTProblem 11.2-4

11.2-1211.2-1411.2-15

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

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

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.

Phase behavior of isobutane-furfural mixture at 37.8Phase behavior of isobutane-furfural mixture at 37.8ooCC

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.

Phase behavior of ethanol-n-hexane system

Phase behavior of ethanol-n-hexane system at P = 0.133 bar

heterogeneousazeotrope

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?

ASSIGNMENTProblem 11.3-1

11.3-211.3-411.3-511.3-16

Partitioning of a Solute Among Two Coexisting Liquid Phases

add solvent shake solute partitionsmixture withsolute

The two liquids are completely immiscible!

The Distribution Coefficient

IIphaseinsoluteofionconcentrat

IphaseinsoluteofionconcentratK

I1

II1

II1x

I1x

xK

COMPLICATIONS1. presence of undissolved solute2. the two liquids are partially miscible

Experimental Determination of K

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.

ASSIGNMENTProblem 11.4-1

11.4-211.4-4