Transcript Solution Thermodynamics: Theory

Chemical Engineering Thermodynamics
Lecturer: Zhenxi Jiang (Ph.D. U.K.)
School of Chemical Engineering
1
Chapter 12
Solution Thermodynamics: Application
2
12.2 Models for the Excess Gibbs Energy
In general GE/RT is a function of T, P, and
composition, but for liquids at low to
moderate pressures it is a very weak
function of P. Therefore the pressure
dependence of activity coefficients is
usually neglected. Thus, for data at
constant T:
G
E
RT
 g ( x1 , x 2 , ..., x N )
(const T )
The Margules equation, Eq. (12.9), is an example of this functionality.
3
12.2 Models for the Excess Gibbs Energy
A number of other equations are in
common use for correlation of activity
coefficients. For binary systems (species 1
and 2) the function most often
E
represented by an equation is G / x1 x 2 R T ,
which may be expressed as a power
series in x1:
G
E
x1 x 2 RT
 a  bx1  cx    
2
1
(const T )
4
12.2 Models for the Excess Gibbs Energy
Because x2=1-x1, mole fraction x1 serves
as the single independent variable. An
equivalent power series with certain
advantages is known as the Redlich/Kister
expansion:
G
E
x1 x 2 RT
 A  B ( x1  x 2 )  C ( x1  x 2 ) 
2
(12.14)
In application, different truncations of this series are
appropriate, and in each case specific expressions for ln  1 and
ln  2 are generated from Eq. (11.96).
5
12.2 Models for the Excess Gibbs Energy
Because x2=1-x1, mole fraction x1 serves
as the single independent variable. An
equivalent power series with certain
advantages is known as the Redlich/Kister
expansion:
G
E
x1 x 2 RT
 A  B ( x1  x 2 )  C ( x1  x 2 ) 
2
(12.14)
In application, different truncations of this series are
appropriate, and in each case specific expressions for ln  1 and
ln  2 are generated from Eq. (11.96).
6
12.2 Models for the Excess Gibbs Energy
7
12.2 Models for the Excess Gibbs Energy
8
12.2 Models for the Excess Gibbs Energy
9
12.2 Models for the Excess Gibbs Energy
Local Composition Models
10
12.2 Models for the Excess Gibbs Energy
Local Composition Models
11
12.2 Models for the Excess Gibbs Energy
Local Composition Models
12
12.2 Models for the Excess Gibbs Energy
Local Composition Models
13
12.3 Property Changes of Mixing
14
12.3 Property Changes of Mixing
15
12.3 Property Changes of Mixing
16
12.3 Property Changes of Mixing
17
12.3 Property Changes of Mixing
18
12.3 Property Changes of Mixing
19
12.3 Property Changes of Mixing
20
12.3 Property Changes of Mixing
21
12.3 Property Changes of Mixing
22
12.3 Property Changes of Mixing
23
12.3 Property Changes of Mixing
24
12.3 Property Changes of Mixing
25
12.3 Property Changes of Mixing
26