5.4 Phase diagrams of binary systems
Φmin=1, Fmax=3
C=2, F=2-Φ+2=4-Φ
Predict by phase law:
Three dimentional diagram
T, P, x
Intercepting plane graph---two dimentional diagrams
T, P, x ----- (T, x)p , (P, x)T or (T, P)x
5.4.1 Phase diagram of miscible binary systems
A
*
AA xpp
B
*
BB xpp
BA ppp
5.4.1.1 Ideal mixed systems:
Two components both follow Raoult’s Law.
( )T, P-x, A+B
)1(*
BA
*
A Axpxp
A
*
B
*
A
*
B )( xppp
( )T, P-x-y
*
B
*
A pp
AA xy A Ay x
* *A BP P
*AP
*BP
xA
Liquid
P
Vapour
Φ=2
F=2-2+1=1(P)
liquid
Liquid/Vapour
A is more volatile than B B is more volatile than A
xx11
d Td T33 d’ d’
xx22
TA*
xx33xx44
T c Tc T22 c’c’
a a’ a a’
b Tb T11 b’ b’
A B TB*
xx 11
TT 11
xx 22
TT 22
xx 33
TT 33
xx22 xx33 xx44
A
The composition variation in the distillation process
How would it be in an closed system?
P-x, liquid(upper line)- gas(lower line)
Getting T-x phase diagram from P-x
Relating P-x and T-x phase diagram
T-x, gas(upper line)-liquid(lower line)
5.4.1.2 The Lever rule
C, total amount of the systems
DE ( tie line ) isothermal
l gCD CEn n
l gCD CEm m
5.4.1.3 The principle of distillation
Simple distillation T T1
T T2Separate a volatile liquid from a non-volatile solute or solid
Theoretical plates: the number of effective vaporization and condensation steps that are required to achieve a condensate of given composition from a given distillate
Fractional distillation