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5.4 Phase diagrams of binary systems

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5.4 Phase diagrams of binary systems

Predict by phase law:

C=2, F=2-Φ+2=4-Φ

Φmin=1, Fmax=3

T, P, x

Three dimentional diagram

Intercepting plane graph---two dimentional diagrams

T, P, x ----- (T, x)p , (P, x)T or (T, P)x

- Liquid-liquid
- Miscible
- Partly-miscible
- Immiscible
- Liquid-solid
- Water-salt
- Solid-solid

5.4.1.1 Ideal mixed systems:

Two components both follow Raoult’s Law.

( )T, P-x, A+B

( )T, P-y, A+B

Liquid

P

Vapour

xA

( )T, P-x-y

liquid

Liquid/

Vapour

Φ=2

F=2-2+1=1(P)

A is more volatile than B

B is more volatile than A

( )PT-x

Ｔ2

Ｔ3

x1

Ｔ1

x2

x3

x2

x3

x4

TB*

The composition variation in the distillation process

TA*

d T3 d’

c T2c’

T

b T1 b’

a a’

x4

x3

x2

x1

A B

A

How would it be in an closed system?

Relating P-x and T-x phase diagram

Getting T-x phase diagram from P-x

P-x，liquid(upper line)- gas(lower line)

T-x，gas(upper line)-liquid(lower line)

C, total amount of the systems

DE（tie line） isothermal

Phase equilibrium variation at constant temperature

---the level rule

T T1

T T2

Simple distillation

Separate 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

P-x and T-x phase diagrams of non-ideal miscible binary systems

Azeotropes

Low-boiling azeotrope

Low-boiling azeotrope

351.28K，95.57

High boiling azeotropes

381.65 K

HCl 20.24

The maximum azeotropic point

- Y: P161 17, 18
- A: P215 8.5(a), 8.6(a)
- Preview:
- Y: 5.5,5.6, 5.7
- A:8.5, 8.6