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Phase Equilibrium - Chemical Process Principles - Lecture Slides, Slides of Chemical Processes

Aligarh Muslim UniversityChemical Processes

Objectives of this course are: (1)Learn about what Chemical Engineers do (2) Learn about basic chemical process units (3) Learn to analyze and solve material balance and energy balance problems. This handout includes: Phase Equilibrium, Graphical Methods for Phase Equilibrium, Vle Phase Diagrams, Boiling Point of N-Heptane, Lever Rule, Eutectic, Solid-Liquid Phase Diagrams, Butanol-Water Demo, Liquid-Liquid Equilibrium, Liquid-Liquid Ternary

Typology: Slides

2012/2013

Uploaded on 08/30/2013

baga.baber
baga.baber 🇮🇳

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Graphical Methods for Phase Equilibrium
Class 21
• Questions about Raoult’s Law
– Dew point
– Bubble point
–Flash
• Graphical methods
– Vapor-liquid
– Lever Rule
– Solid-liquid
– Liquid-liquid
n-pentane and n-heptane at 2 atm
50
60
70
80
90
100
110
120
130
0 0.1 0.2 0.3 0 .4 0.5 0.6 0.7 0 .8 0.9 1
Mole Fraction n-pentane
yi for vapor
xi for liquid
T (C)
Vapor
Liquid
Dew line
Bubble line
Generated from Raoult’s law using the DIPPR vapor pressure correlations
40
50
60
70
80
90
100
110
120
130
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
T (C)
Mole Fraction n-pentane
yi for vapor
xi for liquid
n-pentane and n-heptane at 2 atm
Vapor
Liquid
Dew line
Bubble line
40
50
60
70
80
90
100
110
120
130
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
T (C)
Mole Fraction n-pentane
yi for vapor
xi for liquid
n-pentane and n-heptane at 1.5 atm
Vapor
Liquid
Dew line
Bubble line
VLE Phase Diagrams
(n-pentane/n-heptane)
Mole fraction pentane
(at 1.5 atm) Mole fraction pentane
(at 400 K)
(1) 385 K
(2) 335 K
(3) 358 K
1) What is the boiling point of n-heptane?
2) At what temperature would a liquid mixture of
40% n-heptane and 60% n-pentane begin to boil?
3) At what temperature would a vapor mixture of
40% n-heptane and 60% n-pentane begin to
condense?
VLE Phase Diagrams
(n-pentane/n-heptane)
Mole fraction pentane
(at 1.5 atm) Mole fraction pentane
(at 400 K)
(4) 92% pentane
(5) 39% pentane
(6) 10.2 atm
4) What is the composition of the vapor in equilibrium with a
liquid that is 30% n-heptane and 70% n-pentane?
5) What is the composition of the liquid in equilibrium with a
vapor that is 75% n-pentane and 25% n-heptane?
6) Using the P-xy diagram, what is the vapor pressure of n-
pentane at the temperature for which the diagram was
prepared?
Lever Rule
2 distinct phases and 2 components
• Total m ole balance: nF= nL+ nV
(or nV= nF–n
L)
• Species m ole balance zAnF= xAnL+ yAnV
• Now substitute for nVzAnF= xAnL+ yA(nF–n
L)
• Group F terms on left and L terms on right
(zA-y
A) nF= (xA–y
A) nL
Feed Vapor
Liquid
n
F
z
A
n
L
x
A
n
V
y
A
Feed Vapor
Liquid
Feed Vapor
Liquid
n
F
z
A
n
L
x
A
n
V
y
A
AA
AA
AA
AA
F
Lxy
zy
yx
yz
n
n
pf3

Partial preview of the text

Download Phase Equilibrium - Chemical Process Principles - Lecture Slides and more Slides Chemical Processes in PDF only on Docsity!

Graphical Methods for Phase Equilibrium

Class 21

  • Questions about Raoult’s Law
    • Dew point
    • Bubble point
    • Flash
  • Graphical methods
    • Vapor-liquid
    • Lever Rule
    • Solid-liquid
    • Liquid-liquid

n-pentane and n-heptane at 2 atm

Mole Fraction n-pentane
yi for vapor
xi for liquid
T (C)
Vapor
Liquid
Dew line
Bubble line

Generated from Raoult’s law using the DIPPR vapor pressure correlations

T (C)

Mole Fraction n-pentane yi for vapor xi for liquid

n-pentane and n-heptane at 2 atm

Vapor

Liquid

Dew line

Bubble line

T (C)

Mole Fraction n-pentane yi for vapor xi for liquid

n-pentane and n-heptane at 1.5 atm

Vapor

Liquid

Dew line

Bubble line

VLE Phase Diagrams

(n-pentane/n-heptane)

Mole fraction pentane

(at 1.5 atm)

Mole fraction pentane

(at 400 K)

(1) 385 K
(2) 335 K
(3) 358 K
  1. What is the boiling point of n-heptane?
  2. At what temperature would a liquid mixture of 40% n-heptane and 60% n-pentane begin to boil?
  3. At what temperature would a vapor mixture of 40% n-heptane and 60% n-pentane begin to condense?

VLE Phase Diagrams

(n-pentane/n-heptane)

Mole fraction pentane

(at 1.5 atm)

Mole fraction pentane

(at 400 K)

(4) 92% pentane

(5) 39% pentane

(6) 10.2 atm

  1. What is the composition of the vapor in equilibrium with a liquid that is 30% n-heptane and 70% n-pentane?
  2. What is the composition of the liquid in equilibrium with a vapor that is 75% n-pentane and 25% n-heptane?
  3. Using the P-xy diagram, what is the vapor pressure of n- pentane at the temperature for which the diagram was prepared?

Lever Rule

2 distinct phases and 2 components

  • Total mole balance: n (^) F = nL + nV

(or nV = nF – nL )

  • Species mole balance z (^) A nF = xA nL + yA nV
  • Now substitute for nV z (^) A nF = xA nL + yA (nF – nL )
  • Group F terms on left and L terms on right

(z A - yA) nF = (xA – yA) nL

Feed Vapor

Liquid

n (^) F zA

nL x (^) A

nV yA

Feed Vapor

Liquid

Feed Vapor

Liquid

n (^) F zA

nL x (^) A

nV yA

A A
A A
A A
A A
F
L

y x

y z

x y

z y

n

n

  

 

Lever Rule

Graphical Interpretation (very useful)

Feed Vapor

Liquid

n F zA

nL x (^) A

nV yA

Feed Vapor

Liquid

Feed Vapor

Liquid

n F zA

nL x (^) A

nV yA

A A

A A A A

A A F

L

y x
y z
x y
z y
n
n

T

Mole fraction

LF V

Distance B

Distance A

xA zA yA

T

Mole fraction

LF V

Distance B

Distance A

xA zA yA

  • Distance A corresponds to yA – z (^) A.
  • Distance B corresponds to yV – xA.
  • Therefore, nL /nF = Distance A / Distance B!!
  • In practice, you can use the actual mole fractions or use the

measured distance using a ruler

Intuition: As you get closer to the liquid line, you have more liquid!

VLE Phase Diagrams

(n-pentane/n-heptane)

part (7)

Mole fraction pentane

(at 1.5 atm)

Mole fraction pentane

(at 400 K)

Use lever rule. L/F = (0.58 – 0.3)/(0.58 – 0.22) or 2.8 boxes/(2.8 + 0.8) = 0.

  1. A feed stream of 30% n-pentane and 70% heptane is brought to a pressure of 1.5 atm and a temperature of 360 K. What is the composition and amount of the liquid and the vapor streams in equilibrium at this condition?

xpent = 0.22 ypent = 0.

Mole fraction of A

Solid B + Eutectic Solid A + Eutectic

Solid-Liquid Phase Diagrams What is a Eutectic???

• Solid crystals having a composition that is

a mixture of pure components

• Not in equilibrium with any liquid solution,

but may be in equilibrium with a pure solid

– i.e., a fraction of the solid is pure component,

and the rest is the crystals with mixed

composition

Mole fraction of A

Solid B + Eutectic Solid A + Eutectic

Solid-Liquid Phase Diagrams

Eutectic composition

Eutectic point

(no liquid below

this temperature)

Mole fraction of A

Solid B + Eutectic Solid A + Eutectic

Solid-Liquid Phase Diagrams

  1. What phases are present for a mixture of 30% A at 320 K?

  2. What phases are present for a mixture of 60% A at 320 K?

  3. What phases are present for mixture of 50% A at 300 K?

  4. For a mixture of 80% A, what phases are present at equilibrium at 310 K? How much of each phase is present?

  5. Pure Solid B and solution with 52% A

  6. Solution with 60% A

  7. Solid B and solid eutectic of 65% A

  8. Solid A and solution with 68% A 2/3.2 = 62.5% of material is solution, 37.5% solid A