Course Slides Jan 05 2015(1)

8/10/2019 Course Slides Jan 05 2015(1)

http://slidepdf.com/reader/full/course-slides-jan-05-20151 1/154

Copyright @ Samir H. Mushrif

Samir H [email protected]

http://www.ntu.edu.sg/home/shmushrif/

Division of Chemical and Biomolecular Engineering

School of Chemical and Biomedical Engineering

Nanyang Technological University, Singapore

1




Suraj [email protected]

Division of Chemical and Biomolecular Engineering

School of Chemical and Biomedical Engineering

Nanyang Technological University, Singapore

2




3




4Samir H Mushrif (7) Suraj Vasudevan (6) Introduction to Unit Operations/Separation

Processes

Fundamentals

Phase Equilibria/Diagrams

Thermodynamics of Phase Equilibria

Modeling Phase Equilibria

Distillation

Flash Distillation

Column Distillation

Advanced Binary Distillation

Multicomponent Distillation

Absorption and Stripping

Liquid – Liquid Extraction

Mass Transfer Equipment – Design and

Operation Mass Transfer Analysis

Separation using Membranes

Adsorption and Chromatography

Aspen – HYSYS

All the exams and quizzes will be open book type (Wankat Textbook, handwritten class

notes and Slides only. NO laptops, netbooks, ipads, palmtops, smartphones, tablets)

Final Exam (5060%)

25 30% on Fundamentals and Distillation (Samir)

25 30% on Other Separation Processes (Suraj)

Two quizzes/midterms (35 45% combined)

First on Fundamentals and Distillation (Samir)

Second on Other Separation Processes (Suraj)

Assignments (Upto 5%)

What if you miss a quiz?

Can take it again, but the next

one will be harder.




5

Textbook

• Separation Process Engineering . Phillip C. Wankat, 2nd/3rd Edition, Prentice

Hall, New Jersey. Other Reference Books

• Seader, J.D and Henley, E.J. (1998) New Jersey, Separation Process

Principles, 3rd Edition, John Wiley, 2010

• Cussler E.L, Diffusion; Mass Transfer in Fluid Systems, end Ed. New York:

Cambridge University Press, 3rd Edition, 1997• McCabe, W.L. Smith, J.C. and Harriot P, Unit Operations of Chemical

Engineering, 7th Edition, Singapore: McGraw-Hill, (2005)

• Treybal, R.E. (1981), Mass-Transfer Operations, 3rd Edition, Singapore:

McGraw-Hill

• Perry, RH, Green DW, Perry’s Chemical Engineers’ Handbook, 8th Edition,

McGraw-Hill – Available Online (2008)

Recommended Books

How to read a Unit Operations book?

Page no. X to Page no. Y or Look for the concepts




6

Please attend lectures and tutorials and browse previous lecture notes before you come

for a class. Learning in a class is a lot easier than self –study.

Every lecture is like a step in the ladder. If you miss a step, you may have problem

climbing the next (We will do a brief review at the beginning). You may forget the equations, but not the concepts

Silence in the classroom please. Time will be given for discussion.

Active class participation is strongly encouraged. Ask questions. I shall be in the lecture

theatre 2530 mins. before the lecture begins. Even after the class/tutorial is okay.

Please don’t use laptops, smartphones, ipads etc. in the classroom

Please take notes during the class. Slides only give an overview.

Solve problems and read books. Solve problems to develop your “application” skills; not

because one of them will be in the exam! Watching lecture videos or reading slides is

not sufficient.

Don’t delay your studies till the very last minute

General Recommendations and Policy

Open door policy (N1.2 –B2 –23). 2 hrs. every week for consultation (Let’s decide thetime now!). Come in groups, if possible.

Asking conceptual questions by email … may not be a good idea!

NO consulting 3 days before the exam

Video recording of lectures and slides on the web. Will rerecord, if needed.


http://slidepdf.com/reader/full/course-slides-jan-05-20151 7/154Copyright @ Samir H. Mushrif

7



8Where does this course fit into your curriculum?



9Course Objectives

To learn about different separation processes commonly employed

in industries.

To understand the fundamentals behind these processes and theoperation of separation equipments.

To understand how operating conditions, equipment design and

process variables can affect the separation

To be able to control a process, you have to know the processinside –out

To be able to design some of the most important unit operations like

distillation

Use the state of the art computational tools for design and analysis

of unit operations



10Learning Outcome (Take a look at this slide at the end of the semester )

At the end of the course, you should

Have a list of some of the key separation processes employed in the

industry Be able to read and interpret the thermodynamic data (in the form of

Temperature –Pressure –Composition Diagrams)

Be able to use the data to decide the type of separation method to be

employed

Be able to design single stage processes

Be able to explain how single stage processes can be combined in an

efficient manner to form cascades

Be able to use graphical, mathematical and computational tools to design

countercurrent separations

Be able to design multicomponent systems using HYSYS

Build a strong foundation which will prepare you to learn advanced

separation processes and to handle complications in actual

implementation of these processes



11



12Separations in a Chemical Plant (> 50% of the capital and operating costs)

www.ontime.methanetomarkets.org

Oil Refinery Demonstration

http://www.youtube.com/watch?gl=SG&feature=related&v=zvV2sSMnyKU

http://www.youtube.com/watch?gl=SG&feature=related&v=zvV2sSMnyKU



13History of Unit Operations and Chemical Engineering

Arthur D. Little William H. Walker Warren K. Lewis

Pictures from MIT and ACS websites

“Chemical Engineering” as a distinct profession. Difference between a chemical

engineer and a chemist.

Arthur D. Little coined the term “Unit Operation”

William H. Walker and Arthur D. Little formed a company and later Walker returnedto MIT

Warren K Lewis, the first head of the chemical engineering department at MIT



14Mixing vs. Separation

What is spontaneous, MIXING or SEPARATION? And why?






S T H G






S T H G 1. Change in free energy has to be +ve or –ve?

2. How does the entropy of the system change upon mixing?

3. What is ∆H related to?






S T H G 1. Change in free energy has to be +ve or –ve?

2. How does the entropy of the system change upon mixing?

3. What is ∆H related to?

Water and alcohol mix at room temperature

Oil and water do not mix at room temperature

Oil and water may mix at a higher temperature




19Types of Separation

Distillation

Evaporation

Extraction

Crystallization

Drying

Absorption

OsmosisFiltration

Dialysis

Pervaporation

Adsorption

Ion – Exchange

Centrifugation

Electrolysis




20How to select a separation process?

Feed and Product Conditions

• Concentration of the species to be removed

• Flowrate of the feed

• Temperature, Pressure

• Physical State of the feed (Solid, liquid, gas)

Property Differences amongst the Components

• Molecular• Thermodynamic

• Transport

Characteristics of the Operation

• Ease of Scale – up

• Energy requirement

• Size Limitations

• Temperature, Pressure and Physical state requirements




21Three important questions to ask for separations

Will it happen? If yes, how much?

Equilibrium

How fast?

Kinetics

Sodium Chloride Video

mequilibriu K RT G ln

F r e e

E n e r g y

F r e e

E n e r g y

RT E a

Aek

https://www.youtube.com/watch?v=oZdQJi-UwYs

https://www.youtube.com/watch?v=oZdQJi-UwYs




22Separations vs. Reactions

Typical Properties

• Chemical potential, equilibrium

coefficient, saturation capacity etc.

Reaction Equilibrium analogous to Separation Equilibrium and Reaction Kinetics

analogous to Separation Kinetics

Typical Properties

• Mass transfer coefficient, Diffusion

coefficient (Diffusivity)




23Separations vs. Reactions

Typical Properties

• Chemical potential, equilibrium

coefficient, saturation capacity etc.

Reaction Equilibrium analogous to Separation Equilibrium and Reaction Kinetics

analogous to Separation Kinetics

Typical Properties

• Mass transfer coefficient, Diffusion

coefficient (Diffusivity)

Water + Dimethyl Sulfoxide




24What controls the separation processes?

Many of the separation processes are equilibrium limited.

Thermodynamic equilibrium data is crucial for the design of aseparation process

Mathematical description of the underlying phenomenon is equally

important

For polymers attracted to the surface,

there is no kinetic barrier but the

protein competes with the polymer for

adsorption sites. Polymers that are not

attracted to the surface present a large

steric barrier but not very good

thermodynamic prevention because ofthe ability of the protein to deform the

polymer layer.Satulovsky J et al. PNAS 2000;97:9037-9041

25




25

26




26Thermodynamic Equilibrium

Thermal Chemical Mechanical

Temperatures are

the same

Chemical potentials

are the same

Pressures are the

same

Phase Equilibria

(Phase Creation and Phase Addition type Separation Processes – Distillation)

The equilibrium relationships between phases (such as vapor, liquid, solid) of a chemical

compound or mixture under various conditions of temperature, pressure, and composition McGraw Hill Science and Technology Dictionary

Water and Steam in equilibrium at 100 C and 1 atm. pressure

27




27Phase Diagram of Water (Single Component)

28




28Critical Point of Water

SupercriticalConditions

http://www.science.uva.nl/research/mgrd/video-cp.html

29




29Phase Diagram for a Binary System

Mass Transfer Operations – Treybal

Now composition comes into picture!

30




30Gibb’s Phase Rule

2 P C F

Degrees of Freedom Number of Components Number of Phases

Examples

• How many triple points can be there for water?

• What are the maximum number of phases in a binary mixture?

Liquid

A

Liquid

B

Vapor

A

Vapor

B Number of components = C (i , j, k, …, C )

Number of phases = P (α, β, γ, …, P )

Temperatures = T α , T β , T γ ,… T P

Pressures = pα , p β , pγ ,… p P

Chemical Potentials = μαi , μα j , μαk , … μαC

μ β i , μ

β j , μ

β k , … μ β

C

…

μ P i , μ

P j , μ

P k , … μ P

C

31





Thermal

Chemical

Mechanical

Phase Equilibria: Thermal, Chemical and Mechanical Equilibria

Equations1...

P T T T

P

Equations1... P p p p P

Equations1

...

...

...

P

CCC

P j j j

P

iii

P C

phasestheallof PressureandeTemperatur

phasestheallincomponentsof FractionsMole

21variablesof numberTotal P C P

32





2

1221

Equationsof Numbervariablesof NumberFreedomof Degrees

P C F

P C P C P F

This phase rule is applicable to non – reacting systems

The degrees of freedom correspond to the intensive variables like mole

fractions, pressure and temperature.

Once you select all your degrees of freedom, there exists a unique system.

C P F

1 1 2

1 2 1

1 3 0

33C f f




33Concept of Vapor Pressure – In the context of VLE

What happens if I keep a bowl of water in open for 12 hrs. at 50 C

on a very hot summer day?

What happens if I keep a lid and cover the bowl?

What is the vapor pressure of water at 100 C?

34C t f V P I th t t f VLE




34Concept of Vapor Pressure – In the context of VLE

What happens if I keep a bowl of water in open for 12 hrs. at 50 C

on a very hot summer day?

What happens if I keep a lid and cover the bowl?

What is the vapor pressure of water at 100 C?

35V Li id E ilib i (Si l t bi )




35Vapor – Liquid Equilibria (Single component vs. binary)

Water boils at 100 C under 1 atm. Pressure

At 100 C, vapor pressure of water is equal to 1 atm.

D E

T e m p

e r a t u r e ( C )

q (KJ/kg)A

A

B

B

C

C

D

E

Subcooled

Water

Saturated

Water Only

Water and

Steam

SaturatedSteam Only

Superheated

Steam

How would this curve look at different pressures? Why?

How would this curve look if I have a water (100 C)+ ethanol (78.4 C) mixture?

What will be the boiling point of the mixture?






Single component VLE Binary VLE

Is the composition of the liquid and the vapor phase same?

If not, can you say something about the distribution? Justify your argument.

Vapor pressure of Water and Water + ethanol mixture same as atmospheric pressure






Single component VLE Binary VLE

Is the composition of the liquid and the vapor phase same?

If not, can you say something about the distribution? Justify your argument.

Vapor pressure of Water and Water + ethanol mixture same as atmospheric pressure

A binary mixture boils over a range of temperature and the liquid (andvapor) composition changes during the phase transition. Explain.

38Bi VLE Di (C t t P )




38Binary VLE Diagram (Constant Pressure)

T e m p e r a t u r e ( C )

Mole Fraction of component “A” ( xA, yA)0 1

b

AT

b

BT

Liquid

Vapor

Bubble point

Curve

Dew point

Curve

Liquid + Vapor

xA=0.5

yA=0.81

39Wh t i th diff b t th t VLE di ?




39What is the difference between these two VLE diagrams?

T e m

p e r a t u r e ( C )

Mole Fraction of component“A” ( xA, yA)

T e m








T e m



T e m



A A

A A

A A

A A AB

y x

x y

x x

y y

1

1

1

1VolatlityRelative

41How would the Composition Curve for “A” ( ) look like?




41How would the Composition Curve for “A” ( xA, yA) look like?

T e m



42How would the Composition Curve for “A” (x y ) look like?




Mole Fraction of component“A” ( xA) in Liquid

M o l e F r a c

t i o n o f c o m p o

n e n t

“ A ”

( y A

) i n V a p o r

A x

A y

T e m



A x A y

How would the Composition Curve for “A” ( xA, yA) look like?

43How would the Enthalpy Composition Curve look like?




How would the Enthalpy –Composition Curve look like?

T e m p e

r a t u r e ( C )

Mole Fraction of component

“A” ( xA, yA)

44How would the Enthalpy Composition Curve look like?




How would the Enthalpy –Composition Curve look like?

T e m p e

r a t u r e ( C )


“A” ( xA, yA)

E n t h a l p y ( K J / m o l )


“A” ( xA, yA)

45How would the Pressure Composition Curve look like?




How would the Pressure –Composition Curve look like?

T e m p e

r a t u r e ( C )


“A” ( xA, yA)

46How would the Pressure Composition Curve look like?




How would the Pressure –Composition Curve look like?

T e m p e

r a t u r e ( C )


“A” ( xA, yA)

P r e s s u r e ( a t m . )


“A” ( xA, yA)

47Boiling of a Binary Mixture at Constant Pressure




Boiling of a Binary Mixture at Constant Pressure



b

AT

b

BT

Liquid

Vapor

Bubble point

Curve

Dew point

Curve

L

V

L

A x

V

A y

?andaboutsayyoucanWhat V

A

L

A y x

How do I travel on the composition curve if I transform a liquid of composition “x LA” completely to vapors?






T e m p

e r a t u r e ( C )


b

AT

b

BT

Liquid

Vapor

Bubble point

Curve

Dew point

Curve

L

V

L

A x

V

A y

V

A

L

A

V

A

L

A y x y x ?andaboutsayyoucanWhat






T e m p

e r a t u r e ( C )


b

AT

b

BT

Liquid

Vapor

Bubble point

Curve

Dew point

Curve

L

V

L

A x

V

A y

1 B1 D

1 B

A x

1 D

A x

Tie Line






T e m p

e r a t u r e ( C )


b

AT

b

BT

Liquid

Vapor

Bubble point

Curve

Dew point

Curve

L

V

L

A x

V

A y

1 B2 B

1 D

2 D

2 B

A x

2 D

A x






T e m p

e r a t u r e ( C )


b

AT

b

BT

Liquid

Vapor

Bubble point

Curve

Dew point

Curve

L

V

L

A x

V

A y

1 B2 B

3 B

1 D

2 D

3 D

3 B

A x

3 D

A x

52Mass balance for the two phases




Mass balance for the two phases



b

AT

b

BT

Liquid

Vapor

Bubble point

Curve

Dew point

Curve

L

V

L

A x

V

A y

1 B2 B 1 D

2 D E

phases?)(vaporand)(liquidof amountsrelativethe bewhat would

, pointreachesittillheatedisncompositiowithfeedof molesIf

V L

E x F L

A

2 B

A x

2 D

A x

53Lever – Arm Rule




Lever Arm Rule

2of length

2of length

get,we(b)Equationinto(a)equationfromngSubstituti

(b)

: balanceMaterialA""Component(a)

: balanceMaterialOverall

2

2

22

22

EB

ED

V

L

x x L x xV

F

Vx Lx Fx

V L F

L A B A

D A

L A

x x

x x

L

A

B

A

D

A

L

A

D

A

B

A

L

A

54




55Thermodynamics of Phase Equilibria




Thermodynamics of Phase Equilibria

Thermal Chemical Mechanical

Temperatures are

the same

Chemical potentials

are the same

Pressures are the

same

Phase Equilibria

(Phase Creation and Phase Addition type Separation Processes – Distillation)

The equilibrium relationships between phases (such as vapor, liquid, solid) of a chemical

compound or mixture under various conditions of temperature, pressure, and composition McGraw Hill Science and Technology Dictionary

What is Chemical Potential? And Why does it have tobe equal for a component in all phases at equilibrium?

56Equality of Chemical Potentials




Equality of Chemical Potentials

V

B

L

B

V

A

L

A

B

V

B A

V

A B

L

B A

L

A

B

V

B B

L

B A

V

A A

L

A

B

nT P B

A

nT P AnnT nn P

B A

Vyd Vyd Lxd Lxd

Vyd Lxd Vyd Lxd dG

G P T

dnn

Gdn

n

GdP

P

GdT

T

GdG

B A

P T G

nn P T f G

B

A

A

B B A B A

and

0

)(minmequilibriuatissystemwhen the,and particular aAt

andcomponentsof amounts

and,inchangessmalltodueinchangeThe

,,,

,,,,,,,,

57Do I have a “chemical potential meter”?




p

""componentof fugacitytheis

lngasidealanlike behaveseverythingnotBut

ln

componentinchangetodueis pressureinchangetheIf

pressureof in terms

potentialChemical

can writewegasidealanFor

mics,ThermodynaFrom

,,,

,,,

2

i f

f RTd d

P RTd d

i

P P

RT

n

V

P

RT nV

P n

V

n P

G

i

ii

ii

nT

i

in P T ii

i

nT

i

n P T ii

j j

j j

58VLE in terms of “Fugacity”




g y

V

i

L

i f f

m,EquilibriuLiquid-VaporAt

Fugacity is something like “pressure”

Single component VLE

Water and Steam in equilibrium at 100 C – Vapor pressure of water and

(partial) pressure of steam are equal

P yVP x wwW

59VLE in terms of “Fugacity”




g y

V

i

L

i f f


Fugacity is something like “pressure”

Binary VLE

Vapor and Liquid phases of water and ethanol in equilibrium at T C, VP of

the system equal to P (Ideal gas and Ideal Liquid)

P yVP x iii

60VLE in terms of “Fugacity” (non – ideal systems)




g y ( y )

Where does the non – ideality for gases and liquids come

from?

61VLE in terms of “Fugacity” (non – ideal systems)




g y ( y )

tcoefficienfugacity

statestandardatfugacitycomponent pure

tcoefficienactivity

where

aswritten becanequationAbove


0

i

0i

i

i

iiii

V

i

L

i

f

P y f x

f f

Where does the non – ideality for gases and liquids come

from? – Intermolecular Forces

62How to calculate these coefficients?




Liquid Phase Gas Phasei tCoefficienActivity i tCoefficienFugacity

van Laar

NRTL

UNIQUAC

UNIFAC

Margules

Van der Waals EOS

Redlich – Kwong (RK)

Peng – Robinson (PR)

Elliott, Suresh, and Donohue

(ESD)

63VLE of an ideal system (Ideal Liquid and Ideal Gas)




tCoefficienonDistributi

LawsRaoult'calledalsoisequationaboveThe

1:GasIdealanFor

,1:LiquidIdealanFor


0i

0i

ii

i

i

iii

i

ii

iiii

V

i

L

i

K P

VP

x

y

P yVP x

VP f

P y f x f f

64Binary Vapor Pressure Curve using Raoult’s Law




P P y P yVP xVP x P yVP x

B A P

B

P

A B B A Aiii

B A A A VP xVP x P 1

Mole Fraction of component “A” ( xA)

P r e s s u r e

0 1

T







P r e s s u r e

0 1

T Can you calculate the “red

(P vs.y A)” curve?







P r e s s u r e

0 1

T

P

VP x y

P

VP x y

P

VP x y

P yVP x

B A A

B B B

A A A

A A A

11

????1

1

B

A

A A

A A

VP

VP

y x

x y

Can you calculate the “red








P r e s s u r e

0 1

T

P

VP x y

P

VP x y

P

VP x y

P yVP x

B A A

B B B

A A A

A A A

11

B

A AB

B

A

A A

A A

K

K

VP

VP

y x

x y

VolatilityRelative

1

1

Can you calculate the “red


68How to construct a T – xy diagram for an ideal system?




C T

B AVP

x

x y

VP

VP

y x

x y

AB A

A AB A AB

B

A

A A

A A

log

:EquationAntoine

chartPriesterDeMethodsGraphical

EquationAntoine

data pressurevaporcomponent puretheisneedyouAll

111

1

Can you calculate the boiling point of Ethanol at 1 atm. if I give you

the Antoine Equation parameters?

69De Priester chart




From Separati on Process Engi neeri ng, Thi rd Editi on by Phillip C. Wankat

(ISBN: 0131382276) Copyright © 2012 Pearson Education, Inc. All rights reserved.

70Binary y – x diagram for an ideal system (constant α)





“A” ( xA) in Liquid

M o l e F r a c t i o n o f c o m p o n e

n t

“ A ” ( y

A ) i n V a p o r

A x

A y

Increasing α

71An interesting question





“A” ( xA) in Liquid

M o l e F r a c t i o n o f c o m p o n e

n t

“ A ” ( y

A ) i n V a p o r

A x

A y

11

AB A

A AB A

x x y

Can you prove mathematically

that a ( y,x) curve defined by the

following equation (with

constant α AB) can not look like

the “blue”, “red” or “green”

curves shown in this figure?

72Bubble and Dew Point Calculation




I have a mixture (liquid phase) of two components, A and B, with

mole fractions x A and x B , at pressure P . What is the bubble point of

the mixture?

OR

I have a mixture (vapor phase) of two components, A and B, withmole fractions x A and x B , at pressure P . What is the dew point of

the mixture?

Do not construct the entire (T, xy) diagram.

Antoine equation parameters are given and assume ideal mixture.

73Bubble and Dew Point Calculation




iterate.not,If .1if Check5.

andfractions;mole phasevaportheCalculate4.

at, pressuresvaporcomponent puretheCalculate3.

asguessretemperatuinitialanTake2.

pressuregivenat the

andof pointsBoilingtheCalculate1.

B A

B B B

A A A

initial B A

B

B B

B

A Ainitial

B

B

B

A

y y

P

VP x y

P

VP x y

T VP VP

T xT xT

P

T BT A

74




75Deviations from Ideal Behavior





T o t a l P r e s s u r e

0 1

T

Mole Fraction of component “A” ( xA)0 1

T

BVP

AVP

T o t a l P r e s s u r e

BVP

AVP

What gives rise to non – ideality? – Intermolecular Forces

(Tendency of molecules to escape)

76+ve Deviation from Raoult’s Law




Mole Fraction of component “A” ( xA

)

P r e s s u r e

0 1

T

BVP

AVP

A A A

A A A

A

A A

A A A A

V

A

L

A

VP x P y

P yVP x

VP f

P y f x

f f

A

0A

0A

1:GasIdealanFor

,1:LiquidIdealanFor


idealisphasegasthe

andideal-nonisphaseliquidtheIf

)veislog(

)veislog(

idealityfromdeviationve:1γ

idealityfromdeviationve:1γ

A

A



78Small Deviation vs. Large Deviation





P r e s s u r e

0 1

T

BVP

AVP


P r e s s u r e

0 1

T

BVP

AVP

What is the difference when the deviations are large?

79Small Deviation vs. Large Deviation





P r e s s u r e

0 1

T

BVP

AVP


P r e s s u r e

0 1

T

BVP

AVP

What is the difference when the deviations are large?

Is there a maximum in pressure? Do we have the same pressure for two

different compositions?

80P – xy Curves for Large Deviation from ideality




Mole Fraction of “A” ( x A ,y A)

P r e s s u r e

0 1

Liquid (P vs. x A)

Vapor (P vs. y A)






P r e s s u r e

0 1

Liquid (P vs. x A)

Vapor (P vs. y A)

Can it look like this?Explain mathematically and physically.






P r e s s u r e

0 1

Liquid (P vs. x A)

Vapor (P vs. y A)

Can it look like this?Explain.

B B A A

B A B A A B A

B A B B B A A A

B B A

A

A A

A A A

B A

A

B A A A

x y x y

K K x x K y y

x K x K y x K y

K P

VP

P

VP

x

y K

P yVP x

VP VP

x

P P

VP xVP x P

,

1

and

FugacityVaporFugacityLiquid

ismequilibriuforconditionBut the

0then,inmaximumaisthereIf

1

BA

A

BA

BA






P r e s s u r e

0 1

Liquid (P vs. x A)

Vapor (P vs. y A)


Liquid (P vs. x A)

Vapor (P vs. y A)

P r e s s u r e

What is the difference between these two curves? Explain using intermolecular forcesand thermodynamics Vapor – Liquid composition is the same for a particular composition

The more volatile component becomes a less volatile component

VP at a composition is more than the individual component vapor pressures

10

84T – xy and x – y Curves for Large Deviation from ideality





T e m p e r a t u r e

0 1

Liquid (P vs. x A)

Vapor (P vs. y A)

Mole Fraction of “A” in Liquid ( x A)

0 1 M o l e F r a c t i o

n o f “ A ” i n V a

p o r ( y A

)

Minimum Boiling Azeotrope – Constant Boiling Mixture

85-ve Deviation from Ideality





P r e s s u r e

0 1

T

BVP

AVP

A c t i v i t y C o e f f

. γ

A / B

0 1Mole Fraction of component “A” ( xA)

1 B

A

What will be the boiling point of an azeotrope of a mixture which

shows large – ve deviations from ideality?

86P – xy Curves for Large –ve Deviation from ideality





P r e s s u r e

0 1

Liquid (P vs. x A)

Vapor (P vs. y A)


Liquid (P vs. x A)

Vapor (P vs. y A)

P r e s s u r e

10

What is the difference between these two curves? Explain using intermolecular forcesand thermodynamics Vapor – Liquid composition is the same for a particular composition

The more volatile component becomes a less volatile component

VP at a composition is less than the individual component vapor pressures



88Partial Miscibility – Heteroazeotropes (Large +ve deviations)






0 1

Liquid

(T vs. x A)

Vapor (T vs. y A)




p o r ( y A

)

A

B

C

A

B C

How will the VLE composition look like when you are in the 2 –

phase region?







0 1

Liquid

(T vs. x A)

Vapor (T vs. y A)




p o r ( y A

)

A

B

C

A

B C

A* C*B*

2 Liquids





Mole Fraction of “A” ( x A ,y

A)


0 1

Liquid

(P vs. x A)

Vapor (P vs. y A)

Mole Fraction of “A” in Liquid ( x A

)0 1 M

o l e F r a c t i o


p o r ( y A

)

Why “Heteroazeotropes” are Minimum Boiling Azeotropes?

Why does the liquid phase split at lower temperatures?

91Some examples




Ideal Mixture

• Hexane + Heptane, Benzene + methyl benzene, 1-propanol +

2-propanol

Positive Deviation from Raoult’s Law

• Water + Ethanol (minimum boiling azeotrope)

• CS2 + Acetone (minimum boiling azeotrope)

Negative deviation from Raoult’s Law

• Chloroform + Acetone (maximum boiling azeotrope)

• Water + Nitric Acid (maximum boiling azeotrope)

Heteroazeotropes Isobutanol + Water at 1 atm.

92




93Basic Principle of Distillation (Reduce the pressure)

z




P 1

P 2

z

x y

D

F E

T

T P z F ,,, 1

T P x L ,,, 2

T P yV ,,, 2

Liquid

Vapor

94Basic Principle of Distillation (Increase the temperature)

z




1,,, T P z F

2,,, T P x L

2,,, T P yV

T 1

T 2

z

x y

D F E

P

Liquid

Vapor



96Continuous Flash (Single Stage) Distillation




Which variable can be specified?

QV

L

T

x

y

drum

:suppliedheatof Amount.6 :feedtheof portionVapor5.

:feedtheof portionLiquid.4

:drumflashtheof eTemperatur 3.

:fractionmole phaseLiquid.2

:fractionmole phaseVapor.1

How will the solution procedure be different if

I specify one of the first 5 variables vs.

I specify Q

97Continuous Flash (Single Stage) Distillation

Whi h i bl b ifi d?




Which variable can be specified?

Q

F

V f V

F

Lq L

T

x

y

drum

:suppliedheatof Amount.6

:feedtheof portionVapor5.

:feedtheof portionLiquid.4

:drumflashtheof eTemperatur 3.

:fractionmole phaseLiquid.2

:fractionmole phaseVapor.1

How will the solution procedure be different if

I specify one of the first 5 variables vs.

I specify Q

Material and Energy Balance equations are independent

Material and Energy Balance equations are interdependent

98If T drum is specified …




T drum

x y

F E

Liquid

Vapor

Look into your (T, xy)

diagram and find out the x

and y at the temperatureT drum

After finding x and y, solve

the material balance

equations (overall and

component) to calculate L

and V

Solve the energy balance

equation to get Q

99Graphical solution vs. Numerical Solution

Ideal case Raoult’s Law (Sequential)




Ideal case – Raoult’s Law (Sequential)

Non – ideal case (Iterative)

equations balanceenergyandmaterialSolvent.3

Calculate2.

EquationsAntoine'ordataVPusingat pressurevaporGet the1.

Kx y P VP K

T

drum

drum

procedureiterativey Numericall3.

ncompositioof functionaisand 2.

EquationsAntoine'ordataVPusingat pressurevaporGet the1.

drum

drum

P

VP K

T

100If x or y is specified …




T drum

x y

F E

Liquid

Vapor

Look into your (T,xy)

diagram and find out the

T drum corresponding to the x or y

Find the corresponding x or y

After finding x and y, solve

the material balance

equations (overall and

component) to calculate L

and V

Solve the energy balance

equation to get Q

101If f (V/F ) or q (L /F ) is specified …




ploton the linestraightarepresentsequationThis

1

1

1

of in termsor

11

balance,materialcomponenttheFrom

x,y

z q

xq

q y

q

z f

x f

f y

V F L

z V

F x

V

L yVy Lx Fz

x

y

One of these points is my solution!

But, which one?

f

f 1Slope

y = x = z



103What if I have more than 2 components? (Let’s say 3 …)

: PTPHzzFGiven




11

21

,

,,,

T P

H z z F f

Q drum

drum

T

P

v H y yV ,,, 21

L H x x L ,,, 21

freedomof degree

singlealeft withstillareWe

Equations3

1

3

8,,,,,,,:

,,,,,,:

222

111

2211

1121

iii

LV f

drum

drum f

x K y

LH VH Q FH

Vy Lx Fz

Vy Lx Fz

V L F

T y x y xV LQ

P T P H z z F

RelationsmEquilibriu

BalanceEnergy

component)and(OverallBalanceMaterial

Unknowns

Given

104Multicomponent Flash Distillation

,,,,...,,,: 1121 drumf P T P H z z F Given




11

21

,

,...,,,

T P

H z z F f

Q drum

drum

T

P

v H y yV ,...,,, 21

L H x x L ,...,,, 21

Freedomof degreeoneleft withstillareWe

21and1

Equations

1

24,...,,,,,,,:

,,,, ,,,

11

111

222

111

2211

1121

C

i

i

C

i

i

iii

LV f

C C C

drum

drum f

y x

x K yC

LH VH Q FH

C

Vy Lx Fz

Vy Lx Fz

Vy Lx Fz

V L F

C T y x y xV LQ

RelationstricStoichiome


BalanceEnergy

component)and(OverallBalanceMaterial

Unknowns

105

theallhaveyou willsystemidealanAssuming K

If T drum is specified …




solved becan balanceenergythe

andobtained becan,,,,gettingAfter

MethodRaphson- Newtonusingsolved becanequationAbove

011

1

111

and111

11 and

11

;and

aswritten becanequationsmEquilibriuandequations balancematerialThe

theallhaveyou willsystem,idealanAssuming

1

1

11

V L y x f

f g

f g

f f

f g f K

z K

f K

z K

f K

z

f K

z K y

f K

z x

x K yVy Lx Fz V L F

K

ii

n

n

nn

C

i i

ii

C

i i

iiC

i i

i

i

iii

i

ii

iiiiii

i

106What if more separation is desired?




11,

,,

T P

H z F f

Q drum

drum

T

P

v H yV ,,

L H x L ,,

z

What can I do to achieve this separation?

107



109Cascades (Constant Pressure)




1. Is this the best way to get the desired purity?

2. What am I going to do with streams L2, L1, V 4, V 5?

110Composition of intermediate streams




z

33 , yV

33 , x L22 , yV

11, yV 22 , x L

11, x L

44 , x L

55 , x L

44 , yV

55 , yV

1. Is the composition of V 4and L

2 similar to that of the feed?

2. Is the composition of V 3 and L1 similar?

3. Is the composition of V 5 and L3 similar?

111Feed the intermediate streams back to the flash drums

yV




z F ,

33, yV

22 , yV

11, yV

33 , x L

22 , x L

11, x L

44 , yV

55 , yV

44 , x L

55 , x L

3T

2T

54321 T T T T T

1T

4T

5T

1. How many “Heat Exchangers” do we

have and how many “Flash Drums” do

we have?

2. Is this energetically efficient?

3. How about the size of each flash drum?

112Adding reflux and boilup and combining the heat exchangers

yV




z F ,

33 , yV

22 , yV

11, yV

33 , x L

22 , x L

11, x L

44 , yV

55 , yV

44 , x L

55 , x L

3T

2T

54321 T T T T T

1

T

4T

5

T

D0 L

B6V

Do we really need the “heat exchangers”?

113Let the heat and mass exchange happen simultaneously …




The two streams L4 and V 5 are exchanging “heat” and “mass” with each other

Why not let them do it at the same time?

114From Cascades to Distillation Column




D0 L

55 , x L

B6V

5T

4T

3T

2T

1T

44 , x L

33 , x L

22 , x L

11, x L

55 , yV

44 , yV

33 , yV

22 , yV

11, yV

z F ,

R

S/E

1. Link for Distillation Video1 – Steady State Operation

2. Link for Distillation Video2 – Startup

3. Lab scale Distillation Column Now we have only one reboiler

and one condenser!

115

https://www.youtube.com/watch?v=BaBMXgVBQKk&feature=related

https://www.youtube.com/watch?v=82KHGne2TOw






https://www.youtube.com/watch?v=D0H9FWsk_Ck

https://www.youtube.com/watch?v=D0H9FWsk_Ck












Designing a Binary Distillation Column

Problem Statement:

116




Problem Statement:

I have a feed mixture of components “ A” and “ B” with a composition “ z ”

and I want to separate them to a desired composition

How many stages do I need?

What should be my feed location?

How much is the heat load on my reboiler and condenser?

Which equations do I have?

Material Balance

Energy Balance

Vapor – Liquid Equilibrium Data

117Overall Mass and Energy Balance on a Distillation Column

Q




D D H x D ,,0 L

B B H x B ,,

F F T H z F ,,, D

L R 0

C Q

RQ

D B

DH BH QQ FH

Dx Bx Fz

D B F

D B RC F

D B

,calculatecanwe

specified,isseparation

of degreetheIf

columnon the balance

EnergyandMaterial

118How to calculate heat load?

QHV




condenserthearound balance

EnergyandMaterialWriting

D D H x D ,,0 L

B B H x B ,,

D

L R 0

C Q

RQ

11, H V

1

110

01101

1

However,

1

and

H H x x

x z F RQ

x x

x z F D

Fx x x D

x D F Dx Bx Dx Fz

H H R D H H D LQ

H D LQ H V D LV

D

B D

Bc

B D

B

B B D

B D B D

D DC

DC

Designing a Binary Distillation Column 119

M t i l B l E b l




D0 L

B

z F ,

Material Balances, Energy balances

and Equilibrium Relations:

Rectification section

Feed Tray

Stripping or Exhausting Section

Rectification section – Lets start from the first tray … 120

BalancesMaterialWritingQ




D0 L

11 x L 22 yV

11, y x

5Equations

5and,,,areUnknowns

equations2,Components2

RelationsmEquilibriu,,,

BalanceEnergyWriting

and

12221

1111112222

112212

LV T y x

T xh L x Dh yT QT y H V

Dx x L yV D LV

D DC

D

C Q

5Equations

5and,,,areUnknowns

equations2,Components2RelationsmEquilibriu

,,,


and

BalancesMaterialWriting

23332

2222113333

223323

LV T y x


Dx x L yV D LV

D DC

D

D0 L

22 , y x

C Q

22 x L 33 yV

Rectification section – General set of equations 121





5Equations

5and,,,areUnknowns



,,,


and


111

111111

111

j j j j j

j j j j D DC j j j j

D j j j j j j

LV T y x


Dx x L yV D LV

Can we write a similar set of equations for the stripping section?

Stripping section – General set of equations 122





5Equations

5and,,,areUnknowns



,,


and


11

1111

111

k k k k k

B Bk k k k Rk k k k

Bk k k k k k

LV T y x

x BhT xh LQT y H V

Bx x L yV B LV

Bk k y x ,

RQ

11 k k x L k k yV

How do we know Q R ?

Is the partial reboiler like an additional distillation stage?

1nV

Operating line for the stripping and rectification section 123

What is an “operating line” ?




p g

A quick recap of our flash calculations

An (x,y ) line on which all the points satisfy the material balanceequations

B

k

k k

k

k k

D

j

j

j

j

j

j

x

V

L x

V

L y

xV

L

xV

L

y

1

sectionstrippingfor thelineOperating

1

sectionionrectificatfor thelineOperating

11

1

11

1

What is the slope of the

“operating line” ? +ve

or – ve?

Where do they

intersect the x = y

diagonal?

What is the difference between this “operating line” and the one we saw during the

single stage flash calculation? Are x j and y j +1 in equilibrium with each other?

Lets visualize it graphically … 124




x

y

12

12

2

1

and betweenRelation

1Slope

1TrayforlineOperating

x y

D LV V

L

D x

11, y x

21, y x22

, y x

23

23

3

2

and betweenRelation

1Slope

2TrayforlineOperating

x y

D LV V

L

32 , y x

Constant Molal Overflow (CMO) Approximation 125

How can we have a single straight line as our “operating line” for the




rectification (and stripping) section?

sectionStripping

sectionionRectificat

1

1

21

21

V V V V

L L L L

V V V V

L L L L

k f f

k f f

j

j

Bk k

D j j

xV

L x

V

L y

xV

L x

V

L y

1


1


1

1

Underlying assumption behind CMO 126

11222233 and DxxLyVDxxLyV




11 x L 22 yV

22 x L 33 yV

32

32

21

21

32

2122331122

23

12

2123

11222233

get,we balanceenergythefromAnd

thenandIf

and

y y

H H

x x

hh

H H hh

LV h L H V h L H V

y y

x x

L

V

L LV V

Dx x L yV Dx x L yV D D

The slopes of the liquid and vapor enthalpy lines are equal! They are parallel!

The latent heat does not depend on composition!

CMO Operating line in terms of reflux ratio 127

The operating line equations can also be written in terms of reflux ratio (R ) and




Boilup ratio (V B )

B

B

k

B

Bk

B

B B

D j j

xV

xV

V y

V

V

V

L B LV

B

V V

x R

x R

R y

R

R

V

L

D LV D

L

R

11


1 and

1

1

1


1 and

1

1



Rectification Section (total condenser) 129




x

y

B x

1, n B y x1, nn y x

nn y x ,

nn y x ,1

Combining the rectification and stripping sections 130




x

y

Where do you think the two lines (A, B or C) should intersect and why?

A

B

C

feed z

Equation for the feed line 131

L V




L V

LV

F

z F L L F F

F F x F F F L L

F L L y

F

Fz x L L yV V

F L LV V V L LV F

get,we byrdenominatoandnumeratorthedivingandtwotheCombining

get,we balancecomponenttheFrom

gettray wefeedon theBalanceMaterialtheFrom



Feed Quality 133

L L L f V




L V

L V

F

liquidsubcooled1

q

F L L

L V

L V

F

point bubbleatliquid1

q

F L L

L V

L V

F

feedvaporized partially10

q

F L L

f L

L V

L V

F

pointdewatVapors0

q

L L

f V L V

L V

F

VaporsdSuperheate0

q

L L

f V

Feed Line on the plot 134

= 1




x

y z (Saturated Vapor) q=0

( S a t u r a t e d

L i q u i d ) q =

Where to introduce the feed? 135




x

y

Feed introduced here –

Below the optimum stage

No. of Stages Required = 7

D x B x





x

y


Above the optimum stage


D x B x





x

y


At the optimum stage


D x B x

Limiting Cases – Total Reflux (Minimum No. of Stages) 138

0 D B F




1thenIf

11

sectionstripping

for thelineOperating

1thenIf

1

1

1

sectionionrectificat

for thelineOperating

1

1

slopeV

xV xV

V

y

slope R

x R

x R

R y

B

B B

k B

B

k

D j j

x

y


D x B x

Limiting Cases – Minimum Reflux (Infinite No. of Stages) 139

linesoperatingtwoThe




separationdesiredthe

achievetorequiredare

stagesof numberInfinite

curvemequilibriu

on theintersect

p g

x

y

No. of Stages Required = ∞

D x B x



Open Steam Distillation 141

CQ For separations involving a




D

D

H

x D ,,

0 L

B B H x B ,,

F F T H z F ,,, D

L R 0

C

s H S ,

mixture of a light component

(ex.methanol) and water.

Since the bottom product is rich

in less volatile component

(water), instead of partially

reboiling water ( with a bit of

methanol), lets supply pure

water vapors.

How will the overall balance change?

How will the tray-balance change?

Open Steam Distillation 142

C Q EnergyandMaterial




D

D

H

x D ,,

0 L

B B H x B ,,

F F T H z F ,,, D

L R 0

s H S ,lculate)tables/ca(steam

steamof enthalpytheis

late)data/calcu(enthalpy

obtained becan

andn,compositio product

bottomandtoptheknowweIf

(3)

(2) (1)

columnon the balance

S

D B

D BS C F

D B

H

H H

DH BH SH Q FH

Dx Bx Fz D BS F

Can we solve the material balance independently?

If reflux ratio is specified… 143

EnergyandMaterialWritingC Q11, H V




condenserthearound balance

EnergyandMaterialWriting

D D H x D ,,0 L

B B H x B ,,

D

L R 0

RQ

coupledare balancesEnergyandMaterial

(5)and(2)(1),equations;3and

and,unknowns;threehaveonlyWe

(5) 1

(3),eq.in(4)ngSubstituti

(4) 1

and

1

110

01101

D BS

DH BH H H R DSH FH

H H R D H H D LQ

H D LQ H V D LV

D B DS F

D DC

DC

Internal Balances (Rectification section and Feed line) 144

C Q Is the rectification section of

di ill i l




0 L

B B H x B ,,

F F T H z F ,,, D

L R 0

s H S ,

“Open Steam” distillation column

any different?

Does the feed tray look any

different?

D j j xV

L x

V

L y

1


ion,approximatCMOUnder

1

1

1

1

linefeedfor thelineOperating

z q

xq

q y



Operating lines for Open Steam Distillation 146




x

y

D x B x

sectionionRectificatV

LSlope

1forlineFeed q

sectionStrippingV

L

Slope

B x x- asinterceptanhaslineOperating

diagonal.intersectnotdoeslineOperating B

Bk k

x x y

xV

L x

V

L y

,0atHence

1

Multiple feed streams 147

C Q How many operating lines will be

h i hi di ill i l ?




D x D,0 L

B x B,

11, z F

RQ

22 , z F

there in this distillation column?


C Qion,approximatCMOUnder




D x D,0 L

B x B,

11, z F

RQ

22 , z F

tion

j

tion

tion

D j

D j j

V

x

V

L y

V

Dx x

V

L

xV

L x

V

L y

secsec

sec

11

1

1

1

1

11

1

1SectionforlineOperating

1

2

3

11, LV

22 , LV

33 , LV


C Qion,approximatCMOUnder




D x D,0 L

B x B,

11, z F

RQ

22 , z F

3

2211

3

3

2

11

2

2

11

1

3Section

2Section

1Section

V

z F z F Dx xV

L y

V

z F Dx x

V

L y

V

Dx x

V

L y

D

D

D

1

2

3

11, LV

22 , LV

33 , LV

Multiple feed streams: McCabe – Thiele Method 150

Find x D on the diagonal and draw the

operating line for section–1




operating line for section – 1.

Feed characteristics are given and you

can draw the feed line for F 1 andoperating line for section – 1 intersects

the feed line.

Material balance on feed tray for F 1 and

calculate L2 and V 2 (know the slope).

Draw the operating line for section – 2. Feed characteristics are given and you

can draw the feed line for F 2 and

operating line for section – 2 intersects

the feed line.

Operating line for section – 3 will pass

through x B. x

y

D

x B

x

1forlineFeed F

1Section

2forlineFeed F

2Section

3Section

1 z 2 z

Side stream 151

C Q Will the operating lines look the




D x D,0 L

B x B,

S xS ,

RQ

z F ,

same as those of Multiple feed

streams?



153

C Q

Side stream

ion,approximatCMOUnder




D x D,0 L

B x B,

RQ

z F ,

1

2

3

11, LV

22 , LV

33 , LV

S xS ,

33

3

22

2

11

1

3Section

2Section

1Section

V

Fz Sx Dx xV

L y

V

Sx Dx x

V

L y

V

Dx x

V

L y

S D

S D

D

Side stream: McCabe – Thiele Method 154

Find x D on the diagonal and draw the

operating line for section–1.



operating line for section 1.

Calculate the slope of the operating line

for section – 2 (slope less than theoperating line for section – 1). You can

draw the “pseudo-feed line”. You can

also calculate the y – intercept.

Feed characteristics are given and you

can draw the feed line for F 2 andoperating line for section – 2 intersects

the feed line.

Operating line for section – 3 will pass

through x B.

The last stage in section – 1 has to end at

the intersection of operating lines of

section 1 and section 2

x

y

D

x B x

1Section

2forlineFeed F

2Section

3Section

S x z

Course Slides Jan 05 2015(1)

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Transcript of Course Slides Jan 05 2015(1)