Azeotrophic Dist and Residue Curve-A9R64CD

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AZEOTROPIC DISTILLATIONAND RESIDUE CURVE MAPS

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Exploiting L-L Boundaries in Azeotropic Separationse.g. Separation of water / n-butanol mixtures

Compositionn-butanol

PureWater

Purebutanol

Feed

LL Boundary

LL Boundary

Azeotrope

FeedWater / n-butanol

n-butanol rich phase

Water rich phase

DecanterLL Equilibrium

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Step I: Use the Decanter to Get Around the Azeotrope


PureWater

Purebutanol

Feed

LL Boundary

LL Boundary

Azeotrope

Decanter

Feed A Feed B

Sequence 1

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Step II: Distill the Two Phases (Each Phase in a Column)


PureWater

Purebutanol

LL Boundary

LL Boundary

Azeotrope

Feed A Feed B

Column 1 Column 2

Sequence 1

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Step III: Mix the Two AzeotropicStreams with the Original Feed and

Recycle to Decanter


PureWater

Purebutanol

LL Boundary

LL Boundary

Azeotrope

Decanter

Sequence 1

Feed

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SEQUENCE I

Water

n-butanolDecanter

Column 2

Column 1

Feed B

Feed A

Feed

Azeotrope

Azeotrope

Azeotrope

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AN ALTERNATIVE SEQUENCE: START WITH DISTILLATION


PureWater

Purebutanol

Feed

LL Boundary LL Boundary

Azeotrope

Column 1

Sequence 2

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Step II: Feed Azeotrope to Decanter


PureWater

Purebutanol


Azeotrope

Decanter

Feed A Feed B

Sequence 2

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Step III: Take First Liquid Phase to Column I and Second Liquid Phase to

Column II


PureWater

Purebutanol


Azeotrope

Feed A Feed B

Column 1 Column 2

Sequence 2

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SEQUENCE II

Water

n-butanolDecanter

Column 2

Column 1

Feed B

Feed A

Feed

Azeotrope

Azeotrope

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SIMPLE GRAPHICAL TOOLS TO DEVELOP AZEOTROPIC

SEQUENCES FOR TERNARY SYSTEMS

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Distillation Curves

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k - 1

k

Lk

x i,kV k+1y i,k+1

Vky i,k

TAKE A COLUMN WITH TOTAL REFLUX

x i,k = y i,k+1

Lk = V k+1

From Material Balance:

From Equilibriumy i,k in eqm with x i,k

get corresponding y i,kfrom Bubble Point Calculations

Take a value for x i,k

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How to constructDistillation Curves ?

Bubble Point CalculationGives us vapor composition in equilibrium with known liquid composition

Can march up the column by doing a series of bubble point calculations

Dew Point CalculationGives us liquid composition in equilibrium with known vapor composition

Can march down the column by doing a series of dew point calculations

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Distillation Curve

Region 1 Region 2

Curves move in the direction of increasing temperature i.e., towards the least volatile species present in the mixture

Azeotrope

Species B

Species A Species C

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How to Generate Distillation/Residue Curves on ASPEN

•Make sure your Setup, Components, and Properties specifications are complete.•From the Tools menu, point to Analysis, then Property, then Residue.•On the Residue Curves dialog box, Aspen Plus fills in defaults for all the requiredinformation. You can accept the defaults, or make changes to any of the following information:

Components: Three are required. Use the Component 1, Component 2, and Component 3 lists to choose the three components you wish to study. Only conventional components that are not solids or ions are allowed. Defaults are the first three conventional components listed on the Components Specifications Selection sheet. Pressure: The default is 1 atmValid Phases: You can specify rigorous two phase (Vapor-Liquid) or three phase (Vapor-Liquid-Liquid) calculations. The default is Vapor-Liquid.When finished, click Go to generate the residue curves, or first click the Save As Formbutton to save your interactive Property Analysis to forms within the Data Browser.

Saving an interactive Property Analysis as forms enables you to preserve the input and results of this Property Analysis to view or modifyat a later time. Aspen Plus displays the results in tabular form, in a form window and as a triangular plot.

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Rules: 1. Cannot (typically) cross distillation boundary2. Within the same column, feed, top and bottom lie on a straight line(lever arm principle)

Region 1 Region 2

Azeotrope

Species B

Species A Species C

DistillationBoundary“Separatrix”

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Lever-Arm Principle

F, z

B, x

D, y

F = B + DFz = Bx + Dy = (F-D)x + Dy==> D/F = (z -x)/(y-x)

Column 1

Species B

Species CSpecies A

F, z

D, y

B, x

Arm for D

Arm for B

D/F = Arm for D/Total Arm

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Lever ArmSpecies B

Species CSpecies A

F, z

B, x

Say, D / F = 0.0=> D = 0 and B = F

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Distillation SequencingSpecies B

Species CSpecies A

F, z

B, x

D, y

Say, D / F = 0.10=> Distance from F to B is 10% that from D to B

Lever Arm helps us determine bottoms and distillate locations on composition diagram

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Distillation SequencingSpecies B

Species CSpecies A

F, z

B, x

D, y

So, ideally, as D/F increaseswe expect to finally reach astate where distillate is pureA and bottoms is a mixture ofpure B and C.But, this is notwhat really happens !!!!

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Remember Rule #I:Can’t Cross the Distillation Boundary

Species B

Species CSpecies A

F, z

B, x

D, y

We have a distillation boundarywhich divides composition spaceinto regions 1 and 2. If our feed is in Region 1, it is not possibleto cross the boundary ( except insome very special cases)

Region 1 Region 2

Distillation Boundary

So, LOCATION OF FEED plays a very crucial role in design

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EXAMPLE: ACETONE, CHLOROFORM, BENZENE SYSTEM

Consider the given feed

Benzene80.1 oC

Chloroform61.2 oC

Acetone56.5 oC

F, z

D, y

Region 1 Region 2


34 mol% acetone64.4 oC

Azeotrope

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Case I: Need pure Acetone and Pure Benzene Benzene

80.1 oC

Chloroform61.2 oC

Acetone56.5 oC

F, z

Column I



AzeotropeColumn II

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Case I: Need pure Acetone and Pure Benzene Benzene

80.1 oC

Chloroform61.2 oC

Acetone56.5 oC

F, z

Column I



AzeotropeColumn II

F

Acetone+ Chloroform

Acetone

Benzene

AzeotropeI

II

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F

Acetone+ Chloroform

Acetone

Benzene

AzeotropeI

II

USE NON-VLE METHOD TO SEPARATE THE AZEOTROPE(e.g., decanter for LL Boundaries, membrane, etc.)

Decanter

To anothercolumnor torecycle

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Case II: Need pure Benzene and Pure Chloroform Benzene

80.1 oC

Chloroform61.2 oC

Acetone56.5 oC

F, z

Column I



AzeotropeColumn II

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80.1 oC

Chloroform61.2 oC

Acetone56.5 oC

F, z

Column I



AzeotropeColumn II

Decanter

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80.1 oC

Chloroform61.2 oC

Acetone56.5 oC

F, z

Column I



AzeotropeColumn II

Decanter

Column III

Documents

Azeotrophic Dist and Residue Curve-A9R64CD