6460 azeotropic distillation
DESCRIPTION
azeotropic distillation residue mapsTRANSCRIPT
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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
Compositionn-butanol
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)
Compositionn-butanol
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
Compositionn-butanol
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
Compositionn-butanol
PureWater
Purebutanol
Feed
LL Boundary LL Boundary
Azeotrope
Column 1
Sequence 2
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Step II: Feed Azeotrope to Decanter
Compositionn-butanol
PureWater
Purebutanol
LL Boundary LL Boundary
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
Compositionn-butanol
PureWater
Purebutanol
LL Boundary LL Boundary
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
Distillation Boundary
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
Distillation Boundary
34 mol% acetone64.4 oC
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
Distillation Boundary
34 mol% acetone64.4 oC
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
Distillation Boundary
34 mol% acetone64.4 oC
AzeotropeColumn II
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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
Distillation Boundary
34 mol% acetone64.4 oC
AzeotropeColumn II
Decanter
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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
Distillation Boundary
34 mol% acetone64.4 oC
AzeotropeColumn II
Decanter
Column III