Heterogeneous Azeotropic
Distillation Column Design
Paritta Prayoonyong
Supervisor:
Dr. Megan Jobson
L07 - 1
XXIV PIRC Annual Research Meeting 2007
Outline
1. Introduction and objective
2. Column design methods: review
3. Column design method:
New boundary value method
a. Simple column
b. Double-feed column
c. Column with an intermediate decanter
4. Case study
5. Conclusions and future work
L07 - 2
Heterogeneous Azeotropic Distillation Column Design
1. Introduction and Objective
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Heterogeneous Azeotropic Distillation Column Design
Azeotropes
Pentane / dichloromethane mixture
T
P liquid and vapour
Vapour
compositions are the same
xi = yi
Liquid
Azeotrope
x, y
P cannot be separated by
conventional distillation
xpentane
L07 - 4
Heterogeneous Azeotropic Distillation Column Design
Breaking azeotropes
P Adding an entrainer that does not induce two liquid phases
0 Homogeneous azeotropic distillation
Chloroform
(61.15oC)
1
0.9
0.8
Azeotrope
(63.81oC)
0.7
(0.38, 0.62, 0)
0.6
0.5
0.4
0.3
(0.4, 0.2, 0.4)
0.2
0.1
0
0
0.1
Toluene
(110.6oC)
(Entrainer)
L07 - 5
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Acetone
(56.05oC)
Heterogeneous Azeotropic Distillation Column Design
Breaking azeotropes
P Adding an entrainer that does not induce two liquid phases
0 Homogeneous azeotropic distillation
Chloroform
o
(61.15
C)
1
Vapour
0.9
y(t)
0.8
Azeotrope
(63.81oC)
0.7
0.6
Residue
curve
0.5
0.4
0.3
x(t)
x(t=0)
x(t)
0.2
Liquid
0.1
0
0
0.1
Toluene
(110.6oC)
(Entrainer)
L07 - 6
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Acetone
(56.05oC)
Heterogeneous Azeotropic Distillation Column Design
Breaking azeotropes
P Adding an entrainer that does not induce two liquid phases
0 Homogeneous azeotropic distillation
Chloroform
(61.15oC)
1
Residue curve map
0.9
0.8
Azeotrope
(63.81oC)
0.7
Distilation
boundary
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.1
Toluene
(110.6oC)
(Entrainer)
L07 - 7
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Acetone
(56.05oC)
Heterogeneous Azeotropic Distillation Column Design
Breaking azeotropes
0 Homogeneous azeotropic distillation
Chloroform
D3
Chloroform
D3
Acetone
D2
D1
B3
B1
D2
F
F
B1
D1
B2
Acetone
Toluene
(Entrainer)
Thong, D.Y.C. and Jobson, M., (2001), Chem. Eng. Sci., 56, 4423.
L07 - 8
Heterogeneous Azeotropic Distillation Column Design
B2
B3
Breaking azeotropes
P Adding an entrainer that induces two liquid phases
0 Heterogeneousazeotropicdistillation
Ethanol
Aqueous
rich
phase
Liquid-liquid tie line
A
A
F
F
A
B
B
B
Entrainer
rich
phase
Water
L07 - 9
Immiscible
region
Benzene
(Entrainer)
Heterogeneous Azeotropic Distillation Column Design
Heterogeneous azeotropic distillation
V, y2
Ethanol
I
II
B
Decanter tie line
F, xF
D, xD
L, xR
F
D
B, xB
y2
xR
Water
L07 - 10
I
P Distillation boundary to be
Benzene
crossed by using a decanter
P Decanter is a cheap unit
operation
Heterogeneous Azeotropic Distillation Column Design
Challengesforcolumndesign
‘
Representingvapour-liquid-liquidequilibrium:
highlynon-idealthermodynamicsystem
‘
Lack of design methods for columns with
heterogeneousstages
‘
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Phasesplittingofrefluxisadegreeoffreedom
Multiplesolutionstypicallyfound
Lack of methods to exploit in flowsheet design
Heterogeneous Azeotropic Distillation Column Design
Objective of this work
‘ Develop
a design method for
heterogeneous azeotropic columns
L07 - 12
To be applicable to various types of columns
and decanters
To evaluate column designs
To apply to distillation sequence synthesis
Heterogeneous Azeotropic Distillation Column Design
2. Column Design Methods:
Review
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Heterogeneous Azeotropic Distillation Column Design
Columndesignmethods
forheterogeneousazeotropicdistillation
P No shortcut design method available
P Two graphical methods available
< Boundary value design method
– Pham et al., 1989
< Continuous distillation region based method
– Urdaneta et al., 2002
–
Computationally intensive
–
Does not explicitly give details of column design
e.g. number of stages, feed location
Pham, H.N., Ryan, P.J., and Doherty, M.F., (1989), AIChE J., 35, 1585.
Urdaneta, R.Y., Bausa, J., Bruggemann, S., and Marquardt, W., (2002), Ind. Eng.. Chem. Res., 41, 3849.
L07 - 14
Heterogeneous Azeotropic Distillation Column Design
Boundaryvaluedesignmethod(BVM)
P First
developed
for
homogeneous
V2, y2
azeotropic
distillation*
PCalculation
ofcompositionprofiles
L 1, x 1
2
D, xD, hD
n
Hexane
Stripping
profile
1
Vn+1
yn+1
V
hn+1
0.8
Rectifying
profile
0.6
Vm
ym
V
hm
B
0.4
P Composition profiles
given reflux ratio starting
Ln
xn
from
hnL
distillate
composition
(XD)
< bottoms
composition
(XB)
<
Lm+1
xm+1
L
hm+1
P Calculate column
profiles from
m
F
0
materialandenergy
balances
< phase
equilibrium
<
0.2
2
0
Nonane
0.2
0.4
0.6
0.8
1
V1, y1, hV
1
D
Pentane
L2, x2, h2L
B, xB, hB
Levy, S.G., Van Dongen, D.B., and Doherty, M.F., (1985), Ind. Eng. Chem. Fundam. 24, 1463.
L07 - 15
at a
Heterogeneous Azeotropic Distillation Column Design
Boundaryvaluedesignmethod(BVM)
Hexane
Stripping
profile
1
P The intersection of the profiles is
necessary for the design to be
feasible
0.8
Rectifying
profile
0.6
P The intersection point of the profiles
B
0.4
is the location of the feed
F
0.2
P Number of stages can be counted
0
0
Nonane
L07 - 16
0.2
0.4
0.6
0.8
1
D
Pentane
Heterogeneous Azeotropic Distillation Column Design
Boundaryvaluedesignmethod:
state-of- the-art
• Assess the feasibility of a proposed column
• Give column design details, e.g.
< number of stages, feed location, heat duty of
condenser and reboiler
• Able to determine minimum reflux ratio
• Able to evaluate separation sequences
Gaps:
• Consider columns with homogeneous stages
only
• Double-feed column
< developed for homogeneous mixtures only
• Column with an intermediate decanter
< not yet developed
L07 - 17
Heterogeneous Azeotropic Distillation Column Design
Objectives to extend the boundary value
method for heterogeneous azeotropic
distillation
! BVM is to be developed to be applicable to
" Multiple heterogeneous-stage columns
" Double-feed columns
" Columns with intermediate decanters
! New BVM should be able to be exploited to screen
different designs
" Feasibility of a column specification is identified by the
intersection of composition profiles
" Feasible designs are screened for economic designs by
capital and operating costs
! BVM will be applied to flowsheet synthesis
" Evaluate separation flowsheets
– takingintoaccountvarioustypesofcolumns
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Heterogeneous Azeotropic Distillation Column Design
3. Column Design Method:
New Boundary Value
Design Method
a. Simple Column
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Heterogeneous Azeotropic Distillation Column Design
SpecificationsofBVM
g Heterogeneous distillation
g Homogeneous distillation
by new BVM
B
1
Stripping
profile
Decanter tie line
0.8
F
0.6
D
Rectifying
profile
B
0.4
F
x1
0.2
0
0
0.2
0.4
0.6
0.8
1
D
" Distillate composition
" Distillate composition
" Bottom composition
" Bottom composition
" Phase split ratio of reflux
L07 - 20
Heterogeneous Azeotropic Distillation Column Design
Definition: Phase split ratio of a heterogeneous stage
V2 , y
2
φ1
2
n
V
y n+1
L1, x1
I
Ln
xnI
I I
L1, x1
I
II
Phase split
Ratio of heavy liquid
ratio of = rate to total liquid rate at
stage n
stage n
D, xD
II II
L1, x1
II
Ln
xnII
φn
L IIn
=
L In + L IIn
0 < Nn < 1
φ n , Ln , xn
Degree of freedom :
Phase split ratio of reflux (N1)
II
N1 =
L1
I
II
L 1 + L1
! The existence of heterogeneous stages in the column
depends on the specification of the phase split ratio of
the reflux ( N1)
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Heterogeneous Azeotropic Distillation Column Design
Separation of an acetic acid/water/
n-butyl acetate mixture
Aceticacid
(118oC)
B
1
DI
F
0.8
Stage ?
DII
Ntotal = ?
(Water)
0.6
B
F
0.4
(Acetic acid)
Specify:
0.2
DII
DI
0
0
0.2
n-Butylacetate
(126.1oC)
(Entrainer)
L07 - 22
0.4
D
Azeotrope
0.6
0.8
o
(91 C)
1
Water
(100oC)
distillate
andbottomcompositions
-feedcondition=saturatedliquid
-refluxratio=1.45
-phasesplitratioofreflux=0.58
Heterogeneous Azeotropic Distillation Column Design
Example: multiple column designs
P N1 = 0.58 causes many heterogeneous stages in the
rectifying section of the column
P At the final heterogeneous stage (stage 10), multiple
rectifying profiles can be generated corresponding to
various phase split ratios of this stage
Acetic acid
B
1
Stripping profile
Rectifying profile
0.8
N10 < 0.38
Infeasible designs
0.38 < N10 < 1
Feasible designs
0.6
F
Attractive
designs
0.4
0.2
D
0
0
0.2
n-butyl acetate
L07 - 23
0.4
0.6
0.8
N 10
1
0.9
0.8
0.7
0.6
0.5
0.4
0.38
1
Water
Heterogeneous Azeotropic Distillation Column Design
NR
13.4
12.8
12.2
11.6
11
10.6
10.2
10.1
NS
18
18
18.1
18.6
19.2
20.3
22
25
N Total
31.4
30.8
30.3
30.2
30.2
30.9
32.2
35.1
Validation of the method by rigorous simulation
Acetic acid
B
N10
1
Acetic acid
B
= 0.6
N10
1
NTotal = 30
NTotal = 35
0.8
0.8
0.6
0.6
HYSYS
BVM
F
F
0.4
0.4
0.2
0.2
D
D
0
0
0.0
0.2
0.4
0.6
0.8
n-butyl
acetate
1.0
Water
0
0.2
0.4
0.6
n-butyl
acetate
P Heterogeneous stages in the column give multiple column designs
at an operating reflux ratio
P Results from BVM are in good agreement with rigorous simulation
L07 - 24
= 0.38
Heterogeneous Azeotropic Distillation Column Design
0.8
1
Water
Homogeneous-stage column vs. Heterogeneous-stage column
g Phase splitting only
g
Heterogeneousstages
occursinthedecanter
Acetic acid
B
1
in the column
Acetic acid
B
1
0.8
0.8
Identical
reflux and
reboil ratios
0.6
F
0.4
0.2
0.6
F
0.4
0.2
D
D
0
0
0
n-butyl
acetate
0.2
0.4
0.6
0.8
1
Water
87 stages
0
0.2
n-butyl
acetate
0.4
0.6
30 stages
0 Column with multiple heterogeneous stages gives more attractive design
L07 - 25
Heterogeneous Azeotropic Distillation Column Design
0.8
1
Water
ColumndesignbynewBVM
ä Identify feasible designs
â Initialisation steps :
< Liquid-liquid
equilibrium
calculation
< SpecificationsFeed
- and products compositions
- Phase split ratio of reflux
< Specify - reflux ratio and reboil ratio or feed condition
ã Composition profile calculation of
from the intersection of the
profiles
< Design
parameters
are
obtained
– Number of stages in each section
– Feed location
– Feed condition or reboil ratio
– Condenser and reboiler duty
stripping and rectifying sections from
– Material and energy balances
– Phase equilibrium
< Calculate multiple rectifying profiles for a range of
Nfinal when there are many heterogeneous stages in
å Evaluate designs by
< Capital
cost
< Operating
cost
the rectifying section
L07 - 26
Heterogeneous Azeotropic Distillation Column Design
3. Column Design Method:
New Boundary Value
Design Method
b. Double-feed Column
L07 - 27
Heterogeneous Azeotropic Distillation Column Design
Double-feed
column
V, y2
UpperFeed
x FU
I
II
D, xD
L, xR
LowerFeed
xFL
B, xB
P Double-feed
columnmaybemoreeconomic
P BVMhasbeendevelopedfordouble-
P Somemixturescannotbeseparatedbya
P For
heterogeneous
mixtures,
columns
thanasingle-feedcolumn
< Require
fewer
stages
single-feedcolumn,
1-propanol/1-butanol/water**
< e.g.
feed
columns
separating
homogeneous
mixtures***
with
multiple
heterogeneous
stages
have
not
been
addressed
*Wasylkiewicz, S.K., Kobylka, L.C. and Castillo, F.J.L., (2000), Chem. Eng. J., 79, 219.
**Moussa, A.S. and Jiménez, L., (2006), Ind. Eng. Chem. Res., 45, 4304.
***Levy, S.G., Van Dongen, D.B., and Doherty, M.F., (1985), Ind. Eng. Chem. Fundam. 24, 1463.
L07 - 28
Heterogeneous Azeotropic Distillation Column Design
Double-feed column design by new BVM
â
ä
< Liquid-liquid equilibrium calculation
< Specifications - compositions of upper and lower feeds
- compositions of products
- phase split ratio of reflux
< Specify - reflux ratio and reboil ratio or feed quality
ã
Identify feasible designs from
the intersection of rectifying
and middle profiles
Initialisation steps:
Composition profile calculation of stripping,
rectifying and middle sections from
– Material and energy balances
– Phase equilibrium
< The location of lower feed is chosen
such that the smallest number of
stages is required
< The intersection point is the upper
feed location
< Design parameters are obtained
– Number of stages in each section
– Upper feed location
– Feed condition or reboil ratio
– Condenser and reboiler duty
< Calculate multiple profiles of rectifying section for a
range of Nfinal if the column stages are heterogeneous
< Middle profiles are calculated starting from stages of
stripping section
L07 - 29
å
Evaluate multiple designs by
< Capital cost
< Operating cost
Heterogeneous Azeotropic Distillation Column Design
Separation of 1-propanol/water/1-butanol mixture
1-propanol
(97.15oC)
D2
1
D1I
FU
0.8
D1II
C-1
FL
Relatively
pure water
B1
0.6
FL
C-2
D2
AZ 0.4
(88.43oC)
C-2
B1
1-Propanol
C-1
0.2
0
D1II
Water
(100oC)
D1I
D1
D-1
0
0.2
AZ
(93.95oC)
0.4
0.6
0.8
FU
B2
1
1-Butanol
(117.7oC)
Entrainer
L07 - 30
Water/Butanol
mixture
D-1
Heterogeneous Azeotropic Distillation Column Design
B2
1-Butanol
Double-feed column design by BVM
1-propanol
1
FU
xFU
D
xD
Stage ?
0.8
Lower feed location
(degree of freedom)
0.6
FL
xFL
Stage ?
FL
Ntotal = ?
0.4
B
xB
5
6
4
Middle
profiles
B
0.2
FU
Reflux ratio = 3
0
N1=0.57
0
Water
Lower feed location
(from a stripping stage)
NR
NM
Ntotal
4
5
6
3
3
3
28
26
26
33
32
33
L07 - 31
Stripping
profile
0.2
D
0.4
Upper
feed
location
Heterogeneous Azeotropic Distillation Column Design
0.6
0.8
1
Rectifying 1-butanol
profile
Validation of the method by rigorous simulation
BVM
FU
FL
3
D
28
31
Composition :
1-Propanol
Water
1-Butanol
Flow rate (kmol/h)
Condenser duty (kJ/h)
Reboiler duty (kJ/h)
FU
FL
D
B
0
0
1
60.00
0.5
0.5
0.0
40.00
4.54E+06
4.69E+06
0.0001
0.6999
0.3000
26.83
0.2733
0.0167
0.7100
73.17
B
HYSYS
Reflux ratio = 3
N1=0.57
Composition :
1-Propanol
Water
1-Butanol
Flow rate (kmol/h)
Condenser duty (kJ/h)
Reboiler duty (kJ/h)
FU
FL
D
B
0
0
1
60.00
0.5
0.5
0.0
40.00
4.51E+06
4.45E+06
0.0001
0.6999
0.3000
26.83
0.2733
0.0167
0.7100
73.17
P Results from HYSYS are in good agreement with the specified
compositions for the design method
L07 - 32
Heterogeneous Azeotropic Distillation Column Design
3. Column Design Method:
New Boundary Value
Design Method
c. Column with an Intermediate Decanter
L07 - 33
Heterogeneous Azeotropic Distillation Column Design
Column with an intermediate decanter
P Two-phase liquid on a stage is
D
withdrawn and split into a decanter
F
P One phase is recovered as a product
S
B
P The other phase is refluxed back into
the column at one stage lower than the
draw stage
P A column with an intermediate decanter may be more
economic than a simple column*
< fewer columns required
P BVM has not been developed for columns with
intermediate decanters
* Pucci, A., Mikitenko, P., and Asselineau, L., (1986), Chem. Eng. Sci. 41, 485.
Stichlmair, J.G. and Fair, J.R. (1998), Distillation: principles and practice, Wiley-VCH, 222.
L07 - 34
Heterogeneous Azeotropic Distillation Column Design
Column with an intermediate decanter design
by BVM
ä
â Initialisation steps:
< Liquid-liquid
equilibrium
calculation
< Specifications
- compositions of feed
- compositions of three products
- phase split ratio of reflux
< Specify- reflux ratio and reboil ratio or feed quality
ã
Composition profile calculation of stripping,
rectifying and middle sections from
– Material and energy balances
– Phase equilibrium
Identify feasible designs from
the intersection of rectifying
and middle profiles
< The location of side stream is chosen
such that the smallest number of
stages is required
< The intersection point is the upper
feed location
< Design parameters are obtained
– Number of stages in each section
– Locations of feed and side stream
– Feed condition or reboil ratio
– Condenser and reboiler duty
< Middle profiles are calculated starting from a stage in
stripping section where liquid phase splitting occurs
• side stream location is a degree of freedom
L07 - 35
å
Evaluate designs by
< Capital cost
< Operating cost
Heterogeneous Azeotropic Distillation Column Design
Summary
P BVM has been extended to
< Columns with many heterogeneous stages
< Double-feed columns
< Columns with intermediate decanters
P Method can be used for assessing the feasibility
of a proposed specification and setting up
designs
< Number of stages
< Feed locations
< Reboiler/Condenser duties
P BVM provides reliable designs that agree well
with rigorous simulation
L07 - 36
Heterogeneous Azeotropic Distillation Column Design
4. Case Study
L07 - 37
Heterogeneous Azeotropic Distillation Column Design
Separation of an acetone/water/1-butanol mixture
Acetone
(56.13oC)
1
Distilation
boundary
0.8
Residue curve map:
0.6
P One heterogeneous
II
0.4
azeotrope (saddle)
I
P Two distillation regions
0.2
F
0
0
1-Butanol
(117.92oC)
L07 - 38
0.2
0.4
0.6
0.8
Azeotrope
(93.26oC)
1
Water
(100oC)
Heterogeneous Azeotropic Distillation Column Design
A typical solution
Acetone
D
F
C-1
D-1
C-2
1-Butanol
Water
B
S
Let’s look at how we might develop a simpler
design in three stages
L07 - 39
Heterogeneous Azeotropic Distillation Column Design
Acetone/water/1-butanol Separation
Simple-column sequence
Option 1
L07 - 40
Heterogeneous Azeotropic Distillation Column Design
Flowsheet synthesis: Column 1
Feed: homogeneous in Region I
Alternative 1: D - acetone
M - water/1-butanol mixture,
Acetone
(56.13oC)
1
D
heterogeneous
Alternative 1
Decanting
0.8
relatively pure water
0.6
0.4
II
I
D
0.2
Alternative 2: M - water
D - ternary homogeneous
Alternative 2
mixture, near distillation
boundary
F
M
0
0
1-Butanol
(117.92oC)
0.2
0.4
M
Azeotrope
Water
o
(93.26 C) (100oC)
0.6
0.8
1
P not a useful product
P mix with other streams
or recycle
Choose Alternative 1
L07 - 41
Heterogeneous Azeotropic Distillation Column Design
Flowsheet synthesis: Liquid-phase splitting
Acetone
D
D
1.0
water/1-butanol mixture,
heterogeneous
C-1
F
water/1-butanol
mixture in Region II
0.8
M
0.6
D-1
M2
0.4
II
I
relatively
pure water
C-1
0.2
F
M1
M2
0.0
0.0
1-Butanol
L07 - 42
M1
0.2
0.4
0.6
D-1
0.8
M
1.0
Water
Heterogeneous Azeotropic Distillation Column Design
Feed to
Column 2
Flowsheet synthesis: Column 2
Column 2:
Simple column with integrated decanter
•
The distillation boundary can be crossed
<
High recovery of 1-butanol
Acetone
D
1.0
D
0.8
C-1
F
0.6
S1
M
M1
0.4
I
M2
C-1
0.2
B
F
C-2
M1
0.0
0.0
1-Butanol
L07 - 43
0.2
S2
D-1
II
B
C-2
0.4
0.6
S1
D-1
0.8
M
M2
S2
1.0
Water
Heterogeneous Azeotropic Distillation Column Design
Column design by boundary value method
P Feasibility test
P Column design
Specifications:
}
by Boundary Value Method
P Feed, top and bottom product compositions relate to
each other by overall material balance
P Reflux ratio is specified by trial and error
Column 1
• 97.4 mol% acetone in distillate
• 0.13 mol% acetone in bottom product
• Reflux ratio = 20
Column 2
• 99 mol% 1-butanol in bottom product
• 0.34 mol% acetone in distillate
• Phase split ratio of reflux = 0.086
• Reflux ratio = 0.8
L07 - 44
Heterogeneous Azeotropic Distillation Column Design
Column 1 designed by using BVM
Fixed:
Acetone
compositions
D
1
P Feed, top and bottom product
P Feed condition = saturated liquid
P Reflux ratio = 20
0.8
Results:
0.6
D
0.4
F
8
11
0.2
F
M
C-1
0
0
1-butanol
L07 - 45
0.2
0.4
0.6
0.8
M
1
Water
Condenser duty (kJ/h)
Reboiler duty (kJ/h)
Heterogeneous Azeotropic Distillation Column Design
6.27E+06
6.36E+06
Two-liquid phase splitting
Acetone
D
1.0
0.8
D
F
0.6
C-1
8
11
M
0.4
M1
C-1
0.2
D-1
F
M2
M1
M2
0.0
0.0
1-butanol
L07 - 46
0.2
0.4
0.6
D-1
0.8
M
1.0
Water
Heterogeneous Azeotropic Distillation Column Design
Column 2 designed by using BVM
Fixed:
P Feed, top and bottom product
compositions
P Feed condition = saturated liquid
P Reflux ratio = 0.8
P Phase split ratio of reflux = 0.086
Acetone
D
1
Results:
0.8
D
0.6
8
F
C-1
11
0.4
2
M
C-2
M1
D-1
0.2
F
S1
S2
5
M2
B
M
B
S2
0
0
1-butanol
L07 - 47
0.2
0.4
0.6 M1
S1
S0
0.8
1
Water
Condenser duty (kJ/h)
Reboiler duty (kJ/h)
Heterogeneous Azeotropic Distillation Column Design
1.68E+06
1.72E+06
Validation of the method by rigorous simulation
BVM
F
D
S1
S2
M2
B
0.0995
0.7859
0.1146
0.9700
0.0300
0.0000
0.0060
0.6396
0.3544
0.0017
0.9854
0.0129
0.0009
0.9864
0.0127
0.0000
0.0101
0.9899
100
Flow rate (kmol/h)
Total condenser duty (kJ/h)
10.10
7.95E+06
8.80
13.46
60.17
7.48
Total reboiler duty (kJ/h)
8.08E+06
Composition :
Acetone
Water
1-Butanol
HYSYS
Composition :
Acetone
Water
1-Butanol
Flow rate (kmol/h)
F
D
S1
S2
M2
B
0.0995
0.7859
0.1146
0.9735
0.0265
0.0000
0.0057
0.6396
0.3545
0.0017
0.9854
0.0129
0.0007
0.9866
0.0127
0.0000
0.0101
0.9899
100
10.10
8.74
13.37
60.28
7.50
Total condenser duty (kJ/h)
7.93E+06
Total reboiler duty (kJ/h)
8.06E+06
P Results from HYSYS give good agreement with the specified
compositions for Column 1 and 2
L07 - 48
Heterogeneous Azeotropic Distillation Column Design
Flowsheet
Acetone
water/1-butanol
mixture
D
D
1.0
C-1
8
F
0.8
11
2
M
C-2
M1
0.6
S1
S2
D-1
5
M2
0.4
II
B
I
C-1
0.2
F
B
C-2
M1
0.0
0.0
1-Butanol
L07 - 49
0.2
0.4
0.6
S1
D-1
0.8
M
M2
S2
1.0
Relatively pure
water
Water
Heterogeneous Azeotropic Distillation Column Design
Flowsheet: Introduce a recycle
Acetone
Recycling
D
1.0
D
0.8
8
F
C-1
S1
0.6
11
2
M
II
I
0.2
D-1
C-1
B
0.0
M2
B
C-2
0.2
S2
5
F
0.0
C-2
M1
0.4
S
0.4
1-butanol
0.6
D-1
0.8
M
S
1.0
Water
Results from HYSYS:
F
Composition :
Acetone
0.0995
Water
0.7859
1-Butanol
0.1146
100
Flow rate (kmol/h)
Total condenser duty (kJ/h)
Total reboiler duty (kJ/h)
L07 - 50
D
S
B
Recycle
0.9735
0.0265
0.0000
10.10
4.06E+07
4.07E+07
0.0015
0.9857
0.0129
79.32
0.0000
0.0101
0.9899
10.58
0.0055
0.6391
0.3554
435.70
Heterogeneous Azeotropic Distillation Column Design
Large recycle
condenser and reboiler duty
increases by 400%
Motivations
P Can we share decanter between two columns?
< Reduce capital cost
P Is there a benefit in eliminating the external recycle?
L07 - 51
Heterogeneous Azeotropic Distillation Column Design
Acetone/water/1-butanol Separation
Simple-column sequence
Option 2
L07 - 52
Heterogeneous Azeotropic Distillation Column Design
Sequence 1:
Two columns with two decanters
Acetone
D
1.0
D
C-1
F
0.8
D-2
S1
M
0.6
M1
C-2
S2
D-1
0.4
II
M2
I
B
C-1
0.2
P Tie lines of D-1 and D-2 are very
F
B
C-2
M1
0.0
0.0
1-Butanol
0.2
0.4
0.6
S1
D-1
0.8
M
M2
S2
1.0
Water
close to each other
P D-1 and D-2 perform similar
function
L07 - 53
Heterogeneous Azeotropic Distillation Column Design
Sequence 2:
Two columns with one decanter
P Bottom product of column C-1 (M) is added to the
decanter of next column
Acetone
D
1
D
0.8
C-1
F
0.6
M
0.4
C-2
C-1
0.2
S
F
0
0
1-butanol
L07 - 54
C-2
B
0.2
0.4
S
0.6
0.8
M
1
Water
Heterogeneous Azeotropic Distillation Column Design
B
Converting to two-column sequence
with one decanter
P Applicable to other mixtures with residue curve maps similar
to that of acetone/water/1-butanol mixture
Acetone
(56.13oC)
1
P Azeotrope is a saddle and heterogeneous
D
< Liquid-phase splitting occurs in the bottom of
Column 1 and in the top of Column 2
0.8
0.6
D
C-1
0.4
M
C-1
F
0.2
B
0
C-2
0
1-Butanol
(117.92oC)
L07 - 55
D-2
I
II
0.2
M2
M1
0.4
0.6 S1
D-1
0.8 M
M2
1S2
Water
(100oC)
Heterogeneous Azeotropic Distillation Column Design
M1
C-2
S1
S2
B
Converting to two-column sequence
with one decanter
P Bottom product of Column 1 is chosen to be on a tie line
P Decanter tie line of Column 2 can be chosen to be close to
the tie line of the bottom product of Column 1
D-1 tie line
D-2 tie line
P Decanter 1 and Decanter 2
have the same function
D
D
F
C-1
F
D-2
M
D-1
M2
M1
C-2
C-1
M
S1
C-2
S2
S
B
B
L07 - 56
Heterogeneous Azeotropic Distillation Column Design
Column 2 designed by BVM
Fixed: P Feed,topandbottomproduct
compositions
P Feedcondition=saturatedliquid
P Refluxratio=0.8
P Phasesplitratioofreflux=0.004
Acetone
D
1
Results for C-2:
0.8
D
0.6
8
F
Condenser duty (kJ/h)
Reboiler duty (kJ/h)
C-1
11
M
0.4
2 C-2
S
0.2
5
F
0
1-butanol
L07 - 57
M
B
0
0.2
0.4
0.6
0.8
S
1
Water
Heterogeneous Azeotropic Distillation Column Design
B
2.23E+06
2.28E+06
Validation of the method by rigorous simulation
BVM
F
Composition :
0.0995
Acetone
0.7859
Water
0.1146
1-Butanol
100
Flow rate (kmol/h)
Total condenser duty (kJ/h)
Total reboiler duty (kJ/h)
D
S
B
0.9700
0.0300
0.0000
10.10
8.50E+06
8.64E+06
0.0015
0.9856
0.0129
79.35
0.0000
0.0101
0.9899
10.55
D
S
B
0.9735
0.0265
0.0000
10.10
8.49E+06
8.63E+06
0.0015
0.9856
0.0129
79.35
0.0000
0.0101
0.9899
10.55
HYSYS
F
Composition :
Acetone
0.0995
Water
0.7859
1-Butanol
0.1146
Flow rate (kmol/h)
100
Total condenser duty (kJ/h)
Total reboiler duty (kJ/h)
P Results from HYSYS are in good agreement with the specified
compositions for the design method
L07 - 58
Heterogeneous Azeotropic Distillation Column Design
Acetone/water/1-butanol Separation
Column with an intermediate decanter
Option 3
L07 - 59
Heterogeneous Azeotropic Distillation Column Design
Column with an intermediate decanter
D
F
D
C-1
V
F
M
C-2
S
S
B
The two columns can be combined,
P when the bottom product of C-1 has approximately the same
vapour composition as the top vapour of C-2
Stichlmair, J.G. and Fair, J.R. (1998), Distillation: principles and practice, Wiley-VCH, 222.
L07 - 60
Heterogeneous Azeotropic Distillation Column Design
B
Column with an intermediate decanter
designed using BVM
Fixed: P Feed,topandbottomproduct
compositions
P Feedcondition=saturatedliquid
P Refluxratio=20
P sidestreamlocation=6(frombottom)
Acetone
D
1
Rectifying
profile
0.8
Results:
0.6
D
Middle
profile
0.4
F
11
12
Stripping
profile
0.2
8
14
F
S
B
B
0
0
1-butanol
L07 - 61
0.2
0.4
0.6
0.8
Draw
stage
S
1
Water
Condenser duty (kJ/h)
Reboiler duty (kJ/h)
Heterogeneous Azeotropic Distillation Column Design
6.27E+06
6.41E+06
Validation of the method by rigorous simulation
BVM
Composition:
Acetone
Water
1-Butanol
Flow rate (kmol/h)
HYSYS
Distillate
0.9724
0.0276
0
Bottoms
0
0.0024
0.9976
Side
0.0016
0.9855
0.0129
Distillate
0.9724
0.0276
0
Bottoms
0
0.0024
0.9976
Side
0.0016
0.9855
0.0129
10.1
10.46
79.44
10.1
10.46
79.44
Condenser duty
(kJ/h)
6.26E+06
6.26E+06
Reboiler duty
(kJ/h)
6.41E+06
6.41E+06
P Results from HYSYS are in good agreement with the
specified compositions for the design method
L07 - 62
Heterogeneous Azeotropic Distillation Column Design
Comparison with simple-column sequences
Option 1
D
F
D
8 C-1
1
F
S1
2
M
M2
F
M
S2
5
D
8 C-1
1
C-2
M1
D-1
Option 3
Option 2
2 C-2
S
B
Stages
Total condenser duty (kJ/h)
Total reboiler duty (kJ/h)
14
5
S
Option 1
Option 2
Option 3
18
40.54E+06
40.75E+06
18
8.49E+06
8.63E+06
15
6.26E+06
6.41E+06
stages and less energy
Heterogeneous Azeotropic Distillation Column Design
S
B
B
xB
P Column with intermediate decanter requires fewer
L07 - 63
8
11
12
4. Conclusions and Future work
L07 - 64
Heterogeneous Azeotropic Distillation Column Design
Conclusions
‘
Boundary value method has been extended to
allow its application to columns with multiple
heterogeneous stages
• Phase split ratio of reflux is a degree of freedom
• For a multiple stage heterogeneous column, a number of
possible designs corresponding to phase split ratio of the
last heterogeneous stage can be obtained
‘
Boundary value method has been developed for
design of
• double-feed columns with heterogeneous stages
• columns with intermediate decanters
L07 - 65
Heterogeneous Azeotropic Distillation Column Design
Conclusions
‘
Boundary value method can be used as a tool for
screening options and assessing the feasibility of
proposed columns prior to rigorous simulation
‘
Boundary value method can be used for the
evaluation of columns and will be used to
evaluate separation flowsheets
•
Number of stages at a given reflux ratio is obtained
< Capital and operating costs can be estimated
L07 - 66
Heterogeneous Azeotropic Distillation Column Design
Futurework
‘
Methodology of distillation sequence synthesis for
separating heterogeneous azeotropic mixtures will
be developed
Various options for synthesis will be taken into
account
< Types of columns:
< Types of decanters:
• single-feed
• integrated decanter
• double-feed
• stand alone decanter
• intermediate decanter
< Subcooled decanter
< Operating pressures
< Flowsheet structure
L07 - 67
Heterogeneous Azeotropic Distillation Column Design