Reactions and Separations
Selecting Entrainers for
Vivek Julka
Madhura Chiplunkar
Lionel O’Young
ClearWaterBay Technology, Inc.
D
This systematic methodology uses
residue curve maps to identify and evaluate
substances that can facilitate distillation
by breaking an azeotrope.
istillation is the most widely used separation
process in the chemical process industries. In a
typical chemical plant, distillation columns and
their support facilities can account for about one-third of
the total capital cost and more than half of the total energy
consumption. Consequently, the design and optimization
of the distillation train have a critical impact on the economics of the entire process.
In general, at phase equilibrium, the compositions of the
coexisting vapor and liquid phases are different. Distillation
exploits this difference in the relative volatilities of the individual components in the mixture to achieve the desired
separation. For many mixtures, the order of the components’ relative volatilities does not change over the entire
range of mixture compositions. However, some mixtures
exhibit one or more azeotropes, or points at which the compositions of the coexisting liquid and vapor phases are the
same. As a result, it is not possible to separate these mixtures into their pure constituents via distillation alone.
An azeotrope can be either homogeneous, containing one
liquid phase, or heterogeneous, consisting of two liquid
phases. Heterogeneous azeotropes can be easily separated
using a decanter coupled with one or more distillation
columns, which exploits both vapor-liquid and liquid-liquid
equilibrium driving forces. Homogeneous azeotropic compositions that are pressure-sensitive can be separated using
pressure-swing distillation, which utilizes two or more distillation columns operating at different pressures together
with appropriate recycle strategies to achieve the desired
separation. However, if the change in azeotrope composition is small, the pressure-swing distillation sequence will
have very large recycle flowrates, resulting in an uneconomical process.
In all other cases, the only way to separate homogeneous azeotropic mixtures via distillation is by adding an
extraneous component, referred to as an entrainer or massseparating agent, to facilitate the separation. Entrainers are
also used to enable the separation of non-azeotropic mixtures where the direct separation is either not feasible due
to process constraints (e.g., maximum operating temperature) or highly uneconomical (e.g., due to the presence of
a severe tangent pinch, as in the case of acetic acid and
water).
An entrainer facilitates the separation of an azeotropic
mixture by selectively altering the relative volatilities of the
components in question, thereby effectively “breaking” the
azeotrope. The entrainer is specific to the mixture in question — e.g., benzene is a feasible entrainer for separating
ethanol and water, but not for separating ethanol and methyl
ethyl ketone — so there are no universal entrainers.
Because the choice of an entrainer determines the separation sequence (the number and order of distillation
columns and decanters, and how they are interconnected),
and hence the overall economics of the process, entrainer
selection is a critical step in the synthesis and conceptual
design of azeotropic distillation processes.
Entrainers are commonly selected based on prior experience with the same or a similar process. This approach
rarely identifies novel entrainers that could have a dramatic
impact on the economics of the entire process.
Residue curve map technology
One methodology for determining entrainer feasibility
utilizes residue curve map (RCM) technology. A residue
curve map is a geometric representation of the vaporliquid equilibrium (VLE) phase behavior of multicompoCEP
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Reactions and Separations
nent mixtures, highlighting, in particular, those properties
that directly impact distillation (1). It represents a collection of residue curves, or trajectories of liquid-phase
compositions (mole or mass fractions) as they change
with time. Pure-component vertices, connected by lines
that form the binary edges, bind this composition space.
The boiling points of the pure components and any existing binary, ternary, or multicomponent azeotropes
(mole/mass fractions and boiling points) are indicated on
the diagram. The composition trajectories move from the
lightest component in the mixture to the heaviest — i.e.,
the temperature continually increases as the liquid gets
richer in the heavier component. The directions of the
curves are consistent with the curves on the binary edges.
Methyl Ethyl Ketone
(79.3˚C)
a.
0.9
0.8
0.7
0.6
0.5
0.4
Distillation Region 1
0.3
0.2
0.1
Acetone
(56.1˚C)
64˚C
Binary Azeotrope
Distillation
Region 2
55.2˚C
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Methanol
(64.5˚C)
Distillation Boundary
Methyl Ethyl Ketone
(79.3˚C)
b.
0.9
Residue Curve
0.8
0.7
0.6
0.5
Distillation
Region 1
Distillation
Boundary
0.4
Binary Azeotrope
0.3
64˚C
0.2
0.1
Acetone
(56.1˚C)
Distillation
Region 2
55.2˚C
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Methanol
(64.5˚C)
Binary Azeotrope
■ Figure 1. A residue curve map for acetone/methanol/MEK at 1.0
atm depicts two binary azeotropes and a distillation boundary that
divides the composition space into two distillation regions (a).
Sample residue curves are shown in Figure 1b.
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The general properties of residue curves and how to
sketch the maps are explained in detail in Ref. 1.
The RCM for the ternary system containing acetone,
methanol, and methyl ethyl ketone (MEK) is illustrated in
Figure 1. The composition space is drawn first, the pure
component compositions and temperatures are indicated at
the vertices, and the azeotropes (binary or ternary) and their
temperatures are marked. As shown in Figure 1a, this system
forms two homogenous binary azeotropes (acetone/methanol
and methanol/MEK) and no ternary azeotropes. Once the
temperatures are indicated, an arrow is added on each of the
binary edges in the direction of increasing temperature, i.e.,
from lightest boiler to heaviest boiler (including both pure
components and azeotropes). The residue curves originate at
the lightest boiler, the acetone-MEK azeotrope, and go in the
direction of either MEK or methanol, creating an imaginary
boundary connecting the two binary azeotropes. The dividing curve is called a distillation boundary.
The presence of azeotropes divides the composition
space into distillation regions separated by the distillation
boundary such that the residue curves in each region go in
different directions (i.e., toward different components). As
shown in Figure 1b, the distillation boundary divides the
composition space into Region 1, acetone/methanolMEK/MEK, where the residue curves go toward MEK, and
Region 2, acetone/methanol-MEK/methanol, where the
residue curves go toward methanol. In the case of a multicomponent mixture where more than one azeotrope may
exist, multiple distillation boundaries may also exist. A distillation boundary exists if the residue curves begin at the
same point but end at different points (i.e., in different
regions), or if they begin at different points but end at the
same point (i.e., from different regions).
A distillation boundary represents an impassible
boundary for distillation (although it may be crossed
using other separation techniques, such as liquid-liquid
phase separation, solid-liquid separation, etc.), and the
distillate and bottoms product for each column must lie in
the same distillation region. Consequently, the presence,
location and structure of these boundaries are critical in
determining the multicomponent distillation feasibility.
The general properties and more examples of distillation
boundaries are explained in detail in Ref. 1.
RCM technology has been extensively tested and verified in industry. Residue curve maps have been used to
systematically synthesize distillation sequences to achieve
a desired separation, to determine novel separation
sequences, and to identify and evaluate entrainers (1–3).
RCM technology can also be extended to reactive distillation — depicting the appearance of new azeotropes created
by the reaction (reactive azeotropes), and allowing material
balances and sequences of operations to be determined.
The nature of the RCM changes with the extent of reaction,
i.e., depending on reaction kinetics (4).
To evaluate entrainer feasibility using RCM methodology, first compute the RCM for the system consisting of
the azeotropic components to be separated and the candidate entrainer. Next, check the phase behavior of the system to determine whether a liquid-liquid phase envelope
exists. If one does exist, a liquid-liquid phase region for
the system components can be generated at a certain temperature (e.g., at the temperature of the heterogeneous
azeotrope, at the temperature where the liquid-liquid
region is the largest, or at a desired operating temperature). The tie-lines indicate the two-phase compositions.
Then draw an envelope over the RCM composition
space, superimposing the composition scale (rather than
the temperature scale). The candidate entrainer is feasible
if either (a) the entrainer does not divide the components
to be separated into different distillation regions, or (b)
the entrainer induces a liquid-liquid phase separation and
there exists a liquid-liquid equilibrium tie-line crossing
the distillation boundary. Once a feasible entrainer is
identified, the corresponding separation sequences can be
systematically synthesized from the structure of the
RCM (1, 5).
The workflow for screening entrainers
Various commercial computer tools are available for
generating residue curve maps from a thermodynamic
physical-property model for the system. However, in the
early stages of process development, when decisions
regarding the process structures are generally made, such
detailed thermodynamic models for the system are generally not available and can be very expensive to develop.
Therefore, a step-by-step approach in which the likely
separation boundaries and feasible separation sequences are
first “sketched” is recommended. This synthesis activity is
coordinated with suitable experiments and modeling to verify the feasibility of the candidate processes. This allows a
more comprehensive search with minimum effort, while
greatly facilitating process development (6).
For entrainer selection, the approach begins by sketching
the structure of the RCM (and liquid-liquid phase equilibrium, if necessary) from only the azeotropic temperature, and
approximating composition and solubility data using the
methodology previously described (and discussed in detail
in Ref. 1).
To screen entrainers and determine the sequence for separating a mixture of components A and B:
1. Compile a list of candidate entrainers. Some criteria
for compiling this list include:
a. components that are already present in the
process, especially reactants
b. components that are present on the plant site (so
no new chemical is introduced in the plant’s waste-treatment unit)
c. water (since it forms heterogeneous azeotropes
with many components, the separation is easier, although
the use of water may increase the load on the waste treatment facility)
d. entrainers used for the same or similar components
e. commonly available chemicals.
2. Prepare an RCM for each candidate entrainer:
a. If a detailed thermodynamic physical-property
model is available, compute the RCM for the system of
A, B and the entrainer. If only a partial model is available, the remaining mixture properties can be modeled
using UNIFAC, provided the predictions are in agreement
with available azeotrope data.
b. If no physical-property model is available, sketch
the structure of the RCM from available azeotropic temperature, composition (approximate) and solubility (approximate) data.
c. If neither a physical-property model nor azeotrope
data are available, the required information can either be
estimated using group contribution methods or an educated
guess. These can then be verified experimentally.
3. From the structure of the RCM, determine if the candidate entrainer is feasible for separating components A
and B, i.e., both A and B lie in the same distillation region,
or the entrainer introduces a liquid-liquid tie-line that
crosses the distillation boundary dividing components to
be separated into different distillation regions.
4. Synthesize all the corresponding separation sequences
— the number of distillation columns and decanters, and
their interconnections — from the structure of the RCM by
mass balance. Do this for each feasible entrainer.
5. Identify the entrainer feasibility conditions for the mostpromising candidate entrainers if their feasibility was determined from either azeotropic data or estimated using group
contribution techniques (2b or 2c above). Subsequently,
experimentally verify any of the conditions whose validity
may be in doubt. Once these conditions have been verified, a
detailed thermodynamic physical-property model for the mixture can be developed from experimental data.
6. Design, simulate and optimize the separation
sequences.
Types of experiments
After identifying the key properties or missing data
that need to be verified, determine which experiments are
appropriate to confirm the characteristics desired in an
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Acetone
(56.1˚C)
Entrainer
0.9
0.9
Distillation Boundary
0.8
0.8
Isovolatility Curve
0.7
Binary Azeotrope
0.7
0.6
0.6
0.3
0.3
Distillation
Region 2
Binary Azeotrope
0.1
Isopropanol
(82.3˚C)
80.4˚C
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
entrainer. Various types of vapor-liquid experiments (i.e.,
vapor-liquid and liquid-liquid equilibrium measurements)
can be used in different steps of the entrainer selection
process.
To determine the structure of the RCM for an entrainer,
the boiling point and azeotrope data for the various binary
pairs and/or ternary combinations need to be known. An
experimental device known as a spinning-band distillation
apparatus is used to determine the nature, composition and
temperature of the azeotrope. This device consists of a
spinning band that simulates the stages of distillation, such
that the lightest boiler in the mixture (minimum-boiling
azeotrope or pure component) is distilled first. In the case
of heterogeneous azeotropes, this vapor contains multiple
liquid phases and the composition for each needs to be
determined. Maximum-boiling azeotropes are less prevalent and more difficult to measure. They are measured in a
vapor-liquid equilibrium apparatus as outlined in the next
paragraph. Experiments at different pressures can indicate
how the azeotrope changes with pressure.
To build a thermodynamic physical-property model for
use in detailed system design (Step 5), vapor-liquid and
liquid-liquid equilibrium data are needed. These data can
be collected in an apparatus wherein the mixture is first
equilibrated; vapor and liquid samples are then taken and
the compositions measured. For a heterogeneous system,
additional experiments are needed to measure the phase
splitting of an equilibrated mixture at a certain temperature.
These can indicate the behavior of the liquid-liquid tielines, which is important in determining the feasibility of
the distillation sequence. Experiments at different temperatures can indicate how the size of the liquid-liquid region
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0.2
Isovolatility Curve
0.1
Binary Azeotrope
A
Water
(100˚C)
■ Figure 2. An RCM for isopropanol/water/acetone at 1.0 atm
shows a distillation boundary that divides isopropanol and water
into two separate distillation regions. Therefore, acetone is not a
feasible entrainer for separating isopropanol and water.
50
B
0.9
0.4
Distillation
Region 1
0.4
0.2
0.8
0.5
0.5
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
B
■ Figure 3. In the RCM corresponding to classic extractive distillation for a given A-B-E system such that the isovolatility curve intersects the B-E edge of the composition space, B will be the distillate
from the extractive column. An industrial separation corresponding
to this RCM is water (A), ethanol (B), and ethylene glycol (E).
Extractive Column
Entrainer Recovery Column
B
A
A+B
E
■ Figure 4. An extractive-distillation sequence for separating A
and B using entrainer E requires a double-feed extractive column.
changes so that the optimal decanter temperature can be
selected. Some experimental devices allow experiments to
be conducted at pressures other than atmospheric. The
composition and temperature data are then used to determine thermodynamic model parameters by regression.
Example 1. Is acetone a feasible entrainer
for separating isopropanol and water?
The first step in determining if acetone is a feasible
entrainer for separating isopropanol and water, which form a
minimum-boiling homogeneous azeotrope, is to compute the
residue curve map for the isopropanol/water/acetone system
(Figure 2). An analysis of this RCM shows that the system
exhibits a distillation boundary that divides the composition
space into two distillation regions. Since water and isopropanol lie in different distillation regions, and acetone
does not induce a liquid-liquid phase separation, acetone is
not a feasible entrainer for separating water and isopropanol.
Vapor Mole Fraction (Ethanol)
Vapor Mole Fraction (Ethanol)
1
1
0.95
0.9
Azeotrope
(1.5% Ethylene Glycol)
Azeotrope
(no Ethylene Glycol)
tillate. In addition,
the closer the intersection is to the
0.6
0.8
pure component A
0.8
0.85
0.9
0.95
1
or B, the better the
0.4
Liquid Mole Fraction (Ethanol)
No Ethylene Glycol
entrainer for this
10 mol% Ethylene Glycol
25 mol% Ethylene Glycol
0.2
separation (i.e., the smaller the entrainer-to-feed ratio).
50 mol% Ethylene Glycol
1.5 mol% Ethylene Glycol
Therefore, the isovolatility curve can be used to quickly
0
and efficiently rank candidate entrainers for extractive
0
0.2
0.4
0.6
0.8
1
distillation.
Liquid Mole Fraction (Ethanol)
The component recovered as the extractive-column
■ Figure 5. A pseudo-binary VLE diagram for ethanol/water at fixed
distillate
can also be determined using a pseudo-binary
ethylene glycol compositions shows that as the ethylene glycol
phase diagram, in which VLE data are plotted on an
composition is increased, the ethanol/water pseudo-azeotrope
entrainer-free basis (Figure 5). As the amount of
moves toward ethanol and eventually disappears. At this point,
ethanol is more volatile, so it will be the distillate from the extractive
entrainer is increased, the composition of the pseudocolumn in Figure 4.
azeotrope (i.e., the point at which the pseudo-binary VLE
curve crosses the 45-deg. line) changes until it completely
Example 2. Extractive distillation
disappears. The more volatile of the two components at
In extractive distillation, a heavy (high-boiling, lowthis point will be the distillate from the extractive column.
volatility) entrainer is used to separate a mixture exhibitThe smaller the composition of the entrainer at which the
ing a minimum boiling azeotrope. The typical extractivepseudo-binary azeotrope disappears, the better the
distillation entrainer has a higher boiling point than the
entrainer is (smaller entrainer-to-feed ratio). Consepure components, and it does not form any azeotropes
quently, pseudo-binary phase diagrams can also be used
with either of the pure components.
to rank candidate extractive-distillation entrainers. In
A common industrial example of extractive distillaaddition, these diagrams are very useful for understanding
tion is the use of ethylene glycol to separate ethanol and
the effect of mixed extractive-distillation entrainers.
water. The residue curve map corresponding to a similar
Example 3. Using water to separate
extractive distillation is shown in Figure 3. Since this
n-butanol and n-butyl acetate
RCM does not exhibit any distillation boundary, the
components to be separated (A and B) lie in the same
Since butanol and water form a minimum-boiling homodistillation region, and hence the candidate entrainer (E)
geneous azeotrope, they cannot be separated without the use
is feasible. Analysis of the extractive distillation RCM
of an entrainer. One possible candidate entrainer is water.
reveals that A and B (at all feed compositions) can be
The residue curve map for butanol/butyl-acetate/water
separated using the sequence shown in Figure 4. Note
(Figure 6) shows that this system exhibits three binary
that the first column, the extractive column, must be a
azeotropes (butanol/butyl-acetate [homogeneous],
double-feed column, with two separate feed locations
butanol/water [heterogeneous], butyl-acetate/water [heteroand stages, both above and below each feed. The
geneous]) and a heterogeneous ternary azeotrope, and three
entrainer is introduced at the upper feed location and the
distillation boundaries divide the composition space into
feed to be separated is introduced at the lower location.
three distinct distillation regions. Note that butanol and butyl
One of the components is recovered as the distillate
acetate lie in different distillation regions. However, since
from the extractive column and the other as the distillate
this mixture also exhibits a multiple-liquid-phase region,
from the second column, the entrainer recovery column.
with tie-lines that cross the boundary separating butanol and
The isovolatility curve (the locus of points at which
butyl acetate into different distillation regions, water is a feathe relative volatility of A and B is equal to 1) can be
sible entrainer for separating butanol and butyl acetate.
used to determine which of the two components, A or
The RCM in Figure 6a is similar but not identical to
B, is the distillate from the extractive column. This
the classical ethanol/water/benzene example. The flowcurve (Figure 3) starts at the binary azeotrope and ends
sheet sequence in Figure 6b also resembles one of the
at one of the other edges of the composition triangle. If
feasible sequences for separating ethanol/water using a
it intersects the B-E edge, then B will be the distillate
heterogeneous entrainer. The difference in the RCMs is
from the extractive column; alternatively, if it intersects
in the nature of the multiple-liquid-phase region. The
ethanol/water/benzene system has a Type I phase envethe A-E edge, then A will be the extractive-column dis0.8
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Table 1. Water must satisfy all of the following
thermodynamic conditions in order for it to be a feasible
entrainer for separating butanol and butyl acetate.
Butanol
(117.7˚C)
c
0.9
Material Balance Lines
0.8 116.9˚C
0.7
Multiple-Liquid-Phase Region
0.6
a
Tie-Line
0.5
0.4
d
L2
0.3
Binary Azeotrope
b
92.6˚C
0.2
Ternary
Azeotrope
90.7˚C
0.1
91.2˚C
Butyl Acetate
(126˚C) e
0.1
0.2
0.3
0.4
0.5
0.6
Water
0.7
0.9 L1 (100˚C)
0.8
■ Figure 6a. An RCM for the mixture n-butanol, n-butyl acetate
and water at 1 atm exhibits liquid-liquid equilibrium tie-lines
crossing the distillation boundary that separates butanol and butyl
acetate. Hence, water is a feasible entrainer for separating butanol
and butyl acetate.
b
d
L1
Feed
a
L2
c
e
Butanol
Butyl Acetate
■ Figure 6b. This sequence for separating n-butanol and n-butyl
acetate using water as an entrainer is feasible for all butanol and
butyl acetate feed compositions.
lope, i.e., only a single binary pair (namely benzene/water) exhibits a liquid-liquid behavior, whereas
the butanol/butyl-acetate/water system has a Type II
envelope, where two binary pairs (butanol/water and
butyl-acetate/water, show heterogeneous behavior.
Table 1 lists all the thermodynamic conditions that water
must satisfy to be a feasible entrainer for separating butanol
and butyl acetate using either of the two separation sequences.
This list can be used to determine what experiments are necessary to validate entrainer feasibility (e.g., a simple LLE
experiment could be used to verify that one end of the liquidliquid equilibrium tie-line does indeed lie in the distillation
region that contains butyl acetate). Feasibility conditions are
unique to each particular RCM and describe the thermodynamic conditions necessary to make an entrainer feasible
based on either of the previously discussed rules of feasibility
(that is, the entrainer does not divide the components to be
separated into different distillation regions, or it induces a
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Water and butanol form a minimum-boiling heterogeneous
azeotrope
Water and butyl acetate form a minimum-boiling
heterogeneous azeotrope
Water, butanol and butyl acetate form a ternary
heterogeneous azeotrope
The boiling point of the ternary azeotrope is lower than the
boiling point of butanol and butyl acetate azeotrope
The boiling point of the ternary azeotrope is lower than the
boiling point of butanol and water azeotrope
The boiling point of the ternary azeotrope is lower than the
boiling point of butyl acetate and water azeotrope
One end of the liquid-liquid equilibrium tie-line passing
close to the ternary azeotrope must lie in the butyl
acetate distillation region
liquid-liquid phase separation and there exists a liquid-liquid
equilibrium tie-line crossing the distillation boundary).
An RCM sequencing analysis finds that butanol and butyl
acetate can be separated using the arrangement shown in
Figure 6b. The binary feed and the distillate from the second
column are fed to the first distillation column, either at the
same feed location or at different points. High-purity butanol
is recovered as the bottoms product, while the overhead
vapor is condensed and sent to a decanter. The water-rich
(i.e., entrainer-rich) phase is refluxed back to the first column, while the entrainer-lean phase is sent to the second distillation column, where high-purity butyl acetate is recovered
as the bottoms product. The distillate from the second column is a mixture of all three components and is recycled
back to the first distillation column. This sequence is feasible
for all butanol/butyl-acetate feed compositions. The material
balance for this sequence is depicted in Figure 6a.
The butanol/butyl-acetate/water separation can also be
carried out using another sequence where the order of the
separations is reversed — butyl acetate is recovered from
the first column, butanol from the second. This sequence is
also valid for all butanol/butyl-acetate feed compositions.
Which scheme is more economical is a function of the
feed composition and how the sequences can be integrated
with the rest of the process. This can be determined only
after the conceptual design and simulation of both separation sequences.
Example 4. Diethoxymethane/ethanol
separation using water
A key advantage of using a residue curve map for
entrainer selection is that it can be used to find novel
entrainers and/or separation sequences.
Consider water as a potential entrainer for separating a
binary mixture containing 50 mol% diethoxymethane
(DEM) and 50 mol% ethanol. This binary mixture forms a
minimum-boiling homogeneous azeotrope (2). The residue
Ethanol
(78.3˚C)
Feed
Binary Azeotrope
0.9
78.1˚C
0.8
0.7
76.7˚C
Ternary Azeotrope
0.6
Binary
Azeotrope
76˚C
0.4
Diethoxymethane
Tie-Line
0.3
0.1
80˚C
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Water
(100˚C)
Binary Azeotrope
■ Figure 7. The water/ethanol/DEM system at 1.0 atm exhibits: two
homogeneous binary azeotropes (ethanol/water, ethanol/DEM), one
heterogeneous binary azeotrope (water/DEM), and a ternary homogeneous azeotrope; three distillation boundaries (connecting the
ternary azeotrope to each of the binary azeotropes); and a multipleliquid-phase region (with tie-lines that cross the distillation boundary connecting the ternary azeotrope to the DEM/water azeotrope),
as seen in the RCM.
curve map for DEM/ethanol/water is shown in Figure 7.
The system exhibits three binary azeotropes and a ternary
azeotrope, and it has three distillation boundaries. It also
exhibits a multiple-liquid-phase region.
Water is not a typical heterogeneous entrainer (for example, as benzene is for ethanol dehydration or water is for separating butanol and butyl acetate), because the ternary azeotrope does not lie in the multiple-liquid-phase region. However, a detailed analysis of this RCM shows that it should be
possible to use water to separate the binary mixture using the
sequence of three distillation columns and a decanter shown
in Figure 8. This separation sequence exploits the multipleliquid-phase regions with tie-lines that cross the distillation
boundary connecting the DEM/water azeotrope to the
ternary azeotrope as well as the curved nature of the distilla-
Literature Cited
1.
2.
3.
4.
5.
6.
Water
■ Figure 8. The configuration for separating an equimolar mixture
of DEM and ethanol using water as the entrainer consists of three
distillation columns and a liquid-liquid decanter.
0.2
Diethoxymethane
(87.6˚C)
Ethanol
Multiple-Liquid-Phase Region
0.5
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Distillation Systems,” McGraw-Hill, New York, NY (2001).
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Purification of Diethoxymethane from a Mixture with
Ethanol and Water,” U.S. Patent 4,740,273 (1988).
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U.S. Patent 6,605,738 (1997).
Chiplunkar, M., et al., “Experimental Study of Feasibility
in Kinetically Controlled Reactive Distillation,” AIChE J.,
51 (2), pp. 464–479 (2005).
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for Multicomponent Azeotropic Mixtures,” AIChE J., 44 (6),
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tion boundary that connects the ternary azeotrope to pure
ethanol. Since some of the properties used to compute the
RCM were estimated using group contribution methods, the
latter condition needs to be verified experimentally. (In addition to this sequence, others can be synthesized as well.)
Final thoughts
Although the RCM-based methodology is very powerful and can be used to find innovative new separation
sequences and identify novel entrainers, several limitations have hindered its widespread use in industry. While
there are now good commercially available tools for computing and sketching residue curve maps, they still
require either a good physical-property model or an
extensive azeotrope database. A bigger limitation is that
interpreting the structure of the RCM and synthesizing
feasible separating sequences requires significant knowledge and expertise in RCM technology. However, new
software programs have recently become available that
significantly reduce this hurdle and make the technology
accessible to process engineers and chemists.
CEP
VIVEK JULKA, PhD, is a principal engineer at ClearWaterBay Technology,
Inc. (E-mail: vjulka@cwbtech.com) and is the product manager for the
AzeoDESK software for azeotropic distillation. He is an expert in the
synthesis and conceptual design of separation processes. He
previously worked for AspenTech, and Union Carbide Corp. He holds a
PhD in chemical engineering from the Univ. of Massachusetts Amherst.
MADHURA CHIPLUNKAR, is an advanced engineer at ClearWaterBay
Technology, Inc (E-mail:mchiplunkar@cwbtech.com). Her interests lie
in the synthesis of distillation-based processes, with special emphasis
on azeotropic and reactive systems. She has also been involved in the
development of the AzeoDESK software for azeotropic distillation. She
holds an MS in chemical engineering from the Univ. of Massachusetts
Amherst.
LIONEL O’YOUNG, PhD, is president and co-founder of ClearWaterBay
Technology, Inc. (4000 Valley Blvd., Suite 100, Walnut, CA 91789;
Phone: (909) 595-8928; Fax: (909) 595-6899; E-mail:
lionel@cwbtech.com). He has more than 15 years of experience in
process synthesis and development and owns several process
patents. Before ClearWaterBay Technology, he worked for Mitsubishi
Chemical Corp., Union Carbide Corp., and Linnhoff March, in a variety
of engineering and management positions. He holds BS and PhD
degrees in chemical engineering from the Univ. of Manchester
(formerly UMIST), Manchester, UK. He is a member of AIChE and
recipient of AIChE’s 2007 Computing Practice Award.
CEP
March 2009
www.aiche.org/cep
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