U.S. patent application number 10/632630 was filed with the patent office on 2004-02-12 for method of separating a solid compound from an adduct.
Invention is credited to Hsieh, S. T., Kelkar, Vaibhav, O'Young, Drow Lionel.
Application Number | 20040030201 10/632630 |
Document ID | / |
Family ID | 27804296 |
Filed Date | 2004-02-12 |
United States Patent
Application |
20040030201 |
Kind Code |
A1 |
O'Young, Drow Lionel ; et
al. |
February 12, 2004 |
Method of separating a solid compound from an adduct
Abstract
A method of separating one or more solid compound from an adduct
is provided. More specifically, the present invention provides a
method of separating one or more solid compounds from an adduct by
crystallization wherein certain phase equilibrium conditions are
selectively controlled.
Inventors: |
O'Young, Drow Lionel; (West
Covina, CA) ; Hsieh, S. T.; (San Jose, CA) ;
Kelkar, Vaibhav; (West Covina, CA) |
Correspondence
Address: |
DORSEY & WHITNEY LLP
INTELLECTUAL PROPERTY DEPARTMENT
4 EMBARCADERO CENTER
SUITE 3400
SAN FRANCISCO
CA
94111
US
|
Family ID: |
27804296 |
Appl. No.: |
10/632630 |
Filed: |
July 31, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10632630 |
Jul 31, 2003 |
|
|
|
10099227 |
Mar 13, 2002 |
|
|
|
Current U.S.
Class: |
568/923 |
Current CPC
Class: |
C07C 39/16 20130101;
C07C 39/16 20130101; C07C 37/84 20130101; C07C 37/20 20130101; C07C
37/84 20130101; C07C 37/20 20130101 |
Class at
Publication: |
568/923 |
International
Class: |
C07C 027/26; C07C
029/78 |
Claims
We claim:
1. A method of separating a one or more compounds from a solution
by crystallization, where the solution exhibits at least a ternary
phase equilibrium relationship which is represented by at least a
ternary phase diagram, comprising the steps of: providing the
solution comprised of at least three components in phase
equilibrium, including one or more compound components and a
solvent component, and where the compound components may form an
adduct, and where the solvent component is comprised of two or more
solvents, including at least a first solvent exhibiting a first
phase behavior, and at least a second solvent exhibiting a second
phase behavior; where the at least three components in phase
equilibrium exhibit phase behavior which establishes at least two
compartments in the phase diagram, including an adduct compartment
and at least one pure solid compound compartment; manipulating the
area of the adduct and pure solid compound compartments by
adjusting the concentration ratio of the two or more solvents;
adjusting the composition of the solution prior to crystallization
to place the solution concentration at a location selectively
within a desired compartment; and crystallizing the solution to
form a solid compound, as selected.
2. The method of claim 2 wherein adjusting the composition of the
solution includes adding to, and/or removing from, the solution any
one or more the components.
3. A method of separating a solid product from a solution including
a compound in a process operation, and where the product and
compound may form an adduct, characterized in that: at least two
solvents are provided in the solution, at least a first solvent
exhibiting a high solubility for the product and at least a second
solvent exhibiting a low solubility for the product, and the
concentration of the solvents are selectively controlled such that
the solid product is formed from the solution at selected process
operating conditions.
4. The method of claim 4 wherein a concentration ratio of the two
solvents is adjusted to selectively form either substantially pure
solid product or the adduct.
5. The method of claim 4 wherein the at least two solvents, product
and compound exhibit a ternary phase equilibrium relationship, and
the composition of the solution is selectively adjusted such that
the solution falls within a selected region of the ternary phase
equilibrium relationship.
6. A method of forming a solid product in a reaction process,
comprising the steps of: reacting reactants to form a solution
including at least a compound and a product, where the compound and
product may form an adduct; adjusting the composition of the
solution to include two or more solvents; and separating solid
product from the solution by selectively controlling a
concentration ratio of the two or more solvents, where the two or
more solvents are comprised of at least a first solvent exhibiting
a high solubility for the product and at least a second solvent
exhibiting a low solubility for the product, such that the solid
product is formed.
7. The method of claim 7 wherein the concentration ratio of the two
or more solvents is adjusted to selectively form either
substantially pure solid product or the adduct.
8. The method of claim 7 where the step of adjusting the
composition of the solution includes adding to, and/or removing
from, the solution any one or more of the two solvents or
compound.
9. A method of separating one or more solid compounds from a
solution including one or more components in a process operation,
and where the one or more components may form at least one adduct,
characterized in that: at least two solvents are provided in the
solution, at least a first solvent exhibiting a first phase
behavior and at least a second solvent exhibiting a second phase
behavior, and the concentration of the solvents are selectively
controlled such that a solid compound is formed from the solution
at selected process operating conditions.
10. A method of separating a compounds from a solution by
crystallization, where the solution exhibits at least a ternary
phase equilibrium relationship which is represented by at least a
ternary phase diagram, comprising the steps of: providing the
solution comprised of at least three components in phase
equilibrium, including one or more compound components and a
solvent component, and where the compound components may form an
adduct,; where the at least three components in phase equilibrium
exhibit phase behavior which establishes at least two compartments
in the phase diagram, including an adduct compartment and at least
one pure solid compound compartment; manipulating the area of the
adduct and pure solid compound compartments by adjusting the
concentration of the solvent in the solution such that pure solid
compound is formed by crystallization.
Description
RELATED APPLICATIONS
[0001] This patent application is a continuation-in-part
application of U.S. patent application Ser. No. 10/099,227
(Attorney Docket no. A-71155/MSS) filed on Mar. 13, 2002, the
entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates in general to a method of
separating one or more solid compound from an adduct. More
specifically, the present invention provides a method of separating
one or more solid compounds from an adduct by crystallization
wherein certain phase equilibrium conditions are selectively
controlled.
BACKGROUND OF THE INVENTION
[0003] Separation technologies are often used in the chemical
industry to separate or purify chemical compounds. One widely
employed separation technology is crystallization, wherein one or
more solid compounds are formed from a solution. Crystallization
techniques, such as melt crystallization and solution
crystallization, and the associated unit operations, are well known
in the industry.
[0004] Crystallization becomes more complex when a single solid
component is not easily formed from the solution, but instead an
adduct is formed. An adduct is a compound formed by direct
combination of two or more different compounds or elements. The
adducts are typically formed in simple molecular proportions, such
as an equal molar combination. Formation of the adduct is
undesirable, since it is one or more of the single compounds that
is the product of interest.
[0005] When an adduct of two components is formed, wherein only one
of the two components is the desired product, a variety of recovery
processes are used in prior art techniques to obtain the desired
product. Most techniques center around driving off the undesired
component, such as by melting the adduct and then removing the
undesired components by distillation, and other like means. The
adduct is often first purified by multiple steps of washing the
adduct, dissolving the adduct, and re-crystallizing the adduct. All
such processes are quite costly and energy intensive.
[0006] Accordingly, there is an important need in the industry to
provide a method of separating a compound from an adduct which is
free of such undesirable steps. Direct separation of a compound of
interest would be a significant advance in the industry.
SUMMARY OF THE INVENTION
[0007] Accordingly, the present invention provides a method of
separating one or more solid compounds from solution where the one
or more solid compounds may form an adduct. In particular, the
present invention provides a method of separating one or more solid
compounds or products from an adduct by crystallization wherein
certain phase equilibrium conditions are selectively controlled to
form either one or more of the desired solid compounds or an
adduct. By forming a desired solid compound directly, the costly
and complex recovery steps of the prior art are avoided. By
providing a method that allows one to specifically select the
formation of one or more of the desired solid compounds, or the
adduct, a powerful process development tool is created, whereby
certain operating conditions or variables of a process can be
selectively adjusted to generate the desired phase equilibrium
behavior.
[0008] In one embodiment, the present invention provides a method
of separating one or more solid compounds from a solution including
one or more components in a process operation, and where the one or
more components may form at least one adduct, characterized in
that: at least two solvents are provided in the solution, at least
a first solvent exhibiting a first phase behavior and at least a
second solvent exhibiting a second phase behavior, and the
concentration of the solvents are selectively controlled such that
a solid compound is formed from the solution at selected process
operating conditions.
[0009] In another embodiment of the present invention, a method of
manipulating a phase equilibrium behavior of a solution having two
or more components and which may be represented by a
multi-component phase diagram is provided, characterized in
that:
[0010] the solution is comprised of multiple components, including
at least two components, and a solvent component, and where the at
least two components may form an adduct;
[0011] and where the multiple components exhibit a phase
equilibrium behavior which can be represented by a multi-component
phase diagram and where the components are in phase equilibrium and
exhibit phase behavior which establishes at least two regions in
the phase diagram, an adduct region and at least one pure solid
compound region; and
[0012] wherein the solvent component is comprised of two or more
solvents, at least a first solvent exhibiting a first phase
behavior and at least a second solvent exhibiting a second phase
behavior, and the concentration of the solvents in the solution are
adjusted to selectively manipulate the area of one or more of the
at least two regions.
[0013] In yet another aspect, the present invention provides for
manipulating the relative size of the adduct and pure compound
component regions by adjusting the concentration ratio of the two
or more solvents; adjusting the composition of the solution prior
to crystallization to place the solution concentration at a
location selectively within either the adduct or one of the pure
compound component regions; and crystallizing the solution to form
the desired compound from the solution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Other objects and advantages of the present invention become
apparent upon reading of the detailed description of the invention
provided below and upon reference to the drawings in which:
[0015] FIG. 1A is a solid-liquid phase equilibrium diagram for a
system in which components A and B react to form an adduct C.
[0016] FIG. 1B is a projection of the phase diagram of the binary
system of FIG. 1A along the temperature axis.
[0017] FIG. 2 is a projection of a poly-thermal phase equilibrium
diagram for a ternary system comprising the components A, B and
their adduct C, along with a solvent.
[0018] FIGS. 3 and 4 are projections of a poly-thermal phase
equilibrium diagrams for the system of FIG. 2 illustrating the case
where the solvent compartment becomes very small when the melting
temperature of the solvent is much lower than the melting
temperature of both components A and B.
[0019] FIG. 5 is a projection of a poly-thermal phase equilibrium
diagram for a multi-component system of components A, B, an adduct
C formed from A and B, and Solvent I, showing the phase regions as
a function of the solvent composition according to one embodiment
of the present invention.
[0020] FIG. 6 is a projection of a poly-thermal phase equilibrium
diagram for a multi-component system of components A, B, an adduct
C formed from A and B, and solvent II showing the phase regions as
a function of the solvent composition according to another
embodiment of the present invention.
[0021] FIGS. 7 and 8 are projections of a poly-thermal phase
equilibrium diagrams for a multi-component system of components A,
B and an adduct C formed from A and B, illustrating an overlap
region created by the selection of Solvent I and Solvent II
(collectively referred to as "Solvent") according to another
embodiment of the present invention.
[0022] FIG. 9 is a projection of a poly-thermal phase equilibrium
diagram for a multi-component system of A, B, an adduct C formed
from A and B, and solvent showing maximum recovery of component A
using two different solvents, at a specific feed composition to a
crystallizer according to one embodiment of the present
invention.
[0023] FIG. 10 is a schematic process block diagram of a separation
system which may be used to carry out the method of one embodiment
of the present invention.
[0024] FIG. 11 is a projection of a poly-thermal phase equilibrium
diagram for a multi-component system corresponding to the
separation system of FIG. 10.
[0025] FIG. 12 is a schematic process block diagram of a separation
system which may be used to carry out the method of another
embodiment of the present invention.
[0026] FIG. 13 is a projection of a poly-thermal phase equilibrium
diagram for a multi-component system corresponding to the
separation system of FIG. 12.
[0027] FIG. 14 is a projection of a polythermal phase equilibrium
diagram for a multicomponent system of Example 1, showing the
effect of solvent compositions in the crystallizers, on the overlap
between the pure component phase regions.
[0028] FIGS. 15-17 are projections of a poly-thermal phase
equilibrium diagram illustrating the stream compositions for three
different cases for the separation flowsheet described in Example
2.
[0029] FIGS. 18-19 are projections of a poly-thermal phase
equilibrium diagram illustrating the stream in the separation
flowsheet described in Example 3 for two different solvent
compositions.
[0030] FIG. 20 is a projection of a poly-thermal phase equilibrium
diagram illustrating the stream compositions in the above mentioned
separation flowsheet when utilizing the "swing" in the solvent
composition from Solvent I to Solvent II.
DETAILED DESCRIPTION OF THE INVENTION
[0031] The inventors have discovered a method of separating one or
more solid compounds from a solution an adduct by crystallization
where the one or more solid compounds may form at least one adduct.
Certain phase equilibrium conditions are selectively controlled to
form either the one or more desired solid product(s) or an adduct.
By forming the desired solid compound(s) directly, the costly and
complex recovery steps of the prior art are avoided. By providing a
method that allows one to specifically select the formation of
either the desired solid compound or an adduct, a powerful process
development tool is created, whereby certain operating conditions
or variables of a process can be selectively adjusted to generate
desired phase equilibrium behavior. The invention provides for
manipulation and selective control of the phase equilibrium of a
multi-component liquid/solid phase equilibrium system. Typically
the multi-component phase equilibrium system will be directed to a
ternary or quaternary system; however the method of the present
invention may be applied to a system with any number of
components.
[0032] In general, the present invention is directed to
multi-component phase equilibrium systems, where at least two of
the components form an adduct. For example, the system may be
comprised of a solution of components A and B, and such components
form an adduct C. Either component A or B, or in some instances
both A and B, may be the compound or product which one wishes to
separate from the solution. To illustrate the principles of the
invention, exemplary phase diagrams are used as described below.
Exemplary phase diagrams are shown which have certain
characteristics solely in order to illustrate the invention, and
the invention is not to be construed to be limited in any way to
the specific examples shown.
[0033] Referring to FIG. 1A, a phase diagram for a binary system in
which component A and B form an adduct C is shown. The system is
characterized as a solid and liquid equilibrium with the presence
of a congruently melting solid compound. The maximum in the solid
and liquid equilibrium results from the formation of a solid
addition compound C, which is equi-molar in A and B and with the
molecular formula A-B, that melts at the temperature corresponding
to the maximum, to form a liquid with the same composition. This
type of behavior is well known in the art as congruent melting. On
the phase diagram the x axis represents the mass concentration of
component B and the y axis is the temperature.
[0034] In this example two eutectic points, E.sub.1 and E.sub.2 are
present, and five separate phase regions are characterized that are
important for recovery of solids according to the present
invention: Region I where components A and B are in the liquid
phase; Region II where solid A and a liquid mixture of A and B are
in equilibrium. Region III and IV where solid C (adduct) and a
liquid mixture of A and B are in equilibrium; and Region V where
solid B and a liquid mixture of A and B are in equilibrium. An
additional region below the eutectic point E1 exists where solid A
and solid C are present, and below eutectic point E2 where a
mixture of solid C and solid B are present; however these regions
are not treated further here as recovery of only a pure solid is of
interest.
[0035] FIG. 1B shows the projection of this poly-thermal diagram
along the temperature axis. For a binary system as the one under
consideration, the projection becomes a line, A-B, and the
locations of E.sub.1 and E.sub.2 are placed along the line as shown
in the figure. It should be noted that the location of the
congruent melting point C falls between the two eutectic points E1
and E2.
[0036] The inventors have discovered that this projection of the
binary poly-thermal diagram is useful for process synthesis because
the recovery of each solid can be visualized from this projection.
Referring to FIG. 1A, point F represents the feed composition of
the solution at a specific temperature, which in this example
places the location of point F in Region III. The recovery of solid
adduct C, which can be obtained from this composition can be found
from the polythermal projection shown in FIG. 1B. Using the well
known lever rule, the recovery of solid adduct C is the ratio of FM
to CM. The maximum recovery of pure solid C from this feed is the
ratio of FE.sub.1 to CE.sub.1, because both solid C and solid A
coexist when the temperature drops to eutectic point E.sub.1.
[0037] Similarly, as known in the field, for a starting composition
located in any of the other phase regions, the identity of the
solid recovered, as well as its maximum recovery can be determined
from the projection of the polythermal phase diagram. For point F
located in region I, the maximum recovery of A is given by the
ratio of FE.sub.1 to AE.sub.1. For point F located in region IV,
the maximum recovery of C is given by the ratio of FE.sub.2 to
CE.sub.2. For point F located in region V, the maximum recovery of
B is given by the ratio of FE.sub.2 to BE.sub.2.
[0038] According to the method of the present invention, the
poly-thermal diagram can be employed as a useful tool for process
design and feasibility studies because it identifies the region
where the desired product can be recovered. The projection of the
poly-thermal diagram becomes very useful when the complete phase
diagram is 3-dimensional or 4-dimensional. Of particular advantage
the process alternatives for separating the desired pure components
can be visualized according to the present invention.
[0039] The present invention is now described in more detail. The
inventors have discovered a method of separating one or more solid
compounds from a solution including a solvent and multiple
components and where at least two of the components form one or
more adducts, by selectively controlling the phase equilibrium
conditions through manipulation of the solvent composition and/or
concentration in the solution. This is a very powerful tool and
allows one to generate a separation process with process operating
conditions such as, but not limited to, type of solvent(s);
concentration ratio of solvents when two or more solvent components
are employed; or the mass concentration of any one of, or
combination of, the components fed to a crystallizer.
[0040] In an exemplary embodiment, the system is comprised of three
components: A and B and a solvent S. Components A and B form an
adduct C. Component A and/or B and/or the adduct C may be the
compound of interest for separation from the solution. The isobaric
phase diagram of the ternary system represents an image in
3-dimensional space. The composition coordinates can be plotted in
mole fractions on a triangular grid, and the temperature can be
plotted on an additional axis. However, it is not convenient to
work with multi-dimensional phase diagrams. Fortunately, for this
three component system, much of the important information,
particularly the crystallization boundaries, can be represented on
a 2-dimensional projection onto a triangular base. This is referred
to as the projection of a poly-thermal phase equilibrium diagram.
Please note that the ternary phase equilibrium diagrams are
represented here as right-angled triangular diagrams for clarity as
opposed to the alternative equilateral triangular diagram form also
known in the art. While a three component system is described, it
should be understood by those of ordinary skill in the art that the
system may include other components or solutes such as impurities,
unreacted reactants, isomers and the like; however, for purposes of
describing the present invention we are concerned only with the
primary components in the solution.
[0041] To illustrate the system and method of the present
invention, and in particular the selective control of phase
equilibrium conditions, first the phase diagrams are established
and described. Referring to the FIG. 2, in the exemplary embodiment
four phase regions or compartment are identified in the projection
of the polythermal phase diagram for the ternary system of A, B and
solvent. Components A and B may form an adduct C. When the feed to
the crystallizer is located in compartment A, pure solid A
component is recovered. Compartment C is where a solid adduct of A
and B, called adduct C is recovered. Compartment B is where pure
solid B is recovered. A solvent compartment is present where solid
solvent S may be recovered.
[0042] In this example four binary eutectics are present: E.sub.1,
E.sub.2, E.sub.SA and E.sub.SB. E.sub.1 is the eutectic point
between component A and component C. E.sub.2 is the eutectic point
between component C and component B. E.sub.SA is the eutectic
between solvent S and component A, and E.sub.SB is the eutectic
point between solvent S and component B.
[0043] In this exemplary embodiment, two ternary eutectic are
present, namely E.sub.SAC and E.sub.SBC. E.sub.SAC represents a
ternary eutetic of solvent, component A and component C. E.sub.SBC
represents the ternary eutetic of solvent, component B and
component C. The trajectory of the eutectic points forms the
boundary between the compartments. For example, the boundary
between component B compartment and the component C compartment is
the trajectory of the eutectic points from E.sub.2 to E.sub.SBC. A
straight line is used for simplification to illustrate the concept,
however it should be understood that the actual boundary may be
curved and can be calculated by commercially available
thermodynamic model packages and then preferably is validated by
use of experimental data obtained by routine experimentation within
the teaching of the present invention.
[0044] When a solvent is used which has a melting temperature that
is much lower than the melting temperature of both components A and
B, the size of the solvent compartment in the projected phase
diagram becomes very small as shown in FIG. 3. As the size of the
solvent compartment becomes small, the binary eutectic points
E.sub.SB and E.sub.SA, and the ternary eutectic points E.sub.SAC
and E.sub.SBC move toward the apex of the triangle, i.e. the pure
solvent vertex. Hence in this case, a good approximation of the
compartment size for components A, B and C is simply to draw the
trajectory of the eutectic points from either E.sub.1 or E.sub.2 to
the pure solvent point as shown in FIG. 4.
[0045] Of particular advantage, the inventors have discovered that
a solvent may be employed to manipulate the location of the
boundary of the various compartments, and thus the size of the
compartments in the phase diagram as illustrated in FIGS. 5 and 6.
A solvent is provided in the solution, and the phase equilibrium
behavior is selectively controlled by controlling the composition
and/or concentration of the solvent in the solution.
[0046] The solvent may be comprised of one component, or
alternatively may be comprised of a binary mixture of two or more
solvents components, or even a multi-component mixture and in each
case is collectively referred to as a "solvent." Referring
specifically to FIG. 5, a solvent (Solvent I) is employed. The
Solvent I is selected such that the B compartment varies in size,
in this case the size of compartment B becomes smaller, while the
size of compartment A becomes larger. Thus, Solvent I produces a
first phase behavior in the system. The compartments are
complementary, and as one compartment becomes larger at least one
of the other compartments becomes smaller due to the interaction
among components in the solution due to solubility and the
like.
[0047] FIG. 6 shows how the size of the compartments will change
upon selection of a different solvent. In this example, solvent
II--which again may be a single solvent, a binary mixture or a
multi-component mixture--is used. Here, the size of compartment B
becomes larger while the size of compartment A becomes smaller.
Thus, Solvent II produces a second phase behavior in the system.
This effect of the solvent on the size of the compartments is
sometimes called a "swing" and can be clearly seen when the two
phase diagrams are seen side by side.
[0048] As shown in the figures, when Solvent I is employed it
produces the certain phase diagram due to the interaction among the
components and Solvent I in the solution and their phase behavior
which is governed by a variety of physical properties of the
components such as solubility and the like. A different solvent,
Solvent II produces a different phase diagram again due to Solvent
II's interaction among the components in the system.
[0049] This behavior allows one to manipulate the separation
process to produce the desired compound or product from components
in solution where the components can form one or more adducts
according to the present invention. The effect of the solvent on
separation of the desired product(s) is now discussed in
detail.
[0050] In one embodiment, when the solvent is comprised of a
mixture of solvent components, the at least first and second
solvent components exhibit at least first and second phase
behaviors in the system that are diverse. Alternatively, the effect
of the first and second solvent components on the phase behavior of
the system may be closer, or similar, to each other.
[0051] When characterized in terms of binary solubility, in
particular the binary solubility of the compound of interest in the
solvent component, the first and second solvent components exhibit
solubilities that are preferably opposite; that is, one of the
solvent components exhibits a higher solubility for a given
component relative to the other solvent component which exhibits a
lower solubility for the component. Alternatively, the solubilities
of the given component in the first and second solvent components
may be closer to each other. However, to provide the greatest
flexibility in the operation of the process, it is preferable to
employ solvent components which provide the more diverse phase
behavior in the system.
[0052] Referring to FIGS. 5 and 6, manipulation of the phase
equilibrium using two or more solvents with different phase
behavior is shown according to two embodiments of the present
invention. In general, nature, size and shape of the adduct C and A
and B phase compartments are dependent upon the type of solvent
present in the product solution, as well as the phase equilibrium
behavior of the binary system consisting of components A and B
without the solvent. For example, for the case where adduct C is an
incongruently melting adduct, the adduct composition lies to the
right of the phase boundary between the adduct and pure component
B, as shown in FIG. 7. The terms size or shape of the compartment
is meant to mean the size of the compartment in the projection of
the poly-thermal phase diagram as shown in FIGS. 5-7, and not the
complete poly-thermal phase diagram. As illustrated, the two phase
compartments are complementary, that is when the A compartment
increases the adduct C and/or B compartment(s) decreases.
[0053] According to one preferred embodiment of the invention,
Solvent I and Solvent II are selected such that the boundary by
Solvent I from E.sub.1 to S and the boundary by Solvent II from
E.sub.2 to S are overlapping. In other words, the compartment of
component A when using solvent I, overlaps with the compartment of
component B when using solvent II. This overlapping is
.sub.[VK1]shown on the phase diagram as indicated by the shaded
area on FIG. 8. This overlap has a significant impact on the
ability to selectively control the separation of pure component A
and/or pure component B from the adduct of components A and B.
[0054] Referring to FIG. 9, when Solvent I is used, the feed F is
located in compartment A and the relevant boundary of compartment A
is the line E.sub.1PS (shown as a solid line). Hence, solid A is
recovered and the liquid composition is given by point P. In
contrast, if Solvent II is used, the feed F is located in
compartment B and the relevant boundary for compartment B is the
line E.sub.2QS (shown as a dashed line). Thus, solid B is recovered
and the liquid composition is given by point Q as shown in the
figure.
[0055] As stated above the phase behavior of the system results
from the mutual interaction of all the components present in the
system; however, when selecting the solvent, the binary solubility
data for the system components in various solvents may be used as a
starting point to provide some indication of the type of phase
behavior that may result for the complete system. The binary
solubility data alone is not sufficient to determine the phase
behavior of the complete system, however the binary solubility data
is a useful guideline for initial selection of the solvent
component. Thus, the solvent is characterized most preferably in
terms of its impact on the phase behavior of the system.
Additionally or alternatively, the solvent may be characterized
less reliably in terms of the relative binary solubility of the
components in the solvent. When using solubility as the guideline
for solvent selection, routine experimentation is performed within
the teaching of the present invention to evaluate the suitability
of the selected solvent.
[0056] Given the teaching of the present invention, ternary phase
equilibrium diagrams for different solvent compositions and/or
concentration ratios may be created by those of ordinary skill in
the art without undue experimentation. For example, computer
simulation programs and thermodynamic databases may be used to
develop the approximate location of the boundary of the components
and adduct compartments for different types of solvents and/or
concentration ratios. As stated above the boundary between the
adduct compartment and the other compartments is the trajectory of
eutectic points. The eutectic point is the location where both
adduct and pure component solid coexist. The maximum recovery of
the pure component is the maximum amount of component solid that
can be recovered before adduct solid appears (or coexists with the
component solid).
[0057] More specifically, the establishment of a thermodynamic
model for the multi-component solid liquid equilibrium requires
both theoretical calculation and experimental data for the model
verification. Those of ordinary skill in the art can develop such
thermodynamic models using known principles and tools.
[0058] The physical properties of the each component in the
solution feed such as the heat of fusion, melting point, and heat
capacity are used to establish the thermodynamic model. The
equilibrium relationship between the components and adduct as a
function of temperature is needed. The binary interaction parameter
among the components in the solution is either estimated or
determined from experimental data. The theory for the activity
coefficient is well developed, and a computer software program
providing numerical methods for solving simultaneous non-linear
equations is typically used. Examples of suitable commercially
available software programs for thermodynamic model establishment
include PropertiesPlus from Aspen Technology Inc., HYPROP III from
Hyprotech, and ProPred from CAPEC at the Technical University of
Denmark. The thermodynamic model is for the calculation of the
concentration of the component when it is saturated and is a
function of temperature and concentration. Since the effect of
pressure on the saturation is not very significant in the pressure
range considered in typical separation units, the pressure effect
is not taken into account in this thermodynamic model; however, the
analysis may be extended to consider the pressure effect if
desired.
[0059] Of significant advantage, a process can be designed to
separate an adduct so as to recover one or both the pure components
A and B by use of a "swing" of the solvent effect on phase behavior
between Solvent I and Solvent II according to the present
invention.
[0060] The method of the present invention is carried out in a
separation system which employs crystallization. According to one
embodiment of the present invention, one exemplary embodiment of a
separation system 5 which recovers both the pure components A and
B, is illustrated in FIG. 10. The separation system 5 generally
includes two crystallizer units 10 and 12, liquid/solid separators
14 and 16, and at least one distillation column 18. The separation
system 5 is generally downstream of a reactor system (not shown)
and the solution conveyed to the separation system 5 is a product
stream from the reactor system. The corresponding steam
compositions are shown on the phase diagram is shown in FIG.
11.
[0061] In the exemplary embodiment, feed F at Stream 1 (an adduct
of A and B) is mixed with a recycle stream (Stream 6) to form a
solution stream (Stream 2). This mixing is illustrated in the
projected poly-thermal phase diagram, as shown by the straight in
FIG. 11. In this example Stream 6 contains components A, B and a
solvent whose composition is termed as Solvent I.
[0062] Since the feed F is located in compartment A, solid product
A is crystallized in crystallization unit 10 and then recovered
from a solid/liquid separation device 14 as shown in the process
block diagram of FIG. 10. The liquid from the solid/liquid
separation device is Stream 3 and its composition is expressed on
the projection of the poly-thermal phase diagram.
[0063] Stream 3 is mixed with the overhead of the distillation
column 18 to form Stream 4. Stream 4 contains components A, B, and
a solvent whose composition is termed Solvent II. Stream 4 is
located in compartment B as shown in FIG. 11. Thus, pure solid B is
crystallized in the crystallizer unit 12 and then is recovered from
the solid/liquid separation device 16, as shown in the process
block diagram of FIG. 10. It should be noted that Stream 3 is under
the Solvent I environment. When mixed with the overhead of the
distillation column 18, the solvent composition changes so as to
give Stream 4 under Solvent environment II. Correspondingly, the
phase boundary shifts from that indicated by the solid line to the
one indicated by the dashed line in FIG. 11.
[0064] Conversely, when the overhead from the distillation column
is separated from Stream 5 which is under the Solvent II
environment, the resulting stream (Stream 6) is under the Solvent I
environment. Correspondingly, the applicable phase boundary changes
from the dashed line to the solid line in going from Stream 5 to
Stream 6.
[0065] As described above the present invention provides for
selectively controlling the phase equilibrium regions or
compartments during crystallization by adjusting the composition of
the solvent present in the solution to form a feed solution to a
crystallizer having a certain feed composition such that either
adduct or substantially pure compounds of interest are produced. It
is important to note that although the feed solution to a
crystallizer is comprised of a multitude of components, including
unreacted reactants and byproducts of the reaction, for process
synthesis purposes it is sufficient to consider only the principal
components. As such, the present invention provides a powerful tool
allowing one to selectively operate the system to generate the
desired phase equilibrium region and thus crystallize the desired
compound.
[0066] According to another embodiment of the present invention, an
example of another separation system 9, which recovers the adduct
in an intermediate step, and the single pure component desired from
the separation process in another crystallization step, is shown in
FIG. 12. Separation system 9 usually includes two crystallizer
units 8 and 10, a dissolver unit 13, liquid/solid separator units
15 and 17, and at least one distillation column 19. The separation
system is generally downstream of a reactor system (not shown) and
the solution conveyed to the separation system is a product stream
from the reactor system. A part of the mother liquor from the
separation system may be recycled to the reactor in order to
increase the yield of the desired product. The stream compositions
for the separation process corresponding to FIG. 12 are shown on
the projected polythermal phase diagram in FIG. 13.
[0067] In this exemplary embodiment, components A and B exhibit an
incongruently melting adduct, and component B is the final desired
component from the separation. A phase diagram of this system in
presence of a Solvent was shown earlier in FIG. 7. The incongruent
melting point (E.sub.2) is the point where the adduct melts, and
the liquid composition and the solid composition are not the same.
In the absence of solvent, when the adduct C melts, the liquid
composition is at point E.sub.2 while some solid B is formed as
well. This is why the location of the adduct C is between point
E.sub.2 and pure B. In presence of a solvent, the boundary between
the pure B and the pure adduct C compartment is given be the
trajectory of the incongruent melting points at different solvent
contents. This is shown by the line from the E.sub.2 to the Solvent
vertex in FIG. 7.
[0068] Referring specifically to FIG. 12, in this exemplary
embodiment, feed F at Stream 1 is mixed with a recycle stream
(Stream 6) to form a solution stream (Stream 2). This mixing is
illustrated in the projected poly-thermal phase diagram, as shown
by the straight in FIG. 13. In this example Stream 6 contains
components A, B and Solvent I.
[0069] Since Stream 2 is located in the adduct C compartment, solid
adduct is crystallized in crystallization unit 8 and then recovered
from a solid/liquid separation device 15 as shown in the process
block diagram of FIG. 12. The liquid from the solid/liquid
separation device is Stream 4 and its composition is expressed on
the projection of the poly-thermal phase diagram.
[0070] Stream 3 which is solid adduct C is dissolved in dissolver
13 using the overhead of the distillation column 19 to form Stream
5. Stream 5, containing components A, B, and Solvent I, is located
in compartment B as shown in FIG. 13. Thus, pure solid B is
crystallized in the crystallizer unit 10 and then is recovered from
the solid/liquid separation device 17, as shown in the process
block diagram of FIG. 12. The bottoms from the distillation column
19 is rich in the undesired component A and is recycled to the
reactor where part of it gets converted to the desired component
B.
[0071] While two examples of a separation system are shown herein
for illustration purposes, the method of the present invention may
be carried out in other types of crystallization separation
systems.
[0072] To selectively control the location of the composition in
the solution at the feed to the crystallizer, the composition of
the various components in the solution may be adjusted to certain
amounts (typically weight or mol percent) to place the feed
composition in a crystallizer at a location selectively within a
desired region of the phase diagram. The composition of the
solution at the feed to a crystallizer may be adjusted in a variety
of ways. Any one of, or combination of, the components A and B in
solution, the solvent, or mixture of solvent components may be
added to, or removed, from the solution prior to the crystallizer
to adjust the feed composition to the desired phase compartment.
Alternatively, the composition of reactants fed to a reactor and
the reaction conditions in terms of temperature, conversion, and
the like may be adjusted to provide the desired composition in the
solution from the reactor. For example, the flow rate of reactants
to the reactor may be varied to provide a certain weight or mol
percent of component A or B in the product solution.
[0073] While certain embodiments have been described herein, it
should be understood to those of ordinary skill in the art that the
method of the present invention is applicable to any solid and
liquid system with an adduct, exhibiting either a congruent melting
point or an incongruent melting point. Further, there may be
present one, two or more eutectic points, and there can be multiple
adducts formed.
Experimental
[0074] Simulated experiments are provided below to further
illustrate the system and method of the present invention. These
simulated experiments are provided for illustration purposes only
and are not intended to limit the scope of the invention in any
way.
EXAMPLE 1
[0075] This example refers to one of the processes of recovering
both pure components A and B from their adduct C, by use of a
"swing" of the solvent effect on phase behavior between Solvent I
and Solvent II according to the present invention. This embodiment
of the invention was described earlier and illustrated in FIGS. 10
and 11.
[0076] Solvent I and Solvent II are selected such that the boundary
by Solvent I from E.sub.1 to S and the boundary by Solvent II from
E.sub.2 to S are overlapping. In other words, the compartment of
component A when using solvent I, overlaps with the compartment of
component B when using solvent II.
[0077] In this particular example, the Solvents I and II are both
comprised of a mixture of two solvent components, S.sub.1 and
S.sub.2. S.sub.1 and S.sub.2 are selected such that the compartment
of component A when using S.sub.1, overlaps with the compartment of
component B when using S.sub.2.
[0078] For a given solvent combination (S.sub.1 and S.sub.2), the
maximum overlap possible is fixed. The actual overlap produced in
the process (less than the maximum overlap) is decided by the
actual compositions of solvent (mixture) I and solvent (mixture) II
in the crystallizers 10 and 12, respectively.
[0079] Referring to FIG. 10, the amount and composition of solvent
removed by the solvent recovery unit 18 will determine the extent
of "swing" between Solvent I environment and Solvent II
environment. For a lower solvent flow or a smaller composition
change, the swing, and hence the overlap will be less, while for a
larger solvent flow or a larger composition change, the overlap
will be more.
[0080] This example shows how the swing in the phase boundary
changes as the solvent composition in the crystallizers 10 and 12
changes. The phase boundaries resulting from using different
Solvent compositions in the crystallizer units 10 and 12 are shown
on the phase diagram in the FIG. 14. The dark lines refer to the
boundary between the component B compartment and the Adduct C
compartment, whereas the light lines refer to the boundary between
the component A compartment and the Adduct compartment. Three cases
are considered.
[0081] Case 1:
[0082] When the Solvent I and II environments refer to pure S.sub.1
and pure S.sub.2, the resulting phase boundaries are dotted lines
as shown in FIG. 14, with a corresponding large overlap.
[0083] Case 2:
[0084] The solvent composition in the crystallizer unit 10 (Solvent
I environment) is 80% S.sub.1 and 20% S.sub.2, while the solvent
composition in the crystallizer unit 12 (Solvent II environment) is
20% S.sub.1 and 80% S.sub.2. The phase boundaries are given by
dashed lines, with a lesser overlap.
[0085] Case 3:
[0086] The solvent composition in the crystallizer unit 10 (Solvent
I environment) is 60% S.sub.1 and 40% S.sub.2, while the solvent
composition in the crystallizer unit 12 (Solvent II environment) is
40% S.sub.1 and 60% S.sub.2. The phase boundaries are given by
solid lines, resulting in no overlap between Compartment A and
Compartment B. This will make the process infeasible.
EXAMPLE 2
[0087] This example examines in more detail, the system considered
in Example 1. Although the overlap in the phase boundaries leads to
a feasible process as discussed above, the extent of overlap has a
large effect on the efficiency of the process. A smaller overlap
leads to lower per pass recoveries of pure A and B in the
crystallizers. This leads to a larger flow of the recycle mother
liquor stream (Stream 6).
[0088] This example considers the effect of the solvent flowrate on
the extent of overlap, the recoveries in the crystallizer, and the
recycle flow, for an imaginary chemical system. The feed to the
process is considered to be the equimolar adduct C of A and B, with
a flow rate of 100 kmol/h. This is because starting from the adduct
usually leads to the most difficulty in separation. Similar process
configurations can be devised to separate a feed with a different
composition of A and B than the adduct composition.
[0089] Case 1 considers a small swing in the solvent compositions
of the two crystallizer units, 10 and 12. This is achieved by
having a low solvent recycle flow (such as 60 kmol/h) from the top
of the distillation column 18. The small swing in the solvent
environments results in a small overlap between the component A and
component B compartments, as shown in FIG. 15. Due to the small
overlap, the region of feasible process operation is smaller, and
hence a lower per pass recovery is achieved in the crystallizers 10
and 12. Since the separation duty on the process remains the same,
this leads to a large recycle flow (Stream 6). Case 2 and 3 show
how a larger overlap can lead to a lower recycle and hence a more
efficient process. FIGS. 16 and 17 show the corresponding stream
compositions and the phase diagrams for Case 2 and 3. Table 1
below, summarizes the per pass recoveries in the crystallizers and
the recycle flows for all three cases of the simulated
experiments.
1 TABLE 1 Mother Liquor Per pass Solvent Recycle recovery (%)
Recycle (Stream 6) Case A B (kmol/h) (kmol/h) 1: "Small Overlap"
24.4 53.6 60 360 2: "Medium Overlap" 39.4 72.2 100 160 3: "Large
Overlap" 46.2 79.1 140 110
EXAMPLE 3
[0090] This example examines a system where the components A and B
exhibit an incongruently melting adduct, and component B is the
final desired component from the reaction--separation. This
embodiment of the invention was described earlier and illustrated
in FIGS. 12 and 13. One exemplary embodiment of the process for
separating the desired component B from the mixture of A, B and
solvent is illustrated in FIG. 12. The reactor converts a reactor
feed rich in undesired component A but with a low concentration of
desired component B, into a stream with a higher concentration of
component B. This is the feed to the separation system (Stream 1).
The separation consists of first recovering the incongruently
melting adduct C in crystallizer 8. This is then dissolved in the
dissolver unit 13 using a suitable solvent so as to place the
composition of the resulting stream (Stream 5) in the component B
compartment. Pure component B is then recovered in crystallizer
unit 10.
[0091] The choice of Solvent used has a great impact on the
location of the phase boundaries shown in FIG. 13. This in turn
greatly affects the efficiency for the separation of the adduct C
and the pure component B in the process described above.
[0092] Although a single solvent is sufficient to give a feasible
separation process, this example illustrates how the efficiency of
separation can be enhanced by using a "swing" in the solvent
composition between Solvent I and Solvent II in the two
crystallizer units 8 and 10, so as to achieve phase boundaries
which are advantageous for the particular separation being carried
out in each crystallizer.
[0093] For the above process, the process streams are identified on
the projection of the polythermal phase diagram in FIGS. 18 and 19,
for two different solvent environments, I and II. For solvent I,
the phase boundaries curve in a fashion so as to give a large
compartment for B, while the compartment for the adduct C is small.
On the other hand, for Solvent II, the phase boundaries are such
that while the crystallization compartment for the Adduct C is
large, that for component B is small. This leads to higher per pass
recovery for component B for the case of Solvent I, as compared to
Solvent II, and higher per pass recoveries for the adduct C for the
case of Solvent II as compared to Solvent I.
[0094] In this situation, we may operate the process advantageously
using a solvent swing, such that the crystallizer for component B
is under the Solvent I environment, while the adduct C crystallizer
is under the solvent II compartment. The process streams for such
an operation are identified on the projection of the polythermal
phase diagram in FIG. 20. By thus "swinging" the solvent
composition from one solvent to the other, better per-pass recovery
for both component B and the adduct C are obtained than were
possible using the individual solvents alone. Simulated examples of
this effect are shown in Table 2 below.
2 TABLE 2 Per pass recovery of Per pass recovery of B Case Adduct,
C (%) (%) 1: Solvent I 52.7 85.0 2: Solvent II 65.8 22.9 3: Solvent
I/II 63.5 84.2
[0095] The foregoing description of specific embodiments and
examples of the invention have been presented for the purpose of
illustration and description, and although the invention has been
illustrated by certain of the preceding examples, it is not to be
construed as being limited thereby. They are not intended to be
exhaustive or to limit the invention to the precise forms
disclosed, and obviously many modifications, embodiments, and
variations are possible in light of the above teaching. It is
intended that the scope of the invention encompass the generic area
as herein disclosed, and by the claims appended hereto and their
equivalents.
* * * * *