U.S. patent application number 17/149833 was filed with the patent office on 2021-05-06 for process for preparing polymers.
This patent application is currently assigned to Ascend Performance Materials Operations LLC. The applicant listed for this patent is Ascend Performance Materials Operations LLC. Invention is credited to Shahram AKBARI, Chris SCHWIER, James A. SUTTON, Cihan UZUNPINAR, John M. ZABCIK.
Application Number | 20210130547 17/149833 |
Document ID | / |
Family ID | 1000005341136 |
Filed Date | 2021-05-06 |
![](/patent/app/20210130547/US20210130547A1-20210506\US20210130547A1-2021050)
United States Patent
Application |
20210130547 |
Kind Code |
A1 |
SUTTON; James A. ; et
al. |
May 6, 2021 |
PROCESS FOR PREPARING POLYMERS
Abstract
The present disclosure relates to a process for preparing
polymers using a plug flow reactor. The process includes providing
an aqueous monomer solution comprising amide monomers; evaporating
the aqueous monomer solution to form a concentrated monomer
solution; and polymerizing the concentrated monomer solution in a
plug flow reactor comprising a shell side and a tube side to form a
first process fluid comprising polymers. The concentrated monomer
solution flows on the shell side from the inlet to the outlet.
Inventors: |
SUTTON; James A.; (Houston,
TX) ; ZABCIK; John M.; (Houston, TX) ;
SCHWIER; Chris; (Houston, TX) ; UZUNPINAR; Cihan;
(Houston, TX) ; AKBARI; Shahram; (Houston,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ascend Performance Materials Operations LLC |
Houston |
TX |
US |
|
|
Assignee: |
Ascend Performance Materials
Operations LLC
Houston
TX
|
Family ID: |
1000005341136 |
Appl. No.: |
17/149833 |
Filed: |
January 15, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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16283001 |
Feb 22, 2019 |
10927217 |
|
|
17149833 |
|
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62634546 |
Feb 23, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 5/0012 20130101;
B01J 19/1818 20130101; B01J 2219/00081 20130101; C08G 69/30
20130101; B01J 2219/182 20130101; B01J 19/006 20130101; B01J 19/24
20130101; B01J 2219/2419 20130101; B01J 2219/00162 20130101; C08G
69/28 20130101; B01J 2219/0004 20130101; B01J 2219/00768
20130101 |
International
Class: |
C08G 69/30 20060101
C08G069/30; B01J 19/18 20060101 B01J019/18; B01D 5/00 20060101
B01D005/00; B01J 19/00 20060101 B01J019/00; C08G 69/28 20060101
C08G069/28; B01J 19/24 20060101 B01J019/24 |
Claims
1. A process for preparing polyamides, the process comprising:
providing an aqueous monomer solution comprising amide monomers;
evaporating the aqueous monomer solution to form a concentrated
monomer solution; and polymerizing the concentrated monomer
solution in a plug flow reactor comprising a shell side and a tube
side to form a first process fluid comprising polyamides, wherein
the shell side comprises an inlet and an outlet, wherein the
concentrated monomer solution flows on the shell side from the
inlet to the outlet.
2. The process of claim 1, wherein the tube side comprises a
plurality of U-tubes each including an inlet and an outlet for
conveying a heating fluid therethrough, and wherein the tube side
has a heat transfer area, and wherein the heating fluid has a
specific enthalpy, H value at atmospheric pressure, less than 2,900
kJ/kg.
3. The process of claim 2, wherein a ratio of the heat transfer
area (ft.sup.2) to a total volume (ft.sup.3) of the concentrated
monomer solution ranges from 3:1 to 30:1.
4. The process of claim 2, wherein a ratio of the heat transfer
area (ft.sup.2) to a total volume (ft.sup.3) of heat transfer fluid
ranges from 5:1 to 200:1.
5. The process of claim 2, wherein a skin temperature of the plug
flow reactor is less than 290.degree. C.
6. The process of claim 1, wherein the process has a heat flux rate
less than 11400 BTU/hr-ft.sup.2
7. The process of claim 1, wherein a residence time distribution
varies by +/-8%, based on an average residence time.
8. The process of claim 1, wherein conversion of amide monomer to
polyamides is at least 85%.
9. The process of claim 1, further comprising: separating water
from the concentrated monomer solution to form a water vapor during
polymerization; and supplying the water vapor to a disengagement
region of the plug flow reactor.
10. The process of claim 9 wherein the disengagement region has a
height of at least 0.05 m.
11. The process of claim 10, wherein the vapor stream comprises
less than 15.0.times.10.sup.-7 wt % of entrained liquid.
12. A process for retrofitting a polycondensation process including
an existing evaporator for concentrating a monomer solution and an
existing reactor for forming polyamides, the process comprising:
polymerizing the concentrated monomer solution in a plug flow
reactor comprising a shell side and a tube side to form a first
process fluid, wherein the shell side has an inlet and an outlet;
feeding the first process fluid to the existing reactor; and
polymerizing the first process fluid to form a second process
fluid, wherein the monomer solution flows on a shell side from the
inlet to the outlet.
13. The process of claim 12, wherein the plug flow reactor and the
existing reactor are arranged in series.
14. The process of claim 12, wherein the tube side comprises a
plurality of U-tubes each comprising an inlet and an outlet for
conveying a heating fluid therethrough, and wherein the tube side
has a heat transfer area, and wherein the heating fluid has a
specific enthalpy, H value at atmospheric pressure, less than 2,900
kJ/kg.
15. The process of claim 12, wherein a ratio of the heat transfer
area to a total volume of the concentrated monomer solution is in a
range from 3:1 to 30:1.
16. The process of claim 12, wherein a ratio of the heat transfer
area to a total volume of heat transfer fluid is in a range from
5:1 to 200:1.
17. A system for preparing polymers, comprising: a vessel including
an aqueous monomer solution; an evaporator for concentrating the
aqueous monomer solution to form a concentrated monomer solution; a
plug flow reactor comprising a shell side and a tube side for
polymerizing the concentrated monomer solution to form polyamides,
wherein the shell side comprises an inlet and an outlet, and
wherein the concentrated monomer solution flows on a shell side
from the inlet to the outlet.
18. The system of claim 17, wherein the tube side comprises a
plurality of U-tubes comprising an inlet and an outlet for
conveying a heating fluid therethrough, and wherein the tube side
has a heat transfer area.
19. The system of claim 17, further comprising a second reactor
downstream from the plug flow reactor, wherein the plug flow
reactor and second reactor are arranged in series.
20. A process for preparing polyamides in a plug flow reactor, the
process comprising: selecting a desired first process fluid
molecular weight in a range between 700 g/mol and 150,000 g/mol;
providing an aqueous monomer solution comprising amide monomers;
evaporating the aqueous monomer solution to form a concentrated
monomer solution; polymerizing the concentrated monomer solution in
a plug flow reactor comprising a shell side and a tube side to form
a first process fluid comprising polyamides, controlling a heat
flux rate of the process to be less than 11400 BTU/hr-ft.sup.2; and
maintaining a residence time of a concentrated monomer solution in
the plug flow reactor from 2 minutes to 100 minutes; wherein the
residence time distribution varies by +/-4%; or wherein the first
process fluid molecular weight corresponds to the desired first
process fluid molecular weight.
Description
FIELD
[0001] The present disclosure relates to a process of making
polymers, e.g., polyamides. More specifically, the present
disclosure relates to a process that utilizes a plug flow reactor
configuration that beneficially enables operation at lower
temperatures and prevents gelling, foaming, and impurities in the
polymer product. The present disclosure further relates to a
process for retrofitting an existing polymerization process using
the aforementioned configuration.
BACKGROUND
[0002] Polyamides are conventionally prepared by the condensation
polymerization of a diacid, such as adipic acid, and a diamine,
such as hexamethylene diamine, or by the polymerization of lactams
such as .epsilon.-caprolactam. Conventional processes for preparing
polyamides, e.g., nylon 6,6, utilize well-known components and
configurations usually including a vessel containing a process
fluid, e.g., a salt solution of diacid and diamine, a conventional
polymerization reactor, and further downstream processing, to form
high molecular weight polyamides.
[0003] Using these conventional configurations, these
polymerization processes are generally able to achieve a good
conversion of polyamides. In an effort to increase efficiency and
decrease energy consumption during polycondensation, heat
exchangers and other reactor configurations have been added and/or
modified to improve the efficiency of the process. Unfortunately,
these processes still require large volumes of heat transfer fluid,
which causes a higher temperature change, e.g., heat flux, during
polymerization. In addition, due to the high temperature change,
the melted polymer further contributes to water bubble formation
and steam disengagement, which detrimentally leads to excessive
foaming. The conventional configurations are also known to result
in undesired polymer branching, e.g., gelling.
[0004] Many conventional polymerization processes utilize a
circulating shell and tube heat exchanger (with a process fluid on
the tube side) in combination with a vertical reactor for carrying
out the polycondensation reaction. In the heat exchanger, the
process fluid that is heated is typically on the tube side, and
little or no polymerization takes place. After the process fluid
passes through the tubes, the heated process fluid is fed to the
inlet of the vertical reactor where most polymerization occurs.
Typically, the temperature of the inlet process fluid fed is too
low to initiate polymerization. Thus, a substantial amount of heat
must be added, e.g., via a heat transfer fluid, to initiate the
polymerization reaction transfer. Recent efforts have been made to
reduce the amount of temperature change in the polymerization
reactor, however, a large volume of heating fluid is still
necessary to increase the temperature of the process fluid to the
necessary temperature. This large volume of heating fluid
contributes to the drawbacks mentioned above.
[0005] As one example of a conventional process, International
Application No. WO/2017120112A1 discloses a process for making a
polyetheramine containing polyamide without excessive foaming in
successive batches by providing a controlled heat input rate step
for those batch runs that incorporate polyetheramine containing
polyamide heel from previous runs.
[0006] In addition, US Publication No. 2016/0130397 discloses a
process for continuously preparing polyamide oligomers. This
process comprises continuous conveying of an aqueous solution of
polyamide-forming monomers from a reservoir vessel into an
oligomerization reactor, heating of the aqueous solution beyond a
dissolution or storage temperature, and continuous discharge of the
polyamide oligomers from the oligomerization reactor. The residence
time of the monomer solution in the oligomerization reactor is
limited and the pressure or the partial vapor pressure of the water
is adjusted such that a conversion of monomers to polyamide
oligomers does not exceed a maximum value and/or the polyamide
oligomers formed do not phase-separate or spontaneously crystallize
in solid form. A polyamide oligomer preparable by this process can
be provided continuously in a mixture with water in a process for
preparing a semicrystalline or amorphous, thermoplastically
processable polyamide and then postcondensed to give a polyamide.
This polyamide can be used for production of moldings by means of
injection molding, multicomponent injection molding, injection
molding/welding, extrusion, coextrusion, blow molding or
thermoforming.
[0007] Also, U.S. Pat. No. 6,620,969 discloses a shell-and-tube
heat exchanger for handling an easily polymerizable substance,
comprising a shell having, near the opposite terminals thereof, two
tube sheets respectively furnished with an inlet and an outlet for
shell side fluid, channels disposed one each at the opposite
terminals of said shell, and a multiplicity of heat transfer tubes
having peripheries of opposite terminal parts of said heat transfer
tubes fixed between said tube sheets, adapted to pass said easily
polymerizable substance as a process fluid through said tubes and
effect exchange of heat thereon.
[0008] Although some references may teach the use of a reactor
and/or configurations that attempt to reduce foaming or the change
in temperature, the need still exists for improved reaction
configurations that achieve high conversions and reduce both
foaming and undesired polymer branching, while having high energy
efficiencies.
SUMMARY
[0009] In one embodiment, the disclosure relates to a process for
preparing polyamides, the process comprising: providing an aqueous
monomer solution comprising amide monomers; evaporating the aqueous
monomer solution to form a concentrated monomer solution; and
polymerizing the concentrated monomer solution in a (horizontal)
plug flow reactor comprising a shell side and a tube side to form a
first process fluid comprising polyamides. The shell side comprises
an inlet and an outlet. The concentrated monomer solution flows on
the shell side from the inlet to the outlet and conversion of amide
monomer to polyamides may be at least 85%. The tube side may
comprise a plurality of U-tubes each including an inlet and an
outlet for conveying a heating fluid therethrough, and wherein the
tube side has a heat transfer area, and wherein the heating fluid
has a specific enthalpy, H value at atmospheric pressure, less than
2,900 kJ/kg. A ratio of the heat transfer area (ft.sup.2) to a
total volume (ft.sup.3) of the concentrated monomer solution may
range from 1:1 to 30:1, e.g., from 3:1 to 30:1 and/or a ratio of
the heat transfer area (ft.sup.2) to a total volume (ft.sup.3) of
heat transfer fluid may range from 1:1 to 200:1, e.g., from 5:1 to
200:1 and/or a heat flux rate may be less than 11400
BTU/hr-ft.sup.2. The skin temperature of the plug flow reactor may
be less than 290.degree. C. A temperature change of the heat
transfer fluid from the inlet to the outlet may range from
0.degree. C. to 50.degree. C. A residence time distribution may by
+/-8%, based on an average residence time. The process may further
comprise the steps of separating water from the concentrated
monomer solution to form a water vapor during polymerization;
supplying the water vapor to a disengagement region of the plug
flow reactor, and/or flashing the first process fluid after
polymerization, and the disengagement region may have a height of
at least 0.05 m. In some cases, the skin temperature of the plug
flow reactor is less than 290.degree. C., the ratio of the heat
transfer area to the total volume of concentrated monomer solution
ranges from 3:1 to 20:1, and conversion of amide monomer to
polyamides is greater than 85%. In some cases, the ratio of the
heat transfer area to the volume of heat transfer fluid is greater
than 80:1, a residence time of the concentrated monomer solution
ranges from 50 minutes to 60 minutes, and conversion of amide
monomer to polyamides is greater than 85%. In some cases the
residence time of the concentrated monomer solution in the plug
flow reactor ranges from 2 minutes to 100 minutes, the residence
time distribution varies by +/-4%, based on an average residence
time, and conversion of amide monomer to polyamides is greater than
90%. In some cases, a ratio of the heat transfer area to the volume
of heating fluid ranges from 80:1 to 115:1, and the residence time
distribution varies by +/-2%, based on an average residence time,
and the skin temperature of the reactor is less than 290.degree. C.
In some cases, the vapor stream comprises less than
15.0.times.10.sup.-7 wt % of entrained liquid, e.g., less than
3.0.times.10.sup.-7 wt %. The aqueous monomer solution may comprise
diacid and diamine, and a molar ratio of the diacid to the diamine
may be at least 1:1, a residence time of the concentrated monomer
solution may be from 2 min to 100 min, and a conversion of amide
monomer to polyamides may be greater than 90%. The plug flow
reactor may be operated at a temperature from 200.degree. C. to
300.degree. C. and/or a pressure from 13.5 bar to 18 bar and
conversion of amide monomer to polyamides may be greater than
85%.
[0010] The disclosure also relates to a process for retrofitting a
polycondensation process including an existing evaporator for
concentrating a monomer solution and an existing reactor for
forming polyamides, the process comprising: polymerizing the
concentrated monomer solution in a plug flow reactor comprising a
shell side and a tube side to form a first process fluid, wherein
the shell side has an inlet and an outlet; feeding the first
process fluid to the existing reactor; and polymerizing the first
process fluid to form a second process fluid, wherein the monomer
solution flows on a shell side from the inlet to the outlet. The
plug flow reactor and the existing reactor may be arranged in
series. The tube side may comprise a plurality of U-tubes each
comprising an inlet and an outlet for conveying a heating fluid
therethrough, and wherein the tube side has a heat transfer area,
and wherein the heating fluid has a specific enthalpy, H value at
atmospheric pressure, less than 2,900 kJ/kg. The ratio of the heat
transfer area to a total volume of the concentrated monomer
solution and the ratio of the heat transfer area to a total volume
of heat transfer fluid are as mentioned above. The process may
further comprise the steps of flashing the concentrated monomer
solution to form a flashed monomer solution; and feeding the
flashed monomer solution directly to the plug flow reactor. The
first process fluid may comprise 85 wt. % to 92 wt. % of low
molecular weight polyamides, based on the total weight of the first
process fluid and/or the second process fluid may comprise 93 wt. %
to 97 wt. % of high molecular weight polyamides, based on the total
weight of the second process fluid.
[0011] The disclosure also relates to a system for preparing
polymers, comprising: a vessel including an aqueous monomer
solution; an evaporator for concentrating the aqueous monomer
solution to form a concentrated monomer solution; a plug flow
reactor comprising a shell side and a tube side for polymerizing
the concentrated monomer solution to form polyamides, wherein the
shell side comprises an inlet and an outlet, and wherein the
concentrated monomer solution flows on a shell side from the inlet
to the outlet. The tube side may comprise a plurality of U-tubes
comprising an inlet and an outlet for conveying a heating fluid
therethrough, and wherein the tube side has a heat transfer area.
The system may comprise a second reactor downstream from the plug
flow reactor and/or a preheater for heating the concentrated
monomer solution to a temperature in a range from 180.degree. C. to
230.degree. C. before feeding the concentrated monomer solution to
the plug flow reactor, and/or a flasher for flashing the
concentrated monomer solution, and the plug flow reactor and second
reactor may be arranged in series.
[0012] The disclosure also relates to a process for preparing
polyamides in a plug flow reactor, the process comprising:
selecting a desired first process fluid molecular weight in a range
between 700 g/mol and 150,000 g/mol; providing an aqueous monomer
solution comprising amide monomers; evaporating the aqueous monomer
solution to form a concentrated monomer solution; polymerizing the
concentrated monomer solution in a plug flow reactor comprising a
shell side and a tube side to form a first process fluid comprising
polyamides, controlling a heat flux rate of the process to be less
than 11400 BTU/hr-ft.sup.2; and maintaining a residence time of a
concentrated monomer solution in the plug flow reactor from 2
minutes to 100 minutes; wherein the residence time distribution
varies by +/-4%; or wherein the first process fluid molecular
weight corresponds to the desired first process fluid molecular
weight.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic of a polymerization process with a
plug flow reactor according to one embodiment of the present
disclosure.
[0014] FIG. 2 shows a tube layout of a plug flow reactor according
to one embodiment of the present disclosure.
[0015] FIG. 3 is a schematic of a process for retrofitting an
existing polymerization process with the plug flow reactor
according to one embodiment of the present disclosure
DETAILED DESCRIPTION
Introduction
[0016] Conventional processes for producing polymers, e.g.,
polyamides, utilize configurations including a reservoir vessel
that holds a process fluid, a conventional polymerization reactor,
and further downstream processing. The process fluid is directly
fed to the polymerization reactor, where polymers, e.g.,
polyamides, are formed. Many of these processes, relate to batch
operation, where foaming is different because batch processes have
different drivers that cause foaming than in continuous process,
thus are more sensitive to foaming. In a batch process, the rising
polymer melt viscosity complicates water bubble formation,
migration to the melt surface and steam disengagement from the melt
surface which also contributes to excessive foaming. For example,
WO/2017120112A1 focuses exclusively on problems related to foaming
in a batch process for polyamides incorporating polyetheramine. In
a batch process, e.g., for making Nylon 6,6, the pressure letdown
will have a higher tendency to foam than in the continuous process.
Other conventional processes focus on other problems, not heat
flux, foaming, or gelling. For example, U.S. Pat. No. 6,620,969
focuses on the problem of polymer fouling in a heat exchanger.
[0017] In a conventional polymerization process, a monomer solution
at the pre-processing stage, known as the salt stage, may be added
with other additives. The polymerization process then continues in
multiple processing stages where the pressure and temperature
conditions are carefully adjusted to remove the water, e.g., as
steam, to produce the polymer product. The initial stages in the
process contain the highest water content and consequently have a
high rate of steam release. As the process continues, the water
content is reduced to the residual level in the polymer product.
Typically, the temperature of the inlet process is too low for
polymerization. As such, a substantial amount of heat is required
for polymerization of the nylon salt by charging a large volume of
heat transfer fluid in the outer tube of the reactor. Stated
another way, the conventional processes detrimentally require large
amounts of heat transfer fluid and an accompanying high temperature
change, e.g., heat flux, during polymerization. This heat flux in
the reactor contributes to water bubble formation and steam
disengagement, which creates problems associated with molten
polymer foaming and undesired polymer branching (gelling). In
addition, although these processes may provide mediocre conversion
rates, there is certainly room for improvement. Also, due to the
use of a direct feed from the reservoir vessel to the reactor and
the large amounts of heat transfer fluid, the overall heat
efficiency of these processes leaves much to be desired.
Importantly, the relationship between the heat flux in the reactor
and its effects on the properties of the formed polymers, foaming,
gelling, and/or steam formation have not been explored or
documented in the art.
[0018] It has now been discovered that by evaporating an aqueous
monomer solution, prior to polymerization, to form a concentrated
monomer solution and (continuously) flowing the concentrated
monomer solution on the shell side of a plug flow, shell-and-tube
reactor surprisingly provides for a significant drop in the overall
heat flux. This unexpected decrease in heat flux advantageously
leads to improvements in foaming and/or polymer branching. Without
being bound by theory, it is believed that the evaporation of the
aqueous monomer solution (as opposed to a direct feed from a
reservoir vessel to the reactor) provides the concentrated monomer
solution at a temperature and composition that is particularly
suitable for polymerization, e.g., on the shell side of the
polymerization reactor. It is believed that the temperature and
composition of the concentrated monomer solution entering the
polymerization reactor lead to a significant reduction in heat flux
of the concentrated monomer solution and the heat transfer fluid,
which leads to a reduction in skin temperature and reductions in
the change of temperature of the heat transfer in the
polymerization reactor. In addition, by flowing the specific
concentrated monomer solution on the shell side, the ratio of tube
side heat transfer area to total volume of the concentrated monomer
solution is beneficially increased, which also contributes to
less/lower heat flux. When the aforementioned configuration is
utilized, not only is the heat flux (and the overall heat
efficiency) decreased, but the overall conversion is
synergistically improved as well.
Reaction Configuration
[0019] The present disclosure relates to processes, e.g.,
continuous processes, for preparing polymers utilizing an improved
evaporator/reactor configuration. The processes comprise the steps
of providing an aqueous monomer solution comprising amide monomers;
evaporating the aqueous monomer solution to form a concentrated
monomer solution; and polymerizing the concentrated monomer
solution, e.g., conducting a polycondensation reaction, for example
an amide polymerization reaction, to form a first process fluid
comprising polyamides. As noted above, the processes utilize the
evaporation step prior to the reaction step, and the reaction step
employs a specific reactor configuration. The reaction is conducted
in a plug flow reactor, preferably in a horizontal configuration
(although a vertical and an angled configuration are contemplated)
comprising a shell side and a tube side, and both the shell side
and the tube side comprise an inlet and an outlet, respectively.
The concentrated monomer solution is continuously fed and flows on
the shell side from the shell inlet to the shell outlet. The use of
the these steps and the overall configuration allow the plug flow
reactor to have a high heat transfer area, which advantageously
provides for, inter alia, improvements in heat flux, overall heat
efficiency, and conversion as well as lower levels of skin
temperatures, foaming, and branching.
[0020] In some embodiments, the heat flux rate of the process,
e.g., of the reaction configuration, is less than 11400
BTU/hr-ft.sup.2, e.g., less than 11000 BTU/hr-ft.sup.2, less than
10000 BTU/hr-ft.sup.2, less than 8000 BTU/hr-ft.sup.2, less than
6000 BTU/hr-ft.sup.2, less than 5000 BTU/hr-ft.sup.2, less than
4000 BTU/hr-ft.sup.2, less than 3000 BTU/hr-ft.sup.2, less than
2000 BTU/hr-ft.sup.2, or less than 1500 BTU/hr-ft.sup.2. In terms
of ranges, the heat flux rate of the process may range from 100
BTU/hr-ft.sup.2 to 11400 BTU/hr-ft.sup.2, e.g., from 100
BTU/hr-ft.sup.2 to 10000 BTU/hr-ft.sup.2, from 200 BTU/hr-ft.sup.2
to 8000 BTU/hr-ft.sup.2, from 200 BTU/hr-ft.sup.2 to 6000
BTU/hr-ft.sup.2, from 200 BTU/hr-ft.sup.2 to 5000 BTU/hr-ft.sup.2,
from 200 BTU/hr-ft.sup.2 to 4000 BTU/hr-ft.sup.2, from 300
BTU/hr-ft.sup.2 to 3000 BTU/hr-ft.sup.2, or from 500
BTU/hr-ft.sup.2 to 2500 BTU/hr-ft.sup.2.
[0021] In one embodiment, the tube side comprises a plurality of
heat transfer tubes, e.g., U-tubes, each including an inlet and an
outlet for conveying a heating fluid therethrough. The U-tubes may
be referred to as a tube bundle. In some embodiments, the
concentrated monomer solution flows on the shell side and a heat
transfer fluid flows on the tube side. The tube side, thus
configured, has a heat transfer area that is in contact with the
concentrated monomer solution on the shell side of the plug
reactor. The heat transfer area is the interface between the
plurality of U-tubes and the shell side. For example, the heat
transfer area may be the total surface area of the heat transfer
tubes.
[0022] In some cases, the improvements in heat flux may be
reflected in a high ratio of heat transfer area to the total volume
of the concentrated monomer solution. In one embodiment, the ratio
of heat transfer area to the total volume of the concentrated
monomer solution is greater than 1:1, e.g., greater than 3:1,
greater than 5:1, greater than 7:1, greater than 10:1, greater than
12:1, greater than 15:1, or greater than 20:1. In terms of ranges,
the ratio of the heat transfer area to the total volume of the
concentrated monomer solution may range from 1:1 to 30:1, e.g.,
from 1:1 to 30:1, from 5:1 to 25:1, from 3:1 to 20:1, from 5:1 to
20:1, from 3:1 to 25:1 from 10:1 to 20:1, from 12:1 to 18:1, or
from 14:1 to 17. In terms of upper limits, the ratio of heat
transfer area to the volume of concentrated monomer solution is
less than 30:1, e.g., less than 25:1, less than 20:1, less than
15:1, or less than 10:1.
[0023] In some embodiments the improvements in heat flux may also
be reflected in the high ratio of the heat transfer area to the
total volume of heat transfer fluid. In one embodiment, the ratio
of heat transfer area to the total volume of heat transfer fluid is
less than 200:1, e.g., less than 175:1, less than 150:1, less than
125:1, less than 120:1, less than 100:1, less than 80:1, or less
than 40:1. In terms of ranges, the ratio of heat transfer area to
the total volume of heat transfer fluid may range from 1:1 to
200:1, e.g., from 5:1 to 200:1, from 10:1 to 180:1, from 20:1 to
180:1, from 40:1 to 150:1, from 60:1 to 140:1, from 60:1 to 120:1,
from 80:1 to 125:1, from 80:1 to 115:1, from 90:1 to 120:1 or from
100:1 to 110:1. In terms of lower limits, the ratio of heat
transfer area to the total volume of heat transfer fluid is greater
than 5:1, e.g., greater than 40:1, greater than 60:1, greater than
80:1, greater than 90:1, greater than 120:1, or greater than
150:1.
[0024] In some cases, the process exemplifies improvements
(reductions) in nucleate boiling heat transfer coefficient. The
reduction in this heat transfer coefficient complements reductions
in skin temperature (see below). In some embodiments, the nucleate
boiling heat transfer coefficient is less than 85
BTU/hr-ft.sup.2-.degree. F., e.g., less than 75
BTU/hr-ft.sup.2-.degree. F., less than 65 BTU/hr-ft.sup.2-.degree.
F., less than 55 BTU/hr-ft.sup.2-.degree. F., less than 50
BTU/hr-ft.sup.2-.degree. F., less than 45 BTU/hr-ft.sup.2-.degree.
F., less than 40 BTU/hr-ft.sup.2-.degree. F., less than 35
BTU/hr-ft.sup.2-.degree. F., less than 30 BTU/hr-ft.sup.2-.degree.
F., or less than 25 BTU/hr-ft.sup.2-.degree. F. In terms of ranges,
the nucleate boiling heat transfer coefficient may range from 15
BTU/hr-ft.sup.2-.degree. F. to 85 BTU/hr-ft.sup.2-.degree. F.,
e.g., from 15 BTU/hr-ft.sup.2-.degree. F. to 65
BTU/hr-ft.sup.2-.degree. F., from 20 BTU/hr-ft.sup.2-.degree. F. to
65 BTU/hr-ft.sup.2-.degree. F., from 25 BTU/hr-ft.sup.2-.degree. F.
to 60 BTU/hr-ft.sup.2-.degree. F., from 25 BTU/hr-ft.sup.2-.degree.
F. to 50 BTU/hr-ft.sup.2-.degree. F., from 30
BTU/hr-ft.sup.2-.degree. F. to 50 BTU/hr-ft.sup.2-.degree. F., or
from 35 BTU/hr-ft.sup.2-.degree. F. to 45 BTU/hr-ft.sup.2-.degree.
F.
[0025] Advantageously, the employment of the aforementioned steps
and configuration (and optionally the aforementioned ratios) result
in a lower skin temperature. As used herein, the term "skin
temperature" refers to the temperature of the heat transfer surface
area, e.g., the interface between heat transfer tubes and a monomer
solution on the shell side. It is believed that this lower skin
temperature provides for (or at least contributes to) the benefits
of reducing foaming and preventing undesired polymer branching,
e.g., gelling, because of the lower change in temperature of the
concentrated monomer solution in the plug flow reactor. In one
embodiment, the skin temperature is less than 290.degree. C., e.g.,
less than 280.degree. C., less than 270.degree. C., less than
260.degree. C., or less than 250.degree. C. In terms of ranges, the
skin temperature may range from 240.degree. C. to 290.degree. C.,
e.g., from 250.degree. C. to 280.degree. C., from 260.degree. C. to
280.degree. C., from 270.degree. C. to 280.degree. C., or from
260.degree. C. to 270.degree. C. In terms of lower limits, the skin
temperature is greater than 240.degree. C., e.g., greater than
250.degree. C., greater than 260.degree. C., greater than
270.degree. C., or greater than 280.degree. C.
[0026] Further, due to the ratio and/or skin temperature
improvements, the heating fluid used in the process can be selected
from a wide variety of heat transfer fluids, e.g., steam, organic
condensing vapor, inorganic condensing vapor, or hot oil. In some
embodiments, the heating fluid has a specific enthalpy, H value at
atmospheric pressure, less than 2,900 kJ/kg, e.g., less than 2,700
kJ/kg, less than 2,600 kJ/kg, or less than 2,550 kJ/kg. In terms of
ranges, the heating fluid has an H value (at atmospheric pressure)
that may range from 2,500 kJ/kg to 2,900 kJ/kg, e.g., from 2,550
kJ/kg to 2,800 kJ/kg, from 2,600 kJ/kg to 2,700 kJ/kg, from 2,550
kJ/kg to 2,650 kJ/kg or from 2,550 kJ/kg to 2,600 kJ/kg. In terms
of lower limits, the heating fluid has an H value (at atmospheric
pressure) greater than 2,500 kJ/kg, e.g., greater than 2,550 kJ/kg,
greater than 2,600 kJ/kg, greater than 2,700 kJ/kg, or greater than
2,800 kJ/kg. In some embodiments, the heat transfer fluid is
saturated steam.
[0027] In some embodiments, the thermal conductivity of the heat
transfer fluid, in a temperature range from 25.degree. C. to
300.degree. C., is in a range from 10 mW/mK to 80 mW/mK, e.g., from
20 to 70 mW/mK, from 30 to 60 mW/mK or from 40 to 50 mW/mK. In
terms of upper limits, the thermal conductivity of the heat
transfer fluid is less than 80 mW/mK, e.g., less than 60 mW/mK,
less than 40 mW/mK, less than 30 mW/mK, or less than 20 mW/mK. In
terms of the lower limits, the thermal conductivity of the heat
transfer fluid is greater than 10 mW/mK, e.g., greater than 20
mW/mK, greater than 30 mW/mK, greater than 40 mW/mK, or greater
than 60 mW/mK. For example, the thermal conductivity of the heat
transfer fluid at 50.degree. C. is 20 mW/mK, at 100.degree. C. is
24.8 mW/mK, at 150.degree. C. is 30.8 mW/mK, at 200.degree. C. is
39.1 mW/mK, and at 300.degree. C. is 71.8 mW/mK.
[0028] In some aspects, the thermal conductivity of the heat
transfer fluid is in a range from 22 mW/mK to 106 mW/mK in a
temperature range from 250.degree. C. to 360.degree. C. In other
embodiments, the thermal conductivity of the heat transfer fluid is
in a range from 88 mW/mK to 100 mW/mK in a temperature range from
250.degree. C. to 360.degree. C.
[0029] The plug flow reactor may convey a liquid or gaseous heat
transfer fluid through the tubes, and the concentrated monomer
solution flows on the space around the tubes on the shell side. In
some embodiments, gaseous heat transfer fluids include, for
example, steam or diphyl vapor. In other embodiments, liquid heat
transfer fluids include, for example, a heat transfer oil. The heat
transfer fluid may be fed to the plug flow reactor at a temperature
in the range from 200.degree. C. to 400.degree. C., e.g., from
240.degree. C. to 360.degree. C., from 280.degree. C. to
320.degree. C., or from 200.degree. C. to 250.degree. C. In terms
of upper limits, the temperature of the heat transfer fluid fed
into the plug flow reactor is less than 400.degree. C., e.g., less
than 360.degree. C., less than 320.degree. C., less than
280.degree. C., or less than 240.degree. C. In terms of lower
limits, the temperature of the heat transfer fluid fed into the
plug flow reactor is greater than 200.degree. C., e.g., greater
than 240.degree. C., greater than 260.degree. C., greater than
280.degree. C., or greater than 320.degree. C.
[0030] The present reactor configuration also advantageously
results in a lower change in temperature of the heat transfer
fluid, e.g., steam. It is believed that this lower change in
temperature also contributes to the benefits of reducing foaming
and preventing undesired polymer branching, e.g., gelling. In one
embodiment, the change in temperature of the heat transfer fluid
from the inlet to the outlet of the reactor is less than
110.degree. C., e.g., less than 80.degree. C., less than 60.degree.
C., less than 40.degree. C., or less than 20.degree. C. In terms of
ranges, the change in temperature of the heat transfer fluid from
the inlet to the outlet of the reactor is from 0.degree. C. to
110.degree. C., e.g., from 10.degree. C. to 100.degree. C., from
20.degree. C. to 80.degree. C., from 40.degree. C. to 60.degree.
C., or from 10.degree. C. to 30.degree. C. In terms of lower
limits, the change in temperature of the heat transfer fluid from
the inlet to the outlet of the reactor is greater than 0.degree.
C., e.g., greater than 10.degree. C., greater than 20.degree. C.,
greater than 30.degree. C., or greater than 40.degree. C.
[0031] In particular, when steam is utilized as the heat transfer
fluid, a significantly lower change in temperature of the heat
transfer fluid in the plug flow reactor is achieved. In one
embodiment, the change in temperature of steam from the inlet to
the outlet of the reactor is less than 50.degree. C., e.g., less
than 40.degree. C., less than 30.degree. C., less than 20.degree.
C., or less than 10.degree. C. In terms of ranges, the change in
temperature of the steam is from 0.degree. C. to 50.degree. C.,
e.g., from 5.degree. C. to 40.degree. C., from 10.degree. C. to
30.degree. C., from 15.degree. C. to 25.degree. C., or from
20.degree. C. to 25.degree. C. In terms of lower limits, the change
in temperature of the heat transfer fluid is greater than 0.degree.
C., e.g., greater than 10.degree. C., greater than 20.degree. C.,
greater than 30.degree. C., or greater than 40.degree. C. The
inventors of the present application have found that using the
present reactor configuration utilizing the plug flow reactor with
steam as the heat transfer fluid beneficially reduces foaming and
prevents undesired polymer branching, e.g., gelling.
[0032] In conventional processes that employ lower ratios or higher
skin temperatures, higher H values heating fluids (which are more
expensive) must be employed, e.g., Therminol.RTM., which results in
a greater change in temperature of the heat transfer fluid and the
monomer solution. Thus, the disclosed ratios, skin temperatures,
and changes in temperature provide the benefit of wider heating
fluid options.
[0033] During polymerization in the plug flow reactor, water is
separated from, e.g., boiled off, the concentrated monomer solution
to form water vapor, e.g., a vent stream, in order to form the
first process fluid comprising polymers. This water vapor is
conveyed to a disengagement region of the plug flow reactor to
minimize liquid entrainment in the water vapor. It is believed
that, in addition to the aforementioned benefits, the
configurations may also provide for increased size, e.g., height
and/or volume, of the disengagement region, which advantageously
provides for improved entrainment-related properties For example,
greater disengagement region height, has been found to beneficially
contribute to reductions in foaming. The disengagement region is a
closed volume within the plug reactor employed to devolatilize the
vapor stream by separating the vapor from the liquid interface. The
disengagement region separates the vapor from the liquid interface
of the water vapor boiled off the first process fluid. In some
cases, the disengagement region is a portion of the plug flow
reactor that is not occupied by the tubes. For example, the
disengagement region is an open volume of the plug flow reactor
located above the plurality of tubes. Because of the greater size,
e.g., height of the disengagement region, the process sees the
advantage of reduced entrainment of liquid in the vapor stream
resulting in less foaming.
[0034] Foaming is the formation of gas bubbles within the aqueous
(liquid) monomer solution. In addition to the size/volume benefits
in the disengagement region, the disclosed processes have been
found to decrease foaming in the disengagement region regardless of
the entrainment and/or velocity of the water vapor. It is believed
that the lower heat flux and larger size of the disengagement area
in the reactor contributes to this reduction.
[0035] The plug flow reactor of the present disclosure provides an
improved disengagement function due to its beneficial properties
mentioned above. In conventional reactors, the liquid/gas interface
is adjusted by changing the reactor volume. However, controlling
the interface by controlling the reactor volume is a difficult way
to control the velocity of the fluids. For example, if a
conventional reactor is made tall and skinny, the level control
becomes difficult, vapor velocities increase with increased
entrainment, and reactor costs increase with the increased surface
area. On the other hand, if a conventional reactor is made short
and wide, for large scale plants, shipping the reactor becomes an
issue. As noted above, because of the substantially lower heat flux
in the present plug flow reactor and the larger height of the
disengagement region, the plug flow reactor provides for less
foaming. In some embodiments, anti-foaming additives may be further
added to the water vapor in the disengagement region.
[0036] In some embodiments, disengagement region of the plug flow
reactor configuration has a height that contributes to improvements
in the disengagement region. In some embodiments, the height of the
disengagement region is the distance from the top of the tubes to
the top of the shell. In one embodiment, the disengagement region
has a height greater than 0.05 m, e.g., greater than 0.1 m, greater
than 0.2 m, greater than 0.3 m or greater than 0.4 m. In terms of
ranges, the disengagement region has a height in the range from
0.05 m to 2 m, e.g., from 0.1 m to 2.0 m, from 0.3 m to 1.8 m, from
0.1 m to 1.8 m, from 0.5 m to 1.4 m, from 0.1 m to 1.5 m, 0.1 m to
1 m, from 0.1 m to 0.5 m, from 0.15 m to 1 m, from 0.15 m to 0.5 m,
from 0.2 m to 0.5 m, from 0.2 m to 0.4 m, form 0.6 m to 1.0 m, or
from 0.25 m to 0.35 m. In terms of upper limits, the disengagement
region has a height less than 2 m, e.g., less than 1.8 m, less than
1.5 m, less than 1 m, less than 0.5 m, less than 0.4 m, or less
than 0.35 m.
[0037] In some cases, the water vapor boiled off the first process
fluid (as a vent stream) has a horizontal vapor velocity of greater
than 0.01 m/s, e.g., greater than 0.03 m/s, greater than 0.04 m/s,
or greater than 0.05 m/s. In terms of ranges, the water vapor has a
horizontal velocity in the range from 0.01 m/s to 0.08 m/s, e.g.,
from 0.02 m/s to 0.07 m/s, from 0.03 m/s to 0.06 m/s, or from 0.04
m/s to 0.05 m/s. In terms of upper limits, the water vapor has a
horizontal velocity less than 0.08 m/s, e.g., less than 0.05 m/s,
less than 0.04 m/s, or less than 0.03 m/s.
[0038] In some cases, the water vapor boiled off the first process
fluid (as a vent stream) has a vertical vapor velocity of greater
than 0.002 m/s, e.g., greater than 0.006 m/s, greater than 0.01
m/s, or greater than 0.015 m/s. In terms of ranges, the water vapor
has a vertical velocity in the range from 0.002 m/s to 0.02 m/s,
e.g., from 0.006 m/s to 0.015 m/s, from 0.008 m/s to 0.012 m/s, or
from 0.01 m/s to 0.015 m/s. In terms of upper limits, the water
vapor has a vertical velocity less than 0.02 m/s, e.g., less than
0.015 m/s, less than 0.01 m/s, or less than 0.008 m/s.
[0039] In some embodiments, the water vapor comprises less than
3.times.10.sup.-7 wt % of liquid entrainment, e.g., less than
2.times.10.sup.-7 wt % of liquid, less than 1.5.times.10.sup.-7 wt
% of liquid or less than 1.times.10.sup.-7 wt % of liquid. The
liquid entrainment may be characterized as the ratio of the mass of
the liquid entrainment to the mass of the vapor stream (leaving the
reactor) as a whole. In terms of ranges, the water vapor comprises
liquid entrainment in the range from 1.times.10.sup.-7 wt % to
3.times.10.sup.-7 wt %, e.g., from 1.5.times.10.sup.-7 wt % to
2.5.times.10.sup.-7 wt %, from 2.times.10.sup.-7 wt % to
3.times.10.sup.-7 wt % or from 1.5.times.10.sup.-7 wt % to
2.times.10.sup.-7 wt %. In terms of lower limits, the water vapor
comprises greater than 1.times.10.sup.-7 wt % of liquid
entrainment, e.g., greater than 1.5.times.10.sup.-7 wt %, greater
than 2.times.10.sup.-7 wt %, or greater than 2.5.times.10.sup.-7 wt
%. The disclosed configuration provides for reductions in liquid
entrainment content, which advantageously contribute to process
efficiencies. For example the reduction in entrainment leads to
less loss of product material via the vent stream. In addition, the
lower entrainment levels have less environmental impact due to the
lower amounts of liquid entrainment. Conventional processes have
higher amounts of liquid entrainment, and as such, are less
efficient. In some cases, the entrainment comprises reaction
components such as hexamethylene diamine and/or low boiling
cyclical compounds.
[0040] In some aspects, the larger heat transfer area provides for
lower bubble density, which beneficially provides for lower
liquid/vapor shear. By lowering the liquid/vapor shear (one of the
contributing factors of foaming) foaming is effectively reduced.
Additionally, the increased vertical height of the disengagement
area provides additional time for foam to dissipate before
entrainment. Therefore, although the average vertical vapor
velocity may increase, the horizontal vapor velocity is lower,
which in turn reduces entrainment.
[0041] In some embodiments, the liquid level inside the shell of
the plug flow reactor may affect the total heat transfer area. In
some embodiments, the liquid level inside the shell of the plug
flow reactor may be at least 60%, e.g., at least 60%, at least 70%,
at least 75%, or at least 80%. In some embodiments, the liquid
level inside the shell of the plug flow reactor may be at least
75%. By maintaining a liquid level inside the shell of the plug
flow reactor, lower water vapor entrainment can be achieved.
[0042] Residence time, in particular residence time distribution,
is an important parameter in the polymerization of the concentrated
monomer solution. Importantly, the disclosed processes provide for
improvements in residence time distribution, which is important to
avoid polymer degradation. In some embodiments of the plug flow
reactor, the number and cut of the baffles affects the fluid path
length and zones of recirculation, which can increase the residence
time. Vaporization influences the residence time by presenting
additional blockage (vapor has greater specific volume than liquid)
to the passage of liquid below the free surface.
[0043] The residence time, e.g., the average residence time, of the
concentrated monomer solution in the plug flow reactor may be less
than 100 minutes, e.g., less than 80 minutes, less than 60 minutes,
less than 40 minutes or less than 20 minutes. In some cases, the
residence time may range from 2 minutes to 100 minutes, e.g., from
20 minutes to 80 minutes, from 40 minutes to 60 minutes, from 50
minutes to 60 minutes, or from 55 minutes to 60 minutes. In terms
of lower limits, the residence time of the concentrated monomer
solution in the plug flow reactor may be greater than 2 minutes,
e.g., greater than 10 minutes, greater than 20 minutes, greater
than 40 minutes, greater than 50 minutes or greater than 60
minutes.
[0044] In some embodiments, the residence time distribution varies
by +/-8%, based on the average residence time, e.g., +/-7%, +/-6%,
+/-5%, +/-4%, +/-3%, +/-2%, +/-1%, +/-0.5%, or +/-0.25%. For
example, the residence time distribution is +/-8% based on an
average residence time of 46.5 minutes. In some aspects, at a
confidence interval between 8% and 95%, the average residence time
ranges from 46.4 minutes to 46.7 minutes.
[0045] The use of the disclosed processes provides for
accompanying, synergistic improvements in conversion of amide
monomer to polyamides. In some embodiments, conversion is greater
than 80%, e.g., greater than 85%, greater than 90%, greater than
93%, greater than 95%, greater than 97%, greater than 99%, greater
than 99.5%, or greater than 99.9%. In terms of ranges, conversion
may range from 80% to 99.9%, e.g., from 85% to 99.5%, from 90% to
99%, from 93% to 97%, or from 95% to 97%. In terms of upper limits,
conversion is less than 99.9%, e.g., less than 99.5%, less than
99%, less than 97%, less than 95%, less than 93% or less than
90%.
[0046] In specific embodiments, the combination of the
aforementioned process steps and configuration provides for
synergistic improvements in conversion.
[0047] For example, the skin temperature of the plug flow reactor
may be less than 290.degree. C., the ratio of the heat transfer
area to the total volume of concentrated monomer solution is at
least 25:1, which yields a conversion of amide monomer to
polyamides that is greater than 85%.
[0048] As another example, the ratio of the heat transfer area to
the volume of heating fluid is at least 150:1, a residence time of
the concentrated monomer solution ranges from 40 min to 60 min, and
conversion of amide monomer to polyamides is greater than 90%.
[0049] As another example, a residence time of the concentrated
monomer solution in the plug flow reactor ranges from 50 minutes to
60 minutes, a residence time distribution varies by +/-8%, based on
an average residence time, and conversion of amide monomer to
polyamides is greater than 85%.
[0050] As another example, a ratio of the heat transfer area to the
volume of heating fluid is is in a range from 1:1 to 200:1, the
residence time distribution varies by +/-8%, based on an average
residence time, the skin temperature of the reactor is less than
260.degree. C., and the heating fluid has an H value less than 2800
kJ/kg.
[0051] As another example, the aqueous monomer solution comprises
diacid and diamine at a molar ratio of the diacid to the diamine is
at least 1:1, and a residence time of the concentrated monomer
solution is from 55 minutes to 60 minutes, and a conversion of
amide monomer to polyamides is greater than 85%.
[0052] In some embodiments, the plug flow reactor is operated at
(constant or substantially constant) pressure ranging from 13.5 bar
to 18.5 bar, e.g., from 14 bar to 18 bar, from 14 bar to 17 bar, or
from 15 bar to 16 bar. In terms of upper limits, the plug flow
reactor is operated at a pressure less than 18.5 bar, e.g., less
than 18 bar, less than 17 bar, less than 16 bar, less than 15 bar,
or less than 14 bar. In terms of lower limits, plug flow reactor is
operated at a pressure greater than 13.5 bar, e.g., greater than 14
bar, greater than 15 bar, greater than 16 bar, greater than 17 bar,
or greater than 18 bar.
[0053] In addition, the disclosed processes provide for a lower
change in temperature for the concentrated monomer solution from
the inlet of the plug flow reactor to the outlet of the plug flow
reactor. In some cases, the temperature change of the first process
fluid from the inlet of the plug flow reactor to the outlet of the
plug flow reactor ranges from 0.degree. C. to 150.degree. C., e.g.,
from 25.degree. C. to 150.degree. C., from 25.degree. C. to
125.degree. C., from 50.degree. C. to 100.degree. C., or from
60.degree. C. to 80.degree. C. In terms of upper limits, the change
in temperature is less than 150.degree. C., e.g., less than
125.degree. C., less than 100.degree. C., less than 80.degree. C.,
less than 60.degree. C., less than 50.degree. C. or less than
25.degree. C. In terms of lower limits, the change in temperature
is greater than 0.degree. C., e.g., greater than 25.degree. C.,
greater than 50.degree. C., greater than 60.degree. C., greater
than 80.degree. C., greater than 100.degree. C. or greater than
125.degree. C.
[0054] In some embodiments, the plug flow reactor heats the
concentrated monomer solution to a temperature ranging from
200.degree. C. to 300.degree. C., e.g., from 210.degree. C. to
290.degree. C., from 220.degree. C. to 280.degree. C., from
230.degree. C. to 270.degree. C., from 240.degree. C. to
270.degree. C., from 235.degree. C. to 255.degree. C., or from
250.degree. C. to 260.degree. C. In terms of upper limits, the plug
flow reactor heats the concentrated monomer solution to a
temperature less than 300.degree. C., e.g., less than 280.degree.
C., less than 260.degree. C., less than 250.degree. C., less than
240.degree. C., less than 220.degree. C. or less than 210.degree.
C. In terms of lower limits, plug flow reactor heats the
concentrated monomer solution to a temperature greater than
200.degree. C., e.g., greater than 210.degree. C., greater than
220.degree. C., greater than 240.degree. C., greater than
250.degree. C., greater than 260.degree. C. or greater than
280.degree. C.
[0055] In a particular embodiment, the plug flow reactor is
operated at a temperature from 200.degree. C. to 300.degree. C.,
and the pressure is from 14 bar to 18 bar, and conversion of amide
monomer to polyamides is greater than 95%.
[0056] FIG. 1 shows a continuous polymerization process with a plug
flow reactor according to one embodiment of the present disclosure.
Process 100 includes feeding stage 110. In feeding stage 110,
aqueous monomer solution comprising amide monomers is fed directly
from a feed tank to evaporation stage 120. The feed tank may be
upstream of the evaporator. Evaporation stage 120 evaporates the
aqueous monomer solution to form a concentrated monomer solution,
e.g., a monomer solution with a lower water content than the
aqueous monomer solution.
[0057] In some embodiments, the aqueous monomer solution comprises
diacid and diamine. The molar ratio of the diacid to the diamine in
the aqueous monomer solution may be at least 1:1. In one
embodiment, the ratio of diacid to the diamine in the aqueous
monomer solution is less than 8:1, e.g., less than 6:1, less than
4:1, less than 2:1, or less than 1:1. In terms of ranges, the ratio
of diacid to the diamine in the aqueous monomer solution may range
from 1:2 to 8:1, e.g., from 1:1 to 6:1, or from 2:1 to 4:1. In
terms of lower limits, the ratio of diacid to the diamine in the
aqueous monomer solution is greater than 1:2, e.g., greater than
1:1, greater than 2:1, or greater than 4:1.
[0058] In some embodiments, the concentration of amide monomers in
the aqueous monomer solution is in a range from 50 wt % to 80 wt %,
based on the total weight of the aqueous monomer solution, e.g.,
from 55 wt % to 75 wt % or from 60 wt % to 70 wt %. In terms of
upper limits, the concentration of amide monomers in the aqueous
monomer solution is less than 80 wt %, e.g., less than 75 wt %,
less than 70 wt %, less than 60 wt %, or less than 55 wt %. In
terms of lower limits, the concentration of amide monomers in the
aqueous monomer solution is greater than 50 wt %, e.g., greater
than 55 wt %, greater than 60 wt %, greater than 70 wt %, or
greater than 75 wt %. The balance of the aqueous monomer solution
comprises water and/or additional additives. In some embodiments,
the amide monomers comprises a diacid and a diamine, i.e., nylon
salt.
[0059] After evaporation stage 120, the concentrated monomer
solution comprises amide monomers in a range from 60 to 95%, based
on the total weight of the concentrated monomer solution, e.g.,
from 65% to 90%, from 70% to 85%, or from 75% to 80%. In terms of
upper limits, the concentration of amide monomers in the
concentrated monomer solution is less than 95 wt %, e.g., less than
90 wt %, less than 80 wt %, less than 70 wt %, or less than 65 wt
%. In terms of lower limits, the concentration of amide monomers in
the concentrated monomer solution is greater than 60 wt %, e.g.,
greater than 65 wt %, greater than 70 wt %, greater than 80 wt %,
or greater than 90 wt %.
[0060] The concentrated monomer solution may exit the evaporator at
a temperature in a range from 100.degree. C. to 200.degree. C.,
e.g., from 110.degree. C. to 190.degree. C., from 120.degree. C. to
180.degree. C., from 130.degree. C. to 170.degree. C., from 140 to
160.degree. C., or from 145.degree. C. to 155.degree. C. In terms
of upper limits, the concentrated monomer solution exits the
evaporator at a temperature less than 200.degree. C., e.g., less
than 180.degree. C., less than 160.degree. C., less than
140.degree. C., less than 120.degree. C., or less than 110.degree.
C. In terms of lower limits, concentrated monomer solution exits
the evaporator at a temperature greater than 100.degree. C., e.g.,
greater than 120.degree. C., greater than 140.degree. C., greater
than 160.degree. C., greater than 170.degree. C., greater than
180.degree. C. or greater than 190.degree. C. Preferably, the
evaporator is operated in a temperature range such that no
conversion of the concentrated monomer solution to polymers occurs
in the evaporator. The combination of the evaporator and the plug
flow reactor provides a synergistic effect that leads to greater
conversion. For example, the evaporator allows for the reduced
change in temperature of both the heat transfer fluid and the
concentrated monomer solution in the plug flow reactor. This also
enables the plug flow reactor to use less heat transfer fluid and
operate at lower temperatures than in conventional processes.
[0061] In some embodiments, the aqueous monomer solution is a nylon
salt solution. The nylon salt solution may be formed by mixing a
diamine and a diacid with water. For example, water, diamine, and
dicarboxylic acid monomer are mixed to form a salt solution, e.g.,
mixing adipic acid and hexamethylene diamine with water. In some
embodiments, the diacid may be a dicarboxylic acid and may be
selected from the group consisting of oxalic acid, malonic acid,
succinic acid, glutaric acid, pimelic acid, adipic acid, suberic
acid, azelaic acid, sebacic acid, undecanedioic acid, dodecandioic
acid, maleic acid, glutaconic acid, traumatic acid, and muconic
acid, 1,2- or 1,3-cyclohexane dicarboxylic acids, 1,2- or
1,3-phenyl enediacetic acids, 1,2- or 1,3-cyclohexane diacetic
acids, isophthalic acid, terephthalic acid, 4,4'-oxybisbenzoic
acid, 4,4-benzophenone dicarboxylic acid, 2,6-napthalene
dicarboxylic acid, p-t-butyl isophthalic acid and
2,5-furandicarboxylic acid, and mixtures thereof. In some
embodiments, the diamine may be selected from the group consisting
of ethanol diamine, trimethylene diamine, putrescine, cadaverine,
hexamethyelene diamine, 2-methyl pentamethylene diamine,
heptamethylene diamine, 2-methyl hexamethylene diamine, 3-methyl
hexamethylene diamine, 2,2-dimethyl pentamethylene diamine,
octamethylene diamine, 2,5-dimethyl hexamethylene diamine,
nonamethylene diamine, 2,2,4- and 2,4,4-trimethyl hexamethylene
diamines, decamethylene diamine, 5-methylnonane diamine, isophorone
diamine, undecamethylene diamine, dodecamethylene diamine,
2,2,7,7-tetramethyl octamethylene diamine,
bis(p-aminocyclohexyl)methane, bis(aminomethyl)norbornane, C2-C16
aliphatic diamine optionally substituted with one or more C1 to C4
alkyl groups, aliphatic polyether diamines and furanic diamines,
such as 2,5-bis(aminomethyl)furan, and mixtures thereof. In
preferred embodiments, the diacid is adipic acid and the diamine is
hexamethylene diamine which are polymerized to form nylon 6,6.
[0062] It should be understood that the concept of producing a
polyamide from diamines and diacids also encompasses the concept of
other suitable monomers, such as, aminoacids or lactams. Without
limiting the scope, examples of aminoacids can include
6-aminohaxanoic acid, 7-aminoheptanoic acid, 11-aminoundecanoic
acid, 12-aminododecanoic acid, or combinations thereof. Without
limiting the scope of the disclosure, examples of lactams can
include caprolactam, enantholactam, lauryllactam, or combinations
thereof. Suitable feeds for the disclosed process can include
mixtures of diamines, diacids, aminoacids and lactams.
[0063] Of course, polyamides are only one type of polymer that may
be utilized in the disclosed process. And other polymerization
reactants/reactions are contemplated.
[0064] Process 100 may optionally include preheating stage 130
after evaporation stage 120. The concentrated monomer solution may
be pumped to preheating stage 130 via a pump. In the preheating
stage 130, the preheater may heat the concentrated monomer solution
to a temperature in the range from 180.degree. C. to 230.degree.
C., e.g., from 190.degree. C. to 220.degree. C., from 200.degree.
C. to 210.degree. C., or from 205 to 215.degree. C. In terms of
lower limits, concentrated monomer solution exits the preheater at
a temperature greater than 180.degree. C., e.g., greater than
190.degree. C., greater than 200.degree. C., greater than
210.degree. C. or greater than 220.degree. C. In terms of upper
limits, the concentrated monomer solution exits the preheater at a
temperature less than 230.degree. C., e.g., less than 220.degree.
C., less than 210.degree. C., less than 200.degree. C. or less than
190.degree. C. Preferably, the preheater is operated in a
temperature range such that no conversion of the concentrated
monomer solution to polymers occurs in the preheater. By
introducing the concentrated monomer solution to a polymerization
reactor at a higher temperature, heat flux in the plug flow reactor
may be reduced even further.
[0065] After optional pre-heating stage 130, the concentrated
aqueous monomer solution is fed to polymerization stage 140 to
convert at least a portion of the monomer solution to a polymer,
e.g., to polyamide. In some embodiments, polymerization stage 140
comprises (directly) feeding the concentrated monomer solution from
evaporation stage 120 to polymerization stage 140. Polymerization
stage 140 polymerizes the concentrated monomer solution to form a
first process fluid comprising polyamides.
[0066] During polymerization in polymerization stage 140, water is
boiled off the first process fluid to form water vapor. The water
vapor is supplied to a disengagement region of polymerization stage
140 to minimize liquid entrainment in the water vapor. Entrainment
is the escape of liquid droplets in the water vapor. In addition to
the vapor velocity, entrainment is affected by droplet diameter,
liquid and vapor densities, surface tension and vertical
disengagement height.
[0067] In polymerization processes utilizing a preheater, the inlet
temperature of the concentrated monomer solution in the plug flow
reactor may be higher than in embodiments where the concentrated
monomer solution is directly fed to the plug flow reactor from the
evaporator. In these embodiments, the temperature change of the
concentrated monomer solution from the inlet of the plug flow
reactor to the outlet of the plug flow reactor is in a range from
0.degree. C. to 50.degree. C., e.g., from 5.degree. C. to
45.degree. C., from 15.degree. C. to 35.degree. C., or from
20.degree. C. to 30.degree. C. The plug flow reactor is preferably
operated at constant pressure. During the polymerization reaction
in the plug flow reactor, water of polymerization is devolatilized
and exits the plug flow reactor in a separate stream.
[0068] The plug flow reactor may have a tube layout as shown in
FIG. 2 according to one embodiment of the present disclosure. As
noted above, in some embodiments, the plug flow reactor comprises a
number of tubes (in a bundle), e.g., U-tubes, from 400 to 1,600
tubes, e.g., from 500 to 1,500 tubes, from 600 to 1,200 tubes, or
from 800 to 1000. In terms of upper limits, the number of tubes is
less than 1,600 tubes, e.g., less than 1,400 tubes, less than 1,200
tubes, less than 1,000 tubes, or less than 800 tubes. In terms of
lower limits, the number of tubes is greater than 400 tubes, e.g.,
greater than 600 tubes, greater than 800, greater than 1,000 tubes,
greater than 1,200 tubes, or greater than 1,400 tubes.
[0069] The outer diameter of the tubes may be in the range from 6
mm to 32 mm, e.g, from 10 mm to 28 mm, from 14 mm to 24 mm, from 16
mm to 22 mm or from 18 mm to 20 mm. In terms of lower limits, the
outer diameter of the tubes may be greater than 6 mm, e.g., greater
than 10 mm, greater than 16 mm, greater than 20 mm, greater than 24
mm, or greater than 28 mm. In terms of upper limits, outer diameter
of the tubes may be less than 32 mm, e.g., less than 28 mm, less
than 24 mm, less than 20 mm, less than 16 mm, or less than 12
mm.
[0070] The length of each of the tubes may be in the range from 2 m
to 10 m, e.g, from 4 m to 8 m, from 5 m to 7 m, or from 6 m to 7 m.
In terms of lower limits, the length of each of the tubes may be
greater than 2 m, e.g., greater than 4 m, greater than 6 m, or
greater than 8 m. In terms of upper limits, the length of each of
the tubes may be than less than 10 m, e.g., less than 8 m, less
than 6 m, or less than 4 m.
[0071] In some embodiments, the volume of the total displacement of
the tubes is greater than 1 m.sup.3, e.g., greater than 2 m.sup.3,
greater than 3 m.sup.3, greater than 4 m.sup.3, or greater than 5
m.sup.3. In terms of ranges, the volume of the total displacement
of the tubes is in the range from 1 m.sup.3 to 6 m.sup.3, e.g.,
from 2 m.sup.3 to 5 m.sup.3, from 3 m.sup.3 to 4 m.sup.3, or from 2
m.sup.3 to 2.5 m.sup.3. In terms of upper limits, the volume of the
total displacement of the tubes is less than 6 m.sup.3, e.g., less
than 5 m.sup.3, less than 4 m.sup.3, less than 3 m.sup.3, or less
than 2 m.sup.3.
[0072] In some embodiments, the plug flow reactor may include a
shell having an inner diameter in the range from 1 m to 10 m, e.g,
from 2 m to 8 m, from 4 m to 6 m or from 1 m to 2 m. In terms of
lower limits, the shell may have an inner diameter greater than 1
m, e.g., greater than 2 m, greater than 4 m or greater than 6 m. In
terms of upper limits, the shell may have an inner diameter less
than 10 m, e.g., less than 8 m, less than 6 m or less than 4 m.
[0073] In some embodiments, the cross-sectional area of the shell
covering the tubes may be greater than 0.5 m.sup.2, e.g., greater
than 1 m.sup.2, greater than 1.5 m.sup.2, greater than 2 m.sup.2,
or greater than 2.5 m.sup.2. In terms of ranges, the
cross-sectional area of the shell covering the tubes may be in the
range from 0.5 m.sup.2 to 3 m.sup.2, e.g., from 0.8 m.sup.2 to 2.6
m.sup.2, from 1 m.sup.2 to 2.2 m.sup.2 or from 1.5 m.sup.2 to 2
m.sup.2. In terms of upper limits, the cross-sectional area of the
shell covering the tubes may be less than 3 m.sup.2, e.g., less
than 2.5 m.sup.2, less than 2 m.sup.2, less than 1.5 m.sup.2, or
less than 1 m.sup.2.
[0074] In some embodiments, the volume of the shell covering the
tubes may be greater than 5 m.sup.3, e.g., greater than 7 m.sup.3,
greater than 9 m.sup.3, greater than 11 m.sup.3, or greater than 13
m.sup.3. In terms of ranges, the volume of the shell covering the
tubes may be in the range from 5 m.sup.3 to 15 m.sup.3, e.g., from
7 m.sup.3 to 13 m.sup.3, from 9 m.sup.3 to 11 m.sup.3 or from 10
m.sup.3 to 10.5 m.sup.3. In terms of upper limits, the volume of
the of the shell covering the tubes may be less than 15 m.sup.3,
e.g., less than 13 m.sup.3, less than 11 m.sup.3, less than 9
m.sup.3, or less than 7 m.sup.3.
[0075] In some embodiments, the heat transfer area of the plug flow
reactor may be greater than 200 m.sup.2, e.g., greater than 400
m.sup.2, greater than 500 m.sup.2, greater than 600 m.sup.2, or
greater than 800 m.sup.2. In terms of ranges, the heat transfer
area of the plug flow reactor may be in the range from 200 m.sup.2
to 1,000 m.sup.2, e.g., from 300 m.sup.2 to 900 m.sup.2, from 400
m.sup.2 to 800 m.sup.2 or from 500 m.sup.2 to 700 m.sup.2. In terms
of upper limits, the heat transfer area of the plug flow reactor
may be less than 1,000 m.sup.2, e.g., less than 800 m.sup.2, less
than 600 m.sup.2, less than 500 m.sup.2 or less than 400
m.sup.2.
[0076] The plug flow reactor may have a tube layout as shown in
FIG. 2 according to one embodiment of the present disclosure. In
this embodiment, the plug flow reactor has a BEU exchanger design
as designated by the Tubular Exchanger Manufactures Association
(TEMA). The plug flow reactor may comprise an E-type shell with
U-tube bundles supported by vertical segmental baffles. In some
aspects, the plug flow reactor may include stationary front head,
i.e., a bonnet.
[0077] In some embodiments, the plug flow reactor may be a one
pass, two pass, or four pass design on the tube side. The term
"pass" refers to the number of times the heat transfer fluid passes
through the process fluid in the plug flow reactor. Preferably, the
tube side of the plug flow reactor is a two pass system that allows
the heat transfer fluid to pass the fluid in the shell, e.g.,
concentrated monomer solution or process fluid, two times. For
example, in a two pass system, the first pass and the second pass
may each include 22 rows of tubes, wherein each pass has 617 tubes.
In some embodiments, the tube layout angle may be 90.degree. with
respect to the reactor. In some aspects, the plurality or bundle of
tubes, e.g., U-tubes or straight tubes, utilized in the plug flow
reactor may be a one pass, two pass, or four pass design.
[0078] In one embodiment, the plug flow reactor comprises a single
TEMA E-type shell that utilizes 3/4 inch U-tubes with a 90.degree.
tube layout. The U-tube bundle may be utilized in a 20 foot or 40
foot bundle. The plug flow reactor may further include one or more
single segmental baffles with 45% vertical cut to provide tube
support and promote serpentine flow for mixing. During operation,
the liquid level inside the shell of the plug flow reactor may be
about 75%.
[0079] Referring back to FIG. 1, in some embodiments, process 100
may optionally include second polymerization stage 150 downstream
from first polymerization stage 140. In second polymerization stage
150, the first process fluid is pumped from first polymerization
stage 140 to a second polymerization stage 150. The second
polymerization stage 150 further polymerizes the first process
fluid to form a second process fluid. In some embodiments, first
polymerization stage 140 produces low molecular weight polyamides
which are fed to second polymerization stage 150 to produce higher
molecular weight polyamides. The second process fluid exiting the
second reactor may be pumped downstream for further processing,
e.g., flashing, finishing, drying, etc, to obtain a finished
polymer product.
[0080] In another aspect, the system may further include a flasher.
The concentrated monomer solution may be fed from the evaporator,
optionally to the pre-heater, and then to a flasher before
polymerization in the plug flow reactor. The flasher flashes the
concentrated monomer solution before entering the plug flow
reactor. In some embodiments, the concentrated monomer solution is
flashed in a flash pot.
Retrofitting an Existing Polymerization Process
[0081] The benefits of the process disclosed above may also be
employed to retrofit an existing process. Also disclosed herein is
a process for retrofitting a polycondensation process that already
includes an existing evaporator and an existing reactor for
preparing polyamides. The process comprises the steps of
polymerizing the monomer solution in a first reactor, e.g., a plug
flow reactor as described above, to form a first process fluid,
feeding the first process fluid to the existing reactor; and
polymerizing the first process fluid to form a second process
fluid. The concentrated monomer solution flows on a shell side from
the inlet to the outlet. In this process, the evaporator and plug
flow reactor configuration has the same features discussed above
and provides for the same benefits.
[0082] In some embodiments, the retrofit reactor configuration may
utilize the plug flow reactor with the existing reactor, or the
plug flow reactor may entirely replace the existing reactor. As
described above, the plug flow reactor is a shell and tube plug
flow reactor including a shell having a shell side and a bundle of
tubes having a tube side arranged within a shell. The heat transfer
fluid flows on the tube side and the monomer solution flows on the
shell side. In some embodiments, the plug flow reactor is a
horizontal tubular reactor.
[0083] FIG. 3 shows a polymerization process retrofit with a plug
flow reactor according to one embodiment. In an existing
polymerization process, process 200 includes existing evaporation
stage 220 for concentrating a monomer solution from feeding stage
210 and an existing polymerization stage 250, e.g., a
polymerization reactor, for forming polymers.
[0084] In some embodiments, the polymerization process 200 may
optionally include a preheating stage 230 downstream from the
evaporation stage 220. After evaporation stage 220, the
concentrated monomer solution may be pumped to preheating stage
230. The preheating stage 230 may heat the concentrated monomer
solution to a temperature in the range from 180.degree. C. to
230.degree. C., e.g., from 190.degree. C. to 220.degree. C., from
200.degree. C. to 210.degree. C., or from 205 to 215.degree. C.,
before being introduced to the first polymerization stage 240,
which is a plug flow reactor 240 retrofit in the existing
polymerization process 200. In terms of lower limits, the
preheating stage 230 heats the concentrated monomer solution to a
temperature greater than 180.degree. C., e.g., greater than
190.degree. C., greater than 200.degree. C., greater than
210.degree. C. or greater than 220.degree. C. In terms of upper
limits, the preheating stage 230 heats the concentrated monomer
solution to a temperature less than 230.degree. C., e.g., less than
220.degree. C., less than 210.degree. C., less than 200.degree. C.
or less than 190.degree. C.
[0085] The plug flow reactor in the first polymerization stage 240
may be retrofit upstream from the existing polymerization stage
250. The plug flow reactor includes a shell side having an inlet
and an outlet, and a tube side including a bundle of tubes having a
heat transfer area. The concentrated polymer solution flows on the
shell side of the plug flow reactor to initially polymerize the
concentrated monomer solution from the evaporator to form a first
process fluid. In some embodiments, the first process fluid
comprises low molecular weight polyamides and some water, e.g.,
water of polymerization and solution water, that exits the plug
flow reactor. The concentration of the low molecular weight
polyamides that exits the plug flow reactor is in a range from 70%
to 99.9%, e.g., from 75% to 95%, from 80% to 95%, from 80% to 90%,
from 85% to 95%, or from 90% to 95%. In some embodiments, the
concentration of the low molecular weight polyamides exiting the
plug flow reactor in the first polymerization stage 240 is 92%. The
first process fluid is fed downstream to existing polymerization
stage 250 for polymerizing the first process fluid to form a second
process fluid comprising high molecular weight polyamides.
[0086] The existing polymerization stage 250 may include an
existing reactor comprising an outer tube for a conveying heating
fluid therethrough and an inner tube for conveying the first
process fluid. The outer tube conveys a volume of heat transfer
fluid to heat the first process fluid to temperature in the range
from 200.degree. C. to 300.degree. C., e.g., from 210.degree. C. to
290.degree. C., from 220.degree. C. to 280.degree. C., from
230.degree. C. to 270.degree. C., from 240.degree. C. to
270.degree. C., from 245.degree. C. to 265.degree. C., or from
250.degree. C. to 260.degree. C. The existing polymerization
reactor 250 is operated at constant pressure in the range from 13.5
bar to 18 bar, e.g., 14 bar to 17 bar or 15 bar to 16 bar.
[0087] In some embodiments, the plug flow reactor and the existing
reactor are used in series. In some embodiments, the plug flow
reactor and the existing reactor are used in parallel. In some
aspects, the plug flow reactor is located before the existing
reactor. In some aspects, the plug flow reactor is located after
the existing reactor. As mentioned above, in some embodiments, the
plug flow reactor can entirely replace an existing reactor.
[0088] In one aspect, the first process fluid comprises 85 wt. % to
92 wt. % of low molecular weight polyamides, based on the total
weight of the first process fluid and the second process fluid
comprises 93 wt. % to 97 wt. % of high molecular weight polyamides,
based on the total weight of the second process fluid. The
polymerization may include further conventional downstream
processing steps to obtain the finished polymer product.
[0089] In some aspects, the low molecular weight polyamides have a
molecular weight greater than 500 g/mol, e.g. greater than 700
g/mol, greater than 900 g/mol, greater than 1,200 g/mol or greater
than 1,600 g/mol. In terms of ranges, the low molecular weight
polyamides have a molecular weight in the range from 500 g/mol to
1,800 g/mol, e.g., from 600 g/mol to 1,600 g/mol, from 800 g/mol to
1,400 g/mol, or from 1,000 g/mol to 1,200 g/mol. In terms of upper
limits, the low molecular weight polyamides have a molecular weight
less than 1,800 g/mol, e.g., less than 1,600 g/mol, less than 1,200
g/mol, or less than 800 g/mol.
[0090] In other aspects, the high molecular weight polyamides have
a molecular weight greater than 2,000 g/mol, e.g. greater than
5,000 g/mol, greater than 20,000 g/mol, greater than 50,000 g/mol,
or greater than 100,000 g/mol. In terms of ranges, the high
molecular weight polyamides have a molecular weight in the range
from 2,000 g/mol to 125,000 g/mol, e.g., from 5,000 g/mol to
100,000 g/mol, from 20,000 g/mol to 80,000 g/mol, or from 50,000
g/mol to 80,000 g/mol. In terms of upper limits, the high molecular
weight polyamides have a molecular weight less than 150,000 g/mol,
e.g., less than 120,000 g/mol, less than 100,000 g/mol, or less
than 50,000 g/mol.
[0091] In another embodiment, a system for preparing polymers is
provided. The system includes a vessel, an evaporator, and a plug
flow reactor. The vessel includes an aqueous monomer solution.
During polymerization, the vessel continuously feeds the aqueous
monomer solution to the evaporator. The aqueous monomer solution is
concentrated in the evaporator to provide a concentrated monomer
solution in the ranges disclosed above. The concentrated monomer
solution is then fed to a plug flow reactor comprising a shell side
and a tube side for polymerizing the concentrated monomer solution
to form polyamides. The concentrated monomer solution flows on a
shell side from the inlet to the outlet of the plug flow reactor to
form polymers. The tube side of the plug flow reactor comprises a
plurality of U-tubes comprising an inlet and an outlet for
conveying a heating fluid therethrough. The tube side has a high
heat transfer area. In one aspect, the system may further include a
second reactor downstream from the plug flow reactor that is
arranged in series with the plug flow reactor.\
EXAMPLES
Example 1
[0092] A polyamide production process, as disclosed herein, was
simulated using HTRI modeling software. An evaporation unit
followed by a plug flow reactor (with a shell side and a tube side)
was simulated. The reactor comprised a 24 feet long shell that was
62 inches diameter and contained 617 U-tubes, each 20 feet in
length and 0.75 inches diameter. The concentrated monomer solution
flowed on the shell side from the inlet to the outlet. The
concentrated monomer solution (processing salt solution) had a
concentration ranging from 78 wt % (in) to 95 wt % (out) and was
fed at a rate of 23,491 lb/hr. The reactor was operated at a
simulated pressure of 245 psig and a simulated process bulk fluid
temperature ranging of 210.degree. C. (inlet) to 250.degree. C.
(outlet). The heating fluid temperature was 254.degree. C.
Example 2
[0093] Another polyamide production process, as disclosed herein,
was simulated using HTRI modeling software. An evaporation unit
followed by a plug flow reactor (with a shell side and a tube side)
was simulated. The reactor comprised a 21 feet long shell that was
48 inches diameter and contained 405 U-tubes, each approximately 16
feet in length and 0.75 inches diameter. The concentrated monomer
solution flowed on the shell side from the inlet to the outlet. The
concentrated monomer solution (processing salt solution) had a
concentration ranging from 78 wt % (in) to 95 wt % (out) and was
fed at a rate of 10,410 lb/hr. The reactor was operated at a
simulated pressure of 245 psig and a simulated process bulk fluid
temperature ranging of 210.degree. C. (inlet) to 250.degree. C.
(outlet). The heating fluid temperature was 254.degree. C.
Example 3
[0094] Another polyamide production process, as disclosed herein,
was simulated using HTRI modeling software. An evaporation unit
followed by a plug flow reactor (with a shell side and a tube side)
was simulated. The reactor comprised a 20 feet long shell that was
52 inches diameter and contained 281 U-tubes, each approximately 15
feet in length and 0.75 inches diameter. The concentrated monomer
solution flowed on the shell side from the inlet to the outlet. The
concentrated monomer solution (processing salt solution) had a
concentration ranging from 70 wt % (in) to 85 wt % (out) and was
fed at a rate of 15,000 lb/hr. The reactor was operated at a
simulated pressure of 245 psig and a simulated process bulk fluid
temperature ranging of 193.degree. C. (inlet) to 226.degree. C.
(outlet). The heating fluid temperature was 259.degree. C.
[0095] Heat flux rate, nucleate boiling heat transfer coefficient,
skin temperature, residence time variation, and liquid entrainment
in the vent stream were measured. The results are shown in Table
1.
Comparative Example A
[0096] Polyamide was produced using a conventional polyamide
production process (not a simulation) with a plug flow reactor
comprising a shell and a heating jacket on the outside of the
shell. The reactor comprised a 197 feet long shell that was 17.4
inches diameter and contained a single tube (having a 17.4 inch
diameter). The tube side comprised an inlet and an outlet and the
concentrated monomer solution (processing salt solution) flowed on
the tube side from the inlet to the outlet. The concentrated
monomer solution had a concentration ranging from 78 wt % (in) to
95 wt % (out) and was fed at a rate of 23,491 lb/hr. The reactor
was operated at a pressure of 245 psig and a process bulk fluid
temperature ranging of 210.degree. C. (inlet) to 250.degree. C.
(outlet). The reactor was heated with jacketed with Therminol vapor
heating fluid at a temperature ranging from 305.degree. C. to
323.degree. C. (higher than the simulated examples).
[0097] Heat flux rate, nucleate boiling heat transfer coefficient,
skin temperature, residence time variation, and liquid entrainment
in the vent stream were measured. The results are shown in Table
1.
TABLE-US-00001 TABLE 1 Simulation Performance Parameters Parameter
Example 1 Example 2 Example 3 Comp. Ex. A Heat flux rate, 1.472
1.280 2.248 11.491 BTU/hr-ft.sup.2 Nucleate boiling heat 30 to 49
29 to 54 30 to 54 85 to 150 transfer coefficient,
BTU/hr-ft.sup.2-.degree. F. Skin temperature, .degree. C. 219 to
288 215 to 288 205 to 261 243 to 310 Residence time 0.4% 0.55% --
8.1% variation (+/- %) Liquid entrainment 2.57 .times. 10.sup.-7
1.34 .times. 10-7 4.8 .times. 10-7 15.5 .times. 10.sup.-7 in vent
stream, wt % * Height, inches 17.5 14.25 13 4.3 Ratio 1 * 1:1 to
30:1 17.5 15.3 7.2 2.2 Ratio 2 ** 1:1 to 200:1 112.5 112.3 106.4
4.1 Conversion .sup. 90%+ .sup. 90%+ 90%+ .sup. 90%+ * Ratio 1 is
the ratio of the heat transfer area (ft.sup.2) to a total volume
(ft.sup.3) of the concentrated monomer solution * Ratio 2 is the
ratio of the heat transfer area (ft.sup.2) to a total volume
(ft.sup.3) of heat transfer fluid
[0098] As shown in Table 1, by flowing the concentrated monomer
solution on the shell side from the inlet to the outlet and
employing other disclosed process parameters, the disclosed process
surprisingly achieved a significantly lower heat flux rate, as
compared to that achieved via a conventional process.
Advantageously, this reduction in heat flux rate provided for the
processing improvements, e.g., reductions, in temperature and
temperature deltas during operation, as well as reductions in
detrimental foaming.
[0099] Also, residence time variation was greatly improved
(.+-.0.4% and .+-.0.55% vs. .+-.8.1%), which in turn provided for
higher reactor conversion (at an equivalent average residence
time). With tighter distributions, there was beneficially less time
for the material to degrade. In contrast with conventional
processes that operate with much greater residence time variations,
material is allowed to remain and degrade, which creates process
inefficiencies, e.g., reductions in conversion. Further, the
tighter residence time variations beneficially inhibit any
back-mixing that may occur, which also contributes to higher
overall conversion.
[0100] Importantly, the skin temperature of the disclosed process
was significantly decreased, which contributes to, inter alia,
reductions in foaming and preventing undesired polymer branching,
e.g., gelling. In addition, the nucleate boiling heat transfer
coefficients were lowered significantly, as compared to Comparative
Example A. And these reductions heat transfer coefficient
synergistically complemented the reductions in skin
temperature.
[0101] Further, the Examples clearly demonstrate that the disclosed
configurations provide for notable improvements in liquid
entrainment, e.g., in vent stream. This improvement is beneficial
because it contributes to less loss of product material via the
vent stream and less environmental impact due to the lower amounts
of liquid entrainment.
[0102] Importantly, all of the aforementioned improvements and
benefits were achieved without any reduction in conversion (vs.
conventional processes). For Examples 1-3, conversions were
maintained at high levels, e.g. over 90%. This, the disclosed
processes provide for the beneficial combination of low heat flux,
reduced temperature deltas, reduced foaming, improved residence
time variation, and reduced skin temperature, all while maintaining
high conversion.
Embodiments
[0103] The following embodiments are contemplated. All combinations
of features and embodiments are contemplated.
[0104] Embodiment 1: A process for preparing polyamides, the
process comprising: providing an aqueous monomer solution
comprising amide monomers; evaporating the aqueous monomer solution
to form a concentrated monomer solution; and polymerizing the
concentrated monomer solution in a plug flow reactor comprising a
shell side and a tube side to form a first process fluid comprising
polyamides, wherein the shell side comprises an inlet and an
outlet, wherein the concentrated monomer solution flows on the
shell side from the inlet to the outlet.
[0105] Embodiment 2: An embodiment of embodiment 1, wherein the
tube side comprises a plurality of U-tubes each including an inlet
and an outlet for conveying a heating fluid therethrough, and
wherein the tube side has a heat transfer area, and wherein the
heating fluid has a specific enthalpy, H value at atmospheric
pressure, less than 2,900 kJ/kg.
[0106] Embodiment 3: An embodiment of any of embodiments 1 and 2,
wherein a ratio of the heat transfer area (ft.sup.2) to a total
volume (ft.sup.3) of the concentrated monomer solution ranges from
1:1 to 30:1, e.g., from 3:1 to 30:1.
[0107] Embodiment 4: An embodiment of any of embodiments 1-3,
wherein a ratio of the heat transfer area (ft.sup.2) to a total
volume (ft.sup.3) of heat transfer fluid ranges from1:1 to 200:1,
e.g., from 5:1 to 200:1.
[0108] Embodiment 5: An embodiment of any of embodiments 1-4,
wherein a skin temperature of the plug flow reactor is less than
290.degree. C.
[0109] Embodiment 6: An embodiment of any of embodiments 1-5, the
process has a heat flux rate less than 11400 BTU/hr-ft.sup.2
[0110] Embodiment 7, An embodiment of any of embodiments 1-6,
wherein the skin temperature of the plug flow reactor is less than
290.degree. C., wherein the ratio of the heat transfer area to the
total volume of concentrated monomer solution ranges from 3:1 to
20:1, and conversion of amide monomer to polyamides is greater than
85%.
[0111] Embodiment 8: An embodiment of any of embodiments 1-7,
wherein a ratio of the heat transfer area to the volume of heat
transfer fluid is greater than 80:1, and a residence time of the
concentrated monomer solution ranges from 50 minutes to 60 minutes,
and conversion of amide monomer to polyamides is greater than
85%.
[0112] Embodiment 9: An embodiment of any of embodiments 1-8,
wherein a residence time of the concentrated monomer solution in
the plug flow reactor ranges from 2 minutes to 100 minutes, and
wherein a residence time distribution varies by +/-4%, based on an
average residence time, and conversion of amide monomer to
polyamides is greater than 90%.
[0113] Embodiment 10: An embodiment of any of embodiments 1-9,
wherein a ratio of the heat transfer area to the volume of heating
fluid ranges from 80:1 to 115:1, and wherein the residence time
distribution varies by +/-2%, based on an average residence time,
and the skin temperature of the reactor is less than 290.degree.
C.
[0114] Embodiment 11: An embodiment of any of embodiments 1-10,
wherein the plug flow reactor is a horizontal reactor.
[0115] Embodiment 12: An embodiment of any of embodiments 1-11,
wherein a residence time distribution varies by +/-8%, based on an
average residence time.
[0116] Embodiment 13: An embodiment of any of embodiments 1-12,
wherein conversion of amide monomer to polyamides is at least
85%.
[0117] Embodiment 14: An embodiment of any of embodiments 1-13,
wherein a temperature change of the heat transfer fluid from the
inlet to the outlet ranges from 0.degree. C. to 50.degree. C.
[0118] Embodiment 15: An embodiment of any of embodiments 1-14,
further comprising: separating water from the concentrated monomer
solution to form a water vapor during polymerization; and supplying
the water vapor to a disengagement region of the plug flow
reactor.
[0119] Embodiment 16: An embodiment of any of embodiments 1-15,
wherein the disengagement region has a height of at least 0.05
m.
[0120] Embodiment 17: An embodiment of any of embodiments 1-16,
wherein the vapor stream comprises less than 15.0.times.10.sup.-7
wt % of entrained liquid, e.g., less than 3.0.times.10.sup.-7 wt
%.
[0121] Embodiment 18: An embodiment of any of embodiments 1-17,
wherein the aqueous monomer solution comprises diacid and diamine,
wherein a molar ratio of the diacid to the diamine is at least
1:1.
[0122] Embodiment 19: An embodiment of any of embodiments 1-18,
wherein the molar ratio of the diacid to the diamine is at least
1:1, and a residence time of the concentrated monomer solution is
from 2 min to 100 min, and a conversion of amide monomer to
polyamides is greater than 90%.
[0123] Embodiment 20: An embodiment of any of embodiments 1-19,
wherein the plug flow reactor is operated at a temperature from
200.degree. C. to 300.degree. C. and a pressure from 13.5 bar to 18
bar.
[0124] Embodiment 21: An embodiment of any of embodiments 1-20,
wherein the plug flow reactor is operated at a temperature from
200.degree. C. to 300.degree. C., and the pressure is from 14 bar
to 18 bar, and wherein a conversion of amide monomer to polyamides
is greater than 85%.
[0125] Embodiment 22: An embodiment of any of embodiments 1-21,
further comprising flashing the first process fluid after
polymerization.
[0126] Embodiment 23: A process for retrofitting a polycondensation
process including an existing evaporator for concentrating a
monomer solution and an existing reactor for forming polyamides,
the process comprising: polymerizing the concentrated monomer
solution in a plug flow reactor comprising a shell side and a tube
side to form a first process fluid, wherein the shell side has an
inlet and an outlet; feeding the first process fluid to the
existing reactor; and polymerizing the first process fluid to form
a second process fluid, wherein the monomer solution flows on a
shell side from the inlet to the outlet.
[0127] Embodiment 24: An embodiment of embodiment 23, wherein the
plug flow reactor and the existing reactor are arranged in
series.
[0128] Embodiment 25: An embodiment of any of embodiments 23 and
24, wherein the tube side comprises a plurality of U-tubes each
comprising an inlet and an outlet for conveying a heating fluid
therethrough, and wherein the tube side has a heat transfer area,
and wherein the heating fluid has a specific enthalpy, H value at
atmospheric pressure, less than 2,900 kJ/kg.
[0129] Embodiment 26: An embodiment of any of embodiments 23-25,
wherein a ratio of the heat transfer area to a total volume of the
concentrated monomer solution is in a range from 1:1 to 30:1, e.g.,
from 3:1 to 30:1.
[0130] Embodiment 27: An embodiment of any of embodiments 23-26,
wherein a ratio of the heat transfer area to a total volume of heat
transfer fluid is in a range from 1:1 to 200:1, e.g., from 5:1 to
200:1.
[0131] Embodiment 28: An embodiment of any of embodiments 23-27,
further comprising: flashing the concentrated monomer solution to
form a flashed monomer solution; and feeding the flashed monomer
solution directly to the plug flow reactor.
[0132] Embodiment 29: An embodiment of any of embodiments 23-28,
wherein the first process fluid comprises 85 wt. % to 92 wt. % of
low molecular weight polyamides, based on the total weight of the
first process fluid.
[0133] Embodiment 30: An embodiment of any of embodiments 23-29,
wherein the second process fluid comprises 93 wt. % to 97 wt. % of
high molecular weight polyamides, based on the total weight of the
second process fluid.
[0134] Embodiment 31: A system for preparing polymers, comprising:
a vessel including an aqueous monomer solution; an evaporator for
concentrating the aqueous monomer solution to form a concentrated
monomer solution; a plug flow reactor comprising a shell side and a
tube side for polymerizing the concentrated monomer solution to
form polyamides, wherein the shell side comprises an inlet and an
outlet, and wherein the concentrated monomer solution flows on a
shell side from the inlet to the outlet.
[0135] Embodiment 32: An embodiment of embodiment 31, wherein the
tube side comprises a plurality of U-tubes comprising an inlet and
an outlet for conveying a heating fluid therethrough, and wherein
the tube side has a heat transfer area.
[0136] Embodiment 33: An embodiment of any of embodiments 31 and
32, further comprising a second reactor downstream from the plug
flow reactor, wherein the plug flow reactor and second reactor are
arranged in series.
[0137] Embodiment 34: An embodiment of any of embodiments 31-33,
further comprising a preheater for heating the concentrated monomer
solution to a temperature in a range from 180.degree. C. to
230.degree. C. before feeding the concentrated monomer solution to
the plug flow reactor.
[0138] Embodiment 35: An embodiment of any of embodiments 31-34,
further comprising a flasher for flashing the concentrated monomer
solution.
[0139] Embodiment 36: A process for preparing polyamides in a plug
flow reactor, the process comprising: selecting a desired first
process fluid molecular weight in a range between 700 g/mol and
150,000 g/mol; providing an aqueous monomer solution comprising
amide monomers; evaporating the aqueous monomer solution to form a
concentrated monomer solution; polymerizing the concentrated
monomer solution in a plug flow reactor comprising a shell side and
a tube side to form a first process fluid comprising polyamides,
controlling a heat flux rate of the process to be less than 11400
BTU/hr-ft.sup.2; and maintaining a residence time of a concentrated
monomer solution in the plug flow reactor from 2 minutes to 100
minutes; wherein the residence time distribution varies by +/-4%;
or wherein the first process fluid molecular weight corresponds to
the desired first process fluid molecular weight.
[0140] While the invention has been described in detail,
modifications within the spirit and scope of the invention will be
readily apparent to those of skill in the art. In view of the
foregoing discussion, relevant knowledge in the art and references
discussed above in connection with the Background and Detailed
Description, the disclosures of which are all incorporated herein
by reference. In addition, it should be understood that embodiments
of the invention and portions of various embodiments and various
features recited herein and/or in the appended claims may be
combined or interchanged either in whole or in part. In the
foregoing descriptions of the various embodiments, those
embodiments which refer to another embodiment may be appropriately
combined with other embodiments as will be appreciated by one of
skill in the art.
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