U.S. patent application number 09/775087 was filed with the patent office on 2001-06-28 for apparatus and method for pressurizing a propylene polymerization reactor.
This patent application is currently assigned to Fina Technology, Inc.. Invention is credited to Austin, Don, Griffith, Aron, Nguyen, Thanh, Parker, Wes.
Application Number | 20010005493 09/775087 |
Document ID | / |
Family ID | 22917803 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010005493 |
Kind Code |
A1 |
Nguyen, Thanh ; et
al. |
June 28, 2001 |
Apparatus and method for pressurizing a propylene polymerization
reactor
Abstract
A system for pressurizing a propylene polymerization reactor
includes: a pressurization vessel including an internal heat
exchanger; a pressure sensor for monitoring the pressure in the
vessel, the pressure sensor providing a signal indicative of the
pressure in the vessel; a control valve for supplying heated gas to
a first region of the vessel in response to signals from the
pressure sensor, the first region of the vessel being maintained
above the critical temperature and pressure of propylene; a
temperature sensor for monitoring the temperature in a second
region of the pressurization vessel, the temperature sensor
providing a signal indicative of the temperature in the second
region of the vessel; and a control valve for supplying a cooling
medium to the internal heat exchanger to cool propylene in the
second region below the critical temperature of propylene at the
pressure in the pressurization vessel.
Inventors: |
Nguyen, Thanh; (Sugarland,
TX) ; Parker, Wes; (La Porte, TX) ; Austin,
Don; (League City, TX) ; Griffith, Aron;
(Humble, TX) |
Correspondence
Address: |
Fina Technology, Inc.
P.O. Box 674412
Houston
TX
77267-4412
US
|
Assignee: |
Fina Technology, Inc.
|
Family ID: |
22917803 |
Appl. No.: |
09/775087 |
Filed: |
January 31, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09775087 |
Jan 31, 2001 |
|
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09243217 |
Feb 2, 1999 |
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6214944 |
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Current U.S.
Class: |
422/131 ;
422/242 |
Current CPC
Class: |
B01J 2219/00056
20130101; B01J 2219/00083 20130101; B01J 19/0006 20130101; B01J
2219/00238 20130101; B01J 2219/00108 20130101; Y02P 20/54 20151101;
B01J 19/0013 20130101; B01J 2219/002 20130101; B01J 2219/00162
20130101; B01J 3/008 20130101; B01J 19/1818 20130101; B01J 19/1837
20130101 |
Class at
Publication: |
422/131 ;
422/242 |
International
Class: |
C08F 110/06 |
Claims
What is claimed is:
1. A propylene polymerization system; the propylene polymerization
system including at least one pressurization vessel; the
pressurization vessel containing propylene at a temperature and
pressure above the critical temperature and pressure of propylene;
and wherein the pressurization vessel contains propylene below the
critical temperature of propylene.
2. The system of claim 1 wherein the pressure inside the
pressurization vessel is controlled by the addition of
polypropylene under supercritical conditions.
3. The system of claim 1 wherein the pressure inside the
pressurization vessel is controlled by the addition of an inert
gas.
4. The system of claim 1 wherein the pressurization vessel includes
an internal heat exchanger for cooling propylene liquid below the
critical temperature.
5. The system of claim 2 wherein the level of propylene present in
the pressurization vessel below the critical temperature of
propylene is monitored with a differential pressure sensing
unit.
6. The system of claim 1 wherein the pressure in the pressurization
vessel is between 660 and 800 psig, wherein the pressurization
vessel contains propylene at a temperature above the corresponding
critical temperature of propylene; and wherein the propylene
pressurization vessel contains propylene below the corresponding
critical temperature of propylene.
7. The system of claim 1 wherein the pressure in the pressurization
vessel is between 700 and 730 psig, wherein the pressurization
vessel contains propylene at a temperature above the corresponding
critical temperature of propylene; and wherein the propylene
pressurization vessel contains propylene below the corresponding
critical temperature of propylene.
8. The system of claim 1 wherein the propylene pressurization
vessel contains propylene in an upper region at a temperature and
pressure above the critical temperature and pressure of propylene;
and wherein the propylene pressurization vessel contains propylene
in a lower region below the critical temperature of propylene.
9. The system of claim 8 wherein the temperature in the upper
region of the pressurization vessel is maintained in the range of
200.degree. F. to 280.degree. F.
10. The system of claim 8 wherein the temperature in the upper
region of the pressurization vessel is maintained at approximately
240.degree. F.
11. The system of claim 8 wherein the temperature in the lower
region of the pressurization vessel is maintained in the range from
80.degree. F. to 140.degree. F.
12. The system of claim 8 wherein the temperature in the lower
region of the pressurization vessel is maintained at approximately
100.degree. F.
13. The system of claim 1 wherein the pressurization vessel is
connected to a propylene polymerization reactor for pressurizing
the reactor and wherein the level of propylene below the critical
temperature of propylene at the pressure in the pressurization
vessel is controlled by the discharge from the reactor.
14. The system of claim 13 wherein the pressurization vessel
includes a level controller and the propylene reactor includes a
discharge valve operatively connected to the level controller for
controlling the discharge of propylene from the reactor.
15. A method of polymerizing propylene comprising the steps of:
injecting a heated gas into a pressurization vessel to maintain a
volume of propylene in a first region of the pressurization vessel
in a supercritical temperature and pressure range; cooling a second
region of the vessel to maintain the temperature of the propylene
in the second region below the critical temperature of propylene at
the pressure in the pressurization vessel.
16. The method of claim 15 further comprising the step of
maintaining the temperature of propylene in the first region of the
pressurization vessel in the range of 200.degree. F. to 280.degree.
F.
17. The method of claim 15 further comprising the step of
maintaining the temperature in the first region of the
pressurization vessel at approximately 240.degree. F.
18. The method of claim 15 wherein the temperature in the second
region of the pressurization vessel is maintained in the range from
80.degree. F. to 140.degree. F.
19. The method of claim 15 wherein the temperature in the second
region of the pressurization vessel is maintained at approximately
100.degree. F.
20. A system for pressurizing a propylene polymerization reactor,
the system comprising: a pressurization vessel including an
internal heat exchanger; a pressure sensor for monitoring the
pressure in the vessel, the pressure sensor providing a signal
indicative of the pressure in the vessel; a control valve for
supplying heated gas to a first region of the vessel in response to
signals from the pressure sensor, the first region of the vessel
being maintained above the critical temperature and pressure of
propylene; a temperature sensor for monitoring the temperature in a
second region of the pressurization vessel, the temperature sensor
providing a signal indicative of the temperature in the second
region of the vessel; and a control valve for supplying a cooling
medium to the internal heat exchanger to cool propylene in the
second region below the critical temperature of propylene at the
pressure in the pressurization vessel.
21. The system of claim 20 further comprising a differential
pressure cell for monitoring the level of propylene in the second
region of the pressurization vessel.
Description
TECHNICAL FIELD
[0001] The present invention relates, in general, to a system,
apparatus and method for polymerizing propylene including a
propylene pressurization vessel operated under supercritical
conditions.
BACKGROUND OF THE INVENTION
[0002] Without limiting the scope of the present invention, the
background of the invention is described with reference to
propylene polymerization and copolymerization reactors and systems.
Conventional propylene polymerization systems have been operated
with temperature and pressure ranges well below the critical region
of propylene, for example, below a critical temperature (T.sub.c)
of 197.2.degree. F. and a critical pressure of 655.4 psig. For
example, in more than one conventional process the polymerization
system is typically operated at a temperature of about 140.degree.
F. and 180.degree. F. and a pressure in the range of 440 to 480
psig. Surprisingly, however, it has been discovered that with
presently available propylene polymerization catalysts, production
is increased if the systems are operated outside of the
conventional temperature and pressure ranges previously
employed.
[0003] However, in order to take advantage of the unexpected
benefits of operating outside of conventional temperature and
pressure ranges, it has been found necessary to provide a propylene
pressurization vessel that is operated above the critical
temperature and pressure range of propylene, e.g., in the
supercritical state. Thus, there exists a need for a propylene
polymerization system that includes a pressurization vessel adapted
to operate outside of conventional parameters.
[0004] The present invention provides a method and apparatus for
pressurizing a propylene polymerization system, including a
pressurization vessel operated under supercritical conditions. The
vessel contains propylene in a first region at supercritical
conditions and propylene in a second region at subcritical
conditions. In one embodiment of the invention, pressure in the
pressurization vessel is controlled by the rate of injection of
superheated propylene in the supercritical region. The temperature
of propylene in the zone containing the compressible supercritical
phase may be maintained by controlling the temperature of the
superheated propylene feed. Preferably the temperature of the
superheated propylene is in the range of 200.degree. F. to
280.degree. F., more preferably, the temperature of the superheated
propylene is approximately 240.degree. F. The pressure of the
vessel is preferably in the range of 660 to 800 psig, more
preferably in the range of 700 to 730 psig, most preferably in the
range of approximately 710 psig. The temperature of the dense
subcooled liquid propylene in the vessel is typically in the range
of 80.degree. F. to 140.degree. F., preferably 90.degree. F. to
110.degree. F., and most preferably approximately 100.degree. F.
Operation of the pressurization vessel in this mode allows a
propylene polymerization system to be pressurized and operated at
levels above conventional polymerization temperatures and
pressures, for example, at pressures of 660 to 700 psig.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] For a more complete understanding of the present invention,
including its features and advantages, reference is now made to the
detailed description of the invention, taken in conjunction with
the accompanying drawings in which like numerals identify like
parts and in which:
[0006] FIG. 1 is a schematic of an experimental apparatus for
testing the control and operation of a vessel containing propylene
at supercritical conditions and propylene at subcritical
conditions;
[0007] FIGS. 2 and 3 are graphical representations of propylene
condensation vs. time under varying conditions utilizing the
apparatus of FIG. 1; and
[0008] FIG. 4 is a schematic of a propylene polymerization system
utilizing the pressurization system of the present invention.
DETAILED DESCRIPTION
[0009] While the making and using of various embodiments of the
present invention are discussed in detail below, it should be
appreciated that the present invention provides many applicable
inventive concepts which can be embodied in a wide variety of
specific contexts. The specific embodiments discussed herein are
merely illustrative of specific ways to make and use the invention,
and do not limit the scope of the invention.
EXAMPLE 1
[0010] In order to determine whether effective control of a
propylene pressurization vessel could be maintained under
supercritical conditions, an experimental apparatus 10 was
assembled as generally as illustrated in FIG. 1. Propylene was
charged to the supply cylinder 38 which was then pressurized with
nitrogen. The valve 16 between the supply cylinder 38 and the
pressurization vessel 12 was opened to place an initial charge of
propylene into the vessel 12 through feed line 14 and heat
exchanger 24. After the initial charge of propylene had been
introduced into vessel 12, the valve 16 was closed and the supply
cylinder 38 was refilled with propylene. As illustrated, supply
cylinder 38 is mounted on scale 18 with a weight indicator 20 for
monitoring the weight of the cylinder along with a pressure monitor
28 for monitoring the pressure of the cylinder.
[0011] The steam supply was turned on with valve 22 to supply heat
and to allow the level sensor, a differential pressure ("DP") cell
26, to equilibrate. After the DP cell 26 had stabilized, the
propylene control valve 16 was opened and the vessel 12 was brought
up to operating pressure, in this case 710 psig. Readings from the
DP cell 26 were transmitted to a recording device by level
transmitter 36. Superheated propylene was injected into the top of
the vessel 12 to keep the pressure constant while excess liquid was
drained off the bottom of the tank through discharge valve 46 until
the desired level in the vessel was achieved.
[0012] In order to maintain the temperature in the lower section of
the vessel 12 below the temperature in the upper region 34 of the
vessel, water was supplied to cooling coil 54 via cooling water
valve 50 and supply line 52. Below the critical pressure, the
transition 30 between the dense (liquid) region 32 and compressible
(gas) region 34 in the vessel 12, as viewed in sight glass 48, was
apparent. However, as the pressure was increased to 710 psig and
the operating conditions moved outside of the phase envelop, the
interface (as viewed through a sight glass) between the vapor and
liquid phases in the vessel disappeared. However, due to the
temperature gradient in the vessel, there still existed a dense and
compressible region inside the vessel.
[0013] Since the pressure in the vessel decreased as propylene
condensed, either on the interior wall of the vessel or at the
interface of the dense (liquid) region 32 and the compressible
(vapor) region 34, superheated propylene was added intermittently
to maintain the desired pressure in the vessel.
[0014] Two different experimental procedures were employed during
the test. First, the unit was operated in an increasing level mode,
e.g., the level of the dense (liquid) region was allowed to
increase as propylene in the compressible (vapor) region of the
vessel condensed. Next, the vessel was operated in a constant level
mode. In the constant level mode, fluid was drained from the bottom
region 32 of the vessel via discharge valve 46 in order to maintain
the liquid level in the vessel within a predetermined range near
the middle of the vessel.
[0015] In each case, DP readings, liquid and vapor temperatures,
and supply cylinder weight were recorded at fixed time intervals as
indicated in Tables 1 and 2 below:
1TABLE 1 Condensation Rates at 710 psig with increasing level Vapor
Liquid Cylinder Time Condensation rate Condensation rate Pressure
Time Temp Temp wt. DP level Interval w/DP level vs. cyl. wt w/ cyl.
wt. (psig) (min) (F) (F) (lbs) Reading (min) (lbs/br) (lbs/br) 0
147.0 710 5 273.0 100.2 145.7 205 5.00 710 10 269.0 96.6 145.4 225
5.00 4.36 4.18 710 15 267.6 96.1 145.2 234 5.00 1.96 2.79 710 20
264.7 96.6 145.0 240 5.00 1.31 2.79 710 25 263.1 98.0 144.8 257
5.00 3.71 2.79 710 30 260.1 98.1 144.6 270 5.00 2.84 2.79 710 35
258.0 99.2 144.4 276 5.00 1.31 2.79 710 40 255.6 99.3 144.2 288
5.00 2.62 2.79 710 45 253.2 99.5 144.1 298 5.00 2.18 2.79 710 50
250.7 99.5 143.9 309 5.00 2.40 2.79 710 55 248.2 99.5 143.8 319
5.00 2.18 1.39 710 65 243.9 99.5 143.5 341 10.00 2.40 2.09 710 70
242.9 100.4 143.4 352 5.00 2.40 1.39
[0016]
2TABLE 2 Condensation Rates at 710 psig with constant level Time
Vapor Liquid Cylinder Cond. Rate Cond Rate Cond. Rate Pressure Time
Interval Temp Temp DP level wt. w/cyl. wt w/cyl. wt w/cyl. wt.
(psig) (min) (min) (F) (F) Reading (lbs) (lbs//hr) (lbs//hr)
(lbs/hr) 710 0 0 307.6 68.6 200-210 156.2 710 10 10 303.1 78.8 "
155.2 6.97 710 20 10 292.3 90.1 " 154.5 4.88 710 30 10 232.4 96.6 "
154.0 3.49 5.11 710 40 10 232.9 81 " 153.2 5.58 710 50 10 232.4
74.6 " 152.4 5.58 710 60 10 287.6 72.3 " 151.6 5.58 5.58 5.34 710
70 10 286.2 73 " 150.7 6.27 710 80 10 286.4 81.3 " 150 4.88 710 90
10 284.5 87.6 " 149.3 4.88 5.34 710 100 10 281.2 99.1 " 148.6 4.88
710 110 10 279 95 " 147.9 4.88 710 120 10 275.7 99 " 147.3 4.18
4.65 5.00 710 130 10 273 93.4 " 146.7 4.13 710 140 10 269.1 97.5 "
146.1 4.18 710 150 10 278.2 93.4 " 145.3 5.58 4.65 710 160 10 277
98.8 " 144.6 4.88 710 170 10 271.6 91.8 " 144.1 3.49 710 180 10
270.5 97 " 143.4 4.88 4.42 4.53 710 190 10 279.1 92.8 " 142.6 5.58
710 200 10 276.4 95.9 " 141.9 4.88
[0017] As illustrated by the above example, a propylene
pressurization vessel can be designed, controlled and operated with
distinct regions of the vessel containing propylene in a dense
(liquid) phase and propylene in a compressible supercritical phase.
To achieve a desired pressure in the pressurization vessel, the
vessel may be pressurized with superheated propylene. Graphical
representations of condensation rates vs. time are presented in
FIGS. 2 and 3 in order to further illustrate the test results.
[0018] In one embodiment of the invention, pressure in the vessel
may be controlled by the injection of completely vaporized,
superheated propylene in the supercritical region. The temperature
of propylene in the zone containing the compressible supercritical
phase may be maintained by controlling the temperature of the
superheated propylene. Preferably, the temperature of the
superheated propylene is in the range of 200.degree. F. to
280.degree. F., more preferably, the temperature of the superheated
propylene is in the range of approximately 240.degree. F. The
pressure of the vessel is preferably in the range of 660 to 800
psig, more preferably in the range of 700 to 730 psig, most
preferably in the range of approximately 710 psig. The temperature
of the dense subcooled liquid propylene in the vessel is typically
in the range of 80.degree. F. to 140.degree. F., preferably
90.degree. F. to 110.degree. F., and most preferably approximately
100.degree. F. Operation of the pressurization vessel in this mode
allows a propylene polymerization system to be pressurized and
operated at levels above conventional polymerization temperatures
and pressures, for example at pressures of 660 to 700 psig.
[0019] Referring now to FIG. 4, a propylene polymerization system
or apparatus embodying the invention is schematically illustrated.
As illustrated, the system includes a first loop reactor 110, a
second loop reactor 120 connected in series with the first loop
reactor via line 160, and a propylene pressurization system
generally designated 100. The loop reactors 110 and 120 are
provided with agitators 170 to promote mixing. Although illustrated
in the context of a double loop reactor system, the pressurization
system is, of course, applicable to single reactor systems and
reactors other than loop-type reactors.
[0020] Propylene is supplied to the system via feed line 135 which
provides propylene to both loop reactors and the pressurization
system 100. Propylene fed to the pressurization system passes
through a heat exchanger 116. A steam supply 112 and control valve
114 are provided for heating heat exchanger 116,
[0021] Pressurization system 100 includes a pressurization vessel
130 which is equipped with an internal cooling coil 146 positioned
in the lower portion of the vessel. Cooling water is supplied to
the coil via supply line 140 and the flow of cooling water is
regulated by control valve 142. The first loop reactor 110 and
second loop reactor 120 communicate with the pressurization vessel
130 via lines 132 and 134.
[0022] Pressurization vessel 130 is equipped with an upper
temperature sensor/controller 118 located in the upper portion of
the vessel 130. Alternatively, the temperature sensor 118 may be
located in propylene feed line 172 between the heat exchanger 116
and the pressurization vessel 130. The signal from the sensor 118
is transmitted to control valve 114 in steam supply line 112 to
regulate the flow of steam to heat exchanger 116.
[0023] Pressurization vessel 130 is also provided with a DP cell
150 that provides a signal to level controller 152. The signal from
level controller 152 is transmitted to control valve 154 which
regulates the discharge of propylene and polymer from the second
loop reactor 120. Thus, if the fluid level in pressurization vessel
130 rises above the desired level, the control valve 154 opens to
release propylene and polymer from the system. Alternatively, if
the level in the vessel 130 drops below the desired level, the
level controller 152 transmits a signal to control valve 154 to
close the valve.
[0024] Pressure in the vessel 130 is regulated by the addition of
superheated propylene vapor. The pressurization vessel 130 is
equipped with a pressure controller 124 which is operatively
connected to control valve 126. In operation, as the pressure in
the vessel 130 drops, pressure controller 124 transmits a signal to
control valve 126. Control valve 126 opens in response to the
signal, supplying propylene to heat exchanger 116 wherein the
propylene is superheated prior to introduction to the vessel 130.
During operation, pressure in the vessel is preferably in the range
of 660 to 800 psig, more preferably in the range of 700 to 730
psig, and most preferably in the range of approximately 710
psig.
[0025] In operation, propylene is present in the pressurization
vessel 130 in two distinct phases, a superheated compressible
(vapor) phase, corresponding to upper region 131 of the vessel, and
a subcooled dense (liquid) phase corresponding to region 133 in the
lower portion of the vessel. Typically, the temperature in the
upper region 131 is maintained in the range of 200.degree. F. to
280.degree. F. Preferably, the temperature of the superheated
propylene in the upper region 131 of the vessel is in the range of
approximately 240.degree. F. The temperature of the dense subcooled
liquid propylene in the lower region 133 of the pressurization
vessel is typically in the range of 80.degree. F. to 140.degree.
F., preferably 90.degree. F. to 110.degree. F., and most preferably
approximately 100.degree. F. As used herein, the term "subcooled"
refers to temperature below the critical temperature of propylene
at the relevant pressure.
[0026] The temperature in the lower region 133 of the
pressurization vessel is maintained with internal cooling coil 146.
The pressurization vessel 130 is equipped with a temperature sensor
144 at a location corresponding to the lower region 133 of the
vessel. The flow of cooling water to the coil is controlled by
control valve 142 which opens and closes in response to signals
received from sensor 144. As will be appreciated by those skilled
in the art, other cooling mediums, such as the propylene feed to
the second reactor 120, could be utilized as the cooling
medium.
[0027] An important feature of the present invention is the
combined use of internal cooling of the pressurization vessel 130
and a differential pressure cell 150 in order to control the level
of the dense subcooled liquid propylene in the vessel. Although
propylene is present in the pressurization vessel in two phases,
e.g., a compressible superheated phase and dense subcooled phase,
under supercritical conditions the interface between the two phases
becomes visually undetectable. Consequently, a typical level
monitoring device, for example a sight glass, cannot be used to
control the dense, or fluid phase, level in the pressurization
vessel. Thus, an alternative level monitoring device, e.g., a
differential pressure, is needed to monitor the fluid phase level
in the vessel. However, in order for a differential pressure cell
to be utilized as a level monitoring device, the density gradient
between the superheated propylene in the upper region 131 of the
vessel 130 and the dense, subcooled propylene in the lower region
of the vessel must be significant enough to allow the DP cell to
detect a pressure differential due to the density gradient. The use
of an internal cooling coil 146 in vessel 130 to cool the dense
liquid phase propylene in the lower region 133 of the vessel to a
temperature below the critical temperature provides the required
density gradient, thereby allowing the use of a DP cell as a level
monitoring device.
[0028] For example, in one embodiment of the invention, the vessel
is operated at 710 psig. The temperature in a first or upper region
131 of the vessel, corresponding to the compressible, supercritical
propylene, is maintained at approximately 240.degree. F., whereas
the dense, liquid phase propylene in the lower or second region 133
of the vessel 130 is cooled to approximately 100.degree. F. though
the use of internal cooling coil 146. Since the specific volume of
propylene at 710 psig and 100.degree. F. is 0.033 ft.sup.3/lb and
the specific volume of propylene at 710 psig and 240.degree. F. is
0.145 ft.sup.3/lb, the density ratio between the superheated
propylene in the upper region 131 and the subcooled liquid
propylene in the lower region is 4.39. This density gradient is
sufficient to allow a DP cell to be used as a level indication
device for vessel 130.
[0029] While certain embodiments of the invention have been
illustrated for the purposes of this disclosure, numerous changes
in the composition, method and article of manufacture presented
herein may be made by those skilled in the art, such changes being
embodied within the scope and spirit of the present invention as
defined by the appended claims.
* * * * *