U.S. patent application number 16/033893 was filed with the patent office on 2018-11-15 for operating a polyolefin reactor.
This patent application is currently assigned to Univation Technologies, LLC. The applicant listed for this patent is Univation Technologies, LLC. Invention is credited to Xianyi Cao, David M. Glowczwski, Abarajith S. Hari, Bruce J. Savatsky.
Application Number | 20180326386 16/033893 |
Document ID | / |
Family ID | 49170913 |
Filed Date | 2018-11-15 |
United States Patent
Application |
20180326386 |
Kind Code |
A1 |
Hari; Abarajith S. ; et
al. |
November 15, 2018 |
OPERATING A POLYOLEFIN REACTOR
Abstract
Methods and systems for controlling a polymerization reactor in
a non-sticking regime are disclosed. An exemplary method includes
measuring parameters for the polymerization reaction including a
reactor temperature and a concentration of an induced condensing
agent (ICA) in a polymerization reactor. An equivalent partial
pressure ((P.sub.ICA).sub.equiv) of the ICA is calculated. The
polymerization reactor operation is located in a two dimension
space defined by a reactor temperature dimension and a
((P.sub.ICA).sub.equiv) dimension. The location in the two
dimensional space is compared to an non-sticking regime, defined as
the space between an upper temperature limit (UTL) curve and a
lower temperature limit (LTL) curve. Parameters of the
polymerization reactor are adjusted to keep the reactor within the
non-sticking regime.
Inventors: |
Hari; Abarajith S.;
(Ridgecrest, CA) ; Savatsky; Bruce J.; (Kingwood,
TX) ; Glowczwski; David M.; (Baytown, TX) ;
Cao; Xianyi; (Pearland, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Univation Technologies, LLC |
Houston |
TX |
US |
|
|
Assignee: |
Univation Technologies, LLC
Houston
TX
|
Family ID: |
49170913 |
Appl. No.: |
16/033893 |
Filed: |
July 12, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14424797 |
Feb 27, 2015 |
10029226 |
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PCT/US2013/058002 |
Sep 4, 2013 |
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16033893 |
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61698286 |
Sep 7, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 2219/00051
20130101; G01N 33/442 20130101; G01N 2430/60 20130101; G01N 11/14
20130101; B01J 19/0013 20130101 |
International
Class: |
B01J 19/00 20060101
B01J019/00; G01N 11/14 20060101 G01N011/14; G01N 33/44 20060101
G01N033/44 |
Claims
1.-9. (canceled)
10. A system for controlling a reactor, comprising: a
polymerization reactor, comprising: a gas chromatograph; a
temperature measurement system; and a control system, comprising: a
processor; and a storage system, wherein the storage system
comprises machine readable instructions configured to direct the
processor to: measure a temperature of the polymerization reactor
using the temperature measurement system; measure a concentration
of an induced condensing agent (ICA) and another condensable fluid
in the polymerization reactor using the gas chromatograph;
calculate an equivalent partial pressure ((P.sub.ICA).sub.equiv) of
the ICA in the reactor from the concentration of the ICA and the
other condensable fluid in the polymerization reactor; locating the
reactor operation in a two dimension space defined by a reactor
temperature dimension and a (P.sub.ICA).sub.equiv dimension; and
compare the location in the two dimensional space to a non-sticking
regime defined as the space between an upper temperature limit
(UTL) curve and a lower temperature limit (LTL) curve.
11. The system of claim 10, wherein the storage system comprises
instructions configured to direct the processor to adjust the
conditions in the polymerization reactor to keep the reactor
operation in the non-sticking regime.
12. The system of claim 10, wherein the storage system comprises
instructions configured to direct the processor to adjust the
conditions in the polymerization reactor to return the reactor
operations to the non-sticking regime.
13. The system of claim 11 or 12, wherein adjusting the conditions
comprises adjusting the reactor temperature and/or adjusting the
concentration of the ICA.
14. The system of claim 10, wherein the control system makes
automatic adjustments to keep the reactor in the non-sticking
regime.
15. The system of claim 14, wherein making the automatic
adjustments comprises adjusting the reactor temperature and/or
adjusting the concentration of the ICA.
16. The system of claim 10, comprising a cooling system, wherein
the storage system comprises instructions configured to direct the
processor to adjust the cooling system to change the reactor
temperature.
17. The system of claim 10, comprising an ICA addition system, or a
co-monomer addition system, or both, wherein the storage system
comprises instructions configured to change the amount of ICA or
comonomer added to the reactor to adjust the
(P.sub.ICA).sub.equiv.
18. The system of claim 10, comprising a monomer addition system, a
co-monomer addition system, or a catalyst addition system or any
combinations thereof, wherein the storage system comprises
instructions configured to change the amount of a reactant to
change the reactor temperature.
19.-20. (canceled)
21. The system of claim 10, wherein the polymerization takes place
in the presence of a catalyst selected from the group consisting of
metallocenes, Ziegler-Natta, chromium, chromium oxide, AlCl.sub.3,
cobalt, iron, palladium, and any combinations thereof.
22. (canceled)
Description
FIELD OF THE INVENTION
[0001] Described herein are systems and methods for operating a
polyolefin polymerization reactor. The methods may include
determining a non-sticking operating regime for a polyolefin
polymerization reaction to prevent the materials in the reaction
from agglomerating and operating a polyolefin polymerization
reactor within the non-sticking operating regime.
BACKGROUND
[0002] Polyolefin polymers can be produced using gas phase
polymerization processes. In a typical gas-phase fluidized bed
polymerization process, a gaseous stream containing one or more
monomers is continuously passed through the fluidized bed under
reactive conditions in the presence of a catalyst. The gaseous
stream is withdrawn from the fluidized bed and recycled back into
the reactor. The recycled gas stream is heated in the reactor by
the heat of polymerization. This heat may be removed in another
part of the cycle, for example by a cooling system external to the
reactor such as a heat exchanger.
[0003] The heat generated by the reaction may be removed in order
to maintain the temperature of the resin and gaseous stream inside
the reactor below the polymer melting point or the catalyst
deactivation temperature, or to control polymer properties. Heat
removal can also help prevent excessive stickiness of polymer
particles that may result in agglomeration. Particle agglomerations
may lead to the formation of chunks or sheets of polymer that
cannot be removed from the reactor as product. Further, such chunks
or sheets may fall onto the reactor distributor plate which may
impair fluidization of the bed and may lead to a discontinuity
event. Additionally, since the polymerization reaction is
exothermic, the amount of polymer produced in a fluidized bed
polymerization process is related to the amount of heat that can be
withdrawn from the reaction zone.
[0004] For a time, it was thought that the temperature of the
gaseous stream external to the reactor, otherwise known as the
recycle stream temperature, could not be decreased below the dew
point of the recycle stream without causing problems such as
polymer agglomeration or plugging of the reactor system. The dew
point of the recycle stream is that temperature at which liquid
condensate first begins to form in the gaseous recycle stream. The
dew point can be calculated knowing the gas composition and is
thermodynamically defined using an equation of state. However, as
described in U.S. Pat. Nos. 4,543,399 and 4,588,790, it was found
that a recycle stream can be cooled to a temperature below the dew
point in a fluidized bed polymerization process resulting in
condensing a portion of the recycle gas stream outside of the
reactor. The resulting stream containing entrained liquid can then
be returned to the reactor without causing agglomeration or
plugging phenomena. The process of purposefully condensing a
portion of the recycle stream is known in the industry as
"condensed mode" operation. When a recycle stream temperature is
lowered to a point below its dew point in condensed mode operation,
an increase in polymer production may be possible.
[0005] Cooling of the recycle stream to a temperature below the gas
dew point temperature produces a two-phase gas/liquid mixture that
may have entrained solids contained in both phases. The liquid
phase of this two-phase gas/liquid mixture in condensed mode
operation is generally entrained in the gas phase of the mixture.
Vaporization of the liquid occurs only when heat is added or
pressure is reduced. For example, as described in U.S. Pat. Nos.
4,543,399 and 4,588,790, vaporization can occur when the two-phase
mixture enters the fluidized bed, with the resin providing the
required heat of vaporization. The vaporization thus provides an
additional means of extracting heat of reaction from the fluidized
bed.
[0006] The cooling capacity of the recycle gas can be increased
further while at a given reaction temperature and a given
temperature of the cooling heat transfer medium. This can be
performed by adding non-polymerizing, non-reactive materials to the
reactor, which are condensable at the temperatures encountered in
the process heat exchanger. Such are collectively known as induced
condensing agents (ICAs). Increasing concentrations of ICA in the
reactor causes corresponding increases in the dew point temperature
of the reactor gas, which promotes higher levels of condensing for
higher (heat transfer limited) production rates from the reactor.
Suitable ICAs are selected based on their specific heat and boiling
point properties. In particular, an ICA is selected such that a
relatively high portion of the material is condensed at the cooling
water temperatures available in polymer production plants, which
are compounds typically having a boiling point of about
20-40.degree. C. ICAs include hexane, isohexane, pentane,
isopentane, butane, isobutane, and other hydrocarbon compounds that
are similarly non-reactive in the polymerization process.
[0007] U.S. Pat. No. 5,352,749, describes limits to the
concentrations of condensable gases, whether ICAs, comonomers or
combinations thereof, that can be tolerated in the reaction system.
Above certain limiting concentrations, the condensable gases can
cause a sudden loss of fluidization in the reactor, and a
consequent loss in ability to control the temperature in the fluid
bed. The upper limits of ICA in the reactor may depend on the type
of polymer being produced. For example U.S. Pat. Nos. 5,352,749,
5,405,922, and 5,436,304, characterize this limit by tracking the
ratio of fluidized bulk density to settled bulk density. As the
concentration of isopentane was increased, they found that the bulk
density ratio steadily decreased. When the concentration of
isopentane was sufficiently high, corresponding to a bulk density
ratio of 0.59, they found that fluidization in the reactor was
lost. They therefore determined that this ratio (0.59) was a point
of no return, below which the reactor will cease functioning due to
loss of fluidization. As described in PCT Publication WO
2005/113615(A2), attempts to operate polymerization reactors with
excessive ICA concentrations may cause polymer particles suspended
in the fluid bed to become cohesive or "sticky," and in some cases
cause the fluid bed to solidify in the form of a large chunk.
[0008] Adding to the complexity of control of stickiness while
using ICAs, different polymer products vary widely in their ability
to tolerate ICA materials, some having a relatively high tolerance
(expressed in partial pressure of the ICA in the reactor), e.g., 50
psia, while other polymers may tolerate as little as 5 psia. In
these latter polymers, the heat transfer limited production rates
under similar conditions are substantially lower. Polymers which
possess a more uniform comonomer composition distribution are known
to have a higher tolerance to the partial pressure of the ICA in
the reactor. Typical metallocene catalysts are a good example of
catalysts that may produce polymers having a more uniform comonomer
composition. However, at some point even these metallocene produced
polymers reach a limiting ICA concentration that induces
stickiness. The limiting ICA concentration depends on several
factors in addition to the polymer type, including reactor
temperature, comonomer type, and concentration. Further, with the
effect of temperature, ICA level, and comonomer levels all
affecting on the onset of stickiness, determining the point at
which sticking begins to occur has heretofore been difficult.
[0009] Two articles by Process Analysis & Automation Limited
(PAA), entitled "Agglomeration Detection by Acoustic Emission," PAA
Application note: 2002/111 (2000) and "Acoustic Emission
Technology--a New Sensing Technique for Optimising Polyolefin
Production" (2000), suggest process control in fluidized bed
production of polyolefins may be performed by utilizing acoustic
emission sensors located at various positions on the reactor and
recycle piping. These publications purport to solve the problem of
detecting large polymer agglomerates in a reactor, such as chunks
or sheets, rather than detecting stickiness of the resin particles,
and provide only one specific example, showing the detection of a
chunk of approximately 1.5 meters in diameter within a commercial
fluid bed reactor. There is no mention of the detection of polymer
stickiness or cohesiveness. In effect, the PAA documents describe
the detection of agglomerates after they have been formed in the
reactor, rather than detection of resin stickiness that, if left
unchecked, could lead to the formation of the agglomerates.
[0010] PCT Application Publication Number WO 2003/051929 describes
the use of mathematical chaos theory to detect the onset and
presence of sheeting in a fluid bed reactor. However, like the PAA
articles, the reference does not disclose how to predict when a
resin in a reactor is going to become sticky, or any method
allowing safe operation of a polymerization reactor near its limit
of ultimate cooling capacity for maximum production rates.
[0011] WO 2005/113615 and corresponding U.S. Patent Application
Publication No. 2005/0267269 describe determination in a laboratory
of a critical temperature below which resin in a polymerization
reactor cannot become sticky, and use of this predetermined
critical temperature to control the reactor.
[0012] U.S. patent application Ser. No. 11/227,710 discloses
monitoring of resin stickiness during operation of a polymerization
reactor by generating a time series of readings of acoustic
emissions of the contents of the reactor during steady state
operation. Additional acoustic emission measurements are then
generated and processed to determine whether they deviate from
acoustic emissions indicative of steady state reactor operation.
Such deviation is treated as an indication of onset of excessive
stickiness of polymer particles in the reactor. Corrective action
can be taken (e.g., ICA and/or monomer levels and/or reactor
temperature can be adjusted) when the acoustic emission
measurements are determined to deviate from those of a steady state
reactor. However, this application does not teach the generation of
a reference temperature above which resin in a reactor is predicted
to become sticky.
[0013] Other background references include U.S. Patent Application
Publication Nos. 2004/063871, 2005/0267269; 2007/073010, and WO
2005/049663, and WO 2006/009980; and "Model Prediction for Reactor
Control," Ardell et al., Chemical Engineering Progress, American
Inst. Of Chem. Eng., US, vol. 79, no. 6, (June 1983).
[0014] Even within the constraints of conventional operations,
control of reactors is complex, adding further to the difficulty of
finding operating conditions that may result in higher production
rates. It would be desirable to provide a method of determining a
stable operating condition for gas fluidized bed polymerization,
especially if operating in condensed mode, to facilitate optimum
design of the plant and the determination of desirable process
conditions for optimum or maximum production rates in a given plant
design. It would also be desirable to have a mechanism in
commercial gas-phase reactors to detect the onset of stickiness
that is a better or earlier indicator of the onset of stickiness
than are conventional techniques (e.g., monitoring the fluidized
bulk density as described in U.S. Pat. No. 5,352,749). Such a
mechanism would allow the operators to determine when conditions of
limiting stickiness are being approached, and enable them to take
corrective action before discontinuity events occur, while keeping
the reactors at or near conditions of maximum ICA concentration,
permitting higher production rates with substantially less
risk.
SUMMARY
[0015] An embodiment described herein provides a method for
determining a stickiness temperature in a resin. The method
includes adding the resin to a testing device comprising an
agitator. A vacuum may be pulled on the testing device and an
induced condensing agent (ICA) is added to the testing device. The
agitator is run and the temperature is increased until a value of a
torque used to run the agitator exceeds a limit.
[0016] Another embodiment provides a method for modeling a
stickiness temperature for a resin. The method includes measuring a
stickiness temperature of a resin at each of a plurality of
concentrations of induced condensing agent (ICA) in a testing
device. The density, melt index (MI), and high load melt index
(HLMI) are measured for the resin. A melt flow ratio (MFR) is
calculated by dividing the HLMI by the MI. An equivalent partial
pressure of the ICA is calculated by accounting for the partial
pressure of isomers that accumulate in a reactor. An equation is
determined that relates the stickiness temperature to the
equivalent partial pressure of the ICA, based, at least in part, on
the density, the MI, and the MFR of the resin. The equation may be
determined, for example, using a least squares analysis.
[0017] Another embodiment provides a method of controlling a
polymerization reaction to remain in a non-sticking regime. The
method includes measuring parameters for the polymerization
reaction including a reactor temperature and a concentration of an
induced condensing agent (ICA) in a polymerization reactor. An
equivalent partial pressure ((P.sub.ICA).sub.equiv) of the ICA is
calculated. The polymerization reaction is located in a two
dimension space defined by a reactor temperature dimension and a
((P.sub.ICA).sub.equiv) dimension. The location in the two
dimensional space is compared to an non-sticking regime, defined as
the space between an upper temperature limit (UTL) curve and a
lower temperature limit (LTL) curve. The parameters of the
polymerization reaction are adjusted to keep the polymerization
reaction within the non-sticking regime.
[0018] Another embodiment provides a system for controlling a
reactor. The system comprises a polymerization reactor including a
gas chromatograph, a temperature measurement system, and a control
system. The control system includes a processor and a storage
system, wherein the storage system includes machine readable
instructions. The machine readable instructions are configured to
direct the processor to measure a temperature of the polymerization
reactor using the temperature measurement system, measure a
concentration of an induced condensing agent (ICA) and another
condensable fluid in the polymerization reactor using the gas
chromatograph, calculate an equivalent partial pressure
((P.sub.ICA).sub.equiv) of the ICA in the reactor from the
concentration of the ICA and the other condensable fluid in the
polymerization reactor, locating the reactor operation in a two
dimension space defined by a reactor temperature dimension and a
((P.sub.ICA).sub.equiv) dimension, and compare the location in the
two dimensional space to an non-sticking regime defined as the
space between an upper temperature limit (UTL) curve and a lower
temperature limit (LTL) curve.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1A is a simplified schematic of a reaction system that
can be monitored and controlled in accordance with the methods
described herein.
[0020] FIG. 1B is a simplified block diagram of a control system
that can be used to control the reactor.
[0021] FIGS. 2A and 2B are plots showing a determination of melt
initiation temperature (MIT) curve from a series of differential
scanning calorimetry (DSC) curves.
[0022] FIGS. 3A and 3B are drawings of a testing device used to
measure stickiness temperature.
[0023] FIG. 4 is a process flow diagram showing a method for
measuring stickiness temperature.
[0024] FIG. 5 is a plot of temperature and stirrer speed during a
stickiness temperature test in the testing device of FIG. 3.
[0025] FIG. 6 is plot of partial pressure of isopentane (iC.sub.5)
versus testing device temperature, showing sticking for a resin
made using a metallocene catalyst.
[0026] FIG. 7 is a plot of stickiness temperature of the resin
versus the partial pressure of iC.sub.5 for the resin described
with respect to FIG. 6.
[0027] FIGS. 8A and 8B show plots of the model predictions versus
experimental data for various resins.
[0028] FIG. 9 is a plot of experimental stickiness temperature
versus predicted stickiness temperature for a variety of
resins.
[0029] FIG. 10 is a plot of residuals for each of the data points
of FIG. 9 showing average errors and maximum errors.
[0030] FIG. 11 is a plot of experimental data versus model
predictions.
[0031] FIG. 12 is a process flow diagram of a method for operating
a reactor in a non-sticking regime.
[0032] FIG. 13 is a plot of an operability window for avoiding
agglomeration of resins.
[0033] FIG. 14 is a plot of a pilot plant run showing operation in
a liquid regime in a first case study.
[0034] FIG. 15 is a plot of operations within a non-sticking regime
during a commercial plant run.
[0035] FIG. 16 is a plot of a pilot plant run showing operations in
a liquid regime that led to resin sticking.
[0036] FIG. 17 is a plot of a commercial run within a safe
operating window.
[0037] FIG. 18 is a plot of a pilot plant run performed in both a
sticking and liquid regime.
[0038] FIG. 19 is another plot of a pilot plant run performed in a
liquid regime leading to resin sticking.
DETAILED DESCRIPTION
[0039] Described herein are systems and methods for determining a
non-sticking operating regime (a "safe" regime) for a
polymerization reactor, and operating the polymerization reactor
within the non-sticking regime. As used herein, a non-sticking
operating regime indicates a regime in which resin sticking is not
problematic. The methods may include developing a model of the
non-sticking operating regime which may be integrated into a
control system or used on a separate system to recommend changes to
control reaction parameters.
[0040] The parameters used in developing a model of the
non-sticking operating regime may be based on values measured
during experimental determinations of resin stickiness. For any
single target resin, resin sticking can be measured as a function
of temperature and the equivalent partial pressure of an induced
condensing agent (ICA). For example, this may be performed by
placing the resin in a stirred autoclave reactor with a measured
amount of an ICA, such as isopentane (iC.sub.5), and slowly
increasing the temperature until the resin sticks, causing the
stirrer to stall. A model can then be built that predicts sticking
temperature as a function of the reactor temperature and an
equivalent partial pressure of the ICA. The equivalent partial
pressure is used to account for other condensable materials that
may be present in the reactor, such as hexene and various isomers
of hexene. The model is generally specific to the type of resin
used.
[0041] The model and dew point of the ICA used in the
polymerization reaction are used to determine a non-sticking
operating regime. During the polymerization reaction, the reactor
is controlled to hold the temperature and ICA concentration within
the non-sticking operating regime. The non-sticking operating
regime can provide guidance to help maximize production rates
without agglomeration by controlling the reaction parameters to
allow for increasing both temperature and ICA content, thus
allowing the removal of more heat of reaction.
[0042] Throughout this disclosure, the expression "diluent" (or
"condensable diluent" or "condensable diluent gas") denotes
condensable gas (or a mixture of condensable gases) present in a
polymerization reactor with polymer resin being produced. The
diluent is condensable at the temperatures encountered in the
process heat exchanger. Examples of diluents include induced
condensing agents (ICAs), comonomers, isomers of comonomers, and
combinations thereof. Such materials can include isobutane,
isopentane, hexene, and other materials in the reactor.
[0043] With reference to a product being produced by a continuous
reaction, the expression "instantaneous" value of a property of the
product herein denotes the value of the property of the most
recently produced quantity of the product. The most recently
produced quantity typically undergoes mixing with previously
produced quantities of the product before a mixture of the recently
and previously produced product exits the reactor. In contrast,
with reference to a product being produced by a continuous
reaction, "average" (or "bed average") value (at a time "T") of a
property herein denotes the value of the property of the product
that exits the reactor at time T.
[0044] The expression "dry polymer resin" (or "dry version" of
polymer resin) is used herein to denote polymer resin that does not
contain substantial amounts of dissolved gas. An example of dry
polymer resin is polymer that had been previously produced in a
polymerization reactor and then purged to substantially all
unreacted comonomers and ICAs that had been dissolved in the
polymer at the time of production. As discussed herein, a dry
version of polymer resin has significantly different melting
behavior than would the same polymer resin if it were in the
presence of a significant amount of condensable diluent gas and
comonomer.
[0045] The expression polyethylene denotes a polymer of ethylene
and optionally one or more C.sub.3-C.sub.10 alpha-olefins while the
expression polyolefin denotes a polymer of one or more
C.sub.2-C.sub.10 alpha-olefins.
[0046] FIG. 1A is a simplified cross-sectional view of a
polymerization system 100 that can be monitored and controlled in
accordance with embodiments. The polymerization system 100 includes
a fluidized bed reactor 102. The fluidized bed reactor 102 has a
bottom end 104, a top expanded section 106, a straight section 108,
and a distributor plate 110 within the straight section 108. A
fluidized bed 112 of granular polymer and catalyst particles is
contained within the straight section 108. The bed is fluidized by
the steady flow of recycle gas 114 through the distributor plate
110. The flow rate of the recycle gas 114 is regulated to circulate
the fluidized bed 112, as illustrated in FIG. 1A.
[0047] The polymerization system 100 has a catalyst feeder 116 for
controlling the addition of polymerization catalyst 118 to a
reaction zone 120 within the fluidized bed 112. Within the reaction
zone 120, the catalyst particles react with the ethylene and
comonomer and optionally other reaction gases to produce the
granular polymer particles. As new polymer particles are produced,
other polymer particles are continually withdrawn from the
fluidized bed through a product discharge system 122. After passing
through the product discharge system 122, the polymer granules are
degassed (or "purged") with a flow of inert nitrogen to remove
substantially all of the dissolved hydrocarbon materials.
[0048] The polymerization system 100 also has a cooling loop which
includes a recycle gas line 124, a circulating gas cooler 126, and
a compressor 128, coupled with the fluidized bed reactor 102.
During operation, the cooled circulating gas from the cooler 126
flows through inlet 130 into the fluidized bed reactor 102, then
propagates upward through the fluidized bed 112 and out from the
fluidized bed reactor 102 via outlet 132.
[0049] The expanded section 106 is also known as a "velocity
reduction zone," and is designed to minimize the quantities of
particle entrainment from the fluidized bed. The diameter of the
expanded section 106 generally increases with the distance from
straight section 108. The increased diameter causes a reduction in
the speed of the recycle gas 114, which allows most of the
entrained particles to settle back into the fluidized bed 112,
thereby minimizing the quantities of solid particles that are
"carried over" from the fluidized bed 112 through the recycle gas
line 124.
[0050] One or more temperature sensors 134 may be located in the
fluidized bed, and used with a control system and the cooling loop
to control the temperature T.sub.rx of the fluidized bed 112 near
the process set-point. Heated reactor gas 136, which carries heat
energy from the fluidized bed reactor 102, is withdrawn from the
outlet 132 and is pumped by the compressor 128 to the cooler 126
wherein the temperature of the heated reactor gases 136 is reduced,
and any ICAs present are condensed to a liquid. The recycle gas 114
from the cooler 126, including any condensed liquids, flows to the
reactor inlet 130 to cool the fluidized bed 112. Temperature
sensors (not shown) near the inlet and outlet of the cooler 126 may
provide feedback to a control system (FIG. 1B) to regulate the
amount by which cooler 126 reduces the temperature of the recycle
gas 114 entering the fluidized bed reactor 102.
[0051] The fluidized bed reactor 102 may also include skin
temperature sensors 132, mounted in positions along a wall of the
straight section 108 of the fluidized bed reactor 102 so as to
protrude into the bed from the reactor wall by a small amount,
e.g., about one eighth to one quarter of an inch. The skin
temperature sensors 132 are configured and positioned to sense the
temperature T.sub.w of the resin near the wall of the fluidized bed
reactor 102 during operation.
[0052] The temperature sensors 134 in the fluidized bed 112 can
include a resistance temperature sensor positioned and configured
to sense bed temperature during reactor operation at a location
within the fluidized bed reactor 102 away from the reactor wall.
The resistance temperature sensor can be mounted so as to protrude
into the bed more deeply than the skin temperature sensors 132,
e.g., about 8 to 18 inches away from the reactor wall.
[0053] Other sensors and other apparatuses may be employed to
measure other reaction parameters during a polymerization reaction.
The reaction parameters may include instantaneous and bed-averaged
resin product properties, e.g., melt index and density of the
polymer resin product being produced by the polymerization system
100 during a polymerization reaction. Resin product properties are
conventionally measured by periodically sampling the resin as it
exits the reactor, e.g., about once per hour, and performing the
appropriate tests in a quality control laboratory. The results of
these tests may be used to adjust the model during operations.
[0054] Other measured reaction parameters may include reactor gas
composition, e.g., concentrations and partial pressures of reactant
gases, ICAs, inert gases, and isomers of other materials, such as
nitrogen, inert hydrocarbon, and the like. The reactor gas
composition may be measured with a gas chromatograph system
138.
[0055] The process control variables are controlled to obtain the
desired productivity for the polymerization system 100 and
properties for the resin. For example, the parameters used to
control gas phase composition within the fluidized bed reactor 102
can include the concentration of ICAs and comonomer, the partial
pressure of monomer, and the type and properties of catalysts, and
the temperature of the reaction process. For example, it is known
that a polymerization reaction during a transition may be
controlled by controlling process control variables to ensure that
the product, e.g., the granular resin, has properties compliant
with an initial specification set at the start of the transition,
the product produced during the transition ceases to comply with
the initial specification set at a first time, and the product has
properties compliant with a final specification set at the end of
the transition. In the methods described herein, stickiness of the
resin during the reaction is controlled by a control system
adjusting (or regulating) the temperature and the equivalent
partial pressure of the ICA used in the reaction.
[0056] FIG. 1B is a simplified block diagram of a control system
140 that can be used to control the polymerization system 100. The
control system 140 may be a distributed control system (DCS), a
direct digital controller (DDC), a programmable logic controller
(PLC), or any other suitable system or combination of systems
capable of accepting data and proposing new control settings based
on the model described herein. The control system 140 has a
processor 142 that implements machine readable instructions from a
storage system 144. Illustrative processors may include a single
core processor, a multiple core processor, a virtual processor, a
virtual processor in a cloud implementation, an application
specific integrated circuit (ASIC), or any combinations of these
systems. Illustrative storage devices 144 can include random access
memory (RAM), read only memory (ROM), hard drives, virtual hard
drives, RAM drives, cloud storage systems, optical storage systems,
physically encoded instructions (for example, in an ASIC), or any
combinations of these systems.
[0057] The storage system 144 may include a stickiness model 146
and a two dimensional representation, or map, of a non-sticking
regime 148 that uses process and resin data to generate control
settings for the polymerization system 100. Adjustments to control
settings may be determined based on the output of temperature
sensors 134 and 132, the GC 138, and lab data 150, among others.
After determining new control settings, the control system 140 may
make, or recommend, adjustments, for example, to the process
cooling systems 152, the ICA addition and recycling systems 154,
flow control systems 156, and kill systems 158, among others. Thus,
the control variables can be used in concert with the model
described herein to adjust reactor parameters to keep the reactor
operations in a safe operating regime.
[0058] The methods described herein allow reactor production rates
to be increased, e.g., by increasing reactor temperature and ICA,
while avoiding the conditions in the reactor that may lead to
excessive stickiness or the formation of liquids in the reactor.
These methods use available process and resin property data, and
can be implemented at plant sites either on-line, in process
control systems, or off-line, e.g., using spreadsheets, data bases,
or application specific programs.
[0059] As described herein, the model compensates for compounds
that are present in the polymerization system 100 during
polymerization reactions, such as polyethylene polymerization
reactions using metallocene catalysts. For example, isomers of
various co-monomers are relatively inert and may accumulate in
reactors fitted with recovery systems. Because these isomers can be
present in substantial amounts, they can have an impact on the
stickiness. Accordingly, models that merely use the ICA
concentration may not accurately predict the operating regimes that
avoid sticking.
[0060] The gas chromatograph (GC) 138 can be used to provide
composition data for isomers, in addition to the ICA. For example,
the data from the GC may be analyzed to characterize separately the
1-hexene comonomer and the C.sub.6 and C.sub.6+ isomers of the
comonomer in samples of cycle gas from the reactor. In some
commercial polymerization reactions, isomer concentrations as high
as 2.5 mole percent (of the total reactor gas) may be obtained in
the reactor system, which can be substantially higher than the
approximately 1 to 1.5 mole percent concentration of 1-hexene
comonomer. At these levels, the isomers themselves (excluding the
comonomer) can produce an increased tendency of the resin to stick
and agglomerate. Such data can be incorporated into the model as a
term called the "effective partial pressure" of the ICA. The
effective partial pressure of the ICA adjusts the partial pressure
of the ICA based on the amount of the ICA present.
Stickiness Testing to Develop Model Parameters
[0061] In U.S. Pat. No. 7,774,178 (the '178 patent), tests run in a
pilot plant reactor, in the absence of polymerization, measured the
resin stickiness temperature for a variety of Ziegler-Natta and
metallocene catalyzed resins. The sticking temperature was measured
for these resins with isopentane and without isopentane present in
the cycle gas. The other process conditions held constant for each
test included ethylene partial pressure, hydrogen concentration,
and hexene concentration. Data from the bed sticking temperature
experiments were compared to a melt initiation temperature (MIT)
model which was used to specify a process temperature limit for
polyethylene products based on resin properties and reaction
conditions.
[0062] FIGS. 2A and 2B are plots showing a determination of melt
initiation temperature (MIT) curve from a series of differential
scanning calorimetry (DSC) curves. In FIG. 2A, the x-axis 202
represents the temperature in degrees Celsius, while the y-axis 204
represents the heat flow. An MIT 206 is identified as an
interception point of the tangent lines 208 and 210 between two
sections of the DSC curve. The steeper tangent line 210 represents
a higher energy flow, which occurs as the resin changes phase. A
sequence of MIT 206 values can be plotted against the density of
the resin, as shown in FIG. 2B. In FIG. 2B, the x-axis 212
represents the density, while the y-axis 214 represents the values
for the MIT of each of the individual resins, as determined by the
DSC plots.
[0063] From the data, it was determined that an MIT model generally
predicted a larger decrease in melt initiation temperature due to
the presence of hydrocarbons compared to the change in sticking
temperature seen experimentally, e.g., a displacement was seen
between the MIT for the dry resin versus resin in the presence of
hydrocarbons. A model was developed that correlated the sticking to
theoretical properties of the resins involved. In several cases,
the modeled change in MIT agreed with the observed change in
sticking temperature.
[0064] In addition to the actual sticking temperatures, the '178
patent identified that isopentane depresses the sticking
temperature of metallocene resins. At about 15 mol % isopentane in
the cycle gas, the sticking temperature is depressed by 5-6.degree.
C. Further, the low concentrations of hexene co-monomer typically
used with metallocene catalysts did not affect resin sticking
temperature.
[0065] However, the '178 patent identified that high speed
fluidized bulk density signal and skin thermocouple analysis did
not provide any significant improvement in determining resin
sticking temperature. Further, the melt-initiation temperature
calculations did not accurately predict pilot plant determined
sticking temperatures or the magnitude of the effect when
isopentane was present in the reactor.
[0066] In another study conducted in the same pilot plant, resin
stickiness temperature was measured using bed settling tests at
different concentrations of condensing agents (isohexane and
iC.sub.5) for resins made with the various catalysts of the
previous study to allow comparison with the previous results. It
was determined that the equivalent concentration of the isohexane
is approximately 2.5 times lower than that of isopentane
(iC.sub.5). These results can be used to validate the model created
in this study to capture the operability window for metallocene
catalysts.
Lab Experimental Setup and Sample Data
[0067] Stickiness tests were conducted in a testing device, as
described herein, to gain a better understanding of the operability
window in resin production with various metallocene catalysts.
Through tests on a number of catalysts it was determined that
unique parameters could be developed for each of a number of resins
made using different catalysts. The stickiness risk associated with
the resin made with these catalysts could be reduced by using a
combination of temperature, MI/density/MFR targets, ethylene
partial pressure, induced condensing agent (iC.sub.5 or isohexane)
concentration, and continuity additives.
[0068] FIGS. 3A and 3B are drawings of a testing apparatus 300 that
may be used to measure stickiness temperature. The apparatus 300
uses an autoclave reactor 302 that has a mixing motor 304. The
mixing motor 304 rotates a mixer blade 306 that is inserted into a
bed of resin in the autoclave 302. The temperature in the autoclave
302 is slowly raised until the torque required to turn the mixer
blade 306 overcomes the torque available from the mixing motor 304,
and the mixer blade 306 stops rotating, indicating the temperature
at which the resin sticks or agglomerates. An illustrative mixing
motor 304 that may be used is an air driven motor Model
#2AM-NCC-16, manufactured by Gast Manufacturing, Inc. In FIG. 3A
the mixing motor 304 turns a magnetic coupler 308, which in turn
spins the mixer blade 306. An illustrative magnetic coupler 308
that may be used is a MagneDrive.RTM. 2, manufactured by Autoclave
Engineers.
[0069] The testing device 300 can run the stickiness experiments at
dry conditions, and also in the presence of induced condensing
agents, such as isopentane (iC.sub.5) and isohexane (iC.sub.6).
Although details are presented for a specific testing apparatus
300, it will be understood that any device capable of consistently
measuring the torque of a rotating mixer blade can be used to
develop the model for a particular resin.
[0070] FIG. 4 is a process flow diagram showing a method 400 for
measuring stickiness temperature. The method 400 may be used, for
example, with the testing device 300 of FIGS. 3A and 3B. The method
400 begins at block 402 with the sieving of a resin sample. The
sieving removes agglomerates that can interfere with the stickiness
measurements. For example, the resin sample can be sieved through a
number 12 mesh (having about 1.68 mm openings). At block 404, a
measured amount of the resin is added to the testing device. For
example, about 300 g of sieved polymer resin can be added to the
testing device 300 of FIGS. 3A and 3B. At block 406, the testing
device is placed under a vacuum prior to adding an ICA, such as
iC.sub.5, to ensure proper measurement of the partial pressure of
the ICA. At block 408 an amount of ICA is added to the testing
device to reach a predicted partial pressure. For example, using
the testing device 300 of FIGS. 3A and 3B, five levels are tested
for each resin tested, corresponding to 0, about 25 cc, about 50
cc, about 100 cc, or about 200 cc of added iC.sub.5. At block 410,
the testing device is then stirred at a constant rate. For example,
using the air-operated stirring motor 304 of the testing device 300
of FIGS. 3A and 3B, a constant nitrogen pressure of about 30 psi
(about 207 kPa) is applied to hold a constant torque.
[0071] At block 412, the reactor temperature is increased slowly
until a torque limit is exceeded. For example, using the testing
device 300 of FIGS. 3A and 3B, when the torque limit is exceeded
the mixing motor stops, indicating the stickiness temperature. The
testing is not limited to the stopping of an air-operated mixing
motor. For example, a torque measurement device may be used to
measure the torque applied to the testing device to determine when
the torque exceeds a preset target.
[0072] FIG. 5 is a plot 500 of temperature and stirrer speed during
a stickiness temperature test in the testing device 300 of FIGS. 3A
and 3B. The x-axis 502 represents the test duration in minutes,
while the left y-axis 504 represents the temperature of the testing
device in degrees Celsius. The right y-axis 506 represents the
mixer speed in RPM. During the test, the temperature 508 in the
reactor is slowly increased. For most of the test, the mixer speed
is relatively constant. However, as the resin starts to
agglomerate, the mixer speed starts to slow, as indicated by
reference number 512, before stopping. The point at which the mixer
speed drops to zero is the stickiness temperature 514. As noted,
the test is repeated at a number of different addition levels of
the ICA (e.g., iC.sub.5), providing data that can be used to
characterize the sticking temperature.
[0073] FIG. 6 is plot 600 of partial pressure of isopentane
(iC.sub.5) versus testing device temperature, showing sticking for
a resin made using a metallocene catalyst. In this example, the
resin has a melt index (MI) of 41.72, a density of 0.954 g/cc, and
a melt flow ratio (MFR) of 18.5. In the plot 600, the x-axis 602
represents the temperature in degrees Celsius, while the y-axis 604
represents the partial pressure of iC.sub.5.
[0074] A reference curve 606 indicates the partial pressure of the
iC.sub.5 at the testing device temperature. Subsequent curves 608,
610, 612, and 614 indicate the partial pressure of the resin after
the addition of about 200 cc of iC.sub.5 608, about 100 cc of
iC.sub.5 610, about 50 cc of iC.sub.5 612, and about 25 cc of
iC.sub.5 614. The points 616, 618, 620, and 622 at which each curve
ends indicates the stickiness temperature at the respective partial
pressure.
[0075] FIG. 7 is a plot of stickiness temperature of the resin
versus the partial pressure of iC.sub.5 for the resin described
with respect to FIG. 6. Like numbered items are as discussed with
respect to FIG. 6. The y-axis 702 represents the stickiness
temperature in degrees Celsius. The resin stickiness temperature
704 provides a substantially linear correlation with the iC.sub.5
concentration in the reactor.
Model Development
[0076] The stickiness tests described with respect to FIGS. 1-7
were performed on 12 different resins generated by a three
metallocene catalysts, herein termed Catalyst 1, Catalyst 2, and
Catalyst 3. For each resin, five different iC.sub.5 levels were run
to get a reliable correlation, as described with respect to FIG. 7.
Resin density varied from 0.912 g/cc to 0.954 g/cc, MI varied from
0.5 to 42 g/10 min, and MFR varied from 16 to 36. The stickiness
temperature was correlated as a linear function of iC.sub.5
concentration. The results from the testing allowed the development
of a model to predict the resin sticking temperature T.sub.stick
that encompassed the metallocene catalyst systems tested. The
coefficients of the linear functions were generated as a function
of resin density, MI and MFR. Although the test resins were made
using metallocene catalysts, as the model is empirically generated,
the parameters may be adjusted for other catalyst systems, for
example, by repeating the model development runs for those
resins.
[0077] The basic model equation used to predict the resin sticking
temperature for resins generated by these three catalysts is shown
in Eqn. 1.
T.sub.stick=-C.sub.1*(P.sub.iC5).sub.equiv+C.sub.2 Eqn. 1
[0078] In Eqn. 1, the parameters identified as C.sub.1 and C.sub.2
are determined as shown in Eqns. 2 and 3, respectively. The data
collected from the stickiness temperature measurements described
above can be combined with laboratory data and used in a
multivariable least squares analysis to generate the coefficients
for the equations.
C.sub.1=1.175.times.10.sup.-3*D.sup.-59.736*MI.sup.0.641 Eqn. 2
C.sub.2=180.6*D.sup.3.07*MFR.sup.-0.077 Eqn. 3
[0079] In Eqns. 2 and 3, D represents the density of the resin in
g/cc, MI represents the melt index of the resin (as measured by
ASTM D 1238 190.degree. C. with 2.16 kg weight), and MFR represents
the ratio of the HLMI (as measured by ASTM D 1238 at 190.degree. C.
with 21.6 kg weight) to the MI. The excess isomers of the hexane,
e.g., the hexanes, are accounted for by adjusting the partial
pressure of the ICA (iC.sub.5) to form an effective partial
pressure, as shown in Eqn. 4.
(P.sub.iC5).sub.equiv=P.sub.iC5+2.7*P.sub.6 Eqn. 4
[0080] In Eqn. 4, P.sub.6 represents the partial pressure of the
hexanes in the reactor at the operating temperature. The
coefficient, 2.7, can be changed to reflect the ratio of the
partial pressure of the hexanes to the partial pressure of the
iC.sub.5, or other ICA used.
[0081] FIGS. 8A and 8B show plots of model versus experimental data
for the various resins. Like numbered items are as defined with
respect to FIGS. 6 and 7. For each plot, the individual resin
parameters are shown above the plot as MI/Density/MFR. In each
plot, the individual measurements are shown as the data points,
while the output from the model is shown as a line. As seen in
FIGS. 8A and 8B, the model substantially predicts the experimental
data from lab experiments for resins formed by the different
metallocene catalysts.
[0082] FIGS. 9 and 10 illustrate the accuracy of the model. FIG. 9
is a plot 900 of experimental stickiness temperature 902 versus
predicted stickiness temperature 904 for a variety of resins. FIG.
10 is a plot 1000 of residuals 1002 for each of the data points
1004 of FIG. 9 showing average errors 1006 and maximum errors 1008.
The model has an average error of 2.degree. C. and the maximum
error is about 5.degree. C.
Stickiness Temperature Model Validation
[0083] The model predictions were validated against bed settling
experiments done in a pilot plant scale, gas-phase fluidized bed
reactor. In these experiments, a non-reacting run was performed to
determine the temperatures at which the resin agglomerated. The
test was started by drying the reactor with a high purity nitrogen
purge at elevated temperatures, e.g., greater than about 75.degree.
C. The test resin sample was passed through a 10-mesh screen
(having about 0.25 mm openings) to remove agglomerates, and then
charged to the reactor. Using the nitrogen flow, the resin was
dried to about 10 parts-per-million by volume (ppmv) of water. The
test resin was heated to at least 85.degree. C. and the reactor
conditions were adjusted to the desired ethylene partial pressure,
comonomer concentration, and ICA (iC.sub.5) concentration. A sample
was then collected for measurement of melt flow and particle
size.
[0084] The resin temperature was then increased by about 2.degree.
C. or 3.degree. C. at a rate of about 1.degree. C. every 30
minutes. Once the target temperature was reached, the temperature
was allowed to stabilize for 30 minutes. The fluidized bulk
density, bed weight, and skin temperature were noted. The
circulation compressor was then turned off, and the bed was allowed
to settle on the distributor plate. After about 15 minutes, the
circulation compressor was turned back on to fluidize the resin. If
the bed did not fluidize, the test was ended. If the bed did
fluidize, the reactor was given about five minutes to stabilize
before initiating the next increase in temperature. The procedure
was repeated until the bed agglomerated to the point that
fluidization was lost.
[0085] The properties of the resins used in the experiments,
reactor conditions, experimental stickiness temperatures, and model
predictions are tabulated in Table 1, below. The temperature at
which fluidization was lost is shown in the column labeled "T-s,
exp, .degree. C." The comparative value predicted by the model
described herein is shown in the column labeled "T-s, model,
.degree. C."
[0086] FIG. 11 is a plot of experimental data versus model
predictions. In FIG. 11, the x-axis 1102 represents the predicted
value of the stickiness temperature, while the y-axis 1104
represents the measured stickiness temperature. The experimental
stickiness temperatures from the pilot plant runs, shown as points
1108, and the model predictions, line 1106, show substantial
agreement.
[0087] Generally, the model predictions had an average error of
3.degree. C. from the bed settling experiments. Considering the
size difference with in the experimental setup and variations
within the reactor conditions, the model effectively predicts the
measured data.
TABLE-US-00001 TABLE 1 Polyethylene Resin Sticking Temperature
Tests iC.sub.5 C6 T-s, T-s, Resin Density MI MFR mol % mol %
P-iC.sub.5 exp, .degree. C. model, .degree. C. Catalyst 3 0.9194
0.96 38.5 0.036 0.000 0.112 110 108 Catalyst 1 0.9117 1.05 15.6
0.032 1.185 10.052 106.5 109 Catalyst 2 0.9189 1 26.4 0.015 0.000
0.047 106 111 Catalyst 2 0.9164 0.84 23.2 14.1 1.333 55.047 101 100
Catalyst 1 0.916 0.98 15.9 0.023 0.000 0.072 113 114 Catalyst 1
0.9171 0.99 15.9 0.027 1.259 10.658 112 112 Catalyst 1 0.9162 1 20
0.027 1.259 10.658 108 110 Catalyst 2 0.9354 6.6 20 0.032 0.000
0.100 120 119 Catalyst 2 0.9353 6.43 20.1 8.7 0.667 32.655 116 112
Catalyst 2 0.9187 1.09 32.8 0.031 0.000 0.096 109 109 Catalyst 2
0.9187 1.12 32.8 0.031 1.333 11.292 106 107 Catalyst 2 0.9169 0.66
33.6 0.032 1.778 15.028 100 106 Catalyst 2 0.9168 0.67 33.5 14.4
1.148 54.425 93.95 99.35
Using the Stickiness Temperature Model to Generate a Non-Sticking
Operating Regime
[0088] The stickiness temperature model can be combined with dew
point calculations to define an operability window, e.g., a
non-sticking operating regime in a map of reactor operations, for
the manufacturing of resins made with the currently tested
metallocene catalysts. Other models may be created that are
specific to resins made by other metallocene catalysts, Ziegler
catalysts, or chromium catalysts, among others. As the model is
based on the empirical measurements of resin properties and reactor
conditions, resins generated from mixtures and combinations of
catalysts may also be made.
[0089] FIG. 12 is a process flow diagram of a method 1200 for
operating a reactor in a non-sticking regime. The method 1200
starts at block 1202 with the development of a model for the
stickiness temperature. The model may be developed, for example,
using measurements made with the method 400 discussed with respect
to FIG. 4, and fitting the measured data to develop parameters for
Eqns. 1-4 discussed with respect to FIG. 7. At block 1204, a dew
point for the ICA (e.g., iC.sub.5) can be determined at each of the
equivalent partial pressures for the ICA. The dew point indicates
the conditions of temperature and equivalent partial pressures of
ICA below which liquid ICA starts to condense in the reactor. The
formation of liquid ICA can increase the likelihood of
agglomeration and case operational issues by condensing in
instrumentation taps.
[0090] At block 1206, the stickiness temperature and the dew point
can be used to identify a non-sticking regime, as discussed with
respect to FIG. 13. Once a non-sticking regime is established, at
block 1208 the ICA concentration and temperature can be adjusted to
remain in the safe operating regime. For example, a startup of a
new resin production run may be conducted at a slow initial
production rate. The ICA concentration, temperature, or both may
then be slowly increased to increase the production rate, while
keeping the reactor within the safe operating regime. If a reactor
upset causes operations to leave the non-sticking regime, or
indicates that sticking may be imminent, the control system can
recommend changes to force the operations back into the
non-sticking regime, for example, by lowering or raising the
temperature, by decreasing the amount of ICA returned from the
recycle system, or by injecting a kill solution to slow or stop the
reaction, among others. The control system may identify problematic
operations before the reactor is shut down by agglomeration. The
method 1200 is discussed further with respect to FIGS. 13-19.
[0091] FIG. 13 is a plot 1300 of an operability window for avoiding
agglomeration of resins. As shown in the plot 1300, the temperature
of the reactor and the equivalent partial pressure of the ICA
define a two dimensional space, or map, for reactor operations. In
the plot 1300, the x-axis 1302 represents the equivalent partial
pressure of the ICA, i.e., iC.sub.5 in this example. The equivalent
partial pressure of the iC.sub.5 can be calculated using the
formula in Eqn. 4. The y-axis 1304 represents the sticking
temperature in degrees Celsius. The predicted stickiness
temperature (T.sub.stick) 1306 from the model is plotted as the
upper dashed line. To provide a limit, the T.sub.stick 1306 is
adjusted to a lower value to provide a safety margin, using Eqn
5.
T.sub.reactor,max=T.sub.stick-UTD.sub.max Eqn. 5
[0092] In Eqn. 5, T.sub.reactor,max represents the maximum
operating temperature that can be used without a substantial risk
of agglomeration. UTD.sub.max represents an upper temperature delta
that provides a buffer between the stickiness temperature measured
in the experiments and the temperature at which the stickiness may
actually begin. Typically, a 10.degree. C. margin is allowed below
the stickiness temperature for the reactor to operate safely. Thus,
the value of the T.sub.reactor,max provides the upper temperature
limit 1308 for the reactor.
[0093] In FIG. 13, the dew point (T.sub.dew) 1310 is plotted as the
lower dashed line. Similar to the maximum operating temperature,
the dew point 1310 can be adjusted to provide a wider margin of
safety using Eqn. 6.
T.sub.reactor,min=T.sub.dew+LTD.sub.max Eqn. 6
[0094] In Eqn. 6, LTD.sub.max is a lower temperature delta that
accounts for capillary condensation, which occurs about 10.degree.
C. above the actual dew point of the ICA in the reactor. The value
of the T.sub.reactor,min provides the lower temperature limit 1312
of the reactor.
[0095] The upper temperature limit 1308 and the lower temperature
limit 1312 define a non-sticking regime 1314 for the reactor within
the two dimensional space. Another area defined by these limits
1308 and 1312 is a sticking regime 1316 in which the resin begins
to melt and therefore becomes sticky. Other areas include a
stick+liquid regime 1318, in which both resin melting and iC.sub.5
(or other ICA) condensation make the resin sticking more likely.
Below the upper temperature limit 1308 and the lower temperature
limit 1312 is a liquid regime 1320, in which the iC.sub.5 (or other
ICA) starts to condense and make the resin sticky.
[0096] The square 1322 represents a current reactor condition,
mapped by the temperature and equivalent partial pressure of the
iC.sub.5. To operate the reactor without agglomeration, an operator
maintains the square 1322 representing the current reactor
conditions within the non-sticking regime 1314. The operator can
change reactor parameters to move the square 1322 towards the neck,
at which the limits 1308 and 1312 meet, to increase productivity,
while still staying within the non-sticking regime 1314. It can be
noted that as the square 1322 is pushed closer to the neck,
operations becomes less flexible and the room for error dwindles,
making process upsets, such as temperature and concentration
excursions, more problematic.
Non-Sticking Operating Regime Model Validation
[0097] A series of polymerization experiments were conducted in a
pilot plant reactor to determine the stickiness temperature as a
function of iC.sub.5 concentration of the low density (0.918 g/cc)
and VLDPE (0.912 g/cc) resins made with both Catalyst 1 and
Catalyst 2. The data from the run are shown in Table 2, and the
results may be used to validate the operability window predicted by
the model. Also included are the data from two commercial runs with
Catalyst 1 in a commercial size production facility. Each of the
cases is illustrated with respect to one of the following figures,
as indicated in Table 2.
TABLE-US-00002 TABLE 2 Experimental Data from Pilot Plant and
Commercial Plant Runs CASE 1 CASE C1 CASE 2 CASE C2 CASE 3 CASE 4
FIG. 14 FIG. 15 FIG. 16 FIG. 17 FIG. 18 FIG. 19 Catalyst 1 Catalyst
1 Catalyst 1 Catalyst 1 Catalyst 2 Catalyst 2 facility size pilot
plant commercial pilot plant commercial pilot plant pilot plant Rxn
T (.degree. C.) 80 80 85 85 85 80 iC.sub.5 (mol %) 17.29 12.1 18.9
17 20.3 18.26 iC.sub.5 PP, psia 58.5 64.1 74 66.4 Cycle Gas 72.4
75.02 77 74.1 DP (.degree. C.) Density 0.9122 0.9122 0.9195 0.9175
0.913 0.9174 MI 0.764 1 0.9 0.96 0.6 0.838 MFR 16.9 16.9 16.2 16.2
16.2 30.8
[0098] In the Catalyst 1 runs made in the pilot plant, when the
iC.sub.5 concentration increased beyond a certain limit,
condensation occurred in the taps which made it difficult to
control the bed level. In pilot plant runs made with Catalyst 2,
formation of chunks, sheeting and expanded section fouling were
observed above a certain iC.sub.5 concentration.
[0099] FIG. 14 is a plot 1400 of a pilot plant run showing
operation in a liquid regime in a first case study. Like numbered
items are as described with respect to FIG. 13. The run used
Catalyst 1 to produce a very low density polyethylene (VLDPE)
resin, with the resin and reactor parameters described under Case 1
in Table 2. The square 1402 lies below the lower reactor limit 1312
in the liquid regime 1320 where capillary condensation is expected.
The square 1402 indicates reactor operations at 17.3 mol % iC.sub.5
and a reactor temperature of 80.degree. C., above which the
operation resulted in condensation in the taps and loss of control
in the bed level. The operations may be recovered by lowering the
iC.sub.5 concentration in the reactor, as indicated by an arrow
1404, to lower the equivalent partial pressure of the iC.sub.5, and
shift operations back into the non-sticking regime 1314.
[0100] FIG. 15 is a plot 1500 of operations within a non-sticking
regime during a commercial plant run. Like numbered items are as
described with respect to FIG. 13. The plot 1500 shows the model
prediction of the operability window for the commercial production
of a VLDPE resin with Catalyst 1, with the resin and reactor
parameters described under Case C1 in Table 2. The square 1502
indicates operations at 12.1% iC.sub.5 and a reactor temperature of
80.degree. C. The square 1502 lies within the non-sticking regime
1314, very close to the neck where the limits 1308 and 1312 meet,
which means it is already near the maximum safe production
limit.
[0101] FIG. 16 is a plot 1600 of a pilot plant run showing
operations in a liquid regime 1320 that led to resin sticking. Like
numbered items are as described with respect to FIG. 13. The plot
1600 shows the model prediction of the operability window for the
pilot plant production of a metallocene linear low density
polyethylene (mLLDPE) resin with Catalyst with the resin and
reactor parameters described under Case 2 in Table 2. The square
1602 indicates operations at 18.9% iC.sub.5 and a reactor
temperature of 85.degree. C., which was just below the lower
temperature limit 1312 in the liquid regime 1320. In this area
capillary condensation was expected, and, subsequently, the reactor
did have condensation in the taps and a loss of control in the bed
level. The operations may be recovered by raising the temperature,
as indicated by an arrow 1604, to lower the condensation of the
iC.sub.5, and shift operations back into the non-sticking regime
1314.
[0102] FIG. 17 is a plot 1700 of a commercial run within a
non-sticking regime 1314. Like numbered items are as described with
respect to FIG. 13. The plot 1700 shows the model prediction of the
operability window for commercial production of mLLDPE resin made
with Catalyst 1 with the resin and reactor parameters described
under Case C2 in Table 2. The reactor operations point, indicated
by the square 1702 at 17% iC.sub.5 and a reactor temperature of
85.degree. C., was within the non-sticking regime 1314, but was
close to the lower temperature limit 1312. Any increase in the
iC.sub.5 concentration, or decrease in temperature, may move
operations into the liquid regime 1320 causing stickiness or loss
of reactor control in the resin. As the reactor temperature is
often determined by the requirements for MFR control, the liquid
regime 1320 can be avoided by adjusting the iC.sub.5 level at that
temperature, as indicated by an arrow 1704.
[0103] FIG. 18 is a plot 1800 of a pilot plant run performed in
both a sticking and liquid regime 1318. Like numbered items are as
described with respect to FIG. 13. The plot 1800 shows the
operating window for the production of VLDPE resin with Catalyst 2
with the resin and reactor parameters described under Case 3 in
Table 2. The reactor operations point, indicated by the square 1802
at 20.3% iC.sub.5 and a reactor temperature of 85.degree. C.,
landed in the stick and liquid regime 1318 where both the resin
melting and liquid condensation occur. As could be expected,
operations in this regime 1318 resulted in expanded section fouling
and chunks in the reactor.
[0104] FIG. 19 is another plot 1900 of a pilot plant run performed
in a liquid regime 1318 leading to resin sticking. Like numbered
items are as described with respect to FIG. 13. The plot 1900 shows
the operating window for the production of mLLDPE resin with
Catalyst 2 with the resin and reactor parameters described under
Case 4 in Table 2. The reactor operations point, indicated by the
square 1902 at 18.3% iC.sub.5 and a reactor temperature of
80.degree. C., resided in the liquid regime 1320 where liquid
condensation occurs, causing the resin to stick. Operating at this
point resulted in chunking the entire bed in the reactor.
[0105] As indicated by the examples in FIGS. 14-19, the model
predicts substantially predicts the operating window both in a
pilot plant reactor and in a commercial plant. The model can be
used to set optimum operating conditions to maximize the production
rate by increasing the iC.sub.5 concentration while still remaining
in the non-sticking regime 1314. Further, the model can be used to
identify operations in problematic regimes 1316, 1318, and 1320,
and adjust the reactor conditions before operational problems or
shut-downs occur.
[0106] The methods described herein can be used in determining an
empirical model to prevent sticking in a reactor. For example, the
stickiness temperature varies linearly with the iC.sub.5 partial
pressure over a wide range of resin properties. The stickiness
temperature for resins made with metallocene catalysts has been
correlated to density, MI, MFR, temperature, and the equivalent
partial pressure of the ICA in the reactor. The correlation was
validated with bed settling tests in a pilot reactor and found to
agree within .+-.3.degree. C. Further, the effect of particle size
on resin stickiness temperature is observed to be negligible within
the experimental error for resin melting and iC.sub.5 condensation.
Thus, the methods described herein use the stickiness temperature
correlation and dew point calculations to determine a safe
operability window for polymerization processes using metallocene
catalysts.
Test Conditions and Materials
[0107] In Table 1 and elsewhere herein polymer density refers to
density measured in accordance with ASTM 1505 and ASTM D-1928. A
plaque is made and conditioned for one hour at 100.degree. C. to
approach equilibrium crystallinity. Measurement for density is then
made in a density gradient column. Throughout this disclosure, the
abbreviation "MI" (or I.sub.2) denotes melt index. MI is measured
in accordance with ASTM D1238 (at 190.degree. C., 2.16 kg weight).
Flow index (FI or I.sub.21) is measured in accordance with ASTM
D1238 (190.degree. C., 21.6 kg). The melt index ratio (MIR) is
calculated by determining the ratio of FI to MI (FI/MI).
[0108] In Table 1 and elsewhere herein, Catalyst 1 is a metallocene
catalyst that is commercially available from Univation
Technologies, LLC as XCAT.TM. HP-100 Catalyst. Catalyst 2 is a
silica supported bis(n-propyl-cyclopentadiene) hafnium dimethyl
that was activated with methylalumoxane. Catalyst 3 is a
metallocene catalyst that is commercially available from the
Univation Technologies, LLC as XCAT.TM. EZ-100 Catalyst.
Reactors
[0109] The methods described herein may be used in any number of
pilot plant or commercial size reactors including any number of
designs. For example, the model can be used in commercial-scale
reactions, such as gas-phase fluidized-bed polymerization
reactions, that can be monitored and optionally also controlled in
accordance with the invention. Some such reactions can occur in a
reactor having the geometry of the fluidized bed reactor 102
discussed with respect to FIG. 1.
[0110] In some embodiments, a continuous gas phase fluidized bed
reactor is monitored and optionally also controlled in accordance
with the invention while it operates to perform polymerization. The
polymerization is performed by mixing gaseous feed streams of the
primary monomer and hydrogen together with liquid or gaseous
comonomer, for example, in a mixing tee arrangement. The mixture
can then be introduced below the reactor bed into the recycle gas
line.
[0111] For example, the primary monomer may be ethylene and the
comonomer may be 1-hexene. The individual flow rates of ethylene,
hydrogen, and comonomer are controlled to maintain fixed gas
composition targets. The ethylene concentration is controlled to
maintain a constant ethylene partial pressure. The hydrogen is
controlled to maintain constant hydrogen to ethylene mole ratio.
The hexene is controlled to maintain a constant hexene to ethylene
mole ratio (or alternatively, the flow rates of comonomer and
ethylene are held at a fixed ratio). The concentration of all gases
is measured by an on-line gas chromatograph to ensure relatively
constant composition in the recycle gas stream. A solid or liquid
catalyst is injected directly into the fluidized bed using purified
nitrogen as a carrier. The feed rate of catalyst is adjusted to
maintain a constant production rate.
[0112] The reactor bed, which contains the growing polymer
particles, is maintained in a fluidized state by the continuous
flow of makeup feed and recycle gas through the reaction zone. In
some implementations, a superficial gas velocity of 1 to 3 ft/sec
is used to achieve this, and the reactor is operated at a total
pressure of 300 psig. To maintain a constant reactor temperature,
the temperature of the recycle gas is continuously adjusted up or
down to accommodate any changes in the rate of heat generation due
to the polymerization. The fluidized bed is maintained at a
constant height by withdrawing a portion of the bed at a rate equal
to the rate of formation of particulate product.
[0113] The product is removed continuously or nearly continuously
via a series of valves into a fixed volume chamber, which is
simultaneously vented back to the reactor. This allows for highly
efficient removal of the product, while recycling a large portion
of the unreacted gases back to the reactor. The removed product is
purged to remove entrained hydrocarbons and treated with a small
stream of humidified nitrogen to deactivate any trace quantities of
residual catalyst. In other embodiments, a reactor is monitored and
optionally also controlled in accordance with the invention while
it operates to perform polymerization using any of a variety of
different processes (e.g., slurry, or gas phase processes).
[0114] In some embodiments, a polymerization reaction that is a
continuous gas phase process (e.g., a fluid bed process) is
monitored and optionally also controlled in accordance with the
techniques described herein. A fluidized bed reactor for performing
such a process typically comprises a reaction zone and a so-called
velocity reduction zone. The reaction zone comprises a bed of
growing polymer particles, formed polymer particles and a minor
amount of catalyst particles fluidized by the continuous flow of
the gaseous monomer and diluent to remove heat of polymerization
through the reaction zone. Optionally, some of the re-circulated
gases may be cooled and compressed to form liquids that increase
the heat removal capacity of the circulating gas stream when
readmitted to the reaction zone. This method of operation is
referred to as "condensed mode." A suitable rate of gas flow may be
readily determined by simple experiment. Make up of gaseous monomer
to the circulating gas stream is at a rate equal to the rate at
which particulate polymer product and monomer associated therewith
is withdrawn from the reactor and the composition of the gas
passing through the reactor is adjusted to maintain an essentially
steady state gaseous composition within the reaction zone.
[0115] The gas leaving the reaction zone is passed to the velocity
reduction zone where entrained particles are removed. Finer
entrained particles and dust may be removed in a cyclone and/or
fines filter. The gas is compressed in a compressor and passed
through a heat exchanger wherein the heat of polymerization is
removed, and then returned to the reaction zone.
[0116] A reaction monitored and optionally also controlled in
accordance with some embodiments of the invention can produce
homopolymers of olefins (e.g., homopolymers of ethylene), and/or
copolymers, terpolymers, and the like, of olefins, particularly
ethylene, and at least one other olefin. The olefins, for example,
may contain from 2 to 16 carbon atoms in one embodiment; and in
another embodiment, ethylene and a comonomer comprising from 3 to
12 carbon atoms in another embodiment; and ethylene and a comonomer
comprising from 4 to 10 carbon atoms in yet another embodiment; and
ethylene and a comonomer comprising from 4 to 8 carbon atoms in yet
another embodiment. A reaction monitored and optionally also
controlled in accordance with the invention can produce
polyethylenes. Such polyethylenes can be homopolymers of ethylene
and interpolymers of ethylene and at least one alpha-olefin wherein
the ethylene content is at least about 50% by weight of the total
monomers involved. Exemplary olefins that may be utilized in
embodiments of the invention are ethylene, propylene, 1-butene,
1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methylpent-1-ene,
1-decene, 1-dodecene, 1-hexadecene, and the like. Also utilizable
herein are polyenes such as 1,3-hexadiene, 1,4-hexadiene,
cyclopentadiene, dicyclopentadiene, 4-vinylcyclohex-1-ene,
1,5-cyclooctadiene, 5-vinylidene-2-norbornene and
5-vinyl-2-norbornene, and olefins formed in situ in the
polymerization medium. As may be understood, the choice of the
comonomer affects the determination of the effective partial
pressure of the ICA, which can change the predicted and actual
values for the stickiness temperature.
[0117] When olefins are formed in situ in the polymerization
medium, the formation of polyolefins containing long chain
branching may occur. In the production of polyethylene or
polypropylene, comonomers may be present in the polymerization
reactor. When present, the comonomer may be present at any level
with the ethylene or propylene monomer that will achieve the
desired weight percent incorporation of the comonomer into the
finished resin. In one embodiment of polyethylene production, the
comonomer is present with ethylene in a mole ratio range in the gas
phase of from about 0.0001 to about 50 (comonomer to ethylene), and
from about 0.0001 to about 5 in another embodiment, and from about
0.0005 to about 1.0 in yet another embodiment, and from about 0.001
to about 0.5 in yet another embodiment. Expressed in absolute
terms, in making polyethylene, the amount of ethylene present in
the polymerization reactor may range to up to about 1000
atmospheres pressure in one embodiment, and up to about 500
atmospheres pressure in another embodiment, and up to about 100
atmospheres pressure in yet another embodiment, and up to about 50
atmospheres in yet another embodiment, and up to about 10
atmospheres in yet another embodiment.
[0118] Hydrogen gas is often used in olefin polymerization to
control the final properties of the polyolefin. For some types of
catalyst systems, it is known that increasing concentrations (or
partial pressures) of hydrogen may alter the molecular weight or
melt index (MI) of the polyolefin generated. The MI can thus be
influenced by the hydrogen concentration. The amount of hydrogen in
the polymerization can be expressed as a mole ratio relative to the
total polymerizable monomer, for example, ethylene, or a blend of
ethylene and hexene or propylene. The amount of hydrogen used in
some polymerization processes is an amount necessary to achieve the
desired MI (or molecular weight) of the final polyolefin resin. In
one embodiment, the mole ratio in the gas phase of hydrogen to
total monomer (H.sub.2 to monomer) is greater than about 0.00001.
The mole ratio is greater than about 0.0005 in another embodiment,
greater than about 0.001 in yet another embodiment, less than about
10 in yet another embodiment, less than about 5 in yet another
embodiment, less than about 3 in yet another embodiment, and less
than about 0.10 in yet another embodiment, wherein a desirable
range may comprise any combination of any upper mole ratio limit
with any lower mole ratio limit described herein. Expressed another
way, the amount of hydrogen in the reactor at any time may range to
up to about 10 ppm in one embodiment, or up to about 100 or about
3000 or about 4000 or about 5000 ppm in other embodiments, or
between about 10 ppm and about 5000 ppm in yet another embodiment,
or between about 500 ppm and about 2000 ppm in another
embodiment.
[0119] A reactor monitored and optionally also controlled in
accordance with some embodiments of the invention can be an element
of a staged reactor employing two or more reactors in series,
wherein one reactor may produce, for example, a high molecular
weight component and another reactor may produce a low molecular
weight component.
[0120] A reactor monitored and optionally also controlled in
accordance with the invention can implement a slurry or gas phase
process in the presence of a bulky ligand metallocene-type catalyst
system and in the absence of, or essentially free of, any
scavengers, such as triethylaluminum, trimethylaluminum,
tri-isobutylaluminum and tri-n-hexylaluminum and diethyl aluminum
chloride, dibutyl zinc and the like. By "essentially free," it is
meant that these compounds are not deliberately added to the
reactor or any reactor components, and if present, are present in
less than about 1 ppm in the reactor.
[0121] A reactor monitored and optionally also controlled in
accordance with the invention can employ one or more catalysts
combined with up to about 10 wt % of a metal-fatty acid compound,
such as, for example, an aluminum stearate, based upon the weight
of the catalyst system (or its components). Other metals that may
be suitable include other Group 2 and Group 5-13 metals. In other
embodiments, a solution of the metal-fatty acid compound is fed
into the reactor. In other embodiments, the metal-fatty acid
compound is mixed with the catalyst and fed into the reactor
separately. These agents may be mixed with the catalyst or may be
fed into the reactor in a solution, slurry, or as a solid
(preferably as a powder) with or without the catalyst system or its
components.
[0122] In a reactor monitored and optionally also controlled in
accordance with some embodiments of the invention, supported
catalyst(s) can be combined with activators and can be combined by
tumbling and/or other suitable means, with up to about 2.5 wt % (by
weight of the catalyst composition) of an antistatic agent, such as
an ethoxylated or methoxylated amine, an example of which is
KEMAMINE AS-990, available from ICI Specialties. Other antistatic
compositions include the OCTASTAT family of compounds, more
specifically Octastat 2000, 3000, and 5000.
[0123] Metal fatty acids and antistatic agents can be added as
solid slurries, solutions, or solids (preferably as a powder) as
separate feeds into the reactor. One advantage of this method of
addition is that it permits on-line adjustment of the level of the
additive.
[0124] Examples of polymers that can be produced in accordance with
the invention include the following: homopolymers and copolymers of
C.sub.2-C.sub.18 alpha olefins; polyvinyl chlorides, ethylene
propylene rubbers (EPRs); ethylene-propylene diene rubbers (EPDMs);
polyisoprene; polystyrene; polybutadiene; polymers of butadiene
copolymerized with styrene; polymers of butadiene copolymerized
with isoprene; polymers of butadiene with acrylonitrile; polymers
of isobutylene copolymerized with isoprene; ethylene butene rubbers
and ethylene butene diene rubbers; and polychloroprene; norbornene
homopolymers and copolymers with one or more C.sub.2-C.sub.18 alpha
olefin; terpolymers of one or more C.sub.2-C.sub.18 alpha olefins
with a diene.
[0125] Monomers that can be present in a reactor monitored and
optionally also controlled in accordance with the invention include
one or more of: C.sub.2-C.sub.18 alpha olefins such as ethylene,
propylene, and optionally at least one diene, for example,
hexadiene, dicyclopentadiene, octadiene including methyloctadiene
(e.g., 1-methyl-1,6-octadiene and 7-methyl-1,6-octadiene),
norbornadiene, and ethylidene norbornene; and readily condensable
monomers, for example, isoprene, styrene, butadiene, isobutylene,
chloroprene, acrylonitrile, cyclic olefins such as norbornenes.
[0126] Fluidized bed polymerization can be monitored and optionally
also controlled in accordance with some embodiments of the
invention. The reaction can be any type of fluidized polymerization
reaction and can be carried out in a single reactor or multiple
reactors such as two or more reactors in series.
[0127] In various embodiments, any of many different types of
polymerization catalysts can be used in a polymerization process
monitored and optionally also controlled in accordance with the
present invention. A single catalyst may be used, or a mixture of
catalysts may be employed, if desired. The catalyst can be soluble
or insoluble, supported or unsupported. It may be a prepolymer,
spray dried with or without a filler, a liquid, or a solution,
slurry/suspension, or dispersion. These catalysts are used with
cocatalysts and promoters well known in the art. Typically these
are alkylaluminums, alkylaluminum halides, alkylaluminum hydrides,
as well as aluminoxanes. For illustrative purposes only, examples
of suitable catalysts include Ziegler Natta catalysts, chromium
based catalysts, vanadium based catalysts (e.g., vanadium
oxychloride and vanadium acetylacetonate), metallocene catalysts
and other single-site or single-site-like catalysts, cationic forms
of metal halides (e.g., aluminum trihalides), anionic initiators
(e.g., butyl lithiums), cobalt catalysts and mixtures thereof,
Nickel catalysts and mixtures thereof, rare earth metal catalysts
(i.e., those containing a metal having an atomic number in the
Periodic Table of 57 to 103), such as compounds of cerium,
lanthanum, praseodymium, gadolinium and neodymium.
[0128] The catalyst may comprise a metallocene. Metallocenes as
described herein include "half sandwich" and "full sandwich"
compounds having one or more Cp ligands (cyclopentadienyl and
ligands isolobal to cyclopentadienyl) bound to at least one Group 3
to Group 12 metal atom, and one or more leaving groups bound to the
at least one metal atom. Hereinafter, these compounds will be
referred to as "metallocenes" or "metallocene catalyst components."
The metallocene catalyst component may be supported on a support
material, and may be supported with or without another catalyst
component. In one embodiment, the one or more metallocene catalyst
components are represented by the formula (I):
Cp.sup.ACp.sup.BMX.sub.n (I)
wherein M is a metal atom selected from the group consisting of
Groups 3 through 12 atoms and lanthanide Group atoms in one
embodiment. For example, M may be selected from Ti, Zr, Hf atoms.
Each leaving group X is chemically bonded to M; each Cp group is
chemically bonded to M; and n is 0 or an integer from 1 to 4, and
may be either 1 or 2 in a particular embodiment.
[0129] The Cp ligands are one or more rings or ring systems, at
least a portion of which includes .pi.-bonded systems, such as
cycloalkadienyl ligands and heterocyclic analogues. The Cp ligands
are distinct from the leaving groups bound to the catalyst compound
in that they are not highly susceptible to substitution or
abstraction reactions. The ligands represented by Cp.sup.A and
Cp.sup.B in formula (I) may be the same or different
cyclopentadienyl ligands or ligands isolobal to cyclopentadienyl,
either or both of which may contain heteroatoms and either or both
of which may be substituted by at least one R group. Non-limiting
examples of substituent R groups include groups selected from
hydrogen radicals, alkyls, alkenyls, alkynyls, cycloalkyls, aryls,
acyls, aroyls, alkoxys, aryloxys, alkylthiols, dialkylamines,
alkylamidos, alkoxycarbonyls, aryloxycarbonyls, carbomoyls, alkyl-
and dialkyl-carbamoyls, acyloxys, acylaminos, aroylaminos, and
combinations thereof. In one embodiment, Cp.sup.A and Cp.sup.B are
independently selected from the group consisting of
cyclopentadienyl, indenyl, tetrahydroindenyl, fluorenyl, and
substituted derivatives of each. (As used herein, the term
"substituted" means that the group following that term possesses at
least one moiety in place of one or more hydrogens in any position,
which moieties are selected from such groups as halogen radicals
(e.g., Cl, F, Br), hydroxyl groups, carbonyl groups, carboxyl
groups, amine groups, phosphine groups, alkoxy groups, phenyl
groups, naphthyl groups, C.sub.1 to C.sub.10 alkyl groups, C.sub.2
to C.sub.10 alkenyl groups, and combinations thereof. Examples of
substituted alkyls and aryls include, but are not limited to, acyl
radicals, alkylamino radicals, alkoxy radicals, aryloxy radicals,
alkylthio radicals, dialkylamino radicals, alkoxycarbonyl radicals,
aryloxycarbonyl radicals, carbomoyl radicals, alkyl- and
dialkyl-carbamoyl radicals, acyloxy radicals, acylamino radicals,
arylamino radicals, and combinations thereof).
[0130] In one embodiment, each leaving group X in the formula (I)
above may be independently selected from the group consisting of
halogen ions, hydrides, C.sub.1-12 alkyls, C.sub.2-12 alkenyls,
C.sub.6-12 aryls, C.sub.7-20 alkylaryls, C.sub.1-12 alkoxys,
C.sub.6-16 aryloxys, C.sub.7-18 alkylaryloxys, C.sub.1-12
fluoroalkyls, C.sub.6-12 fluoroaryls, and C.sub.1-12
heteroatom-containing hydrocarbons, and substituted derivatives
thereof. As used herein, the phrase "leaving group" refers to one
or more chemical moieties bound to the metal center of the catalyst
component, which can be abstracted from the catalyst component by
an activator, thus producing a species active towards olefin
polymerization or oligomerization.
[0131] The structure of the metallocene catalyst component may take
on many forms, such as those disclosed in, for example, U.S. Pat.
Nos. 5,026,798, 5,703,187, and 5,747,406, including a dimer or
oligomeric structure, such as disclosed in, for example, U.S. Pat.
Nos. 5,026,798 and 6,069,213. Others include those catalysts
described in U.S. Patent Application Publication Nos.
US2005/0124487A1, US2005/0164875A1, and US2005/0148744. In other
embodiments, the metallocene may be formed with a hafnium metal
atom, such as is described in U.S. Pat. No. 6,242,545.
[0132] In certain embodiments, the metallocene catalysts components
described above may include their structural or optical or
enantiomeric isomers (racemic mixture), and, in one embodiment, may
be a pure enantiomer.
[0133] In various embodiments, a polymerization reaction monitored
and optionally also controlled in accordance with the invention can
employ other additives, such as (for example) inert particulate
particles.
[0134] It should be understood that while some embodiments of the
present invention are illustrated and described herein, the
invention is not to be limited to the specific embodiments
described and shown. The phrases, unless otherwise specified,
"consists essentially of" and "consisting essentially of" do not
exclude the presence of other steps, elements, or materials,
whether or not, specifically mentioned in this specification, as
long as such steps, elements, or materials, do not affect the basic
and novel characteristics of the invention, additionally, they do
not exclude impurities normally associated with the elements and
materials used.
[0135] For the sake of brevity, only certain ranges are explicitly
disclosed herein. However, ranges from any lower limit may be
combined with any upper limit to recite a range not explicitly
recited, as well as, ranges from any lower limit may be combined
with any other lower limit to recite a range not explicitly
recited, in the same way, ranges from any upper limit may be
combined with any other upper limit to recite a range not
explicitly recited. Additionally, within a range includes every
point or individual value between its end points even though not
explicitly recited. Thus, every point or individual value may serve
as its own lower or upper limit combined with any other point or
individual value or any other lower or upper limit, to recite a
range not explicitly recited.
[0136] As used herein, "substantially," "generally," and other
words of degree are relative modifiers intended to indicate
permissible variation from the characteristic so modified. It is
not intended to be limited to the absolute value or characteristic
which it modifies but rather possessing more of the physical or
functional characteristic than its opposite, and preferably,
approaching or approximating such a physical or functional
characteristic.
[0137] All numerical values are "about" or "approximately" the
indicated value, and take into account experimental error and
variations that would be expected by a person having ordinary skill
in the art. Further, various terms have been defined above. To the
extent a term used in a claim is not defined above, it should be
given the broadest definition persons in the pertinent art have
given that term as reflected in at least one printed publication or
issued patent. All patents, test procedures, and other documents
cited in this application are fully incorporated by reference to
the extent such disclosure is not inconsistent with this
application and for all jurisdictions in which such incorporation
is permitted.
[0138] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
can be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *