U.S. patent application number 11/236998 was filed with the patent office on 2007-03-29 for method for seed bed treatment before a polymerization reaction.
Invention is credited to Agapios K. Agapiou, Eric J. Markel, Richard B. Pannell.
Application Number | 20070073012 11/236998 |
Document ID | / |
Family ID | 37441633 |
Filed Date | 2007-03-29 |
United States Patent
Application |
20070073012 |
Kind Code |
A1 |
Pannell; Richard B. ; et
al. |
March 29, 2007 |
Method for seed bed treatment before a polymerization reaction
Abstract
In some embodiments, a method in which at least one continuity
additive ("CA") and a seed bed are pre-loaded into a reactor, and a
polymerization reaction is optionally then performed in the
reactor. In other embodiments, at least one flow improver, at least
one CA, and a seed bed are pre-loaded into a reactor. Pre-loading
of a reactor with a CA can significantly improve continuity of a
subsequent polymerization reaction in the reactor during its
initial stages, including by reducing sheeting and fouling. The CA
can be pre-loaded in dry form (e.g., as a powder), or in liquid or
slurry form (e.g., as an oil slurry). To aid delivery of a dry CA
to the reactor and combination of the dry CA with a seed bed in the
reactor, the dry CA can be combined with a flow improver and the
combination of CA and flow improver then loaded into the reactor.
Alternatively, the CA and flow improver can be sequentially loaded
into the reactor, and then mixed together (and mixed with a seed
bed) in the reactor after both the CA and flow improver have been
separately loaded into the reactor.
Inventors: |
Pannell; Richard B.;
(Kingwood, TX) ; Agapiou; Agapios K.; (Humble,
TX) ; Markel; Eric J.; (Kingwood, TX) |
Correspondence
Address: |
UNIVATION TECHNOLOGIES LLC
5555 SAN FELIPE, SUITE 1950
HOUSTON
TX
77056
US
|
Family ID: |
37441633 |
Appl. No.: |
11/236998 |
Filed: |
September 28, 2005 |
Current U.S.
Class: |
526/74 ; 526/88;
526/901 |
Current CPC
Class: |
Y02P 20/582 20151101;
C08F 2/34 20130101; C08F 10/00 20130101; C08F 2/005 20130101; C08F
10/00 20130101; C08F 10/00 20130101 |
Class at
Publication: |
526/074 ;
526/088; 526/901 |
International
Class: |
C08F 2/00 20060101
C08F002/00 |
Claims
1. A method for preparing a reactor for performance of a
polymerization reaction in the reactor, said method including the
steps of: (a) loading a seed bed into the reactor; and (b)
pre-loading at least one continuity additive into the reactor.
2. The method of claim 1, also including the step of: (c) after
steps (a) and (b), performing the polymerization reaction in the
reactor including by performing at least an initial stage of the
reaction in the presence of the continuity additive.
3. The method of claim 2, wherein the reaction is an olefin
polymerization reaction.
4. The method of claim 1, wherein steps (a) and (b) are performed
sequentially.
5. The method of claim 4, wherein the reactor includes at least one
tube, the tube is positioned and configured for introducing a
substance into the reactor through said tube, step (a) is performed
before step (b), and step (b) includes the step of introducing the
continuity additive into the seed bed through the tube.
6. The method of claim 1, wherein steps (a) and (b) are performed
simultaneously.
7. The method of claim 1, also including the steps of: (c) after
steps (a) and (b), removing moisture and air from the reactor; and
(d) after step (c), performing the polymerization reaction in the
reactor including by performing at least an initial stage of the
reaction in the presence of the continuity additive.
8. The method of claim 1, also including the steps of: (c) after
steps (a) and (b), drying the seed bed and the continuity additive,
thereby removing moisture and air from the reactor; and (d) after
step (c), performing the polymerization reaction in the reactor
including by performing at least an initial stage of the reaction
in the presence of the continuity additive.
9. The method of claim 1, also including the step of: (c)
pre-loading at least one flow improver into the reactor.
10. The method of claim 9, also including the step of: after steps
(a), (b), and (c), performing the polymerization reaction in the
reactor including by performing at least an initial stage of the
reaction in the presence of the continuity additive and the flow
improver.
11. The method of claim 9, wherein the continuity additive is a dry
continuity additive, and also including the step of: before
performing steps (b) and (c), combining the dry continuity additive
with the flow improver, and then performing steps (b) and (c) by
pre-loading a combination of the continuity additive and the flow
improver into the reactor.
12. The method of claim 11, wherein the continuity additive
includes a carboxylate metal salt and the flow improver includes a
colloidal particulate material.
13. The method of claim 12, wherein the reaction is an olefin
polymerization reaction.
14. The method of claim 11, wherein the continuity additive
includes a carboxylate metal salt and the flow improver includes a
colloidal silica.
15. The method of claim 14, wherein the reaction is an olefin
polymerization reaction.
16. The method of claim 11, wherein the continuity additive
includes a carboxylate metal salt and the flow improver includes a
fumed silica.
17. The method of claim 16, wherein the reaction is an olefin
polymerization reaction.
18. The method of claim 11, wherein the flow improver includes
alumina.
19. The method of claim 18, wherein the reaction is an olefin
polymerization reaction.
20. The method of claim 1, wherein the continuity additive is
pre-loaded in dry form.
21. The method of claim 1, wherein the continuity additive is
pre-loaded as a powder.
22. The method of claim 1, wherein the continuity additive is
pre-loaded in liquid form.
23. The method of claim 1, wherein the continuity additive is
pre-loaded as a slurry.
24. The method of claim 1, wherein the continuity additive includes
a metal stearate.
25. The method of claim 24, wherein the metal stearate is aluminum
stearate.
26. The method of claim 1, wherein the continuity additive includes
a carboxylate metal salt.
27. The method of claim 26, wherein the carboxylate metal salt is
one of a mono-carboxylic acid salt, a di-carboxylic acid salt, and
a tri-carboxylic acid salt.
28. The method of claim 26, wherein the carboxylate metal salt is
represented by the formula M(Q).sub.x (OOCR).sub.y, where M is a
metal from Groups 1 to 16 and the Lanthanide and Actinide series, Q
is one of hydrogen, a halogen, a hydroxy group, a hydroxide group,
an alkyl group, an alkoxy group, an aryloxy group, a siloxy group,
a silane group, a sulfonate group, and siloxane, R is a hydrocarbyl
radical having from 2 to 100 carbon atoms, x is an integer from 0
to 3 inclusive, y is an integer from 1 to 4 inclusive, and x+y=z,
where z is the valence of the metal.
29. The method of claim 26, wherein the carboxylate metal salt is
an aluminum carboxylate.
30. The method of claim 1, wherein the continuity additive includes
an antistatic agent.
31. The method of claim 30, wherein the antistatic agent is
represented by the formula, R.sub.mXR'.sub.n, where R is one of a
branched chain hydrocarbyl group, a straight chain hydrocarbyl
group, and a substituted hydrocarbyl group having at least one
carbon atom, R' is an alkyl hydroxy group, X is at least one
heteroatom, and n is such that the formula has no net charge.
32. The method of claim 26, also including the step of: (c) after
steps (a) and (b), performing the polymerization reaction in the
reactor including by performing at least an initial stage of the
reaction in the presence of the continuity additive, and wherein
the carboxylate metal salt has a melting point greater than the
temperature in the reactor during the polymerization reaction.
33. The method of claim 1, wherein the reaction is an olefin
polymerization reaction.
34. A method for preparing a reactor for performance of a
polymerization reaction in the reactor, said method including the
steps of: (a) preparing treated seed bed material by combining seed
bed material with at least one continuity additive; and (b)
pre-loading the treated seed bed material into the reactor.
35. The method of claim 34, also including the step of: (c) after
steps (a) and (b), performing the polymerization reaction in the
reactor including by performing at least an initial stage of the
reaction in the presence of the continuity additive.
36. The method of claim 35, wherein the reaction is an olefin
polymerization reaction.
37. The method of claim 34, wherein the continuity additive
includes a metal stearate.
38. The method of claim 34, wherein the continuity additive
includes a carboxylate metal salt.
39. The method of claim 38, wherein the carboxylate metal salt is
one of a mono-carboxylic acid salt, a di-carboxylic acid salt, and
a tri-carboxylic acid salt.
40. The method of claim 38, wherein the carboxylate metal salt is
represented by the formula M(Q).sub.x (OOCR).sub.y, where M is a
metal from Groups 1 to 16 and the Lanthanide and Actinide series, Q
is one of hydrogen, a halogen, a hydroxy group, a hydroxide group,
an alkyl group, an alkoxy group, an aryloxy group, a siloxy group,
a silane group, a sulfonate group, and siloxane, R is a hydrocarbyl
radical having from 2 to 100 carbon atoms, x is an integer from 0
to 3 inclusive, y is an integer from 1 to 4 inclusive, and x+y=z,
where z is the valence of the metal.
41. The method of claim 34, wherein the continuity additive
includes an antistatic agent.
42. The method of claim 41, wherein the antistatic agent is
represented by the formula, R.sub.mXR'.sub.n, where R is one of a
branched chain hydrocarbyl group, a straight chain hydrocarbyl
group, and a substituted hydrocarbyl group having at least one
carbon atom, R' is an alkyl hydroxy group, X is at least one
heteroatom, and n is such that the formula has no net charge.
43. A method for preparing a reactor, having a seed bed present
therein, for performance of a polymerization reaction in the
reactor, said method comprising the step of: (a) while the seed bed
is present in the reactor, loading at least one continuity additive
into the reactor before performing the polymerization reaction in
said reactor.
44. The method of claim 43, also including the step of: (b) after
step (a), performing the polymerization reaction in the reactor
including by performing at least an initial stage of said reaction
in the presence of the continuity additive.
45. The method of claim 44, wherein air and moisture are present
with the seed bed in the reactor during step (a), and also
including the step of: (c) removing at least some of the moisture
and air from the reactor after step (a) but before step (b) in
preparation for performing the polymerization reaction.
46. The method of claim 44, wherein the reaction is an olefin
polymerization reaction.
47. The method of claim 46, wherein the reactor includes at least
one tube, the tube is positioned and configured for introducing a
substance into the reactor through said tube, and step (a) includes
the step of introducing the continuity additive into the seed bed
through the tube.
48. The method of claim 44, also including the step of: (c) after
step (a) but before step (b), purging reactants from a previous
polymerization reaction from the reactor.
49. The method of claim 43, also including the step of: (b)
pre-loading at least one flow improver into the reactor before
performing the polymerization reaction in said reactor.
50. The method of claim 49, also including the step of: (c) after
steps (a) and (b), performing the polymerization reaction in the
reactor including by performing at least an initial stage of the
reaction in the presence of the continuity additive and the flow
improver.
51. The method of claim 50, wherein the continuity additive is a
dry continuity additive, and also including the step of: before
performing steps (a) and (b), combining the dry continuity additive
with the flow improver, and then performing steps (a) and (b) by
pre-loading a combination of the continuity additive and the flow
improver into the reactor.
52. The method of claim 50, wherein the reaction is an olefin
polymerization reaction.
53. The method of claim 49, wherein the continuity additive
includes a carboxylate metal salt and the flow improver includes a
colloidal particulate material.
54. The method of claim 49, wherein the continuity additive
includes a carboxylate metal salt and the flow improver includes a
colloidal silica.
55. The method of claim 49, wherein the continuity additive
includes a carboxylate metal salt and the flow improver includes a
fumed silica.
Description
FIELD OF THE INVENTION
[0001] The invention pertains to methods for seed bed treatment
before performance of a polymerization reaction (e.g., an olefin
polymerization reaction) to improve continuity of the reaction.
BACKGROUND OF THE INVENTION
[0002] One commonly used method for producing polymers is gas phase
polymerization. During operation to produce polyolefins by
polymerization, a conventional gas phase fluidized bed reactor
contains a fluidized dense-phase bed including a mixture of
reaction gas, polymer (resin) particles, catalyst, and catalyst
modifiers. Before such a polymerization reaction, a "seed bed" is
typically loaded into the reactor or is present in the reactor from
a previous polymerization operation. The seed bed is (or consists
essentially of) granular material that is or includes polymer
material. The polymer material can but need not be identical to the
desired end product of the reaction. An example of seed bed
material is metallocene polyethylene.
[0003] It is known to introduce a continuity additive ("CA") into a
reactor during a fluidized bed polymerization reaction to reduce
sheeting and/or fouling in the reactor during polymerization. Such
use of a continuity additive, optionally with a flow improver, is
described in U.S. Pat. No. 6,482,903, issued Nov. 19, 2002; U.S.
Pat. No. 6,660,815, issued Dec. 9, 2003; U.S. Pat. No. 6,306,984,
issued Oct. 23, 2001; and U.S. Pat. No. 6,300,436, issued Oct. 9,
2001, all assigned to the assignee of the present invention. A
continuity additive is typically not catalytic, but is typically
combined with a catalyst (and typically also with a flow improver)
before or after being introduced into the reactor. Examples of CAs
are aluminum stearate, other metal stearates, and Atmer AS 990 (an
ethoxylated stearyl amine, available from Ciba Specialty Chemicals
Co, Basel, Switzerland).
[0004] U.S. Pat. No. 6,300,436 and U.S. Pat. No. 6,306,984 describe
an olefin polymerization process (e.g., a gas phase or slurry phase
process) in a reactor the presence of a catalyst composition
comprising a carboxylate metal salt. The carboxylate metal salt is
a continuity additive ("CA") which significantly reduces sheeting
and/or fouling in the reactor during polymerization. The catalyst
composition is produced by combining, contacting, blending and/or
mixing a catalyst system (e.g., a supported catalyst system) with
the carboxylate metal salt. The catalyst system can be a transition
metal catalyst compound (e.g., a bulky ligand metallocene-type
catalyst compound). The carboxylate metal salt can be blended
(e.g., tumble dry blended) with a supported catalyst system or
polymerization catalyst comprising a carrier. The polymerization
catalyst can be dry and free flowing and the metal carboxylate salt
mixed or blended with the catalyst can be in solid form.
Alternatively, the carboxylate metal salt is added to a reactor
(containing reactants and a catalyst system) during polymerization
without previously having been combined, blended, contacted, or
mixed with the catalyst system.
[0005] U.S. Pat. No. 6,300,436, U.S. Pat. No. 6,306,984, and U.S.
Pat. No. 6,482,903 teach that carboxylate metal salts that may be
suitable for use as continuity additives are any mono- or di- or
tri-carboxylic acid salt with a metal portion from the Periodic
Table of Elements. Examples include saturated, unsaturated,
aliphatic, aromatic or saturated cyclic carboxylic acid salts where
the carboxylate ligand has preferably from 2 to 24 carbon atoms,
such as acetate, propionate, butyrate, valerate, pivalate,
caproate, isobuytlacetate, t-butyl-acetate, caprylate, heptanate,
pelargonate, undecanoate, oleate, octoate, palmitate, myristate,
margarate, stearate, arachate and tercosanoate. Examples of the
metal portion includes a metal from the Periodic Table of Elements
selected from the group of Al, Mg, Ca, Sr, Sn, Ti, V, Ba, Zn, Cd,
Hg, Mn, Fe, Co, Ni, Pd, Li and Na.
[0006] Examples of carboxylate metal salts that may be suitable for
use as continuity additives are represented by the general formula
M(Q).sub.x (OOCR).sub.y, where M is a metal from Groups 1 to 16 and
the Lanthanide and Actinide series, preferably from Groups 1 to 7
and 13 to 16 (preferably Groups 2 and 13, and most preferably Group
13); Q is a halogen or hydrogen, or a hydroxy, hydroxide, alkyl,
alkoxy, aryloxy, siloxy, silane sulfonate group, or siloxane; R is
a hydrocarbyl radical having from 2 to 100 carbon atoms, preferably
4 to 50 carbon atoms; and x is an integer from 0 to 3 and y is an
integer from 1 to 4 and the sum of x and y is equal to the valence
of the metal. In a preferred embodiment of the above formula, y is
an integer from 1 to 3, preferably 1 to 2, especially where M is a
Group-13 metal.
[0007] Non-limiting examples of R in the above formula include
hydrocarbyl radicals having 2 to 100 carbon atoms that include
alkyl, aryl, aromatic, aliphatic, cyclic, saturated or unsaturated
hydrocarbyl radicals. For example, R can be a hydrocarbyl radical
having greater than or equal to 8 carbon atoms (preferably greater
than or equal to 17 carbon atoms) or R can be a hydrocarbyl radical
having from 17 to 90 carbon atoms (preferably from 17 to 54 carbon
atoms).
[0008] Non-limiting examples of Q in the above formula include one
or more, same or different, hydrocarbon containing group such as
alkyl; cycloalkyl, aryl, alkenyl, arylalkyl, arylalkenyl or
alkylaryl, alkylsilane, arylsilane, alkylamine, arylamine, alkyl
phosphide,; alkoxy having from 1 to 30 carbon atoms. The
hydrocarbon containing group may be linear, branched, or even
substituted. For example, Q can be an inorganic group such as a
halide, sulfate or phosphate.
[0009] For some applications, a carboxylate metal salt employed as
a CA has a melting point from about 30.degree. C. to about
250.degree. C. (preferably from about 100.degree. C. to about
200.degree. C.). For some applications, the carboxylate metal salt
employed as a CA is an aluminum stearate having a melting point in
the range of from about 135.degree. C. to about 65.degree. C. For
typical applications, the carboxylate metal salt employed as a CA
has a melting point greater than the polymerization temperature in
the reactor.
[0010] Other examples of carboxylate metal salts that may be
suitable for use as continuity additives include titanium
stearates, tin stearates, calcium stearates, zinc stearates, boron
stearates and strontium stearates.
[0011] For some applications, a carboxylate metal salt is combined
(for use as a continuity additive) with an antistatic agent such as
a fatty amine, for example, Atmer AS 990/2 zinc additive, a blend
of ethoxylated stearyl amine and zinc stearate, or Atmer AS 990/3,
a blend of ethoxylated stearyl amine, zinc stearate and
octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate. Both the AS
990/2 and 990/3 blends are available from Crompton Corporation of
Memphis, Tenn.
[0012] U.S. Pat. Nos. 6,482,903 and 6,660,815 teach performance of
an olefin polymerization process (e.g., a gas phase or slurry phase
process) in a reactor in the presence of a catalyst composition
including a catalyst system (e.g., a supported bulky ligand
metallocene-type catalyst system), at least one carboxylate metal
salt, and at least one flow improver. The flow improver can be a
colloidal particulate material (e.g., Snowtex colloidal silica,
available from Nissan Chemical Industries, Tokyo, Japan, or another
colloidal silica). Other examples of the flow improver that are
disclosed in U.S. Pat. No. 6,482,903 include a colloidal silica
(e.g., Cabosil, available from Cabot), a fumed silica, a syloid,
and alumina. U.S. Pat. Nos. 6,482,903 and 6,660,815 teach that the
carboxylate metal salt is preferably contacted with the flow
improver prior to use in the reactor or contact with a
polymerization catalyst, and that a catalyst system can be
combined, contacted, blended, or mixed with a composition of at
least one carboxylate metal salt and at least one flow improver
before use in a reactor.
[0013] U.S. Pat. Nos. 6,482,903 and 6,660,815 also teach that
because carboxylate metal salts are difficult to handle (e.g.,
because their morphology is poor and because they have low bulk
density and fluffy consistency), a combination of a carboxylate
metal salt and a flow improver can be handled and combined with a
supported catalyst system in a substantially improved manner than
can the carboxylate metal salt alone.
[0014] U.S. Pat. Nos. 6,300,436 and 6,306,984 teach that when
starting up a polymerization reaction, especially a gas phase
process, there is a higher tendency for operability problems to
occur. They also teach performing the initial stages of such a
reaction (before the process has stabilized) in the presence of a
polymerization catalyst and carboxylate metal salt mixture to
reduce or eliminate start-up problems. They also teach implementing
a transition after the initial stages of the reaction (i.e., when
the reactor has begun to operate in a stable state) to cause the
reaction to proceed in the presence of the same (or a different)
polymerization catalyst but not in the presence of the carboxylate
metal salt.
[0015] However, the present inventors have recognized that a
reactor can be vulnerable to sheeting and/or fouling during the
critical initial stage(s) of a polymerization reaction (before the
reaction has stabilized) even if each such initial stage is
performed in the presence of a CA, if the concentration of the CA
is low. The present inventors have also recognized that the
concentration of CA in a reactor is typically too low to eliminate
this vulnerability if the CA is introduced during the initial
stage(s) of the polymerization reaction (i.e., after the reaction
has begun).
[0016] Before the present invention, it had not been known how
reliably to prevent sheeting and/or fouling during the critical
initial stage(s) of a polymerization reaction.
SUMMARY OF THE INVENTION
[0017] In a class of embodiments of the inventive method, a
continuity additive ("CA") is pre-loaded into a reactor (in which a
seed bed is present and a polymerization reaction can be performed)
or a mixture of a CA and a seed bed are pre-loaded into a reactor
(in which a polymerization reaction can be performed). Optionally,
a polymerization reaction is then performed in the reactor. In
other embodiments of the inventive method, a flow improver and a CA
are pre-loaded into a reactor in which a seed bed is present, or a
mixture of a CA, a flow improver, and a seed bed are pre-loaded
into a reactor (in which a polymerization reaction can be
performed). Optionally, a polymerization reaction is then performed
in the reactor. In some embodiments of the inventive method, a CA
is pre-loaded into a seed bed present in a reactor from a previous
polymerization operation. Optionally, a polymerization reaction is
then performed in the reactor. In some embodiments of the inventive
method, a CA with a flow aid is pre-loaded into a seed bed present
in a reactor from a previous polymerization operation. Optionally,
a polymerization reaction is then performed in the reactor.
[0018] Pre-loading of the reactor in accordance with the invention
can significantly improve continuity of the polymerization reaction
during at least one initial stage (before the reaction has
stabilized), including by reducing sheeting and fouling. The
initial stage (or stages) of a polymerization reaction are the most
critical in the sense that there is typically a higher tendency for
operability problems to occur before the reaction has stabilized
than after it has stabilized.
[0019] Herein, the expression that a reactor (in which a
polymerization reaction can be performed) is "pre-loaded" with a CA
(or a combination of a CA and at least one other substance) denotes
that the CA (or combination) is loaded into the reactor before the
start of the polymerization reaction. Due to its function, a seed
bed in a reactor is always "pre-loaded" in the reactor in the sense
that it is loaded prior to and in preparation for a reaction which
may or may not subsequently occur (in contrast with being loaded at
or after the start of the reaction). Pre-loading in accordance with
the invention is typically accomplished by loading a seed bed
(typically consisting essentially of granular material) into a
reactor before the start of a polymerization reaction, and then
combining a CA (or a combination of a CA and at least one other
substance) with the seed bed in the reactor before the start of the
reaction. Alternatively, pre-loading in accordance with the
invention can be accomplished by preparing treated seed bed
material (by combining seed bed material with at least one CA) and
then loading the treated seed bed material into the reactor before
the start of a polymerization reaction, or loading a CA (or a
combination of a CA and at least one other substance) into a
reactor (in which a seed bed is already present) before the start
of a polymerization reaction.
[0020] In a class of embodiments, the invention is a method
comprising the steps of:
[0021] (a) loading a seed bed into a reactor (typically an empty
reactor);
[0022] (b) loading a continuity additive ("CA"), or a combination
of a CA and a flow improver, into the reactor; and
[0023] (c) after steps (a) and (b), performing a polymerization
reaction in the reactor.
[0024] Steps (a) and (b) can be, and typically are, performed with
air and moisture present in the reactor. Typically, moisture and
air are removed from the reactor (e.g., by performing a drying
operation) after steps (a) and (b) but before step (c) to prepare
the reactor for performance of the reaction.
[0025] In preferred embodiments in this class, pre-loading the
reactor (in step (b)) with the CA or combination eliminates or
significantly reduces sheeting and fouling that would otherwise
occur (if the reactor were not pre-loaded with the CA or
combination) during at least one initial stage of the
polymerization reaction, and optionally also otherwise improves
continuity during at least one initial stage of the polymerization
reaction.
[0026] Alternatively, pre-loading of at least one CA in accordance
with the invention can be accomplished by treating a seed bed
existing in a reactor (from a previous polymerization operation)
before the start of a new polymerization reaction. The seed bed can
be from a polymerization reaction that used the same or a different
catalyst system as the catalyst system to be employed in the new
polymerization reaction.
[0027] In a class of embodiments, the invention is a method
comprising the steps of:
[0028] (a) when a seed bed is present in a reactor (e.g., a seed
bed remaining in the reactor from a previous polymerization
operation performed in the reactor), loading a continuity additive
("CA"), or a combination of a CA and a flow improver, into the
reactor; and
[0029] (b) after step (a), performing a polymerization reaction in
the reactor.
[0030] Typically, air and moisture are present (with the seed bed)
in the reactor during step (a). Typically, the moisture and air are
removed from the reactor (e.g., by performing a drying or purging
operation) after step (a) but before step (b) to prepare the
reactor for performance of the reaction.
[0031] In a class of preferred embodiments, a CA is pre-loaded in
dry form (e.g., as a powder) into the reactor. In other preferred
embodiments, the CA is pre-loaded into the reactor in liquid or
slurry form (e.g., as an oil slurry) or as a component of a mixture
of solids, liquids, or at least one solid and at least one liquid.
For example, a solid and/or a liquid CA can be pre-loaded (in
accordance with some embodiments) with a carrier liquid (e.g., a
hydrocarbon or hydrocarbon oil) into a reactor. To aid delivery of
a dry CA to a reactor and combination of the dry CA with a seed bed
in the reactor, the dry CA can be combined with a flow improver and
the combination of CA and flow improver then loaded into the
reactor. Alternatively, a CA and a flow improver can be
sequentially loaded into the reactor, and then mixed together (and
mixed with a seed bed) in the reactor after both the CA and flow
improver have been separately loaded into the reactor. The improved
flow properties of the combined CA and flow improver allow for
delivery of the CA as a solid (e.g., to pre-load the reactor with a
specific, predetermined amount of CA for smooth start up
operation).
[0032] In typical embodiments, a specific amount of CA is
pre-loaded into a reactor based on the weight of a seed bed in (or
to be loaded into) the reactor. In general, embodiments of the
invention can include any of the steps of: pre-loading a CA into a
reactor and then loading a seed bed into the reactor; loading a
seed bed into a reactor and then pre-loading a CA into the reactor;
simultaneously pre-loading a CA and a seed bed into a reactor; and
combining (e.g., mixing) a seed bed with a CA and then loading the
combination into a reactor. In any of these embodiments, the CA may
be loaded (e.g., pre-loaded) with a flow aid.
[0033] In various embodiments of the invention, a CA is pre-loaded
into a reactor in any of a number of different ways, including
by:
[0034] pretreatment of a seedbed in the reactor with a flow-aid
modified CA;
[0035] introduction of the CA with (and during) loading of a seed
bed into the reactor (for example, the seed bed material can be
combined with the CA before the combination is loaded into the
reactor);
[0036] introduction of the CA during the reactor condition build-up
stage after purging is complete;
[0037] introduction of the CA directly into the seed bed via a tube
inserted into the seed bed (e.g., through a catalyst support
tube);
[0038] introduction of dry CA (that has been pre-weighed) into the
reactor; and
[0039] introduction of dry CA (that has been pre-weighed into a
metal container) into the reactor using pressurized nitrogen.
[0040] As used herein, the phrase "catalyst support tube" denotes a
tube (typically a heavy walled tube) extending from about 0.1
R.sub.R to 0.6 R.sub.R into a reactor through which another tube
optionally be placed, where R.sub.R is the radius of the reactor.
CA may be pre-loaded in accordance with the invention either
through a catalyst support tube or another tube optionally placed
through the inner opening of a catalyst support tube.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIG. 1 is a simplified cross-sectional view of a system
including fluidized bed reactor (10), which can be pre-loaded in
accordance with the invention.
[0042] FIG. 2 is a simplified cross-sectional view of another
fluidized bed reactor which can be pre-loaded in accordance with
the invention.
[0043] FIG. 3 is a simplified cross-sectional view of another
fluidized bed reactor which can be pre-loaded in accordance with
the invention.
[0044] FIG. 4 is a formula identifying a class of antistatic agents
that can be employed as continuity additives in accordance with
some embodiments of the invention.
[0045] FIG. 5 is a formula identifying a class of antistatic agents
that can be employed as continuity additives in accordance with
some embodiments of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0046] A system including a reactor that can be pre-loaded in
accordance with the invention will be described with reference to
FIG. 1. The FIG. 1 system includes fluidized bed reactor 10.
Reactor 10 has a bottom end 11, a top section 19, a cylindrical
(straight) section 14 between bottom end 11 and top section 19, and
a distributor plate 12 within section 14. The diameter of each
horizontal cross-section of section 19 is greater than the diameter
of straight section 14. In operation, dense-phase surface 18 is the
boundary between lean phase material present within reactor 10
(above dense-phase surface 18) and dense-phase material 16 within
reactor 10 (in the volume bounded by section 14, plate 12, and
surface 18). In operation, freeboard surface 20 of reactor 10
includes the inner surface of top section 19 and the portion of the
inner surface of section 14 above surface 18.
[0047] The FIG. 1 system also has a cooling control loop which
includes circulating gas cooler 30 and compressor 32, coupled with
reactor 10 as shown. During operation, the cooled circulating gas
flows from cooler 30 through inlet 34 into reactor 10, then
propagates upward through the bed and out from reactor 10 via
outlet 33. The cooling fluid (whose temperature has increased
during its flow through reactor 10) is pumped by compressor 32 from
outlet 33 back to cooler 30. Temperature sensors (not shown) near
the inlet and outlet of cooler 30 typically provide feedback to
cooler 30 and/or compressor 32 to control the amount by which
cooler 30 reduces the temperature of the fluid entering its inlet
and/or flow rate through compressor 32.
[0048] Conventionally, a seed bed is pre-loaded in reactor 10
before the start of a polymerization reaction therein. The seed bed
typically consists essentially of granular material. At the start
of the polymerization reaction, dense-phase material 16 in the
reactor includes the seed bed.
[0049] In a class of embodiments of the inventive method, a
continuity additive ("CA") and a seed bed are pre-loaded into a
reactor (e.g., reactor 10) in which a polymerization reaction can
be performed. Optionally, a polymerization reaction is then
performed in the reactor. In other embodiments of the inventive
method, a flow improver, a CA, and a seed bed are pre-loaded into a
reactor (e.g., reactor 10) in which a polymerization reaction can
be performed. Optionally, a polymerization reaction is then
performed in the reactor.
[0050] Pre-loading of reactor 10 with a CA (or a CA and a flow
improver) and a seed bed in accordance with the invention can
significantly improve continuity of a polymerization reaction
subsequently performed in the reactor during the reaction's initial
stage or stages (before the reaction has stabilized), including by
reducing sheeting and fouling. In some embodiments, pre-loading in
accordance with the invention is accomplished by loading the seed
bed into reactor 10 and then combining a CA (or a combination of a
CA and a flow improver) with the seed bed in the reactor before the
start of a polymerization reaction in the reactor.
[0051] In a class of embodiments, the invention is a method
comprising the steps of:
[0052] (a) loading a seed bed into reactor 10 (or another reactor
in which a polymerization reaction can be performed);
[0053] (b) loading a CA, or a combination of a CA and a flow
improver, into the reactor; and
[0054] (c) after steps (a) and (b), performing a polymerization
reaction in the reactor. Steps (a) and (b) can be performed either
simultaneously or sequentially. Steps (a) and (b) can be and
typically are performed with air and moisture present in the
reactor. Typically, moisture and air are removed from the reactor
(e.g., by performing a drying operation) after steps (a) and (b)
but before step (c) to prepare the reactor for performance of the
reaction. For example, in some embodiments, moisture and air are
removed from the reactor by performing a drying operation.
[0055] Pre-loading of reactor 10 with a CA (or a CA and a flow
improver) in accordance with the invention, when a seed bed exists
in the reactor, can significantly improve continuity of a
polymerization reaction subsequently performed in the reactor
during the reaction's initial stage or stages (before the reaction
has stabilized), including by reducing sheeting and fouling. In
some embodiments, pre-loading in accordance with the invention is
accomplished by having an existing seed bed in reactor 10 and then
combining a CA (or a combination of a CA and a flow improver) with
the seed bed in the reactor before the start of a polymerization
reaction in the reactor.
[0056] In a class of embodiments, the invention is a method
comprising the steps of:
[0057] (a) when a seed bed is present in a reactor (e.g., a seed
bed remaining in reactor 10 from a previous polymerization
operation performed in reactor 10), loading a continuity additive
("CA") or a combination of a CA and a flow improver into the
reactor; and
[0058] (b) after step (a), performing a polymerization reaction in
the reactor.
[0059] Typically, air and moisture are present (with the seed bed)
in the reactor during step (a). Typically, the moisture and air are
removed from the reactor (e.g., by performing a drying or purging
operation) after step (a) but before step (b) to prepare the
reactor for performance of the reaction.
[0060] In another class of embodiments, the invention is a method
comprising the steps of:
[0061] (a) loading a seed bed, and either a continuity additive
("CA") or a combination of a CA and a flow improver, into a
reactor; and
[0062] (b) after step (a), performing a polymerization reaction in
the reactor.
[0063] Typically, air and moisture are present (with the seed bed)
in the reactor during step (a). Typically, the moisture and air are
removed from the reactor (e.g., by performing a drying or purging
operation) after step (a) but before step (b) to prepare the
reactor for performance of the reaction.
[0064] In a class of preferred embodiments, the CA is loaded into
reactor 10 in dry form (e.g., as a powder). Alternatively, the CA
is loaded into reactor 10 in liquid or slurry form (e.g., as an oil
slurry) or in a mixture of solids, liquids, or at least one solid
and at least one liquid. In some embodiments in which a CA is
pre-loaded into reactor 10 (or another reactor) in accordance with
the invention in slurry form, the CA typically comprises 2%-50% by
weight of the slurry (or 5%-35% by weight of the slurry in
preferred embodiments, or 10%-30% by weight of the slurry in more
preferred embodiments).
[0065] To aid delivery of a dry CA to a reactor (e.g., reactor 10)
and combination of the dry CA with a seed bed in the reactor, the
dry CA can be combined with a flow improver and the combination of
CA and flow improver then loaded into the reactor. Alternatively,
the CA and flow improver can be sequentially loaded into the
reactor, and then mixed together (and mixed with a seed bed) in the
reactor after both the CA and flow improver have been separately
loaded into the reactor. The improved flow properties of the
combined CA and flow improver allow for delivery of the CA as a
solid (e.g., to pre-load the reactor with a specific, predetermined
amount of CA for smooth start up operation).
[0066] In typical embodiments, a specific amount of CA is
pre-loaded into reactor 10 based on the weight of a seed bed in (or
to be loaded into) the reactor. In various embodiments of the
invention, a CA is pre-loaded into reactor 10 (or another reactor)
in any of a number of different ways, including by:
[0067] pretreatment of a seed bed in the reactor with a flow-aid
modified CA (a CA combined with a flow improver);
[0068] introduction of the CA with (and during) loading of a seed
bed into the reactor;
[0069] introduction of the CA during the reactor condition build-up
stage after purging is complete;
[0070] introduction of the CA directly into the seed bed via a tube
located within the seedbed (For example, CA 7 can be pre-loaded
into a seed bed in reactor 10 of FIG. 1 via one or more of catalyst
support tubes 8. Typically, a total of eight support tubes 8 would
extend through the wall of reactor 10, with the outlet end of each
within the seed bed. However, only four of tubes 8 are shown in
FIG. 1); and
[0071] introduction of dry CA (that has been pre-weighed into a
metal container) into the reactor using pressurized nitrogen.
[0072] The CA pre-loaded into a reactor in accordance with the
invention can have any composition provided that it will improve
continuity of a polymerization reaction subsequently performed in
the reactor during at least one initial stage of the reaction
(before the reaction has stabilized), including by reducing
sheeting and fouling. Examples of CAs suitable for improving
continuity of a variety of polymerization reactions are described
in above-referenced U.S. Pat. Nos. 6,482,903; 6,660,815; 6,306,984;
and 6,300,436. Typically, a CA is not catalytic but is combined
with a catalyst (and optionally also with a flow improver) before
or after being introduced into the reactor.
[0073] Examples of CAs that can be employed in different
embodiments of the invention include: aluminum stearate, other
metal stearates, Atmer AS 990 (an ethoxylated stearyl amine,
available from Ciba Specialty Chemicals Co, Basel, Switzerland),
and carboxylate metal salts.
[0074] Carboxylate metal salts that may be suitable for use in
accordance with the invention as continuity additives (CAs) include
any mono- or di- or tri-carboxylic acid salt with a metal portion
from the Periodic Table of Elements. Examples include saturated,
unsaturated, aliphatic, aromatic or saturated cyclic carboxylic
acid salts where the carboxylate ligand has preferably from 2 to 24
carbon atoms, such as acetate, propionate, butyrate, valerate,
pivalate, caproate, isobuytlacetate, t-butyl-acetate, caprylate,
heptanate, pelargonate, undecanoate, oleate, octoate, palmitate,
myristate, margarate, stearate, arachate and tercosanoate. Examples
of the metal portion includes a metal from the Periodic Table of
Elements selected from the group of Al, Mg, Ca, Sr, Sn, Ti, V, Ba,
Zn, Cd, Hg, Mn, Fe, Co, Ni, Pd, Li and Na.
[0075] Carboxylate metal salts that may be suitable for use in
accordance with the invention as CAs include those represented by
the general formula M(Q).sub.x (OOCR).sub.y, where M is a metal
from Groups 1 to 16 and the Lanthanide and Actinide series,
preferably from Groups 1 to 7 and 13 to 16 (preferably Groups 2 and
13, and most preferably Group 13); Q is a halogen, hydrogen, or a
hydroxy, hydroxide, alkyl, alkoxy, aryloxy, siloxy, silane
sulfonate group, or siloxane; R is a hydrocarbyl radical having
from 2 to 100 carbon atoms, preferably 4 to 50 carbon atoms; and x
is an integer from 0 to 3 and y is an integer from 1 to 4 and the
sum of x and y is equal to the valence of the metal. In a preferred
embodiment of the above formula, y is an integer from 1 to 3,
preferably 1 to 2, especially where M is a Group-13 metal.
[0076] Non-limiting examples of R in the above formula include
hydrocarbyl radicals having 2 to 100 carbon atoms that include
alkyl, aryl, aromatic, aliphatic, cyclic, saturated or unsaturated
hydrocarbyl radicals. For example, R can be a hydrocarbyl radical
having greater than or equal to 8 carbon atoms (preferably greater
than or equal to 17 carbon atoms) or R can be a hydrocarbyl radical
having from 17 to 90 carbon atoms (preferably from 17 to 54 carbon
atoms).
[0077] Non-limiting examples of Q in the above formula include one
or more, same or different, hydrocarbon containing group such as
alkyl; cycloalkyl, aryl, alkenyl, arylalkyl, arylalkenyl or
alkylaryl, alkylsilane, arylsilane, alkylamine, arylamine, alkyl
phosphide,; alkoxy having from 1 to 30 carbon atoms. The
hydrocarbon containing group may be linear, branched, or even
substituted. For example, Q can be an inorganic group such as a
halide, sulfate or phosphate.
[0078] In other examples, a carboxylate metal salt that may be
suitable for use as a CA in accordance with the invention is an
aluminum carboxylate. For example, it can be one of the aluminum
mono, di- and tri-stearates, aluminum octoates, oleates and
cyclohexylbutyrates. For example, the carboxylate metal salt can be
(CH.sub.3(CH.sub.2).sub.16 COO).sub.3Al, an aluminum tri-stearate
(preferred melting point 115.degree. C.),
(CH.sub.3(CH.sub.2).sub.16 COO).sub.2-A-OH, an aluminum di-stearate
(preferred melting point 145.degree. C.), or
CH.sub.3(CH.sub.2).sub.16 COO--Al--(OH).sub.2, an aluminum
mono-stearate (preferred melting point 155.degree. C.).
[0079] Commercially available examples of carboxylate metal salts
include Crompton Aluminum Stearate #18, Crompton Aluminum Stearate
#22, Crompton Aluminum Stearate #132 and Crompton Aluminum Stearate
EA Food Grade, all available from Crompton Corporation, of Memphis,
Tenn.
[0080] For some applications, a carboxylate metal salt employed as
a CA in accordance with the invention has a melting point from
about 30.degree. C. to about 250.degree. C. (preferably from about
100.degree. C. to about 200.degree. C.). For some applications, the
carboxylate metal salt employed as a CA in accordance with the
invention is an aluminum stearate having a melting point in the
range of from about 135.degree. C. to about 65.degree. C. For
typical applications, the carboxylate metal salt employed as a CA
has a melting point greater than the polymerization temperature in
the reactor.
[0081] Other examples of carboxylate metal salts that may be
suitable for use as continuity additives in accordance with the
invention include titanium stearates, tin stearates, calcium
stearates, zinc stearates, boron stearate and strontium
stearates.
[0082] In some embodiments of the invention, a carboxylate metal
salt is combined (for use as a continuity additive to be pre-loaded
into a reactor) with an antistatic agent such as a fatty amine, for
example, Atmer AS 990/2 zinc additive, a blend of ethoxylated
stearyl amine and zinc stearate, or Atmer AS 990/3, a blend of
ethoxylated stearyl amine, zinc stearate and
octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate. Both the AS
990/2 and 990/3 blends are available from Crompton Corporation of
Memphis, Tenn.
[0083] An example of a flow improver, that can be combined with a
CA (e.g., a carboxylate metal salt) in dry form and then pre-loaded
in a reactor in accordance with a class of embodiments of the
invention for improving continuity of a subsequent olefin
polymerization process in the presence of a catalyst composition
including a catalyst system (e.g., a supported bulky ligand
metallocene-type catalyst system), is a colloidal particulate
material (e.g., Snowtex colloidal silica, available from Nissan
Chemical Industries, Tokyo, Japan, or Aerosil colloidal silica,
available from Degussa, or another colloidal silica). Other
examples of a flow improver for use in accordance with the
invention are a colloidal silica (e.g., Cabosil, available from
Cabot), a fumed silica, a syloid, and alumina.
[0084] Another example of a substance that can be employed as a CA
(in accordance with some embodiments of the invention) is an
antistatic agent of any of the types described in U.S. Pat. No.
6,245,868, issued Jun. 12, 2001. As described in U.S. Pat. No.
6,245,868, an antistatic agent is any organic compound containing
at least one electron rich heteroatom from Groups IV, V and/or VI
and a hydrocarbyl moiety. Non-limiting examples of typical
heteroatoms include silicon, oxygen, nitrogen, phosphorus, and
sulfur. The antistatic agent should also contain at least one
active hydrogen atom attached to the heteroatom. In some
embodiments, it is preferable that the hydrocarbyl moiety have a
molecular weight sufficient to give it solubility in typical
hydrocarbon solvents, such as, for example a cyclic aliphatic or
aromatic hydrocarbon, for example toluene.
[0085] Examples of antistatic agents that can be employed as CAs in
accordance with some embodiments of the invention are represented
by the formula, R.sub.mXR'.sub.n, where R is a branched or straight
chain hydrocarbyl group or substituted hydrocarbyl group or groups
having one or more carbon atoms, R' is an alkyl hydroxy group such
as --CH.sub.2 CH.sub.2OH, X is at least one heteroatom (an O, N, P
or S atom or a combination thereof), and n is such that the formula
has no net charge. Non limiting examples are the following general
structures with R being a hydrocarbyl group are: RNH.sub.2,
R.sub.2NH, (R'C(OH).sub.n R'')NH.sub.2, (R'C(OH).sub.n
R'').sub.2NH, RCONH.sub.2, RCONHR, RN(ROH).sub.2, RCO.sub.2H,
RC(O)NROH, RC(S)OH, and R.sub.2PO.sub.2H. These compounds include
amines, alcohols, phenols, thiols, silanols, diols, polyols,
glycols, acids, and ethers.
[0086] Other examples of antistatic agents that can be employed as
CAs in accordance with some embodiments of the invention are
expressed by the formula shown in FIG. 4, where R.sup.3 is hydrogen
or a branched or preferably a straight chain alkyl group having 1
to 50 carbon atoms. R.sup.1 and R.sup.2 can be the same or
different and can be the same as R.sup.3 or contain another
heteroatom (e.g., O, N, P or S).
[0087] Other examples of antistatic agents that can be employed as
CAs in accordance with some embodiments of the invention are
expressed by the formula shown in FIG. 5 for a hydroxy containing
alkyl tertiary amine, where R.sup.1 is hydrogen or a linear or
branched alkyl group of from 1 to 50 carbon atoms (preferably
greater than 12 carbon atoms), and R.sup.2 can be a hydroxy group
such a (CH.sub.2).sub.xOH radical, where x is an integer from 1 to
50 (preferably from 2 to 25).
[0088] Other examples of antistatic agents that can be employed as
CAs in accordance with some embodiments of the invention are
quaternary ammonium compounds, and hydrocarbyl sulfates or
phosphates. Tertiary amines, ethoxylated amines and polyether
compounds are other examples of antistatic agents that can be
employed as CAs in accordance with some embodiments of the
invention. Antistatic agents employed as CAs in accordance with the
invention can be synthetically derived or otherwise.
[0089] When a CA has been pre-loaded in reactor 10 (or another
reactor) in accordance with the invention, one or more sensors
(e.g., acoustic carryover probes or static carryover probes) can be
used to monitor the presence of the CA in the reactor's cycle gas
loop. In response to the output of such a sensor, the operator can
determine whether more CA should be loaded into the reactor.
[0090] In some embodiments, a CA is pre-loaded into a reactor to
cause the CA to be present in the reactor in a concentration
(relative to the weight of a seed bed also present in the reactor)
in one of the following ranges: 2 ppm by weight to 3% by weight, or
preferably 5 ppm to 1000 ppm, or more preferably 5 ppm to 200 ppm,
or more preferably 10 ppm to 100 ppm, or most preferably 15 ppm to
50 ppm by weight.
[0091] Reactor 10 can be implemented as a mLLDPE
(metallocene-catalyzed, linear low-density polyethylene)
reactor.
[0092] FIG. 2 is a simplified cross-sectional view of another
fluidized bed reactor which can be pre-loaded in accordance with
the invention. The FIG. 2 reactor has a cylindrical (straight)
section between its bottom end and its top section, and a
distributor plate 12 within the straight section. In operation,
dense-phase surface 88 is the boundary between lean phase material
present within the reactor (above dense-phase surface 88) and
dense-phase material 86 within the reactor (in the volume bounded
by the straight section, plate 12, and surface 88).
[0093] FIG. 3 is a simplified cross-sectional view of another
fluidized bed reactor which can be pre-loaded in accordance in
accordance with the invention. The FIG. 3 reactor has a cylindrical
(straight) section between its bottom end and its top section, and
a distributor plate 12 within the straight section. The diameter of
each horizontal cross-section of the top section is greater than
the diameter of the straight section, but the top section of the
FIG. 3 reactor is shaped differently than the top section of
reactor 10 of FIG. 1. In operation of the FIG. 3 reactor,
dense-phase surface 98 is the boundary between lean phase material
present within the reactor (above dense-phase surface 98) and
dense-phase material 96 within the reactor (in the volume bounded
by the straight section, plate 12, and surface 98).
[0094] We next describe examples of commercial-scale reactions
(e.g., commercial-scale, gas-phase fluidized-bed polymerization
reactions) that can be performed in a reactor that has been
pre-loaded in accordance with the invention. Some such reactions
can occur in a reactor having the geometry of reactor 10 of FIG. 1,
or the geometry of the FIG. 2 or FIG. 3 reactor. In different
embodiments of the invention, any of a variety of different
reactors is pre-loaded and optionally also then operated to perform
a polymerization reaction in accordance with the invention.
[0095] In some embodiments, a continuous gas phase fluidized bed
reactor is pre-loaded in accordance with the invention before it
operates to perform polymerization as follows. The fluidized bed is
made up of polymer granules. Liquid or gaseous feed streams of the
primary monomer and hydrogen together with liquid or gaseous
comonomer are combined and introduced into the recycle gas line
upstream of the fluidized bed. For example, the primary monomer is
ethylene and the comonomer is hexene. The individual flow rates of
ethylene, hydrogen and comonomer are controlled to maintain fixed
composition targets. The ethylene concentration is controlled to
maintain a constant ethylene partial pressure. The hydrogen is
controlled to maintain a constant hydrogen to ethylene mole ratio.
The hexene is controlled to maintain a constant hexene to ethylene
mole 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. Its rate is adjusted to maintain a constant production
rate. The reacting bed of growing polymer particles is maintained
in a fluidized state by the continuous flow of the make up feed and
recycle gas through the reaction zone. In some implementations, a
superficial gas velocity of 1-3 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. The product is removed semi-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 at the same time recycling
a large portion of the unreacted gases back to the reactor. This
product is purged to remove entrained hydrocarbons and treated with
a small steam of humidified nitrogen to deactivate any trace
quantities of residual catalyst.
[0096] In other embodiments, a reactor is pre-loaded in accordance
with the invention and then operated to perform polymerization
using any of a variety of different processes (e.g., solution,
slurry, or gas phase processes). For example, the reactor can be a
fluidized bed reactor that is operated to produce polyolefin
polymers by a gas phase polymerization process. This type of
reactor and means for operating such a reactor are well known. In
operation of such reactors to perform gas phase polymerization
processes, the polymerization medium can be mechanically agitated
or fluidized by the continuous flow of the gaseous monomer and
diluent.
[0097] In some embodiments, a polymerization reaction is performed
in a reactor that has been pre-loaded in accordance with the
invention. The reaction can be a continuous gas phase process
(e.g., a fluid bed process). 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. The gas
leaving the reaction zone is passed to the velocity reduction zone
where entrained particles are removed. The gas is compressed in a
compressor, passed through a heat exchanger wherein the heat of
polymerization is removed, and then returned to the reaction
zone.
[0098] The reactor temperature of the fluid bed process can range
from 30.degree. C. or 40.degree. C. or 50.degree. C. to 90.degree.
C. or 100.degree. C. or 110.degree. C. or 120.degree. C. or
150.degree. C. In general, the reactor temperature is operated at
the highest temperature that is feasible taking into account the
sintering temperature of the polymer product within the reactor.
The polymerization temperature or reaction temperature typically
must be below the melting or "sintering" temperature of the polymer
to be formed. Thus, the upper temperature limit in one embodiment
is the melting temperature of the polyolefin produced in the
reactor.
[0099] In other embodiments, a reactor that has been pre-loaded in
accordance with the invention is then operated to effect
polymerization by a slurry polymerization process. A slurry
polymerization process generally uses pressures in the range of
from 1 to 50 atmospheres and even greater and temperatures in the
range of 0.degree. C. to 120.degree. C., and more particularly from
30.degree. C. to 100.degree. C. In a slurry polymerization, a
suspension of solid, particulate polymer is formed in a liquid
polymerization diluent medium to which monomer and comonomers and
often hydrogen along with catalyst are added. The suspension
including diluent is intermittently or continuously removed from
the reactor where the volatile components are separated from the
polymer and recycled, optionally after a distillation, to the
reactor. The liquid diluent employed in the polymerization medium
is typically an alkane having from 3 to 7 carbon atoms, a branched
alkane in one embodiment. The medium employed should be liquid
under the conditions of polymerization and relatively inert. When a
propane medium is used the process must be operated above the
reaction diluent critical temperature and pressure. In one
embodiment, a hexane, isopentane or isobutane medium is
employed.
[0100] In other embodiments, a reactor that has been pre-loaded in
accordance with the invention is operated to perform particle form
polymerization, or a slurry process in which the temperature is
kept below the temperature at which the polymer goes into solution.
In other embodiments, a reactor that has been pre-loaded in
accordance with the invention is a loop reactor or one of a
plurality of stirred reactors in series, parallel, or combinations
thereof. Non-limiting examples of slurry processes include
continuous loop or stirred tank processes.
[0101] A reactor that has been pre-loaded in accordance with some
embodiments of the invention can be operated to produce
homopolymers of olefins, e.g., 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 reactor that has been pre-loaded 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. When olefins are
formed in situ in the polymerization medium, the formation of
polyolefins containing long chain branching may occur.
[0102] 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 of from 0.0001
(comonomer:ethylene) to 50, and from 0.0001 to 5 in another
embodiment, and from 0.0005 to 1.0 in yet another embodiment, and
from 0.001 to 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 1000 atmospheres
pressure in one embodiment, and up to 500 atmospheres pressure in
another embodiment, and up to 200 atmospheres pressure in yet
another embodiment, and up to 100 atmospheres in yet another
embodiment, up to 50 atmospheres in yet another embodiment, and up
to 30 atmospheres in yet another embodiment.
[0103] 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
(partial pressures) of hydrogen increase the melt flow (MF) and/or
melt index (MI) of the polyolefin generated. The MF or 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 hexane or propene. The amount of hydrogen used in
some polymerization processes is an amount necessary to achieve the
desired MF or MI of the final polyolefin resin. In one embodiment,
the mole ratio of hydrogen to total monomer (H.sub.2:monomer) is
greater than 0.00001. The mole ratio is greater than 0.0005 in
another embodiment, greater than 0.001 in yet another embodiment,
less than 10 in yet another embodiment, less than 5 in yet another
embodiment, less than 3 in yet another embodiment, and less than
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 10
ppm in one embodiment, or up to 100 or 3000 or 4000 or 5000 ppm in
other embodiments, or between 10 ppm and 5000 ppm in yet another
embodiment, or between 500 ppm and 2000 ppm in another
embodiment.
[0104] A reactor that is pre-loadable in accordance with some
embodiments of the invention is 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.
[0105] A reactor that has been pre-loaded in accordance with some
embodiments of the invention can be operated to 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.
[0106] A reactor that has been pre-loaded in accordance with some
embodiments of the invention can be operated to perform a reaction
that employs one or more catalysts combined with up to 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 or a slurry with or without the catalyst system or its
components.
[0107] In a reactor that has been pre-loaded 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 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 Atmer
AS-990 (Ciba Specialty Chemicals, Basel, Switzerland). Other
antistatic compositions include the Octastat family of compounds,
more specifically Octastat 2000, 3000, and 5000.
[0108] Metal fatty acids and antistatic agents can be added as
either solid slurries or solutions 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.
[0109] Examples of polymers that can be produced in accordance with
the invention include the following: homopolymers and copolymers of
C2-C18 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 C2-C18 alpha olefin;
terpolymers of one or more C2-C18 alpha olefins with a diene.
[0110] Monomers that can be present in a reactor that has been
pre-loaded in accordance with the invention include one or more of:
C2-C18 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.
[0111] Fluidized bed polymerization (e.g., mechanically stirred
and/or gas fluidized) reactions can be performed in some reactors
that have been pre-loaded in accordance with the invention. Such a
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.
[0112] In various embodiments, any of many different types of
polymerization catalysts can be used in a polymerization process
performed in a reactor that has been pre-loaded in accordance with
the 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.
[0113] In various embodiments, a polymerization reaction performed
in a reactor that has been pre-loaded in accordance with the
invention can employ other additives, such as (for example) inert
particulate particles.
[0114] It should be understood that the term "includes" in the
claims denotes "is or includes."
[0115] 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.
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