U.S. patent application number 12/179368 was filed with the patent office on 2009-03-05 for method for reducing depositions in polymerization vessels.
Invention is credited to J. Davis Deborah, Michael F. McDonald, Timothy D. Shaffer, Pamela J. Wright.
Application Number | 20090062496 12/179368 |
Document ID | / |
Family ID | 39768508 |
Filed Date | 2009-03-05 |
United States Patent
Application |
20090062496 |
Kind Code |
A1 |
Shaffer; Timothy D. ; et
al. |
March 5, 2009 |
Method for Reducing Depositions in Polymerization Vessels
Abstract
Provided is a method for reducing depositions in polymerization
vessels, where the method includes the steps of providing a
reaction vessel having polymerization contact surfaces, polishing a
majority of the polymerization contact surfaces to have an average
percent excess surface areas (SAxs) of 2% or less, introducing a
catalyst system and at least one monomer or comonomer mixture in
the reaction vessel, and polymerizing the at least one monomer or
comonomer mixture. The catalyst may be soluble in the diluent used
for polymerization. The method may be useful for low temperature
polymerization systems.
Inventors: |
Shaffer; Timothy D.;
(Hackettstown, NJ) ; Wright; Pamela J.; (Easton,
PA) ; Deborah; J. Davis; (Pasadena, TX) ;
McDonald; Michael F.; (Kingwood, TX) |
Correspondence
Address: |
EXXONMOBIL CHEMICAL COMPANY
5200 BAYWAY DRIVE, P.O. BOX 2149
BAYTOWN
TX
77522-2149
US
|
Family ID: |
39768508 |
Appl. No.: |
12/179368 |
Filed: |
July 24, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60969268 |
Aug 31, 2007 |
|
|
|
Current U.S.
Class: |
526/348 ;
422/131 |
Current CPC
Class: |
C08F 210/12 20130101;
C08F 210/12 20130101; C08F 210/12 20130101; C08F 210/12 20130101;
C08F 2/01 20130101; C08F 2500/03 20130101; C08F 236/08 20130101;
C08F 2/14 20130101; C08F 2500/02 20130101 |
Class at
Publication: |
526/348 ;
422/131 |
International
Class: |
C08F 210/00 20060101
C08F210/00; B01J 19/00 20060101 B01J019/00 |
Claims
1. A method of producing an isoolefin polymer by polymerization,
the method comprising the steps of: a. dissolving a catalyst
system; b. providing at least one monomer or comonomer mixture in a
reaction vessel, the reaction vessel having polymerization contact
surfaces wherein a majority of the polymerization contact surfaces
have an average percent excess surface area (SAxs) of 2% or less,
wherein the average percent excess surface area is measured
according to the following equation: SAxs=100*((Sm/Sg)-1), wherein
Sm is the measured surface area and Sg is the geometric surface
area of the area being measured; c. introducing the dissolved
catalyst into the reaction vessel; and d. polymerizing the at least
one monomer or comonomer mixture to produce an isoolefin
polymer.
2. The method of claim 1, wherein the polymerization contact
surfaces have been finished by electropolishing to have an average
percent excess surface area (SAxs) of 2% or less.
3. The method of claim 1, wherein the method further comprises the
step of cleaning the reaction vessel, wherein the step of cleaning
the reaction vessel comprises refinishing the polymerization
contact surfaces to have an average excess surface area of 2% or
less.
4. The method of claim 1, wherein at least 80% of the
polymerization contact surfaces have an average percent excess
surface area of 2% or less.
5. The method of claim 1, wherein the polymerization contact
surfaces of the reaction vessel have an average percent excess
surface area of 1% or less.
6. The method of claim 1, wherein the polymerization is a
carbocationic polymerization.
7. The method of claim 1, wherein the polymerization is a slurry
polymerization process.
8. The method of claim 1, wherein the catalyst is dissolved in a
diluent and has a solubility in the diluent of at least 95%.
9. The method of claim 1, wherein the polymerization occurs at a
temperature of between -10.degree. C. and the freezing point of the
polymerization mixture.
10. The method of claim 1, wherein the comonomer mixture comprises
a C.sub.4 to C.sub.6 isoolefin monomer and a multiolefin.
11. A method of reducing film deposition and agglomeration in a
reaction vessel, comprising the steps of: a. providing a reaction
vessel having polymerization contact surfaces; b. polishing a
majority of the polymerization contact surfaces to have an have an
average percent excess surface area (SAxs) of 2% or less, wherein
the average percent excess surface area is measured according to
the following equation: SAxs=100*((Sm/Sg)-1), wherein Sm is the
measured surface area and Sg is the geometric surface area of the
area being measured; c. introducing a catalyst system and at least
one monomer or comonomer mixture in the reaction vessel; and d.
polymerizing the at least one monomer or comonomer mixture.
12. The method of claim 11, wherein the polymerization contact
surfaces are polished by electropolishing.
13. The method of claim 11, wherein at least 80% of the
polymerization contact surfaces are polished.
14. The method of claim 11, wherein the comonomer mixture comprises
a C.sub.4 to C.sub.6 isoolefin monomer and a multiolefin
15. The method of claim 11, wherein the polymerization occurs at a
temperature of less than 0.degree. C.
16. The method of claim 11, wherein the polymerization is a slurry
polymerization process.
17. The method of claim 11, wherein the catalyst is dissolved in a
diluent and has a solubility in the diluent of at least 95%.
18. A polymerization reaction vessel having polymerization contact
surfaces wherein a majority of the polymerization contact surfaces
have an average percent excess surface area (SAxs) of 2% or less,
wherein the average percent excess surface area is measured per the
following equation: SAxs=100*((Sm/Sg)-1), wherein Sm is the
measured surface area and Sg is the geometric surface area of the
area being measured.
19. The reaction vessel of claim 21, wherein at least 80% of the
polymerization contact surfaces have an average percent excess
surface area of 2% or less.
20. The reaction vessel of claim 21, wherein the polymerization
contact surfaces comprise at least one of interior surfaces/walls
of the vessel, interior or exterior walls/surfaces of heat exchange
tubes in the vessel.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application relates to and claims priority to U.S.
Provisional Patent Application Ser. No. 60/969,268 entitled "Method
for Reducing Depositions in Polymerization Vessels" which was filed
on Aug. 31, 2007, the disclosure of which is incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] This disclosure relates to a method for reducing polymer
depositions that occur during polymerizations. More specifically,
the present disclosure relates to a method for reducing polymer
buildup on the interior walls of reaction vessels employing
dissolved catalysts. Even more specifically, the present disclosure
relates to a method for reducing polymer film depositions on the
interior walls of reaction vessels during low temperature
polymerization employing dissolved catalysts.
BACKGROUND OF THE INVENTION
[0003] Isoolefin polymers are prepared in carbocationic
polymerization processes, generally under low temperatures in the
range of 0.degree. C. to -150.degree. C. Heat is usually generated
during polymerization, and various methods are used to remove the
generated heat. These various methods generally require a large
surface area for heat transfer so that the temperature of the
polymerization slurry remains constant or nearly constant.
[0004] During some polymerizations, there can be a number of issues
that arise during the process. First, there is a tendency of the
polymer to form or deposit on the reactor surfaces. This manner of
polymer formation or deposition occurs when the polymer accumulates
directly on the reactor surfaces, and is referred to herein as
"film deposition" or "deposition." As the film deposition
accumulates, the heat transfer coefficient between the reactor
slurry and the refrigerant decreases, leading to an increase in the
polymerization temperature of the reactor slurry. As the reactor
slurry temperature increases, the polymerization process becomes
less stable since it is more difficult to achieve the desired
molecular weight of the polymer product. When this happens, the
reactor must generally be taken offline, warmed to above ambient
temperatures, and solvent washed before being refilled with feed
and chilled back down to polymerization temperatures.
[0005] Additionally, during carbocationic polymerization processes,
there can be a tendency for the polymer particles in the reactor to
agglomerate with each other and to collect on the reactor wall,
heat transfer surfaces, impeller(s), and the agitator(s)/pump(s).
This is referred to herein as "polymer agglomeration," "particle
agglomeration," or "agglomeration." While the rate of polymer film
deposition on the reactor surfaces is generally proportional to the
rate of polymerization, particle agglomeration depends more on the
characteristics of the slurry, flow conditions, particle adhesion,
etc. The rate of agglomeration increases rapidly as reaction
temperatures rise. Agglomerated particles tend to adhere to and
grow and plate-out on all surfaces they contact, such as reactor
discharge lines, as well as any heat transfer equipment being used
to remove the exothermic heat of polymerization, which is critical
since low temperature reaction conditions must be maintained.
[0006] As reductions in film deposition and agglomeration may lead
to longer periods of time between reactor cleaning/washes, it would
be desirable to have a method for reducing film deposition and
agglomeration in polymerization vessels. Others have attempted to
address these problems in reaction vessels; however, there still
remains a need for improved methods for reducing film depositions
and agglomeration in polymerization vessels.
[0007] U.S. Patent Application Pub. No. 2005/0095176 discloses a
loop reactor wherein the goal is to prevent the creation of fine
particulates, or fines, during olefin polymerization wherein the
process is suitable for the copolymerization of ethylene and a
higher 1-olefin. A first polymerization is generated that actually
creates a film/coating on the reactor walls so that larger
particulates formed during the desired polymerization are not
broken or chipped by a non-smooth reactor wall.
[0008] US Patent Application Pub. No. 2005/0277748 discloses a
method of polymerizing an olefinic monomer system with a catalyst.
The olefinic monomer system is comprised of a single monomer or a
combination of two or more monomers wherein monomers are defined as
ethylene and higher 1-olefins. The polymerization reactor has an
inner surface whose arithmetic mean surface roughness of 1.0 .mu.m
or less. In the disclosed polymerizations, the agglomeration and
film deposition was also avoided by the use of a solid
catalyst.
[0009] EP Patent Application Pub. No. 0 107 127 A1 discloses a
process for olefinic polymerization in which the reaction vessels
are finished to a defined surface roughness of 2.5 .mu.m or less.
The application further discloses that the polymerization process
employs a solid catalyst and specifically teaches that the catalyst
must be of a defined size to minimize any buildup on the reaction
vessel. Additionally, an agent is added to the vessel to assist in
reducing polymer buildup. In the disclosed polymerizations, the
monomer systems employ ethylene and higher 1-olefins as
monomers.
[0010] Additional references of interest include: U.S. Pat. Nos.
3,923,765; 4,049,895; and 4,192934 and U.S. Patent Application
Publication No. 2007/0187078.
SUMMARY OF THE INVENTION
[0011] In one aspect, this disclosure relates to a method for
reducing film deposition and agglomeration in a reaction vessel.
The method comprises the steps of providing a reaction vessel
having polymerization contact surfaces, polishing a majority of the
polymerization contact surfaces to have an average percent excess
surface areas (SAxs) of 2% or less, introducing a catalyst system
and at least one monomer or comonomer mixture in the reaction
vessel, and polymerizing the at least one monomer or comonomer
mixture. In one embodiment, this invention relates to the reduction
of film deposition and agglomeration in polymerization systems
employing a dissolved catalyst. In another embodiment, the
reduction of film deposition and agglomeration is in low
temperature polymerization systems. In some embodiments, a
reduction in film deposition and agglomeration of up to 75% may be
realized as compared to reaction vessels with SAxs values of
greater than 2%.
[0012] In another aspect this disclosure relates to a method for
producing an isoolefin polymer by polymerization. The method
comprises the steps of dissolving a catalyst system, providing at
least one monomer or comonomer mixture in a reaction vessel,
introducing the dissolved catalyst in the reaction vessel, and
polymerizing the at least one monomer or comonomer mixture to
produce an isoolefin polymer. A majority of the polymerization
contact surfaces in the reaction vessel have an average percent
excess surface area (SAxs) of 2% or less. In one embodiment, the
method for producing an isoolefin by polymerization occurs at low
polymerization temperatures.
[0013] In a further aspect, this disclosure relates to a
polymerization reaction vessel having polymerization contact
surfaces where a majority of the polymerization contact surfaces
have an average percent excess surface area of 2% or less. In some
embodiments, at least 80% of the polymerization contact surfaces
have an average percent excess surface area of less than 2%. The
polymerization contact surfaces may include one or more of the
interior surfaces/walls of the reaction vessel, or
interior/exterior surfaces of the heat exchange tubes in the
reaction vessel.
[0014] These and other features, aspects, and advantages of the
present disclosure will become better understood with regard to the
following description and appended claims.
BRIEF DESCRIPTION OF THE FIGURES
[0015] FIG. 1 is a picture taken by e-RAM at 2000.times.
magnification of a sample of Reactor A's surface as it was
received.
[0016] FIG. 2 is a picture taken by e-RAM at 2000.times.
magnification of a sample of Reactor B's surface after it was
mechanically polished.
[0017] FIG. 3 is a picture taken by e-RAM at 2000.times.
magnification of a coupon of the same metal used to construct
Reactor C after it was electropolished.
[0018] FIG. 4 is a picture taken by e-RAM at 2000.times.
magnification of a coupon of the same metal used to construct
Reactor D after it was mechanically polished and then
electropolished.
[0019] FIG. 5 is a graph of the reactor vessel's interior surface
roughness versus film ratio.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Various specific embodiments, versions and examples of the
invention will now be described, including preferred embodiments
and definitions that are adopted herein for purposes of
understanding the claimed invention. While the following detailed
description gives specific preferred embodiments, those skilled in
the art will appreciate that these embodiments are exemplary only,
and that the invention can be practiced in other ways. For purposes
of determining infringement, the scope of the invention will refer
to any one or more of the appended claims, including their
equivalents, and elements or limitations that are equivalent to
those that are recited. Any reference to the "invention" may refer
to one or more, but not necessarily all, of the inventions defined
by the claims.
[0021] Disclosed herein is a method of producing an isoolefin
polymer by polymerization. The method comprises the steps of
dissolving a catalyst system, providing at least one monomer or
comonomer mixture in a reaction vessel, introducing the dissolved
catalyst in the reaction vessel, and polymerizing the at least one
monomer or comonomer mixture to produce an isoolefin polymer. A
majority of the polymerization contact surfaces in the reaction
vessel have an average percent excess surface area (SAxs) of less
than 2%.
[0022] In one embodiment, at least 80% of the polymerization
contact surfaces of the reaction vessel have a SAxs of less than
2%.
[0023] In some embodiments, the polymerization contact surfaces of
the reaction vessel have a SAxs of less than 1%, or less than 0.6%,
or in other embodiments less than 0.1%.
[0024] In another embodiment, the polymerization is a carbocationic
polymerization.
[0025] In yet another embodiment, the polymerization is a slurry
polymerization process.
[0026] In one aspect of the disclosed polymerization method, and in
combination with any of the above described embodiments or aspects,
the catalyst employed in the polymerization is dissolved in a
diluent and has a solubility in the diluent of at least 95%. In
some embodiments the catalyst may have a solubility in the selected
diluent of at least 99%.
[0027] In another aspect of the disclosed polymerization method,
and in combination with any of the above described embodiments or
aspects, the polymerization occurs at a temperature of less than
0.degree. C. In one embodiment, the polymerization occurs at a
temperature in the range of -10.degree. C. to the freezing point of
the polymerization mixture.
[0028] In another aspect of the disclosed polymerization method,
and in combination with any of the above disclosed embodiments or
aspects, the monomer or comonomer mixture is selected from
hydrocarbon monomers, homopolymers, copolymers, interpolymers, and
terpolymers. In one embodiment, the comonomer mixture comprises a
C.sub.4 to C.sub.6 isoolefin monomer and a multiolefin.
[0029] In some embodiments, and in combination with any of the
above described embodiments or aspects, the polymerization method
further comprises the step of cleaning the reaction vessel, wherein
the polymerization contact surfaces are refinished to have a SAxs
of 2% or less.
[0030] Also disclosed herein is a method of reducing film
deposition and agglomeration in a reaction vessel. The method
comprises the steps of providing a reaction vessel having
polymerization contact surfaces, polishing a majority of the
polymerization contact surfaces to have an average percent excess
surface area (SAxs) of 2% or less, introducing a catalyst system
and at least one monomer or comonomer mixture in the reaction
vessel, and polymerizing the at least one monomer or comonomer
mixture. In some embodiments, this method of reducing film
deposition and agglomeration is in low temperature polymerization
systems. In other embodiments, film deposition and agglomeration is
reduced in polymerization systems employing a complexed, or
dissolved, catalyst.
[0031] In some embodiments the polymerization contact surfaces are
electropolished.
[0032] In one embodiment, at least 80% of the polymerization
contact surfaces of the reaction vessel have a SAxs of less than
2%.
[0033] In some embodiments, the polymerization contact surfaces of
the reaction vessel have a SAxs of less than 1%, or less than 0.6%,
or in other embodiments less than 0.1%.
[0034] In another embodiment, the polymerization is a carbocationic
polymerization.
[0035] In yet another embodiment, the polymerization is a slurry
polymerization process.
[0036] In one aspect of the disclosed method for reducing film
deposition and agglomeration, and in combination with any of the
above described embodiments or aspects, the catalyst employed in
the polymerization is dissolved in a diluent and has a solubility
in the diluent of at least 95%. In some embodiments the catalyst
may have a solubility in the selected diluent of at least 99%. In
further embodiments, the catalyst is dissolved in the diluent prior
to mixing the catalyst with the monomer or comonomer mixture.
[0037] In another aspect of the disclosed method for reducing film
deposition and agglomeration, and in combination with any of the
above described embodiments or aspects, the polymerization occurs
at a temperature of less than 0.degree. C. In one embodiment, the
polymerization occurs at a temperature in the range of -10.degree.
C. and the freezing point of the polymerization mixture.
[0038] In another aspect of the disclosed method for reducing film
deposition and agglomeration, and in combination with any of the
above disclosed embodiments or aspects, the monomer or comonomer
mixture is selected from hydrocarbon monomers, homopolymers,
copolymers, interpolymers, and terpolymers. In one embodiment, the
comonomer mixture comprises a C.sub.4 to C.sub.6 isoolefin monomer
and a multiolefin.
[0039] Useful monomers include any hydrocarbon monomer that is
polymerizable using carbocationic olefin polymerization. Preferred
monomers include one or more of olefins, alpha-olefins,
disubstituted olefins, isoolefins, conjugated dienes,
non-conjugated dienes, styrenics and/or substituted styrenics, and
vinyl ethers. Isoolefin refers to any olefin monomer having two
substitutions on the same carbon while multiolefin refers to any
monomer having two double bonds. The styrenic may be substituted
(on the ring) with an alkyl, aryl, halide, or alkoxide group.
Preferably, the monomer contains 2 to 20 carbon atoms, more
preferably 2 to 9, even more preferably 3 to 9 carbon atoms.
Examples of preferred olefins include styrene, para-alkylstyrene,
para-methylstyrene, alpha-methyl styrene, divinylbenzene,
diisopropenylbenzene, isobutylene, 2-methyl-1-butene,
3-methyl-1-butene, 2-methyl-2-pentene, isoprene, butadiene,
2,3-dimethyl-1,3-butadiene, .beta.-pinene, myrcene,
6,6-dimethyl-fulvene, hexadiene, cyclopentadiene, piperylene,
methyl vinyl ether, ethyl vinyl ether, isobutyl vinyl ether, and
the like. Monomer may also be combinations of two or more monomers.
Styrenic block copolymers may also be used as monomers. Preferred
block copolymers include copolymers of styrenics, such as styrene,
para-methylstyrene, alpha-methylstyrene, and C.sub.4 to C.sub.30
diolefins, such as isoprene, butadiene, and the like. Particularly
preferred monomer combinations include isobutylene and para-methyl
styrene; isobutylene and isoprene; as well as homopolymers of
isobutylene.
[0040] The monomers may be present in the polymerization medium in
an amount ranging from 75 wt % to 0.01 wt % in one embodiment,
alternatively 60 wt % to 0.1 wt %, alternatively from 40 wt % to
0.2 wt %, alternatively 30 to 0.5 wt %, alternatively 20 wt % to
0.8 wt %, and alternatively from 15 wt % to 1 wt % in another
embodiment.
[0041] Isoolefin polymers are prepared in carbocationic
polymerization processes. Of special importance is butyl rubber
which is a copolymer of isobutylene with a small amount of
isoprene. Butyl rubber is made by low temperature cationic
polymerization that generally requires that the isobutylene have a
purity of greater than 99.5 wt % and that the isoprene have a
purity of greater than 98.0 wt % to prepare high molecular weight
butyl rubber.
[0042] In one embodiment, butyl polymers are prepared by reacting a
comonomer mixture, the mixture having at least (1) a C.sub.4 to
C.sub.6 isoolefin monomer component such as isobutylene with (2) a
multiolefin or conjugated diene monomer component. The C.sub.4 to
C.sub.6 isoolefin may be one or more of isobutylene,
2-methyl-1-butene, 3-methyl-1-butene, 2-methyl-2-butene, and
4-methyl-1-pentene. The multiolefin may be one or more of a C.sub.4
to C.sub.14 conjugated diene such as isoprene, butadiene,
2,3-dimethyl-1,3-butadiene, .beta.-pinene, myrcene,
6,6-dimethyl-fulvene, hexadiene, cyclopentadiene, and
piperylene.
[0043] The polymerization process may also result in terpolymers
and tetrapolymers comprising any combination of the monomers listed
above. Preferred terpolymers and tetrapolymers include polymers
comprising isobutylene, isoprene, and divinylbenzene; polymers
comprising isobutylene, para-alkylstyrene (preferably paramethyl
styrene), and isoprene; polymers comprising cyclopentadiene,
isobutylene, and paraalkyl styrene (preferably paramethyl styrene);
polymers of isobutylene cyclopentadiene, and isoprene; polymers
comprising cyclopentadiene, isobutylene, and methyl
cyclopentadiene; and polymers comprising isobutylene,
paramethylstyrene, and cyclopentadiene.
[0044] Useful catalysts systems include any Lewis acid(s) or other
metal complex(es) used to catalyze the polymerization of the
monomers described above, and may include at least one initiator,
and optionally other minor catalyst component(s). Additionally, the
components of the catalyst system are soluble in the diluent used
for the polymerization. When referring to the solubility of the
catalyst components, what is meant is the ability of the component
to dissolve or blend uniformly in the diluent, becoming molecularly
or ionically dispersed in the diluent. The catalyst components
should have a solubility in the diluent such that at least 95% of
the component is molecularly or ionically dispersed in the diluent.
In another embodiment, the catalyst components have at least a 98%
solubility; and in still another embodiment, the catalyst
components have at least a 99% solubility; and in still yet another
embodiment, the catalyst components have at least a 99.5%
solubility.
[0045] The Lewis acid (also referred to as the co-initiator or
catalyst) may be any Lewis acid based on metals from Group 4, 5,
13, 14, and 15 of the Periodic Table of the Elements, including
boron, aluminum, gallium, indium, titanium, zirconium, tin,
vanadium, arsenic, antimony, and bismuth. One skilled in the art
will recognize that some elements are better suited in the practice
of the invention depending on the monomers being polymerized. In
one embodiment, the metals are aluminum, boron, and titanium, with
aluminum being desirable. Illustrative examples include AlCl.sub.3,
(alkyl)AlCl.sub.2, (C.sub.2H.sub.5).sub.2AlCl,
(C.sub.2H.sub.5).sub.3Al.sub.2Cl.sub.3, BF.sub.3, SnCl.sub.4, and
TiCl.sub.4. Particularly preferred Lewis acids may be any of those
useful in cationic polymerization of isobutylene copolymers
including: aluminum trichloride, aluminum tribromide, ethylaluminum
dichloride, ethylaluminum sesquichloride, diethylaluminum chloride,
methylaluminum dichloride, methylaluminum sesquichloride,
dimethylaluminum chloride, boron trifluoride, and titanium
tetrachloride, with ethylaluminum dichloride and ethylaluminum
sesquichloride being preferred. Lewis acids such as
methylaluminoxane ("MAO") and specifically designed weakly
coordinating Lewis acids such as B(C.sub.6F.sub.5).sub.3 are also
suitable Lewis acids.
[0046] Useful initiators include those which are soluble in a
suitable diluent with the chosen Lewis acid to yield a complex
which rapidly reacts with the selected monomers to form a
propagating polymer chain. Illustrative examples include Bronsted
acids such as H.sub.2O, HCl, RCOOH (wherein R is an alkyl group),
alkyl halides, such as (CH.sub.3).sub.3CCl,
C.sub.6H.sub.5C(CH.sub.3).sub.2Cl, and
2-chloro-2,4,4-trimethylpentane. Transition metal complexes, such
as metallocenes and other such materials that can act as single
site catalyst systems, such as when activated with weakly
coordinating Lewis acids or Lewis acid salts, may also be used to
initiate isobutylene polymerization.
[0047] In a preferred embodiment, the Lewis acid is present at
anywhere from about 0.1 times the moles of initiator present to
about 200 times the moles of initiator present. In a further
preferred embodiment, the Lewis acid is present at anywhere from
about 0.8 times the moles of initiator present to about 20 times
the moles of initiator present. In a preferred embodiment the
initiator is present at anywhere from about 0.1 moles per liter to
about 10.sup.-6 moles per liter. One skilled in the art will
realize that greater or lesser amounts of initiator may also be
used depending on the catalyst and monomer being polymerized.
[0048] The amount of the catalyst employed will depend on the
desired molecular weight and molecular weight distribution of the
polymer being produced. Typically the range will be from about
1.times.10.sup.-6 moles per liter to 3.times.10.sup.-2 moles per
liter and most preferably from 1.times.10.sup.-4 to
1.times.10.sup.-3 moles per liter.
[0049] In one embodiment, the reactor and the catalyst system are
substantially free of water. Substantially free of water is defined
as less than 30 ppm (based upon total weight of the catalyst
system), preferably less than 20 ppm, preferably less than 10 ppm,
preferably less than 5 ppm, preferably less than 1 ppm. However,
when water is selected as an initiator, it may be added to the
catalyst system to be present at greater than 30 ppm, preferably
greater than 40 ppm, and even more preferably greater than 50 ppm
(based upon total weight of the catalyst system).
[0050] The diluent or diluent mixture is selected based upon its
solubility in the polymer. Certain diluents are soluble in the
polymer. Preferred diluents have little to no solubility in the
polymer. While diluent may be trapped within the polymer during the
polymerization process, preferably the diluent is chosen so that
the polymer is not soluble in the diluent.
[0051] Suitable diluents in the present disclosure include
halogenated hydrocarbons, especially chlorinated and/or fluorinated
hydrocarbons, and the like. Specific examples include but are not
limited to the halogenated versions of methane, ethane, propane,
butane, isobutane, 2-methylbutane, 2,2-dimethylbutane,
2,3-dimethylbutane, pentane, 2-methylpentane, 3-methylpentane,
methylcyclopentane, 2,2-dimethylpentane, 2,3-dimethylpentane,
2,4-dimethylpentane, 3,3-dimethylpentane, 2,2,4-trimethylpentane,
3-ethylpentane, hexane, isohexane, 2-methylhexane, 3-methylhexane,
3-ethylhexane, 2,5-dimethylhexane, heptane, 2-methylheptane,
octane, nonane, decane, dodecane, undecane, cyclopropane,
cyclobutane, cyclopentane, methylcyclopentane,
1,1-dimethylcycopentane, cis-1,2-dimethylcyclopentane,
trans-1,2-dimethylcyclopentane, trans-1,3-dimethylcyclopentane,
ethylcyclopentane, cyclohexane, methylcyclohexane, benzene,
toluene, xylene, ortho-xylene, para-xylene, and meta-xylene,
preferably the chlorinated versions of the above, and more
preferably fluorinated versions of all of the above. Brominated
versions of the above are also useful. Specific examples include,
methyl chloride, methylene chloride, ethyl chloride, propyl
chloride, butyl chloride, chloroform, and the like.
[0052] Hydrofluorocarbon(s) can be used as diluents, either alone
or in combination with other diluents. As used herein,
hydrofluorocarbons ("HFCs" or "HFC") are defined to be saturated or
unsaturated compounds consisting essentially of hydrogen, carbon,
and fluorine, provided that at least one carbon, at least one
hydrogen, and at least one fluorine are present. Specific examples
include fluoromethane, difluoromethane, trifluoromethane,
1,1-difluoroethane, 1,1,1-trifluoroethane, and
1,1,1,2-tetrafluoroethane. In one embodiment, the HFC is used in
combination with a chlorinated hydrocarbon such as methyl chloride.
Additional embodiments include using the HFC in combination with
hexanes or methyl chloride and hexanes. In another embodiment the
diluents such as HFCs are used in combination with one or more
gases inert to the polymerization such as carbon dioxide, nitrogen,
hydrogen, argon, neon, helium, krypton, xenon, and/or other inert
gases that are preferably liquid at entry to the reactor. Preferred
gases include carbon dioxide and/or nitrogen.
[0053] In one embodiment, the diluent comprises non-perfluorinated
compounds or the diluent is a non-perfluorinated diluent.
Perfluorinated compounds consist of carbon and fluorine. However,
in another embodiment, when the diluent comprises a blend, the
blend may comprise perfluorinated compounds, preferably, the
catalyst, monomer, and diluent are present in a single phase or the
aforementioned components are miscible with the diluent as
described in further detail below. In another embodiment, the blend
may also comprise those compounds consisting of chlorine, fluorine,
and carbon.
[0054] In another embodiment, non-reactive olefins may be used as
diluents in combination with other diluents such as HFCs. Examples
include, but are not limited to, ethylene, propylene, and the
like.
[0055] In another embodiment the diluents, including HFCs, are used
in combination with one or more nitrated alkanes, including C.sub.1
to C.sub.40 nitrated linear, cyclic, or branched alkanes. Preferred
nitrated alkanes include, but are not limited to, nitromethane,
nitroethane, nitropropane, nitrobutane, nitropentane, nitrohexane,
nitroheptane, nitrooctane, nitrodecane, nitrononane, nitrododecane,
nitroundecane, nitrocyclomethane, nitrocycloethane,
nitrocyclopropane, nitrocyclobutane, nitrocyclopentane,
nitrocyclohexane, nitrocycloheptane, nitrocyclooctane,
nitrocyclodecane, nitrocyclononane, nitrocyclododecane,
nitrocycloundecane, nitrobenzene, and the di- and tri-nitro
versions of the above.
[0056] The polymerization process may be practiced in continuous or
batch processes. Possible reactors for the process include any
reactor selected from the group consisting of a continuous flow
stirred tank reactor, a plug flow reactor, a tubular reactor, and
an autorefrigerated boiling-pool reactor.
[0057] During polymerization, heat is removed by use of heat
transfer surfaces, wherein polymerization occurs on one side of the
heat transfer surface and coolant is present on the other side. An
example is a reactor where tubes containing coolant run inside the
reactor polymerization zone. Another example would be where the
polymerization occurs inside a tube and the coolant is present on
the outside of the tube in a shell.
[0058] This invention may also be practiced in batch reactors where
the monomers, diluent, and catalyst are charged to the reactor and
then polymerization proceeds to completion (such as by quenching)
and the polymer is then recovered.
[0059] In certain embodiments, the polymerization is a slurry
polymerization process. The polymerization is carried-out in a
continuous polymerization process in which the catalyst,
monomer(s), and diluent are present as a single phase. In slurry
polymerization, the monomers, catalyst(s), and initiator(s) are all
miscible in the diluent or diluent mixture, i.e., constitute a
single phase, while the polymer precipitates from the diluent with
good separation from the diluent.
[0060] When using a continuous flow stirred tank-type reactor, the
reactor is generally fitted with an efficient agitation means, such
as a turbo-mixer or impeller(s), an external cooling jacket and/or
internal cooling tubes and/or coils, or other means of removing the
heat of polymerization to maintain the desired reaction
temperature, inlet means (such as inlet pipes) for monomers,
diluents, and catalysts (combined or separately), temperature
sensing means, and an effluent overflow or outflow pipe which
withdraws polymer, diluent, and unreacted monomers among other
things, to a holding drum or quench tank. Preferably, the reactor
is purged of air and moisture.
[0061] The reactors are preferably designed to deliver good mixing
of the catalyst and monomers within the reactor, good turbulence
across or within the heat transfer tubes or coils, and enough fluid
flow throughout the reaction volume to avoid excessive polymer
accumulation or separation from the diluent.
[0062] In order to reduce film deposition and agglomeration,
various surfaces within the reaction vessel are finished to have
reduced surface roughness. In preferred embodiments, the heat
transfer surfaces, such as the interior surfaces/walls of the
reaction vessel, or interior or exterior walls/surfaces of heat
exchange tubes in a reaction vessel, are finished to have a reduced
microscopic surface roughness. Other surfaces of the reaction
vessel that have contact with the components of the polymerization
mixture, such as a tank agitator, may also be finished to have
reduced microscopic surface roughness.
[0063] It is desirable to reduce film deposition and agglomeration
as much as possible, as any accumulation may change the dynamics
within the reaction vessel. Accumulated film deposition and
agglomeration may lead to regions within the reaction vessel where
there is reduced fluid flow and even regions where there is little
to no fluid flow (i.e., dead zones). These regions of reduced fluid
flow and regions with little to no fluid flow may in turn lead to
increased film deposition and agglomeration in other regions of the
reaction vessel. Additionally, when there is film deposition and
agglomeration deposits, these deposits may break-off of the surface
and lead to plugging within the reaction vessel, agitators and/or
impeller(s), and in the outflow line or exit port. Thus, in
preferred embodiments a majority of the polymerization contact
surfaces are finished to have reduced microscopic surface
roughness. Additionally, if necessary, after the reaction vessel
has been in operation for a period of time, it may be necessary to
refinish the polymerization contact surfaces of the vessel.
[0064] The polymerization contact surfaces may be finished to have
reduced microscopic surface roughness by polishing. In some
embodiments the polymerization contact surfaces are mechanically
polished. In other preferred embodiments the polymerization contact
surfaces are electropolished. In further embodiments, the
polymerization contact surfaces may be mechanically polished and
then electropolished. In still other embodiments, the
polymerization contact surfaces may be electropolished and then
mechanically polished.
[0065] The magnitude of the film deposition and agglomeration may
be reduced by preparing surfaces in which the measured surface area
approaches the geometric surface area. While contact profilometry
may generally be used to measure a surface's roughness, it does not
adequately describe the polymerization contact surface's
characteristics in such a way to provide for a reduction in film
deposition and agglomeration. Preferably the prepared surface's
roughness is characterized by the determination of the microscopic
surface area. The microscopic surface area may be measured by an
electronic roughness analyzing microscope (e-RAM), by atomic force
microscopy (AFM), by phase shifting interferometry, or by laser
confocal scanning microscopy. The measured microscopic surface area
(Sm) may then be compared to the geometric surface area (Sg) to
determine the percent excess surface area (SAxs) by the Equation.
The percent excess surface area value characterizes how much larger
the measured surface area is than the geometric surface area.
SAxs=100*((Sm/Sg)-1), EQUATION
where Sm is the measured surface area and Sg is the geometric
surface area of the area being measured.
[0066] The measured surface area (Sm) may be measured by e-RAM,
AFM, phase shifting interferometry, or by laser confocal scanning
microscopy. For example, the Sm may be measured using an e-RAM such
as the ERA-8900FE available from Elionix. Methods for calculating
Sm are described in N. K. Myshkin et al., Surface Roughness and
Texture Analysis in Microscale, 254 Wear 1001-1009 (2003) and J.
Rudzitis et al., Automated System for Three-Dimensional Roughness
Testing, Initiatives of Precision Engineering at the Beginning of
the Millennium 10.sup.th International Conference on Precision
Engineering Jul. 18-20, 2001, Yokohama, Japan (Springer, US 2002),
both of which are incorporated by reference.
[0067] The geometric surface area (Sg) is the area being measured
when measuring the Sm. If the Sg analyzed is too large it may not
adequately describe the polymerization contact microscopic
surface's characteristics. For example, a surface may have a large
scale waviness or texture and still have an adequate SAxs value if
it is microscopically smooth. Or a surface may be smooth on a large
scale yet be microscopically rough, thereby having an inadequate
SAxs value. However, if the Sg analyzed is too small then it may
not be representative of the reaction vessel's surface. Thus, it is
preferred that the Sg is about 1000 .mu.m.times.1000 .mu.m or less,
or about 500 .mu.m.times.500 .mu.m or less, or even more preferably
about 100 .mu.m.times.100 .mu.m or less. In some embodiments the Sg
has an area of about 10,000 .mu.m.sup.2 or less, or 6,400
.mu.m.sup.2 or less, or 2,700 .mu.m.sup.2 or less, or 2,500
.mu.m.sup.2 or less, or even 2000 .mu.m.sup.2 or less, or in some
embodiments 1500 .mu.m.sup.2 or less or 1000 .mu.m.sup.2 or less.
In other embodiments, the Sg is an area in the range of about 100
.mu.m.sup.2 to about 10,000 .mu.m.sup.2, or in the range of about
200 .mu.m.sup.2 to about 5000 .mu.m.sup.2, or in the range of about
500 .mu.m.sup.2 to about 3000 .mu.m.sup.2.
[0068] Reductions in film deposition and agglomeration may start to
be seen when the SAxs value is 5% or less. Further reductions in
film deposition and agglomeration may be achieved when the
polymerization contact surfaces are finished so that they have a
SAxs value of less than 2%. In some embodiments, reducing the SAxs
of the polymerization contact surfaces to 2% or less (as measured
by e-RAM at 2000.times. magnification) may lead to a reduction in
the film deposition by up to 75% relative to reactors with greater
SAxs values.
[0069] Preferably the polymerization contact surfaces are finished
so that they have a SAxs value of 2% or less, or 1% or less, or in
some embodiments 0.6% or less. In some embodiments the
polymerization contact surfaces may have a SAxs value of 0.25% or
less, or 0.1% or less. In other embodiments, the polymerization
contact surfaces may have a SAxs value of 0.8% or less, or 0.5% or
less, or 0.25% or less, or 0.1% or less, or in further embodiments
0.05% or less.
[0070] Those surfaces which contact the polymerization medium may
be defined as the polymerization contact surfaces. A majority of
the polymerization contact surfaces are finished to the above
desired SAxs value. In one embodiment, at least 80% of the
polymerization contact surfaces are finished to the above desired
SAxs. In another embodiment, at least 90%, most preferably at least
97% of the polymerization contact surfaces are finished to the
above desired SAxs value.
[0071] In some embodiments the heat transfer surfaces of the vessel
may be finished to have the above desired SAxs value. The heat
transfer surfaces include all surfaces contained within the
reaction vessel (exclusive of any feed stream inlet, overflow, or
discharge piping) that might have contact with the components of
the polymerization system immediately before, during, and after
polymerization occurs and which are capable of heat transfer. At a
minimum, at least 50% of all heat transfer surfaces in the reaction
vessel are finished to the above desired SAxs value. Preferably, at
least 80% of all heat transfer surfaces in the vessel have the
desired finish. Even more preferably, at least 95% of all heat
transfer surfaces in the vessel have the desired finish.
[0072] Preferably the polymerization contact surfaces and/or heat
transfer surfaces are electropolished. In one embodiment, a reactor
surface with a SAxs value of from 6% to 8% is electropolished until
it has an SAxs value of 2% or less. In other embodiments, heat
transfer surfaces may first be mechanically polished and then
electropolished to achieve the desired SAxs value. In further
embodiments, the heat transfer surfaces may be mechanically
polished in order to obtain the desired SAxs value, however, this
may require a greater number of polishing steps when the starting
SAxs value of the heat transfer surface is large.
[0073] It is also contemplated that the turbulence within the
reaction vessel may impact the film deposition and agglomeration.
For example, in a commercial scale reactor the turbulence, as
measured by the Reynolds number, may be 10 to 20 times greater than
the turbulence within a laboratory scale reactor. Thus, when the
turbulence is less, such as in a laboratory scale reactor, the
surface may need to be have a smaller SAxs value (e.g., 0.5% or
less, or 0.1% or less) in order to obtain the same reductions in
film deposition and agglomeration that may be achieved in a
commercial scale reactor (where there is more turbulence) which has
a larger SAxs value (e.g., 2% or less).
[0074] The polymerization reaction temperature is selected based on
the target polymer molecular weight and the monomer to be
polymerized as well as process and economic considerations, e.g.,
rate, temperature control, etc. The temperature for the
polymerization is less than 0.degree. C., preferably between
-10.degree. C. and the freezing point of the slurry in one
embodiment, and in the range of -25.degree. C. to -120.degree. C.
in another embodiment. In yet another embodiment, the
polymerization temperature is in the range of -40.degree. C. to
-100.degree. C., and in the range of -70.degree. C. to -100.degree.
C. in yet another embodiment. In yet another desirable embodiment,
the temperature range is from -80.degree. C. to -100.degree. C.
Different reaction conditions will produce products of different
molecular weights. Synthesis of the desired reaction product may be
achieved through monitoring the course of the reaction by
examination of samples taken periodically during the reaction.
[0075] In one embodiment, the polymerization temperature is within
10.degree. C. above the freezing point of the diluent, in another
embodiment within 8.degree. C. above the freezing point of the
diluent, in yet another embodiment within 6.degree. C. above the
freezing point of the diluent, in a further embodiment within
4.degree. C. above the freezing point of the diluent, in still
another embodiment within 2.degree. C. above the freezing point of
the diluent, in another embodiment within 1.degree. C. above the
freezing point of the diluent.
[0076] The order of contacting the monomer feed-stream, catalyst,
initiator, and diluent may vary. In one embodiment, the initiator
and Lewis acid are pre-complexed by mixing together in the selected
diluent for a prescribed amount of time ranging from 0.01 second to
10 hours, and then the pre-complex is injected into the continuous
reactor through a catalyst nozzle or injection apparatus. In
another embodiment, a Lewis acid and the initiator are added to the
reactor separately. In yet another embodiment, the initiator is
blended with the feed monomers before injection to the reactor.
Desirably, the monomer is not contacted with the Lewis acid, or the
Lewis acid combined with the initiator before the monomers enter
the reactor. In preferred embodiments, the catalyst is dissolved
either prior to introduction with the monomer or comonomer mixture
or after introduction with the monomer or comonomer mixture.
[0077] When the initiator and Lewis acid are allowed to pre-complex
by mixing together in the selected diluent, this occurs at
temperatures between 80.degree. C. and the freezing point
temperature of the diluent, with a contact time between 0.01
seconds and several hours, or between 0.1 seconds and 5 minutes,
preferably less than 3 minutes, preferably between 0.2 seconds and
1 minute before injection into the reactor.
[0078] The overall residence time in the reactor can vary. The time
being dependant on many factors, including, but not limited to,
catalyst activity and concentration, monomer concentration, feed
injection rate, production rate, reaction temperature, and desired
molecular weight. Residence time will generally be between about a
few seconds and five hours, and typically between about 10 and 60
minutes. Variables influencing residence time include the monomer
and diluent feed injection rates and the overall reactor
volume.
[0079] The catalyst to monomer ratio utilized will be those
conventional in this art for carbocationic polymerization
processes. In one embodiment, the monomer to catalyst mole ratios
will typically be in the range of 500 to 10000, and in the range of
2000 to 6500 in another embodiment. In yet another desirable
embodiment, the mole ratio of Lewis acid to initiator is in the
range of 0.5 to 10, or 0.75 to 8. The overall concentration of the
initiator in the reactor is typically in the range of 5 to 300 ppm
or in the range of 10 to 250 ppm. The concentration of the
initiator in the catalyst feed stream is typically in the range of
50 to 3000 ppm in one embodiment. Another way to describe the
amount of initiator in the reactor is by its amount relative to the
polymer. In one embodiment, there is from 0.25 to 20 moles
polymer/mole initiator and from 0.5 to 12 mole polymer/mole
initiator in another embodiment.
[0080] The reactor will contain sufficient amounts of the catalyst
system to catalyze the polymerization of the monomer containing
feed-stream such that a sufficient amount of polymer having desired
characteristics is produced. The feed-stream in one embodiment
contains a total monomer concentration greater than 20 wt % (based
on the total weight of the monomers, diluent, and catalyst system),
or greater than 25 wt % in another embodiment. In yet another
embodiment, the feed-stream will contain from 30 wt % to 50 wt %
monomer concentration based on the total weight of monomer,
diluent, and catalyst system.
[0081] Catalyst efficiency (based on Lewis acid) in the reactor is
maintained between 10,000 pounds of polymer per pound of catalyst
and 300 pounds of polymer per pound of catalyst and desirably in
the range of 4000 pounds of polymer per pound of catalyst to 1000
pounds of polymer per pound of catalyst by controlling the molar
ratio of Lewis acid to initiator.
[0082] In one embodiment, the polymerization of cationically
polymerizable monomers (such as polymerization of isobutylene and
isoprene to form butyl rubber) comprises several steps. First, a
reactor having a pump impeller capable of up-pumping or
down-pumping is provided. The pump impeller is typically driven by
an electric motor with a measurable amperage. The reactor typically
is equipped with parallel vertical reaction tubes within a jacket
containing liquid ethylene. The total internal volume, including
the tubes, is at least 30 to 50 liters and more typically at least
5,000 to 8,000 liters, thus capable of large scale volume
polymerization reactions. The reactor typically uses liquid
ethylene to draw the heat of the polymerization reaction away from
the forming slurry. The pump impeller keeps a constant flow of
slurry, diluent, catalyst system, and unreacted monomers through
the reaction tubes. A feed-stream of the cationically polymerizable
monomer(s) (such as isoprene and isobutylene) in a polar diluent is
charged into the reactor, the feed-stream containing less than
0.0005 wt % of cation producing silica compounds, and typically
free of aromatic monomers. The catalyst system is then charged into
the reactor, the catalyst system having a Lewis acid and an
initiator present in a molar ratio of from 0.50 to 10.0. Within the
reactor, the feed-stream of monomers and catalyst system are
allowed to contact one another, the reaction thus forming a slurry
of polymer (such as butyl rubber), wherein the solids in the slurry
have a concentration of from 20 vol % to 50 vol %. Finally, the
thus formed polymer (such as butyl rubber) is allowed to exit the
reactor through an outlet or outflow line while simultaneously
allowing the feed-stream charging to continue, thus constituting
the continuous slurry polymerization. The present disclosure
improves this process in a number of ways, e.g., by ultimately
reducing the amount of polymer accumulation on the reactor walls,
heat transfer surfaces, agitators and/or impeller(s), and in the
outflow line or exit port, as measured by pressure inconsistencies
or "jumps."
[0083] In one embodiment, the resultant polymer is a
polyisobutylene/isoprene polymer (butyl rubber) that has a
molecular weight distribution of from about 2 to 5, and an
unsaturation in the range of 0.5 to 2.5 mole per 100 mole of
monomer. This product may be subjected to subsequent halogenation
to afford a halogenated butyl rubber.
EXAMPLES
[0084] The present invention will now be further described with
reference to the following non-limiting examples.
[0085] Polymerizations were conducted in a laboratory-scale
continuous reactor constructed of stainless steel and designed to
permit the introduction of monomer and catalyst feeds as well as
the continuous removal of the polymer product. Mixing was provided
by a three-bladed impeller mounted on a stainless steel shaft and
driven by an external electric motor. The motor was run at 1200 rpm
to 1600 rpm. The reactor was also equipped with a thermocouple to
monitor the temperature of the reactor contents. The reactor was
cooled to the desired reaction temperature by immersing the
assembled reactor into a pentane or isohexane bath in an inert
atmosphere glove box. The temperature of the stirred hydrocarbon
bath was controlled to .+-.2.degree. C. All apparatus in liquid
contact with the reaction medium were dried at 120.degree. C. and
cooled in a nitrogen atmosphere before use.
[0086] Four reactors, which differed only by the quality of their
internal surface finishes, were used in the polymerization examples
below. One reactor was used as received (Reactor A). Two other
reactors (Reactors C and D) were electropolished to different final
surface finishes as characterized by the arithmetic average surface
roughness, R.sub.a. Reactor C was electropolished only. Reactor D
was first mechanically polished and then electropolished. Reactor B
was only mechanically polished in order to achieve an Ra value
similar to the Ra value for Reactor C.
[0087] The arithmetic average surface roughness (Ra) was measured
on each reactor using a Mahr Pocket Surf profilometer. Between six
and twenty-one separate measurements were taken on at least six
randomly chosen different areas of the reactor surface. The R.sub.a
values obtained from each of these measurements were then averaged
and are presented in Table 1 for each reactor, along with the
standard deviation of these values.
[0088] Surface area measurements were made with an electronic
roughness analyzing microscope ("e-RAM") (the e-RAM used was a
ERA-8900FE available from Elionix) at 2000.times. magnification on
two random samples representing each reactor surface. The measured
surface area (Sm) was determined for each sample using an analysis
area (Sg) of 45.times.60 .mu.m and the SAxs values were calculated
according to the Equation. The two SAxs values are listed in Table
1. The surface area of the "as received" reactor (Reactor A) and
the mechanically polished reactor (Reactor B) was determined from a
piece of the reactor itself. For Reactors C and D, coupons of the
same metal used to construct the reactors were polished using the
same procedures that were applied to the reactors, as described
above. These coupons were analyzed by e-RAM. The surface of
Reactors C and D were replicated using acetate replicating tape, a
common method used to study metal surfaces that are either
difficult to sample or when harvesting a portion of the metal is
not desired. The replicating tapes were sputter coated with gold
and imaged by Scanning Electron Microscope (SEM). The SEM images
were processed to provide a negative image of the replicating tape,
which itself is a negative image of the reactor surface. This
procedure produces a positive image that represents the surface of
the metal as if one were able to image it directly. The SEM images
captured at 1500.times. were then compared to the 2000.times.
images from e-RAM of the coupons to confirm that the coupon samples
were representative of the reactor surfaces. The SAxs values for
Reactors C and D were determined from the representative coupons.
Two SAxs values are reported for each reactor in Table 1.
TABLE-US-00001 TABLE 1 SAxs Values and Average Ra Values of Reactor
Surfaces Average +/-Ra Standard SAxs Reactor Ra, .mu.m Deviation
(two values) A 0.33 0.09 12.6, 12.8 B 0.15 0.02 0.23, 0.15 C 0.18
0.04 0.03, 0.04 D 0.10 0.04 0.03, 0.03
[0089] FIG. 1 is a picture taken by e-RAM at 2000+ magnification of
a random sample of Reactor A's surface as it was received. FIG. 2
is a picture taken by e-RAM at 2000.times. magnification of a
random sample of Reactor B's surface after it was mechanically
polished. FIG. 3 is a picture taken by e-RAM at 2000.times.
magnification of a coupon of the same metal used to construct
Reactor C after it was electropolished. FIG. 4 is a picture taken
by e-RAM at 2000.times. magnification of a coupon of the same metal
used to construct Reactor D after it was mechanically polished and
then electropolished. The e-RAM pictures in FIGS. 1-4 show a
geometric surface area (Sg) of 60 .mu.m.times.45 .mu.m. As seen in
FIGS. 1-4, and as demonstrated by the Ra and SAxs values for the
Reactors in Table 1, the four reactors have different microscopic
surface roughness.
[0090] Isobutylene (available from Matheson Tri-Gas or ExxonMobil
Chemical Company) and methyl chloride (available from Air Gas) were
dried by passing the gas through three stainless steel columns
containing barium oxide and were condensed and collected as liquids
in the glove box. 1,1,1,2-Tetrafluoroethane (134a) (available from
National Refrigerants) was dried by passing the gas through three
stainless steel columns containing 3 .ANG. molecular sieves and was
condensed and collected as a liquid in the glove box. Isoprene
(available from Aldrich) was either distilled prior to use or used
as received. Isoprene was charged to the monomer feed at 2.8 wt %
with respect to isobutylene. HCl solutions were prepared in either
methyl chloride or 134a by dissolving gaseous HCl (available from
Aldrich, 99% pure) into the condensed liquid at low temperature.
The concentration of the HCl in these prepared solutions was
determined by standard titration techniques. In the examples below,
the diluent composition referred to as the "blend" is a 50/50 wt/wt
mixture of 134a and methyl chloride.
[0091] The slurry copolymerizations were performed by first
preparing the monomer and catalyst feeds. The monomer feed was
prepared in a glass or metal reservoir and comprised isobutylene,
isoprene, the selected diluent, and ethanol. A catalyst feed was
prepared for each copolymerization in a separate reservoir. The
catalyst feed was prepared by adding a predetermined amount of the
stock HCl solution and a hydrocarbon solution of ethylaluminum
dichloride (EADC). The EADC/HCl molar ratio in the catalyst feed
for all examples was 3.0.
[0092] An initial monomer feed was also prepared and charged into
the reactor for the purpose of starting the polymerization run. The
concentration of monomer in this initial charge was 10 wt %
isobutylene. Isoprene was also charged to this initial monomer feed
at 2.8 wt % relative to isobutylene. All feeds were chilled to the
same temperature as the reactor using the chilled hydrocarbon bath
of the glove box. Polymerizations in the blend were conducted at a
reactor temperature of about -75.degree. C.+-.3.degree. C. Near the
beginning of the polymerization, the temperature of the bath was
lowered a few degrees to provide an initial difference in
temperature between the bath and the reactor contents. The
copolymerizations were begun by introducing the catalyst. The
catalyst flow rate was controlled to provide for a constant
differential temperature between the reactor and the bath to
achieve the target polymerization temperature for the run.
Optionally, the temperature of the bath was lowered to aid in
achieving the polymerization temperature target. Addition of
monomer feed from the reservoir was introduced into the reactor
approximately 10 minutes after the reaction commenced as evidenced
by the formation of precipitated polymer particles (slurry
particles). The run was continued until the monomer feed in the
reservoir was exhausted or until the desired amount of monomer feed
was consumed. Generally, the average monomer conversion in these
runs was better than 75% and at times as high as 99%.
[0093] At the end of the run, the contents of the reactor were
emptied and the polymer film on the wall of the vessel below the
vapor-liquid interface was collected, dried and weighed. The total
amount of polymer produced during the run was also collected dried
and weighed. A film ratio was then calculated for each run by
dividing the mass (in milligrams, mg) of the wall film by the mass
(in grams, g) of the total amount of polymer produced in the
experiment. The film ratios presented below have the units of mg of
film per g of polymer produced.
[0094] Several examples are presented for each reactor of defined
wall smoothness to demonstrate a range of film ratios produced in a
given reactor, see Table 2. The data for each reactor of defined
wall smoothness can then be averaged and presented in graphical
form with error bars indicating the high and low values obtained
for the given reactor, see FIG. 1.
TABLE-US-00002 TABLE 2 Average Film Ratios for Butyl
Polymerizations Run Reactor Wall Product Product Film Ratio (mg
Series Reactor Electropolished Average SAxs Mw MWD film/g polymer)
1 A N 12.7 113 3.0 2.4 2 A N 12.7 252 3.5 3.9 3 A N 12.7 125 2.6
3.6 4 A N 12.7 147 3.3 3.9 5 A N 12.7 153 2.7 3.2 6 A N 12.7 285
2.9 3.4 7 A N 12.7 216 2.8 3.1 8 B N 0.19 153 2.7 3.5 9 B N 0.19
161 3.0 3.0 10 B N 0.19 146 2.8 3.6 11 C Y 0.035 209 2.9 0.71 12 C
Y 0.035 153 2.8 0.94 13 C Y 0.035 173 3.3 0.70 14 C Y 0.035 136 2.9
1.98 15 C Y 0.035 143 3.3 1.13 16 C Y 0.035 200 3.6 1.06 17 C Y
0.035 165 3.1 1.29 18 C Y 0.035 214 3.8 1.14 19 D Y 0.030 227 3.1
0.93 20 D Y 0.030 294 3.3 0.87 21 D Y 0.030 288 3.1 0.90 22 C Y
0.035 161 3.7 0.65 23 C Y 0.035 153 3.6 0.63 24 C Y 0.035 215 3.9
0.92
[0095] Comparing the average film ratios for each reactor with the
reactor's Ra value, demonstrate that the Ra value did not
adequately characterize the fundamental surface features that
result in the reduction of film ratio that is observed by polishing
the reactor surface. However, the reduction of film ratio brought
about by polishing the reactor was well described by the SAxs
value. If just the Ra values of the reactors are compared, they
would suggest that polymerizations conducted in Reactors B and C
would produce similar film ratios, however, the actual film ratios
obtained demonstrate that Reactors B and C are different. The SAxs
values of Reactors B and C demonstrate why these two reactors
produced a different average film ratio.
[0096] When numerical lower limits and numerical upper limits are
listed herein, ranges from any lower limit to any upper limit are
contemplated. While the illustrative embodiments of the invention
have been described with particularity, it will be understood that
various other modifications will be apparent to and can be readily
made by those skilled in the art without departing from the spirit
and scope of the invention. Accordingly, it is not intended that
the scope of the claims appended hereto be limited to the examples
and descriptions set forth herein but rather that the claims be
construed as encompassing all the features of patentable novelty
which reside in the present invention, including all features which
would be treated as equivalents thereof by those skilled in the art
to which the invention pertains.
* * * * *