Method for Reducing Depositions in Polymerization Vessels

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.

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Description
CROSS REFERENCE TO RELATED APPLICATION

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

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

Isoolefin polymers are prepared in carbocationic polymerization processes, generally under low temperatures in the range of 0° C. to −150° 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.

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.

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.

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.

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.

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 μm or less. In the disclosed polymerizations, the agglomeration and film deposition was also avoided by the use of a solid catalyst.

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 μm 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.

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

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%.

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.

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.

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

FIG. 1 is a picture taken by e-RAM at 2000× magnification of a sample of Reactor A's surface as it was received.

FIG. 2 is a picture taken by e-RAM at 2000× magnification of a sample of Reactor B's surface after it was mechanically polished.

FIG. 3 is a picture taken by e-RAM at 2000× 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× magnification of a coupon of the same metal used to construct Reactor D after it was mechanically polished and then electropolished.

FIG. 5 is a graph of the reactor vessel's interior surface roughness versus film ratio.

 DETAILED DESCRIPTION OF THE INVENTION

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.

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%.

In one embodiment, at least 80% of the polymerization contact surfaces of the reaction vessel have a SAxs of less than 2%.

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%.

In another embodiment, the polymerization is a carbocationic polymerization.

In yet another embodiment, the polymerization is a slurry polymerization process.

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%.

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° C. In one embodiment, the polymerization occurs at a temperature in the range of −10° C. to the freezing point of the polymerization mixture.

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 C4 to C6 isoolefin monomer and a multiolefin.

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.

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.

In some embodiments the polymerization contact surfaces are electropolished.

In one embodiment, at least 80% of the polymerization contact surfaces of the reaction vessel have a SAxs of less than 2%.

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%.

In another embodiment, the polymerization is a carbocationic polymerization.

In yet another embodiment, the polymerization is a slurry polymerization process.

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.

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° C. In one embodiment, the polymerization occurs at a temperature in the range of −10° C. and the freezing point of the polymerization mixture.

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 C4 to C6 isoolefin monomer and a multiolefin.

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, β-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 C4 to C30 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.

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.

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.

In one embodiment, butyl polymers are prepared by reacting a comonomer mixture, the mixture having at least (1) a C4 to C6 isoolefin monomer component such as isobutylene with (2) a multiolefin or conjugated diene monomer component. The C4 to C6 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 C4 to C14 conjugated diene such as isoprene, butadiene, 2,3-dimethyl-1,3-butadiene, β-pinene, myrcene, 6,6-dimethyl-fulvene, hexadiene, cyclopentadiene, and piperylene.

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.

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.

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 AlCl3, (alkyl)AlCl2, (C2H5)2AlCl, (C2H5)3Al2Cl3, BF3, SnCl4, and TiCl4. 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(C6F5)3 are also suitable Lewis acids.

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 Brønsted acids such as H2O, HCl, RCOOH (wherein R is an alkyl group), alkyl halides, such as (CH3)3CCl, C6H5C(CH3)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.

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 10−6 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.

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 1×10−6 moles per liter to 3×10−2 moles per liter and most preferably from 1×10−4 to 1×10−3 moles per liter.

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).

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.

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.

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.

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.

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.

In another embodiment the diluents, including HFCs, are used in combination with one or more nitrated alkanes, including C1 to C40 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 10th International Conference on Precision Engineering Jul. 18-20, 2001, Yokohama, Japan (Springer, US 2002), both of which are incorporated by reference.

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 μm×1000 μm or less, or about 500 μm×500 μm or less, or even more preferably about 100 μm×100 μm or less. In some embodiments the Sg has an area of about 10,000 μm2 or less, or 6,400 μm2 or less, or 2,700 μm2 or less, or 2,500 μm2 or less, or even 2000 μm2 or less, or in some embodiments 1500 μm2 or less or 1000 μm2 or less. In other embodiments, the Sg is an area in the range of about 100 μm2 to about 10,000 μm2, or in the range of about 200 μm2 to about 5000 μm2, or in the range of about 500 μm2 to about 3000 μm2.

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× magnification) may lead to a reduction in the film deposition by up to 75% relative to reactors with greater SAxs values.

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.

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.

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.

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.

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).

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° C., preferably between −10° C. and the freezing point of the slurry in one embodiment, and in the range of −25° C. to −120° C. in another embodiment. In yet another embodiment, the polymerization temperature is in the range of −40° C. to −100° C., and in the range of −70° C. to −100° C. in yet another embodiment. In yet another desirable embodiment, the temperature range is from −80° C. to −100° 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.

In one embodiment, the polymerization temperature is within 10° C. above the freezing point of the diluent, in another embodiment within 8° C. above the freezing point of the diluent, in yet another embodiment within 6° C. above the freezing point of the diluent, in a further embodiment within 4° C. above the freezing point of the diluent, in still another embodiment within 2° C. above the freezing point of the diluent, in another embodiment within 1° C. above the freezing point of the diluent.

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.

When the initiator and Lewis acid are allowed to pre-complex by mixing together in the selected diluent, this occurs at temperatures between 80° 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.

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.

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.

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.

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.

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.”

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

The present invention will now be further described with reference to the following non-limiting examples.

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° C. All apparatus in liquid contact with the reaction medium were dried at 120° C. and cooled in a nitrogen atmosphere before use.

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, Ra. 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.

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 Ra 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.

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× 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 45×60 μm 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× were then compared to the 2000× 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 1 SAxs Values and Average Ra Values of Reactor Surfaces Average +/−Ra Standard SAxs Reactor Ra, μm 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

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× 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× 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× 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 μm×45 μm. 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.

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 Å 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.

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.

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° C±3° 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%.

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.

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 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

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.

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.

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° C. and the freezing point of the polymerization mixture.

10. The method of claim 1, wherein the comonomer mixture comprises a C4 to C6 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 C4 to C6 isoolefin monomer and a multiolefin

15. The method of claim 11, wherein the polymerization occurs at a temperature of less than 0° 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: wherein Sm is the measured surface area and Sg is the geometric surface area of the area being measured.

SAxs=100*((Sm/Sg)−1),

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.

Patent History
Publication number: 20090062496
Type: Application
Filed: Jul 24, 2008
Publication Date: Mar 5, 2009
Inventors: Timothy D. Shaffer (Hackettstown, NJ), Pamela J. Wright (Easton, PA), J. Davis Deborah (Pasadena, TX), Michael F. McDonald (Kingwood, TX)
Application Number: 12/179,368
Classifications
Current U.S. Class: From Hydrocarbon (526/348); Organic Polymerization (422/131)
International Classification: C08F 210/00 (20060101); B01J 19/00 (20060101);