WO2025250319A1 - Methods for improving gas-phase polymerization - Google Patents

Abstract

Disclosed is a method for improving the integrity of a polymer coating on a reaction zone side of a wall of a reactor, wherein an interface between the polymer coating and the wall comprises an active catalyst. The method comprises: a) water washing the polymer coating; b) exposing the polymer coating to a treat gas comprising nitrogen and i) oxygen in an amount greater than or equal to 2 mol%; and/or ii) water in an amount greater than or equal to 200 ppm; or c) a combination thereof.

Description

METHODS FOR IMPROVING GAS-PHASE POLYMERIZATION

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of U.S. Provisional Application No. 63/653,338, filed May 30, 2024, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] Embodiments of the present invention generally relate to gas phase olefin polymerization. More particularly, some embodiments relate to methods to improve the integrity of reactor wall coatings in gas phase polymerization reactors.

BACKGROUND OF THE INVENTION

[0003] Gas phase polymerization converts a gaseous monomer feed into solid polymer granules. The gaseous monomer, and optional comonomer, is introduced under pressure into a reaction vessel containing a catalyst and optionally an activator. Once polymerization begins, the monomer molecules diffuse to the growing polymer chains within the reactor. The resulting polymer is obtained as a granular solid which is fluidized within the reactor with the monomer and catalyst.

[0004] Gas phase polymerization is particularly prone to depositing solid particles on the reactor walls and other process exposed surfaces of the reactor due to static charge or electrical attraction between a metal surface and the polymer. Over time, the solids can accumulate and grow to form a solid sheet of polymer on the metal, such as a reactor wall. This phenomenon is common in the art and is known as “sheeting.” Polymer sheets on the walls of the reactor can grow in height and thickness to the point where the weight of the sheet overcomes any attractive forces between the sheet and the metal and falls to the bottom of the reactor, resulting in plugging or blocking fluid flow paths on feed nozzles and/or the distribution plate at the base of the fluidized bed. In either case, the solid polymer can plug or block monomer injection, catalyst injection, and/or product discharge. The solid polymer can also inhibit or interfere with fluidization within the reactor. As a result, the polymer product can become off spec and/or polymerization can come to a stop. To remove the solid polymer, the reactor is usually purged and shut down, which is both costly and time-consuming.

[0005] A correlation exists between reactor sheeting and the presence of excess static charges, either positive or negative, in the reactor during polymerization (see, for example, U.S. Pat. Nos. 4,803,251 and 5,391,657). This is evidenced by sudden changes in static levels followed closely by deviation in temperature at the reactor wall. When the static charge levels on the catalyst and resin particles exceed critical levels, electrostatic forces drive the particles to the grounded metal walls of the reactor. The residency of these particles on the reactor wall facilitates melting due to elevated temperatures and particle fusion. Following this, disruption in fluidization patterns is generally evident, such as, for example, catalyst feed interruption, plugging of the product discharge system, and the occurrence of fused agglomerates (sheets) in the product.

[0006] It has been found that the presence of polymer coating on the bed wall of a gas phase (fluidized bed) polymerization reactor is desirable for reducing the tendency of the reactor to form sheets. Without being bound by theory, it is believed that the presence of certain reactor wall coatings (e.g., polymer coatings) inhibits the triboelectric charge transfer that would otherwise occur as the resin in the fluidized bed rubs against the metal reactor walls. Without being bound by theory, it is further believed that inhibiting the triboelectric of charge transfer has the effect of minimizing (or reducing) the accumulation of electrostatic charge on the resin. It is well known the accumulation of electrostatic charge on the resin can contribute to the formation of sheets in the reactor.

[0007] Certain pretreatment techniques have been used to install a polymer coating on the bed wall of a gas phase polymerization reactor to prevent or control sheeting and/or plugging within the reactor. For example, a liquid catalyst has been sprayed onto the walls of the reactor and reacted with the monomer to produce a polymer coating or layer on the reactor wall that serves as an insulation layer to prevent product polymer growth thereon. Early versions of this technique are described in more detail in U.S. Pat. Nos. 4,532,311, 4,792,592, and 4,876,320. Current techniques incorporate many improvements to the process as disclosed in Publ. Pat. App. No. US 2010/0184927 Al. In fact, some current wall coating methods produce polymer wall coatings having improved insulation properties due in some part to greater thickness of the wall coating. However, some of these thicker polymer wall coatings have resulted in operational problems believed to be caused by a portion of the catalyst used in the pretreatment process to produce polymer wall coating remaining active. When the reactor is placed in service to produce polymer product, reaction conditions in the reactor cause the active catalyst at the interface between the polymer coating and the reactor wall to resume polymerization. Such polymerization causes breaks in the adhesion between the polymer coating and the reactor wall, in some cases leading to failure of portions of the polymer coating. [0008] There is a need, therefore, for improved methods for generation of the polymer coating and/or treatment of the polymer coating that can prevent or reduce undesired polymer growth between the polymer coating and the reactor wall and related adhesion failure within a reactor during gas phase polymerization.

SUMMARY OF THE INVENTION

[0009] This disclosure provides a method for improving the integrity of a polymer coating on a reaction zone side of a wall of a reactor, wherein an interface between the polymer coating and the wall comprises an active catalyst. The method comprises water washing the polymer coating and/or exposing the polymer coating to a treat gas comprising nitrogen and i) oxygen in an amount greater than or equal to 2 mol %, and/or ii) water in an amount greater than or equal to 200 ppm. [0010] In some embodiments, water washing comprises opening the reactor for entry, spraying water on the polymer coating in an amount sufficient to hydrolyze at least a portion of the active catalyst, and closing the reactor.

[0011] Optionally, the treat gas may be circulated at a superficial velocity in the range of from 1.0 ft/sec (0.30 meters/sec) to 3.0 ft/sec (0.91 meters/sec) and a temperature in the range of from 33°F (0°C) to 110°F (43°C).

[0012] The foregoing has outlined rather broadly the features and technical advantages of embodiments of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter, which form the subject matter of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent processes do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, together with further objects and advantages, will be better understood from the following description.

BRIEF DESCRIPTION OF THE DRAWING

[0013] The claimed subject matter may be understood by reference to the following description taken in conjunction with the accompanying drawing, in which:

[0014] Figure is a schematic drawing of a gas-phase fluidized bed reaction system. [0015] While the disclosed process and system are susceptible to various modifications and alternative forms, the drawing illustrates the context in which the disclosed processes are to be interpreted. It should be understood, however, that the description herein of a specific embodiment is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Illustrative embodiments of the subject matter claimed below will now be disclosed. In the interest of clarity, some features of some actual implementations may not be described in this specification. It will be appreciated that in the development of any such actual embodiments, numerous implementation-specific decisions must be made to achieve the developer’s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0017] The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than the broadest meaning understood by skilled artisans, such a special or clarifying definition will be expressly set forth in the specification in a definitional manner that provides the special or clarifying definition for the term or phrase.

[0018] For example, the following discussion contains a non-exhaustive list of definitions of several specific terms used in this disclosure (other terms may be defined or clarified in a definitional manner elsewhere herein). These definitions are intended to clarify the meanings of the terms used herein. It is believed that the terms are used in a manner consistent with their ordinary meaning, but the definitions are nonetheless specified here for clarity.

Definitions

[0019] As used herein, “a” or “an” when used in conjunction with the term “comprising” in the claims or the specification means one or more than one, unless the context dictates otherwise. [0020] As used herein, “about” means the stated value plus or minus the margin of error of measurement or plus or minus 10% if no method of measurement is indicated.

[0021] As used herein, “gal/sf” means gallons per square foot.

[0022] As used herein, “gpm/sf’ means gallons per minute per square foot.

[0023] As used herein, the “high molecular weight polymer coating” denotes a coating comprising at least 25 wt% of an insoluble polymer fraction and a soluble polymer fraction having at least 10 wt% polymers (based upon the total weight of the high molecular weight polymer coating) exhibiting a molecular weight as measured by high temperature GPC (using a trichloro benzene solvent at 150°C, sample prepped at 160°C for 2 hr, microwaved at 175°C for 2 hr) of greater than or equal to 5.0E5, 6.0E5, 8.0E5, or 1.0E6 Daltons or greater.

[0024] As used herein, “L/m²” means liters per square meter.

[0025] As used herein, “Lpm/m²” means liters per minute per square meter.

[0026] As used herein, “mol%” means mole percentage of a component as a fraction of the total composition comprising such component.

[0027] As used herein, “polyethylene” denotes a polymer of ethylene and optionally one or more C3-C18 alpha-olefins, while the term “polyolefin” denotes a polymer of one or more C2-C18 alpha-olefins and optionally one or more comonomers. An “olefin” is an unsaturated hydrocarbon that contains at least one carbon-carbon double bond. An alpha-olefin is a hydrocarbon that contains at least one carbon-carbon double bond at one end of a carbon chain (e.g., 1 -butene, vinyl- cyclohexane). For the purposes of this disclosure, ethylene shall be considered an a-olefin.

[0028] As used herein, “solution catalyst” is used herein to denote a solution of at least one catalyst in at least one solvent. For example, chromocene (or another polymerization catalyst) dissolved in an aromatic solvent, such as, toluene (or another solvent) is a solution catalyst.

[0029] As used herein, “treat gas” is gas that is circulated through the reactor and contacted with the chromocene polymer coating to improve the long-term integrity of the polymer coating. Treat gas comprises primarily an inert gas, such as nitrogen, and further includes oxygen, water, or a combination thereof as described in more detail elsewhere in this disclosure.

[0030] The embodiments illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of’ or “consist of’ the various components and steps. Gas Phase Polymerization System

[0031] In any embodiment herein, a fluidized bed reactor may be provided wherein at least a portion of a reactor internal surface is coated with a semi-conductive coating. As used herein, a “fluidized bed reactor” refers to the reactor vessel in a fluidized bed polymerization system. The fluidized bed polymerization system can be any gas-phase fluidized bed polymerization process, for example a polyethylene, polypropylene, or ethylene-propylene rubber gas-phase polymerization system. Referring to Figure, a fluidized bed polymerization system may comprise a reactor vessel 2, a recycle line 4, a circulating compressor 6, and a cooler 8. The reactor vessel 2, may comprise a bottom head 10, a gas-distributor plate 12, a straight section (also referred to as a bed section) 14, an expanded section 16, and a dome 18. As used herein, “a reactor internal surface” refers to any surface inside of the reactor vessel. In at least one embodiment, the reactor internal surface may be: the inside of the bottom head 10, straight section 14, expanded section 16, or dome 18; or the top or bottom of the gas-distributor plate 12. In some embodiments, the reactor internal surface may refer to support tubes 20, a gas deflector 22, or surfaces of other components inside the reactor vessel. In any embodiment herein, the term “inner surface of a polyolefin reaction system” may include any surface inside of the reactor vessel 2, recycle line 4, circulating compressor 6, or cooler 8 of a fluidized bed polymerization system. Generally, in a fluidized gas bed process used for producing polymers, a gaseous stream containing one or more monomers is continuously cycled through a fluidized bed in the presence of a catalyst under reactive conditions. The gaseous stream is withdrawn from the fluidized bed and recycled back into the reactor. Simultaneously, polymer product is withdrawn from the reactor and fresh monomer is added to replace the polymerized monomer. (See, for example, U.S. Pat. Nos. 4,543,399; 4,588,790; 5,028,670; 5,317,036; 5,352,749; 5,405,922; 5,436,304; 5,453,471; 5,462,999; 5,616,661; and 5,668,228; the substance of which are fully incorporated herein by reference for purposes of U.S. patent practice.)

Treatment of the Polymer Coating

[0032] Disclosed herein is a method for improving the integrity of a polymer coating on a reaction zone side of a wall of a reactor, wherein an interface between the polymer coating and the wall comprises an active catalyst. The method comprises one or a combination of steps directed to deactivating the catalyst used for building the polymer coating. Chromocene catalysts are frequently used for building a polymer coating as an insulation layer to mitigate generation of static charge on polymer particles in a fluidized bed in a gas phase polymerization reactor. Typically, exposure to the atmosphere when a reactor is opened after a chromocene treatment for inspection of the polymer coating and final cleaning and preparation of reactor internals has been sufficient to deactivate residual catalyst behind the polymer coating. With a progression toward thicker polymer coatings to improve insulation performance, an unintended consequence is that the thicker polymer coating also functions to protect the chromocene. The method herein uses water and oxygen, either alone or in combination, to more aggressively permeate the polymer coating to deactivate residual chromocene catalyst that is not deactivated by exposure of the polymer coating to the atmosphere.

[0033] Chromocene is a metallocene, consisting of two cyclopentadienyl rings bound to a chromium center. In its catalytically active form, chromocene can coordinate with monomers like ethylene to facilitate polymerization. The presence of water can lead to hydrolysis, where water molecules react with the chromium center of the chromocene molecule. This reaction alters the electronic and structural configuration of the chromocene, effectively reducing or eliminating its ability to catalyze the polymerization reaction. The hydrolysis process can result in the formation of hydroxylated species or other chromium compounds that are not effective as polymerization catalysts. These new compounds lack the ability to effectively coordinate with the ethylene monomers.

[0034] Oxygen can deactivate a chromocene catalyst through a mechanism involving oxidation and the alteration of the catalyst's active sites. Chromocene, like many organometallic compounds, is sensitive to oxygen due to its reactive metal center. When chromocene, which contains a chromium (II) center, is exposed to oxygen (O2), an oxidation reaction can occur. Oxygen, being a strong oxidizing agent, reacts with the chromium center, altering its oxidation state. This reaction typically results in the formation of chromium (III) or higher oxidation state species. The new chromium species formed are not effective as catalysts for the polymerization reactions for which chromocene is typically used.

[0035] Circulation of carbon dioxide or water prior to deactivate catalyst prior to opening the reactor for inspection of the polymer coating. These procedures were sufficient to permit vessel entry. However, permeation rate of carbon dioxide through the polymer coating is much slower than oxygen due to the relative sizes of the molecules. Furthermore, the CO2 and water concentrations and limited circulation times were insufficient to reach active catalyst under a thicker layer of polymer coating.

[0036] In some embodiments, the method comprises water washing the polymer coating. [0037] In some embodiments, the method comprises exposing the polymer coating to a treat gas comprising nitrogen along with oxygen in an amount greater than or equal to 2 mol%, greater than or equal to 4 mol%, greater than or equal to 6 mol%, greater than or equal to 8 mol%, or greater than or equal to 10 mol%.

[0038] In some embodiments, the method comprises exposing the polymer coating to a treat gas comprising nitrogen along with water in an amount greater than or equal to 200 ppm, greater than or equal to 500 ppm, greater than or equal to 1,000 ppm, greater than or equal to 1,500 ppm, or greater than or equal to 2,000 ppm.

[0039] In some embodiments, the method comprises water washing the polymer coating and exposing the polymer coating to a treat gas comprising nitrogen along with oxygen in an amount greater than or equal to 2 mol%, greater than or equal to 4 mol%, greater than or equal to 6 mol%, greater than or equal to 8 mol%, or greater than or equal to 10 mol%.

[0040] In some embodiments, the method comprises water washing the polymer coating and exposing the polymer coating to a treat gas comprising nitrogen and water in an amount greater than or equal to 200 ppm, greater than or equal to 500 ppm, greater than or equal to 1,000 ppm, greater than or equal to 1,500 ppm, or greater than or equal to 2,000 ppm.

[0041] In some embodiments, the method comprises exposing the polymer coating to a treat gas comprising nitrogen and i) oxygen in an amount greater than or equal to 2 mol%, greater than or equal to 4 mol%, greater than or equal to 6 mol%, greater than or equal to 8 mol%, or greater than or equal to 10 mol%, and water in an amount greater than or equal to 200 ppm, greater than or equal to 500 ppm, greater than or equal to 1,000 ppm, greater than or equal to 1,500 ppm, or greater than or equal to 2,000 ppm.

[0042] In some embodiments, the method comprises water washing the polymer coating, followed by exposing the polymer coating to a treat gas comprising nitrogen and i) oxygen in an amount greater than or equal to 2 mol%, greater than or equal to 4 mol%, greater than or equal to 6 mol%, greater than or equal to 8 mol%, or greater than or equal to 10 mol%, and water in an amount greater than or equal to 200 ppm, greater than or equal to 500 ppm, greater than or equal to 1,000, ppm, greater than or equal to 1,500 ppm, or greater than or equal to 2,000 ppm.

- Water Washing

[0043] In some embodiments, water washing comprises: opening the reactor for entry; spraying water on the polymer coating in an amount sufficient to hydrolyze at least a portion of the active catalyst; and closing the reactor. Water washing can be implemented by entry of one or more personnel each with a water hose with a spray nozzle. The volume of water and the delivery pressure of the water both contribute to the effectiveness of the water wash. Higher volumes and/or higher pressures and the pressures lead to more effective deactivation of the residual catalyst.

[0044] In some embodiments, water is sprayed on the polymer coating at an average intensity of greater than or equal to 3.3E-3 gpm/sf (0.136 Lpm/m²), or in the range of from 6.7E-3 gpm/sf (0.27 Lpm/m²) to 3.3E-2 gpm/sf (0.33 Lpm/m²), from LOE-2 gpm/sf (0.41 Lpm/m²) to 2.7E-2 gpm/sf (1.09 Lpm/m²), or from 1.33E-2 gpm/sf (0.54 Lpm/m²) to 2.0E-2 gpm/sf (0.82 Lpm/m².

[0045] In some embodiments, water is sprayed on the polymer coating at an average amount in the range of from 3.3E-3 gal/sf (0.136 L/m²) to 3.3E-1 gal/sf (13.6 L/m²), from 6.7E-2 gal/sf (2.7E-1 L/m²) to 1.67E-1 gal/sf (6.8 L/m²), or from 3.3E-2 gal/sf (1.36 L/m²) to 8.3E-2 gal/sf (3.4 L/m²).

[0046] In some embodiments, water is sprayed on the polymer coating is at a temperature in the range of from 33°F (0°C) to 110°F (43°C), from 40°F (4°C) to 100°F (38°C), from 50°F (10°C) to 90°F (32°C), or from 60°F (16°C) to 80°F (27°C).

Treat Gas

[0047] In some embodiments, exposure of the polymer coating to treat gas is implemented by first closing the reactor containing air at atmospheric conditions. After closure, the reactor can be pressured up with nitrogen from an external source to a pressure in the range of from 60 psig (4.1 barg) to 160 psig (11.0 bar), from 80 psig (5.5 barg) to 140 psig (9.7 bar), or from 100 psig (6.7 barg) to 120 psig (8.3 bar). Circulation of the treat gas through the reactor is then started using the circulating compressor. While circulating, the treat gas is heated to a temperature in the range of from 150°F (66°C) to 200°F (93°C), from 160°F (71°C) to 190°F (88°C), or from 170°F (77°C) to 180°F (82°C). In some embodiments, the oxygen content of the treat gas is greater than or equal to 2 mol%, greater than or equal to 4 mol%, greater than or equal to 6 mol%, greater than or equal to 8 mol%, or greater than or equal to 10 mol%.

[0048] In some embodiments, exposure of the polymer coating to treat gas is implemented by first closing the reactor containing air at atmospheric conditions. After closure, the reactor can be purged by and pressured up with nitrogen from an external source to a pressure in the range of from 60 psig (4.1 barg) to 160 psig (11.0 bar), from 80 psig (5.5 barg) to 140 psig (9.7 bar), or from 100 psig (6.7 barg) to 120 psig (8.3 bar). Circulation of the treat gas through the reactor is then started using the circulating compressor. While circulating, the treat gas is heated to a temperature in the range of from 150°F (66°C) to 200°F (93°C), from 160°F (71°C) to 190°F (88°C), or from 170°F (77°C) to 180°F (82°C). In some embodiments, water is added to the circulating treat gas to produce a concentration of water in the treat gas. In some embodiments, the water concentration in the treat gas is greater than or equal to 200 ppm, greater than or equal to 500 ppm, greater than or equal to 1,000 ppm, greater than or equal to 1,500 ppm, or greater than or equal to 2,000 ppm.

[0049] In some embodiments, exposure of the polymer coating to treat gas is implemented by first closing the reactor containing air at atmospheric conditions. After closure, the reactor can be pressured up with nitrogen from an external source to a pressure in the range of from 60 psig (4.1 barg) to 160 psig (11.0 bar), from 80 psig (5.5 barg) to 140 psig (9.7 bar), or from 100 psig (6.7 barg) to 120 psig (8.3 bar). Circulation of the treat gas through the reactor is then started using the circulating compressor. While circulating, the treat gas is heated to a temperature in the range of from 150°F (66°C) to 200°F (93°C), from 160°F (71°C) to 190°F (88°C), or from 170°F (77°C) to 180°F (82°C). In some embodiments, water is added to the circulating treat gas to produce a concentration of water in the treat gas. In some embodiments, the treat gas has an oxygen content in an amount greater than or equal to 2 mol%, greater than or equal to 4 mol%, greater than or equal to 6 mol%, greater than or equal to 8 mol%, or greater than or equal to 10 mol%, and a water concentration in an amount greater than or equal to 200 ppm, greater than or equal to 500 ppm, greater than or equal to 1,000 ppm, greater than or equal to 1,500 ppm, or greater than or equal to 2,000 ppm.

[0050] In some embodiments, the treat gas is circulated through the reactor at a superficial velocity in the range of from 1.0 ft/sec (0.30 meters/sec) to 3.0 ft/sec (0.91 meters/sec), from 1.05 ft/sec (0.32 meters/sec) to 2.5 ft/sec (0.76 meters/sec), from 1.10 ft/sec (0.34 meters/sec) to 2.0 ft/sec (0.61 meters/sec), or from 1.15 ft/sec (0.35 meters/sec) to 1.5 ft/sec (0.45 meters/sec); and/or [0051] In some embodiments, the treat gas is circulated at a temperature in the range of from 33°F (0°C) to 110°F (43°C), from 40°F (4°C) to 100°F (38°C), from 50°F (10°C) to 90°F (32°C), or from 60°F (16°C) to 80°F (27°C).

[0052] In some embodiments, the treat gas is circulated for a time period greater than or equal to 6 hours, or in the range of from 12 hours to 72 hours, from 18 hours to 60 hours, or from 24 hours to 48 hours.

- Solution Catalyst Treatment

[0053] In some embodiments of the method, in addition to the limitations of any one of the foregoing sets of embodiments, the polymer coating is the product of a solution catalyst treatment. For reactors that have been in service, this treatment is often referred to as a retreatment. To perform such retreatment, the bad (e.g., contaminated) polymer coating is removed from the bed wall by grit blasting. The reactor is then sealed and purged with nitrogen to remove oxygen and moisture.

[0054] After the bed wall is cleaned (e.g., by grit blasting) and the reactor is sealed and purged, such methods include the step of injecting a chromium-containing compound in solution (e.g., chromocene dissolved in toluene) into the reactor and circulating the injected compound so that some of the catalyst is deposited on the reactor's bed wall. The deposited catalyst is then oxidized, and the reactor is then opened for cleaning. The next step in this retreatment method is to purge the reactor with nitrogen and then activate the deposited catalyst by introducing ethylene and an alkyl to the reactor. The chromium-containing compound (e.g., chromocene) acts as a catalyst to polymerize the ethylene in the presence of alkyl to form the coating.

[0055] In a class of embodiments, the invention is a method for treating at least one interior surface (e.g., a bed wall) of a fluidized bed polymerization reactor system, including a step of applying a solution catalyst at least substantially uniformly and in liquid form (e.g., in the form of liquid droplets of the solution catalyst) to each said surface. Typically, the applied solution catalyst is dried (or allowed to dry) to leave a dry coating of catalyst on each surface and a polymerization reaction (catalyzed by the catalyst) is then performed to form on each surface a polymer coating that reliably functions as an insulating layer that reduces static charging in the reactor system (and thereby reduces the potential for sheeting) during subsequent polymerization reactions in the reactor system. The best drying temperature and other best parameters for drying the solvent component of the solution catalyst (e.g., toluene) after applying the solution catalyst in liquid form in accordance with the invention will depend on the particular situation. Any of a broad range of drying parameters (e.g., drying temperature) may be best depending on the particular situation.

[0056] In some embodiments, the interior surface to be treated is the bed wall of the reactor system. Typically, the reactor includes a distributor plate and a recycle line, and the at least one interior surface to be treated is or includes at least one of the distributor plate, the recycle line, and the bed wall of the reactor system. In preferred embodiments, liquid droplets of the solution catalyst are applied to each interior surface (on which the polymer coating is to be formed) to coat each such surface at least substantially uniformly with liquid solution catalyst before the applied solution catalyst evaporates or undergoes sublimation. [0057] In a class of embodiments, the catalyst component of the solution catalyst is or includes a chromium containing compound (“CCC”). In some such embodiments, the CCC is chromocene. In some embodiments (including some in which the solution catalyst includes chromocene), the solvent component of the solution catalyst is toluene. In other embodiments, the solvent component is benzene, isopentane, hexane, or another solvent suitable for the particular application (including the particular catalyst to be applied and method of dispersion to be employed). A polar solvent (e.g., water) is unacceptable for use as the solvent when the catalyst is chromocene. In a class of preferred embodiments in which the catalyst component is a CCC, the polymer coating formed (by a polymerization reaction catalyzed by the catalyst) is polyethylene. In general, the solvent should be inert and the solution catalyst should be introduced into an inert gaseous environment in the reactor system so that the catalyst does not react until after it has been applied to each relevant surface and the desired polymer coating-forming polymerization has commenced. Typically, the solvent functions merely to carry the catalyst and to aid in the catalyst's dispersal within the reactor and application (in liquid form) to the bed wall.

[0058] Application of solution catalyst in liquid form to an interior surface of a reactor system in accordance with the invention can result in formation of a thicker coating of polymer on the surface (during a subsequent polymerization reaction catalyzed by the applied catalyst) than if the solution catalyst were allowed to evaporate or sublimate before application. Increased thickness of the polymer coating is expected to make the coating more effective in minimizing static charging of the system during polymerization operation after formation of the coating (“normal” polymerization operation). More importantly, application of the catalyst in liquid form in accordance with preferred embodiments of the invention increases the applied catalyst's reactivity during the subsequent process of forming a polymer coating on each surface to be coated, thus reducing the risk that a polymer coating of insufficient thickness will be formed on at least some areas of each surface to be coated. Application of solution catalyst in liquid form to reactor surfaces in accordance with preferred embodiments of the invention is expected to allow more reliable formation of effective and reliable polymer coatings on the surfaces and to reduce the likelihood of failed attempts to form effective and reliable polymer coatings.

[0059] In some embodiments in which a solution catalyst whose catalyst component is chromocene (or another CCC) is applied to at least one interior surface of a reactor system, each such surface is cleaned and roughened (e.g., by grit blasting), and then undergoes oxidization (e.g., by opening the reactor system to expose each surface to ambient air during and/or after the grit blasting, for example, for a 48 hour interval following the grit blasting), and then solution catalyst is applied to each cleaned, roughened, and oxidized surface. After application of the solution catalyst (preferably in accordance with any preferred embodiment of the invention) to each surface, a protective polymer coating is typically formed on each surface (preferably after the applied CCC undergoes a controlled oxidation step typically followed by purging of excess oxygen from the system). In general, the desired polymer coating is formed on each surface (typically the bed wall and optionally also at least one other surface) by polymerization catalyzed by the deposited catalyst (where the desired polymer coating is polyethylene and the deposited catalyst is a CCC, the polymerization is typically performed after controlled oxidization of the deposited CCC followed by purging of excess oxygen from the system). To initiate formation of the polymer coating, ethylene and a poison scavenger/cocatalyst (e.g., triethylaluminum (TEA1), triisobutylaluminum (TiBAl), trimethylaluminum (TMA), di ethyl aluminum chloride (DEAC), diisobutylaluminum hydride (DiBAl-H), ethylaluminum sesquichloride (EASC), ethylaluminum dichloride (EADC), aluminum sesquichloride, or a combination thereof or another aluminum alkyl) are typically added to the system. Chromocene and other CCC catalysts are typically used to polymerize ethylene but not other monomers. An oxidation step, following solution catalyst application, is typically required where the applied catalyst is chromocene, but such an oxidation step may not be required for other CCC catalysts (e.g., silyl chromate). New single site CCC catalysts may be used to polymerize monomers other than ethylene, but it is unlikely that such single site CCC catalysts would need to undergo post-application oxidation. For additional details of building the polymer coating, see Publ. Pat. App. No. US 2010/0184927 Al, the contents of which are fully incorporated herein by reference.

[0060] In some embodiments, the solution catalyst treatment is characterized by the polymer coating has an average thickness in the range of from 10 mils (0.25 mm) to 90 mils (2.3 mm), from 15 mils (0.38 pm) to 80 mils (2.0 mm), from 20 mils (0.51 mm) to 70 mils (1.78 mm), from 25 mils (0.64 mm) to 60 mils (1.52 mm), or from 30 mils (0.76 mm) to 50 mils (1.27 mm).

[0061] In some embodiments, the polymer coating is a high molecular weight polyethylene homopolymer, comprising at least 25 wt% of an insoluble polymer fraction and a soluble polymer fraction having at least 10 wt% polymers (based upon the total weight of the high molecular weight polymer coating) exhibiting a molecular weight as measured by high temperature GPC (using a trichloro benzene solvent at 150°C, sample prepped at 160°C for 2 hr, microwaved at 175°C for 2 hr) of greater than or equal to 5.0E5, 6.0E5, 8.0E5, or 1 .0E6 Daltons or greater Daltons or greater, and in some instances up to 2.0E6 Daltons.

[0062] In some embodiments, the surface of the wall comprises carbon steel. Fluidized bed polymerization reactors are often constructed of carbon steel, typically rated for operation at pressures up to about 30 bars (about 3.1 megapascals), and have interior surfaces composed of carbon steel. The normal appearance of the interior surfaces is that of plain, uncoated metal.

[0063] In some embodiments, the catalyst comprises a chromium-containing compound. In some embodiments, the poison scavenger/cocatalyst comprises an aluminum alkyl, wherein in further embodiments, the aluminum alkyl comprises tri ethyl aluminum (TEA1), triisobutylaluminum (TiBAl), trimethylaluminum (TMA), diethylaluminum chloride (DEAC), diisobutylaluminum hydride (DiBAl-H), ethylaluminum sesquichloride (EASC), ethylaluminum dichloride (EADC), aluminum sesquichloride, or a combination thereof. In some embodiments, the chromium-containing compound is characterized by one or more of the following: a) the chromium-containing compound comprises a bis(cyclopentadienyl) chromium (II) compound having the following formula: wherein

R' and R" are the same or different C1-C20 saturated or unsaturated, aliphatic, alicyclic, and/or aromatic hydrocarbon radicals, or R' and R" are one or more of methyl, ethyl, propyl, butyl, pentyl, cyclopentyl, cyclohexyl, allyl, phenyl, and naphthyl radicals; and n' and n" are the same or different integers of 0-5; and/or b) the chromium-containing compound comprises a chromic acetyl acetonate, chromic nitrate, chromous or chromic acetate, chromous or chromic chloride, chromous or chromic bromide, chromous or chromic fluoride, chromous or chromic sulfate, and polymerization catalysts produced from chromium compounds where the chromium may be present in the plus 2 or 3 valence state. Certain Embodiments

[0064] Disclosed herein is a method for improving the integrity of a polymer coating on a reaction zone side of a wall of a reactor, wherein an interface between the polymer coating and the wall comprises an active catalyst.

[0065] In some embodiments, the method comprises water washing the polymer coating.

[0066] In some embodiments, the method comprises exposing the polymer coating to a treat gas comprising nitrogen along with oxygen in an amount greater than or equal to 2 mol%, greater than or equal to 4 mol%, greater than or equal to 6 mol%, greater than or equal to 8 mol%, or greater than or equal to 10 mol%.

[0067] In some embodiments, the method comprises exposing the polymer coating to a treat gas comprising nitrogen along with water in an amount greater than or equal to 200 ppm, greater than or equal to 500 ppm, greater than or equal to 1,000 ppm, greater than or equal to 1,500 ppm, or greater than or equal to 2,000 ppm.

[0068] In some embodiments, the method comprises water washing the polymer coating and subsequently exposing the polymer coating to a treat gas comprising nitrogen along with oxygen in an amount greater than or equal to 2 mol%, greater than or equal to 4 mol%, greater than or equal to 6 mol%, greater than or equal to 8 mol%, or greater than or equal to 10 mol%.

[0069] In some embodiments, the method comprises water washing the polymer coating and subsequently exposing the polymer coating to a treat gas comprising nitrogen along with water in an amount greater than or equal to 200 ppm, greater than or equal to 500 ppm, greater than or equal to 1,000 ppm, greater than or equal to 1,500 ppm, or greater than or equal to 2,000 ppm.

[0070] In some embodiments, the method comprises exposing the polymer coating to a treat gas comprising nitrogen and i) oxygen in an amount greater than or equal to 2 mol%, greater than or equal to 4 mol%, greater than or equal to 6 mol%, greater than or equal to 8 mol%, or greater than or equal to 10 mol%, and water in an amount greater than or equal to 200 ppm, greater than or equal to 500 ppm, greater than or equal to 1,000 ppm, greater than or equal to 1,500 ppm, or greater than or equal to 2,000 ppm.

[0071] In some embodiments, the method comprises water washing the polymer coating, followed by exposing the polymer coating to a treat gas comprising nitrogen and i) oxygen in an amount greater than or equal to 2 mol%, greater than or equal to 4 mol%, greater than or equal to 6 mol%, greater than or equal to 8 mol%, or greater than or equal to 10 mol%, and water in an amount greater than or equal to 200 ppm, greater than or equal to 500 ppm, greater than or equal to 1,000, ppm, greater than or equal to 1,500 ppm, or greater than or equal to 2,000 ppm.

[0072] In some embodiments of the method comprising water washing, water washing comprises: opening the reactor for entry; spraying water on the polymer coating in an amount sufficient to hydrolyze at least a portion of the active catalyst; and closing the reactor. In further embodiments, water washing can be further characterized by one or more of the following: a) water is sprayed on the polymer coating at an average intensity of greater than or equal to 3.3E-3 gpm/sf(0.136 Lpm/m²), or in the range offrom 6.7E-3 gpm/sf (0.27 Lpm/m²) to 3.3E-2 gpm/sf (0.33 Lpm/m²), from 1.0E-2 gpm/sf (0.41 Lpm/m²) to 2.7E-2 gpm/sf (1.09 Lpm/m²), or from 1.33E-2 gpm/sf (0.54 Lpm/m²) to 2.0E-2 gpm/sf (0.82 Lpm/m²); b) water is sprayed on the polymer coating at an average amount in the range of from 3.3E-3 gal/sf (0.136 L/m²) to 3.3E-1 gal/sf (13.6 L/m²), from 6.7E-2 gal/sf (2.7E-1 L/m²) to 1.67E-1 gal/sf (6.8 L/m²), or from 3.3E-2 gal/sf (1.36 L/m²) to 8.3E-2 gal/sf (3.4 L/m²); and c) water is sprayed on the polymer coating is at a temperature in the range of from 33 °F (0°C) to 110°F (43°C), from 40°F (4°C) to 100°F (38°C), from 50°F (10°C) to 90°F (32°C), or from 60°F (16°C) to 80°F (27°C).

[0073] In some embodiments of the method comprising the treat gas, the treat gas is circulated: a) at a superficial velocity in the range of from 1.0 ft/sec (0.30 meters/sec) to 3.0 ft/sec (0.91 meters/sec), from 1.05 ft/sec (0.32 meters/sec) to 2.5 ft/sec (0.76 meters/sec), from 1.10 ft/sec (0.34 meters/sec) to 2.0 ft/sec (0.61 meters/sec), or from 1.15 ft/sec (0.35 meters/sec) to 1.5 ft/sec (0.45 meters/sec); b) at a temperature in the range of from 33 °F (0°C) to 110°F (43 °C), from 40°F (4°C) to 100°F (38°C), from 50°F (KFC) to 90°F (32°C), or from 60°F (16°C) to 80°F (27°C); and/or c) for a time period greater than or equal to 6 hours, greater than or equal to 12 hours, greater than or equal to 18 hours, or greater than or equal to 24 hours.

[0074] In some embodiments of the method, in addition to the limitations of any one of the foregoing sets of embodiments, the polymer coating is the product of a solution catalyst treatment. In further embodiments, the solution catalyst treatment comprises: a) opening a reactor for entry; b) mechanically cleaning the reactor wall to remove polymer and/or contaminants the solution catalyst treatment process; c) sealing the reactor; d) purging the reactor with an inert gas to remove oxygen and/or water; e) wetting a surface of the reactor wall with a solution catalyst in liquid form and then drying or allowing drying to form a dry coating of the dried solution catalyst on the surface; f) introducing oxygen to the reaction zone in an amount sufficient to oxidize the dried solution catalyst on the surface of the reactor wall to produce a coating of an oxidized catalyst; g) purging the reaction zone to reduce the oxygen to an amount insufficient to interfere with a next polymerization step; and h) introducing ethylene and a poison scavenger/cocatalyst to the reaction zone to contact the oxidized catalyst at a temperature and pressure and for a time period sufficient to produce the polymer coating.

[0075] In some embodiments of the method, the solution catalyst treatment is characterized by one or more of the following: a) the polymer coating has an average thickness in the range of from 10 mils (0.25 mm) to 90 mils (2.3 mm), from 15 mils (0.38 pm) to 80 mils (2.0 mm), from 20 mils (0.51 mm) to 70 mils (1.78 mm), from 25 mils (0.64 mm) to 60 mils (1.52 mm), or from 30 mils (0.76 mm) to 50 mils (1.27 mm); b) the polymer coating is a high molecular weight polyethylene homopolymer, wherein in further embodiments, the high molecular weight polyethylene has a weight average molecular weight greater than or equal to greater than or equal to 5.0E5, 6.0E5, 8.0E5, or 1.0E6 Daltons or greater Daltons or greater, and in some instances up to 2.0E6 Daltons; c) the surface of the wall comprises carbon steel; d) the catalyst comprises a chromium-containing compound; and e) the poison scavenger/cocatalyst comprises an aluminum alkyl, wherein in further embodiments, the aluminum alkyl comprises triethylaluminum (TEA1), triisobutylaluminum (TiBAl), trimethylaluminum (TMA), di ethyl aluminum chloride (DEAC), diisobutylaluminum hydride (DiBAl-H), ethylaluminum sesquichloride (EASC), ethylaluminum dichloride (EADC), aluminum sesqui chloride, or a combination thereof.

[0076] In some embodiments of the method, the chromium-containing compound is characterized by one or more of the following: a) the chromium-containing compound comprises a bis(cyclopentadienyl) chromium (II) compound having the following formula: wherein

R' and R" are the same or different C1-C20 saturated or unsaturated, aliphatic, alicyclic, and/or aromatic hydrocarbon radicals, or R' and R" are one or more of methyl, ethyl, propyl, butyl, pentyl, cyclopentyl, cyclohexyl, allyl, phenyl, and naphthyl radicals; and n' and n" are the same or different integers of 0-5; and b) the chromium-containing compound comprises a chromic acetyl acetonate, chromic nitrate, chromous or chromic acetate, chromous or chromic chloride, chromous or chromic bromide, chromous or chromic fluoride, chromous or chromic sulfate, and polymerization catalysts produced from chromium compounds where the chromium may be present in the plus 2 or 3 valence state.

Test Methods/Polymer Characterization

[0077] Gel permeation chromatography (“GPC”) 4D Methodology: Unless otherwise indicated, the distribution and the moments of molecular weight (M_w, Mn, Mz, M_w/M_n, etc.), the comonomer content (C2, C3, Ce, etc ), the branching index (g'), and CCDI (Mw-specific, 5-95, and Mn-Mz) are determined by using a high temperature Gel Permeation Chromatography (Polymer Char GPC-IR) equipped with a multiple-channel band-filter based Infrared detector IR5, an 18- angle light scattering detector and a viscometer. Three Agilent PLgel 10-pm Mixed-B LS columns are used to provide polymer separation. Aldrich reagent grade 1,2,4- trichlorobenzene (“TCB”) with 300 ppm antioxidant butylated hydroxytoluene (“BHT”) is used as the mobile phase. The TCB mixture is filtered through a 0.1-um Teflon filter and degassed with an online degasser before entering the GPC instrument. The nominal flow rate is 1.0 ml/min. and the nominal injection volume is 200 l. The whole system including transfer lines, columns, and detectors are contained in an oven maintained at 145°C. A given amount of polymer sample is weighed and sealed in a standard vial with 80-pl flow marker (heptane) added to it. After loading the vial in the autosampler, polymer is automatically dissolved in the instrument with 8 ml added TCB solvent. The polymer is dissolved at 160°C with continuous shaking for about 1 hour for most polyethylene samples or 2 hours for polypropylene samples. The TCB densities used in concentration calculation are 1.463 g/ml at room temperature and 1.284 g/ml at 145°C. The sample solution concentration is from 0.2 to 2.0 mg/ml, with lower concentrations being used for higher molecular weight samples. The concentration (c), at each point in the chromatogram is calculated from the baseline-subtracted IR5 broadband signal intensity (T), using the following equation: c = fH, where is the mass constant. The mass recovery is calculated from the ratio of the integrated area of the concentration chromatography over elution volume and the injection mass which is equal to the pre-determined concentration multiplied by injection loop volume. The conventional molecular weight (IR MW) is determined by combining universal calibration relationship with the column calibration which is performed with a series of monodispersed polystyrene (PS) standards ranging from 700 to 10M g/mole. The MW at each elution volume is calculated with following equation: tog , where the variables with subscript “PS” stand for polystyrene while those without a subscript are for the test samples. In this method, aps=0.67 and Kps=0.000175, while a and K for other materials are as calculated and published in literature (Sun, T. et al. Macromo/ecu/es 2001, 34, 6812), except that for purposes of this invention and claims thereto, a=0.695 and K=0.000579 for linear ethylene polymers, a=0.705 and K=0.0002288 for linear propylene polymers, a=0.695 and K=0.000181 for linear butene polymers, a is 0.695 and K is 0.000579 x (1 - 0.0087 x w2b + 0.000018 x (w2b)²) for ethyl ene-butene copolymer where w2b is a bulk weight percent of butene comonomer, a is 0.695 and K is 0.000579 x (1 - 0.0075 x w2b) for ethylene-hexene copolymer where w2b is a bulk weight percent of hexene comonomer, and a is 0.695 and K is 0.000579 x (1 - 0.0077 x w2b) for ethyleneoctene copolymer where w2b is a bulk weight percent of octene comonomer. Concentrations are expressed in g/cm³, molecular weight is expressed in g/mole, and intrinsic viscosity (hence K in the Mark-Houwink equation) is expressed in dl/g unless otherwise noted. EXAMPLE

[0078] The following example is included to demonstrate some embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the example which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

[0079] Following a chromocene retreat on a gas phase reactor, it was discovered that chromocene catalyst that was used to create the chrome treat polymer wall had remained active even after opening the reactor to atmosphere following execution of a chrome treat. The remaining active chromocene allowed polymer to grow underneath the polymer coating when the reactor was put into normal service to produce polyethylene products, and the polymer coating was exposed to normal gas phase polymerization reaction conditions. This additional polymer growth resulted in some of the original coating falling off the reactor wall, much the same as the sheeting that the polymer coating was generated to prevent. This resulted in operational and product quality issues as well as exposing areas of the reactor wall, thus creating areas susceptible to historical sheeting risks.

[0080] It was previously believed that opening the reactor to atmospheric conditions and exposing to the new chrome treat wall to oxygen was adequate to deactivate any residual active chromocene in the polymer. In previous chromocene treatments, there was evidence of some continued polymer growth, but the mechanism was not well understood since it was thought that the chromocene was inherently deactivated by opening the reactor to atmosphere following a chromocene treatment.

[0081] After further analysis, it was discovered that the polymer coating and the polymer coating acted as a protective barrier from oxygen to such an extent that some of the chromocene catalyst remained active after the reactor was cleaned and closed in preparation for normal operations. In this case, the polymer layer was thicker than in previous chromocene treatments, and the amount of chromocene under the polymer was at a higher concentration than previous chromocene treatments. When exposed to polymerization conditions and reactor gas constituents after start-up, the remaining chromocene catalyst continued polymerization at a rate significant enough for sections of the polymer coating to fall off the reactor wall. The thicker polymer coating initially provided an effective insulation layer to reduce the generation of static charge in the polymer particles. It was unexpectedly discovered that a thicker polymer coating would require additional time for oxygen to permeate through the polymer to reach the active chromocene such that the time the reactor was open to the atmosphere during final cleaning and preparations was insufficient to fully deactivate the residual chromocene catalyst. It is believed that the time required to accomplish the required deactivation by exposure to the atmosphere would require the reactor to remain offline for an unacceptable period of time.

[0082] Both water and oxygen are good agents for deactivation of chromocene. It was determined that the required deactivation might be accomplished by one or more of three additional treatment steps.

1) Manual water washing was implemented when the reactor was opened after the chromocene treatment to inspect the polymer coating, performed final cleaning of the reactor, and complete other routine preparations for startup of the polymerization process to produce polyethylene product. Manual water washing was performed by personnel entering the reactor with a hose to spray pressurized water on to the polymer coating. Scaffolding was installed with decking at 8-foot intervals to permit access by person for more uniform application of the water wash. The person applying the water wash spent from 2-5 minutes on each decking level using a hand-held hose having a water flow of 5 gpm (19 Lpm) to assure complete wetting of the entire reactor wall.

2) After closure of the reactor, the reactor system was purged with nitrogen and the circulating compressor was started to produce the desired superficial velocity of gas in the reactor. Water from water pots was added into the recirculating nitrogen at a temperature of about 80°C to achieve a water content of about 200 ppm. This water addition utilized the same equipment used to kill catalyst and neutralize pyrophoric materials after initial shutdown of the reactor prior to opening for entry of maintenance personnel. Circulation was maintained for approximately 24 hours.

3) In addition to the water, oxygen was added to the circulating nitrogen to achieve an oxygen content of about 7 mol%.

[0083] In this example, with a polymer coating of 50 mils (1.27 mm), the above steps were adequate to deactivate the chromocene. However, more time and/or severity of one or more of the above steps may be needed for a thicker polymer coating to allow the water and/or oxygen to adequately diffuse through the polymer layer and deactivate the chromocene. These new steps may allow for polymer coatings having greater thicknesses. Additionally, any one or any two of the above steps may be implemented for a greater time and/or severity may be used to accomplish the same level of deactivation.

[0084] For the sake of brevity, only certain ranges are explicitly disclosed herein. However, in addition to recited ranges, any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as, ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. Additionally, within a range includes every point or individual value between its end points even though not explicitly recited. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited.

[0085] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. All patents, test procedures, and other documents cited in this application are fully incorporated herein by reference for all jurisdictions in which such incorporation is permitted. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the processes, equipment, means, methods, and/or steps described in the specification. As one of the ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, equipment, means, methods, and/or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein, may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, equipment, means, methods, and/or steps.

Claims

CLAIMS What is claimed is:

1. A method for improving the integrity of a polymer coating on a reaction zone side of a wall of a reactor, wherein an interface between the polymer coating and the wall comprises an active catalyst, the method comprising: a) water washing the polymer coating; b) exposing the polymer coating to a treat gas comprising nitrogen and i) oxygen in an amount greater than or equal to 2 mol%, on the basis of total moles of the treat gas; ii) water in an amount greater than or equal to 200 ppm on the basis of total moles of the treat gas; or iii) a combination thereof; or c) a combination thereof.

2. The method of claim 1, wherein water washing comprises: a) opening the reactor for entry; b) spraying water on the polymer coating in an amount sufficient to hydrolyze at least a portion of the active catalyst; and c) closing the reactor.

3. The method of claim 0, wherein water is sprayed on the polymer coating at an average intensity of greater than or equal to 3.3E-3 gpm/sf (0.136 Lpm/m²).

4. The method of claim 0 or claim 3, wherein water is sprayed on the polymer coating at an average amount, on the basis of area of the polymer coating, in the range of from 3.3E-3 gal/sf (0.136 L/m²) to 3.3E-1 gal/sf (13.6 L/m²).

5. The method of claim 0 or any one of claims 3-4, wherein water is sprayed on the polymer coating at a temperature in the range of from 33°F (0°C) to 110°F (43°C).

6. The method of claim 0 or any one of claims 2-5, wherein the treat gas is circulated through the reactor at a superficial velocity in the range of from 1.0 ft/sec (0.30 meters/sec) to 3.0 ft/sec (0.91 meters/sec).

7. The method of claim 0 or any one of claims 2-6, wherein the treat gas is circulated through the reactor at a temperature in the range of from 33°F (0°C) to 110°F (43°C).

8. The method of claim 0 or any one of claims 2-7, wherein the treat gas is circulated through the reactor for a time period greater than or equal to 6 hours.

9. The method of claim 1 or any one of claims 2-8, wherein the polymer coating is the product of a solution catalyst treatment.

10. The method of claim 0, wherein the solution catalyst treatment comprises: a) opening a reactor for entry; b) mechanically cleaning the reactor wall to remove polymer and/or contaminants from the solution catalyst treatment process; c) sealing the reactor; d) purging the reactor with an inert gas to remove oxygen and/or water; e) wetting a surface of the reactor wall with a solution catalyst in liquid form and then drying or allowing drying to form a dry coating of the dried solution catalyst on the surface; f) introducing oxygen to the reaction zone in an amount sufficient to oxidize the dried solution catalyst on the surface of the reactor wall to produce a coating of an oxidized catalyst; g) purging the reaction zone to reduce the oxygen to an amount insufficient to interfere with a next polymerization step; and h) introducing ethylene and a poison scavenger/cocatalyst to the reaction zone to contact the oxidized catalyst at a temperature and pressure and for a time period sufficient to produce the polymer coating.

11 . The method of claim 0, wherein the polymer coating is a high molecular weight polyethylene homopolymer.

12. The method of claim 0, wherein the high molecular weight polyethylene homopolymer has a weight average molecular weight greater than or equal to 5.0E5.

13. The method of claim 0 or any one of claims 11-12, wherein the surface of the wall comprises carbon steel.

14. The method of claim 0 or any one of claims 11-13, wherein the catalyst comprises a chromium-containing compound.

15. The method of claim 0, wherein the chromium-containing compound comprises a bis(cyclopentadienyl) chromium (II) compound having the following formula: wherein

R' and R" are the same or different C1-C20 saturated or unsaturated, aliphatic, alicyclic, and/or aromatic hydrocarbon radicals; and n' and n" are the same or different integers of 0-5.

16. The method of claim 0, wherein R' and R" are one or more of methyl, ethyl, propyl, butyl, pentyl, cyclopentyl, cyclohexyl, allyl, phenyl, and naphthyl radicals.

17. The method of claim 0, wherein the chromium-containing compound comprises a chromic acetyl acetonate, chromic nitrate, chromous or chromic acetate, chromous or chromic chloride, chromous or chromic bromide, chromous or chromic fluoride, chromous or chromic sulfate, and polymerization catalysts produced from chromium compounds where the chromium may be present in the plus 2 or 3 valence state.

18. The method of claim 0 or any one of claims 11-17, wherein the poison scavenger/cocatalyst comprises an aluminum alkyl.

19. The method of claim 0, wherein the aluminum alkyl comprises the poison scavenger/cocatalyst comprises triethylaluminum (TEA1), triisobutylaluminum (TiBAl), trimethylaluminum (TMA), diethylaluminum chloride (DEAC), diisobutylaluminum hydride (DiBAl-H), ethylaluminum sesqui chloride (EASC), ethylaluminum dichloride (EADC), aluminum sesqui chloride, or a combination thereof.