BR112021005613B1 - RAPID ACTIVATION PROCESS AND ACTIVATION TREATMENTS FOR CHROME CATALYST TO PRODUCE HIGH MELTING INDEX POLYETHYLENES - Google Patents

Abstract

RAPID ACTIVATION PROCESS AND ACTIVATION TREATMENTS FOR CHROME CATALYST TO PRODUCE HIGH MELTING INDEX POLYETHYLENES. These are processes for activating chromium polymerization catalysts that can use lower maximum activation temperatures and shorter activation times than conventional activation methods and that provide polyethylenes with high melt indices, broader molecular weight distributions. and lower content of long chain branching. The activation process may comprise heating a chromium catalyst supported in an inert atmosphere to a first temperature (T1) during a first holding time (tH1), followed by allowing the chromium catalyst to reach a second temperature (T2), at which point inert atmosphere and then place the chromium catalyst in contact with an oxidative atmosphere for a second holding time (tH2), where T2 may be less than or equal to T1. Additional activation treatments and conditioning steps are disclosed which can be used to increase the melt index potential of Phillips (Cr/silica) catalysts.

Description

CROSS REFERENCE TO RELATED ORDERS

[001] This application claims the priority benefit of Provisional Patent Application No. U.S. 62/735,999, filed on September 25, 2018, which is incorporated into this document by reference in its entirety.

FIELD OF TECHNIQUE

[002] This disclosure relates to supported chromium catalysts, methods for activating the chromium catalysts, and processes for forming polyethylene using the activated chromium catalysts.

BACKGROUND

[003] Chromium catalysts are widely used to polymerize olefins, with chromium oxides supported on silica, alumina or similar supports being among the most prevalent catalysts for this process. A characteristic of supported chromium catalysts is the need to activate the catalysts before their use in any polymerization process.

[004] Typical commercial activation processes include calcining or heating large quantities of the supported catalyst in dry air, often in a fluidized bed activator. These activation procedures generally require heating the catalyst slowly to high activation temperatures, maintaining the activation temperature for an extended period of time, and then cooling the catalyst for several hours before the catalyst is discharged from the catalyst vessel. activation. The entire activation process can take 24 to 36 hours, which can be a hindrance in the overall polymerization process.

[005] Improved activation processes are needed that can decrease overall activation cycle time, while still providing catalysts with the desired activity and resulting polymer properties. Also needed are processes using chromium catalysts that can provide polymers with higher melt indices than those provided by conventional chromium catalysts or chromium catalysts that are activated in a conventional manner. These processes can allow activation at lower maximum temperatures and provide greater efficiency and yield for the activation process.

DISCLOSURE SUMMARY

[006] This summary is provided to present various concepts in a simplified form, which are further described below in the detailed description. This summary is not intended to identify necessary or essential characteristics of the claimed subject matter, nor is the summary intended to limit the scope of the claimed subject matter.

[007] In one aspect, this disclosure provides new processes for activating supported chromium catalysts that can shorten the overall activation cycle time and provide an activated catalyst that unexpectedly provides improved polyethylene properties compared to polyethylenes that are activated using conventional methods. The shorter activation times provided by the processes disclosed in this document may result in activator debottlenecking and higher activator yields. In other aspects, lower maximum activation temperatures are possible using the disclosed methods, which can provide polyethylenes with improved physical properties, such as broader molecular weight distributions or lower long-chain branching (LCB) content. In some aspects, lower polymerization reactor temperatures may be used with the catalysts disclosed herein, which may result in decreased swelling, increased solids, and increased production rates and catalyst activities. In some aspects, higher concentrations of ethylene can be used with the catalysts disclosed herein, which can provide greater productivity, lower catalyst costs, and improved polymer mechanical properties.

[008] In some aspects, this disclosure provides a process for activating a supported chromium catalyst, wherein the process comprises:

[009] a) heating a chromium catalyst supported in an inert atmosphere to a first temperature (T1) at a first rise rate (RR1);

[0010] b) maintain the chromium catalyst at the first temperature in the inert atmosphere for a first waiting time (tH1);

[0011] c) allowing the chromium catalyst to reach a second temperature (T2) in the inert atmosphere at a second rise rate (RR2), followed by exposing the chromium catalyst to an oxidative atmosphere;

[0012] d) maintain the chromium catalyst at the second temperature in the oxidative atmosphere for a second waiting time (tH2); It is

[0013] e) allowing the chromium catalyst to cool to a temperature below the second temperature in an inert atmosphere, in the oxidative atmosphere or in any sequential combination of an inert atmosphere and an oxidative atmosphere over a cooling time (tC) , to provide an activated chromium catalyst.

[0014] In this aspect, the first temperature (T1) may be greater than or equal to the second temperature (T2), that is, T2 is less than or equal to T1. For example, the first temperature (T1) may be greater than the second temperature (T2), and the step of allowing the chromium catalyst to reach the second temperature (T2) in the inert atmosphere may be carried out by allowing the catalyst to of chromium cool under a flow of inert gas. In a further aspect, the first waiting time (tH1) may be greater than the second waiting time (tH2). Alternatively, the first hold time (tH1) may be equal to the second hold time (tH2).

[0015] According to another aspect, with regard to steps a) to e) of the activation process disclosed above, if desired, step a), of heating the supported chromium catalyst to the first temperature (T1), may be preceded by a conditioning step or conditioning process, wherein the conditioning process comprising heating the supported chromium catalyst to a conditioning temperature (TC) in an oxidative atmosphere at a conditioning rise rate (RRC) and maintaining the chromium catalyst at TC in the oxidative atmosphere for a conditioning time (tC) to provide a conditioned chromium catalyst.

[0016] In a further aspect, the conditioning process may involve cycling between an oxidative atmosphere and an inert atmosphere one or more times, which may burn organic compounds in the catalyst. In this regard, the “conditioning temperature”, TC, is considered the first temperature to which the catalyst is heated at the beginning of the cycling process. This aspect of disclosure has been found to be useful for large-scale commercial embodiments of the activation process. In the aspect, for example, with respect to steps a) to e) of the activation process disclosed above, if desired, step a) of heating the supported chromium catalyst to the first temperature (T1) may be preceded by a process of conditioning, where the conditioning process comprises:

[0017] a) heat the supported chromium catalyst to a conditioning temperature (TC) in an inert atmosphere at a conditioning rise rate (RRC) and maintain the chromium catalyst at TC in the inert atmosphere for a first conditioning time (tC1);

[0018] b) exposing the supported chromium catalyst to an oxidative atmosphere for a second conditioning time (tC2);

[0019] c) exposing the supported chromium catalyst to an inert atmosphere for a third conditioning time (tC3); It is

[0020] d) repeat steps b) and c) between 0 and 15 times to provide a conditioned chromium catalyst.

[0021] In this aspect of catalyst conditioning, the formal “conditioning temperature”, TC, can be considered as the first temperature to which the catalyst is heated at the beginning of the cycling process, although conditioning in this aspect actually occurs at over a temperature range.

[0022] In yet another aspect, a process for polymerizing olefins using a supported chromium catalyst is provided, wherein the process comprises:

[0023] a) activating the supported chromium catalyst according to steps a) to e) of the process disclosed above to provide the activated chromium catalyst;

[0024] b) under polymerization conditions, bring into contact, in a reaction zone, the activated chromium catalyst with at least one C2 to C8 mono-1-olefin to form an olefin polymer.

[0025] While not intended to be bound by theory, it has been found that the olefin polymer prepared using the activated supported catalysts of this disclosure can have a melt index (MI) greater than the MI of a reference polyolefin, in that the reference polyolefin is prepared under conditions identical to the olefin polymer using the disclosed catalysts, with the exception that a reference chromium catalyst is used in the preparation of the reference polyolefin, which is activated via:

[0026] i) heating the air-supported chromium catalyst to an activation temperature (T1), for example, from about 600 °C to about 1,000 °C) and maintaining the chromium catalyst at the activation temperature in the air for 3 hours; It is

[0027] ii) allowing the chromium catalyst to cool below 371 °C (700 °F) in air, followed by purging to or at room temperature in an inert atmosphere to provide the activated reference chromium catalyst.

[0028] According to other aspects, this disclosure provides unconventional activation protocols and processes, which can be used to increase the melt index potential of Phillips catalysts (Cr/silica). For example, some activation processes have been found to produce polyethylenes using a Phillips catalyst with a melt index of up to 30. The molecular weight (MW) distribution obtained in these processes can be reduced, for example, they can resemble to Ziegler-derived injection molding resins. In addition to achieving higher catalyst melt index potential, the activation treatments disclosed herein can also be used to improve a number of operating problems. In some aspects, for example, the disclosed processes can decrease catalyst cost, improve resin color, decrease gel count, reduce swelling, which allows for higher solids, increase sedimentation efficiency, control matrix, shorten the activation cycle and improve the properties of the polymer by reducing the activation temperature without loss of MI.

[0029] In one aspect, a process is provided for the pre-reactor reduction of Cr(VI) to Cr(II), i.e., before loading the catalyst into the reactor. For example, it was found that treating the catalyst in CO at about 350 °C can reduce hexavalent chromium, almost quantitatively, into a divalent species. CO-reduced catalysts generally exhibit no or short induction times and may produce a slightly reduced molecular weight (MW) distribution, especially if the support contains titania. Higher melt index polyethylenes can be provided using this activation treatment.

[0030] In a further aspect, this disclosure provides processes for the anhydrous impregnation of chromium. Although conventional impregnation involves the attachment of Cr(VI) to silica through esterification with pairs of silanol groups on a fully hydrated surface, Cr(VI) has been found to attach through reactions with siloxanes under anhydrous conditions. The resulting catalysts can produce polyethylenes with very high melt indices (low MW) and, if titania is present, the usual MI response can be further intensified.

[0031] In another aspect, a process is provided for the improved surface dehydroxylation of the surface support used in the Phillips catalyst in one- or two-step activation processes. In one aspect, carbon- and sulfur-containing compounds, such as CS2, COS, or CH3SH, have been found to be effective in promoting dihydroxylation, whereas non-carbon-containing sulfur compounds, such as S, H2S, or SO2, have not had this. It is made. Polyethylenes with a higher melt index can also be obtained using this activation treatment.

[0032] This summary and the detailed description below provide examples and are only explanatory of the invention. Therefore, the foregoing summary and the following detailed description should not be considered restrictive. Additional features or variations thereof may be provided in addition to those set forth herein, such as, for example, various combinations and subcombinations of features thereof described in the detailed description.

BRIEF DESCRIPTION OF FIGURES

[0033] Figure 1 illustrates a plot of MW (weight average molecular weight) versus the branching distribution of Cr/silica-titania polymers (5% Ti) activated at 700 ° C (parent) followed by CO at 350 ° C (reduced to CO), at a reaction temperature of 95 °C.

[0034] Figure 2 demonstrates that the severity of the reduction treatment influences the activity of Cr/silica catalysts, presenting two samples of a Cr/silica catalyst, activated at 540 °C and 760 °C, which were exposed to treatments of gradually more severe CO reduction, as determined by both temperature and time.

[0035] Figure 3 provides a plot of dehydroxylation temperature versus melting index for a Cr/silica-titania catalyst. The results in the bottom row are from aqueous CrO3 applied to silica-titania, which was then calcined at the temperature represented graphically. The results in the top row are from the support alone that was calcined at a graphically represented temperature, then CrO3 in CH3CN was applied, followed by calcination at 250 °C. The reaction temperature was 102 °C.

[0036] Figure 4 presents a graph of the secondary calcination temperature versus melt index and demonstrates the characteristics of a silica-titania polymer that was calcined at 820 ° C and then impregnated with an anhydrous Cr solution, followed by by a secondary calcination step in air. Melt viscosity was measured at 190 °C and 0.1 s-1.

[0037] Figure 5 graphically represents the secondary calcination temperature in relation to the melting index and shows that the order of impregnation of Cr in relation to Ti can be important in 2-step activation. The top row is data for silica-titania, calcined in air at 815 °C, impregnated with an anhydrous Cr solution, and then heated in air to the temperature shown. The bottom row is data for Cr/silica, calcined in air at 815 °C, impregnated with anhydrous Ti, and then heated in air to the temperature shown. In this case, the first Ti catalyst produces polymer with the higher melt index.

[0038] Figure 6 graphs the titania loading in relation to the melt index and shows that the melt index of a polymer made by a 2-step activated catalyst is highly sensitive to the titania level. The bottom row shows the data for Cr/silica titanated and calcined at 815 °C. The top row shows silica titanated and calcined at 815 °C, followed by Cr applied in hexane and then calcined at 260 °C.

[0039] Figure 7 illustrates the data for the melt index as a function of chromium coverage. The MI and activity of the polymer are influenced by Cr loading in the two-step activation process. These data are for silica-titania calcined at 871 °C, treated with dicumene Cr(0) in pentane at various loadings, and calcined in air at 540 °C. Saturation by Cr(VI) occurred at about 0.43 nm-2 of Cr.

[0040] Figure 8 provides a graph of dehydroxylation as a function of temperature. The extent of dihydroxylation of silicas treated in various gases as a function of high temperatures is shown, where measurements were made via reaction with CH3MgI and referenced to the hydroxyl population (-OH) measured at 200 °C.

[0041] Figure 9 plots the secondary calcination temperature versus melt index, which shows that the 2-step activation process produced higher melt index polymers when the silica-titania support was calcined for the first time. , in CO or CS2 instead of in air. Dehydroxylation, as indicated by the calcination in gas shown at 870 °C, was followed by treatment with 1% Cr in hexane and then calcination in air at the temperature shown. The reaction temperature was 107 °C.

[0042] Figure 10 shows the calcination temperature versus the melting index for Cr/silica-titania that was reduced to the temperature shown, in the atmosphere shown, for three hours and then reoxidized in air for 2 hours at the same temperature . Reduction in CS2 produced polymers with a higher melt index.

[0043] Figure 11A and Figure 11B present molecular weight (Figure 11A) and fluidity (Figure 11B) data as a function of reoxidation temperature, for a commercial two-stage activation, as follows. Cr/silica-titania was calcined for three hours at 871 °C in N2, CO or CS2 and then in air for two hours at the indicated temperature. The MW and fluidity (similar to the melt index) of the resulting polymers are represented graphically. Fluidity is the inverse of melt viscosity, measured at 0.1 s-1.

[0044] Figure 12 shows a graph of oxidation temperature versus melting index for two of reduction and reoxidation or Cr(III)/silica-titania “R&R” activations that produce different results. The top line for Amorphous: raised to 870 °C in N2. For the crystalline sample, the temperature was raised to 650 °C in air and then to 870 °C in N2 to form α-Cr2O3. Both crystalline and amorphous samples were then treated in CO at 870 °C for three hours, followed by two hours in dry air at the temperature shown. The crystalline catalyst was more difficult to reoxidize and therefore produced lower melt index polymers, as shown by the crystalline catalyst (bottom curve) requiring a higher temperature (750 °C) than the amorphous catalyst (650 °C) to achieve the maximum melt index in the polymer.

[0045] Figure 13 illustrates the conversion to Cr(VI) as a function of the titanium (Ti) coating. Although the presence of Ti during reduction and reoxidation or activation of (R&R) significantly reduces the MW of the polymer and increases its melt index (MI), Ti also destabilizes Cr and therefore reduces the conversion to Cr( SAW). These data are for Cr/titananated silica heated in CO to 871 °C and then in air to 600 °C.

[0046] Figure 14 provides a plot of reoxidation temperature versus melt index for a commercial two-stage activation, showing that the dehydroxylation step in CO is time dependent, so that longer holding times result in a polymer higher melt index. The calcination time in CO at 871 °C varied from 0.5 to about 7 h.

[0047] Figure 15 graphically represents the reoxidation temperature versus the melting index in a two-stage commercial activation, in which the reoxidation step is more efficient if carried out in an atmosphere of high concentration of O2. This graph shows the melt index values of polymers obtained from Cr/silica-titania that was reduced in CO at 871 °C and subsequently reoxidized at various temperatures in varying amounts of oxygen.

DETAILED DESCRIPTION OF DISCLOSURE DEFINITIONS

[0048] To more clearly define the terms used in this document, the following definitions are provided. Unless otherwise indicated, the following definitions apply to this disclosure. If a term is used in this disclosure but is not specifically defined herein, the definition in the IUPAC, Compendium of Chemical Terminology, 2nd ed. (1997), may be applied, provided that the definition does not conflict with any other disclosure or definition applied herein, or render undefined or unenforceable any claim to which this definition is applied. To the extent that any definition or usage provided by any document incorporated herein by reference conflicts with the definition or usage provided herein, the definition or usage provided herein prevails.

[0049] Although compositions and processes are described in terms of “comprising” multiple components or steps, compositions and processes may also “consist essentially of” or “consist of” multiple components or steps, unless otherwise stated .

[0050] The terms “a”, “an” and “the”, “a” are intended to include plural alternatives, for example, at least one. For example, the disclosure of “a conditioning step”, “a diluent”, “a catalyst” and the like is intended to cover one or more of a step, diluent, catalyst and the like. With respect to compounds or compositions and unless otherwise specified, this disclosure is intended to encompass mixtures or combinations of more than one of the recited diluent, the catalyst and the like.

[0051] The terms "which includes", "with" and "which has", as used herein, are defined as comprising (i.e., open language) unless otherwise specified.

[0052] For any particular compound or group disclosed herein, any name or structure presented is intended to encompass all conformational isomers, regioisomers, stereoisomers and mixtures thereof that may arise from a particular set of substituents, unless otherwise specified mode. The name or structure also encompasses all enantiomers, diastereomers and other optical isomers (if any), whether in enantiomeric or racemic forms, as well as mixtures of stereoisomers, as would be recognized by one skilled in the art, unless otherwise specified. For example, a general reference to pentane includes n-pentane, 2-methylbutane and 2,2-dimethylpropane; and a general reference to a butyl group includes an n-butyl group, a sec-butyl group, an iso-butyl group and a t-butyl group.

[0053] The term "ambient" temperature, as understood by the person of ordinary skill in the art, means the temperature of the environment in which the process is conducted (not the temperature of the process), which may include the ambient temperature which is about 20°C to about 25°C (or about 68°F to about 77°F)).

[0054] Unless otherwise specified, reference to a molecular weight of a polymer which may be abbreviated as MW, refers to the weight average molecular weight (also abbreviated as MW) of the polymer. The abbreviation MI refers to the melt index of the polymer.

[0055] Various numerical ranges are disclosed in this document. When Claimants disclose or claim a range of any type, Claimants' intention is to disclose or claim individually every possible number that such range could reasonably encompass, including extreme points of the range, as well as any sub-ranges and combinations of sub-ranges encompassed therein, to unless otherwise specified. For example, when disclosing a temperature of 70°C to 80°C, the Applicant's intention is to individually recite 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C , 77 °C, 78 °C, 79 °C and 80 °C, including any subranges and combinations of subranges encompassed therein, and these methods of describing such ranges are interchangeable. Additionally, all numeric endpoints of ranges disclosed in this document are approximate unless excluded by condition. As a representative example, if Applicants assert that one or more steps in the processes disclosed herein can be conducted at a temperature in a range of 10°C to 75°C, this range should be interpreted as encompassing temperatures in a range of " about” 10 °C to “about” 75 °C.

[0056] Values or ranges may be expressed herein as “about”, “around” a particular value and/or “about” another particular value. When such values or ranges are expressed, other disclosed embodiments include the specific value recited, from a particular value and/or to another particular value. Likewise, when values are expressed as approximations, by the use of the antecedent "about", it will be understood that the particular value forms another modality. It will be further understood that there are a number of values disclosed therein, and that each value is also disclosed in this document as "about" that particular value, in addition to the value itself. In another aspect, the use of the term "about" means ±20% of the declared value, ±15% of the declared value, ±10% of the declared value, ±5% of the declared value or ±3% of the declared value.

[0057] Applicants reserve the right to withdraw or exclude any individual elements from any such group of values and ranges, including any sub-ranges or combinations of sub-ranges within the group that may be claimed according to a range or in any similar manner, if, for any reason, Claimants choose to claim less than the full measure of disclosure, for example, to take into account a reference that Claimants may not be aware of at the time of filing the request. Furthermore, Applicants reserve the right to withdraw or exclude any individual substituents, analogues, compounds, ligands, structures or groups thereof or any elements of a claimed group, if for any reason Applicants choose to claim less than the measure full disclosure, for example, to take into account a reference that Applicants may not be aware of at the time of filing the application.

[0058] The terms “contact product”, “contacting” and the like are used herein to describe compositions and methods in which components are brought into contact together and in any order, in any manner and by any means. duration of time unless otherwise specified. For example, components can be placed on contacts through blending or blending. Furthermore, unless otherwise specified, contact of any component may occur in the presence or absence of any other component of the compositions and methods described herein. The combination of additional materials or components may be done by any suitable method. Furthermore, the term “contact product” includes mixtures, blends, solutions, slurries, reaction products and the like, or combinations thereof. Although “contact product” can and often does include reaction products, it is not necessary for the respective components to react with each other. Likewise, “bringing into contact” two or more components can result in a reaction product or a reaction mixture. Consequently, depending on the circumstances, a “contact product” can be a mixture, a reaction mixture or a reaction product.

[0059] Throughout this disclosure, reference is made to "rise rates" of heating or cooling, such as a first rise rate (RR1) or a second rise rate (RR2). Rising rates are expressed in degrees per unit of time, such as °C/minute or °F/minute. In the event that the rise rate is not a constant rate, the rise rate may refer to an average rate of rise over the heating or cooling time.

[0060] Although any methods and materials similar or equivalent to those described in this document may be used in practicing or testing the invention, typical methods and materials are described in this document.

[0061] Persons skilled in the art will readily observe that many modifications are possible in the exemplary embodiments disclosed herein, without departing materially from the new teachings and advantages according to this disclosure. Accordingly, all such modifications and equivalents are intended to be included within the scope of this disclosure as defined in the following claims. Therefore, it should be understood that one may resort to various other aspects, modalities, modifications and equivalents thereof which, after reading the description of this document, may be suggested to the person skilled in the art without departing from the spirit of the present disclosure or the scope of attached claims.

[0062] All publications and patents mentioned in this document are incorporated into this document by way of reference for the purpose of describing and disclosing, for example, the constructs and methodologies that are described in the publications that may be used in connection with the invention currently described. Any publications and patents discussed above and throughout the text are provided solely for disclosure prior to the filing date of this application. Nothing herein should be construed as an admission that the inventors do not have the right to backdate such disclosure by virtue of the prior invention.

[0063] Provided in this disclosure are processes for activating chromium polymerization catalysts, which can use lower maximum activation temperatures and shorter activation times than conventional activation methods and provide polyethylenes with high melt indices, molecular weight distributions wider and lower content of long chain branching. Among other things, the processes comprise heating a chromium catalyst supported in an inert atmosphere to a first temperature (T1) during a first holding time (tH1), followed by allowing the chromium catalyst to reach a second temperature (tH1). T2) in an inert atmosphere and then contacting the chromium catalyst with an oxidative atmosphere for a second holding time (tH2), where T1 is greater than or equal to T2.

CATALYST ACTIVATION PROCESS

[0064] In one aspect, a process for activating a supported chromium catalyst is provided, wherein the process comprises: a) heating a supported chromium catalyst in an inert atmosphere to a first temperature (T1) at a first rate of rise (RR1);

[0065] b) maintain the chromium catalyst at the first temperature in the inert atmosphere for a first waiting time (tH1);

[0066] c) allowing the chromium catalyst to reach a second temperature (T2) in the inert atmosphere at a second rise rate (RR2), followed by exposing the chromium catalyst to an oxidative atmosphere;

[0067] d) maintain the chromium catalyst at the second temperature in the oxidative atmosphere for a second waiting time (tH2); It is

[0068] e) allowing the chromium catalyst to cool to a temperature below the second temperature in an inert atmosphere, in the oxidative atmosphere or in any sequential combination of an inert atmosphere and an oxidative atmosphere over a cooling time (tC) , to provide an activated chromium catalyst.

[0069] According to this aspect, the first temperature (T1) may be greater than the second temperature (T2), or the first temperature (T1) may be equal to the second temperature (T2). In one aspect, for example, the first temperature (T1) may be greater than the second temperature (T2), and the step of allowing the chromium catalyst to reach the second temperature (T2) in the inert atmosphere or in the oxidative atmosphere may be carried out by allowing the chromium catalyst to cool under a flow of inert gas or under a flow of an oxidative atmosphere. In another aspect, step e) may comprise allowing the chromium catalyst to cool to a temperature below the second temperature in an inert atmosphere or in the oxidative atmosphere over a cooling time (tC) to provide an activated chromium catalyst.

[0070] An inert atmosphere used in the disclosed processes may comprise, consist of, or may be selected from carbon dioxide (CO2), helium, argon, nitrogen or any combination of said gases, and may also be a vacuum. However, an inert atmosphere is not limited to these gases or conditions (vacuum) and may also include other gases that do not oxidize chromium to Cr(VI) under the aforementioned conditions. In one aspect, the disclosed process can be carried out in a fluidized bed that can provide consistent exposure of the supported catalyst particles to activation conditions.

[0071] An oxidizing atmosphere used in the disclosed processes may comprise, consist of, or may be selected from pure oxygen or ambient air containing oxygen, or a combination or mixture of air and nitrogen, or a combination of mixture of oxygen and nitrogen, but an oxidizing atmosphere is not limited to these gases. Anhydrous or dry air or oxygen can be used. For example, the oxidative atmosphere may comprise air or oxygen with a dew point of less than about -40°C, less than about -50°C, less than about -60°C, less than about -70°C. C or lower than about -80°C, for example about -82°C (-116°F). The oxidizing atmosphere includes a gas that contains about 5 volume percent (volume percent) to about 100 volume percent oxygen. Alternatively, an oxidizing atmosphere may include a gas that contains from about 10 volume % to about 50 volume % oxygen or from about 15 volume % to about 30 volume % oxygen. For purposes of this disclosure, the term "air" refers to an oxidizing atmosphere. Other oxidizing compounds that may be used in an oxidizing atmosphere include, but are not limited to, nitrous oxide (N2O), nitrogen dioxide (NO2), nitric oxide (NO), halogenated compounds that contain oxygen, such as iodine pentoxide (I2O5) or chlorine monoxide (Cl2O) and/or other oxygen-releasing materials, including suitable combinations thereof. Furthermore, any of these oxidizing gases can be used in combination with, or in mixture with, nitrogen. Contact of the supported chromium catalyst particles with the oxidizing atmosphere can also be accomplished in a fluidized bed that can provide consistent exposure of the supported catalyst particles to the activation conditions.

[0072] In step a) of the process disclosed above, a supported chromium catalyst is heated in an inert atmosphere to a first temperature (T1) and a first rise rate (RR1). In this aspect, for example, T1 may be from about 500°C to about 1000°C, such as from about 550°C to about 900°C, from about 600°C to about 870°C, or from about 650°C to about 850°C. Alternatively, T1 may be, for example, about 500°C, about 525°C, about 550°C, about 575°C, about 600°C, about 625°C, about 650°C. °C, about 675 °C, about 700 °C, about 725 °C, about 750 °C, about 775 °C, about 800 °C, about 825 °C, about 850 °C , about 875 °C, about 900 °C, about 925 °C, about 950 °C, about 975 °C or about 1,000 °C, or any range between any of these values.

[0073] Also in step a) of the process disclosed above, in one aspect, the first rate of rise (RR1) may be, for example, greater than about 0.5 °C/minute, greater than about 1 .0°C/minute, greater than about 1.5°C/minute or greater than about 1.8°C/minute, and wherein the upper limit of the first rate of rise, in each occurrence, is of around 5°C/minute. Alternatively, the first rate of rise (RR1) may be, for example, about 1°C/minute, about 1.25°C/minute, about 1.35°C/minute, about 1.5°C/minute. °C/minute, about 1.8 °C/minute or about 2 °C/minute, or any range in between any of these values.

[0074] In step b) of the process disclosed above, once the supported chromium catalyst is heated in an inert atmosphere and at a first temperature (T1), the chromium catalyst can be maintained at the first temperature, in an inert atmosphere, during a first waiting time (tH1). In one aspect, the first holding time (tH1) may be, for example, less than about 15 hours, less than about 10 hours, less than about 6 hours, less than about 5 hours , less than about 4 hours or less than about 3 hours, and wherein the lower limit of tH1, in each occurrence, is about 15 minutes. Alternatively, the first holding time (tH1) may be, for example, about 15 hours, about 12 hours, about 10 hours, about 6 hours, about 5 hours, about 4 hours, about 3 hours or about 2 hours, or any range between any of these values.

[0075] In step c) of the process disclosed above, once the heated supported chromium catalyst is maintained at the first temperature in the inert atmosphere for a first holding time (tH1), then the chromium catalyst can reach a second temperature (T2) in the inert atmosphere at a second rate rise (RR2), followed by exposure of the chromium catalyst to an oxidative atmosphere. When referring to allowing the chromium catalyst to reach a second temperature (T2), that is, it is generally intended to reflect that heating is stopped or that less heat is applied than was used to bring the catalyst to the first temperature, and The heated catalyst is allowed to lose heat to the system and the environment. Therefore, the second rate of rise RR2 may reflect the rate at which the naturally heated catalyst will lose heat to the environment by continuing the same flow of inert gas, but simply by reducing the heat input, for example, by turning off some or all heating directed to the catalyst and the vessel. For example, allowing the chromium catalyst to reach the second temperature T2 can be accomplished by continuing the flow of inert gas while heating is stopped and allowing the heated catalyst to cool slowly. Once the catalyst reaches the second desired temperature (T2), the catalyst can then be exposed to an oxidative atmosphere.

[0076] In one aspect, the second temperature T2 may be less than or equal to the first temperature T1. For example, in some aspects, T2 may be determined by the formula T2 (°C) = T1 (°C)-K (°C), and where K may be selected from, for example, about 0 °C, about of 25°C, about 50°C, about 100°C, about 150°C or about 200°C, or any range in between any of these values. Alternatively, when T2 (°C) = T1 (°C)-K (°C), K can be selected from a temperature greater than or equal to 25 °C, greater than or equal to 50 °C, greater than or equal to 100°C, greater than or equal to 150°C, or greater than or equal to 200°C, and wherein the upper limit of K is about 350°C, about 400°C, about 450 °C or approximately 500 °C. That is, T2 can be in a range from about 25°C lower than T1 to about 500°C lower than T1 and in ranges between any of these recited values.

[0077] In step d) of the process disclosed above, once the catalyst is allowed to reach the second temperature (T2) in an inert atmosphere and then exposed to an oxidative temperature, the chromium catalyst can be maintained at the second temperature in the oxidative atmosphere for a second holding time (tH2). In one aspect, for example, the second holding time (tH2) may be less than 3 hours, less than 2 hours, less than 1 hour, less than 30 minutes, less than 15 minutes, less than 10 minutes, less than 5 minutes or less than 1 minute, and where the lower limit of tH2, in each occurrence, is around 30 seconds. In a further aspect, the second holding time (tH2) may be, for example, about 1 hour, about 45 minutes, about 30 minutes, about 15 minutes, about 10 minutes, about 5 minutes, about 2 minutes or about 30 seconds, or anywhere in between.

[0078] In step e) of the process disclosed above, after maintaining the chromium catalyst at the second temperature in the oxidative atmosphere for a second holding time (tH2), then the chromium catalyst is allowed to cool to a temperature below the second temperature in an oxidative atmosphere, such as the oxidative atmosphere used in step d), or, alternatively, in an inert atmosphere over a cooling time (tC), or, alternatively, in any sequential combination of an inert atmosphere and of an oxidative atmosphere (which may start with an inert atmosphere or oxidative atmosphere) over a cooling time (tC) to provide an activated chromium catalyst. In one aspect, for example, the cooling time (tC) may be, for example, less than 6 hours, less than 4 hours, less than 3.5 hours, less than 3 hours, less than 1 hour, less than 30 minutes or less than 5 minutes, and where the lower limit of tC, in each occurrence, is about 30 seconds. In a further aspect, the cooling time (tC) may be about 4 hours, about 3.5 hours, about 3 hours, about 2.5 hours, about 2 hours, about 1.5 hours , about 1 hour, about 45 minutes, about 30 minutes, about 15 minutes, about 10 minutes, about 5 minutes, or about 1 minute, or any range in between any of these values. Thus, cooling step e) may comprise allowing the chromium catalyst to cool to a temperature below the second temperature in a sequence of inert atmosphere followed by oxidative atmosphere, or a sequence of oxidative atmosphere followed by inert atmosphere, over a period of time. cooling time (tC) to provide an activated chromium catalyst. Both aspects of starting the cooling step e) with an inert atmosphere or an oxidative atmosphere are covered by the specification in any sequential combination of an inert atmosphere and an oxidative atmosphere.

[0079] In various aspects and embodiments, particularly in large-scale commercial embodiments, the activation steps after the holding time (tH1) at the first temperature (T1), which are "cooling" steps generally corresponding to steps c) to e ) in the above process, the simple approach of T2 (step c)) for a holding time tH2 (step d)), followed by cooling in an inert atmosphere (step e)), can be replaced by the following cooling sequence. Specifically, in this regard, the cooling sequence may constitute what may be termed a "mobile" oxidation, allowing the catalyst to cool in an oxidative atmosphere, such as air from a temperature of a temperature of Y to °C (°F) and subsequently changing the atmosphere back to an inert atmosphere such as N2. In this aspect, step b) of the process set out above can be immediately followed by this new mobile oxidation cooling sequence. For example, in this "mobile" oxidation step, the catalyst is allowed to cool in air or another oxidative atmosphere from a temperature of X at °C (°F) to Y at °C (°F), followed by by exposing the catalyst to an inert atmosphere, such as nitrogen. In this aspect, the temperature X at °C (°F) may be less than or equal to the first temperature T1. Temperature Y at °C (°F) may be lower than X at °C (°F), and temperature Y at °C (°F) may be from about 260 °C (500 °F) to about 426.67°C (800°F) or from about 315.56°C (600°F) to about 371.11°C (700°F). Alternatively, the temperature Y at °C (°F) may be about 426.67 °C (800 °F), about 412.78 °C (775 °F), about 398.89 °C (750 °F). F), about 385°C (725°F), about 371.11°C (700°F), about 357.22°C (675°F), about 343.33°C (650° F), about 329.44°C (625°F), about 315.56°C (600°F), about 301.67°C (575°F), about 287.78°C ( 550°F), about 273.89°C (525°F), or about 260°C (500°F), or any range in between. Also in this regard, 1,050°F) to about 676.67°C (1,250°F). Alternatively, the temperature °F), about 579.44 °C (1,075 °F), about 593.44 °C (1,100 °F), about 607.22 °C (1,125 °F), about 621.11 °C (1,150 °F), about 635 °C (1,175 °F), about 648.89 °C (1,200 °F), about 662.78 °C (1,225 °F), about 676.67 °C (1,250 °F), about 690.56 °C (1,275 °F), or about 704.44 °C (1,300 °F), or any range in between.

[0080] In a further aspect of this "mobile" oxidation step, the cooling rise rate can be from about -17.67°C (0.2°F/min) to about -11.11°C (12°F/min), from about -17.50°C (0.5°F/min) to about 10°C/min (50°F/min), from about -17.22° C (1°F/min) to about 8°C/min (46.4°F/min) or from about -16.94 (1.5°F/min) to about 7°C/min (44.6°F/min). Cooling times in an oxidative atmosphere, such as air from X to °C (°F) to Y to °C (°F), can be greater than 1 min, greater than 5 min, greater than 15 min , greater than 30 min, greater than 1 h, greater than 2 h or greater than 5 h. Cooling times in an oxidative atmosphere from less than 30 min. This particular aspect of the "mobile" oxidation step in the catalyst activations of this disclosure has been found to be particularly useful for large commercial activations, e.g., involving the loading of at least 45.35 kg (100 lb (pounds)) of unactivated catalyst, at least 90.71 kg (200 lb), at least 136.07 kg (300 lb), at least 181.43 kg (400 lb), at least 226.79 kg (500 lb), at least 272.15 kg (600 lb) or even at least or up to 453.59 kg (1,000 lb) of unactivated catalyst.

[0081] In a further aspect, step e) of the process disclosed above may comprise exposing the chromium catalyst to an inert atmosphere or an oxidative atmosphere, while allowing the chromium catalyst to cool to a temperature of less than about 300°C, 250°C, less than about 240°C, less than about 230°C, less than about 220°C, less than about 210°C, less than about 205 °C, less than about 204 °C, less than about 200 °C, less than about 190 °C, less than about 180 °C, less than about 170 °C, less than about about 160°C, less than about 150°C, less than about 140°C, less than about 130°C, less than about 120°C, less than about 110°C or less than about 100 °C over the cooling time (tC), to provide the activated chromium catalyst, wherein the lower temperature limit, at each occurrence, is about room temperature. Therefore, step e) may comprise exposing the chromium catalyst to an inert atmosphere while allowing the chromium catalyst to cool over the cooling time (tC), or may comprise simply allowing the chromium catalyst to cool. in the oxidative atmosphere used in the previous step or in any other oxidative atmosphere, if desired, over the cooling time (tC) to provide the activated chromium catalyst.

[0082] Disclosed processes for activating chromium polymerization catalysts can use lower maximum activation temperatures and shorter activation times than conventional activation methods. For example, the activation process set out in steps a) to e) above may be carried out over a period of time of less than 16 hours, less than 15 hours, less than 14 hours, less than 13 hours, less than 12 hours, less 11 hours or less than 10 hours, and where the lower limit of the time period, in each occurrence, is about 4 hours. In another aspect, for example, the activation process set forth in steps a) to e) above may be carried out over a period of time of about 16 hours, about 15 hours, about 14 hours, about 13 hours, about 12 hours, about 11 hours, about 10 hours, about 9 hours, or about 8 hours, or any range in between any of these values.

[0083] In one aspect, the catalyst support may be an oxide, such as a refractory oxide support comprising, consisting of, or selected from silica, alumina, silica-alumina, titania-coated silica, aluminophosphate , other metal oxides or combinations thereof. In another aspect, the catalyst support may be a spherical and/or spheroidal refractory oxide support. In one aspect, the supported chromium catalyst may be a Cr/silica catalyst or a Cr/titania coated silica catalyst.

[0084] This disclosed activation process can be carried out on a bench or laboratory scale, or on a commercially viable scale, such as using 226.79 kg (500 pounds) of supported chromium catalyst or more, generally in a fluidized bed. The activation process established in steps a) to e) above and the optional conditioning process can be carried out in a common heating zone, or from step a) to step e), and the optional conditioning process can be carried out in at least least two different heating zones. This process for activating a supported chromium catalyst and the optional conditioning process can be carried out in batch mode or they can be carried out in continuous mode.

[0085] Various types of activator vessels, equipment or apparatus can be used to activate catalysts in accordance with this disclosure, including, but not limited to, rotary calciners, static container drying and fluidized beds. These equipment can operate in static or discontinuous mode or in a continuous mode. In the case of a static or batch mode, a vessel or apparatus containing a catalyst bed may be sequentially subjected to several stages of the activation process. For a continuous mode, the process stages may occur in a series of zones through which the catalyst passes on its way through the activation apparatus.

[0086] In a fluidized bed activator, fluidization gas flows upward through a grid plate to form the fluidized bed of supported catalyst particles. In one aspect, the gas flow for fluidized bed activators can be in the range of about 0.01 to about 30 cm/s (from about 0.01 to about 1 foot per second). Alternatively, the gas velocity may be in the range of about 1.5 to about 15 cm/s (from about 0.05 to about 0.5 ft/s) or from about 3 cm/s to about 9 cm/s (from about 0.1 to about 0.3 ft/s).

[0087] Catalysts suitable for activation according to this disclosure include any catalysts suitable for polymerizing olefins and comprising chromium on a support. In one aspect, the chromium content may be in the range of about 0.1 weight percent (wt%) to about 10 wt%, which is the weight percentage based on the total weight of the catalyst. Alternatively, the chromium content may be in the range of about 0.2% by weight to about 5% by weight, from about 0.3% by weight to about 3.5% by weight, or from about 0. .5% by weight to about 2% by weight. Suitable supports for chromium catalysts include, but are not limited to, silica, alumina, aluminophosphates, metal oxides, such as oxides of titanium, zirconium, boron, zinc, magnesium and the like, or combinations thereof. Suitable supports may also contain other promoters including, but not limited to, fluoride, sulfate, fluoroborates, silicofluorides and the like, if desired. Suitable catalysts can be purchased from commercial sources, such as Grace Davison Division of WR Grace & Company, Columbia, Md.

CATALYST CONDITIONING PROCESS

[0088] In another aspect of the disclosed process, a catalyst conditioning step or conditioning process can be used prior to steps a) to e) of the process described above. Therefore, this disclosure provides a process comprising steps a) to e), referred to above, wherein step a) of heating the supported chromium catalyst to the first temperature (T1) is preceded by a conditioning process, wherein the The conditioning process comprises heating the supported chromium catalyst to a conditioning temperature (TC) in an oxidative or inert atmosphere at a rate of conditioning riser (RRC), and maintaining the chromium catalyst at TC in the oxidative atmosphere for a conditioning time (tC) to provide a conditioned chromium catalyst. The oxidative atmosphere used in the conditioning process may be any oxidative atmosphere disclosed herein, for example, the oxidative atmosphere may comprise air or oxygen. The oxidative atmosphere may also comprise air or oxygen having a dew point of less than about -40°C, less than about -50°C, less than about -60°C, less than about -70°C, or less than about -80°C, for example about -82°C (-116°F).

[0089] In one aspect, for example, the conditioning temperature (TC) may be from about 200°C to about 450°C, from about 250°C to 400°C, or from about 275°C to 375°C. Alternatively, the conditioning temperature (TC) may be about 200°C, about 225°C, about 250°C, about 275°C, about 300°C, about 325°C, about 350°C. °C, about 375 °C, about 400 °C, about 425 °C or about 450 °C or any range between any of these values. Although not intended to be bound by theory, this process of initial catalyst conditioning in air at low temperatures is thought to burn residual organic contaminants left from catalyst preparation, such as Cr acetate or Ti ligands, and provide an enhanced activation process and the catalyst itself, without fully oxidizing the chromium in the catalyst to Cr(VI).

[0090] In one aspect, for example, the conditioning rise rate (RRC) can be from about 0.5 °C/minute to about 5 °C/minute. Alternatively, for example, the rate of rise conditioning (RRC) may be about 1°C/minute, about 3°C/minute, about 1°C/minute, or about 2°C/minute or any range between any of these values.

[0091] In one aspect, the conditioning process may include maintaining the chromium catalyst in TC in the oxidative atmosphere for a conditioning time (tC). In some aspects, for example, the conditioning time (tC) may be less than about 5 hours, less than about 3 hours, less than about 2.5 hours, less than about 2 hours , less than about 1.5 hours, less than about 1 hour, or less than about 0.5 hours. In one aspect, the conditioning time (tC) may be 0 hours, such that the conditioning process comprises heating the supported chromium catalyst to a conditioning temperature (TC) in an oxidative atmosphere at a rise rate of conditioning (RRC), followed by continuous heating of the chromium catalyst supported in an inert atmosphere to the first temperature (T1) at the first rise rate (RR1), without any conditioning waiting time (tC). In this regard, the conditioning rise rate (RRC) and the first rise rate (RR1) can be the same or different, so that RRC can be greater than, equal to, or less than RR1. In a further aspect, the conditioned chromium catalyst may be exposed to an inert atmosphere after heating the supported chromium catalyst to a conditioning temperature (TC) in an oxidative atmosphere. In one aspect, the conditioning process can be carried out in a fluidized bed and the subsequent catalyst activation process can also be carried out in the fluidized bed, if desired.

[0092] In a further aspect, the conditioning process may involve cycling between an oxidative atmosphere and an inert atmosphere one or more times in which it burns the organic compounds in the catalyst. In this regard, the “conditioning temperature”, TC, is considered the first temperature to which the catalyst is heated at the beginning of the cycling process. This aspect of disclosure has been found to be useful for large-scale commercial embodiments of the activation process. In the aspect, for example, with respect to steps a) to e) of the activation process disclosed above, if desired, step a) of heating the supported chromium catalyst to the first temperature (T1) may be preceded by a process of conditioning, where the conditioning process comprises:

[0093] a) heat the supported chromium catalyst to a conditioning temperature (TC) in an inert atmosphere at a conditioning rise rate (RRC) and maintain the chromium catalyst at TC in the inert atmosphere for a first conditioning time (tC1);

[0094] b) exposing the supported chromium catalyst to an oxidative atmosphere for a second conditioning time (tC2);

[0095] c) exposing the supported chromium catalyst to an inert atmosphere for a third conditioning time (tC3);

[0096] d) repeat steps b) and c) between 0 and 15 times to provide a conditioned chromium catalyst.

[0097] In this aspect of the cycling process for conditioning the catalyst, the formal "conditioning temperature" TC can be considered as the first temperature to which the catalyst is heated at the beginning of the cycling process, although conditioning in this aspect actually occur over a temperature range. Specifically, after exposure to an oxidative atmosphere, the temperature typically increases as organics are burned, and after re-exposure to an inert atmosphere, the temperature decreases until the next exposure to an oxidative atmosphere. This cycling between oxidative and inert atmospheres can occur 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or even 15 times, up to about 20 times if desired, or any range in between. For example, the number of oxidizing atmosphere/inert atmosphere cycles may be 1 to 10, 2 to 8, or 3 to 6. The oxidative and inert atmospheres used in any of the conditioning processes or steps may be any oxidative atmospheres. and inert disclosed in this document. For example, the oxidative atmosphere may be air or a mixture of oxygen and nitrogen with a different percentage of oxygen than in air, for example 50% oxygen and 50% nitrogen.

[0098] With each step, the increase in temperature after subsequent exposure to the oxidative atmosphere is generally less than the increase in temperature after the previous exposure to the oxidative atmosphere. Therefore, organic materials and compounds are removed over a "conditioning temperature range." In one aspect, for example, this "conditioning temperature range" may be from about 260°C (500°F) to about 537.78°C (1,000°F), from about 315.56°C (600°F) to about 482.22°C (900°F) or from about 371.11°C (700°F) to about 426.67°C (800°F). According to another aspect, the exotherm generated by these short bursts of air may be less than about 148.89°C (300°F), less than about 93.33°C (200°F), less than about 37.78°C (100°F) or less than about 10°C (50°F). Because the exotherm decreases with each subsequent cycle, the lower limit of the exotherm can be about -1.11 °C (30 °F), about -3.89 °C (25 °F), about -6.67 °C (20 °F), about -9.44 °C (15 °F), about -12.22 °C (10 °F), or about -15 °C (5 °F). Furthermore, in aspects, the time durations for the bursts of exposure to the oxidative atmosphere may be from about 1 min to about 30 min, from about 2 min to about 15 min, from about 2 to about 10 min or from about 2 min to about 5 min.

ACTIVATED CATALYST

[0099] This disclosure also provides a supported chromium catalyst prepared in accordance with the disclosed process. In one aspect, the catalyst support may be an oxide, such as a refractory oxide support that comprises, consists of, or is selected from silica, alumina, silica-alumina, titania-coated silica, aluminophosphate, other oxides of metal or combinations thereof. For example, the supported chromium catalyst may be a Cr/silica catalyst or a Cr/titania coated silica catalyst. Processes for preparing supported chromium catalysts prior to activation have been disclosed, for example, in U.S. Patent Nos. 4,151,122; 4,234,462; 5,093,300; 7,981,832; and 9,006,363 and in M. P. McDaniel et al., Journal of Catalysis, 82, 98 to 109 (1983) and M. P. McDaniel et al., Applied Catalysis A, 335, 252 to 261 (2008), each of which is incorporated to this document by way of reference in the relevant part.

[00100] The activated chromium catalyst according to this disclosure may contain relatively low levels of chromium (VI). In one aspect, for example, the activated chromium catalyst may comprise, for example, by weight, less than 1.0% Cr(VI), less than 0.8% Cr(VI), less than 0.6% % Cr(VI), less than 0.5% Cr(VI), less than 0.4% Cr(VI), less than 0.3% Cr(VI), less than 0.2% Cr(VI), less than 0.1% Cr(VI) or less than 0.05% Cr(VI), and wherein the lower limit of activated chromium catalyst by weight in each occurrence is about of 0.01% Cr(VI). In a further aspect, the activated chromium catalyst may comprise, for example, by weight, about 0.6% Cr(VI), about 0.5% Cr(VI), about 0.4% Cr(VI), about 0.3% Cr(VI), about 0.2% Cr(VI), about 0.1% Cr(VI), or about 0.05% Cr(VI). These low levels of chromium(VI) contrast with conventional air activation of supported chromium catalysts, which can include from 0.8 wt% to 2 wt% Cr(VI).

[00101] It has been found that the activated supported catalysts of this disclosure can provide olefin polymer with a melt index (MI) greater than the MI of a reference polyolefin prepared under conditions identical to the olefin polymer using the disclosed catalysts. , with the exception that a reference chromium catalyst is activated by oxidation in air in a conventional manner. That is, in the disclosed catalysts that are activated as described herein, a lower polymerization temperature is required to provide a polyolefin with the same melt index as the reference polyolefin prepared using a conventionally activated catalyst.

[00102] In one aspect, for example, this disclosure provides a Cr/titania coated silica catalyst prepared in accordance with the disclosed processes, wherein:

[00103] a) the activated chromium catalyst comprises less than 0.5% Cr(VI) by weight; It is

[00104] b) under polymerization conditions, the activated chromium catalyst is placed in contact, in a reaction zone, with at least one C2 to C8 mono-1-olefin to form an olefin polymer with a melt index (MI) greater than the MI calculated from the following equation:MI > 8x [0.00050124exp(0.00830795«T)] x [0.0994(PV)3 - 0.7843(PV)2 + 2, 0147(PV) - 0.8824] x [-0.6102(Ti)3 + 1.2715(Ti)2 + 0.003(Ti) + 0.2];

[00105] where T (°C) is the average temperature used under polymerization conditions, PV (cm3/g or ml/g) is the pore volume of the activated chromium catalyst and Ti (atoms/nm2) is the concentration of titanium on activated chromium catalyst. In this regard, the pore volume can be in a range of about 0.3 ml/g (cm3/g) to about 5.0 ml/g, from about 0.4 ml/g to about 4.5 ml/g, from about 0.5 ml/g to about 4.0 ml/g, from about 0.5 ml/g to about 3.5 ml/g, from about 0.5 ml/g to about from 3.0 ml/g, from about 0.5 ml/g to about 2.5 ml/g, from about 0.7 ml/g to about 2.3 ml/g, from about 1.0 ml/g to about 2.2 ml/g, from about 1.2 ml/g to about 2.0 ml/g, or from about 1.4 ml/g to about 1.7 ml/g. Alternatively, the pore volume may be about 0.3 ml/g, about 0.4 ml/g, about 0.5 ml/g, about 0.6 ml/g, about 0.7 ml /g, about 0.8 ml/g, about 0.9 ml/g, about 1.0 ml/g, about 1.1 ml/g, about 1.2 ml/g, about 1.3 ml/g, about 1.4 ml/g, about 1.5 ml/g, about 1.6 ml/g, about 1.7 ml/g, about 1.8 ml/g g, about 1.9 ml/g, about 2.0 ml/g, about 2.1 ml/g, about 2.2 ml/g, about 2.3 ml/g, about 2 .4 ml/g or about 2.5 ml/g, about 3.0 ml/g, about 3.5 ml/g, about 4.0 ml/g, about 4.5 ml/g or about 5.0 ml/g, or any ranges or combinations of ranges therebetween. Also in this aspect, the concentration or coverage of titanium (atoms/nm2) can be from about 0 atoms/nm2 to about 5 atoms/nm2, from about 0 atoms/nm2 to about 4.5 atoms/nm2, from about 0 atom/nm2 to about 4.0 atoms/nm2. Alternatively, the titanium concentration may be 0 atom/nm2, about 0 atom/nm2, about 0.1 atom/nm2, about of 0.4 atom/nm2, atom/nm2, about 0.7 atom/nm2, atom/nm2, about 1.0 atom/nm2, atom/nm2, about 1.3 atom/nm2, atom/nm2 , about 1.6 atom/nm2, atom/nm2, about 1.9 atom/nm2, about 0.2 atom/nm2, about 0.3 about 0.5 atom/nm2, about 0, 6 about 0.8 atom/nm2, about 0.9 about 1.1 atom/nm2, about 1.2 about 1.4 atom/nm2, about 1.5 about 1.7 atom/nm2 nm2, about 1.8 about 2.0 atoms/nm2, about 2.2 about 2.6 atoms/nm2, about 2.8 about 3.2 atoms/nm2, about 3.4 about of 3.8 atoms/nm2, about 4.0 to about 4.4 atoms/nm2, about 4.6 to 5.0 atoms/nm2, or any range or combination of ranges therebetween.

[00106] In a further aspect, this disclosure provides a supported Cr/titania coated silica catalyst prepared in accordance with the disclosed processes, wherein:

[00107] a) the activated chromium catalyst comprises less than 0.5% Cr(VI) by weight; It is

[00108] b) under polymerization conditions, the activated chromium catalyst is placed in contact, in a reaction zone, with at least one C2 to C8 mono-1-olefin to form an olefin polymer with a melt index (MI) greater than the MI calculated from the following equation:MI > 4.8x [0.0994(PV)3 - 0.7843(PV)2 + 2.0474(PV) - 0.8824] x[ -0.6102(Ti)3 + 1.2715(Ti)2 + 0.003(Ti) + 0.2];

[00109] where PV (cm3/g) is the pore volume of the activated chromium catalyst and Ti (atoms/nm2) is the titanium concentration in the activated chromium catalyst. In this aspect, the pore volume may be in any range as disclosed immediately above, or the pore volume may be about any volume (ml/g) as disclosed immediately above. Furthermore, the titanium concentration may be in any range as disclosed immediately above, or the titanium concentration may be about any concentration or coverage (atoms/nm2) as disclosed immediately above.

PROCESS TO POLYMERIZE OLEFINS

[00110] Catalysts activated according to this disclosure can be used in any type of olefin polymerization reactor known in the art that is used to polymerize olefin monomers to form olefin homopolymers or copolymers. In one aspect, such reactors may comprise or may be selected from slurry reactors, gas phase reactors, solution reactors, or any combinations thereof. For example, gas phase reactors may comprise or may be selected from fluidized bed reactors or tubular reactors. In another example, the slurry reactors may comprise or may be selected from vertical circuit or horizontal circuit reactors. In one aspect, the solution reactors may comprise or may be selected from stirred tank or autoclave reactors. Any of these reactors can be combined into multiple reactor systems operated in parallel or in series. The catalyst can also be used to produce ethylene polymers in a particle form process, as disclosed in U.S. Patent Nos. 3,624,063; 5,565,175; and 6,239,235, each of which is incorporated herein by reference in pertinent part. Various other polymerization processes are disclosed in U.S. Patent Nos. 3,248,179; 4,424,341; 4,501,885; 4,613,484; 4,737,280; and 5,597,892; each of which is incorporated herein by reference in pertinent part.

[00111] Activated catalysts, according to this disclosure, can be used for the polymerization of olefins to form homopolymers or copolymers of olefin monomers. Suitable olefin monomers include, but are not limited to, ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, 3-ethyl-1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene and combinations or mixtures thereof. The molecular weight of the polymer can be controlled by various means known in the art, including, but not limited to, adjusting the temperature, introducing or varying the amount of hydrogen present, or varying the catalyst compounds or other conditions.

[00112] Therefore, in one aspect, this disclosure also provides a process for polymerizing olefins with the use of a supported chromium catalyst, in which the process may comprise:

[00113] a) activating the supported chromium catalyst, according to the process disclosed in this document, to provide activated chromium catalyst; It is

[00114] b) under polymerization conditions, bring into contact, in a reaction zone, the activated chromium catalyst with at least one C2 to C8 mono-1-olefin to form an olefin polymer.

[00115] In this olefin polymerization process, activating the supported chromium catalyst to provide the activated chromium catalyst may comprise: a) heating a supported chromium catalyst in an inert atmosphere to a first temperature (T1) and at a first rate lifting (RR1); b) maintaining the chromium catalyst at the first temperature in the inert atmosphere for a first waiting time (tH1); c) allowing the chromium catalyst to reach a second temperature (T2) in the inert atmosphere at a second rise rate (RR2), followed by exposing the chromium catalyst to an oxidative atmosphere; d) maintaining the chromium catalyst at the second temperature in the oxidative atmosphere for a second waiting time (tH2); and e) allowing the chromium catalyst to cool to a temperature below the second temperature in an inert atmosphere or in the oxidative atmosphere over a cooling time (tC), to provide an activated chromium catalyst as described herein. The first temperature (T1) can be greater than or equal to the second temperature (T2) (T2 < T1).

[00116] In another aspect, this disclosure also provides a process for polymerizing olefins with the use of a supported chromium catalyst, wherein the process may comprise:

[00117] a) conditioning the supported chromium catalyst, according to the process disclosed herein, to provide the conditioned chromium catalyst;

[00118] a) activating the conditioned supported chromium catalyst, according to the process disclosed in this document, to provide the activated chromium catalyst; It is

[00119] b) under polymerization conditions, bring into contact, in a reaction zone, the activated chromium catalyst with at least one C2 to C8 mono-1-olefin to form an olefin polymer.

[00120] For example, in this aspect, a process for polymerizing olefins using a supported chromium catalyst is provided, in which the process may comprise:

[00121] 1) conditioning a supported chromium catalyst, wherein the conditioning process comprises:

[00122] a) heating a supported chromium catalyst to a conditioning temperature (TC) in an inert atmosphere and at a conditioning rise rate (RRC) and maintaining the chromium catalyst at TC in the inert atmosphere for a first time conditioning (tC1);

[00123] b) exposing the supported chromium catalyst to an oxidative atmosphere for a second conditioning time (tC2);

[00124] c) exposing the supported chromium catalyst to an inert atmosphere for a third conditioning time (tC3);

[00125] d) repeating steps b) and c) between 0 and 15 times using independently selected subsequent conditioning times (tCS) with each step to provide a conditioned chromium catalyst;

[00126] 2) activating the conditioned supported chromium catalyst, wherein the activation process comprises:

[00127] a) heating a chromium catalyst supported in an inert atmosphere to a first temperature (T1) at a first rise rate (RR1);

[00128] b) maintain the chromium catalyst at the first temperature in the inert atmosphere for a first waiting time (tH1);

[00129] c) allowing the chromium catalyst to reach a second temperature (T2) in the inert atmosphere at a second rise rate (RR2), followed by exposing the chromium catalyst to an oxidative atmosphere;

[00130] d) maintain the chromium catalyst at the second temperature in the oxidative atmosphere for a second waiting time (tH2); It is

[00131] e) allowing the chromium catalyst to cool to a temperature below the second temperature in an inert atmosphere, in the oxidative atmosphere or in any sequential combination of an inert atmosphere and an oxidative atmosphere over a cooling time (tC ), to provide an activated chromium catalyst; It is

[00132] 3) under polymerization conditions, bring into contact, in a reaction zone, the activated chromium catalyst with at least one C2 to C8 mono-1-olefin to form an olefin polymer.

[00133] In one aspect of this olefin polymerization process using a supported chromium catalyst, the at least one C2 to C8 mono-1-olefin may comprise ethylene. The at least one C2 to C8 mono-1-olefin may comprise ethylene and at least one C3 to C8 mono-1-olefin comonomer. For example, the at least one C2 to C8 mono-1-olefin may comprise ethylene and at least one of propylene, 1-butene, 1-hexene or 1-octene.

[00134] In another aspect of this olefin polymerization process, the activated chromium catalyst may be a Cr/silica catalyst and may comprise, by weight, less than 0.5% Cr(VI), wherein the Cr/silica polymer olefin is characterized by a high charge melt index (HLMI, g/10 min) of more than 100 g/10 min. In another aspect of this olefin polymerization process, the activated chromium catalyst may comprise, by weight, less than 0.4% Cr(VI), and wherein the olefin polymer is characterized by a high charge melt index. (HLMI, g/10 min) of more than 100 g/10 min.

[00135] In another aspect of this olefin polymerization process, the activated chromium catalyst may be a Cr/silica-titania catalyst, for example, a Cr/silica catalyst that has been impregnated with titanium. In one aspect, titanium can be impregnated into or onto the Cr/silica catalyst by contacting the Cr/silica catalyst with a solution of a titanium compound, such as a titanium alkoxide, e.g. n-titanium(IV) propoxide, as understood by a person of ordinary skill in the art. In this aspect, the activated catalyst may contain about 2.0 wt% Ti, about 2.2 wt% Ti, about 2.4 wt% Ti, about 2.6 wt% Ti, about 2.6 wt% Ti, about 2.6 wt% Ti, about 2.6 wt% Ti, Ti, about 2.8 wt% Ti, about 3.0 wt% Ti, about 3.2 wt% Ti, about 3.4 wt% Ti, about 3. 6 wt% Ti, about 3.8 wt% Ti, about 4.0 wt% Ti, about 4.2 wt% Ti, about 4.4 wt% Ti , about 4.6 wt% Ti, about 4.8 wt% Ti, or about 5.0 wt% Ti, or any ranges in between. In one aspect, the activated catalyst may contain from about 2.0 wt% Ti to about 5.0 wt% Ti, from about 2.3 wt% Ti to about 4.5 wt% Ti. weight Ti, from about 2.5 wt% Ti to about 4.0 wt% Ti, from about 2.7 wt% Ti to about 3.7 wt% Ti, from about 2.8 wt% Ti to about 3.5 wt% Ti or about 3.0 wt% Ti to about 3.3 wt% Ti. In another aspect, Cr/silica-titania catalysts can have almost the same chromium content as Cr/silica catalysts.

[00136] Another aspect of the olefin polymerization process is that the activated catalyst, as disclosed in this document, can produce a polyolefin with the same melt index (MI, g/10 min) as a polyolefin produced by the same process, except for the use of a conventionally activated chromium catalyst, but at a lower temperature compared to the conventionally activated chromium catalyst. Using the same conditions, including temperature, the olefin polymer prepared using the disclosed catalyst can have a melt index (MI, g/10 min) greater than the MI of the reference polyolefin made using a conventionally activated chromium catalyst.

[00137] Therefore, herein disclosed is a process for polymerizing olefins with the use of a supported chromium catalyst, wherein the process may comprise: a) activating the supported chromium catalyst, in accordance with the process disclosed in this document, to supply the activated chromium catalyst; and b) under polymerization conditions, contact, in a reaction zone, the activated chromium catalyst with at least one C2 to C8 mono-1-olefin to form an olefin polymer; on what:

[00138] a) the olefin polymer has a melt index (MI) greater than the melt index (MIR) of a reference polyolefin; It is

[00139] b) wherein the reference polyolefin is prepared under conditions identical to the olefin polymer, with the exception that a reference chromium catalyst is used in the preparation of the reference polyolefin, which is activated through:

[00140] i) heating the supported chromium catalyst to an activation temperature of 600 °C to 1,000 °C (T1) in air and maintaining the chromium catalyst at the activation temperature in air for 3 hours; It is

[00141] ii) allowing the chromium catalyst to cool below 371 °C (700 °F) in air, followed by purging to or at room temperature in an inert atmosphere to provide the activated reference chromium catalyst.

[00142] In this aspect, the olefin polymer prepared using the disclosed catalyst can have a melt index (MI, g/10 min) at least 10% higher, at least 15% higher, at least 20% higher, at least at least 25% greater, at least 50% greater, at least 100% greater, at least 200% greater, at least 300% greater or at least 500% greater than the MI of the reference polyolefin, and wherein the upper limit of the The melt index of the olefin polymer is about 1,000% higher than the MI of the reference polyolefin.

[00143] Also in this regard, the activation time of the activated chromium catalyst may be less than about 80%, about 70%, about 60%, about 50% or about 40% of the reference chromium catalyst. activated. The olefin polymer prepared using the disclosed catalyst may have a melt index (MI) of about 10%, about 20%, about 30%, about 40%, about 50%, about 60% , about 70%, about 80%, about 90% or about 100% greater than the melt index (MIR) of the reference polyolefin. Furthermore, the olefin polymer prepared using the disclosed catalyst may have a broader molecular weight distribution based on Mw/Mn, Mz/Mn, or any appropriate ratio of Mn, Mw, Mx. Mv or M(z+n) compared to the reference polyolefin. In some aspects, the olefin polymer prepared using the disclosed catalyst may have a higher long chain branching (LCB) content compared to the reference polyolefin. According to another aspect, the high charge melt index (HLMI, g/10 min), may be greater than about 20, greater than about 30, greater than about 40, greater than about greater than approximately 50, greater than approximately 75, greater than approximately 100, greater than approximately 125, greater than approximately 150, greater than approximately 175, or greater than approximately 200, or numbers in between of these values. In this regard, the upper limit of the high charge melt index (HLMI, g/10 min) can be around 300.

REDUCTION OF THE PREREACTOR IN CR(II)

[00144] Most commercial manufacturing of polyethylene with the Phillips catalyst is carried out with Cr(VI)/silica as the catalyst, where Cr(VI) can be reduced by ethylene in the reactor to form a lower oxidation state active precursor , for example, Cr(II) or Cr(III). In one aspect, this disclosure provides for the reduction of Cr(VI) to Cr(II) before the catalyst is added to the reactor. In one aspect, for example, it has been found that treatment in carbon monoxide (CO) at about 350 ° C reduces the hexavalent chromium Cr(VI) almost quantitatively to a divalent Cr(II) species. This reduction using CO can be followed by flushing residual CO with an inert gas, such as N2, before the catalyst cools. Although not intended to be bound by theory, it is believed that residual CO can be chemically absorbed and can poison the catalyst.

[00145] Carbon monoxide (CO) begins to react with Cr(VI)/silica even at room temperature, although this reaction may be slow, so that over a period of several hours, the Cr(VI) may become largely reduced at 25°C. Following this process, N2 purging at higher temperatures can be used to remove adsorbed CO. It can be seen that catalysts reduced in CO have a green color in vacuum or argon, but they turn sky blue when N2 is added, and the reduced catalyst turns a deeper indigo blue when it is exposed to ethylene. If the catalyst, after reduction in CO at 350 °C, is cooled in CO, it may have a violet color. CO-reduced catalysts generally exhibit no or short induction times, and this feature can be useful when low reaction temperatures are desired or when higher activity is desired.

[00146] In one aspect, the CO-reduced catalysts in accordance with this disclosure can produce a slightly reduced MW distribution polymer compared to conventionally activated catalysts, for example, when the support contains titania, as shown in Figure 1 .The low MW bump contributed by titania is partially removed by CO reduction. Without wishing to be limited to theory, this observation may suggest that some sites associated with titania do not survive reduction or that these sites tend to be less stable. Due to this change in MW (molecular weight) distribution, the potential melt index of CO-reduced catalysts is reduced by up to half. The polymer produced by CO-reduced catalysts may have a slightly higher MW and the elasticity may be slightly decreased. These trends are especially noticeable if the catalyst has first undergone a "two-step" activation, as described in this document below, which can amplify the effect of titania. Titania-free catalysts have been observed to follow these same trends when treated with CO, but to a lesser extent or degree.

[00147] In one aspect, the temperature for reduction in CO may be from about 250°C to about 525°C, from about 275°C to about 475°C, or from about 300°C to about 400°C. At lower temperatures, the reduction may be incomplete, and at higher temperatures, the Cr(II) species may be somewhat unstable, as illustrated in Figure 2. In Figure 2, samples of Cr/silica catalyst, activated at 540 °C and 760 °C, were exposed to gradually more severe CO reduction treatments, as determined by both temperature and time. In each series, the first reduction treatment at 316 °C improved the average activity. However, with more severe reduction treatments at higher temperatures, the catalyst initially activated at 540 °C lost almost all of its activity. In contrast, the catalyst activated at 760 °C was almost unaffected. While not intended to be bound by theory, this result suggests that Cr(II) species may react with surface OH groups, which may produce inactive Cr(III), and may also suggest that the catalyst may have a smaller OH population when activated at 760 °C than when activated at 540 °C. Furthermore, it is believed that the OH groups may not become mobile enough to react until the reduction temperature approaches the previous annealing temperature.

ANHYDROUS CHROME IMPREGNATION

[00148] The attachment of Cr(VI) to silica can be described as an esterification with pairs of silanol groups on a fully hydrated surface. It is generally thought that such a reaction cannot occur if the silica has first been calcined above 600 °C and if the chromium impregnation has been done from an anhydrous, aprotic solvent to avoid rehydration of the surface. of silica. However, in one aspect of this disclosure, such a catalyst can be made such that Cr(VI) attaches to the silica surface through reaction with siloxanes. Although not limited by theory, it is believed that more reactive siloxanes can be deformed or distorted. Such catalysts can provide some useful properties, including the ability to produce extremely high melt index (low molecular weight, MW) polymers. Furthermore, although not limited by theory, it is believed that the reaction of chromium with deformed siloxanes can place chromium in an environment in which it can be highly reactive. If titania is present, the usual MI response may be further intensified compared to when titania is not present. This observation may indicate a more selective insertion of Cr(VI) into the more polar and perhaps also deformed Ti-O-Si oxide surface bridges. Scheme 1 illustrates the possible insertion of Cr (CrO3) into siloxanes after anhydrous impregnation.SCHEME 1

[00149] In one aspect, the performance of a catalyst prepared by anhydrous impregnation of chromium is shown in Figure 3. Silica-titania (2.2 Ti atoms in nm-2) was first calcined in air at various temperatures until 870 °C for 3 h, as illustrated. Each sample was then impregnated with a solution of CrO3 in CH3CN (acetonitrile) to obtain catalysts containing 0.5% by weight of Cr. The catalysts were then subjected to a second calcination step in air at just 250 °C for 1 h to fix the chromium and eliminate the solvent. This procedure is called "two-step" activation because two calcination steps are involved, the first without chromium and preferably at a relatively high temperature to dehydroxylate the support and a second at a lower temperature to attach the chromium.

[00150] These catalysts prepared by this anhydrous chromium impregnation were then tested for polymerization activity, and Figure 3 illustrates the melt index (MI) values of the polymers obtained. The MI is plotted against the temperature of the first calcination step, i.e., the dehydroxylation temperature. The melting index increases with increasing temperature up to the sintering point at about 800°C to 900°C. It then decreases, in a manner similar to that of the conventional aqueous chromium-impregnated catalyst (i.e., a "one-step" activation).

[00151] For comparison, the "one-step" activation is also shown in Figure 3. For this one-step activation, other samples of the same virgin silica-titania support were impregnated with aqueous CrO3 and then calcined in several temperatures up to 871 °C. Therefore, this activation is conventional one-step activation and is represented by the bottom line in Figure 3. At each temperature, the two-step procedure produces polymer with 10 times higher melt index compared to the standard one-step method (note that the y-axis is a logarithmic scale).

[00152] Figure 4 provides additional results related to anhydrous chromium impregnation. The same two-step procedure as described above was repeated, except the first calcination temperature (for dehydroxylation) was set at 820 °C and the second calcination temperature (for chromium attachment) was varied. Again, these catalysts were tested for polymerization activity and the melt index values of the polymers produced are plotted against temperature. Secondary calcination temperatures of only about 150 °C produced active catalysts, as the support was already dehydroxylated. The polymers showed higher melt index values at all temperatures than those obtained from a conventional one-step activation of the same support impregnated with aqueous chromium. The catalyst calcined at 250 °C produced polymer with a superior melt index, which was about 1,000 times higher than that produced by activating a step at the ideal temperature.

[00153] The molecular weight is also shown in Figure 4. High melt index values generally indicate a low MW. Melt viscosity is also shown, as measured at a low shear rate (0.1 s-1), which is an indication of ease of flow under gravity in rotational molding operations. The melt viscosity of the polymer decreased significantly as the melt index increased.

[00154] For this anhydrous chromium impregnation, the chromium compound can be impregnated into the carrier using any anhydrous and aprotic solvent. The source of chromium can be a hexavalent chromium compound, such as bis(t-butyl) chromate in pentane or bis(triphenylsilyl) chromate in toluene, and even crown ethers can be used to dissolve Cr(VI) salts. in organic solvents. Alternatively, the chromium source does not need to be Cr(VI), as it will be oxidized during the second calcination step. Examples include lower valence compounds (lower oxidation state), such as diarenechrome(0) compounds in heptane or toluene, or trivalent chromium compounds, such as chromium tris(acetylacetonate) in toluene or dry ether, or even in phase gas, or CrCl3 in THF. Even chromyl chloride vapor can be used without solvent. The residual chloride is burned during the second calcination step. The second ideal calcination temperature (step 2, chromium attachment) varies with the accompanying anion, some of which may burn more easily than others.

[00155] Contrary to the usual trend, the melt index values shown in Figure 4 decrease when the catalyst is calcined at higher temperatures (in the second stage). Although not limited by theory, it is believed that the trend may indicate that these sites associated with titania are thermally unstable and may reorganize into another form (producing low-MI polymer), perhaps changing titania. Comparing the two-step point at 820 °C in Figure 4 with the one-step point at 820 °C in Figure 3, it is seen that they are almost the same. These two points correspond to the same level of dehydroxylation as the carrier (820 °C) and that chromium experienced the same temperature (again 820 °C). At the highest temperatures in this comparison, there is little or no difference between one-step and two-step activation.

[00156] It has been found that other activation treatments achieve similar improvements in MI from the reaction of chromium with siloxanes. In one aspect, organic compounds that can hydrolyze Cr-O-Si bonds can result in the redistribution of chromium, and this rearrangement can increase the melt index of the polymer produced if the silica surface is not significantly rehydroxylated. For example, a Cr/silica-titania catalyst was calcined at 800 °C in a one-step activation as described above. Subsequently, the calcined catalyst was cooled and slurried in hexane, to which one mole of t-butyl alcohol was added per mole of chromium. The solution turned slightly orange when t-butanol was added. Not intending to be limited by theory, it is thought that this color change may indicate hydrolysis of the Cr-O-Si bonds. The hexane was evaporated and the dried catalyst was then calcined again in air at just 300°C. The resulting catalyst was very active for the polymerization of ethylene, and the melting index of the polymer was increased tenfold through this treatment with t-butanol (from 0.2 without treatment to 2.0 with t-butanol). Again, although not intended to be bound by theory, the alcohol is believed to have hydrolyzed at least some of the chromium species, breaking the bonds linking it to the carrier and allowing redistribution into Ti.

[00157] In one aspect, a variation of the above activation was conducted, in which the order of addition of titanium and chromium was reversed. Cr/silica was calcined (dehydroxylated) at 815 °C and subsequently treated with titanium isopropoxide in hexane. The dried catalyst was calcined a second time at several lower temperatures to burn off the organics and attach the chromium. It was observed that even this treatment produced an increase in the melt index of the polymer. These catalysts were very active and the polymers obtained exhibited high melt index values. The bottom curve in Figure 5 is a plot of these MI values versus the secondary calcination temperature. When the catalyst was calcined at higher temperatures at about 250 °C, the MI values dropped. While not intended to be bound by theory, this result suggests that even exposure to titanium ester and subsequent oxidation could cause a redistribution of chromium that allowed considerable interaction with titania and this suggests that much of the titanate ester may react with enough dehydroxylated silica to form an effective silica-titania support.

[00158] The MI values of the polymers in Figure 5 (lower curve) are considerably lower than the values obtained from normal two-step activation of the same support, as is also shown in Figure 5 as the upper curve. In the upper curve of Figure 5, the silica was 1) dried and treated with titanium isopropoxide, 2) calcined at 800 °C, 3) impregnated with CrO3 in CH3CN, and 4) calcined again at various lower temperatures. Thus, the two curves can also be considered as representing the opposite order of impregnation, i.e. titanium first (top curve) vs. chrome first (bottom curve). Noting that the melt index y-axis is a logarithmic scale, the two series in Figure 5 are observed to give significantly different melt index polymers. In one aspect, in the data illustrated in the lower curve, when the remaining titanium ester groups are burned at lower temperatures, the catalyst is exposed to significant amounts of water vapor, which works in opposition to the two-step increase. However, the behavior represented by the lower curve in Figure 5 still definitely exhibits characteristics of the two-step process. The two curves merge at a temperature close to 800 °C, where the two processes effectively become a one-step activation at a temperature of about 800 °C, i.e. the first calcination temperature and the second calcination temperature. calcination are almost the same.

[00159] In one aspect, two-step activation can provide a more pronounced melt index response to the presence of titania than the one-step method. Figure 6 shows an example of this behavior. The lower curve (one step) represents the catalysts that were made by titanating Cr/silica with titanium tetraisopropoxide, followed by activation at 815 °C in air. The upper curve (two steps) represents the catalysts that were made by titanating silica (without Cr), followed by impregnation of 0.5 wt% Cr as bis(t-butyl) chromate in hexane. Final calcination was carried out at 260 °C to attach the chromium. These catalysts were tested for ethylene polymerization and the resulting polymer was analyzed for melt index. Figure 6 provides a graph of the melt index values obtained from the polymers made with each series of catalysts. Both curves show the increasing melt index as more titanium was added to the catalyst. However, the two-step activation method gives much higher values for each titanium content, and the separation between the two curves grew considerably as titania was added to each catalyst. Again, note that the y-axis is a logarithmic scale. Not intending to be limited by theory, it is thought that this pattern, in Figure 6, indicates that the two-step activation may tend to bring more chromium into contact with the titania, and a second calcination at 815 °C brings the MI back. downward, perhaps indicating that the site associated with titania may be thermally unstable and possibly migrate to another form.

[00160] In one aspect, the chromium loading was also varied to study which sites are populated first in the two-step procedure. An example of this study is provided in Figure 7. A silica-titania cogel (2.5 wt% Ti) was calcined at 871 °C, impregnated with various amounts of dicumenochrome(0) in pentane, and then calcined again at 540 °C. After polymerization at 107 °C, the products were analyzed. Figure 7 illustrates a graph of catalyst activity, polymer molecular weight (weight average molecular weight, MW), and polymer melt index relative to the hexavalent chromium Cr(VI) coverage that was measured. At low chromium coverages, for example, up to about 0.2 Cr in nm-2 (chromium atoms per nm2 of surface area), almost all of the chromium was converted to Cr(VI). Beyond this chromium loading, however, the conversion became less efficient, reaching saturation at about 0.45 Cr(VI) in nm-2, although the total chromium loading reached 1.3 Cr atoms. in nm-2 (chromium atoms per nm2 of surface area).

[00161] Even the first increments of added chromium produced high melt index polymer, where the melt index is about twice as high as that of activating a step at a similar level of dehydroxylation. Both the polymer melt index and catalyst activity peaked at only about 0.15 Cr(VI) in nm-2. Although not limited by theory, this behavior suggests that titania-associated sites were among the first to be populated and later chromium increments did not contribute as much to the increase in MI. Again, although not limited by theory, it is conceivable, and is consistent with the loss in catalyst activity, that an excess of chromium changes the previous binding of chromium to the surface, such as from chromate to dichromate species.

IMPROVED DEHYDROXYLATION

[00162] This disclosure also provides chemical methods for achieving improved surface dehydroxylation for improved catalyst performance in both one-step and two-step activations. In one aspect, for example, calcination of the support in CO (carbon monoxide) further reduces silanol concentrations. Not intended to be limited by theory, this may occur through a type of water gas shift reaction, such as that suggested in Scheme 2. In another aspect, compounds containing carbon and sulfur, such as CS2, COS, or CH3SH, also were found to be effective in promoting dehydroxylation. Non-carbon sulfur compounds such as S, H2S or SO2 have not been shown to be effective. Although not limited by theory, it is thought that the H (hydrogen) of a surface OH (hydroxyl) group can be removed as H2S, and the O (oxygen) of a surface OH (hydroxyl) group can be removed as CO ( or when COS is used, possibly as CO2). It is believed that elemental sulfur vapor may also evolve from the reaction, but it does not appear to have been left in the holder. Thus, Scheme 2 illustrates that silica dehydroxylation is enhanced: (A) by CO, through a water gas shift type reaction; (B) by CS2, through an unknown reaction, such as the reaction suggested in this document; or (C) by replacement of bromide or iodide, followed by burning. SCHEME 2

[00163] Figure 8 illustrates examples of these improved dehydroxylation techniques. The silanol population in plain silica was measured by reaction with CH3MgI after several activation treatments. The samples were calcined at temperatures from 200 °C to almost 1,000 °C in three atmospheres, N2, CO and CO, in which CS2 (1 ml) was vaporized. The y-axis in Figure 8 represents the extent of dehydroxylation observed after these treatments. Values are referenced to silica calcined at 200 °C in N2, which was considered as total hydroxylation for this comparison. On this scale, 100% dehydroxylation means that all OH groups have been removed. As seen in Figure 8, calcination in N2 removed silanol groups and higher temperatures led to greater dehydroxylation. However, even at 950 °C, only about 80% of the OH population (at 200 °C) was removed. Calcination in CO was more effective, causing more dehydroxylation, starting at about 550 °C to 600 °C, the temperature at which the two curves (representing calcination in CO vs. N2) separate. The treatment of silica in CS2 vapor caused even more dehydroxylation, and one sample reached 97% removal of the OH group at 950 °C. In one aspect, sulfur appears to become an effective dehydroxylating agent at lower temperatures than CO. At about 400 °C, the curve in Figure 8 representing the results of CS2 dehydroxylation separates from that representing dehydroxylation under N2.

[00164] These improved dehydroxylation treatments can influence the performance of the catalyst and the resulting polymer, as illustrated in the examples in Table 1. In each case, silica-titania (2.5 wt% Ti) was calcined at 870 °C in the atmosphere shown. Then, 0.5 wt% Cr was impregnated into the carrier as dicumenochrome(0) in pentane, followed by a final calcination treatment in air at 316 °C to 593 °C. Therefore, each sample received a two-step activation, in which the first calcination step was carried out in the atmosphere listed in Table 1. Each catalyst was then tested for ethylene polymerization activity, and the polymer that was produced was retrieved and analyzed.

[00165] In one aspect, it was found that the MW weight average molecular weight of the polymer (Table 1) decreased significantly when CO was used as the calcining gas for the support, although the chromium and CO were never in contact with each other. with the other. While not intended to be bound by theory, this finding suggests that CO affects catalyst performance through its influence on the support alone. It was found that the use of CS2 as the calcination gas reduced the polymer's molecular weight (MW) by about two-thirds. The reduced MW also manifests itself in other properties, including increased melt index and reduced melt viscosity. For example, the use of CO more than doubled the melt rate and CS2 increased the melt rate about 60 times. The last row of Table 1 reports fluidity, which, like melt index, is an indication of how easily the molten polymer flows at low shear rates. While melt index measures flow rate (shear) under constant shear stress, fluidity measures shear stress at constant shear rate (0.1 s-1). Like melt index, fluidity indicates how easily the molten polymer flows at low shear rates. Fluidity is the inverse of melt viscosity and, like MI, varies inversely with molecular weight.

[00166] TABLE 1 Dehydroxylation improved by various chemical reactions. The silica-titania was calcined at 870 °C in the indicated gas, and then it was impregnated with dicumene Cr(0) in hexane, and finally it was calcined in air at 300 °C to 593 °C.

[00167] In the last two tests (experiments) represented in Table 1, the silanol groups were replaced by halide groups. Bromide and iodide groups were selected instead of fluoride and chloride because these halogens can be easily burned from the silica surface, leaving the siloxane. In these experiments, silica-titania samples were treated with I2 or Br2 vapor in the presence of CO at 871 °C. Analysis of the treated silica-titania sample at this point revealed the presence of large amounts of halide in the support. Subsequently, these treated samples were exposed to dry air, also at 871 °C, which released these halogenated groups by oxidation back to I2 or Br2 gas. The presence of each halogen (Br2 or I2) in the output gas was confirmed by its dark reddish-brown or violet color. These samples were then impregnated with chromium and subjected to a second calcination as described above, resulting in a two-step activation. These two catalysts were found to be highly active for ethylene polymerization, and the resulting polymer was, again, recovered and analyzed.

[00168] In one aspect, this halide dehydroxylation method can result in an improvement in polymerization behavior, as illustrated in Table 1. For example, this halide dehydroxylation method significantly increased the melt index potential of the catalyst , so that the lower MW polymer was produced. However, it was observed that not all of the iodide was burned during the activation process, because a small amount of one species survived the air treatment (even at 871 °C) to produce a highly reactive, yellow paramagnetic surface species. Without intending to be limited to theory, this reactive species could be an iodate species of some kind. Silica treated and activated in this way exhibited a strong oxidizing capacity and reacted with many organic compounds.

[00169] Figure 9 illustrates the results of three series of two-step activations, each of which includes one of the chemical dehydroxylation methods described above. For the results in Figures 9, silica-titania (2.5 wt% Ti) was calcined at 871 °C in air, CO or CS2. Each support was impregnated with 1 wt% Cr as dicumenochrome(0) in hexane, and the samples were subsequently subjected to a second calcination in dry air at lower temperatures in the range of 160 °C to 871 °C. These catalysts were tested at 107 °C for polymerization activity, and the resulting polymer was recovered and analyzed.

[00170] Figure 9 is a graph of the melt index values of these polymers in relation to the second calcination temperature. In each series, Figure 9 shows that a maximum melt index value was achieved when the catalyst was oxidized at about 400 °C to 500 °C. This behavior is similar to the data represented in Figures 4 and 5, although the melt index peak is shifted to higher temperatures in the activations of Figure 9. At all temperatures tested, samples that were treated in CO produced polymers of higher MI than samples calcined in air alone. Similarly, samples calcined in CS2 produced polymers with even higher melt index (note that the y-axis of Figure 9 is a logarithmic scale). Although not limited by theory, it is believed that the drop in MI observed when the samples were oxidized at 500°C to 900°C is another indication that the sites associated with titania were thermally unstable and tended to reorganize at higher temperatures. high.

[00171] Table 2 provides data for the surface areas and pore volumes of silica samples calcined at various temperatures. The upper series in Table 2 represents samples calcined in air, while the lower series represents samples calcined in CO. Each sample was then impregnated with 1 wt% Cr as dicumenochrome(0) in pentane, followed by oxidation in air at 540 °C. They were then tested for polymerization activity at 107 °C. The onset of sintering is clearly shown in Table 2 by the abrupt drop in surface area and pore volume as seen in the air calcination data. However, when calcination was carried out in CO, this transition occurred only at higher temperatures and was less severe than calcination in air. Therefore, the data in Table 2 suggests that these improved dehydroxylation techniques tend to inhibit sintering. Another indication of sintering may be the drop in the melting rate of polymers produced using the catalyst. For example, in one test, silica titanated at 1.5 Ti in nm-2 (i.e., Ti«nm-2 atoms) lost 40% of its pore volume when calcined at 871 °C in air, but only 10% when calcined in CO. Although not limited to any particular theory, this behavior suggests that surface OH groups, or traces of water vapor in the gas stream, may promote sintering (as in hydrothermal treatments) and their removal via reaction with CO may slow down the sintering process.

[00172] TABLE 2 Calcination in CO, instead of dry air or N2, inhibits the usual thermal sintering. Cr/silica was calcined as shown below and then impregnated with 1% Cr as dicumene Cr(0) in pentane and then calcined at 540 °C. Sintering is evident by the drop in porosity or melt index of the polymer. The reaction temperature was 107 °C.

[00173] The melt indices of the polymers produced using the catalysts in Table 2 were determined. The silica samples represented in Table 2 were subsequently impregnated with 1 wt% Cr as dicumenochrome in hexane, followed by a second calcination in air at 540 °C to oxidize the chromium. These catalysts were then tested for polymerization activity, the resulting polymer was recovered and analyzed, and the melt index values that characterize these polymers are shown in Table 2. Dehydroxylation in CO provided polymers with a higher melt index than those obtained when calcination was carried out in air. In each series, as the silica was calcined at progressively higher temperatures, the melt index of the polymer increased until it reached the sintering point. Then, the melting index value decreased at higher calcination temperature, as was also observed upon one-step activation.

COMMERCIAL ASPECTS

[00174] In one aspect, a variation on the two-step activation process used for anhydrous chromium impregnation can be used in commercial practice. In this aspect, the virgin catalyst already containing chromium can be subjected to an activation that comprises, consists essentially of or consists of, two consecutive steps. First, the primary step (dehydroxylation) is conducted in a non-oxidizing atmosphere, which is used to minimize, reduce, or prevent the attachment of low-valent chromium (lower oxidation state) to the support. Second, the temperature is maintained (Figure 10) or reduced (Figure 11A and Figure 11B) and the reducing atmosphere is replaced with dry air, to oxidize, disperse, and attach the chromium to the surface. In this process, only one calcination process is used, which includes a high-temperature dehydroxylation step in CO, N2, CS2 and the like, followed by a low-temperature oxidation and Cr attachment step in dry air. Therefore, this procedure provides a route to the same two-step activation chemistry used for anhydrous chromium impregnation, but without the anhydrous impregnation. Not limited by any particular theory, it is thought that large crystallites or chromium domains may result from the first step, which require a slightly higher temperature in the secondary step for full oxidation (or, in some cases, reoxidation).

[00175] Figure 10 illustrates this approach and demonstrates some of the benefits of improved dehydroxylation. For the data in Figure 10, Cr/silica-titania (2.5 wt% Ti) was calcined at various temperatures for 3 h in a non-oxidizing atmosphere (N2, CO, or CS2), followed by 2 h in dry air. at the same temperature. These catalysts were then tested for polymerization activity and the resulting polymers were analyzed. In all three cases, the polymer melt index increased as the catalyst calcination temperature was increased. Due to improved dehydroxylation, calcination in CS2 resulted in higher MI values than calcination in CO, calcination in CO resulted in higher MI values than calcination in N2. Obviously, N2 treatment would correspond to a one-step activation, because in this case the primary and secondary steps were conducted at the same temperature.

[00176] Figure 11A and Figure 11B provide polymer data for catalyst activations in which the secondary step (chromium attachment) is conducted at a lower temperature than the primary step (dehydroxylation). In Figures 11A and 11B, Cr/silica-titania (2.5 wt% Ti) was calcined in N2, CO or CS2, but always at 871 °C. The temperature of the secondary stage in air ranged from 300 °C to 900 °C. These catalysts were then tested for ethylene polymerization and the resulting polymers were analyzed. Instead of the melt index, Figure 11A shows the molecular weight, which reached a minimum, and the fluidity shown in Figure 11B, which reached a maximum as a function of the treatment temperature. Both extremes in molecular weight and fluidity occurred when the catalysts were oxidized at about 600 °C. Like melt index, fluidity indicates how easily the molten polymer flows at low shear rates. Fluidity is the inverse of melt viscosity and, like MI, varies inversely with molecular weight.

[00177] Thus, each response went through a peak, which we can call ideal, similar to the response observed in the anhydrous impregnation method, as shown in Figure 9. However, the ideal temperature of the second treatment was slightly higher in this case compared to the anhydrous impregnation method. Not limited by any particular theory, these observations may indicate greater difficulty in oxidizing chromium and dispersing Cr(VI). In this example, the response was maximized when dehydroxylation occurred at 871 °C and Cr(VI) dispersion occurred at about 600 °C. Note that the 871°C data points in Figure 11A and Figure 11B correspond to the 871°C points in Figure 10.

[00178] If the reduced catalyst is left with large crystallites of a-Cr2O3 (detectable by X-ray diffraction), reoxidation at 750 °C or a higher temperature may be necessary to obtain the maximum melt index in the resulting polymer, because this form of chromium can be more difficult to oxidize and disperse. In this regard, the method by which the catalyst is initially heated to the dehydroxylation temperature can determine the optimal oxidation temperature desired later. For example, and although not limited by theory, the presence of water vapor during initial heating, or the presence of Cr(VI) during heating in N2, can stimulate the growth of crystallites of a-Cr2O3, and Cr( VI) can act as a flux in the growth of such crystallites. Thus, if the thermal rise at 871 °C is in N2, even if followed by CO at 871 °C, differences in performance were observed depending on whether the virgin catalyst contained chromium that was hexavalent Cr(VI) or trivalent Cr(III). The former is thought to tend to produce larger a-Cr2O3 crystallites. Furthermore, if a catalyst containing trivalent chromium is heated to 600 °C in dry air, which forms Cr(VI) and then in N2 at 871 °C, this treatment also promotes the growth of large crystallites that are more difficult to reoxidize later.

[00179] Although not intended to be limited to theory, it is believed that Figure 12 shows data that reflects the formation of -Cr2O3 crystallite. The upper curve in Figure 12 represents Cr/silica-titania that was heated to 870 °C in N2. The lower curve (Figure 12) represents the same catalyst, but heated to 650 °C in air, which creates Cr(VI) and then to 870 °C in N2, which allows the decomposition of Cr(VI) in a-Cr2O3. Subsequently, each catalyst was kept in CO at 870 °C for 3 h, followed by oxidation in air for 2 h at the temperature indicated in Figure 12. These catalysts were then tested and the resulting polymer was analyzed. The crystalline catalyst (bottom curve) required a higher temperature (750 °C) than the amorphous catalyst (650 °C) to achieve the maximum melt index in the polymer. It is seen that higher oxidation temperature also decreased the magnitude of melt index (MI) improvement. Thus, the amorphous catalyst was oxidized more easily, requiring a lower temperature and, consequently, produced a polymer with a higher melt index than the crystalline catalyst. At temperatures above 750 °C, when the a-Cr2O3 crystallites are finally oxidized and dispersed, the two curves appear to correspond.

[00180] As illustrated in Figure 11A and Figure 11B, CS2 was the most effective atmosphere for dehydroxylation in this activation procedure, as it was in the anhydrous impregnation technique, as shown in Figure 9. In the experiment in Figures 11A and 11B, a series of catalysts was calcined in air, another in CO and yet another in CS2, each at 871 °C. A black chromium sulfide material formed when chromium-containing catalysts were reduced to CS2, COS, or other organic sulfur compounds. However, the second calcination in air easily oxidized the chromium sulfide material back to Cr(VI) oxide and no sulfur was detected in the final catalyst.

[00181] It is observed that catalysts treated with sulfur may present an orange color or even a more intense red color after final oxidation. Although it is not intended to be limited to theory, it is believed that the cause of the red color may indicate the formation of high levels of dichromate, as dehydroxylation may favor dichromate species. The red color may be associated with the use of sulfides to obtain more extreme levels of dehydroxylation. Exposure of a sulfur-treated catalyst to water vapor completely reversed the melt index benefit. Organic selenium and tellurium compounds promoted the catalyst as much as sulfur compounds.

[00182] Another indication that sites associated with titania are less stable at high temperature was observed by measuring the concentration of Cr(VI) in catalysts activated by the two-step process. Figure 13 depicts a series of Cr/silica catalysts that have been titanated at various levels and then activated by the commercial two-stage approach disclosed herein. Specifically, these catalysts were heated to 871 °C in CO and held at this temperature for 3 h and then oxidized in air at 600 °C for 2 h. These catalysts were tested for polymerization activity and the resulting polymers were analyzed. Figure 13 provides a plot of the logarithm of polymer melt index versus titania loading in the catalyst, and Figure 13 can be compared with Figure 6, representing anhydrous chromium impregnation. In each figure, a strong response of the polymer melt index to the titania content of the catalyst is observed. This trend is confirmed by the MW of the polymer, which is also shown in Figure 13.

[00183] Thus, these data suggest that there is a strong tendency to create sites associated with titania by each of the published procedures. The Cr(VI) coverages of the catalysts in Figure 13 were determined and are also shown in Figure 13. The conversion to Cr(VI) became less efficient with the addition of titania, indicating lower stability at 600 °C. These values can be compared with the initial chromium loading of 0.38 Cr atoms in nm-2. At high titania loadings (3 to 4 Ti atoms in nm-2), the catalyst was found to contain almost no Cr(VI).

[00184] It can be seen that when silica is heated in air, it does not immediately become dehydroxylated because an annealing process is involved, which can take up to 24 hours to reach equilibrium, depending on the temperature. In a series of experiments illustrated in Figure 14, the calcination time in CO at 871 °C was varied from 0.5 to about 7 h to determine whether this form of dehydroxylation is also time dependent. The curve in Figure 14 shows the dehydroxylation process approaching equilibrium in about 12 h, which is approximately similar to the time observed when calcination was carried out in air. Thus, it appears that surface mobility may be operating for dehydroxylation even in the presence of CO.

[00185] In one aspect, for chromium redistribution to occur using reduction and reoxidation activation, also called "R&R" activation, a sufficiently "detached" chromium is considered beneficial upon entering the oxidation step. For example, the chromium in the usual virgin catalyst, Cr(III)/silica, is already sufficiently detached from the surface, and heating it in N2 or CO will not change this unattached status. However, if Cr(III)/silica is first oxidized to Cr(VI)/silica, such as during a heating step in air, chromium can bind to the silica surface. Therefore, for R&R activation, chromium can be sufficiently detached from the surface during the dehydroxylation treatment in N2 or CO to assist in the redistribution of Cr(VI) during the final oxidation step.

[00186] In this regard, Table 3 provides data comparing a conventional Cr/silica activation in air at 871 °C before (line 1) and after (line 2) reduction in CO and reoxidation in air, both at 350 °C. These catalysts were then tested and the resulting polymers analyzed, and it was observed that there was no increase in MI. It is thought that this reduction treatment did not sufficiently highlight the chromium to cause a redistribution of the chromium during subsequent air treatment at 350°C. Furthermore, this treatment did not give the MI boost as in a two-step activation. However, when the Cr(II) catalyst was subsequently treated in N2 at 871 °C (line 3), followed by oxidation at 350 °C, an improvement in MI was observed. Therefore, although not limited by theory, it is believed that this N2 treatment at 871 °C may involve some rearrangement of chromium (perhaps into larger domains) but does not appear to cause any additional dehydroxylation. However, this treatment produced a large IM improvement in the polymer, which is characteristic of two-step activation (Table 3). Once Cr(VI) was formed, high temperatures were apparently favorable to chromium detachment.

[00187] TABLE 3 When Cr(VI) is reduced during the R&R (reduction and reoxidation) process, high temperature is required to separate the Cr from the surface and allow it to reattach during the reoxidation step.

[00188] Not bound by any particular theory, it is thought that the degree of agglutination that occurs during this detachment may affect or determine how severe a reoxidation treatment is necessary. The temperature required for reoxidation may also depend on the reoxidation atmosphere. In one aspect, Figure 15 shows the melt index values of polymers obtained from Cr/silica-titania that was reduced in CO at 871 °C and subsequently reoxidized at various temperatures in varying amounts of oxygen. A high temperature (820 °C) was required for optimal reoxidation when the atmosphere contained only 10% O2. However, the required reoxidation temperature dropped to 760 °C when the treatment was at 21% O2 and to just 630 °C when it was at 100% O2. Thus, more oxygen in the atmosphere tended to reoxidize and redisperse chromium at lower temperatures.

[00189] When a catalyst activated by the two-step procedure was then reduced in CO at 350 °C, the advantages of two-step activation appeared to be diminished or even lost. For example, the MW distribution was changed so that the low MW bounce was lost. Although not tied to any particular theory, this finding may indicate that the final reduction step provides an opportunity for these thermally unstable, titania-associated sites to migrate back to their usual configuration. This behavior further provides further evidence that two-step activation preferentially deposits Cr(VI) on titania, leaving an exceptionally high population of titania-associated sites.

[00190] In a further aspect, the time used in the final treatment in air can affect the resulting melt index, with short oxidation times providing good improvements in the melt index. This behavior may be due to the occupation of acidic sites, which are perhaps the most reactive initially. Although not limited by theory, it is believed that longer holding times in air at high temperatures may allow the initially formed Cr(VI) species to migrate to lower energy surface positions, perhaps more basic sites, which reduces the potential of MI. In this regard, Table 4 presents some examples of the influence of time during the second stage, where oxidation times as short as 5 minutes can produce some exceptional improvements in melt index. In Table 4 and throughout, h are hours and min are minutes.

[00191] TABLE 4 The influence of oxidation time

[00192] The activation methods disclosed in this document were developed where high melt index may be desired in chromium catalysts. For example, using conventional air activation conditions, a melt index of 3 can be considered an achievable melt index result of the Magnapore catalyst. In contrast, the activation treatments disclosed herein provide polymers with higher melt index values, for example, about 30 MI (g/10 min, in commercial reactors). It is observed that CO activation provides good commercial results with superior MI polymers being produced. However, additional methods are disclosed that can also produce superior MI polymers.

[00193] In a further aspect, the disclosed activation treatments can be used to provide additional advantages, beyond simply a higher melt index of polyethylene. For example, high MI potential can be converted into higher productivity, for example, by increasing the ethylene concentration, or it can provide better sedimentation efficiency, or it can provide lower reactor temperature and achieve higher solids. The disclosed activation methods can also be used to shorten the activation time and therefore to increase the capacity of the activator.

EXAMPLES

[00194] Aspects of the invention can be further illustrated by the following examples, which should not be interpreted in any way that imposes limitations on the scope of this invention. Various other aspects, embodiments, modifications and equivalents thereof which, after reading the description of the present document, may be suggested to persons of ordinary skill in the art without departing from the spirit of the present invention or the scope of the appended claims.

[00195] Two commercially available chromium catalysts were selected, a silica coated with Cr/Ti (catalyst A) and a simple Cr/silica (catalyst B). Catalyst A was prepared from a silica with a surface area of about 450 m2/g, a pore volume of about 1.55 ml/g and an average particle size of about 80 microns. This silica was heated under nitrogen purge for 3 h at 200 °C, cooled to room temperature, and then impregnated with 1 wt% Cr (as chromium (III) acetate) in methanol solution. Methanol was evaporated, and then the obtained Cr/silica was impregnated with 3.0 to 3.3% Ti as a titanium propoxide heptane solution. After the heptane was evaporated under a nitrogen purge at about 120 °C, the finished catalyst was calcined as described hereinafter.

[00196] Various titanium compounds that can be used for impregnating silica in the preparation of catalysts, according to this disclosure, include, but are not limited to, titanium(IV) ethoxide (Ti(OEt)4), titanium isopropoxide (IV) (Ti(O-i-Pr)4), titanium n-propoxide(IV) (Ti(O-n-Pr)4), titanium n-butoxide(IV) (Ti(O-n-Bu)4), ( triethanolaminate)titanium(IV)isoproxide, titanyl acetylacetonate, titanium diacetylacetonate diisopropylate, titanium alkyl esters and the like. Furthermore, various Ti(III) compounds can also be used for the impregnation of silica in the preparation of catalysts in accordance with this disclosure.

[00197] The Cr/silica B catalyst was purchased from W.R. Grace under the trade name 969MS. It is characterized by a titanic content of 0% by weight, a surface area of about 300 m2/g, a pore volume of about 1.60 ml/g, an average particle size of about 100 microns and a chromium loading of 1.0% by weight. Polymerization tests were carried out in a 2.2 l stainless steel reactor equipped with a marine agitator that rotated at 500 rpm. The reactor was surrounded by a steel jacket through which a mixture of steam and water was passed, which was adjusted to maintain a constant temperature of 105 °C ± 0.5 °C with the help of electronic control instruments.

[00198] Unless otherwise stated, a small amount (about 0.01 to 0.10 grams) of the solid catalyst was first charged under nitrogen into the dry reactor. Then, 1.2 liters of isobutane liquid was charged and the reactor heated to the specified temperature of 105 °C. Finally, ethylene was added to the reactor to equal a fixed pressure, typically 3,792,116.35 Pa (550 psig), which was maintained throughout the experiment. Stirring was allowed to continue for the specified time, usually about an hour, or until about 3,000 grams of PE was produced per gram of catalyst, and activity was observed by recording the flow of ethylene into the reactor to maintain the set pressure.

[00199] After the allotted time, the ethylene flow was stopped and the reactor slowly depressurized and opened to recover the granular polymer powder. In all cases, the reactor was clean, with no indication of wall fouling, coating or other forms of deposition. The polymer powder was then removed and weighed. Activity was specified as grams of polymer were produced per gram of solid catalyst loaded per hour.

[00200] Table 5 provides a series of examples in which 50 ml samples of these catalysts were activated in the laboratory activator tube described above according to a specific activation protocol, and a catalytic olefin polymerization assay was performed to examine the properties of the catalyst and the resulting polymer provided by this catalyst activation. Two catalysts were used in the examples in Table 5: catalyst A (Cr/Ti coated silica, 3.2% Ti) and catalyst B (Cr/silica).

[00201] TABLE 5 Example of catalyst activations, associated catalyst and polymer properties. A

[00202] As Table 5 illustrates, the activation protocols were varied and the resulting polymer properties are compared. Two control runs are shown in Table 5 for comparison, in which longer conventional activation times were used for catalyst activation. The examples in Table 5 were activated in a fluidized bed using the following parameters: loaded catalyst, 50 ml (10 to 20 g); heating rise rate is 4°C/min, gas velocity is 1.524 cm/s (0.05 ft/s); and the cooling rise rate is about 2 °C/min using the gases specified in the table. The activator tube itself was a 5.08 cm (2 inch) diameter quartz tube with a sintered quartz distribution plate fused into the frame through the tube. The tube also had a thermal well that allowed a thermocouple to be placed inside the bed to read the temperature.

[00203] The Activation Parameters column in Table 5 includes fluidization gas, storage temperatures and holding times. For activation examples that list two gases (N2, air), the Activation Parameters in Table 5 indicate the activation sequence shown. At the end of each activation, the catalyst was then removed from the furnace and flushed with nitrogen gas before storage for use.

[00204] The data in Table 5 illustrate a substantial increase in the HLMI in the examples where the catalyst is activated in accordance with this disclosure, versus the HLMI of the polymers obtained from the comparative catalyst tests, when the air oxidation step is enough. For example, Examples 1 to 3 and 6 to 7 of catalyst A show substantially increased HLMI from control Examples 8A and 8B of catalyst A. Examples 4 and 5 demonstrate that the relatively low air activation temperature (T2) 400 °C for 18 minutes (tH2) does not provide sufficient activation to achieve the increased HLMI over control Examples 8A and 8B. However, a longer air holding time of 48 minutes (tH2) at an air activation temperature (T2) of 400 °C activates the catalyst to provide the substantially increased HLMI in the polyolefin resulting from Control Example 8.

[00205] Likewise, for Catalyst Examples B 10 to 12B, a substantially increased HLMI from Catalyst Control Examples B 13A and 13B is seen. The activation of Example 9, compared to the activations of Examples 10 to 12B, includes a lower N2 activation temperature (T1) and/or a lower air activation temperature (T2) and shorter time (tH2) and the resulting polymer does not achieve an increased HLMI comparable to that of Examples 10 to 12B. Compared to catalyst B control Examples 13A and 13B, the HLMI of Example 9 is only slightly increased relative to the control Example 13A polymer.

EXAMPLES 14 TO 17

[00206] Table 2 shows some examples of activation profiles that meet this disclosure and the total time to complete activation. All of these activations appear to be shorter than the typical 30-hour control activation on conventionally activated catalysts.

[00207] TABLE 6 Examples of catalyst activation times and temperatures. AInitial temperature above ambient indicates that the activation vessel was already hot from previous activations when loaded with the catalyst to be activated.B After the oxidation waiting time (tH2), the catalyst was allowed to cool to approximately 204 °C (about 400 °F) before being poured into a feed hopper.

[00208] The Examples in Table 6 demonstrate the much shorter total activation cycle compared to the 24 h to 30 h total activation cycle time in conventionally activated catalysts. Furthermore, as demonstrated in the data in Table 5, the polyolefin resulting from the disclosed activation process can provide HLMI values superior to what conventionally activated catalysts can provide.

[00209] The following examples (Examples 18 to 20) demonstrate a commercial scale activation, in which 226.79 kg (500 lbs) of catalyst A (3.0% by weight Ti) were charged under flow of nitrogen at about 3.048 cm/s (0.1 ft/s), in a 121.92 cm (48 inch) activator vessel that has already been heated to 315.56 °C (600 °F).

EXAMPLE 18

[00210] In Example 18, after charging the catalyst, the temperature was raised to 399 °C (750 °F) while the catalyst was allowed to fluidize in nitrogen at a flow rate of about 7.31 cm/s (0 .24 ft/s). After four hours under this condition, the nitrogen was changed to a mixture of 50% nitrogen and 50% air for three minutes (min). The temperature began to rise and soon reached 418 °C (785 °F) without any additional heating being applied. Then the atmosphere was changed back to 100% nitrogen and over the course of about 15 min the temperature was cooled again to 399 °C (750 °F). Then, the atmosphere was changed again to 50% nitrogen and 50% air for three minutes. This time, the temperature only rose to 410 °C (770 °F). The gas was changed back to 100% nitrogen and within 10 minutes the temperature was cooled back to 399 °C (750 °F). A third 3-minute exposure to 50% nitrogen and 50% air brought the temperature to 410 °C (770 °F). A fourth cycle resulted in an exotherm at 407 °C (765 °F) and this time it cooled even without removing 50% of the nitrogen and 50% of the air. Although not intended to be limited to theory, this observation is believed to reflect that the majority of organics in the catalyst have already been oxidized and removed. The atmosphere was then changed back to 100% pure nitrogen and the temperature was heated to 677 °C (1,250 °F) at a rise rate of -16.28 °C/min (2.7 °F/min). min) and with a gas velocity of 73.15 cm/s (2.4 ft/s). The catalyst was left to fluidize at this temperature in nitrogen for an additional 6 hours and then a sample was taken for further analysis (sample 18A).

[00211] After this treatment, the catalyst temperature was reduced to 510 °C (950 °F) under 73.15 cm/s (2.4 ft/s) nitrogen flow (the cooling rate was typically about 93.33°C/hour (200°F/hour)). At this temperature, the atmosphere changed to 100% air (73.15 cm/s (2.4 ft/s)). An exotherm (without application of additional heat) was observed that rose to 549 °C (1,020 °F) in about 5 minutes. Within the next 10 minutes, however, the temperature dropped to 510 °C (950 °F). Air cooling was allowed to continue at a rate of -14.89°C/min (5.2°F/min). When the temperature reached 343°C (650°F), the atmosphere was again changed to pure nitrogen and the catalyst was purged for about 2 hours when the temperature finally dropped and was maintained at 316°C (600°F). . It was unloaded and stored under nitrogen. A sample (sample 18B) was taken from the vessel for testing. The results are shown in Table 7.

[00212] TABLE 7

[00213] Also shown in Table 7 is a control test (Example 19) using the same Cr/silica-titania catalyst (3.0% Ti) that was used in Example 18. In this case, 226.79 kg (500 pounds) of catalyst were again charged into the same commercial activator vessel at 315.56 °C (600 °F). The catalyst was then heated to 676.67 °C (1,250 °F) in air at a rate of 16.28 °C/min (2.7 °F/min) and a gas velocity of 73.15 cm/s (2.4 ft/s). The catalyst was held at this temperature for 8 hours and then cooled in air at 315.56 °C (600 °F) at 65.56 °C/h (150 °F/h). After purging in nitrogen at this temperature for 3 hours, it was discharged into a storage vessel under nitrogen. A sample of this catalyst was then taken and tested for polymerization behavior. The results are again shown in Table 7, along with reference catalyst 8B, which is a laboratory activation of catalyst A, i.e. using Catalyst A control Example 8B shown in Table 5. Note that the HLMI and MI of inventive assays 18-1 and 18-2 were considerably higher than those of control assay 19 and reference assay 8B.

EXAMPLE 20

[00214] Yet another commercial test was done with 226.79 kg (500 pounds) of Catalyst A (3.2% Ti) in Example 20. The catalyst was, again, charged under nitrogen at 315.56 °C ( 600 °F) and then heated under nitrogen flow of 7.31 cm/s (0.24 ft/s) at a rise rate of -16.28 °C/min (2.7 °F /min) at 371.11 °C (700 °F). The conditioning procedure used in Example 18 was repeated in this Example. That is, 3-minute bursts of 50% air were applied, resulting in an exotherm initially of 7.22 °C (45 °F), followed by a 10 to 15 minute cooldown in pure nitrogen. The second cycle produced a temperature increase of 4.44 °C (40 °F). Seven cycles in total were conducted, each time the exotherm decreased by a few degrees. In the seventh cycle, the temperature rose to -6.67 °C (20 °F) and then began to cool before the air was removed. The atmosphere was then changed back to pure nitrogen and the bed was heated to -16.28°C/min (2.7°F/min) to 677°C (), where the bed was held for 6 hours. The bed was then cooled in nitrogen at -13.89°C/min (7°F/min) to 575°C (1,067°F) and the atmosphere changed to clean air. An exotherm at 607.18 °C (1,126 °F) occurred over the next 5 minutes, after which the temperature was reduced to 607.18 °C (1,022 °F) in a controlled fall of 51 min to a medium fall rate of about -17.3°C/min (0.8°F/min) during this period. The cooling rate was then changed to - 13.94 °C/min (6.9 °F/min). The atmosphere was changed back to pure nitrogen when the temperature reached 315.56 °C (600 °F). Thus, for the entire oxidation period using the "mobile" oxidation step, the temperatures from X at °C (°F) to Y at °C (°F), as explained in this document, were X = 975 ° C (1,067 °F) and Y = 371.11 °C (700 °F), taking 1.98 hours, giving an average fall rate of -15.78 °C (3.6 °F/min). A catalyst sample was taken for testing and the results are also shown in Table 7. Note again that the melt index and HLMI obtained are considerably higher than the control tests.

EXAMPLES 21 TO 29

[00215] As established in Example 18, a sample designated Sample 18A was taken after the initial activation steps, but before the final oxidation step. In the experiments that follow, small portions of that Sample 18A were then oxidized in air (1.524 cm/s (0.05 ft/s)) for 30 minutes at various temperatures from 650°C to 400°C. This Sample 18A catalyst activated under different oxidation conditions was then subjected to polymerization tests, the results of which are shown in Table 8. All of these tests produced polymers with melt index and HLMI values substantially higher than the control 8A and 8B (see Table 5). It can also be observed that, at the lower temperatures, the catalyst was not oxidized enough to obtain the best activity, suggesting that longer oxidation times were necessary in these tests.

[00216] TABLE 8

EXAMPLE 30

[00217] In this example, a low Ti version of the Cr/titania coated silica catalyst was activated, in accordance with the present disclosure; first by calcining in nitrogen at 675 °C (T1) for a relatively short period of 4 hours (TH1), followed by one of two different oxidative atmosphere activation steps or processes: [1] in method A, the catalyst was oxidized in air for 30 min at 650 °C to provide Catalyst A; and [2] in method B, the catalyst was oxidized in air for 30 min at 450 °C to provide Catalyst B. Catalyst A was found to produce a polyethylene with an HLMI of 65 to 66 g/10 min and, although Catalyst B has considerably lower activity than Catalyst A, Catalyst B was found to produce a polyethylene with an HLMI of 138 g/10 min.

[00218] The invention is described above with reference to numerous aspects and specific embodiments and examples. Many variations will be suggested to those skilled in the art in light of the above detailed description. All such obvious variations are within the full intended scope of the appended claims. Other aspects of the invention may include, but are not limited to, the following aspects. Many aspects are described as "comprising" certain components or steps, but alternatively may "consist essentially of" or "consist of" those components or steps unless specifically indicated otherwise.

[00219] Aspect 1. Process for activating a supported chromium catalyst, wherein the process comprises:

[00220] a) heating a chromium catalyst supported in an inert atmosphere to a first temperature (T1) at a first rise rate (RR1);

[00221] b) maintain the chromium catalyst at the first temperature in the inert atmosphere for a first waiting time (tH1);

[00222] c) allowing the chromium catalyst to reach a second temperature (T2) in the inert atmosphere at a second rise rate (RR2), followed by exposing the chromium catalyst to an oxidative atmosphere;

[00223] d) maintaining the chromium catalyst at the second temperature in the oxidative atmosphere for a second waiting time (tH2); It is

[00224] e) allowing the chromium catalyst to cool to a temperature below the second temperature in an inert atmosphere, in the oxidative atmosphere or in any sequential combination of an inert atmosphere and an oxidative atmosphere over a cooling time (tC) , to provide an activated chromium catalyst.

[00225] Aspect 2. Process according to Aspect 1, wherein step e) comprises exposing the chromium catalyst to an inert or oxidative atmosphere, while allowing the chromium catalyst to cool to a temperature of less than about 250°C, less than about 240°C, less than about 230°C, less than about 220°C, less than about 210°C, less than about 205°C, less than about 204°C, less than about 200°C, less than about 190°C, less than about 180°C, less than about 170°C, less than about 160°C, less than about 150°C, less than about 140°C, less than about 130°C, less than about 120°C, less than about 110°C, or less than about 100 °C over the cooling time (tC), to provide the activated chromium catalyst, wherein the lower temperature limit, at each occurrence, is about room temperature.

[00226] Aspect 3. Process, according to Aspect 1, wherein step e) comprises exposing the chromium catalyst to an inert atmosphere, while allowing the chromium catalyst to cool over the cooling time (tC), to provide the activated chromium catalyst.

[00227] Aspect 4. Process, according to Aspect 1, wherein step e) comprises allowing the chromium catalyst to cool in the oxidative atmosphere over the cooling time (tC) to provide the activated chromium catalyst.

[00228] Aspect 5. Process according to Aspect 1, wherein step e) comprises allowing the chromium catalyst to cool in the inert atmosphere followed by an oxidative atmosphere over the cooling time (tC) to provide the catalyst activated chrome.

[00229] Aspect 6. Process according to Aspect 1, wherein step e) comprises allowing the chromium catalyst to cool in the oxidative atmosphere followed by an inert atmosphere over the cooling time (tC) to provide the catalyst activated chrome.

[00230] Aspect 7. Process according to Aspect 1, wherein step e) comprises allowing the chromium catalyst to cool in the inert atmosphere followed by an oxidative atmosphere and followed by an inert atmosphere over the cooling time ( tC) to provide the activated chromium catalyst.

[00231] Aspect 8. Process, according to any of Aspects 1 to 7, in which the oxidative atmosphere is a mixture of 50% oxygen and 50% nitrogen.

[00232] Aspect 9. Process, according to any one of Aspects 1 to 7, in which the oxidative atmosphere is air.

[00233] Aspect 10. Process, according to any one of Aspects 1 to 7, in which the first temperature (T1) is greater than the second temperature (T2) (T2 is less than T1).

[00234] Aspect 11. Process, according to any one of Aspects 1 to 7, wherein the first temperature (T1) is equal to the second temperature (T2).

[00235] Aspect 12. Process, according to any one of Aspects 1 to 7, wherein the first temperature (T1) is greater than the second temperature (T2), and wherein the step of allowing the chromium catalyst reaching the second temperature (T2) in the inert atmosphere comprises cooling the chromium catalyst under a flow of inert gas.

[00236] Aspect 13. Process, according to any one of Aspects 1 to 12, in which the inert atmosphere comprises nitrogen or argon.

[00237] Aspect 14. Process, according to any one of Aspects 1 to 12, in which the inert gas used in each step is nitrogen.

[00238] Aspect 15. Process, according to any one of Aspects 1 to 14, in which the oxidative atmosphere comprises air or oxygen.

[00239] Aspect 16. Process according to any one of Aspects 1 to 14, wherein the oxidative atmosphere comprises air or oxygen having a dew point less than about -40 ° C, less than about -50 ° C , less than about -60°C, less than about -70°C, or less than about -80°C, for example, about -82°C (-116°F).

[00240] Aspect 17. Process according to any one of Aspects 1 to 16, wherein T1 is from about 500 °C to about 1,000 °C, from about 550 °C to about 900 °C, from from about 600°C to about 870°C or from about 650°C to about 850°C.

[00241] Aspect 18. Process according to any one of Aspects 1 to 16, wherein T1 is about 500 °C, about 525 °C, about 550 °C, about 575 °C, about 600°C, about 625°C, about 650°C, about 675°C, about 700°C, about 725°C, about 750°C, about 775°C, about 800° C, about 825 °C, about 850 °C, about 875 °C, about 900 °C, about 925 °C, about 950 °C, about 975 °C or about 1,000 °C .

[00242] Aspect 19. Process, according to any one of Aspects 1 to 18, wherein the first rate of rise (RR1) is greater than about 1 °C/minute, greater than about 1.35 °C/minute minute, greater than about 1.5°C/minute or greater than about 1.8°C/minute, and wherein the upper limit of the first rate of rise, in each occurrence, is about 5°C/minute. minute.

[00243] Aspect 20. Process according to any one of Aspects 1 to 18, wherein the first rate of rise (RR1) is about 1 °C/minute, about 1.25 °C/minute, about 1.35°C/minute, about 1.5°C/minute, about 1.8°C/minute or about 2°C/minute.

[00244] Aspect 21. Process according to any one of Aspects 1 to 20, wherein the first holding time (tH1) is less than about 15 hours, less than about 10 hours, less than about 6 hours, less than about 5 hours, less than about 4 hours, or less than about 3 hours, and wherein the lower limit of tH1, in each occurrence, is about 15 minutes.

[00245] Aspect 22. Process according to any one of Aspects 1 to 20, wherein the first holding time (tH1) is about 15 hours, about 12 hours, about 10 hours, about 6 hours , about 5 hours, about 4 hours, about 3 hours or about 2 hours.

[00246] Aspect 23. Process, according to any one of aspects 1 to 22, wherein T2 (°C) = T1 (°C)-K (°C), and wherein K is selected from about 0°C, around 25°C, around 50°C, around 100°C, around 150°C or around 200°C.

[00247] Aspect 24. Process, according to any one of aspects 1 to 22, wherein T2 (°C) = T1 (°C)-K (°C), and wherein K is selected from a temperature greater than 25 °C, greater than 50 °C, greater than 100 °C, greater than 150 °C or greater than 200 °C, and where the upper limit of K, in each occurrence, is about 500 °C.

[00248] Aspect 25. Process, according to any one of Aspects 1 to 24, wherein the second holding time (tH2) is less than 1 hour, less than 30 minutes, less than 15 minutes, less than 10 minutes, less than 5 minutes or less than 1 minute, and where the lower limit of tH2, in each occurrence, is around 30 seconds.

[00249] Aspect 26. Process according to any one of Aspects 1 to 24, wherein the second holding time (tH2) is about 1 hour, about 45 minutes, about 30 minutes, about 15 minutes , about 10 minutes, about 5 minutes, about 2 minutes or about 30 seconds.

[00250] Aspect 27. Process, according to any one of Aspects 1 to 26, in which the chromium catalyst is allowed to cool for a cooling time (tC) of less than 4 hours, less than 3.5 hours, less than 3 hours, less than 1 hour, less than 30 minutes or less than 5 minutes, and where the lower limit of tC, in each occurrence, is about 30 seconds.

[00251] Aspect 28. Process, according to any one of Aspects 1 to 26, in which the chromium catalyst is allowed to cool for a cooling time (tC) of about 4 hours, about 3.5 hours, about 3 hours, about 2.5 hours, about 2 hours, about 1.5 hours, about 1 hour, about 45 minutes, about 30 minutes, about 15 minutes, about 10 minutes, about 5 minutes or approximately 1 minute.

[00252] Aspect 29. Process, according to any one of Aspects 1 to 28, wherein the activated chromium catalyst comprises, by weight, less than 0.6% Cr(VI), less than 0.5% Cr(VI), less than 0.4% Cr(VI), less than 0.3% Cr(VI), less than 0.2% Cr(VI), less than 0.1% Cr( VI) or less than 0.05% Cr(VI), and wherein the lower limit of the activated chromium catalyst, by weight and at each occurrence, is about 0.01% Cr(VI).

[00253] Aspect 30. Process according to any one of Aspects 1 to 28, wherein the activated chromium catalyst comprises, by weight, about 0.6% Cr(VI), about 0.5% Cr(VI), about 0.4% Cr(VI), about 0.3% Cr(VI), about 0.2% Cr(VI), about 0.1% Cr( VI) or about 0.05% Cr(VI).

[00254] Aspect 31. Process according to any one of Aspects 1 to 30, wherein the process is carried out over a period of time of less than 16 hours, less than 15 hours, less than 14 hours, less than 13 hours, less than 12 hours, less than 11 hours or less than 10 hours, and where the lower limit of the time period, in each occurrence, is approximately 4 hours.

[00255] Aspect 32. Process according to any one of Aspects 1 to 30, wherein the process is carried out over a period of time of about 16 hours, about 15 hours, about 14 hours, about 13 hours, about 12 hours, about 11 hours, about 10 hours, about 9 hours or about 8 hours.

[00256] Aspect 33. Process according to any one of Aspects 1 to 32, wherein the process is carried out with at least 226.79 kg (500 pounds) of supported chromium catalyst.

[00257] Aspect 34. Process according to any one of Aspects 1 to 32, wherein the supported chromium catalyst is a Cr/silica catalyst or a Cr/titania coated silica catalyst.

[00258] Aspect 35. Process, according to any one of Aspects 1 to 34, wherein the process is carried out in a fluidized bed.

[00259] Aspect 36. Process, according to any one of aspects 1 to 35, wherein step a), of heating the supported chromium catalyst to the first temperature (T1), is preceded by a conditioning process, in that the conditioning process comprises heating the supported chromium catalyst to a conditioning temperature (TC) in an oxidative atmosphere at a conditioning rise rate (RRC), and maintaining the chromium catalyst at TC in the oxidative atmosphere for a conditioning time (tC) to provide a conditioned chromium catalyst.

[00260] Aspect 37. Process, according to any one of aspects 1 to 35, wherein step a), of heating the supported chromium catalyst to the first temperature (T1), is preceded by a conditioning process, in that the conditioning process comprises:

[00261] a) heat the supported chromium catalyst to a conditioning temperature (TC) in an inert atmosphere at a conditioning rise rate (RRC) and maintain the chromium catalyst at TC in the inert atmosphere for a first conditioning time (tC1);

[00262] b) exposing the supported chromium catalyst to an oxidative atmosphere for a second conditioning time (tC2);

[00263] c) exposing the supported chromium catalyst to an inert atmosphere for a third conditioning time (tC3); It is

[00264] d) repeat steps b) and c) between 0 and 15 times to provide a conditioned chromium catalyst.

[00265] Aspect 38. Process, according to Aspect 37, in which steps b) and c) are repeated between 2 and 10 times.

[00266] Aspect 39. Process, according to Aspect 37, in which steps b) and c) are repeated between 3 and 8 times.

[00267] Aspect 40. Process according to any one of Aspects 36 to 39, wherein the conditioning temperature (TC) is from about 200 ° C to about 425 ° C, from about 250 ° C to about from 400°C or from about 300°C to about 375°C.

[00268] Aspect 41. Process according to any one of Aspects 36 to 39, wherein the conditioning temperature (TC) is about 200 ° C, about 225 ° C, about 250 ° C, about 275°C, about 300°C, about 325°C, about 350°C, about 375°C, about 400°C, about 425°C or about 450°C.

[00269] Aspect 42. Process, according to any of Aspects 36 to 41, in which the oxidative atmosphere comprises air or oxygen.

[00270] Aspect 43. Process according to any one of Aspects 36 to 41, wherein the oxidative atmosphere comprises air or oxygen having a dew point less than about -40 ° C, less than about -50 ° C , less than about -60°C, less than about -70°C, or less than about -80°C, for example, about -82°C (-116°F).

[00271] Aspect 44. Process according to any one of Aspects 36 to 43, wherein, after the conditioning process, the conditioned chromium catalyst is exposed to an inert atmosphere.

[00272] Aspect 45. Process, according to any one of Aspects 36 to 44, wherein the process is carried out in a fluidized bed.

[00273] Aspect 46. Process, according to any one of Aspects 1 to 45, wherein step a) through step e) are carried out in a common heating zone.

[00274] Aspect 47. Process, according to any one of Aspects 1 to 45, wherein step a) through step e) are carried out in at least two different heating zones.

[00275] Aspect 48. Process according to any one of Aspects 1 to 47, wherein the process for activating a supported chromium catalyst is carried out in a batch mode.

[00276] Aspect 49. Process according to any one of Aspects 1 to 47, wherein the process for activating a supported chromium catalyst is carried out in a continuous mode.

[00277] Aspect 50. Supported chromium catalyst prepared as defined in the process of any of Aspects 1 to 49.

[00278] Aspect 51. Supported chromium catalyst prepared as defined in the process of any one of Aspects 1 to 49, wherein the supported chromium catalyst is a Cr/silica catalyst or a Cr/titania coated silica catalyst.

[00279] Aspect 52. Supported Cr/titania coated silica catalyst prepared as defined in the process of any of Aspects 1 to 49, wherein:

[00280] a) the activated chromium catalyst comprises less than 0.5% Cr(VI) by weight; It is

[00281] b) under polymerization conditions, the activated chromium catalyst is placed in contact, in a reaction zone, with at least one C2 to C8 mono-1-olefin to form an olefin polymer with a melt index (MI) greater than the MI calculated from the following equation:MI > 8x [0.00050124exp(0.00830795«T)] x [0.0994(PV)3 - 0.7843(PV)2 + 2, 0147(PV) - 0.8824] x [-0.6102(Ti)3 + 1.2715(Ti)2 + 0.003(Ti) + 0.2];

[00282] where T (°C) is the average temperature used under polymerization conditions, PV (cm3/g) is the pore volume of the activated chromium catalyst and Ti (atoms/nm2) is the concentration of titanium in the catalyst activated chrome.

[00283] Aspect 53. Supported Cr/titania coated silica catalyst prepared as defined in the process of any of Aspects 1 to 49, wherein:

[00284] a) the activated chromium catalyst comprises less than 0.5% Cr(VI) by weight; It is

[00285] b) under polymerization conditions, the activated chromium catalyst is placed in contact, in a reaction zone, with at least one C2 to C8 mono-1-olefin to form an olefin polymer with a melt index (MI) greater than the MI calculated from the following equation: MI > 4.8x [0.0994(PV)3 - 0.7843(PV)2 + 2.0474(PV) - 0.8824] x [ -0.6102(Ti)3 + 1.2715(Ti)2 + 0.003(Ti) + 0.2];

[00286] where PV (cm3/g) is the pore volume of the activated chromium catalyst and Ti (atoms/nm2) is the concentration of titanium in the activated chromium catalyst.

[00287] Aspect 54. Supported Cr/titania coated silica catalyst prepared as defined in the process of any of Aspects 52 or 53, wherein:

[00288] PV (pore volume) is in a range of about 0.3 ml/g (cm3/g) to about 5.0 ml/g, from about 0.4 ml/g to about 4, 5 ml/g, from about 0.5 ml/g to about 4.0 ml/g, from about 0.5 ml/g to about 3.5 ml/g, from about 0.5 ml/g to about 3.0 ml/g, from about 0.5 ml/g to about 2.5 ml/g, from about 0.7 ml/g to about 2.3 ml/g, from about 1, 0 ml/g to about 2.2 ml/g, from about 1.2 ml/g to about 2.0 ml/g or from about 1.4 ml/g to about 1.7 ml/g; It is

[00289] the concentration of Ti is in a range from about 0 atoms/nm2 to about 5 atoms/nm2, from about 0 atoms/nm2 to about 4.5 atoms/nm2, from about 0 atoms/nm2 to about 4.0 atoms/nm2, from about 0 atoms/nm2 to about 3.5 atoms/nm2 or from about 0 atoms/nm2 to about 3.0 atoms/nm2.

[00290] Aspect 55. Process for polymerizing olefins using a supported chromium catalyst, wherein the process comprises:

[00291] a) activating the supported chromium catalyst, according to the process of any one of Aspects 1 to 49, to provide the activated chromium catalyst; It is

[00292] b) under polymerization conditions, bring into contact, in a reaction zone, the activated chromium catalyst with at least one C2 to C8 mono-1-olefin to form an olefin polymer.

[00293] Aspect 56. Process according to Aspect 55, wherein the at least one C2 to C8 mono-1-olefin comprises ethylene.

[00294] Aspect 57. Process according to Aspect 55, wherein the at least one C2 to C8 mono-1-olefin comprises ethylene and at least one comonomer of C3 to C8 mono-1-olefin.

[00295] Aspect 58. Process according to aspect 55, wherein the at least one C2 to C8 mono-1-olefin comprises ethylene and at least one of propylene, 1-butene, 1-hexene or 1-octene.

[00296] Aspect 59. Process according to any one of Aspects 55 to 58, wherein the activated chromium catalyst is a Cr/silica catalyst and comprises, by weight, less than 0.5% Cr(VI) , and wherein the olefin polymer is characterized by a high charge melt index (HLMI, g/10 min) greater than 100 g/10 min.

[00297] Aspect 60. Process according to any one of Aspects 55 to 58, wherein the activated chromium catalyst comprises, by weight, less than 0.4% Cr(VI), and wherein the olefin polymer It is characterized by a high charge melt index (HLMI, g/10 min) exceeding 100 g/10 min.

[00298] Aspect 61. Process for polymerizing olefins, according to any one of Aspects 55 to 60, wherein

[00299] a) the olefin polymer has a melt index (MI) greater than the melt index (MIR) of a reference polyolefin; It is

[00300] b) wherein the reference polyolefin is prepared under conditions identical to the olefin polymer, with the exception that a reference chromium catalyst is used in the preparation of the reference polyolefin, which is activated through:

[00301] i) heating the chromium catalyst supported in air to an activation temperature T1, for example from 600 °C to 1,000 °C and maintaining the chromium catalyst at the activation temperature in air for 3 hours; It is

[00302] ii) allowing the chromium catalyst to cool below the activation temperature in air to provide the activated reference chromium catalyst.

[00303] Aspect 62. Process for polymerizing olefins according to Aspect 61, wherein the olefin polymer has a melt index (MI, g/10 min) at least 25% higher, at least 50% higher, at least at least 100% greater, at least 200% greater, at least 300% greater, or at least 500% greater than the MI of the reference polyolefin, and wherein the upper limit of the melt index of the olefin polymer is about 1,000% greater than the MI of the reference polyolefin.

[00304] Aspect 63. Process for polymerizing olefins, according to any one of Aspects 61 to 62, wherein the activation time of the activated chromium catalyst is about 80%, about 70%, about 60%, about 50% or about 40% of the reference chromium catalyst activated.

[00305] Aspect 64. Process for polymerizing olefins according to any one of Aspects 61 to 63, wherein the melt index (MI) of the olefin polymer is about -12.22 °C (10 °F) , about -6.67°C (20°F), about -1.11°C (30°F), about 4.44°C (40°F), about 10°C (50° F), about 15.56°C (60°F), about 21.11°C (70°F), about 26.67°C (80°F), about 32.22°C ( 90°F) or about 37.78°C (100°F) greater than the melt index (MIR) of the reference polyolefin.

[00306] Aspect 65. Process for polymerizing olefins according to any one of Aspects 61 to 64, wherein the olefin polymer has a broader molecular weight distribution based on Mw/Mn, Mz/Mn or any appropriate ratio of Mn, Mw, Mx. Mv or M(z+n) compared to the reference polyolefin.

[00307] Aspect 66. Process for polymerizing olefins, according to any one of Aspects 61 to 65, wherein the olefin polymer has a lower long chain branching (LCB) content compared to the reference polyolefin.

[00308] The following references may provide background information or other information relating to various aspects or embodiments of this disclosure, and each such reference is incorporated herein by reference. 1. M. P. McDaniel, M. B. Welch, J. Catal. 82 (1983) 110. 2. (a) M. P. McDaniel, M. B. Welch, J. Catal., 82 (1983) 98. (b) in: F.E. Bailey Jr. (Ed.), Initiation of Polymerization, A.C.S. Symposium Series 212, ACS Symposium, Las Vegas, 1983, p. 191 to 206, Paper 15. (c) Org. Coat. Appl. Polym. Sci. Proc., 46 (1981) 708 to 713. 3. M. P. McDaniel, Transition Metal Catalyzed Polymerizations, in: R. P. Quirk (Ed.), Alkenes and Dienes, vol. 4, MMI Press, Midland, MI, 1983, p. 713, Part B. 4. Hawley, G.R. and McDaniel, M.P., US Patent No. 4,333,860, issued June 8, 1982, 1983, and US Patent No. 4,368,301, issued January 11, both by Phillips Petroleum Co. 5. Delap, J.A., Patent No. US 3,976,632, issued August 24, 1976, by Phillips Petroleum Co. 6. Nasser, B.E. and Delap, J.A., Patent No. US 4,188,471, issued on February 12, 1980, by Phillips Petroleum Co. 7. Witt, D.R., Patent No. US 4,001,196, issued January 4, 1977, by Phillips Petroleum Co. 8. M. P. McDaniel, Patent No. US 4,489. 172, issued December 18, 1984, and US Patent No. 4,559,394, issued December 17, 1985, both by Phillips Petroleum Co. 9. A. Clark, J.P. Hogan, R.L. Banks, W.C. Lanning, Ind. Chem Eng. 48 (1956) 1,152. 10. E. Garrone, G. Ghiotti, A. Zecchina, NATO ASI Ser., Ser. C 326 (1990) 393 to 406, (Olefin Metathesis Polym. Catal.). 11. McDaniel, M.P. and Welch, M.B., US Patent No. 4,177,162, issued December 4, 1979, and US Patent No. 4,277,587, issued July 7, 1981, both by Phillips Petroleum Co. 12 . McDaniel, M.P., US Patent No. 4,248,735, issued February 3, 1981, and US Patent No. 4,297,460, issued October 27, 1981, both by Phillips Petroleum Co. 13. M.P. McDaniel, J Phys. Chem. 85 (1981) 532. 14. McDaniel, M. P., J. Phys. Chem. 85 (1981) 537. 15. McDaniel, M.P., US Patent No. 4,308,172, issued December 29, 1981, and US Patent No. 4,357,451, issued November 2, 1982, both by Phillips Petroleum Co 16. L.M. Baker, W.L. Carrick, J. Org. Chem. 35 (1970) 775. 17. Noshay, A. and Karol, F.J., ”Chemical activation of silica supports for chromocene-based polyethylene catalysts” in Transition Metal Catalyzed Polymerization, Proc. Int. Symp., 2nd, held in Akron, OH in 1986, (Quirk, RP) Cambridge Univ. Press, Cambridge, 396 to 416, 1988. 18. Pullukat, T. J., Hoff, R. E., and Shida, M., J. Appl. Polym. Sci., 26, 2927 (1981). 19. McDaniel, M.P. and Welch, M.B., US Patent No. 4,151,122, issued April 24, 1979, and US Patent No. 4,182,815, issued January 8, 1980, both by Phillips Petroleum Co. 20 . McDaniel, M.P., Sanbrano, J.A. and Johnson, M.M., Patent No. US 4,397,769, issued August 9, 1983, and Patent No. US 4,460,756, issued July 17, 1984, both by Phillips Petroleum Co. 21. McDaniel, M.P. and Welch, M.B., Patent No. US 4,247,421, issued January 27, 1981 by Phillips Petroleum Co. 22. R.L. Burwell, G.L. Haller, K.C. Taylor, J.F. Read, Adv. Catal. 20 (1969) 1. 23. D. Cornet, R. L. Burwell, J. Am. Chem. Soc. 90 (1968) 2,489. 24. McDaniel, M. P. and Burwell, R. L., J. Catal., 36, 394 (1975). 25. McDaniel, M. P. and Burwell, R. L., J. Catal., 36, 404 (1975). 26. Mangnus, P.J., Ellison, A., Scheffer, B. and Moulijn, J.A., Bull. Soc. Chim. Belg.. 96, 977 (1987). 27. Hawley, G.R., US Patent No. 4,295,998, issued October 20, 1981, and US Patent No. 4,331,789, issued May 25, 1982, both by Phillips Petroleum Co. 28. M.P. McDaniel, K.S. Collins, E. A. Benham, Journal of Catalysis, 252 (2007) 281 to 295.

Claims (19)

1. Process for activating a supported chromium catalyst characterized by comprising: a) heating a supported chromium catalyst in an inert atmosphere to a first temperature (T1) at a first rate of rise (RR1); b) maintaining the chromium catalyst at the first temperature in the inert atmosphere for a first waiting time (tH1); c) allowing the chromium catalyst to reach a second temperature (T2), in an inert atmosphere, at a second rise rate (RR2), where T2 is less than or equal to T1, followed by exposing the chromium catalyst to a oxidative atmosphere; d) maintaining the chromium catalyst at the second temperature in the oxidative atmosphere for a second waiting time (tH2); and e) allowing the chromium catalyst to cool to a temperature below the second temperature in an inert atmosphere, in the oxidative atmosphere, or in any sequential combination of an inert atmosphere and an oxidative atmosphere over a cooling time (tC), to provide an activated chromium catalyst; f) that the second waiting time (tH2) is less than 1 hour and more than 30 seconds. 2. Process according to claim 1, characterized by the fact that T1 is 500°C to 1,000°C. 3. Process, according to claim 1, characterized by the fact that the first elevation rate (RR1) is greater than 1°C/minute and less than 5°C/minute. 4. Process, according to claim 1, characterized by the fact that the first waiting time (tH1) is less than 15 hours and greater than 15 minutes. 5. Process according to claim 1, characterized by the fact that T2 is in a range from 25°C lower in relation to T1 to 500°C lower in relation to T1. 6. Process according to claim 1, characterized by the fact that the activated chromium catalyst comprises, by weight, less than 0.6% Cr(VI). 7. Process according to claim 1, characterized by the fact that it is carried out over a period of time of less than 16 hours. 8. Process according to claim 1, characterized by the fact that the supported chromium catalyst is a Cr/silica catalyst or a Cr/titania coated silica catalyst. 9. Process, according to claim 1, characterized by the fact that step a), of heating the supported chromium catalyst to the first temperature (T1), is preceded by a conditioning process, in which the conditioning process comprises heating the supported chromium catalyst to a conditioning temperature (TC) in an oxidative atmosphere at a conditioning rise rate (RRC) and maintaining the chromium catalyst at TC in the oxidative atmosphere for a conditioning time (tC) to provide a conditioned chromium catalyst. 10. Process, according to claim 1, characterized by the fact that step a), of heating the supported chromium catalyst to the first temperature (T1), is preceded by a conditioning process, in which the conditioning process comprises: i) heating the supported chromium catalyst to a conditioning temperature (TC) in an inert atmosphere at a conditioning rise rate (RRC) and maintaining the chromium catalyst at TC in the inert atmosphere for a first conditioning time ( tC1); ii) exposing the supported chromium catalyst to an oxidative atmosphere for a second conditioning time (tC2); iii) exposing the supported chromium catalyst to an inert atmosphere for a third conditioning time (tC3); and iv) repeating steps ii) and iii) between 0 and 15 times to provide a conditioned chromium catalyst. 11. Process, according to claim 10, characterized by the fact that steps ii) and iii) are repeated between 2 and 10 times. 12. Process according to claim 10, characterized by the fact that the conditioning temperature (TC) is 200°C to 425°C and in which the oxidative atmosphere comprises air or oxygen. 13. Supported chromium catalyst characterized in that it is prepared according to the process as defined in claim 1. 14. Process for polymerizing olefins using a supported chromium catalyst characterized by comprising: activating the supported chromium catalyst, as defined in the process of claim 1, to provide the activated chromium catalyst; and under polymerization conditions, contacting, in a reaction zone, the activated chromium catalyst with at least one C2 to C8 mono-1-olefin to form an olefin polymer. 15. Process according to claim 14, characterized by the fact that at least one C2 to C8 mono-1-olefin comprises ethylene and at least one comonomer of C3 to C8 mono-1-olefin. 16. Process for polymerizing olefins, according to claim 14, characterized by the fact that: the olefin polymer has a melt index (MI) greater than the melt index of a reference polyolefin (MIR); and wherein the reference polyolefin is prepared under conditions identical to the olefin polymer, with the exception that a reference chromium catalyst is used in the preparation of the reference polyolefin, which is activated by means of: heating the supported chromium catalyst in air to an activation temperature, T1, and maintaining the chromium catalyst at the activation temperature in air for 3 hours; and allowing the chromium catalyst to cool below the activation temperature in air to provide the activated reference chromium catalyst. 17. Process for polymerizing olefins, according to claim 14, characterized by the fact that the olefin polymer has a high charge melt index (HLMI) greater than 40, greater than 50 or greater than 75. 18. Process for polymerizing olefins, according to claim 19, characterized by the fact that: the activated chromium catalyst comprises less than 0.5% Cr(VI) by weight; and under polymerization conditions, the activated chromium catalyst is placed in contact, in a reaction zone, with at least one C2 to C8 mono-1-olefin to form an olefin polymer with a higher melt index (MI). than the MI calculated from the following equation: MI > 8x[0.00050124exp(0.00830795«T)] x [0.0994(PV)3 - 0.7843(PV)2 + 2.0147(PV) - 0.8824] x [-0.6102(Ti)3 + 1.2715(Ti)2 + 0.003(Ti) + 0.2]; where: T (°C) is the average temperature used in the polymerization conditions; PV (cm3/g) is the pore volume of activated chromium catalyst and is in a range of 0.3 ml/g (cm3/g) to 5.0 ml/g; and Ti (atoms/nm2) is the concentration of titanium in the activated chromium catalyst and is in a range of 0 atoms/nm2 to 5 atoms/nm2. 19. Process for polymerizing olefins, according to claim 14, characterized by the fact that: the activated chromium catalyst comprises less than 0.5% Cr(VI) by weight; and under polymerization conditions, the activated chromium catalyst is placed in contact, in a reaction zone, with at least one C2 to C8 mono-1-olefin to form an olefin polymer with a higher melt index (MI). than the MI calculated from the following equation: MI > 4.8x[0.0994(PV)3 - 0.7843(PV)2 + 2.0474(PV) - 0.8824] x [- 0.6102 (Ti)3 + 1.2715(Ti)2 + 0.003(Ti) + 0.2]; where: PV (cm3/g) is the pore volume of the activated chromium catalyst and is in a range of 0.3 ml/g (cm3/g) to 5.0 ml/g; and Ti (atoms/nm2) is the concentration of titanium in the activated chromium catalyst and is in a range of 0 atoms/nm2 to 5 atoms/nm2.