EP4110836A1 - Chromium-on-silica catalysts and methods of making the same - Google Patents
Chromium-on-silica catalysts and methods of making the sameInfo
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- EP4110836A1 EP4110836A1 EP20717355.0A EP20717355A EP4110836A1 EP 4110836 A1 EP4110836 A1 EP 4110836A1 EP 20717355 A EP20717355 A EP 20717355A EP 4110836 A1 EP4110836 A1 EP 4110836A1
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- catalyst
- catalyst composition
- hydrogel
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F10/00—Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F10/02—Ethene
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
- C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
- C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
- C01B33/152—Preparation of hydrogels
- C01B33/154—Preparation of hydrogels by acidic treatment of aqueous silicate solutions
- C01B33/1546—Preparation of hydrogels by acidic treatment of aqueous silicate solutions the first formed hydrosol being converted to a hydrogel by introduction into an organic medium immiscible or only partly miscible with water
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
- C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
- C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
- C01B33/157—After-treatment of gels
- C01B33/158—Purification; Drying; Dehydrating
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F110/00—Homopolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F110/02—Ethene
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F210/00—Copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F210/14—Monomers containing five or more carbon atoms
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F210/00—Copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F210/16—Copolymers of ethene with alpha-alkenes, e.g. EP rubbers
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F4/00—Polymerisation catalysts
- C08F4/02—Carriers therefor
- C08F4/025—Metal oxides
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F4/00—Polymerisation catalysts
- C08F4/06—Metallic compounds other than hydrides and other than metallo-organic compounds; Boron halide or aluminium halide complexes with organic compounds containing oxygen
- C08F4/22—Metallic compounds other than hydrides and other than metallo-organic compounds; Boron halide or aluminium halide complexes with organic compounds containing oxygen of chromium, molybdenum or tungsten
- C08F4/24—Oxides
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2410/00—Features related to the catalyst preparation, the catalyst use or to the deactivation of the catalyst
- C08F2410/06—Catalyst characterized by its size
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2500/00—Characteristics or properties of obtained polyolefins; Use thereof
- C08F2500/07—High density, i.e. > 0.95 g/cm3
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2500/00—Characteristics or properties of obtained polyolefins; Use thereof
- C08F2500/12—Melt flow index or melt flow ratio
Definitions
- the present disclosure generally relates to silica catalysts for polyethylene production. More particularly, the present disclosure relates to Chromium/Silica (Cr/Si0 2 ) catalysts used for the production of high density polyethylene (HDPE). Methods of making such catalyst using base-set gels and methods of using such catalysts in HDPE applications, particularly small blow molding HDPE applications, are also disclosed.
- Chromium/Silica (Cr/Si0 2 ) catalysts used for the production of high density polyethylene (HDPE).
- supported chromium oxide catalysts used in the industry generally comprise chromium oxide and supports containing one or more of silica, titania, thoria, alumina, zirconia or aluminophosphates.
- Phillips-type catalyst which comprises chromium oxide supported on silica gel (e.g. Cr/Si0 2 ).
- This type of catalyst is a popular polymerization catalyst for the production of HDPE, primarily because it produces HDPE with a broad molecular weight distribution, which is particularly suitable for blow molding applications.
- Commercial silica supports for Phillips-type catalysts are typically produced from inorganic silicate, with sodium silicate being most widely used. As a result, commercial Phillips-type catalysts have varying levels of sodium impurity depending on the washing procedure employed to produce the silica supports.
- Cr/Silica catalysts are commercially used for the production of HDPE for small blow molding applications. Such catalysts are typically activated at high temperature, such as one ranging from 750 - 850 °C, in order to achieve polymer MI targets. As these activation temperatures are very close to the sintering temperature of the Cr/Silica catalysts, the ability to boost catalyst MI potential by further increasing activation temperature is very limited. Although modifying Cr/Silica catalysts with metals, such as A1 and Ti, can substantially increase catalyst MI potential, these modifications also broaden the molecular weight distribution of the HDPE produced as well as increase catalyst manufacturing cost. Both are undesirable for SBM applications.
- a composition such as a catalyst precursor, or a catalyst comprising a Cr coated silica support with defined levels of alkali or alkaline earth metals (including for example, Na, Mg, or Ca) and A1 exhibiting increased MI potential.
- a catalyst composition comprising a Cr coated silica support with defined levels of Na and Al, such that the resulting Cr/Silica catalyst has increased MI potential.
- the present application is directed to a catalyst composition comprising a silica-containing substrate comprising a catalytically active metal consisting of Cr.
- the catalyst comprises Al in an amount of less than 50 ppm and Na in an amount of less than 800 ppm of the catalyst composition.
- the amounts of Na and Al are present in a Na:Al molar ratio greater than 5, greater than 10, greater than 20, even greater than 30, such as a molar ratio ranging from 10-40. It is appreciated that the molar ratio may comprise any combination of these end points, such as a range of 5 to 10, 5 to 20, 5 to 30, and the like, or 5 to 40, 10 to 40, 20 to 40, or other combinations thereof.
- the method comprises reacting a metal silicate, such as sodium silicate, with an acid to form a hydrosol that transforms into a hydrogel precursor and substantially leaching the A1 impurity associated with the sodium silicate by washing to reduce the amount of A1 impurity to an amount of less than 50 ppm in the resulting catalyst precursor.
- a metal silicate such as sodium silicate
- the method further comprises ageing the hydrogel precursor to form a hydrogel having a surface area greater than 200 m 2 /g, such as greater than 250 m 2 /g. In one embodiment the hydrogel exhibits a surface area of approximately 300 m 2 /g.
- the aging process comprises mixing the hydrogel precursor with a neutral or basic aqueous solution to form an aqueous dispersion exhibiting neutral or basic pH.
- FIG. 1 is a flow chart showing the general steps used in a base-set gel process for making silica support and Cr/Silica catalyst according to an embodiment of the present disclosure.
- FIG. 2 is a graph comparing A1 leaching profile for hydrogel precursors soaked in acid water at temperatures ranging from 20 to 90 °C for the process shown in FIG. 1.
- the total amount of acid, including acid used for gel forming and acid for acidification before soaking, is about 20% in excess of the NazO in sodium silicate used for gel forming.
- FIG. 3 is a graph comparing melt index (MI) for homo and copolymers prepared from Cr/Silica catalysts having various A1 content and Na:Al ratios made according to the process described in FIG. 1.
- silica gels used herein are described as either “acid-set gels” or “base-set gels.”
- Both types of gels are produced using a silicate, such as a sodium silicate, and a mineral acid such as sulfuric acid via an acid-base reaction.
- a silicate such as a sodium silicate
- a mineral acid such as sulfuric acid
- An “acid-set gel” is a gel formed by the acid-base reaction that is not stoichiometric but utilizes more acid than base, such as a greater volume or weight percent of acid.
- a “base-set gel” is a gel formed by the described acid- base reaction that is not stoichiometric but utilizes more base than acid, such as a greater volume or weight percent.
- Cr-only catalyst refers to a catalyst without other added multivalent metal of oxidation state of +3 or higher.
- composition is sometimes referred to as “catalyst composition” and is meant to describe an unactivated catalyst precursor, as well as a catalyst that has been activated.
- the product typically contains a Cr compound with Cr in +3 oxidation state.
- This product is a catalyst precursor as it is not catalytically active for ethylene polymerization.
- This catalyst precursor has to be activated in oxidative atmosphere (such as heating in fluidized bed reactor in dry air) to convert Cr from +3 to +6 oxidation state.
- the activated product is more accurately referred to as the catalyst.
- cold water wash refers to wash water having a temperature of 55
- hydrosol refers to a mixture of metal silicate and acid in liquid form.
- hydrogel precursor refers to an unwashed and/or unaged hydrogel.
- hydrogel refers to a washed and aged hydrogel.
- alcogel refers to a hydrogel that is further washed with an organic solvent to make the hydrogel substantially free of water, such as by replacing water in the hydrogel with alcohol.
- dried gel which is also known as a “support precursor” refers to a dried gel before sizing.
- Support precursor refers to a dried gel before sizing.
- Support precursor refers to a dried gel before sizing.
- Support precursor refers to a dried gel before sizing.
- Support precursor refers to a dried gel before sizing.
- Support precursor refers to a dried gel before sizing.
- Support precursor refers to dried gel after sizing.
- MI melt index
- HLMI high load melt index
- MI potential of a Cr catalyst described herein is a function of, and is directly proportional to, the MI of the polymer produced from that catalyst.
- MI potential of the Cr catalyst is directly proportional to the MI of the polymerized ethylene. The higher the MI of the polymer, the higher the catalyst MI potential.
- the MI, HLMI and density are measured on polyethylene pellets, which are obtained by processing stabilized polymer powders using a single screw extruder under nitrogen.
- the levels of chromium in the catalyst composition are measured by X-ray fluorescence (“XRF”), using a PANalytical Magix Pro Automatic Sequential Spectrometer. Samples are calcined at 1000 °C in air and then prepared as fused beads using a lithium borate flux. Fusion is typically between 1000 °C and 1250 °C. Cr level is reported as the weight percentage of the catalyst precursor after calcination at 1000 °C.
- XRF X-ray fluorescence
- Adsorption Spectroscopy (AA) using a Perkin-Elmer Analyst 100 Spectrometer and Inductively Coupled Plasma (“ICP”) Spectroscopy using an ACTIVATM HORIBA Jobin Yvon ICP-AES spectrometer, respectively.
- Samples of catalyst precursor are digested with hydrofluoric acid (HF).
- HF hydrofluoric acid
- S1F 4 silicon tetrafluoride
- Na and A1 levels are reported as the parts per million of the catalyst precursor after drying at 120 °C.
- Autosorb-6 Testing Unit from Quantachrome Corporation. Samples are first outgassed at 350 °C for at least 4 hours on the Autosorb-6 Degassing Unit. A multipoint surface area is calculated using BET theory taking data points in the P/Po range 0.05 to 0.30. A pore volume measurement is recorded at P/Po of 0.984 on the desorption leg. Average pore diameter is calculated using the following equation assuming cylindrical pores.
- the particle size is measured by laser light scattering using an apparatus such as a
- Mie theory predicts how light is scattered by spherical particles and takes into account the refractive index of the particles.
- the real value used for silica refractive index is 1.4564 and the imaginary value is 0.1.
- the refractive index for the water dispersant is 1.33.
- the catalyst support typically acts as a dispersing agent for the active Cr centers, and directly affects the resulting polymer characteristics.
- SA Surface area
- PV pore volume
- pore size distribution of the catalyst may affect the resulting polymer.
- higher pore volume (thus larger pore) Cr/Si0 2 catalysts produce polymers with a lower MW and higher MI.
- A1 content results in a Cr/silica catalyst having a higher MI potential than a base-set gel with a higher A1 impurity content but at the same Na content.
- the Inventors have discovered that regardless of the A1 impurity content, a Cr/silica catalyst having an increased Na content in general leads to higher MI potential. It was also discovered that using a Na content that is too high (for example when the A1 impurity content is high), will cause catalyst sintering at the given activation temperature, typically 750-850 °C. Thus, it is desirable to keep the A1 impurity level as low as possible. As described in the Background section, and one skilled in this art would appreciate, this is generally not the norm. Rather, traditional base- set gel processes in general lead to gels with higher A1 impurity content.
- ⁇ silica gel production typically uses sodium silicate such as sodium silicate with SiChiNaiO weight ratio of 3.2, and a mineral acid such as sulfuric acid via an acid-base reaction.
- the acid-base reaction is almost never stoichiometric - either more acid is used (in this case the gel formed is called an acid-set gel) or less acid is used (in this case the gel formed is called a base-set gel).
- Base-set gel process is widely used for commercial silica gel manufacturing as the process is conducive for making silica gel particles of spherical shape and with particle size ranging from tens of microns to several millimeter size.
- a catalyst composition having a support with defined levels of Na and Al that results in a Cr/Silica catalyst of increased MI potential. While not wishing to be bound by theory, it is believed that both acid sites and base sites in the silica supports (thus catalysts) increase the MI potential of Cr/Silica. Na introduces base site whereas Al introduces acid site. When both Na and Al are present, they can cancel each other’s effects due to acid-base neutralization.
- the silica support has an Al content of less than 50 ppm, such as less than 25 ppm, or even an amount ranging from 10-40 ppm of the catalyst composition.
- the final catalyst composition can comprise Na in an amount ranging from 50 to 800 ppm, from 200 to 800 ppm, or 200 to 700 ppm such as less than about 600 ppm, or even an amount ranging from about 50-600 ppm of the catalyst composition.
- the catalytically active metal comprises Cr, which may be added to the silica support using at least one Cr compound.
- the chromium compound is a chromium oxide or a compound which can be converted to chromium oxide by calcination.
- the chromium-containing compound may be a water-soluble compound or an organic solvent soluble compound.
- Non-limiting examples include chromium acetate, nitrate, sulfate, acetylacetonate, chromium trioxide, ammonium chromate, tert-butyl chromate and other soluble chromium compounds.
- the catalyst described herein sufficient amounts of at least one of the described chromium-containing compounds should be employed so that the catalyst contains Cr in an amount ranging from 0.01 to 3 wt.%. In certain embodiments, the catalyst contains Cr in amount ranging from 0.1 to 2 wt.%, such as in an amount ranging from 0.25 to 1.5 wt.%.
- a process for preparing a catalyst composition comprising a Cr coated support with particularly defined levels of Na and Al.
- the method comprises reacting a metal silicate, such as sodium silicate with an acid to form a hydrosol which subsequently solidifies into a hydrogel precursor.
- a metal silicate such as sodium silicate
- the method further comprises treating the hydrogel precursor to reduce the amount of Al impurity and to form a hydrogel. Therefore, in a broader sense, there is described a method comprising making a gel and Al leaching it to reduce the Al to a desired level.
- the Al is adjusted in the silica support to achieve an amount less than 50 ppm of the catalyst composition, such as an amount less than 25 ppm. In one embodiment, Al is adjusted in the silica support to achieve an amount ranging from 10-40 ppm of the catalyst composition. In one embodiment, a high purity silicate that has a very low Al content may be used. This could eliminate the need to treat the hydrogel precursor to remove Al, assuming the Al content level in the silicate is sufficiently low. However, high purity silicate can be expensive and is not readily available. [0045] The method described herein may also be performed to adjust the Na content in the final catalyst composition to an amount less than 800 ppm of the catalyst composition.
- the final catalyst composition includes amounts of Na ranging from 50 to 800 ppm, from 200 to 800 ppm, or 200 to 700 ppm such as less than about 600 ppm, or even an amount ranging from about 50-600 ppm of the catalyst composition.
- the resulting Na:Al molar ratio is typically adjusted to a value as described herein.
- the method further comprises ageing the hydrogel precursor to form a hydrogel having a surface area greater than 200 m 2 /g, or greater than 250 m 2 /g or such as about 300 m 2 /g, wherein ageing comprises mixing the hydrogel precursor with a neutral or basic solution to form an aqueous dispersion having a pH of at least 6, such as about 8-9 and at a temperature ranging from 70-100 °C for a time ranging from 4-36 hours.
- the method may further comprise drying the gel, using any common techniques known in the industry, such as spray drying, flash drying or a solvent-wash/drying technique, to produce a dried gel (support precursor).
- the method may also comprise a post-drying step, such as milling, sieving and/or classifying the precursor into support of desired particle size distribution which is subsequently impregnated with a chromium compound to form a Cr on silica catalyst.
- the process of adjusting the Na content of the catalyst may be performed before or during the impregnation step to achieve Na in an amount of less than 800 ppm of the catalyst composition, such that the amount of Na is adjusted to achieve a Na:Al molar ratio greater than 5, greater than 10, greater than 20, even greater than 30, such as a molar ratio ranging from 10-40.
- the reaction product of the sodium silicate and acid is a basic hydrosol having an H2S04:Na20 molar ratio typically ranging from 0.7 to 0.95.
- the method of treating the basic hydrogel precursor to reduce the amount of A1 impurity may comprise a bead process.
- the bead process comprises spraying the basic hydrosol into the air to solidify it into beads, and catching the beads in an acidic solution to provide a gel dispersion of pH less than 2, such as less than 1 and at temperature lower than ⁇ 60 °C, such as lower than 55 °C.
- the gel is soaked in this acidic solution for a period of no less than 2 hours.
- A1 leaching at acidic pH was shown to be particularly sensitive to temperature, with leaching preferably done at 60 °C or below, such as 55 °C or below.
- leaching was least efficient for 90°C and not very efficient for 70°C. Extended time does not improve leaching at these temperatures.
- Leaching was found to be most efficient at 50°C within the time period studied. Without being bound by any theory, it is presumably due to faster kinetics at 50 °C than at 20 °C. Leaching at 20°C is not as efficient as at 50°C within the time period studied but looks like it can leach out more A1 if given longer time. While not being bound by any theory, at equilibrium % A1 leached is shown to improve with lower temperatures but higher temperature is preferred for kinetic consideration.
- pH In an embodiment, the pH should stay below -3-4 until most of the A1 impurity is removed from the system, not just from the gel but also from the liquid phase that is in contact with the gel. At pH above 3-4, A1 will redeposit onto the silica surface. Accordingly, a pH ⁇ 2, such as ⁇ 1 is desirable for A1 leaching from the gel structure into the liquid phase, but to prevent A1 redeposits onto silica surface, pH of the liquid phase should be kept at ⁇ 3-4 until the liquid phase is substantially free of the leached Al. In one embodiment, washing in water acidified to a pH -3 at ambient temperature maybe the best way to reduce the residual Al content to the lowest level.
- washing can be done at higher temperature ( ⁇ 60 °C) for the entire washing, or at least for the first several hours to remove the majority of the leached Al then washed at even higher temperature. If more acid is used for acidification prior to pre-washing, washing can be done with neutral water as well. As previously described, the pH of the gel/water dispersion should not exceed pH 3-4 before the majority of the leached Al is removed from the dispersion.
- soaking and pre-washing may be performed as separate steps, in an embodiment, soaking and pre-washing can also be combined. For example, if the pre-washing is done at pH -2 or less and at temperature ⁇ 60 °C, it has the same effect as soaking, and can be more efficient than soaking, depending if and how often the liquid phase is refreshed.
- the beads caught in the acidic solution are subsequently washed in water acidified to a pH -3 at ambient temperature, prior to aging in water that is pH adjusted to 8-9 using aqueous NH 4 OH and at 70-90 °C for 4-36 hours to achieve a gel having a surface area greater than 200 m 2 /g, or greater than about 250 m 2 /g, such as about 300 m 2 /g.
- the gel can be washed again after aging to further reduce alkali and alkaline earth metal impurities.
- the pH of the aged hydrogel can be lowered to approximately 2 and the silica hydrogel can be washed with neutral water or in an embodiment, water acidified to a pH -3.
- the hydrogel can be dried by one of the techniques known to the art.
- One suitable method is flash drying.
- Another suitable method is spray drying.
- Another suitable method is washing the hydrogel with an organic solvent and subsequently drying the gel under vacuum.
- the dried gel is sized to the desired particle size distribution to form silica support.
- the method further comprises adjusting the Na content of the catalyst before, for example by adjusting washing process, or during the impregnation step to achieve Na in an amount less than 800 ppm of the catalyst composition, and Na:Al molar ratio as described herein.
- a method for preparing a composition comprising: reacting a sodium silicate comprising Al as an impurity, with an acid to fonn a hydrosol; allowing the hydrosol to form a gel precursor; treating the gel precursor to reduce the amount of Al; aging the gel precursor to form a hydrogel having a surface area greater than 200 m 2 /g, such as 300 m 2 /g, wherein ageing comprises mixing the gel precursor with a neutral or base solution to form a hydrogel having a pH of at least 6; and drying to produce a dried gel that is then impregnated with a chromium compound to form a Cr on silica catalyst composition.
- processing steps that can be used including milling the hydrogel to form particles of a desired size, or sieving/classifying the dried gel to produce support of desired particle size distribution.
- Particles of catalyst precursor according to the present disclosure may have a d90 (diameter at which 90% by volume of the particles have a diameter less than) of 500 pm or less, for example 400 pm or less.
- the particles may have a d50 of 300 pm or less.
- the particles may also have dlO of 1pm or more, for example 10 pm or more.
- the particles have a d50 from 1 to 300 pm, from 5 to 250 pm or from 25 to 150 pm.
- the particles may be prepared by comminution combined with size classification by means such as sieving or air classification, or the particles may be prepared by a route such as spray-drying followed by size classification.
- An ethylene polymerization catalyst is obtained or obtainable from the compositions described herein by heating a catalyst precursor composition in a non-reducing atmosphere, such as an oxidizing atmosphere, at a temperature from 200 to 1200 °C for an activation period from 30 minutes to 15 hours, such as from 400 to 850 °C from about 4 hours to 12 hours.
- a non-reducing atmosphere such as an oxidizing atmosphere
- the resins produced by the catalysts described herein are particularly suitable for small blow molding applications.
- the catalysts in order to use the disclosed catalysts to produce resins, the catalysts must first be activated using a thermal step, such as in a fluidized bed reactor.
- the catalyst can be activated in a fluidized bed reactor in dry air, such as at a temperature ranging from 750 to 850 °C, for example at 800 to 850 °C for a time ranging from 30 minutes to 15 hours, such as 6 hours.
- the methods according to the present disclosure are applicable in the preparation of polyethylene and copolymers of ethylene in which combined ethylene is present in an amount of at least 25 mole percent, such as at least 50 mole percent, or at least 75 mole percent.
- Copolymers can be prepared from mixtures of ethylene, and one or more C3 to C8 a-alkenes.
- Examples 1 and 2 below describe base set gels having low A1 content that are prepared from standard purity and high purity sodium silicate, respectively.
- a base-set gel process for producing silica support for a Cr on Silica catalyst according to the present disclosure is provided herein. This process started from a sodium silicate that contained A1 as an impurity. Through a series of steps, shown in the flow chart of Fig. 1, the A1 and Na content were reduced to acceptable levels and ratios in the resulting catalysts.
- the dilute sodium silicate solution of 3.3 weight ratio SiCFiNa O was first reacted with dilute sulfuric acid to form a hydrosol having the following composition: 12 wt.% SiCh; FhSCbiNaaO in a molar ratio of 0.8.
- the sodium silicate solution contains about 400 ppm A1 on S1O2 weight basis. As a result, the resulting hydrosol was basic.
- the beads were washed with water that was acidified to a pH ⁇ 3 at ambient temperature, which resulted in the beads being substantially free of Na and Al. After the washing step, aqueous NH 4 OH was then added to the solution to raise the pH to ⁇ 9. Aging was conducted at 70 °C for about 16 hours to achieve a gel having a surface area of about 300 m 2 /g.
- Acid was then added to lower the pH to ⁇ 2.
- the beads were then washed with water that was acidified to a pH ⁇ 3.
- the beads were further washed with methanol to substantially free of water (such as ⁇ 2 wt% water) and dried to produce support precursor, and subsequently sized to d50 of about 100 pm to generate a support.
- Comparative catalyst 1 this catalyst was a silica support comprising approximately
- Catalyst A was a silica support modified according to this invention, to generate a support with low Al content, ⁇ 20 ppm, and Na content, 16ppm. This support was impregnated with 1 wt% Cr using a methanol solution of chromium acetate.
- Catalyst B this catalyst was the same silica support for Catalyst A but was impregnated with 1 wt.% Cr and about 400 ppm Na using a methanol solution containing chromium acetate and sodium formate. Properties of Comparative Catalyst 1, and Inventive Catalysts A and B are provided in Table 1.
- Catalyst properties [0073] These catalyst samples were evaluated for both homo- and co-polymerization.
- For homo-polymerization about lOg of catalyst was activated in a fluidized bed reactor in dry air. The temperature was held at 850 °C for 6 hours before cooling. Air was switched to nitrogen at 300 °C. About 0.17 g of activated catalyst was charged into a 2.5L slurry polymerization reactor. Polymerization was conducted with 10 mol% ethylene in isobutane at 102 °C. Polymerization reaction was terminated when about 425 g polyethylene was produced. For co-polymerization, catalysts were activated similarly except at 815 °C. Polymerization was also done similarly except at 100 °C and with 5 mL 1 -hexene.
- This Example describes methods that were used to prepare both inventive and comparative supports.
- the process used to make these different supports is the same except that the inventive support was made using high purity sodium silicate from PQ (tradename CRYSTAL ® FS).
- the high purity silicate used to prepare the inventive support contains ⁇ 20ppm A1 on S1O2 weight basis. Beads formed with 12% S1O2 and Fl 2 S0 4 :Na 2 0 molar ratio 0.8 and were caught in ammonium sulfate solution. Aging was conducted at 70°C for 16 hours. Beads were then acidified to pH ⁇ 2 and washed with water acidified to pH ⁇ 3. Hydrogel beads were subsequently washed with methanol and dried under vacuum, milled/classified to the desired particle size distribution.
- Comparative 2 was prepared the same way as Comparative 1 except it was made from a different batch of preparation and a different batch of silicate, e.g. a sodium silicate of normal purity.
- silicate e.g. a sodium silicate of normal purity.
- the sodium silicate used is PQ’s N-clear silicate and it typically contains 300 ⁇ 400ppm A1 on S1O2 weight basis.
- Catalyst C is prepared the same way as Comparatives 1 and 2 except from support prepared from high-purity silicate as described above.
- Catalyst D was prepared the same way as Catalyst C except that a small amount of Na formate was added to the Cr coating solution during catalyst preparation.
- Catalyst properties and polymerization evaluation results are summarized in Table 3 and Table 4, respectively. Polymerization evaluation was conducted the same way as Example 1 except that homo-polymerization was performed at 107°C instead of 102 °C.
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US4119773A (en) | 1977-06-22 | 1978-10-10 | National Distillers And Chemical Corporation | Olefin polymerization catalyst |
CA1243010A (en) * | 1983-10-07 | 1988-10-11 | William Kirch | Zirconia-titania-silica tergels and their use as catalyst supports |
US5284811A (en) | 1990-05-14 | 1994-02-08 | Phillips Petroleum Company | Polymerization catalysts and processes |
US6838068B2 (en) * | 2000-06-30 | 2005-01-04 | Mitsubishi Chemical Corporation | Silica gel |
CN1227157C (en) * | 2001-09-25 | 2005-11-16 | 三菱化学株式会社 | Silica |
JP2003192713A (en) * | 2001-12-27 | 2003-07-09 | Mitsubishi Chemicals Corp | Silica gel carrier for olefin polymerization catalyst and olefin polymerization catalyst |
DE10257740A1 (en) * | 2002-12-10 | 2004-06-24 | Basell Polyolefine Gmbh | Preparation of supported, titanized chromium catalysts for the polymerization or copolymerization of olefins, e.g. ethylene, used in film production, involves the use of protic medium comprising titanium and chromium compounds |
DE102006004705A1 (en) * | 2006-01-31 | 2007-08-02 | Basell Polyolefine Gmbh | Production of (co)polyethylene for blown film uses chromium catalyst on silicate support heat-activated under oxidative conditions and melt mixing with sterically-hindered phenol and phosphite antioxidants at sufficient energy input |
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