CA1073891A - Low temperature hydrocarbyloxide treatment of catalyst - Google Patents

Abstract

Abstract of the Disclosure A process for producing a catalyst comprising activating a supported chromium oxide at a temperature within the range of 500-2000°F; thereafter treating said thus-activated catalyst with from 0.5-10 weight percent, based on the weight of said catalyst of a hydrocarbyl aluminum hydrocarbyloxide at a temperature below 80°F. Ethylene homopolymers and copolymers are made in a particle form process over a catalyst which is treated as a relatively low temperature with aluminum hydrocarbyloxide. This catalyst is capable of pro-ducing high melt flow polymer at lower temperatures and also produces polymer having exceptionally high shear response. This catalyst is useful for produc-ing ethylene homopolymers and copolymers in a particle from process. There are certain applications where it is necessary to have properties such as high shear response of the type which can be obtained with solution process polymers. In accordance with the invention, such a polymer can be produced in slurry systems utilizing the catalyst made as described hereinabove.

Description

107~91 23858 LOW TEMPE~ATURE HYDROCARBYLOXIDE
TREATMENT OF CATALYST
Background of the Invention mi5 invention relates to modified supported chromium oxide olefin polymerization catalysts.
Supported chromium oxide catalysts ca~ be used to prepare olefin polymers in a hydrocarbon solution to give a product having excellent characteristics from many standpoints. It is comparatively simple to control molecular weight in these systems simply by varying the temperature, with lower molecular weight (high MI) polymer being produced at higher temperatures.
Supported chromium oxide chromium oxide catalysts can also be used to prepare olefin polymers in a slurry system wherein the polymer is produced in the form of small particles of solid material suspended in the diluent. This process, frequently referred to as a particle-form process has the adv~ntage of being less complex but does not produce polymers which are exactly com-parable to solution polymers. There are certain applications where it is necessary to have properties such as high shear response, associated with solution process polymer. In addition, there is an inherent limitation in the particle-form process with respect to controlling molecular weight by ad~usting the temperature, since increases in temperature to effect higher melt index polymer causes the polymer to go into solution and thus destroys the particle-~orm process.
Brief Summary of the Invention It is an ob~ect o~ this invention to provide a method for producing rel~tively high melt index polymer in a particle-form process; it is a further obJect of this invention to lower the temperature at which a given molecular weight polymer can be produced in a particle-form process; it is yet a fur*her object of this invention to provide polymer produced by a particle-rorm process which has characteristics associated with solution polymerized polymer; and it i~ still yet a further object of this invention to produce polymer from q particle-form process having high shear response.

1073t~91 In accordance with this invention, a supported chromium oxide catalyst is treated with aluminum hydrocarbyloxide at a temperature below about 80F.
Statement of the Invention The invention, as particularly indicated and distinctly claimed herein, is a process for producing a catalyst comprising activating a supported chormium oxide at a temperature within the range of 500-2000Fj thereafter treating said thus-activated catalyst with from 0.5-10 weight percent, based on the weight of said catalyst of a hydrocarbyl aluminum hydrocarbyloxide at a temperature below 80F.
The said temperature may be within the range of 0 to 60F. and said aluminum hydrocarbyloxide in a hydrocarbon solvent may be slowly added to a slurry of said catalyst in a hydrocarbon diluent while subjecting said slurry to vigorous mixing.
The said hydrocarbyl aluminum hydrocarbyloxide may be selected from the group consisting of diphenylaluminum phenoxide, p-tolylaluminum dibutoxide, di-n-propylaluminum methylcyclohexoxide, isobutylaluminum diiso-butoxide, dimethylaluminum methoxide, diethylaluminum ethoxide, diethylaluminum n-propoxide, diethylaluminum t-butoxide, diisobutylaluminum isobutoxide, di-n-propylaluminum n-propoxide, di-2-methylpentylaluminum ethoxide, dimethyl-aluminum decanoxide, and diethylaluminum phenoxide.
The said hydrocarbyl aluminum hydrocarbyloxide may be a dialkyl-aluminum alkoxide, for example diethyl~uminum ethoxide.
The said chromium oxide may be supported on a precipitated silica, for example on silica coprecipitated with a titanium compound.
The invention, as particularly indicated and distinctly claimed herein, also provides a process which comprises contacting at least one poly-merizable olefin under polymerization conditions with a catalyst produced by activating a supported chromium oxide at a temperature with;n the range of 500 to 2000F, thereafter treating said thus activated catalyst with from 0.5 to 10 weight percent, based on the weight of said catalyst, of a hydro-carbyl aluminum hydrocarbyloxide, said contacting being carried out in a ..

liquid diluent at a temperature such that at least a substantial part of polymer produced is insoluble in said diluent.
The said olefin may be at least one aliphatic mono-l-olefin having

2 to 8 carbon atoms per molecule, for example ethylene from which said polymer thus produced is ethylene homopolymer.
The said contacting may be carried out at a temperature within the range of 150-233F and substantially all of said polymer may be in particle-form.
The said diluent may be a paraffin or a cycloparaffin, or mixture thereof, having 3 to 12 carbon atoms per molecule, preferably selected from the group consisting of propane, isobutane, cyclohexane, normal decane, and methylcyclohexane, and especially it may be isobutane.
The said polymer thus produced may be a copolymer selected from the group consisting of ethylene/propylene, ethylene/l-butene, ethylene/l-hexene, and ethylene/l-octene wherein 95 to 99 mole percent of said polymer is poly-merized ethylene.
The said hydrocarbyl aluminum hydrocarbyloxide may be selected from the group consisting of diphenylaluminum phenoxide, p-tolyaluminum dibu-toxide, di-n-propylaluminum methylcyclohexoxide, isobutylaluminum diisobutoxide, dimethylaluminum methoxide, diethylaluminum ethoxide, diethylaluminum n-propoxide, diethylaluminum t-butoxide, diisobutylaluminum isobutoxide, di-n-propylaluminum n-propoxide, di-2-methylpentylaluminum ethoxide dimethylaluminum decanoxide, and diethylaluminum phenoxide, and preferably diethylaluminum ethoxide.
The said chromium oxide may be supported on a precipitated silica, for example on a silica coprecipitated with a titanium compound.
The said hydrocarbyl aluminum hydrocarbyloxiae may be dialkyl aluminum alkoxide.
Descri~tion of the Drawi~
In the drawings, forming a part hereof, Figure 1 is a graph showing the relationship between shear response and melt lndex for ethylene-hexene-l copolymers made in accordance with the invention and for polymer made using a catalyst outside the scope of the invention; Figure 2 is a graph showing the relationship between shear response and the temperature at which aluminum ~ - 2a -~073891 hydrocarbyloxide treatment is effected. Figure 3 is a graph showing the relationship between the reactor temperature necessary to form a given melt index and the temperature at which the aluminum hydrocarbyloxide treatment is carried out. Figure 4 is a graph showing the relationship between the comonomer feed required in a copolymer to produce a given melt index, and the aluminum hydrocarbyloxide treatment temperature.
Description of the Preferred Embodiments The invention is primarily concerned with the preparation of poly-mers in a particle-form process at a relatively low temperature for a given melt index, or in the alternative, the production of a relatively high melt index polymer at a given temperature. The polymers which are produced with the catalyst made in accordance with this invention are preferably normally solid homopolymers or copolymers of ethylene with another l-olefin containing

3 to 8 carbon atoms per molecule. As an example, the olefin polymer can be produced from at least one aliphatic mono-l-olefin having 2 to 8 carbon atoms per lecule. Exemplary copolymers include those of ethylene/propylene, ethyl-ene/l-~utene, ethy~ene/l-hexene, and ethylene/l-octene and the like. The ma~or portion of such copolymers is derived from ethylene and generally con-sists of about 95 to 99 mole percent of ethylene. These polymers are well suited for extrusion, blow molding, injection molding, and the like.
Suitable supports for the chromium oxide include silica, silica-alumina, silica-titania, and the like. The supports are particulate in nature and they can be prepared by precipitation and coprecipitation techni-_ 2b -ques or by mixing silica with other refractory materials. For example, sodium æilicate can be added to an acid such as sulfuric acid (or an acid salt), the resulting precipitate aged for at lea~t one hour, the water-soluble salts removed, and then the water removed by ~eotropic distillation with a material such as ethyl acetate. m e mixing of the silicate into the acid (or vice versa) is preferably done slowly and with vigorous stirring so that, for instance, 0.5 to 15, preferably 1-5 percent of the silicate is added per minute. Silica constitutes the ma,jor portion of the support with the other metal compound or compounds when used making up from 0.1 to about 20 weight percent Or the finished catalyst. The support can also be impregnated with a pro ter metal compound such as a titanium compound prior to activation.
Alternatively, it can be coprecipitated with a titanium compound. The sup-port is admixed with 0.1 to about 10 weight percent of a chromium compound prior to activation.
The chromium compound can be a water-soluble salt such as chromium nitrate, chromium acetate, chromium trioxide, and the like, or an oreanic chromium compound such as tert-butylchromate, chromium acetylacetonate, and the like. m e organochromium compound can be dissolved in a non-aqueous solvent such as pentane, hexane, benzene and the like and the solution iB
added to the support which is preferably substantially dry. The resulting mixture is dried ~nd activated in dry air at an elevated temperature gen-erally within the range of 500-2000F, preferably 750-1200F. for about one-h~lf hour to 50 hours, more preferably 2 to 10 hours. At least a substantial portion of the chromium in lower valence states is converted to the hexa-valent form.
After activation, the catalyst is cooled and treated with a hydro-carbyl aluminum hydrocarbyloxide at a temperature of 80F or below, pref-erably 0 to 80F, re preferably 0 to 60F.
The low temperature treatment with the aluminum hydrocarbyloxide can be carried out either prior to eharging the activated catalyst to the reactor or the catalyst cnn be treated in situ in the reactor prior to bringing the reactor up to the désired operating temperature and introducin6 ~o73~9~

the monomer.
The hydrocarbyl aluminum hydrocarbyloxides are those represented by the following formula AlRa(OR')b wherein R and R' are the same or different and are alkyl, ar~l or cycloalkyl radicals or combinations thereof such as alkar~l, alkylcycloalkyl, etc., each radical containing from 1 to about 10 carbon atoms, preferably 1 to 6, and wherein a and b are integers of 1 or 2, and a plus b = 3. Exemplary com-pounds include diphenylaluminum phenoxide, p-tolylaluminum dibutoxide, di-n-propylaluminum methylcyclohexoxide, isobutylalu~inum diisobutoxide, dimethyl-aluminum methoxide, diethylaluminum ethoxide, diethylaluminum n-propoxide, diethyl aluminum t-butoxide, diisobutylaluminum isobutoxide, di-n-propyl-aluminum n-propoxide, di-2-methylpentylaluminum ethoxide, dimathylaluminum decanoxide, diethylaluminum phenoxide, and the like. Presently preferred are the diaIkylaluminum alkoxides. m e hydrocarbyl aluminum hydrocarbyloxideæ
can be prepared by reacting a hydrocarbon solution of a trihydrocarbyl alumi-num with a hydrocarbon solution of an alcohol at about a 1/1 to 1/2 molar ratio. After the reaction is completed, the required amount of solution is used to treat the activated catalyst. The solvent is preferably the same as that used as the diluent in the polymerization, i.e., isobutane, pentane, or the like, but can also be different.
The amount of ~luminum hydrocarbyloxide c&n range from about 0.5 to about 10 weight percent based on the weight of the activated catalyst being treated, with about 1 to about 8 weight percent being preferred.
In instances where the aluminum hydrocarbyloxide is premixed with the catalyst prior to contact with monomer, it is preferred that the aluminum hydrocarbyloxide solution be added slowly to a slurry of the catalyst with vigorous mixing by stirring for instance, since it reacts quickly with the catalyst and thus if the aluminum hydrocarbyloxide is simply poured over the catalyst or into a diluent containing the catalyst, the first portion of the catalyst to be contacted will incorporate a large percentage of the aluminum hydrocarbyloxide and the rest will get less or none. I'he mixing should ~07389~
continue for a short time after the last of the aluminum hydrocarbyloxide is added.
The particle-form process in which the catalyst o~ the present invention is particularly applicable is a process in which at least one olefin is polymerized at a temperature in the range of about 150-233~, pre-ferably 190-230~F. The catalyst is maintained in suspension and is contacted with the olefin or mixture of olefins in an Drganic medium at pressures suffi-cient to maintain the medium and at least a portion of the olefins in the liquid phase. The mediu~ and temperatures are such that the poly~er produced is insoluble in the medium and is recovered in the form of solid particles.
The organic medium (diluent) is generally a par~ffin and/qr cycloparaffin having from 3 to 12 carbon atoms per molecule. Representative examples include propane, butane, isobutane, pentane, isopentane, eyclohexane, normal dodecane, methylcyclohexane and the like. Pressures can range from about 100 to 700 psig ~r higher, and ca~alyst concentrations can range from about 0.001 to about 1 weight percent based on the weight of the reactor contents.
Hydrogen can be used to modify the molecular weight of the polymers produced in the process if desired. The process for preparing the polymers in particle-form is broadly disclosed in British 853,414, complete specification published November 9, 1960, and later variations are disclosed in U. S. 3,644,323 issued February 22, 1972.
Polymers produced with the catalyst of the instant invention are readily processed in conventional plastics ~abrication equipment. One measure of the processability is the melt index of the polymers, those having high melt indices being more easily handled than those having low melt indices.
Melt indices o~ the polymers produced in the ins~ant invention can range from about 0.1 to abQut 20 or eVen higher.
Broad molecular ~eight distribution pqlymers arq produced with the catalyst of this invention. One indicatiQn qf b~eadth of molecular weight distribution is giyen by the ratio between high load melt in~ex (H~MI) deter-mined according to ASTM D1238-57T, Condition F, and melt index (MI) deter-mined according to ASTM Dl230-57T, Condition E. S$milarly, the ratio between a "CIL" flow rate and melt index can be determined by measuring the "CIL"
flow rate in a plastometer manufactured by Canadian Industries Limited (CIL).
In this method the flow rate of the polymer is determined at 1500 psig gas pressure through a capillary tube 0.176 inches long and 0.01925 inches inner diameter at 190C. Polymers with broad molecular weight distributions are more shear sensitive and therefore exhibit higher ~ILMI/MI or CIL/MI
ratiOs than polymers with narrow molecular weight distributions. Broad lecular weight distribution polymers, particularly those having a melt in-dex of about 0.2-0.3 are quite useful in blow molding containers and the like since they exhibit good melt flow properties snd the molded articles ha~e good resistance to environmental stress cracking.
The low temperature treatment of the catalyst with the aluminum hydrocarbyloxide unexpectedly results in increasing the shear response com-pared with polymers made with the same catalyst treated at 90 to 100F
treating temperatures. Other unexpected effects resulting from the low temp-erature treated catslyst compared with the 90 to 100F treated catalysts are a substantially reduced reactor temperature needed to make polymer of a certain melt index and an increased amount of l-hexene to make a copolymer ~f a given density at a given melt index.
Example 1 Copolymers of ethylene and l-hexene were made in a particle-form process using isobut~ne as diluent and catalysts consisting of micro-spheroidal silica containing 2 weight percent chromium trioxide (add~d as an aqueous solution prior to spray drying the silica) which were activated for 5 hours at 900F, cooled and treated at the indicated temperatures with a hydro-carbon solution of diethylaluminum ethoxide (DEAL-E) sufficient to add 3.5 weight percent alko~ide. Procesæ conditions were ad~usted so that copolymers of nominal 0.950-0.952 g/cc density were made. Producti~ities of 3000-5000 lbs/lb of catalyst were obtained. Hydroeen was used to control molecular weight. The results are presented on FiEure 1.
Inspection of the data shows that a copolymer made with a catalyst treated at 5-10F, according to the instant invention, had a melt index of O.32 and an ~LMI/MI ratio of 191. Actually this measured value is believed to have been sub~ect to substantial experimental error. A calculated value based on Figure 2 gives a value of about 16~ which is still well above the line representing the expected value. A copolymer made with catalyst treated with alkoxide at 90-100F had a melt index o~ 0.28 but the HLMI/MI ratio is 144, considerably lower than the first copolymer. A copolymer made with catalyst not treated with alkoxide had a melt index of 0.37 and an HLMItMI ratio of 94. Some difficulty was experienced in getting homogeneous polymer of 0.3 melt index with cat~lyst treated at 5-10F and having 3.5 percent DEALE but other runs making 0.5 melt index polymer at catalyst treatment temperatures of about 5-10F gave the same unexpected improvement in HLMI/MI ratio. Homo-geneous polymer could be made at 0.3 melt index using 5-10F treated catalyst by using a lower amount of DEALE.
Example 2 Copolymers of ethylene and l-hexene were prepared in a particle-form process using isobutane as diluent and catalysts consisting of micro-spheroidal silica containing 2 weight percent chromium trioxide which wereactivated for 5 hours at 900F, cooled and treated with a hydrocarbon solu-tion of diethylaluminum ethoxide at temperatures ranging from 40 to 100F.
Sufficient solution was added to give 3.5 weieht percent alkoxide. Process conditions were ad~usted to produce copolymers of nominal 0.950 g/cc density and 0.30 melt index in all cases. The results are presented in Figure 2.
Inspection of the curve shows that a linear relationship exis-ts between alkoxide catalyst treatment between about 40 to 100F and polymer HLMI/~I ratio to make the specified polymer at the indicated alkoxide level.
As the alkoxide catalyst treatment temperature decreases the HLMI/MI ratio of polymer produced increases.

E~ample 3 Copolymers of ethylene and l-hexene were prepared as in the pre-ceding Examples. In one series the alkoxide treatment temperature was varied from 40 to 100F. Process conditions were ad~usted in all cases so that copolymers of nominal 0.950 g/cc density and 0.30 melt index were made.
The results are presented in Figures 3 and 4.
Consideration of the curve in Figure 3 shows that alkoxide-treatment temperatures of 80-100F requires a reactor temperature of about 208-209F
in order to make copolymers of the specified properties. When the alkoxide treatment temperature falls below 80F the reactor temperature decreases rapidly, For example, when the aIkoxide treat~ent takes place at 40F, the required reactor temperature to make polymer of the specified properties is about 198F or about ten degrees less.
Inspection of the curve presented in Figure 4 indicates that the amount of comonomer required to make a copolymer o~ a given density and melt . index is also dependent upon the alkoxide catalyst treatment temperature.
~ ~ the treating temperature decreases the amount of comonomer required in-- creases.
The differences in reactor temperature requirements and comonomer '~ 20 requirements are significant. Understanding them is important in practicing the particle-form process correctly with the Plkoxide-treated chromia-silica catalyst and such understanding allows more flexibility of operation as well -as greater control of shear response of the produced polymers.
While this invention has been described in detail ~or the purpose of illustration, it is not to be construed as limited thereby but is intended to cover all changes and modifications within the spirit and scope thereof.

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Claims (20)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for producing a catalyst comprising:
activating a supported chromium oxide at a temperature within the range of 500-2000°F; thereafter treating said thus-activated catalyst with from 0.5-10 weight percent, based on the weight of said catalyst of a hydro-carbyl aluminum hydrocarbyloxide represented by the formula A1R2(OR')b wherein R and R' are the same or different and are alkyl, aryl or cycloalkyl radicals or combinations thereof such as alkaryl, alkylcycloalkyl, etc., each radical containing from 1 to about 10 carbon atoms, preferably 1 to 6, and wherein a and b are integers of 1 or 2, and a plus b = 3 at a temperature below 80°F.

2. The process according to claim 1 wherein said temperature is within the range of 0 to 60°F and said aluminum hydrocarbyloxide in a hydro-carbon solvent is slowly added to a slurry of said catalyst in a hydrocarbon diluent while subjecting said slurry to vigorous mixing.

3. The process according to claim 1 wherein said hydrocarbyl aluminum hydrocarbyloxide is selected from the group consisting of diphenylaluminum phenoxide, p-tolylaluminum dibutoxide, di-n-propylaluminum isobutylaluminum diisobutoxide, dimethylaluminum methoxide, diethylaluminum ethoxide, diethylaluminum n-propoxide, diethylaluminum t-butoxide, diisobutyl-aluminum isobutoxide, di-n-propylaluminum n-propoxide, di-2-methylpentyl-aluminum ethoxide, dimethylaluminum decanoxide, and diethylaluminum phenoxide.

4. The process according to claim 1 wherein said hydrocarbyl aluminum hydrocarbyloxide is a dialkylaluminum alkoxide.

5. The process according to claim 1 wherein said hydrocarbyl aluminum hydrocarbyloxide is diethylaluminum ethoxide.

6. The process according to claim 1 wherein said chromium oxide is supported on a precipitated silica.

7. The process according to claim 6 wherein said chromium oxide is supported on silica coprecipitated with a titanium compound.

8. A process which comprises contacting at least one polymerizable olefin under polymerization conditions with a catalyst produced by activating a supported chromium oxide at a temperature within the range of 500 to 2000°F, thereafter treating said thus-activated catalyst with from 0.5 to 10 weight percent, based on the weight of said catalyst, of a hydrocarbyl aluminum hydrocarbyloxide represented by the formula A1Ra(0R')b wherein R and R' are the same or different and are alkyl, aryl or cycloalkyl radicals or combina-tions thereof such as alkaryl, alkylcycloalkyl, etc., each radical containing from 1 to about 10 carbon atoms, preferably 1 to 6, and wherein a and b are integers of 1 or 2, and a plus b = 3 at a temperature below 80°F, said con-tacting being carried out in a liquid diluent at a temperature such that at least a substantial part of polymer produced is insoluble in said diluent.

9. The process according to claim 8 wherein said olefin is at least one aliphatic mono-l-olefin having 2 to 8 carbon atoms per molecule.

10. The process according to claim 9 wherein said olefin is ethylene and said polymer thus produced is ethylene homopolymer.

11. The process according to claim 9 wherein said contacting is carried out at a temperature within the range of 150-233°F and substantially all of said polymer is in particle-form.

12. The process according to claim 9 wherein said diluent is a paraffin or a cycloparaffin, or mixture thereof, having 3 to 12 carbon atoms per molecule.

13. The process according to claim 9 wherein said diluent is selected from the group consisting of propane, isobutane, cyclohexane, normal decane, and methylcyclohexane.

14. The process according to claim 9 wherein said diluent is iso-butane.

15. The process according to claim 9 wherein said polymer thus pro-duced is a copolymer selected from the group consisting of ethylene/propylene, ethylene/l-butene, ethylene/l-hexene, and ethylene/l-octene wherein 95 to 99 mole percent of said polymer is polymerized ethylene.

16. The process according to claim 9 wherein said hydrocarbyl aluminum hydrocarbyloxide is selected from the group consisting of diphenyl-aluminum phenoxide, p-tolylaluminum dibutoxide, di-n-propylaluminum methyl-cyclohexoxide, isobutylaluminum diisobutoxide, dimethylaluminum methoxide, diethylaluminum ethoxide, diethylaluminum n-propoxide, diethylaluminum t-butoxide, diisobutylaluminum isobutoxide, di-n-propylaluminum n-propoxide, di-2-methylpentylaluminum ethoxide, dimethylaluminum decanoxide, and diethyl-aluminum phenoxide.

17. The process according to claim 9 wherein said hydrocarbyl alum-inum hydrocarbyloxide is diethylaluminum ethoxide.

18. The process according to claim 9 wherein said chromium oxide is supported on a precipitated silica.

19. The process according to claim 18 wherein said chromium oxide is supported on a silica coprecipitated with a titanium compound.

20. The process according to claim 9 wherein said hydrocarbyl alum-inum hydrocarbyloxide is a dialkyl aluminum alkoxide.