GB1563739A - Silica support catalyst and processes - Google Patents

Description

(54) SILICA SUPPORT, CATALYST AND PROCESSES (71) WE, UNION CARBIDE CORPORATION, a Corporation organized and existing under the laws of the State of New York, United States of America, of 270, Park Avenue, New York, State of New York 10017, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to the low pressure polymerization of ethylene with catalyst compositions comprising silica supports.

Ethylene may be homopolymerized or interpolymerized at low ( 6 1000 psi) or high ( > 1000 psi) pressure with catalyst compositions comprising transition metal compounds such as chromium oxide, and chromocene compounds deposited on inorganic oxide supports such as silica, silica-alumina, thoria and zirconia. For these catalyst compositions to be useful for commercial purposes, to date, in these reactions it has been found necessary in all cases, to dry the supports first to remove free moisture therefrom and then to activate the supports, before or after the deposition of the transition metal compound thereon, at temperatures of the order of 300"C., and preferably at 500 to 8000C. for periods of at least 8 hours.

In some cases, this high temperature activation step must also be conducted under specific and restricted types of gas phase conditions.

Even when the catalysts are prepared under these stringent conditions, their utility, from a commercial point of view, also causes additional disadvantages, in that reproducibility of the catalyst composition is difficult to control and the activation equipment is apt to burn-out under the long term, high-temperature use to which it must be subjected.

United States Patent Specification No. 3,207,699 discloses the treatment of dry calcined acidic silica-alumina with trimethyl silane at elevated temperatures for the purposes of providing an improved acidic catalyst for various purposes. Silica, when treated in the same manner, was not useful for the same purposes.

United States Patent Specification No. 3,687,920 discloses the simple addition of various silane compounds to supported chromocene compounds wherein the supports, including silica, are thermally activated at elevated temperatures prior to the deposition of the chromocene compound, or the use of the silane compound. The purpose of the addition of the silane compound to the catalysts, which are used in the polymerization of ethylene, is to improve the productivity of the catalysts.

United States Patent Specification No. 3,879,368 discloses the treatment, with certain strong reducing agents and certain silane compounds of supported chromocene compounds wherein the supports, including silica, are thermally activated prior to the deposition of the chromocene compound, or these of the strong reducing agents or silane compounds. The use of the strong reducing agents and silane compounds allows for the use of supports which are activated at relatively low temperatures. The resulting compositions are used as catalysts for ethylene polymerization and provide higher yields of polymer which have a relatively broad molecular weight distribution.

It has now been found that commercially useful catalysts for the polymerization of ethylene which comprise transition metal compounds, and especially chromocene compounds, deposited on silica supports can be prepared without the need for thermally activating the support or the supported metal compound at elevated temperatures if the dried support is treated with hydro silane compounds in the presence of a base prior to the deposition of the transition metal compound on the support. Such a treatment provides a modified support to which the hydrosilane compound is chemically anchored.

Accordingly, the present invention provides a method of preparing a silica support which comprises treating a silica support which has been dried at a temperature and for a time which is sufficient to remove surface-adsorbent water, but insufficient to cause significant loss of silanol groups via condensation, with at least one hydrosilane, in the presence of a halogen-free base, which hydrosilane is silane or a compound having the structure: RntSi)H4-n wherein R is a hydrocarbon group containing from 1 to 10 carbon atoms and n is an integer of 1 to 3 inclusive.

The invention also provides a catalyst composition comprising a transition metal compound deposited on a silica support of the present invention.

The invention further provides a process for polymerizing on ethylene charge which comprises contacting the charge with a catalyst composition of the present invention.

The silica materials used as a support in the catalyst compositions of the present invention are preferably porous materials having a high surface area, that is, a surface area in the range of from 50 to 1000 square meters per gram, and a particle size of from 25 to 200 microns. For use in a fluid bed reactor process, the support particles are preferably capable of subdivision, which is the ability of the support particle to rupture when used in a fluidized bed as described below and in the presence of a growing polymer (thereon) and thereby to extend itself to form many particles having a low catalyst residue from a single initial support particle.

Any grade of support can be used but microspheroidal intermediate density (MSID) silica having a surface area of 350 square meters per gram and a pore diameter of about 200 , (W. R. Grace's G-952 grade), and intermediate density (ID) silica having a surface area of 285 m2/gr and a pore diameter of 164 (W. R. Grace's G-56 grade) are preferred. Other grades such as the G-968 silica, as designated by W. R. Grace and Co., having a surface area of 700 square meters per gram, and a pore diameter of 50-70 A, is also quite satisfactory. Variations in melt index control and in polymer productivity can be expected between different grades of supports.

When incorporated in a porous silica support of high surface area, as described herein, the transition metal compound forms active sites both on the surface and in the pores of the support. Although the actual mechanism of the process is not entirely understood, it is believed that the polymers begin to grow at the surface as well as in the pores of the supported catalyst. When a pore-grown polymer becomes large enough in a fluidized bed, it ruptures the support thereby exposing fresh catalyst sites in the inner pores of the support.

The supported catalyst may thus subdivide many times during its lifetime in a fluidized bed and thereby enhance the production of low catalyst residue polymers, thereby eliminating the need for recovering the catalyst from the polymer particles. If the support is too large, it may resist rupture thereby preventing subdivision which would result in catalyst waste. In addition, a large support may act as a heat sink and cause "hot spots" to form in a fluid bed system.

For the purposes of the present invention the silica support is heated prior to any treatment with the silane compound, at a temperature and for a time which is sufficient to remove surface-adsorbed water, but insufficient to cause significant loss of silanol groups via condensation. Preferably a temperature of from 100 to 300"C. more preferably from 150 to 250"C, for a period of from 1 to 48 hours is used.

The silica may also be dried by azeotropically distilling off the adsorbed surface water from the support. This can be accomplished by the azeotropic distillation of a slurry of the silica support in an azeotropic diluent. Again the temperature and the time must fulfil the above conditions. The hydrosilane compounds which are used in the present invention are silane (Sill4) and hydrocarbylsilane compounds having the structure Rn+Si4-n wherein R is a C1 to C10 hydrocarbon group - and n is an integer of 1 to 3, inclusive, and preferably 1. Where a hydrocarbyl silane compound contains more than one R group, these R groups may be the same or different. The R groups include saturated and unsaturated aliphatic and aromatic groups, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, amyl, decyl, phenyl and benzyl groups.

The preferred hydrocarbyl silane compounds include methyl silane, dimethyl silane, ethyl silane, diethyl silane, propyl silane, dipropyl silane, butyl silane, dibutyl silane, amyl silane and diamyl silane.

The hydrosilane compounds may be used individually or in combination with one another for the treatment of the support. The treatment of the support with the hydrosilane compound is accomplished by bringing the hydrosilane into contact with the support in the presence of a base. This is preferably done at atmospheric pressure and at a temperature of from 60 to 80"C. Higher pressures and/or temperatures may also be used. The contact may be facilitated by dissolving the hydrosilane in a hydrocarbon solvent therefor and then immersing the support in the solution, and then adding a base.

The solvents for the hydrosilane include aliphatic and aromatic hydrocarbon solvents such as n-hexane, heptane, benzene and toluene.

Preferably from 0.2 to 2.0, and more preferably from 0.4 to 0.8, moles of the hydrosilane are used per mole of silanol group on the surface of the silica support. This will correspond depending on the hydrosilane compound used, to from 4 to 20 weight percent of the hydrosilane compound, based on the combined weight of the hydrosilane compound and the silane support.

The bases used in the preparation of the supports of the present invention are basic materials, preferably fugitive, i.e., having a boiling point, at atmospheric pressure, of 4 1500C. These materials have a pH, in water or other suitable solvent of 7.

The fugitive bases are preferably tertiary amines. These amines include trimethyl amine, diethyl methyl amine, ethyl dimethyl amine, triethyl amine, and n-propyl diethyl amine.

Other base compounds which may be used include alkali metal oxides, hydroxides and alcoholates. However, these other base compounds are more difficult to remove from the reaction systems than the tertiary amines, which are volatile, and soluble in organic solvents.

The base compounds may be used individually or in combination with each other. They are devoid of halogen atoms.

Preferably from 0.1 to 2.0, and more preferably from 0.9 to 1.1, moles of the base are used per mole of silane compound employed. The treatment of the support with the hydrosilane compound in the presence of the base in accordance with the present invention is believed to cause a chemical anchoring of the hydrosilane compound onto the support, with the simultaneous evolution of hydrogen gas, as is shown in the following equation,

(Support Si-O-H + H3SiR base (supports Si-C-SiH2R + H2 The transition metal used is preferably an organochromium compound e.g. chromocene or a fused ring chromium compound.

The chromocene compound is also known as a bis (cyclopentadienyl) chromium [II] compound which has the structure:

wherein R' and R" are each individually a C1 to C20, inclusive, hydrocarbon group, and n' and n" are each individually 0 or an integer of 1 to 5, inclusive. The R' and R" hydrocarbon groups may be saturated or unsaturated, they may include aliphatic, alicyclic and aromatic radicals such as methyl, ethyl, propyl, butyl, pentyl, cyclopentyl, cyclohexyl, allyl, phenyl and naphthyl groups.

The bis (cyclopentadienyl) chromium [II] compounds which may be used as catalysts on the silica supports in accordance with the present invention may be prepared as disclosed in United States Patents Specification Nos. 2,870,183 and 3,071,605.

The chromocene compounds may be used individually or in combination with one other.

The chromocene compounds are preferably deposited on the silica support from a solution thereof. This is preferably done by immersing the silica support in a solution of the chromocene compound and then evaporating the solvent under atmospheric or reduced pressure. The deposition of the chromocene compound is conducted after the treatment of the silica support with the silane compound.

The chromocene compound is used in such quantities as to enable from 0.1 to 3.0 weight percent of the chromium in the chromocene compound to be deposited on the support based on the combined weight of the silica support and the chromium metal.

After the treatment of the support with the hydrosilane and the chromocene compound the resulting catalyst composition can be used, as is, without further treatment, in the polymerization of ethylene, as disclosed below.

The composite catalyst is in the form of powdery free-flowing solid particles.

The composite catalyst is prepared from, based on the total weight of the essential three elements thereof, from 80 to 96 weight % of the silica support, from 3.5 to 19.5 weight % of the hydrosilane compound, and from 0.5 to 10 weight % of the chromocene compound.

From lx 10-6 to 1x10-4 weight % of the composite catalyst is used per mol of monomer being polymerized. The amount of catalyst being employed may vary depending on the type of polymerization procedure being employed.

Ethylene may be polymerized with the composite catalyst of the present invention alone or with one or more particular comonomers other than ethylene.

The comonomers which are used with ethylene in the monomeric charge being copolymerized in accordance with the present invention may be one or more alpha-olefins containing from 3 to 12, inclusive, carbon atoms. The monomers may be C3 to C12 mono-olefins or C4 to Cl2 non-conjugated di-olefins.

These mono-olefins which are to be used as comonomers include propylene, butene-1, pentene-1, 3-methylbutene-l, hexene- 1, 4methylpentene-1, 3-ethyl-butene-1, heptene- 1, octene-l decene-1, 4,4-dimethyl-pentene-1, 4,4-diethylhexene-1, 3,4-di-methylhexene-1, 4-butyl-1-octene, 5-ethyl-1-decene, and 3,3-dimethylbutene-1. Among the diolefins which may be used are 1,5-hexadiene, dicyclopentadiene, and ethylidene norbornene.

The polymers which are prepared in accordance with the teaching of the present invention are solid materials which have densities of from 0.945 to 0.970, inclusive, and melt indices of from 0.1 to 100 or more.

The preferred polymers are the homopolymers of ethylene. The interpolymers will contain at least 50 weight %, and preferably at least 80 weight %, of ethylene.

After the composite catalysts have been formed, the polymerization reaction is conducted by contacting the monomer charge, substantially in the absence of catalyst poisons, with a catalytic amount of the composite catalyst at a temperature and at a pressure sufficient to initiate the polymerization reaction. If desired, an inert organic solvent may be used as a diluent and to facilitate materials handling.

The polymerization reaction is carried out at temperatures of from 30"C. or less up to 200"C or more, depending to a great extent on the operating pressure, the pressure of the entire monomer charge, the particular composite catalyst being used and its concentration.

The selected operating temperature is also dependent upon the desired polymer melt index since temperature is also a factor in adjusting the molecular weight of the polymer.

Preferably, the temperature is from 30"C. to 1000C. in the conventional slurry or "particle forming" process which is conducted in an inert organic solvent medium. As with most catalyst systems, the use of higher polymerization temperatures tends to produce lower weight average molecular weight polymers, and consequently polymers of higher melt index.

The pressure used can be any pressure sufficient to initiate the polymerization of the monomer charge and can be from subatmospheric pressure, using an inert gas as a diluent, to superatmospheric pressure of up to about 1,000,000 psig (pounds per square inch gauge), or more but the preferred pressure is from atmospheric up to 1000 psig. As a general rule, a pressure of from 20 to 800 psig is preferred.

When an inert organic solvent medium is employed in the process of this invention it should be one which is inert to all the other components and products of the reaction system and be stable at the reaction conditions being used. It is not necessary, however, that the inert organic solvent medium also serve as a solvent for the polymer produced. The inert organic solvents which may be used include saturated aliphatic hydrocarbons, such as hexane, heptane, pentane, isopentane, isooctane, and purified kerosene; , saturated cycloaliphatic hydrocarbons, such as cyclohexane, cyclopentane, dimethyl- cyclopentane and methylcyclohexane; aromatic hydrocarbons such as benzene, toluene, and xylene; and chlorinated hydrocarbons, such as chlornbenzene tetrachloroethylene, and orthodichlorobenzene. Particularly preferred solvent media are cyclohexane, pentane, isopentane, hexane and heptane.

When it is preferred to conduct the polymerization to a high solids level as hereinbefore set forth, it is, of course, desirable that the solvent be liquid at the reaction temperature.

For example, when operating at a temperature which is lower than the solution temperature of the polymer in the solvent, the process can be essentially a slurry or suspension polymerization process in which the polymer actually precipitates out of the liquid reaction medium and in which the catalyst is suspended in a finely divided form.

This slurry system is of course dependent upon the particular solvent employed in the polymerization and its solution temperature for the polymer prepared. Consequently in the "particle form" embodiment, it is most desirable to operate at a temperature which is lower than the normal solution temperature of the polymer in the selected solvent. For example, polyethylene prepared herein may have a solution temperature in cyclohexane of about 90"C., whereas in pentane its solution temperature may be about llO"C. It is characteristic of this article form" polymerization system that a high polymer solids content is possible even at low temperatures, if sufficient agitation is provided so that adequate mixing of the monomer with the polymerizing mass can be accomplished. It appears that while the polymerization rate may be slightly slower at the lower temperature, the monomer is more soluble in the solvent medium, thus counteracting any tendency to low polymerization rates and/or low yields of polymer.

It is also characteristic of the slurry process that the monmer appears to have substantial solubility characteristics even in the solids portion of the slurry so that as long as adequate agitation is provided, and the polymerization temperature is maintained, a broad range of size of solid particles in the slurry can be provided. Experience has shown that the slurry technique can produce a system having more than fifty per cent solids content, provided conditions of sufficient agitation are maintained. It is particularly preferable to operate the slurry process in the range of from 30 to 40 weight per cent of polymer solids.

Recovery of the polymer from the solvent medium is, in this embodiment, reduced to a simple filtration and/or drying operation and no efforts need be expended in polymer clean up and catalyst separation or purification. The residual concentration of catalyst in the polymer is so small it can be left in the polymer.

When the solvent serves as the principal reaction medium, it is of course, desirable to maintain the solvent medium substantially anhydrous and free of any possible catalyst poisons such as moisture and oxygen, by redistilling or otherwise purifying the solvent before use in this process. Treatment with an absorbent material such as high surface area silicas, aluminas, molecular sieves and similar materials are beneficial in removing trace amounts of contaminants that may reduce the polymerization rate or poison the catalyst during the polymerization reaction.

By conducting the polymerization reaction in the presence of hydrogen, which appears to function as a chain transfer agent, the molecular weight of the polymer may be further controlled.

Experience has shown that hydrogen may be used in the polymerization reaction in amounts varying from 0.001 to 10 moles of hydrogen per mole of olefin monomer. For most polymerization reactions, however, the entire molecular weight range may be obtained by using from 0.001 to 0.5 mole of hydrogen per mole of monomer.

The homo- or inter- polymerization of ethylene with the catalysts of this invention can also be accomplished in a fluid bed reaction process. An example of a fluid bed reactor and process which can be used for this purpose is disclosed in British Patent Specification No.

1,253,063.

The following Examples are designed to illustrate the present invention and are not intended as a limitation upon the scope thereof.

Examples 1 to 8 A series of eight catalysts were prepared with and without various silane compounds to demonstrate the utility of such compounds in accordance with the teachings of the present invention. For comparative purposes, the catalyst of Example 1 was made without any silane or amine compound. Examples 7 and 8 are also comparative Examples.

The support used for each catalyst was intermediate grade silica which had a surface area of 300 square meters per gram and an average particle size of 200 . The support was first thermally treated under nitrogen for 18 hours at 200"C. The thus heated support contained approximately 2.5 mmole of silanol groups per gram. Eight grams (20 mmoles SiOH) of this silica was then slurried in about 100 ml of n-hexane and about 1.4 grams (16 mmole) of butyl silane was then added. The silane compound was thus used in such amounts as to provide 0.8 moles of silane compound per mol of silanol group on the silica support. The other hydrosilane compounds of this invention can be similarly used in such amounts as to provide about 0.2 to 2.0 moles of silane per mole of silanol group on the silica. The slurry was then heated up to a reflux temperature of about 75"C. and 1.9 grams (20 mmoles) of triethyl amine was then slowly added to the refluxing system over a period of about one hour. Where used, the amine was used at a (C2H5)3N/=SiOH ratio ranging from 0.1 to 1.0.

The system was then allowed to reflux overnight ( 18 hours). Chemical anchoring of the silane compound to the support and simultaneous evolution of hydrogen is believed to have occurred during the treatment. The system was then cooled, the silica was washed in n-hexane and dried in vacuo at 80"C., all under waterfree conditions.

The silane compound used for each support is indicated in Table I below, as is also listed the ratio of silane compound to silanol groups.

The supported catalyst was then prepared by slurrying 0.4, 0.8 or 1.0 gram of the support prepared above in about 100 ml of n-hexane and then adding 20 mg of bis(cyclopentadienyl )chromium to the slurry. The slurry is stirred for about 30 minutes to allow the chromium compound to deposit on the support. The amount of the support used for each catalyst is also indicated in Table I.

Each of the eight catalyst systems prepared as described above were used to homopolymerize ethylene at 60-700C. in 500 ml n-hexane under a pressure of 25 psi of H2 and an ethylene pressure of 175 psi. Each reaction was conducted for about 30 minutes. The yields of polymer produced in each experiment are also listed in Table I. The polymer produced in each case was a solid high density (a 0.95) material. A review of these data indicates that it is only when the hydrosilane compounds of the present invention are employed to modify the catalyst support (Examples 2 to 8) that active catalysts are obtained. The preferred hydrosilane compounds (Examples 2 and 3) provide supported catalysts which provide relatively high yield of polymer.

Table I Yield of Ratio of polymer grams of Silane SiH/ produced Example support used SiOH grams 1 0.4 None 0 2 1.0 butyl silane 1.0 152 3 1.0 amyl silane 1.0 128 4 1.0 diethyl silane 1.0 73 5 0.4 triethyl silane 1.0 32 6 1.0 triethyl silane 1.0 22 7 0.4 (CH3siho)x* 3.0 17 8 0.8 (CH3SiHO)x* 3.0 21 * polymethylhydrosiloxane in which x = 35.

Examples 9 to 12 A series of four supported catalysts were prepared using a silica-alumina support to demonstrate that such a support is not useful in the present invention. For comparison purposes the catalysts of Example 9 and 10 were made without any silane or amine compound.

The supports were silica-alumina containing about 87 weight percent of silica and about 13 weight percent of alumina. The support had a surface area of about 475 square meters per gram. The supports were thermally treated under nitrogen for 18 hours. The support of Example 9 was so treated at 6000C., whereas the supports of Examples 10 to 12 were so treated at 200"C. The supports of Examples 11 and 12 were then treated with butyl silane and triethyl amine as disclosed in Examples 1 to 8, using a silane /SiOH ratio of 1.0, and a (C2H)3N/SiOH ratio of 1.0. Table II below lists the activation temperature of the support, and the silane compound and amine used in each Example.

The supported catalyst was then prepared as in Examples 1 to 8 using 0.4 or 0.8 grams of the support. The amount of the support used for each catalyst is also indicated in Table II.

Each of the four catalyst systems prepared as described above were used to homopolymerize ethylene as in Examples 1 to 8. The yields of polymer produced in each experiment are also listed in Table II. The polymer produced in Example 9 was a solid high density (0.95) material. A review of the data of Table II indicates that a silica-alumina support is not useful in the present invention, and must be thermally activated at relatively high activation temperatures to produce acceptable results.

Table II Yield of Support Polymer Grams of Activation Silane produced.

Example support Temp., "C. used grams 9 0.4 600 None 70 10 0.4 200 None 0 11 0.4 200 butyl 0 silane 12 0.8 200 butyl 0 silane Examples 13 to 14 An ethylene polymerization catalyst of the present invention was compared with a catalyst prepared as disclosed in the United Kingdom Patent 1,253,063. The prior art catalyst was prepared by depositing 4 weight percent of chromocene on a silica support which had been thermally activated under nitrogen at 750"C. for 8 hours. The support for the prior art catalyst had a surface area of 300 square meters per gram and an average particle size of 200 A. The chromocene compound was added to the support as disclosed above in Paragraph B of Examples 1 to 8.

A catalyst of the present invention was prepared as in Examples 1 to 8, using the same support as for the prior art catalyst, butyl silane, triethyl amine and chromocene. This support also was made with 4 weight percent of chromocene, and was dried at 250"C. for 18 hours under nitrogen.

Each catalyst was then used to homopolymerize ethylene in a fluid bed reactor of the type disclosed in United Kingdom Patent 1,253,063. The reactions were conducted at 100"C. under an ethylene pressure of 300 psi and at a space time yield of 4. to 5. The reactions were conducted over a period of about 200 hours. Hydrogen was used as a molecular weight regulator. The average results which were obtained, in terms of the properties of the polymers that were produced, are disclosed below in Table III. The polymers were produced at a rate of about 30 to 40 pounds per hour. Table III also lists the salient characteristics of two catalysts.

The test results disclosed in Table III indicate that the catalyst of the present invention made with the support which had been thermally treated at 2500C., and further treated with butyl silane, was essentially equivalent in performance to the prior art catalyst which had been thermally treated at 750"C.

Table III Polymer Properties Support Productivity average drying C4H9SiH3/ of catalyst particle temp. #SiOH (lbs. polymer/ H2/C2H4 Melt % diameter Example C ratio lbs. catalyst) ratio Index MFR Density Extractables4 (inches) 13 750 o 270,000 0.061 7.1 42 0.963 2.9 0.012 14 250 1.0 272,000 0.064 6.5 47 0.964 3.6 0.010 1 Melt Index is determined by ASTM D-1238, at 190 C., reported as grams per 10 minutes.

2 MFR is melt flow ratio which is ratio of melt index/flow index wherein flow index is measured at 10 times the weight used in the melt index test.

3 Density is determined by ASTM D-1505 and wherein the test plaque is conditioned for one hour at 120 C. to approach equilibrium crystallinity.

4 % extractables are determined by extraction in boiling cyclohexane for # 10 hours.

In addition to the chromocene compounds disclosed above, other transition metal compounds which may be used on the silica supports of the present invention, as catalysts, include the fused ring bis (indenyl)- and bis(fluorenyl)- chromium [II] compounds disclosed in British Patent Application No. Serial No. 1561910 54167/76.

These supported fused ring compounds are used in amounts of from 0.001 to 25%, or more, by weight, based on the combined weight of the fused ring compound and the silica support. These fused ring compounds may be deposited on the silica support of the present invention in the same manner as are the chromocene compounds, as disclosed above. The supported fused ring compounds may be used as ethylene polymerization catalysts.

These fused ring organochromium compounds have the structure: Ar-CrII-Ar' wherein Ar and Ar' are each individually an indenyl radical of the structure:

wherein the R5,s are each individually a C1 to C1 to C10, inclusive, hydrocarbon group, and m is 0 or an integer from 1 to 4, inclusive and x is 0, 1, 2 or 3, or a fluorenyl radical of the structure:

wherein the Rb's are each individually a C1 to Cl0, inclusive, hydrocarbon group, and m' and m" are each individually 0 or an integer from 1 to 4, inclusive, and Z is H or Rb. The Rb hydrocarbon groups may be saturated or unsaturated, and they may include aliphatic, alicyclic and aromatic radicals such as methyl, ethyl, propyl, butyl, pentyl, cyclopentyl, cyclohexyl, allyl, phenyl and naphthyl groups.

The fused ring compounds which may be used on the silica supports in accordance with the present invention may be prepared as disclosed in Advances in Organometallic Chemistry by J.M. Birmingham, F.().A. Stone and R. West, Eds., Academic Press, New York, 1964, pages 377 to 380.

Claims (29)

WHAT WE CLAIM IS:

1. A method of preparing a silica support which comprises treating a silica support, which has been dried at a temperature and for a time which is sufficient to remove surface-adsorbed water, but insufficient to cause significant loss of silanol groups via condensation, with at least one hydrosilane in the presence of a halogen-free base, which hydrosilane is silane or a compound having the structure: Rni+H4n wherein R is a hydrocarbon group containing from 1 to 10 carbon atoms and n is an integer of 1 to 3 inclusive.

2. A method as claimed in claim 1 wherein the support has been dried at from 100 to 300"C for from 1 to 48 hours.

3. A method as claimed in claim 2 wherein the support has been dried at from 150 to 250"C. for from 1 to 48 hours.

4. A method as claimed in any one of the preceding claims wherein the base comprises a fugitive base (as hereinbefore defined).

5. A method as claimed in claim 4 wherein the fugitive base comprises a tertiary amine.

6. A method as claimed in any one of the preceding claims wherein the silica support has a surface area of from 50 to 1000 square meters per gram and a particle size of from 25 to 200 microns.

7. A method as claimed in any one of the preceding claims wherein the dried support is treated by dissolving the hydrosilane in a hydrocarbon solvent at from 60C to 80"C., immersing the support in the solution, and then adding to the solution the base.

8. A method as claimed in any one of the preceding claims wherein from 0.1 to 2.0 moles of base are used per mole of hydrosilane.

9. A method as claimed in claim 8 wherein from 0.9 to 1.1 moles of base are used per mole of hydrosilane.

10. A method as claimed in any one of the preceding claims wherein the support is treated with from 0.2 to 2.0 moles of the hydrosilane per mole of silanol group on the surface of the support.

11. A method as claimed in claim 10 wherein the support is treated with from 0.4 to 0.8 moles of the hydrosilane per mole of silanol group on the surface of the support.

12. A method as claimed in any one of the preceding claims wherein n is 1.

13. A method as claimed in claim 12 wherein the hydrosilane is butyl silane.

14. A method as claimed in claim 1 substantially as hereinbefore described in any one of Examples 2 to 6 or Example 14.

15. A silica support when prepared by a method as claimed in any one of the preceding claims.

16. A catalyst composition comprising a transition metal compound deposited on a silica support as claimed in claim 15.

17. A catalyst composition as claimed in claim 16 wherein the transition metal compound is a chromocene compound of the formula:

wherein R' and R" are each individually a C1 to Qo' inclusive, hydrocarbon group, and n' and n" are each individually 0 or an integer of 1 to 5 inclusive, and wherein from 0.5 to 10 weight percent of the chromocene compound is deposited on the support, based on the total weight of the catalyst composition.

18. A catalyst composition as claimed in claim 16 wherein the transition metal compound is a fused ring organochromium compound of the formula: Ar-CrIl-Ar' wherein Ar and Ar' are each individually an indenyl radical of the structure:

wherein the Ra's are each individually a C1 to Cl0, inclusive, hydrocarbon group, and m is 0 or an integer from 1 to 4, inclusive and xis 0, 1, 2 or 3, or fluorenyl radical of the structure:

wherein the Rb's are each individually a C1 to Cl0, inclusive, hydrocarbon group and m' and m" are each individually 0 or an integer from 1 to 4, inclusive, and Z is H or Rb, and wherein from 0.001 to 25 weight percent of the fused ring organochromium compound is deposited on the support, based on the combined weight of the support and the fused ring organochromium compound.

19. A catalyst composition as claimed in claim 17 wherein from 0.1 to 3 weight percent of transition metal is deposited on the support, based on the total weight of the catalyst composition.

20. A catalyst composition as claimed in claim 16 substantially as hereinbefore described in any one of Examples 2 to 6 or Example 14.

21. A process for polymerizing an ethylene charge which comprises contacting the charge with a catalyst composition as claimed in any one of claims 16 to 20.

22. A process as claimed in claim 21 as appendant to claim 17 wherein from 1 x 10.6 to 1x10-4 weight percent of the catalyst composition is used per mol of ethylene charge.

23. A process as claimed in claim 21 or claim 22 wherein the ethylene charge consists only of ethylene.

24. A process as claimed in claim 21 or claim 22 wherein the ethylene charge consists of ethylene and not more than 50 weight percent of at least one comonomer other than ethylene, which comonomer is either a C3 to C12 alpha-olefin which is a mono-olefin, or a non-conjugated di-olefin containing from 4 to 12 carbon atoms.

25. A process as claimed in any one of claims 21 to 24 wherein the ethylene charge is polymerized at a temperature of from 30 to 1000C and at a pressure of from 20 to 800 psig.

26. A process as claimed in any one of claims 21 to 24 wherein the ethylene charge is polymerized in the presence of from 0.001 to 10 moles of hydrogen per mole of ethylene charge.

27. A process as claimed in claim 26 wherein the ethylene charge is polymerized in the presence of from 0.001 to 0.5 moles of hydrogen per mole of ethylene charge.

28. A process as claimed in claim 21 substantially as hereinbefore described in any one of Examples 2 to 6 or Example 14.

29. An ethylene polymer when produced by a process as claimed in any one of claims 21 to 28.