NO150440B - PROCEDURE FOR TREATING A SILICON Dioxide SUPPLIER WITH A SILANE COMPOUND - Google Patents

Description

The present invention relates to a method for treating a silicon dioxide carrier with a silane compound.

to prepare an ethylene polymerization catalyst containing a transition metal..

The ethylene can be homopolymerized or interpolymerized by

low (-70 kg/cm 2 ) or high (> 70 kg/cm 2 ) pressures with catalyst compositions comprising transition metal compounds, such as chromium oxide and chromocene compounds, deposited on inorganic oxide supports, such as silicon dioxide, silicon dioxide-alumina, thorium oxide and zirconium oxide.

In order for these catalyst compositions to be usable

for commercial purposes, in these reactions until now in all cases it has been necessary, before or after intended-

ning of the transition metal compound on the support, first to

drying the supports to remove free moisture, and then activating the supports at temperatures of the order of -300°C, and preferably at 500-800°C for a period of at least 8 hours.

In simple cases, this high-temperature activation must also be carried out under special and limiting types of gas phase conditions.

Even when the catalysts are produced under these strict conditions, their use from a commercial point of view still causes further shortcomings in that the reproducibility of the catalyst composition is difficult to control and the activation equipment tends to burn out during the long periods of use under high temperature.

US-PS 3,207,699 describes the treatment of dry calcined

acidic silica-alumina with trimethylsilane at elevated temperatures in order to provide an improved acidic . catalyst for various purposes. Silica was,

when it was treated in the same way, not usable for the same purpose.

US-PS 3,687,920 describes simple addition of various silane compounds to supported chromocene compounds in which the support, including silicon dioxide, is thermally activated at elevated temperatures prior to deposition of the chromocene compound, or use of the silane compound. The purpose of adding the compound to the catalysts, which are used in the polymerization of ethylene, is to improve the productivity of the catalysts.

US-PS 3,879,368 describes treatment with certain strong reducing agents and certain silane compounds, of supported chromocene compounds in which the supports, including silicon dioxide, are thermally activated prior to deposition of the chromocene compound, or the use of the strong reducing agents or silane compounds. The use of the strong reducing agents and the silane compounds allows the use of carriers which are activated at relatively low temperatures. The resulting compositions are used as catalysts for ethylene polymerization and give higher polymer yields with a relatively broad molecular weight distribution.

It has now been found that commercially usable catalysts for the polymerization of ethylene, and which comprise chromocene compounds deposited on silica supports, can be prepared without the need for thermal activation of the support or the supported chromium compound at elevated temperatures, if the dried support is treated with hydrosilane compounds in the presence of a base before depositing the chromocene compound on the support. Such a treatment provides a modified carrier to which the hydro-silane coupling is chemically anchored.

The object of the present invention is to produce a method for treating a silicon dioxide carrier with a silane compound to produce an ethylene polymerization catalyst containing a transition metal, and this method is characterized by the carrier being dried at a temperature of 100 - 300°C and then in the presence of a volatile base is treated with silane" or a hydrosilane compound of the formula

where R is a hydrocarbon group containing 1-10 carbon atoms and n is an integer from and including 1 to 3, the treatment being carried out before the carrier is treated with the transition metal compound.

The silicon dioxide materials that can be used as carriers in the catalyst compositions are porous substances with a high surface area, i.e. a surface area within the range of approx. 50 to approx. 1000 m 2/g, and a particle size.-! at approx. 25-200 nm. For use in a fluidized bed process, the carrier particles are preferably ready for further division, i.e.

that the particles have the ability to break up into smaller pieces when they are used in a fluidized bed as described below and in the presence of a growing polymer (on the particles), thereby even forming many particles with low catalyst residue from a simple original carrier particle.

Any quality of carrier can be used, but microspheroidal silica particles, of medium density (MSID) and with a surface area of o 350 m 2 /g and a pore diameter of approx. 200 Å, ("G-952"), as well as silica with an average density (ID) and a surface area of o 285 m 2 /g and a pore diameter of 164 Å ("G-56"), are preferred. Other grades, such as silicon dioxide "G-968", with a surface area of 700 m 2 /g and a pore diameter of o 50-70 Å, are also very satisfactory. Variations in the melt index control and in the polymer productivity can be expected between different carrier grades.

When incorporated into a porous silicon dioxide carrier with a high surface area, as described herein, the chromo-cene phosphor compound forms active sites on the surface and in the pores of the carrier. Although the true mechanism of the process is not fully understood, it is believed that the polymer begins to grow on the surface as well as in the pores of the supported catalyst. When a polymer that has grown in a particle pore becomes large enough in a fluidized bed, it ruptures the support thereby exposing new catalyst sites in the inner pores of the support. The supported catalyst can thus be further divided many times during its lifetime in a fluidized bed and thereby increase the production of polymers with low catalyst residue, which eliminates the need for recovery of catalyst from the polymer particles. If the carrier is too large,

it can resist cracking and thereby prevent further breakdown, resulting in loss of catalyst. Furthermore, a large carrier can act as a heat source and cause "hot spots" to form in a fluidized bed system.

In the method according to the invention, the silicon dioxide carrier is heated before any treatment with the silane compound to a temperature between 100 and 300°C and preferably 105-250°C for a period of approx. 1-48 hours, which is sufficient to remove surface adsorbed water, but insufficient to cause significant loss of silanol groups due to condensation.

Silicon dioxide can also be dried by azeotropic distillation

of adsorbed surface water from the carrier. This can be done by azeotropic distillation of a slurry of the silicon dioxide carrier in an azeotropic diluent.

The hydrosilane compounds used in the method according to the present invention comprise silane (SiH^) and hydrosilane compounds with the structure:

in which R is a C^-C^ hydrocarbon residue and n is an integer from and including 1 to and including 3, preferably 1, Where a hydrosilane

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.

The preferred hydrosilane 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 can be used individually or

in combination with each other for treatment of the carrier. Treatment of the carrier with the hydrosilane compounds is carried out by bringing the hydrosilane into contact with the carrier in the presence of a base. This preferably takes place at atmospheric pressure and a temperature of the order of 60-80°C.

Higher pressures and/or temperatures can also be used. The contact is facilitated by dissolving the hydrosilane in a hydrocarbon solvent for this and then dipping the carrier in the solution and then preferably adding a base.

The solvents for the hydrosilanes include aliphatic

and aromatic hydrocarbon solvents, such as n-hexane, heptane, benzene and toluene.

About. 0.2-2, preferably approx. 0.4-0.8 mol of hydrosilane is used per mol of silanol group on the surface of the silica support. This corresponds, depending on the hydro-silane coupling used, to approx. 4-20% by weight hydrosilane compound, based on the combined weight of the hydrosilane compound and the silane carrier.

The base used in the method according to the invention,

are basic substances, preferably volatile, i.e. with a boiling point at an atmospheric pressure of -150°C. These substances have a pH in water or other suitable solvents of 11.

The volatile bases are preferably tertiary amines. These amines include e.g. trimethylamine, diethylamine, ethyldimethylamine, triethylamine, n-propyldiethylamine, etc.

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

The basic compounds can be used individually or in combination with each other. They do not contain halogens.

About. 0.1-2.0 and preferably approx. 0.9-1.1 mol of base is used per moles of silane compound used. Treatment of the support with the hydrosilane compound in the presence of the base is believed to cause a chemical anchoring of the hydrosilane compound on the support with the concomitant evolution of hydrogen gas,

as shown according to the present equation,

The following examples are intended to illustrate the present invention.

Examples 1-8

A series of 8 catalysts with and without different silane compounds was prepared to demonstrate the utility of such compounds. For comparison purposes, the catalyst in ex. 1 prepared without any silane or amine.

The support used in each catalyst was silicon dioxide of average quality with a surface area of 300 m 2 /g and an average particle size of o 200 Å. The support was first thermally treated under nitrogen for 18 hours at 200°C. The carrier thus heated contained approximately 2.5 mmol of silanol groups per gram. 8 g (20 mmol <=>SiOH) of this silicon dioxide was then slurried for approx. 100 ml of n-hexane, and approx. 1.4 g (16 mmol) of butyl silane was then added. The silane compound was thus used in such quantities that it gave 0.8 ml of silane compound per mol of silanol group on the silica support. The other hydrosilane compounds can be used in the same way in such quantities that approx. 0.2-2.0 mol silane/mol silanol group on the silicon dioxide. The slurry was then heated to a reflux temperature of approx. 75°C after which 1.9 g or 20 mmol of triethylamine was slowly added to the refluxing system over a period of 1 hour. Where used, the amine was used at a (C2^5^3N/<H>SiOH ratio within the range 0.1-1.0. The system was then allowed to reflux overnight, i.e. approx. 18 hours. Chemical anchoring of the silane compound on the support and simultaneous evolution of hydrogen was assumed to have occurred during the treatment. The system was then cooled, the silica slurry was washed in n-hexane and dried in vacuo at 80°C,

all under anhydrous conditions.

The silane compound, which was used for each carrier, is indicated in the following table I, where the ratio between the silane compound and the silanol groups is also indicated.

The supported catalyst was then prepared by slurrying 0.4, 0.8 or 1.0 g of the support, prepared as above, for approx. 100 ml of n-hexane with subsequent addition of 20 mg of bis(cyclopentadienyl)chromium to the slurry. The slurry was stirred for approx. 30 min. to allow the chromium compound to deposit on the support. The amount of carrier used for each catalyst is also indicated in Table I.

Each of the 8 catalyst systems, prepared as indicated above, was used to homopolymerize ethylene with

60-70°C in 500 ml of n-hexane under a pressure of 1.75 kg/cm<2>

and an ethylene pressure of o 12.25 kg/cm 2. Each reaction was carried out for approx. 30 min. The yields of polymer produced in each experiment are also given in Table I. The polymer produced in each case was a high density solid (-0.95). A study of these data suggests that it is only when the hydrosilane compound according to the invention is used to modify the catalyst carrier (ex. 2-8) that active catalysts are obtained. The preferred hydrosilane compounds (ex. 2 and 3) give supported catalysts with relatively high polymer yields.

Examples 9-12.

A series of 4 supported catalysts was produced by

using a silica-alumina support, to show that. such a carrier cannot be used. For comparison purposes, the catalysts in ex. 9 and 10 prepared without any silane or amine.

The carriers were silicon dioxide-alumina containing approx. 87% by weight silicon dioxide and approx. 13% by weight aluminum oxide. The carriers had a surface area of approx. 475 m2/g. The supports were thermally treated under nitrogen for 18 hours. The carrier in ex. 9 was thus treated at 600°C, while the carriers according to ex. 10-12 were treated like this at 200°C. The carriers in ex. 11 and 12 were then treated with butylsilane and triethylamine. as described in ex. 1-8, using a silane/<s>SiOH ratio of 1.0, and a (C2H5)N<=>SiOH ratio of 1.0. Table II below indicates the activation temperature for the supports and the silane compound and amine used in each example.

The supported catalysts were then prepared as indicated

in ex. 1-8 using 0.4 or 0.8 g carrier. The amount of carrier used in each catalyst is also indicated in the table

II.

Each of the 4 catalyst systems, which were prepared as described above, was used to homopolymerize ethylene, as in ex. 1-8. The yield of polymer produced in each example is also given in Table II. The polymer that was produced in ex. 9, was a solid with a high density (-0.95). A study of the data set forth in Table II suggests that a silica-alumina support is not usable according to the present invention and must be thermally activated at relatively high activation temperatures in order to

give acceptable results.

Examples 13 and 14.

A supported ethylene polymerization catalyst as described was compared with a catalyst prepared as described in GB-PS 1,253,063.

The catalyst according to the state of the art was produced by

to deposit 4% by weight of chromocene on a silica support which was thermally activated under nitrogen at 750°C for 8 hours. The carrier had a surface area of 300 m 2 /g and an average particle size of 200 Å. The chromocene compound was added to the carrier, as described above in section B in ex. 1-8.

A catalyst as described was prepared as in ex. 1-

8 using the same carrier as described above, butylsilane, triethylamine and chromocene. This support was also prepared at 4 wt% chromocene. The carrier was dried at 250°C

for 18 hours under nitrogen.

Each catalyst was then used to homopolymerize ethylene in a fluidized bed reactor of the type described in GB-PS 1,253,063. The reaction was carried out at 100°C under an ethylene pressure of 21 kg/cm 2 and at a "space time yield" of 4-5. The reaction was carried out in a period of approx. 200 hours. Hydrogen was used as a molecular weight regulator. The average results obtained, expressed in terms of the properties of the polymers produced, are described below in Table III. The polymers were produced in an amount of approx. 15-20 kg/hour. Table III also shows certain essential properties for the 2 catalysts.

The experimental results, which are described in Table III suggest

that the catalyst produced with the carrier which was thermally treated at 250°C and then treated with butylsilane according to the present invention, was essentially equivalent in terms of performance to the catalyst according to the state of the art, which was thermally treated at 750°C.

In addition to the chromocene compounds described above

are other transition metal compounds, which can be used on treated silicon dioxide carriers according to the invention, as catalysts, condensed ring compounds such as bis(indenyl) and bis(fluorenyl)chromium(II) compounds as described in US-PS 644,814.

These supported, condensed ring compounds are used in quantities of approx. 0.001-25% or more by weight, and based on the combined weight of the condensed ring compound and the silica carrier. These condensed ring compounds can be deposited on the silicon dioxide carrier according to the invention in the same way as the chromocene compounds described above. The supported condensed ring compounds can be used as ethylene polymerization catalysts. These condensed organochromic ring compounds have the structure:

wherein Ar and Ar' are the same or different and are indenyl radicals of the structure: wherein the R's are the same or different from and including C,-C1n a ± iu hydrocarbon radicals and m is an integer from and including 0-4 and x is 0 , 1, 2 or 3, and fluorenyl residues with the structure:

where the R's may be the same or different from and including C^-C^Q hydrocarbon residues and rn' and m" may be the same or different whole numbers from and including 0 to 4 and Z is H or R^ and z is 0 or 1. The R^ hydrocarbon residues may be saturated or unsaturated and they may include aliphatic, alicyclic and aromatic residues, such as methyl, ethyl, propyl, butyl, pentyl, cyclopentyl, cyclohexyl, allyl, phenyl and naphthyl residues.

The fused ring compounds which can be used on the silica supports according to the compound can be prepared as described in "Advances in Organometallic Chemistry" by J.M. Birmingham, F.G.A. Stone and R. West, Eds., Academic Press, New York, 1964, pp. 377-380.

Claims (1)

Process for treating a silicon dioxide support with a silane compound to produce an ethylene polymerization catalyst containing a transition metal, characterized in that the support is dried at a temperature of 100 - 300°C and then, in the presence of a volatile base, treated with silane or a hydrosilane compound of the formula in which R is a hydrocarbon group containing 1-10 carbon atoms and n is an integer from and including 1 to 3, the treatment being carried out before the support is treated with the transition metal compound.