FI60715C - FOERFARANDE FOER FRAMSTAELLNING AV EN OLEFINPOLYMERISATIONSKATALYSATOR - Google Patents

Description

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Patent- oeh registerstyrelsen 'Aradkan utlajd oeh «l.skrtfMn publicarad 30.11.8l (32) (33) (31) Requested« uolkau »—prioritet (71) Phillips Petroleum Company, Fifth and Keeler, Bartlesville, Oklahoma 7) 4001+, USA (US) (72) Donald Reinhold Witt, Bartlesville, Oklahoma, Benny Emil Nasser, Jr., Bartlesville, Oklahoma, USA (US) (7 * 0 Berggren Oy Ah (5¾) Process for the preparation of an olefin polymerization catalyst - Förfarande för framställning av en olefinpolymerisationskatalysator

The present invention relates to a process for the preparation of a novel olefin polymerization catalyst and to its use in the polymerization of olefins for the preparation of solid polymers.

A process for polymerizing olefins, e.g., ethylene and propylene, by contact with a chromium-containing catalyst is well known, e.g., from U.S. Patent 2,825,721 and CA Patent 853-14, which are incorporated herein by reference.

In general, this process involves contacting an olefin under olefin polymerization conditions with a catalyst containing a chromium on a support. If desired, the catalyst may contain additives such as titanium which properties of polymers. In the latter case, the catalyst can be prepared by the process disclosed in U.S. Patent 3,622,521, which is also incorporated herein by reference.

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As disclosed in the latter patent, chromium can be precipitated on a support using a combination of aqueous and non-aqueous solutions, and titanium can be precipitated on a support using a method substantially free of water. It has now been found that the catalyst can be prepared by simpler methods in an aqueous system without the use of hydrocarbons as solvents.

According to the invention there is provided a process for preparing a support suitable for use in a mixture comprising an olefin polymerization catalyst comprising mixing an alkali metal silicate and an acid together to form a hydrogel, passing a solution containing a chromium compound into contact with the hydrogel and dehydrating hydrogel to form a chromium-containing xerogel suitable as a polymerization catalyst, the chromium being in a form that can be converted to a hexavalent state after activation of the mixture.

According to a previously known method, an alkali metal silicate is added to an acid to form a hydrogel. The hydrogel is allowed to stand and washed to form a substantially alkali metal-free aqueous gel, and water is removed from the aqueous gel to provide a xerogel. The xerogel is impregnated with chromium and, if desired, additives. The saturated support is then activated by previously known methods to convert chromium to the hexavalent state and to prepare a catalyst active for olefin polymerization, wherein the olefin polymerization is carried out using previously known methods.

In the process according to the invention, the alkali metal silicate is introduced into the acid and the acid is not introduced into the silicate. Silicate is added to the volume of acid used in any suitable manner, while the mixture is suitably stirred to promote the reaction between the silicate and the acid. The alkali metal silicate is preferably introduced into the acid at a controlled rate. The silicate is added at such a rate that an average of about 0.1-15% by weight of the total amount of sodium silicate to be added to the acid is added per minute of the addition time. Addition time means the total time during which the addition is carried out, whether such addition is continuous or intermittent. For example, most of the silicate can be added quickly and the remaining part of the silicate is added slowly, as long as the average rate of silica addition is maintained.

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After gel formation, the mixture is allowed to stand. This can be accomplished in a temperature range of about 18-93 ° C. Generally, downtime longer than 1 hour is used. Chromium can be added to the hydrogel before standing at any time, during the standing period, or after the end of the standing period.

After standing, the gel is mixed to prepare a slurry that is washed with either water, ammonium salt solution, or dilute acid to bring the alkali metal content of the gel to less than about 0.1% by weight. Although various ammonium salts and dilute acid solutions can be used, the most preferred salts are those such as ammonium nitrate and ammonium salts of organic acids, which decompose and evaporate during subsequent calcination. Water is removed from the hydrogel.

Water is preferably removed from the chromium-containing hydrogel by contacting the hydrogel with an oxygen-containing organic, water-soluble compound. Azeotropic distillation can be used to separate water and organic compound from the hydrogel. If desired, water can be removed by washing the gel with a liquid oxygen-containing compound. Residual water, if used, and the oxygen-containing compound can then be removed by drying under appropriate conditions to form a xerogel.

The process according to the invention comprises the above-mentioned steps modified with respect to the process by which at least part of the chromium is added to the support. By means of the invention, at least a part of the total amount of chromium is added to the hydrogel by contacting the chromium compound with this hydrogel, whereby at least a part of the chromium can be converted to a hexavalent state during the next activation.

The chromium is introduced into the hydrogel in some suitable manner. It can be introduced, for example, into the hydrogel at any time after the formation of the hydrogel in the form of an aqueous chromium solution. If added in the form of an aqueous chromium solution, it is preferably passed after the hydrogel has been allowed to stand and washed and contacted with the organic compound used to remove the water.

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Alternatively, the chromium compound may be added in the form of a water-free chromium solution, the solvent containing an organic oxygen-containing compound which is also used to remove water from the hydrogel.

Alternatively, the chromium compound may be added as a solid or liquid which is either brought into direct contact with the hydrogel or added to a hydrogel mixture containing water and / or an organic oxygen-containing compound.

Any final chromium content of the catalyst can thus be provided in the hydrogel, with the final chromium content of the activated catalyst preferably being in the range of about 0.1 to 10% by weight. If desired, some of the chromium can be combined with the xerogel after its recovery.

The chromium compound can be contacted with the hydrogel at such a concentration that the initial concentration of chromium decreases during the subsequent processing steps, i. during washing, etc. to the desired shape. Similarly, the chromium compound can be contacted with the hydrogel in several steps, either before or after the preparation of the washed hydrogel, but before the water is separated therefrom. The chromium compound is preferably added to the hydrogel after it has been washed substantially free of alkali metal, the addition being carried out in a single step which combines the desired amount of chromium compound from the aqueous solution in the hydrogel.

The chromium compound can be contacted with the gel by mixing or soaking the gel in a chromium solution. The chromium compound is preferably added to the gel with minimal agitation. Any conventionally used chromium compounds can be used for this purpose. Examples of such compounds are chromium trioxide, chromium sulfate, chromium acetate and t-butyl chromate.

In summary, either an alkali or an acid may contain either a chromium-containing compound or an additive compound, or both. The chromium-containing compound can be added to the hydrogel at any time after its formation before the hydrogel is converted to a xerogel. Either the additive-containing compound or the chromium-containing compound or both can be added to the xerogel after its recovery.

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Preparation of the reference monitor

Catalyst I was prepared by passing a sodium silicate solution into a sulfuric acid solution containing a titanium compound to form a hydrogel. The hydrogel was washed substantially free of sodium ions with ammonium nitrate solution. The washed hydrogel was contacted with ethyl acetate using azeotropic distillation to form a xerogel. The xerogel was saturated with aqueous chromium trioxide, dried, and the chromium-saturated titanium-containing silica was activated to form a catalyst containing about 2.5 wt% titanium and about 1 wt% chromium.

Preparation of the catalyst according to the invention

The process of the invention was used to prepare Catalyst II. The method for preparing Catalyst I was used to form a washed hydrogel. The washed hydrogel was then contacted with aqueous chromium trioxide. The chromium-containing hydrogel was then contacted with ethyl acetate to prepare a xerogel according to the method used to prepare Catalyst I. The xerogel was then activated to form a catalyst containing about 2.5% by weight titanium and about 1% by weight chromium.

The above catalysts, prepared under substantially identical conditions except for a characteristic feature of the invention, were used separately for the polymerization of ethylene at a temperature of about 110 ° C in a process in which the substance to be treated was in particulate form under substantially similar conditions, with the following results:

Catalyst Polymerization, g / g Polymer Melt Index I 4910 0.54 II 5000 5.5

It is apparent from the above values that the process of the invention provides a catalyst that can be used to prepare a polymer having a superior melt index.

When carrying out the process according to the invention, it is preferred that the silica content of the hydrogel is in the range from about 5 to 12% by weight and that the gelation is carried out at a temperature in the range from 0 to 70 ° C at a pH of about 3 to 8.

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The hydrogel is preferably allowed to stand for at least 2 hours at a temperature in the range of about 25-100 ° C.

The invention can be carried out using organic compounds such as ethyl acetate, acetone and the like to dehydrate the hydrogel.

Activation of the catalyst is preferably accomplished by activating the catalyst at a temperature of about 870 ° C for about 5 hours.

This catalyst is very suitable for polymerizing ethylene at a temperature of about 110 ° C and generally at polymerization temperatures up to about 260 ° C, as disclosed in the aforementioned U.S. Patent 3,622,521.

The method of the invention may be used as the sole method of impregnating the support with chromium, or in combination with other methods of impregnating the support with either chromium or an additive either before, simultaneously with or after the use of the method of the invention.

Claims (2)

7 60715 1. A process for the preparation of an olefin polymerization catalyst in the form of a chromium oxide, which contains a chromium oxide ring, a coloring agent which is chromium-free or hexavalent, and which is a silica gel, which forms an alkali metal av en kiseldioxidhydrogel; aldra hydrogel; avlägsna aikaiimetalljoner; and the hydrogel account of the xerogel genome of the bromide and the organic color of the chromium, the color of the chromium oxide, the color of the chromium, the color of the chromium, iri-förlivas i kiseldioxiden under det att kiseldioxidon föreligger i form av hydrogel. A process for preparing an olefin polymerization catalyst by attaching to a silica gel a chromium compound which can be converted to chromium oxide in which at least a portion of the chromium is k-valent to silica prepared by adding an aqueous solution of an early metal silicate to an acid to form a silica hydrogel; standing hydrogel; removing alcohol metal ions and converting the hydrogel to a xerogel by contacting it with a water-soluble organic oxygen compound, removing water from the hydrogel and then heating the resulting composition to convert chromium to chromium oxide in which at least a portion of the chromium is hexavalent, the chromium compound being is a hydrogel. Process according to Claim 1, characterized in that an aqueous solution of the chromium compound is added to the hydrogel after the hydrogel has been washed free of alkali metal ions. Use of a polymerization catalyst prepared by a process according to claim 1 or 2 in the polymerization of ethylene. 2. The method according to claim 1, which comprises the addition of water to a chromium-free solution, is determined to be based on an alkali metal ion.