DE2242752A1 - PROCESS FOR POLYMERIZING AETHYLENE - Google Patents

Description

> - £ OlS ©: B3SBSCHI.i: iSS: HEIM:

31 august 19-22

MKISZSICHSHl

S-457

HBSSiLBQH- & BSfEIiOPMSM GOMPiJIY Pittsiburgh, Pennsylvania, iLst.A.

¥ experienced Kimm polymerizing iron ethylene

this application becomes priority void 3 September 1971 .aias eier WSA-JPateiitiaaiineläiiaag Serial Ιο. 177 864 in Aiisprucli

The application for ireicseliietleiie BlasvceiciioriniiaiigsTerfahren is continued , inevitably feaekt in the desired shape, in the walls of the envelope to the outside blessing a lorira ιτ, οη (the solitary shape "aiiifgeiblasen". Bas JEüllbel is dia? When the bolyethylene bucket emerges from the die _{9 it} tends to swell, whereby its walls become thicker than the mistress openings also in this IPaIIe the diameter of the melted n extrudates _; Larger than the diameter of the compression molding »The ratio of the diameter of the extrudate to the diameter of the extrusion opening is called

ΊΙΙΙΙΟΐ (Olli!) Ii lOl Il ■ · LIXIGBUHIIJ EBIMHIBT

XAMKi 11111. "y» »3tiiii»! BAiKK ai'0a »iOBatw aciro» »ms * ·« · loiiioHnciiomoi mDxchii »im '«

Denotes swelling ratio of the polymer.

For successful blow molding, it is crucial that nan is able to keep the swelling ratio of the polymer under control during this process step. If ζ · Β. two polymer batches which are processed by blow molding have different swelling ratios, this leads to a difference in the finished weight of the product manufactured by blow molding if the machine conditions are not matched to the difference in the swelling ratio. Therefore, there is a technical need to provide controlled "source ^11" polyethylene.

Ke also adds that polyethylene, which is suitable for one application, does not necessarily have to be suitable for another application. To the need for polymers with different swelling ratios To satisfy this, a method of controlling the amount of swelling of the polymer must be developed.

The invention is therefore based on the object of providing a linear low-pressure polyethylene with the desired swelling ratio by using a method for controlling the polymerization of ethylene.

According to the invention, this object is achieved in that one the hydrogen concentration and / or the activation temperature of the catalyst in the polymerization of the Ethylene on a chromium oxide catalyst containing a silica support controls.

The production of low pressure polyethylene by polymerizing of ethylene in the presence of chromium (VI) oxide on silica is described in US Pat. No. 2,825,721, to which reference is expressly made here.

The catalyst can be impregnated by known methods, for example by directly mixing the solid components and the like. To achieve the optimum activity, the catalyst mixture is made of chromium oxide and silica usually preferably for sufficient

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Period of time heated to an elevated temperature to complete the activity of the catalyst for the polymerization reaction. The catalyst is preferably heated under non-reducing conditions Conditions in an atmosphere of "for example oxygen, air, nitrogen, carbon dioxide, helium, argon, krypton or xenon. Reducing gases such as hydrogen or carbon monoxide may be included in the activation atmosphere if the residence time of the catalyst in it is so "limited is that there is no substantial reduction in hexavalent chromium; however, the presence of such .gases and generally the presence of reducing agents is usually undesirable. . -

The temperature and duration of the activation can be set within) further limits fluctuate and are closely related to each other by "longer activation times at lower temperatures are required and vice versa. By marrying Catalysts made from solid silica with solid chromium oxide can be activated at lower temperatures as catalysts, which are produced by impregnating silica with aqueous solutions of chromium compounds. Catalysts made by mixing the dry ingredients will usually be at least 177 ° G and not substantially activated above about 816 ° C. By soaking in silica Catalysts made with an aqueous solution of a chromium compound are usually used at temperatures of at least 232 ° C, but also not above 816 ° C. The activation time is in the range of 1 second at the highest temperature up to 50 hours or more at the lowest temperature.

The chromium oxide catalyst can be prepared by powdered silica with a solution of chromium oxide or a compound which can be converted into chromium oxide by calcination soaks, then dries, and 3 to 10 hours or longer activated at temperatures from 232 to 816 ° C, preferably from 399 to 816 ° C. The activation is carried out, in- ' by heating the catalyst in a gas stream that

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preferably contains oxygen and is practically anhydrous. The dew point of the activating gas should be below 24 ° C and preferably, be below -18 ° C. Inert gases such as carbon dioxide and nitrogen can be used for activation.

The swelling ratio of ethylene polymers is decisive for determining the usability of the ethylene polymer in question for a specific processing method. A difference of 4 ° in the swelling ratio can make the polymer unsuitable for certain technical purposes. It has been found that the swelling ratio of polyethylene is correspondingly reduced by increasing the hydrogen concentration in the polymerization zone when using a chromium oxide-silica catalyst and is increased accordingly by reducing the hydrogen concentration in the polymerization zone. It has also been found that the swelling ratio of the polyethylene is significantly increased by lowering the activation temperature of the chromium oxide-silica catalyst used for the polymerization of the ethylene. When the activation temperature is increased, the swelling ratio of the resulting polyethylene is reduced. If, therefore, the activation temperature of the catalyst is lowered and the hydrogen concentration in the polymerization zone is increased, the end result is a polyethylene with a swelling ratio which is between the swelling ratio which is established when using a catalyst activated at the lower temperature and the swelling ratio which occurs when using a catalyst activated at a higher temperature at an increased hydrogen concentration.

In controlling the continuous ethylene polymerization process the swelling ratio of the polymer can be determined with the aid of conventional analyzers which are included in the operation switched on or independent of it, can be determined, for example, for the determination of the melt index are used, and the activation temperature of the catalyst and / or the hydrogen concentration in the poly

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309810/1034 ORKlNAL INSPECTED

The merization zone can be adjusted to the measured values in such a way that a product with the desired swelling ratio is obtained. It was found, for example, that in the production of a linear polyethylene with a Sehmelzindex of 0.3 in the presence of a Ghromoxid-Iieselsämrekatalysators an increase in the hydrogen concentration in the reaction mixture 0.3 mol percent leads to a mfickgang the source ratio of 12.5 $ . If, in the manufacture of the same polyethylene, the operating temperature of the catalyst is reduced from 816 to 704 ° C., the swelling ratio increases

Example 1 '"_.

In this and the following examples, ethylene is polymerized in a 189 1-capacity Seaktionssehlange with a clear width of 15 cm. Ber! Catalyst "consists of chromium oxide on silicon dioxide and contains 2.0 percent by weight OrO, and Cr ₂ O," with a medium concentration of silicon dioxide of 97.0 percent by weight. The maximum concentration of Cr pO ^ in the catalyst! Is O ₃ 2%, and the catalyst contains other YezronreäTnigmigeje in lower concentrations.

The catalyst is activated for 4 strands! At an elevated temperature for at least 8 hours in the fluidized bed at 816 G, the activated catalyst is cooled and stored in a storage container of nitrogen.

In the present example, ethylene is continuously used in the reaction mixture in the presence of isobutane at 104 ° C. an overpressure of 39 _a 2 kg / em and an average Yerweilzeit of 3 »1 hour polymearlsierib. The ethylene concentration in the Isolbiataai is 4. <»52 percent by weight, and in the isobutane a concentration of 0.30 percent by weight of hexene is innegeteia. Catalyst activated at 816 ° C is fed to the EeaktioMsseialaiELge at such a rate that the catalyst coaisiemibraitioii remains camouflaged in the Eeaktionszone at 0.1145 € rewi © Jh.tspr © Eeiit k © M ©.

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The resulting linear polyethylene is continuously obtained from the reaction coil in a yield of 22,900 kg per kg of catalyst. The melt index and the swelling ratio of the polyethylene are determined by extrusion of the linear polyethylene through an extrusion opening of 2.10 mm diameter at 190 ° C. in accordance with ASTM test standard D-1238-57T ¹ . The melt index is 0.30 and the swelling ratio is 1.56.

Example 2

Example 1 is followed, but the catalyst is activated at 704 ° G. The linear polyethylene obtained continuously from the reaction coil has in this case, determined according to Example 1, a melt index of 0.30 and a swelling ratio of 1.65.

A comparison of those obtained in Examples 1 and 2 Swelling Ratios shows that the swelling ratio increases by 5.8 # when the activation temperature of the catalyst changes 112 ° C decreases.

Example 3

You work according to Example 1, but with a Wasserst off concentration of 0.29 mole percent of the reaction mixture in the response queue. In this case, the linear polyethylene continuously withdrawn from the reaction coil, determined according to Example 1, a Sehmel index of 0.30 and a swelling ratio of 1.40.

A comparison of Examples 1 and 3 shows that the swell ratio of the product by introducing 0.29 mole percent Hydrogen in the reaction mixture decreases by $ 10.3.

Example 4

One works according to Example 2 and in this case a linear polyethylene with a melt index of 0.27 and a swelling ratio of 1.63.

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Example 5

Example 4 is used but with a hydrogen concentration in the reaction mixture of 0.31 mol percent., The linear polyethylene continuously withdrawn from the reaction coil in this case has a melt index of 0.27 and a swell ratio of 1.54.

A comparison of the results of Examples 4 and 5 shows that by increasing the hydrogen concentration in of the polymerization zone, the swelling ratio is reduced by $ 5.5 has been.

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Claims (8)

Gulf Research & Development Company S-457 Claims 1 J A process for polymerizing ethylene in the presence iines chromium oxide-silica catalyst, characterized in that one determines the swelling ratio of the polyethylenes produced and the Aktivierungsteinperatur of the catalyst and / or the hydrogen feed rate accordingly adjusts to the polymerization, is that a polyethylene with the desired swelling ratio forms . 2. The method according to claim 1, characterized in that a polyethylene with the desired swelling ratio by Setting the activation temperature of the catalyst generated according to the measured value of the swelling ratio. 3. The method according to claim 1, characterized in that a polyethylene with the desired swelling ratio by Adjusting the hydrogen feed rate to the polymerization zone according to the measured value of the swelling ratio generated. 4. The method according to claim 1, characterized in that a polyethylene with the desired swelling ratio by Adjusting both the activation temperature of the catalyst as well as the hydrogen feed rate to the polymerization zone generated according to the measured value of the swelling ratio. 5. The method according to claim 1, characterized in that the swelling ratio of the resulting polyethylene through 309810/103 Reduction of the activation temperature of the catalyst increased » 6. The method according to claim 1, characterized in that the swelling ratio of the resulting polyethylene through Increase the activation temperature of the catalyst 7. The method according to claim 1, characterized in that the swelling ratio of the resulting polyethylene by increasing the rate of hydrogen feed to the polymerization zone belittles. 8. The method according to claim 1, characterized in that one increases the swelling ratio of the resulting polyethylene, by reducing the hydrogen feed rate to PoIymerisations "zone.. ■ ■ _ 9 _ 309810/1034