DE1442814B - Process for producing an olefin polymerization catalyst - Google Patents

Description

Chromium oxide support catalysts are in their suitability Olefins, especially ethylene, are valuable Testing polymers to polymerize is known. However, certain polymerization processes in which a chromium oxide-like catalyst used tends to be a polymer having a molecular weight to produce that is higher than is desired for certain purposes. Such polymers with high molecular weight show a correspondingly low melt index, which is a measure of the extrudability or processability of the polymer. An example of such a procedure is that Particle Shape - Polymerization Process (Reaction in a non-solvent below the softening point of the polymer), which is economically attractive, but in which polymers of unsuitable or undesirable molecular weight.

The melt index is generally a function of the molecular weight of the polymer. There is no optimum melt index as the end use of the polymeric material requires specific properties. For example, a polyethylene door tube requires a melt index that is relatively low while A door bottle production or door decoration purposes suitable polyethylene a slightly higher Melt index required. As a result, a polyethylene polymerization process is in which polymers of varying but controlled melt index are produced are of particular value. This is especially important if the process has other important properties, such as e.g. B. high productivity or simplified and economical operation.

From French patent specification 1 190 591 it is already known that chromium oxide is applied to silica gels for the production of polymerization catalysts, using a gel which has an average pore diameter of at least 65 and a surface area of at least 450 m ² / g, and that then the mass is activated at temperatures up to 815 ° C. This method is fundamentally different from that of the present invention. In the French patent, for example, a catalyst support with a surface area of at least 450 m ² / g, a pore diameter of at least 65 Å, preferably from 75 to 150 Å, and an activation ^{temperature of 230 to 815 °} C., preferably of from 230 to 815 ° C., during the treatment of the catalyst 400 to 620 ⁰ C, described.

In the German Auslegeschrift 1051004 in Column 3/4 as a preferred support for a chromium oxide impregnated olefin polymerization catalyst a mixture or a compound of silicon dioxide and aluminum oxide described, wherein it is stated that a silicon dipoxide carrier SS with a small surface area and large pores is more effective than a carrier with an extremely large one Surface and small pore size.

However, it could not be inferred from these patents that there is a specific, narrow, very critical range for the activation temperature as well as for the pore diameter and surface size within which a particularly high melt index of the polymer is obtained. High melt index polymers have a lower molecular weight and such polymers are easier to extrude and process. Ks is a particular advantage that with the catalyst that can be prepared according to the invention, such easily processable polymers can be prepared directly without the need for post-treatment of the polymers, for. B. is necessary by pyrolysis.

The crfiiidiingsgc accordingc method for the preparation of an olefin polymerisalion catalyst by applying chroynoxide in a manner known per se to a silica gel and subsequent activation consists in that a silica gel is used which has a density of less than about 0.2 g / ml, a pore diameter of 200 to 500 Å and a surface area of 250 to 350 m ² / g, and that the product obtained is then activated at 870 to 935 ° C.

It has been found that polymers which have been produced in the presence of the catalyst which can be produced according to the invention Much higher melt index than polymers that, in the presence of similar catalysts, obtained according to the previously known methods.

A high purity silica gel with an oil absorption of about 300 kg / 100 kg is particularly useful as a carrier of the chromium oxide catalyst according to the invention.

The product of silica-chromium oxide with a content of 0.01 to 50 and preferably 0.5 to 5.0 percent by weight of chromium (Cr) can be prepared by conventional measures, e.g. B. Impregnation and other processes as detailed in U.S. Patent 2,825,721. The activation of the Chromoxydkatalysators is usually stirred at temperatures of about 538-1100 ⁰ C and preferably from about 650 to 930 ⁰ C.

The catalyst obtainable according to the invention is for use in the polymerization of olefins with C ₂ to C ₈ including monoolefins with up to 8 carbon atoms and no branching closer to the double bond than in the 4-position, diolefins, e.g. B. butadiene and isoprene, conjugated diolefins and copolymers thereof, such as. B. ethylene-butylene and ethylene-propylene, suitable. It is particularly useful for the polymerization of ethylene in the known particulate or suspension type of polymerization process.

The following examples serve to further illustrate the invention.

Example I.

An amount of 40 g of Davison "Syloid 244" cicelic acid gel with a surface area of about 250 m ² / g, a pore volume of about 2.2 cni ³ / g and a pore diameter of about 350 Å was mixed with 160 ml of aqueous solution with a Content of 0.786 g of dissolved CrO ₃ impregnated. The slurry obtained was dried to 149 ⁰ C, reduced to a particle size corresponding to a number of stitches per square centimeter 576-1600 and hei 852 ⁰ C activated for 5 hours. The catalyst contained 1% chromium.

A 0.0844 g portion of the catalyst prepared as above was placed in a 1.3 liter stainless steel reactor equipped with a stirrer along with 454 g of n-pentane. The reaction vessel was closed, the temperature adjusted to 99 ° C., and sufficient ethylene was passed in to maintain a pressure of 3 tons, 6 kg / cm ² . After 80 minutes the supply of ethylene was stopped.

brochcn, the reaction vessel opened to the volatile Blow off ingredients and place the particulate polymer in an oven at reduced pressure overnight Print dried. The yield of polymer cream was 104.5 g, which corresponds to a yield of 1240 g polymer cream / g Catalytic converter. The polymer had a high load shinel index of 8.5

Various other polymerization approaches were carried out, the catalyst base and the Activation parameters have been changed. With the exception of these changes, the other approaches were carried out in a practically identical manner to that described above. The results are summarized in the following table.

Influence of catalyst support and activation temperature on ethylene polymerization

454 g of Pcntane as a diluent - 31.6 kg'cnr reaction pressure 1300 ml reaction vessel - 99 C reaction temperature

10
U

approach
No. Catalyst activation
temperature
C. reaction time
Minutes yield
8 / g *> High-stress sea melt index
of the polymer ¹ ) "Syloid 244" -Tra ger, 1.0 ° / ₀ chromium
A, surface 250 m ² / g) (Pore diameter 350 1 800 7.9 2 850 8.5 3 900 9.9 4th 950 7.6 5 1000 1460 1.3 100 1240 80 1250 150 1340 HO 900 100

Silicon dioxide — aluminum oxide, 1.25% chromium (approximate pore diameter 70 A, surface area 5IOm ² / g)

6th 760 7th 816 8th 871 9 899

70

90

150

150

975

1060

900

380

Silicon dioxide, 1.0% chromium (approximate pore diameter 190 Å, surface 250m ² / g)

649
760

90

75

3050
2330

*) Grams of total catalyst.
') ASTM-D 1238.

1.2
2.5
2.8
2.6

1.4
2.6

The values show that the catalyst made from "Syloid 244" is a high polyethylene Melt index results.

The chromium oxide incorporated in the catalyst according to the invention should preferably be at least some of the ι chromium contained in the 6-valent state.

The pore diameter, as indicated above, was determined as follows: It was the standard BET surface area was measured. The pore volume was then determined according to the method of W. B. I η η e s, Analytical Chemistry, 28, 332 (1956), measured and the pore diameter then from the determined by the following equation:

,. , Pore volume (in cm ³ / g) ■ 4 x 10 * pore diameter (in A) =

Example 2

A series of experiments was carried out in which ethylene was polymerized to a solid polymer at 104 "C and 24atü. The reaction time in each experiment was between 70 and 90 minutes , 1 percent by weight aluminum oxide) with a surface area of about 350 m ² / g, a pore diameter of about 200 Å and a bulk density of about 0.15 g per minute

Surface (in m ² / g)

manufactured. Each catalyst contained about 2 weight percent chromium. Each catalyst was in activated practically anhydrous air for 5 hours, and the activation temperature was varied, the .Effect of the activation temperature on the catalyst productivity and the melt index of the To show polymer. The catalyst concentration in the reaction mixture was 0.06 g per 3.3 kg n-pentane. Ethylene was fed at a rate of 8 percent by weight based on n-pentane. The following results were obtained:

ainlwiinrakiivic- productivity Schmcl / .inikw runjislcnipciatiir kg polyinci ASTM-I) 1238 C. per kg of Kntah Niitor Hcdinpuni! 1·' 538 2620 4.7 3790 3.7 593 4860 4.5 4330 4.6 649 4190 7.1 4790 7.2 3970 6.8 704 4 (XX) 12.0 4250 10.2 4940 10.0 760 3620 13.5 3680 14.0 816 4820 16.8 4610 17.0 870 4440 18.3 43 (X) 21.5 935 4050 25.5 4310 25.3 982 1970 13.4

The above data show that when the activation temperature rises from 538 to 649 C, a significant increase in the intensity of the obtained Polymer was obtained. The increase continued as the level of activity continued to rise 935 ° C rose, but above this the melting index began to fill again.

Claims (2)

Patent claims: 1. A process for the preparation of an Olefinpolymerisat ionskatalysatnrs by applying Chromium oxide in a known manner on a silica gel and subsequent activation, characterized in that a Silica gel is used 'that has a density less than about 0.2 g'nil. a porcelain knife of 200 to 5 (K) Å and a surface area of 250 to 350 mVg, and that subsequently the product obtained is activated at 870 to 935.degree. 2. The method according to claim 1, characterized in that that the product is activated so long that at least part of the Chmmo.wds is in 6werligen condition.