DE2622755A1 - METHOD FOR MANUFACTURING POLYOLEFINS - Google Patents

Description

Gelsenkirchen-Scholven, May 10th, 1976

Veba-Chemie Aktiengesellschaft Gelsenkirchen-Scholven

Process for the production of polyolefins

The polymerization of 1-olefins with Ziegler catalysts from transition metal compounds from subgroups IV to VIII of the periodic table and organometallic compounds from I to III. Main group has long been known. It has also long been known that it can be advantageous to apply the transition metal component to a catalyst support. Thus, in DAS 12 14 001, oxides of metals of V. or VI. Subgroup of the periodic system in combination with Alumniumalkylen _t described example is given as a chromium oxide catalyst on silica together with aluminum triisobutyl. The catalyst support should have as large a surface area as possible between about 1 and about 1,500 m / g. They often have such high molecular weights that the customary processes for further processing the polymers into molded parts are impossible due to insufficient melt flow. Furthermore, the polyolefins obtained with the known supported catalysts have extremely high ash contents as a result of the extremely low catalyst activity.

Recently, a process described in DOS 15 20 792 for the polymerization of ethylene has become known, in which chromium oxide

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activated on silica and alumina as a carrier with reaction products of alkyl compounds of an element of group III b of the periodic table with a diolefin. This catalyst is used at temperatures from 120 ⁰ C to 200 ⁰ C and

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Pressures of about 10 kg / cm to 40 kg / cm of ethylene in an inert Solvent polymerized, whereby higher molecular weights should be achieved than by previously known processes «Over physical properties of the catalyst support and application-related The Offenlegungsschrift does not disclose any properties of the polymers obtained with this catalyst refer to. The required high polymerisation temperatures bring it with it that the resulting polymers are obtained in solution from which they are laboriously obtained have to.

Furthermore, it has been proposed in DOS 23 14 412, a Chromium oxide catalyst made by calcining on silica gel chromium trioxide applied or aluminum silicate and activation with aluminum alkyl has been produced, a further reduced Transition metal compound, preferably a titanium halide. The advantage of this process is said to be that in this way polymers with narrower molecular weight distributions are obtained than without the addition of a titanium halide, wherein the properties of the polymers by varying the catalyst composition can be adapted to the respective application requirements. However, this procedure harbors a very significant disadvantage in itself - apart from the fact that there is a very precise dosage of the chromium and titanium components arrives - because with the technical application of this process it is not always foreseeable in which proportions the two transition metal components form polymers, as there are slight fluctuations in the production conditions, for example with regard to the purity of the starting materials or the reactor temperature for the two catalyst components can have different effects, so that the reproducibility of the polymer composition is not guaranteed is. Furthermore, a perfect homogenization of the so produced

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Asked polymer powder is often not given because the two catalyst components polymer powder with different Properties such as structure and size distribution of the polymer »grains result in»

The object was therefore to find a method which avoids the disadvantages of the previously known methods. It was found that chromium oxide-containing supported catalysts give polymers with favorable processing and finished part properties can be produced if you look at the properties of the catalyst support and the production of the supported catalysts has very specific requirements.

The invention therefore relates to a process for the production of polyolefins with high molecular non-uniformity, which are particularly suitable for processing into molded parts by the extrusion process, by polymerizing ethylene, optionally mixed with other! -Olefins and with the addition of hydrogen, with catalysts which have been obtained by thermal treatment of chromium (VI) oxide on silica gel as a support and subsequent reaction with an aluminum alkyl, in inert hydrocarbons as diluents at pressures of 1 to 100 atm, preferably 10 to 40 atm and temperatures of < 100 ⁰ C, characterized in that a silica

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gel with a specific surface area of 100 m / g to 350 m / g is used, which after its impregnation with chromium (VI) oxide is subjected to a thermal treatment at temperatures of 550 ^° C. to 850 ^° C.

Those silica gels are preferably used as catalyst supports, which have the highest possible degree of chemical purity, an average pore diameter of at least about 50 S, average Particle sizes from about 20 / U to 120 μ and good flowability of the powder. Silica gels of this quality can be produced by spray drying a silica sol. It however, it is also possible to use silica gels whose properties are somewhat outside of these specified specifications. Is of particular importance in the method according to the invention

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the specific surface area of the silica gel used; she

should be.

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should not be smaller than 100 m / g and not larger than 350 m / g

The catalyst carrier is advantageously impregnated by adding an aqueous chromic acid solution in such an amount that the aqueous solution is completely adsorbed by the silica gel without the powdery nature of the silica gel being impaired. The volume of aqueous chromic acid solution that can be adsorbed in this way depends on the pore volume of the silica gel and is generally hardly less than 20% by weight, based on the silica gel. The amount of chromic anhydride used to prepare the aqueous solution is preferably such that the loading of the silica gel with chromium oxide is between about 0.3% by weight and about 3% by weight, based on the anhydrous silica gel. The so impregnated silica gel is subsequently heated at temperatures of 550 ° C to 850 ⁰ C in dried air, wherein the duration of the thermal treatment is not critical. It can range from a few minutes to a few hours. The calcination temperature influences: the average molecular weight of the polymers prepared with the catalyst under otherwise identical circumstances in such a way that lower average molecular weights are obtained at a higher calcination temperature. Before the catalyst is used for polymerization, it is activated by adding organoaluminum compounds. As an organoaluminum compound, for example, triethyl, triisobutyl, isoprenyl, tri-n-octyl, tri-n-tetradecyl or tri-n-octadecyl aluminum can be used. Of the trialkylaluminum compounds, those whose alkyl groups have a carbon number of J = 8 are preferably used.

The polymerization can be carried out either in the gas phase or in suspension using an inert hydrocarbon which is liquid under the process conditions. In general, pressures in the range from 10 atm to 100 atm and temperatures between about 50 ^° C. and about 90 ^° C. will be selected , So that the

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Polymers are obtained directly as free-flowing powders. The activity of the catalyst prepared according to the invention is so high that measures to remove the catalyst components from the polymer are not necessary.

The polymers prepared according to the invention have excellent properties Properties on. With extruders, even at high throughputs, they are free of melt fractures to form molded parts of high practical value processable. For example, hollow bodies produced from the polymers according to the invention by the blow molding process are iron shows an exceptionally favorable relationship between stress cracking resistance and rigidity. From the inventively produced Pipes made from polymers are characterized by their excellent fatigue strength.

It was surprising and in no way to be foreseen that such advantageous application properties of the invention produced polymers determined by the specific surface area of the silica gel used as a catalyst support will. When using a silica gel with a specific surface area smaller than that according to the invention, only one is very high low chromium loading of the support is possible, provided that sufficient chromium is used during the polymerization shall be. This gives polymers with a relatively high silica gel content. If you choose a higher load of the Silica gel, then the chromium is only partially used during the polymerization and you get polymers that are relatively have a high chromium content. The disadvantageous consequences of this are that you get polymers, either as a result of their high silica gel content tend to increase the absorption of humidity, which is formed during further processing of bubbles in the melt, or as a result of their increased chromium content in the further processing in undesirable Wise greenish discoloration. Furthermore, during processing into molded parts, nuisance from odors can occur, which can still adhere to the finished molded parts in a disruptive manner, so that their utility value is considerably reduced.

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The aging stability is also considerably reduced compared with the product manufactured according to the invention. When using silica gels with larger specific surface areas than the specific surface areas according to the invention, catalysts are obtained which, compared to the polyethylenes according to the invention, produce the average molecular weight of which is too high for processing in conventional extruders. Ethylene polymers with improved melt flow can only be achieved when using these catalysts not according to the invention by drastic measures to regulate the molecular weight during the polymerization, for example by using high partial pressures of hydrogen. Economically acceptable space-time yields cannot be achieved in this way. Of Kachteil it is further characterized in that as by-product for technical applications worthless niedermolekule? It is made of polyethylene in a considerable amount, which is obtained solved for the greater part in the liquid suspension medium, thereby making a return of the suspending medium after separation of the powdery polymer impossible in the polymerization reactor . The high molecular weight ethylene polymers also have disadvantageous properties for their use as plastics, such as high ash contents, high swelling ratios of the melt during processing by extrusion and poor performance properties of the hollow bodies made from these polymers such as low drop resistance, discoloration and odor formation.

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example 1

a) Preparation of the catalyst component A.

5 kg of silica gel with a specific surface area of 190 m ² / g (trade name silica K 322 from DEGUSSA) were mixed with a solution of 41.6 g of chromium (VI) oxide in 1667 ml of water for 5 minutes in a fluid mixer mixed with a stirrer speed of 950 min. ^{The silica gel impregnated in this way was then heated to 800 °} C. in the course of 30 minutes in a rotary tube furnace with dried air in countercurrent (superficial speed: 0.04 m / sec) and left at this temperature for 15 minutes.

b) Polymerization of ethylene ^A.

Into a steel autoclave of a 2-1 Hexanschnittes 63/80 ⁰ C and 0.56 g of tri-n-octyl-aluminum (catalyst component B) were added under nitrogen for 1 1 and 0.170 g of catalyst component A prepared according to 1a), melted in a Glass tube. After displacing the nitrogen with ethylene, 6.4 atmospheres of hydrogen were injected and then ethylene up to a total pressure of 32 atmospheres. At the same time, the reactor contents were heated to 75 ⁰ C. The small glass tube was then destroyed by switching on the stirrer, whereupon the components A and B formed the catalyst. The polymerization was carried out for 1 hour at 75 ^° C. and a stirrer speed of 1000 min, the total pressure being maintained by forcing in ethylene. The reactor was then depressurized and, after the reactor contents had cooled, the polyethylene formed was filtered off and dried. The yield of polyethylene was 367 g, corresponding to 23.9 kg per mg atom of chromium. The viscosity number according to DIN 53 728 was 340 cnr / g, corresponding to an average molecular weight Μ _γ of 147 · 10 ^. The molecular non-uniformity (Μγ / ^ - Ι) was determined to be 16 by gel chromatography. The filtrate contained 1.7% of the total polymer in dissolved low molecular weight polyethylene.

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Example 2

With the catalyst component A prepared according to Example 1a and tri-n-octylaluminum as catalyst component B, ethylene was continuously polymerized in a stirred tank. A hexane fraction in the Sicdelage between 63 and 80 ° C. was chosen as the suspension medium. The concentration of catalyst component A in the reaction vessel was 133 mg / l, that of component B (tri-n-octylaluminum) was 200 mg / l. The stirred reactor was atm with a total pressure of 35 and operated at a bottom temperature of 75 ⁰ C. At a level in the reactor of 300 l, the mean residence time of the catalyst in the reactor was two hours; the stirrer of the polymerization vessel was operated for 150 minutes. The two catalyst components were only metered into the suspension medium shortly before entry into the reactor, in order to ensure that the catalyst residence time in the suspension medium was as short as possible. Hydrogen was used to set the desired molecular weight; the hydrogen concentration in the gas space of the polymerization reactor was approx. 25% by volume. The powdery polymer formed in the reactor was separated from the suspension medium on a centrifuge and dried ^{at about 80 ° C. in a partially evacuated container.}

A polymer produced in this way had the following properties:

Melt flow index MFIΊ90 / 5 ^x = 0.35 g / 10 min

Viscosity number I according to,

DIN 53 728 = 430 cm ^ / g

mean molecular weight M = 193 x 10 ^ density at 23 ° C = 0.960 g / cm ³

Molecular uniformity U = 34 (U = M _w / M _n -1, with the molecular weights determined according to the gel chromatographic method
became)

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The consumption of catalyst component A under the above-mentioned test conditions was 1,200 mg / kg PE; this resulted in a proportion of 7.8 ppm of Cr ₂ O ₁ in the polymer. The n-heptane-soluble, low molecular weight fraction in the centrifuge filtrate was 2.3 %.

The polymer was able to form large hollow bodies and with high throughput in the entire processing area without melt fracture Pipes with a completely smooth surface are processed. Particularly The very good mechanical properties of the finished parts should be emphasized, in particular the very good resistance to stress cracking with high rigidity and the good drop resistance of the blown hollow bodies *

Stress crack resistance at _. _{Λ nnr} . . 50 ⁰ C, according to ASTM-D 1693-70 "* ' ^{υυυ η}

Elasticity di
DIN 53 457

Modulus of elasticity according to = 20 600 kp / cm

Tensile impact strength according to = 580 cmkp / cm DIN 53 448

Example 3

⁰ A propylene polymerized - in the manner described in Example 2 was manner to the product produced according to Example 1a catalyst component A and tri-n-octyl aluminum as a catalyst component B of ethylene with addition of 15 wt.. The concentration of catalyst component A in the reactor was 47 mg / l, of tri-noctylaluminum 71 mg / l. Propylene had a strong molecular weight regulating effect, so that for an average molecular weight of Ry s = 157. 10- ⁵ only 1 vol .-% Vfesserstoff was required. The consumption of catalyst component A was 520 mg / kg PE ^ 3.4 ppm Cr ₂ O. A polymer produced in this way had the following characteristics:

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-Vb-

Melt flow index MFI 190/5 = 0.56 g / 10 min according to DIN 53 735

Viscosity number I according to = 360 cm ^ / g DIN 53 728

average molecular weight M _v = 157 · 10 ³ Density at 23 ⁰ C = 0.952 g / cm ³

molecular non-uniformity U = 17

The polymer could be extruded without difficulty at a high output to form pipes and large hollow bodies with completely smooth surfaces. Processing into spiral tubes also resulted in smooth surfaces without cracks in the edges. The processing performed in accordance with DIN 8075 internal pressure creep test showed, for example, the test voltage of 3 "0 N / mm and a testing tempera door of 80 ⁰ C, a rupture strength of 509 h; the requirement according to DIN 8075 is 170 hours under the above test conditions.

V e rp; weight example 1

a) Preparation of the catalyst component A.

5 kg of silica gel with a specific surface area of

663 m / g (trade name Silica F-5 from Ketjen) were, as described in Example 1a, impregnated with 41.6 g of chromium (VI) oxide and thermally treated.

b) Polymerization of ethylene

The procedure was as in Example 1b, but using 0.170 g of the silica gel with the specific

Surface area of 663 m / g of catalyst component A produced and 1.69 g of tri-n-octylaluminum (catalyst component B). In order to achieve a similar average molecular weight of the polyethylene as in the polymer obtained according to Example 1b, but at the total pressure of 32 atm a water

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partial pressure of 25.6 ata can be set. The yield of polyethylene was only 58 g, corresponding to 3.8 kg per mgAtoni chromium. The viscosity number according to DIH 53,728 was 320 cnr / g, corresponding to an average molecular weight M of 136-10. The molecular non-uniformity was determined to be 31 by gel chromatography. The filtrate contained 6.2% of the total polymer in dissolved low molecular weight polyethylene.

Comparative example 2

With the catalyst component A prepared according to Comparative Example 1a and tri-n-octylaluminum as catalyst component B, ethylene was polymerized continuously. The apparatus described in Example 2 was used. The concentration of catalyst component A in the reactor was 200 mg / l, of tri-n-octylaluminum 300 mg / l. The setting of sufficiently low average molecular weights proved to be extremely difficult. Only with a hydrogen supply of 60 vol .-% with a simultaneous propene supply of 15 wt .-% and a reactor ^{temperature of 85 0} C was an average molecular weight M of 214 · 10 ^ achieved. At the same total pressure of 35 atmospheres as in Examples 2 and 3, the high hydrogen content resulted in a considerably higher catalyst consumption: 2900 mg / kg PE ^ 19 ppm Cr ₂ O ^. In addition, due to the high hydrogen content, the amount of undesirable, low molecular weight polymer in the centrifuge filtrate rose to 4.4% by weight 6. A polymer produced in this way had the following characteristics:

Melt flow index MFI 190/5 = 0.14 g / 10 min according to DIN 53 735

Viscosity number I according to = 470 cm / g DIN 53 728

mean molecular weight M _y = 214. 10 ³ density at 23 ⁰ C = 0.943 g / cni ³

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This test product caused considerable difficulties in processing into finished parts. Processing into pipes was only possible with approximately twice the melt pressure and increased plasticizing capacity compared to the materials produced according to Examples 2 and 3. The emerging melt pulsed so strongly that the thicknesses of the pipes varied between 0.5 mm and 6 mm and thus the manufacture of salable pipes was not possible.

Comparative example. ;?

a) Preparation of the catalyst component A.

30 g of silica gel with a specific surface area of 50 m / g (trade name Aerosil OX pO from DEGUSSA) were mixed with a solution of 0.22 g of chromium (VI) oxide in 2 ml of water. The mixture was stirred for 4 hours. The silica gel impregnated in this way was then ^{brought to 800 °} C. in a stream of dry air and left at this temperature for half an hour.

b) Polymerization of ethylene

With 0.200 g of this catalyst component A and 0.48 g of tri-n-octylaluminum (catalyst component B) was a Ethylene polymerization carried out as described in Example 1b. The yield of polyethylene was only 72 g, accordingly 5.5 kg per mg of chromium.

Example 4
a) Preparation of the catalyst component A.

5 kg of silica gel with a specific surface area of 166 m 2 / g (trade name Ketjensil 101-R from Ketjen) were, as described in Example 1a, impregnated with 41.6 g of chromium (VI) oxide and then thermally treated. The heating time was 10 minutes and the thermal treatment at 800 ^° C. was 5 minutes.

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b) Polymerization of ethylene

With 0.185 g of this catalyst component A and 0.53 g of tri-n-octylaluminum (catalyst component B) was a Ethylene polymerization carried out as described in Example 1b. The yield of polyethylene was 250 g, accordingly 17.2 kg per mg atom of chromium. The viscosity number according to DIN 53 728 was 370 cm / g, corresponding to an average molecular weight M of 162 × 10 6. The molecular non-uniformity was determined to be 27 by gel chromatography.

Example 5

a) Preparation of the catalyst component A.

5 kg of silica gel with a specific surface area of 300 m / g (trade name Silicagel Grade 952 from Pa. Grace) were, as described in Example 1a, impregnated with 41.6 g of chromium (VI) oxide and thermally treated.

b) Polymerization of ethylene

With 0.184 g of this catalyst component A and 0.61 g of tri-n-octylaluminum (catalyst component B) was a Ethylene polymerization carried out as described in Example 1b. The yield of polyethylene was 358 g, correspondingly 21.5 kg per mg atom of chromium. The viscosity number according to DIN 53 728 was 390 cm / g, corresponding to an average Molecular weight M of 172 · 10 ♦ The molecular non-uniformity was determined to be 27 by gel chromatography.

Example 6

a) Preparation of the catalyst component A.

The procedure was as in Example 1a. The impregnated silica gel was not heated to 800 ⁰ C, but at 700 ⁰ C.

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b) Polymerization of ethylene

With 0.183 g of this catalyst component A and 0.61 g of tri-n-octylaluminum (catalyst component B), an ethylene polymerization was carried out as described in Example 1b. The yield of polyethylene was 400 g, corresponding to 24.2 kg per mg of chromium. The viscosity number according to DIN 53 728 was 420 cm / g, corresponding to an average molecular weight M of 187 · 10 7. The molecular non- uniformity was determined by gel chromatography in 17.

Example 7

With 0.159 g of the catalyst component prepared according to Example 1a A and 0.93 g of tri-n-tetradecyl aluminum (catalyst component B) an ethylene polymerization was carried out as described in Example 1b. The yield of polyethylene was 318 g, corresponding to 21.2 kg per mg atom of chromium.

The viscosity number according to DIN 53 728 was 350 cm ³ / g,

corresponding to an average molecular weight JL. from 152 10. The molecular non-uniformity was determined to be 30 by gel chromatography.

Example 8

With 0.185 g of the catalyst component prepared according to Example 1a A and 0.33 g of tri-isobutyl aluminum (catalyst component B) an ethylene polymerization was carried out as described in Example 1b. The yield of polyethylene was 170 g, corresponding to 10.1 kg per mg of chromium. The viscosity number according to DIN 53 728 was 390 cm / g, correspondingly

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an average molecular weight M of 172 x 10 6. The molecular Inconsistency was determined to be 27 by gel chromatography.

Example 9

With the catalyst component A prepared according to Example 1a and tri-isobutylaluffiinium as catalyst component B was Ethylene is continuously polymerized. The polymerization

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took place in a fluidized bulk powder without application a suspending agent. The procedure was as follows:

In a container 50 kg of polyethylene powder were .fluidisiert by means of an ethylene / hydrogen mixture. The gas mixture was freed after passing through the fluidized bed in a filter of fine-grained fractions and then fed to a blower which, again balances the pressure loss which the gas stream suffers "Before and behind the fan was ever a heat exchanger installed in the circulation to the gas mixture depending to be able to cool or heat up as required. Before the gas stream entered the reaction vessel, tri-isobutylaluminum was metered into it by means of a membrane pump. The catalyst component A was introduced quasi-continuously in small portions into the reaction vessel. The reaction vessel was atm with a total pressure of 30 and a temperature in the fluidized bed of 70 ⁰ C. On average, 30 g of catalyst component A and 19.7 g of catalyst component B were metered in per hour. The hydrogen supply in the gas cycle was approx. 35% by volume. The resulting polymer was withdrawn in portions from the reaction vessel via a pressure lock and passed into an expansion vessel. The experiment was interrupted after a running time of 19 hours. The consumption of catalyst component A was 920 mg / kg PE £ 6 ppm

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Claims (1)

Process for the production of polyolefins with high molecular inhomogeneity, which are particularly suitable for processing into molded parts by the extrusion process, by polymerizing ethylene, optionally in a mixture with other 1-olefins and with the addition of hydrogen, with catalysts that are thermally treatment obtained from chromium (VI) oxide on silica as the carrier and subsequent reaction with an aluminum alkyl, atm as a diluent under pressures of 1 to 100 in inert hydrocarbons, preferably 10-40 atm and, characterized at temperatures vonOOO ⁰ C that as a carrier a silica gel with a ρ ρ specific surface area of 100 m / g to 350 m / g is used, which after its impregnation with chromium (VI) oxide is subjected to a thermal treatment at temperatures of 550 ^° C. to 850 ^° C. f.t / uü. 7098A9 / OU6 ORIGINAL INSPECTS »