DE1271400B - Process for the production of polyethylene - Google Patents

Description

Process for the production of polyethylene It is known that one Ethylene according to the so-called low-pressure process by Professor Ziegler at moderate levels Temperatures and pressures using mixed catalysts made from titanium compounds and organometallic compounds of aluminum such as alkyl aluminum halides etc., can polymerize. In general, the titanium compound used is Titanium tetrachloride and then receives high molecular weight, as thermoplastic plastics suitable products. If, on the other hand, the tetraalkyl esters of ortho-titanic acid are used, this only leads to so-called oligomers, mostly the dimers and trimers, des Ethylene.

It is also known in principle, ethylene in the presence of catalysts made from halogen ortho-titanic acid esters and alkyl aluminum sesquichlorides, optionally after separation of the precipitate obtained in the reaction additional alkyl aluminum sesquichloride was added to polymerize.

The invention relates to a process for the production of polyethylene by low pressure polymerization of ethylene with the help of mixed catalysts Halo-ortho-titanic acid esters and alkylaluminum sesquichlorides, which are characterized is that mixed catalysts are used which are obtained by reacting the alkyl aluminum sesquichlorides and the halogen-ortho-titanic acid ester in the atomic ratio Al: Ti of 2: 1 to 2.5 : 1 have been obtained, optionally after separation of the reaction obtained precipitate further alkylaluminum sesquichloride in an atomic ratio of Al: ei (in the halogeno-ortho-titanic acid ester previously used) of 0.108: 1 was added has been.

It has been found that if these special atomic ratios are observed Al: Ti, which were not used in the prior art methods Polyethylene is obtained with a molecular weight which is favorable for processing. at Al: Ti atomic ratios outside the range of 2: 1 to 2.5: 1 becomes a too obtained high molecular weight.

The chloro-ortho-titanic acid esters are primarily used as halogen-ortho-titanic acid esters into consideration, but also the fluoro-ortho-titanic acid esters, the iodo-ortho-titanic acid esters and in particular the bromotho-titanic acid esters are useful. As a halogen orthotitanic acid ester the esters of dihalo and trihalo-ortho-titanic acid are particularly suitable, the alcohol component of these esters, for example, of lower aliphatic Alcohols, such as methyl alcohol, ethyl alcohol, n- and iso-butyl alcohol, 2-ethylhexyl alcohol, Isopropyl alcohol, cyclohexyl alcohol or benzyl alcohol, as well as phenols can be formed, e.g. B.

Dimethoxy-titanium-dichloride Ti (OCHs) aCl2 Diethoxy-titanium-dichloride Ti (OC2H5) Cl2 Di-n-butoxy-titanium dichloride Ti (OC4Hs) aCla Di-iso-butoxy-titanium dichloride Ti (O-i-C4H9) 2 Cl2 Di-phenoxy-titanium-dichloride Ti (OC6Hs) 2Cl2 Di-iso-butoxy-titanium-dibromide Ti (O-i-C4Hs) aBr2 Mono-methoxy-titanium-trichloride Ti (OCH3) Cl3 Mono-iso-butoxy-titanium-trichloride Ti (O-i-C4H9) Cl3 mono-phenoxy-titanium-trichloride Ti (OC6Hs) Cl3 mono-iso-butoxy-titanium-tribromide Ti (O-i-C4H9) 2Br3 The esters of monohalo-ortho-titanic acid are also suitable. These can be from the same alcohols mentioned above are formed. One possible example is Tri-iso-butoxy-titanium monochloride Ti (O-i-C4H9) 3Cl.

These halo-ortho-titanic acid esters can be prepared in a known manner produce. The reaction mixtures are used as alkyl aluminum sesquichlorides of metallic aluminum with alkyl chlorides.

The mixed catalysts are preferably obtained by the Alkyl aluminum sesquichlorides and the halo-ortho-titanic acid esters in concentrated form Form or diluted with a suitable diluent at a temperature between -20 and 200 "C can act on each other. Each of the components be submitted. It is also possible both of the components at the same time to be introduced into the conversion vessel.

It can be advantageous to produce the mixed catalysts by one expediently with the inert ones customary in low-pressure polymerization Diluents dilute halo-ortho-titanic acid esters at temperatures between -20 and 200 ° C, expediently between 20 and 150 "C, the alkyl aluminum sesquichloride lets act, separates the precipitate that forms, with a diluent washes out, resuspended in a diluent, and then with more alkyl aluminum sesquichloride offset in the specified atomic ratio. This new addition of alkyl aluminum sesquichloride takes place advantageously in the presence of ethylene. The solids content of the thus obtained Mixed catalyst suspensions should be about 0.1 to 25010, expediently about 0.5 to 50lot based on the diluent. In this way of working you can use the the polymerization occurs during the reduction of the halogen ortho-titanic acid esters disturbing and the work-up of the polymers burdensome by-products, for example Monoalkylaluminum dichlorides and aluminum chloride, remove and therefore preserve particularly effective and high-yield mixed catalysts.

The polymerization is expediently carried out by introducing the ethylene in a 0.1 to 250/0, expediently 0.5 to 50 /, suspension of the mixed catalysts in an inert diluent. It is advantageous to take the implementation of the Catalyst components in the presence of ethylene. As an inert diluent primarily hydrocarbons are possible. Aliphatic, cycloaliphatic and aromatic hydrocarbons, such as. B. butane, hexane, cyclohexane, Isopropylcyclohexane, benzene, toluene and mixtures of aliphatic and cycloaliphatic or aliphatic or aromatic hydrocarbons.

Furthermore, halogenated hydrocarbons, such as. B. Carbon tetrachloride or chlorobenzene.

The polymerization can be pressureless, or with a slight negative pressure be carried out at overpressure. A lower or higher pressure than normal pressure however, it is usually not required. One works at a temperature between -20 and 200 "C, preferably between 20 and 1500C.

It is advisable to move the polymerization batch during the reaction with the help of suitable stirring devices. The heat of polymerization is internal or external cooling with a suitable coolant or by evaporative cooling discharged. The polymerization is terminated when one that is no longer stirrable Mixture has reached The polymerization mixture is worked up in a known manner, for example by adding an alcohol such as methanol or isopropanol, and then Filtration.

Those using the mixed catalysts used according to the invention Polyethylenes produced have a very uniform structure and stand out by a very low methyl branching as well as by the low number of almost exclusively terminal double bonds before the known low-pressure polyethylenes the end. As a result, they exhibit superior mechanical properties as well excellent resistance to aging.

Example 1 In a reaction vessel equipped with a stirrer, which is flushed with dry nitrogen, is in a solution of 6 parts of di-iso-butoxy-titanium dichloride, Ti (O-i-C4H9) 2C12, in 800 parts isopropylcyclohexane freshly distilled over sodium at room temperature a solution of 5.57 parts of ethylaluminum sesquichloride in 40 parts of isopropylcyclohexane (corresponding to an atomic ratio of Al: ei = 2: 1) are added, while heating to 50 ° C. and passing in ethylene. Vigorous polymerization begins of the ethylene, so that the temperature can be kept at 50 "C by external cooling got to.

After 45 minutes of polymerization, the batch is due to the result Polymer only just stirrable. The ethylene supply is then interrupted, there 200 parts of n-butanol are added, filtered off, and the polymer is then treated with Methanol and filtered again. After drying, 115 parts of a white, fine flaky polymer of reduced viscosity 2.4 (with p-xylene at 110 "C measured in a 0.10 / 0 solution) that contains less than 0.01% TiO2 and 0.01% Cl and has the following properties: notched impact strength: 46, tear strength: 304 kg / cm2, elongation at break: 6530 / o, flow strength: 243, flow elongation: 170 / o.

Example 2 Follow the procedure of Example 1 using 4.95 parts of ethylaluminum sesquichloride and 5.3 parts of di-iso-butoxy-titanium dichloride (Al / Ti atomic ratio = 2: 1) repeated, 145 parts of polyethylene are obtained with a reduced viscosity of 1.9.

Example 3 Following the procedure of Example 1 using 6.2 parts of ethyl aluminum sesquichloride and 5.3 parts of diisobutoxytitanium dichloride repeated (Al / Ti atomic ratio 2.5: 1), 120 parts of polyethylene are obtained with a reduced viscosity of 2.2.

Example 4 In a reaction vessel equipped with a stirrer becomes a solution of 5.1 parts of mono-isobutoxy-titanium-trichloride, Ti (OC4H9) Cl2, isopropylcyclohexane freshly distilled over sodium in 800 parts with introduction of ethylene is a solution of 5.57 parts of ethylaluminum sesquichloride in 40 parts Isopropylcyclohexane (corresponding to an atomic ratio Al: ei = 2: 1) was added. Then the mixture is heated to 50 "C and ethylene is introduced at the same time, whereupon vigorous polymerization begins. The polymerization is then ended and, as described in Example 1, worked up. 160 g of a white one are obtained Polymer of the reduced viscosity 2.4.

The polymer gives press plates with the following properties: Notched impact strength: 17.5 cmkg / cm3, tensile strength: 285 kg / cm2, elongation at break: 646 0 / o, flow strength: 242 kg / cm2, flow elongation: 210 / o.

Example 5 In a reaction vessel equipped with a stirrer become a solution of 5.1 parts of monoiso-butoxy-titanium trichloride, Ti (O-i-C4H9) Cl3 , in 100 parts of hexane 7 parts of ethylaluminum sesquichloride (corresponding to an atomic ratio Al: Ti = 2.5: 1) given. After stirring for one hour at 50 "C., the Precipitation Sucked off with the exclusion of air and moisture, slurried again in 500 parts of hexane and sucked off again. The precipitate is then suspended in 1000 parts of hexane and ethylene is passed in at 50 "C. 0.3 part of ethylaluminum sesquichloride is then added as a molar solution in hexane, whereupon vigorous polymerization begins. By With external cooling, the temperature is kept at 50 ° C. After 6/4 hours, 165 parts of polymer are present emerged, which, as described in Example 1, are isolated. The obtained polyethylene has a reduced viscosity of 1.9 and gives press plates with the following properties: Notched impact strength: 6.9 cmkg / cm2, tensile strength: 212 (249) kg / cm2, elongation at break: 717 (741) ° / os yield strength: 237 (243) kg / cm2, yield elongation: 17 (17) ° / o.

(Aging values after 7 days of storage in the circulating air drying cabinet at 100 "C in brackets.) Example 6 In one equipped with a stirrer Reaction vessel to a solution of 6 parts of diiso-butoxy-titanium dichloride, Ti (O-i-C4H9) pClp, in 100 parts of isopropylcyclohexane 7 parts of ethylaluminum sesquichloride (corresponding to an atomic ratio of Al: Ti = 2.5: 1). After stirring at 50 "C for one hour is the precipitation under air and Exclusion of moisture suctioned off, back in 500 parts of isopropylcyclohexane slurried and again filtered off with suction. The precipitation it is then suspended in 1000 parts of isopropylcyclohexane and ethylene is passed at 50 "C. a. Then add 0.3 parts of ethylaluminum sesquichloride as an imolar solution, whereupon a vigorous polymerization begins. The temperature is maintained by external cooling to 50 "C. After 6/4 hours, 150 parts of polymer have formed, which are as in the example 1 described can be isolated. The polyethylene obtained has a reduced viscosity of 2.2 and gives press plates with the following properties: Notched impact strength: 19.1 cmkg / cm2, tensile strength: 296 (288) kg / cm2, elongation at break: 720 (687) 0 / o, flow strength: 226 (225) kg / cm2, flow elongation: 17 (17) 0 / o (aging values after 7 days of storage in brackets in the circulating air drying cabinet at 100 ° C.) According to the IR analysis contains the polymer for 1000 carbon atoms 0.06 intermediate trans, 0.21 terminal vinyl and 0.04 terminal vinylidene double bonds and 6 methyl groups.

Comparative experiments If you work under the conditions as in Example 1, but instead of 6 parts of di-isobutoxytitanium dichloride and 5.57 parts of ethylaluminum sesquichloride, the amounts listed in the following table are obtained: | Ethyl aluminum sesqui- | Diisobutoxytitanium dichloride | Al / Ti- | Polyethylene | Reduced viscosity chloride No. | (Parts) | (Parts) i ton atomic ratio I (parts) | of the polymers 1 2.78 6.0 1: 1 87 11.0 2 3.70 5.3 1.5: 1 98 9.0 These figures show that with Al / Ti atomic ratios lower than 2: 1 it is not possible to produce polyethylene with reduced viscosities of 1.9 to 2.4 - which corresponds to average molecular weights of around 100,000 (88,000 to 118,000). With an Al / Ti atomic ratio of 1.5: 1, a polyethylene with a reduced viscosity, which corresponds to a molecular weight of 454,000, is produced.

Polyethylenes with molecular weights well over 100,000 are only extremely difficult or impossible to process, for example to spray or to press. In contrast, this is possible with the polyethylenes of molecular weights in the range of 100,000 still good. These polyethylenes have been used in the production of mechanically particularly stressed large containers, such as tubs, tubs, buckets, Garbage cans, baskets, etc., enforced in practice.

In the range of the Al / Ti atomic ratios used according to the invention As the table shows, the highest polyethylene yields are obtained.

If the Al / Ti atomic ratios used according to the invention are exceeded, so the yields go down, and the reduced viscosities of the polyethylene increase. Also for economic reasons - larger amounts of ethyl aluminum sesquichloride correspond to higher catalyst costs - are higher Al / Ti atomic ratios anyway less favorable.

It results accordingly for the Al / Ti atomic ratios used according to the invention an optimum of polymer yields and polymer properties.

Claims (1)

Claim: Process for the production of polyethylene by low-pressure polymerisation of ethylene with the help of mixed catalysts from halogen ortho-titanic acid esters and Alkylaluminium sesquichlorides, dadu.rch characterized in that mixed catalysts used by reacting the alkyl aluminum sesquichlorides and the halo-ortho-titanic acid ester have been obtained in an Al-Ti atomic ratio of 2: 1 to 2.5: 1, where appropriate after separation of the precipitate obtained in the reaction, further alkylaluminum sesquichloride in an atomic ratio of Al: Ti, based on the previously used halogen n - ortho - titanic acid ester, of 0.108: 1 has been added. Documents considered: French patents No. 1148791,1154219; interpreted documents of Belgian patents nos. 534792, 549448.