DE1720983A1 - Process for the polymerization of ethylene - Google Patents

Description

Dr.T./be

Process for the polymerization of ethylene

Company IMHICO AG, Zurich / Switzerland

Ethylene can "at bridges over 1ooo at and temperatures up to about 4oo ° 0 in the presence of oxygen or a compound which splits off free radicals under the reaction conditions be polymerized in a stirred autoclave or in a tubular reactor.

The strongly exothermic polymerization reaction requires precise regulation of the reactor temperature, otherwise charring of the polymerization mixture occurs leading to explosive decomposition.

A known method for high pressure polymerization of ethylene in tubular reactors therefore sees the The catalyst is fed in at several points in the reactor. This measure works for longer periods of operation However, to no essential stabilization of the system, since the heat of polymerization occurring per throughput is in no way reduced wildly.

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In another known process, the polymerisation gomic flÜEGi ^ e inerto coolant added. A major disadvantage of this method is in the Separation of the relatively large Kengen cooling liquid from the polymer-residual gas mixture.

In a further known process, 1-at-alysator-half ethylene is introduced at several points in the direction of flow behind a ca derlying points of the reactor. However, this process can only be used industrially when using gaseous catalysts. The use of solid catalysts, generally in the form of a solution or suspension, fails in practice due to the impossibility of adding sufficient quantities of the solid or liquid catalyst or the catalyst-containing liquid to the gaseous ethylene for polymerisation initiation and of compressing this mixture to high pressures and introduce the 'reactor.

It has now been found that ethylene in tubular Reaktcran at pressures of at least 800 at and temperature. . on a maximum of 400 ° C, optionally in the presence of ion comonomers and / or Ktjtenransfermittel and / or moderators particularly advantageous .ift can be polymerized if, according to the invention ε.- ^ ner or meieren in & τζ . * - direction consecutive places c>. Reactor;

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the (those) the temperature of the reaction mixture Maximum achieved by solid or liquid polymerization catalysts or ethylene free from catalyst-containing liquids, the temperature of which is below the temperature of the reaction mixture s is at the injection point, into the reactor is introduced and the reaction mixture separated therefrom at one or more one behind the other in the direction of flow Position of the reactor at which the temperature of the reaction mixture above the light-off temperature the polymerization lies, solid or liquid L ^ talr / sator or a catalyst-containing liquid is supplied.

The polymerization temperature, in particular its lower and upper limit, depends on the type of used Catalyst. While hyponitrites generally have a polymerisation-initiating effect already at about 50 ° C show, require certain peroxides, such as. B. bis (4-ethyl-2-octenyl) peroxide, Temperatures of over 2oo ° C.

The catalysts used are all those which catalyze the high pressure polymerization of ethylene, under normal conditions non-gaseous compounds into consideration, in particular i-erc -.e, peresters, azo compounds, azines, hyponitrixia. The ". -W ^ ymerization can be done using ... one single Catalyst or several, separately injected

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BATH ORIGINAL

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Catalysts or a catalyst mixture carried out will. The total amount of catalyst "is generally less than 1,000 ppm, the catalyst being preferred is present as a solution or suspension in an organic liquid.

Chain transfer agents can also be added to the polymerization mixture lind / or moderators, such as hydrogen, Aliphatic, cycloaliphatic, aromatic, chlorinated organic Compounds, alcohols, aldehydes and ketones, can be added.

The present invention can be applied equally well to the homopolymerization and also to the copolymerization of ethylene. Suitable comonomers are e.g. B. oC olefins, butadiene, acrylic and alkacrylic compounds, vinyl, vinylene and vinylidene compounds, unsaturated alcohols, alkylene oxides, carbon monoxide and sulfur dioxide.

The process according to the invention leads to a substantial increase in the conversion of the per throughput Ethylene to polyethylene. In addition, it is possible to determine the molecular weight distribution of the polyethylene produced in this way to vary as much as possible as desired. For example, when using, one obtains over the entire length of the reactor uniform polymerization conditions a polymer! ; rt '

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with a particularly narrow molecular weight range. The use several separately introduced catalysts with a corresponding division of the reactor into different temperature zones on the other hand leads to products with a very "broad molecular weight distribution. It is also possible depending on the choice of polymerization temperature, d. H. des or of catalysts to produce polyethylenes of various densities. The generated by the process according to the invention Polyethylene is characterized by its particularly high quality and excellent processability.

Example;

100,000 parts to 1,700 atmospheres of compressed ethylene fed hourly to the beginning of a tubular reactor. At the point of the reactor where the ethylene has a temperature of about 165 ° C. is reached, 2.8 parts of lauroyl peroxide dissolved in a benzene-cyclohexane mixture are fed in. The temperature of the reaction mixture rises rapidly due to the heat of polymerization released to 26o ° C. At this point, a further 6,700 parts of compressed ethylene are fed to the reactor, resulting in a Lowering the temperature of the polymerization mixture leads. At the point where the temperature of the reaction mixture

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until it has dropped to 180 ° C., a further 2.2 parts of lauroyl peroxide dissolved in benzene-cyclohexane are introduced. After leaving the reactor , the polymerization mixture is worked up in the customary manner, 3280 parts of polyethylene having a density of about 0.92 being obtained per hour.

Patent claims

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Claims (1)

Patent entitlement Process for the polymerization of ethylene in tubular reactors at pressures of at least 800 atm and temperatures of not more than 4,000 ° C., optionally in the presence of comonomers and / or chain transfer agents and / or moderators, characterized in that one or more of them are arranged one behind the other in the direction of flow Place the reactor. at which or at which the temperature of the reaction mixture reaches a maximum, ethylene free from solid or liquid polymerization catalysts or from catalyst-containing liquids, the temperature of which is below the temperature of the reaction mixture at the injection point, is introduced into the reactor and the reaction mixture is separated therefrom Solid or liquid catalyst or a catalyst-containing liquid is fed in at one or more points in the reactor lying one behind the other in the direction of flow, at which the temperature of the reaction mixture is above the start temperature of the polymerization. 109831/1675