| 摘要 |
Polyethylene is made by continuously polymerizing ethylene in the presence of a catalyst consisting of aluminium particles, a halide of a metal of Group IVa, Va or VIa of the Mendeleeff Periodic Table and, if desired aluminium chloride, and keeping the aluminium particles in constant movement during the polymerization so that the polyethylene formed on the surfaces of the aluminium particles is stripped off by a rubbing action between the particles and/or any other solid surfaces and separating the detached polyethylene. The aluminium may be activated with a halogen or a halogen-containing compound prior to the polymerization, e.g. ethylene bromide, hydrogen chloride, or aluminium chloride. The polymerization may be effected in the presence of a liquid diluent in which the halide of the metal is soluble but the polyethylene insoluble, e.g. by mixing vapours of the diluent with ethylene, and/or under pressures up to 200 atmospheres. Suitable metal halides are vanadium trichloride, titanium tetrachloride, chromyl chloride, and vanadium oxychloride. Diluents mentioned are heptane, cyclohexane, benzene, ethylbenzene, and mixtures. The aluminium may be in the form of balls, cylinders or cubes or coarse chips preferably with a diameter or an edge length of 5 to 20 millimetres. The aluminium may be pure or alloyed with magnesium, silicon, manganese, iron, copper, or zinc. In order to accelerate the separation of polyethylene from the aluminium particles, small steel or porcelain balls may be mixed with the aluminium. When the polymerization is effected in bulk, the aluminium particles are charged into a vessel with a perforated sieve-like bottom which retains the particles therein, and a mixture of the ethylene and the vapour of the metal halide passed through the particles at a velocity such that the aluminium particles are kept in rapid motion and the separated polyethylene collected from the gas stream via a separator. The polyethylene may be purified by washing with an alcohol. |
