CS195281B2 - Alpha-olefins polymerisation method - Google Patents

Abstract

alpha-Olefins are polymerised in the presence of a catalyst system composed of (a) an Al cpd. of formula AlR3 or AlRxY3-x (where R is alkyl, aryl or cycloalkyl; x is 1-2; Y is halogen or H) and (b) the combination product of a transition metal chloride and TiCl3 supported on a material of high specific surface area (pref. an oxide of Gp. II-IV). The catalyst is highly active and the support requires no preliminary treatment. The catalyst remains stable in the presence of H2 and in the polymerisation of ethylene, a very narrow range of mol. wt. distribution is obtained.

Description

(54) A-olefin polymerization process

The invention relates to a process for the polymerization of aolefins, in particular ethylene, by means of a catalyst system consisting of an alkylaluminum and a reaction product of a transition metal chloride and titanium tetrachloride finely dispersed on a material with a large specific surface area.

It is known to use catalytically active titanium halides in low pressure polymerization of α-olefins. These halides are prepared by the reduction of titanium tetrahalides with alkyl aluminum or alkyl halide compounds. The reaction is generally carried out under an inert atmosphere and in the presence of an inert solvent. The catalyst thus obtained is subsequently used together with the alkyl metal compounds to polymerize α-olefins in suspension in an organic solvent at an appropriate monomer pressure.

However, the titanium halide halides exhibit impurities due to the presence of aluminum compounds and do not show very good catalytic activity, so that the resulting polymer requires costly purification operations to remove catalytic residues.

Furthermore, a process for the polymerization of cr-olefins using a catalyst comprising mixed crystals of TiCl 2 or TiCl 2 with metal halides in combination with alkyl-aluminum compounds is known.

Recently, processes have been proposed in which titanium halides are deposited on inorganic materials to provide polymerization catalysts with improved efficiency. Carriers used include, for example, oxide or magnesium hydroxide; however, it is to be understood that the catalytic activity of the titanium compound carried on these materials varies considerably, depending on the chemical nature of the surface of the compounds. case treated with Grignard reagents, alkyl aluminum compounds or hydrogen to improve their efficacy.

SUMMARY OF THE INVENTION The present invention provides a process for the polymerization of α-olefins by means of a catalyst system having high catalytic efficiency and not requiring pretreatment of the support.

Claims (1)

The present invention relates to a process for the polymerization of α-olefins, characterized in that the reaction is carried out in the presence of a catalytic system consisting of an aluminum compound selected from compounds of the general formulas A1R3 and A1R _X Y3- _X , 1952В1 kde R is an alkyl, aryl or cycloalkyl radical, x is an integer from 1 to 2, Y is halogen or hydrogen, and the reaction product of a transition metal chloride and a tetrachloride chloride of the formula MCl _n. NTiCk, where M represents vanadium, manganese, iron or cobalt and n is a number equal to the valence M deposited on a material with a large specific surface area, the transition metal being present in an amount of 0.1 to 10, preferably 1 to 3% by weight based on the weight of the carrier. The reaction products described are very chemically stable, since the tetrachloride and the transition metal chloride are lysostructural; moreover, they contain titanium in the optimum valence stage to achieve the best catalytic efficiency. These reaction products are prepared by the process of the present application, which comprises depositing the transition metal compound at the lowest valence stage on a support, heating to reflux temperature in TiCl4 and removing excess TiCl4. The material used as the carrier is selected from the group of materials having a large specific surface area, such as oxides of the elements belonging to Class II. to IV. groups of the periodic system elements. Preferably, the material used as the support is selected from silica, silica and alumina, ZnP2, MnO, ТЮ2, CaO. As previously stated, the catalyst systems of the present invention do not need to be pretreated since the efficiency of the catalyst systems of the present invention is high and homogeneous, although the chemical nature of the support is subject to variation; however, said carriers may also be pretreated with Grigard reagents or aluminum alkyl halides to further improve the properties thereof. In any case, the efficiency of the catalyst systems of the present invention in polymerization reactions is higher compared to carrier-only processes treated only with TICU, while the other conditions remain the same. The catalysts of the invention exhibit good properties in the presence of hydrogen and, in the case of ethylene polymerization, cause a narrow molecular weight distribution. The polymerization reaction is carried out in a manner known per se at temperatures ranging from 0 to 200 ° C and at a pressure of 0.01 to 5 MiPa. The polymerization is carried out in a steel autoclave equipped with an anchor stirrer, the operations being carried out at a pressure higher than atmospheric pressure. The catalyst is fed together with the solvent and the alkyl compound. The autoclave is thermostatized to a polishing temperature, whereupon the Ig and ethylene are supplied at a pressure corresponding to the desired pressure ratio. The reaction is terminated by the addition of alcohol to the autoclave.