METHOD FOR PRODUCING POLYOLEFINES IN THE FORM OF POWDER BY POLYMERIZATION IN THE GASEOUS PHASE

The invention relates to a method of producing polyolefins in powder form, by polymerizing ethylene or copolymerizing ethylene and propylene and/or butylene-(1). The reaction is carried out in the presence of a catalyst comprising a mixture of: (1) a vanadium component obtained by reacting (a) a mixture of vanadyl(V)-chloride and vanadyl(V)-alcoholate in a molar ratio of 1:2 to 2:1, or a reaction product of vanadyl(V)-chloride with a lower alcohol in a molar ratio of 1:2 to 1:1, with (b) ethylaluminum dichloride, diethylaluminum chloride, isobutylaluminum dichloride and/or diisobutylaluminum chloride in a molar ratio V:A1 of 1:3 to 1:1, in an inert solvent, with stirring at a specific stirring power of 0.1 to 20 000 watts/m3, and separating the solid thus obtained; (2) a finely divided silica xerogel in a weight ratio of from 0.5:1 to 10:1 based on the vanadium component; (3) a polyolefin in powder form possessing trickling ability, having an average particle diameter up to 1 000 .mu.m and being practically free from very fine grained material, in an amount of from 0.5 to 3.0 grams per milligram of the vanadium component, calculated as vanadium peroxide; and (4) an alumino-organic compound of the general formula RnAlX3-n, wherein R signifies a saturated hydrocarbon radical with 2 to 20 carbon atoms, X signifies a halogen atom, and n is a number from 1 to 3, or a product of the reaction between trialkyl aluminum or dialkylaluminum-hydride and a 1.3 diolefin, in an amount of from 0.1 to 3.0Mmole per gram of powdered polyolefin.