Manufacture of olefin polymers

Claim 1

A process for the manufacture of an olefin polymer by polymerizing one or more α-monoolefins of 2 to 8 carbon atoms at from 60° to 160° C, and an olefin pressure of from 0.5 to 40 bars, by means of a catalyst obtained from a silicon-containing material (component a), an organo-metallic compound containing alkyl groups (component b) and a chromium compound (component c), wherein the catalyst employed is obtained by (1) first bringing into contact (1.1) an alkogel (component a) of the empirical formula SiO.sub.2 · m Al.sub.2 O.sub.3 · n ROH where m is a number from 0 to 2, n is a number such that the content of ROH in the alkogel is from 1 to 85 percent by weight and R is alkyl of 3 to 8 catbon atoms, said alkogel having been prepared from a silicic acid hydrogel containing from 10 to 25 percent by weight of solids, calculated as silicon dioxide, by replacing the water in the hydrogel by an alcohol of the formula ROH defined above, and (1.2) an aluminum compound containing alkyl groups (component b) of the general formula R'.sub.p Al(OR").sub.3-p where R' is alkyl of 1 to 8 carbon atoms, R" is open-chain alkyl of 1 to 8 carbon atoms or cyclic alkyl of 5 to 8 carbon atoms and p is a number from 1 to 3, with intimate mixing, to form a solid-phase reaction product, (2) then bringing into contact (2.1) the solid-phase reaction product obtained from stage (1) and (2.2) a solution of a chromium compound (component c), which compound is chromium trioxide or a chromium compound which is converted to chromium trioxide under the conditions of stage (3), with intimate mixing and evaporation of the solvent, and (3) finally keeping the product obtained from stage (2) in an anhydrous stream of gas, containing oxygen at a concentration of more than 10 percent by volume, for from 10 to 400 minutes, at from 600° to 1,000° C, with the proviso that (I) the catlyst contains from 0.1 to 10 parts by weight of component b (calculated as aluminum) and from 0.3 to 10 parts by weight of component c (calculated as chromium trioxide) per 100 parts by weight of component a (calculated as silicon dioxide), and (II) that the product obtained from stage (1) or from stage (2) is dried and comminuted, before being used further in the next stage, until it no longer loses weight in the course of 30 minutes at 100° C under a pressure of 10 mm Hg and has attained a particle diameter of from 20 to 2,000 μum.