Patent ID: RE40140

Claim:
A process for preparing a catalyst for the polymerization of olefins, which comprises: a) preparation of a finely divided silica xerogel by a1) use of a particulate silica hydrogel which contains from 10 to 25% by weight of solid (calculated as SiO 2 ), is largely spherical and has a particle diameter of from 1 to 8 mm and is obtained by a11) introduction of a sodium or potassium water glass solution into a rotating stream of an aqueous mineral acid, both longitudinally and tangentially to the stream, a12) spraying of droplets of the resulting silica hydrosol into a gaseous medium, a13) allowing the sprayed hydrosol to solidify in the gaseous medium, a14) freeing the resulting largely spherical hydrogel of salts without prior aging by washing, a2) extraction of at least 60% of the water present in the hydrogel by means of an organic liquid, a3) drying of the resulting gel up to until the dried product experiences no further weight loss at 180° C and a reduced pressure of 13 mbar no further weight loss occurs over a period of for 30 minutes (xerogel formation) a4) adjustment of the particle diameter of the xerogel obtained to from 20 to 2000 μm, b) loading of the xerogel with chromium from a solution of chromium trioxide or a chromium compound which is converted into chromium trioxide under the conditions of step c), and c) activation of the resulting product at from 400 to 1100° C. in a water-free gas stream comprising oxygen in a concentration of above 10% by volume, wherein a fluoride doping with a fluorinating agent is carried out in step c) together with the activation at 400 to 900° C. in air.