Olefin polymerisation catalyst based on silicic acid xerogels - and contg. chromium oxide, leaving low catalyst residues in the polymer

摘要

The catalyst is prepd. by (A) preparing a silicic acid-xerogel by (i) extracting >=60%, pref. >=90% of the water contained in a silicic acid-hydrogen contg. 10-25 (esp. 14-20)% solids (calc. as SiO2), with a 1-4C alkanol and/or a 3-5C alkanone; (ii) drying the gel from (i) at 180 degrees C/10 torr/30 mins. until there is no further wt. loss (xerogel formation); (iii) comminuting the xerogel to a dia. of 20-2000 mu, pref. 40-300 mu; (B) admixing the xerogel with solid, finely divided chromium trioxide at 100-300 degrees C/0.001-250 torr, until the xerogel takes up 0.1-10% (calc. on the xerogel and as Cr) chromium trioxide; (C) maintaining the prod. from (B) in a gas stream free from water and contg. >10 vol. % O2 at 400-1000 degrees C/10-1000 mins. The hydrogel used in (A) comprises spherical particles of dia. 1-8 (pref. 2-6)mm. The catalyst is used for the homo- and co-polymerisation of 2-8C monoolefins and esp. for ethylene in suspension or in the dry phase. It has partic. high productivity.