Polymerization process utilizing a catalyst prepared by aging of a chromium-containing gel at high pH

摘要

A silica hydrogel containing chromium is aged under conditions such that at least a portion of the aging is carried out at a pH within the range of 7 to 9. The resulting hydrogel is converted to a xerogel by treating with a volatile organic liquid. The desired pH can be obtained either by adding a basic material such as ammonia to the hydrogel prior to or during the aging process or by using a chromium component which inherently gives a higher pH and/or resists the natural tendency for the pH to decrease during aging. An example of such a chromium compound is chloropentammine chromium(III) chloride. The resulting catalyst on activation is particularly suitable for olefin polymerization under conditions where higher melt flow polymer is desired.