Effects of diethylaluminum ethoxide pre‐reduction and chromium loading over bistriphenylsilyl chromate/silica for ethylene polymerization

Abstract

AbstractBistriphenylsilyl chromate (BC)/silica (S‐2 catalyst) is a commercially used high‐density polyethylene (HDPE) catalyst with great importance. In this work, the catalytic performance of this catalyst was tried to be improved by increasing the loading amount of Cr and pre‐reducing with diethylaluminum ethoxide (DEALE). It is found that, when the Cr loading amount was doubled, the productivity in gPE · g−1Cat became almost doubled as well, indicating the maintenance of overall efficiency for Cr centres. Meanwhile, pre‐reduction of BC/silica with a small amount of DEALE (the molar ratio of DEALE/Cr < 2.4) was adequate to promote its productivity greatly, while large dose of DEALE led to the activity decay fast, which might originate from the over‐reduction of the Cr centre, as well as pore blockages caused by the added DEALE. Moreover, it is found that both the increased Cr loading and DEALE pre‐reduction offered an alternative way to reduce the weight‐average molecular weight (MW) and molecular weight distribution (MWD) of the polyethylene products mainly by shaving the high MW shoulder.