A new chromium-based catalyst coated with paraffin for ethylene oligomerization and the effect of chromium state on oligomerization selectivity

Abstract

A new method is proposed in which a chromium-based catalyst system containing chromium(III) tris (2-ethylhexanoate) (Cr(EH) 3), 2,5-dimethylpyrrole (2,5-DMP), GeCl 4 and triethylaluminum (TEA) coated with solid paraffin is used for oligomerization of ethylene. GC-MS and 1 H -NMR analyses show that the coated catalyst system prepared via this approach is air-insensitive so it can be stored under ambient conditions. The selectivity for 1-hexene is up to 97.91 wt.%, and only slightly decreases when the catalyst system is exposed in air for 24 h; in contrast, the selectivity is only 35.6% for its non-coated counterpart. XPS reveals that an attachment of atmospheric oxygen to catalyst makes the chemical state of chromium change from Cr 3+ to Cr 6+. Such a change, in turn, reduces remarkably its selectivity for 1-hexene.