Computer-aided ligand screening to develop polymer-free catalyst in Cr-catalyzed ethylene oligomerization

Abstract

Preventing the formation of undesirable polymer in ethylene oligomerization is a major challenge since the presence of these insoluble materials can cause severe reactor fouling. Based on previous experimental data, the concomitant formation of these solid compounds can be divided in two types. Detailed discussion in combination with mathematical analysis revealed that the low-molecular weight waxes (low-Mw waxes) are most likely the tail products of the Schulz-Flory distribution while high-molecular weight polyethylene (high-Mw PE) may be catalyzed by multiple active sites independent from the oligomerization cycle. Controlling the Schulz-Flory coefficient (K value) to remain in a lower range is crucial in achieving plentiful C4–C8 components and inhibiting polymer formation at the same time. Attempting to predict the K value, the energetic disparities of key transition states which control 1-butene selectivity have been extracted as a chemical descriptor to establish a general model. Promising ligands derived from computer-aided screening are expected to avoid the inherent waxes formation. Plausible strategies for the elimination of external polymerization sites are also suggested. The combination of them may provide a chance to develop more polymer-free catalysts to meet the requirements of industrial manufacturing.