Phillips ethylene trimerization catalyst

Scheme 36 Synthesis of self-activating ethylene oligomerization catalysts as analogues to the Phillips trimerization catalyst...

Phillips Petroleum discloses a process for the trimerization of ethylene to 1-hexene [13]. According to patents, the process employs a complex catalyst system comprising 2,5-dimethylpyrrole, triethylaluminum, and diethylaluminum chloride in combination with a chromium(III) salt in the presence of a solvent. The purity of 1-hexene in the hexene fraction is reported higher than 99%. The main byproducts are decenes and polymer. 

The selective trimerization and tetramerization of ethylene to form 1-hexene and 1-octene has become an important process to generate monomers for the synthesis of LLDPE. 1-Hexene was detected as a byproduct in the polymerization of ethylene catalyzed by homogeneous chromium complexes. Chromium complexes have now been identified that catalyze this oligomerization to form 1-hexene with remarkably high selectivity. Phillips patented the combination of 2,5-dimethylpyrrole, triethylalu-minum, and diethylaluminum chloride with a chromium(lll) salt, and researchers at Union Carbide patented a catalyst generated from chromium(lll) 2-ethylhexanoate and hydrolyzed triisobutylaluminum. - Researchers at BP have described a particularly active and selective catalyst based on a chromium(lll) precursor, a bis(diphosphino)amine ligand, (o-MeO-C H ),PN(CH,)P(o-MeOC H ) and methylaluminoxane (MAO). " ... 

Pyrrolyl-Based Chromium/Organoaluminum Catalysts New Insight into the Phillips Ethylene Trimerization Catalysf ... 

The Phillips catalyst, based on a Cr/2,5-dimethylpyrrole precursor and TEA as a cocatalyst, is the only commercial catalytic system for ethylene trimerization [164] and has thus been extensively studied [139, 140]. Based on DFT calculations, a redox mechanism involving a Cr(ll)/Cr(lV) couple has been proposed [154, 165]. Also, the pyrrole derivative ligand, able to interact with one or two metal centers through the nitrogen lone pair and/or the aromatic Jt-system, may play a key role for the stabilization of heterodinuclear Cr/Al species formed after activation. 

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