Insights on the Mechanism for Ethylene Tetramerization

Selective tetramerization of ethylene to produce 1-octene may be viewed as an extension of the well-studied process for ethylene trimerization to form 1-hexene, which is commercially practiced by Chevron Phillips Chemical (CPChem) and others. The tetramerization reaction was first reported by researchers at SASOL in 2004, but CPChem and others have also reported proprietary systems. Tetramerization reactions are always coupled with some degree of 1-hexene formation, with 1-octene:1-hexene ratios typically varying from 1:2 to 4:1. These mixtures imply the intertwining of the tetramerization and trimerization catalytic cycles, and the primary products are always formed with two types of coproducts. These coproducts include cotrimer and cotetramer C10–C14 species resulting from product reincorporation, as well as other byproducts ranging from C2 species to waxes, and various cyclic hydrocarbons. Gas chromatography (GC) is used to deconvolute these overlapping catalytic cycles, and a model for using GC data to explain the ethylene efficiency in each cycle is presented.