Chromium catalyzed tetramerization of ethylene in a continuous tube reactor—Proof of concept and kinetic aspects

Highly selective processes for the tri- and tetramerization of ethylene offer an interesting alternative to conventional ethylene oligomerization processes that are constrained by yielding mathematical distributions of linear α-olefins. This inherent lack of selectivity often makes it difficult for full slate producers to respond to changing market demands in each product segment. This is the first known report on the continuous tri- and tetramerization of ethylene in a continuous plug flow tubular reactor. Standard run times of 10 h and a catalyst comprising Cr(acac) 3, 1,2-dimethylpropyl-bis(diphenylphosphino)amine ligand and the aluminum-based activator MMAO-3A was used. Activities exceeding 3,700,000 g/(g Cr h) and combined selectivities for 1-hexene and 1-octene of more than 90% were achieved. The influence of temperature, catalyst concentration, and ethylene concentration in the reactor on reaction rate (catalyst activity) and selectivity has also been investigated. In addition, supporting kinetic studies were performed in a semi-batch reactor setup with the aim to explain the influence of ethylene concentration on product selectivity found in the continuous runs. It was found that the reaction orders in ethylene for 1-hexene and 1-octene are different, with 1-octene formation being significantly more sensitive to ethylene concentration. Our paper reports the first continuous tri- and tetramerization of ethylene in a plug flow tubular reactor utilizing a catalyst comprising Cr(acac) 3, 1,2-dimethylpropyl-bis(diphenylphosphino)amine ligand and the aluminum-based activator MMAO-3A. Ligand of the catalytic system for the continuous selective tri- and tetramerization of ethylene.