Ethylene oligomerization with mixed ligands

Abstract

The selective oligomerization of ethylene to produce a mixture comprising octene and hexene is conducted in the presence of a catalyst system comprising a source of chromium; two different P-N-P ligands and an activator. The phosphorus atoms of both ligands have ortho-fluoro phenyl substituents. The nitrogen atom of the first ligand has an isopropyl substituent. The nitrogen of the second ligand has a larger / bulkier hydrocarbyl substituent on the N atom. The hexene produced by the process of this invention has very high alpha selectivity.

Description

technical field [0001] The present invention relates to the selective oligomerization of ethylene using chromium catalysts with P-N-P ligands. Background technique [0002] In the presence of simple aluminum alkyl catalysts (in the so-called "chain growth" process) or alternatively in the presence of organometallic nickel catalysts (in the so-called Shell higher olefins, or "SHOP" process), alpha olefins It can be produced commercially by oligomerization of ethylene. Both of these processes typically produce crude oligomer products with a broad distribution of even-numbered carbon-atom alpha olefins (ie, butene-1, hexene-1, octene-1, etc.). The individual alpha olefins in the crude oligomer product are then typically separated in a series of distillation columns. Butene-1 is generally the least valuable of these olefins, as it is also produced in large quantities as a by-product in various cracking and refining processes. Hexene-1 and octene-1 often command relatively hig...

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Problems solved by technology

However, we have observed that the alpha selectivity of hexenes produced with these catalysts can be slightly reduced as process conditions are optimized to promote very high catalyst activity (>1×10 ethylene consumed per gram of Cr per hour 6 gram)

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