Chromium Catalyst Diphosphine Ligands Ethylene Oligomerization
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Solution Overview
Problem
Current chromium-based catalyst systems for ethylene oligomerization face challenges such as low activity, high polymer co-product formation, and selectivity towards heavy oligomers, especially at elevated temperatures, which complicates the production of 1-octene and 1-hexene with minimal unwanted co-products.
Innovation Solution
A process using a catalyst system comprising a source of chromium and a novel diphosphine ligating compound, specifically designed to optimize ethylene oligomerization conditions, which includes a ligating compound with specific aromatic moieties and a linking group, and optionally an activator, to enhance catalyst performance and selectivity towards 1-octene and 1-hexene while reducing polymer formation and heavy oligomer selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If chromium-based catalyst systems with conventional diphosphine ligands are used for ethylene oligomerization, then catalyst activity can be maintained, but polymer co-product formation increases and selectivity towards heavy oligomers worsens at elevated temperatures
Solution Approach 1:
The patent modifies the diphosphine ligand structure by introducing specific substituents (such as fluorine atoms at ortho positions, methoxy groups, or alkyl groups) on the aromatic rings to change the electronic and steric parameters of the catalyst system. These parameter changes in the ligand structure enable the catalyst to maintain high activity while suppressing polymer formation and heavy oligomer production, particularly at elevated temperatures above 80°C where conventional catalysts fail.
Solution Approach 2:
The invention applies local quality modification by placing specific functional groups (fluorine, methoxy, alkyl) at particular positions (ortho positions) on the aromatic rings of the diphosphine ligand. This localized modification of the ligand structure creates specific steric and electronic environments at the catalyst active site, which selectively promotes tetramerisation to 1-octene while minimizing unwanted polymer co-product formation.
2Productivity
If reaction temperature is elevated to increase reaction rate, then productivity improves, but selectivity towards heavy oligomers increases and catalyst stability decreases
Solution Approach 1:
The patent changes the thermal stability parameters of the catalyst system by incorporating robust diphosphine ligands with electron-withdrawing groups (such as fluorine atoms) that strengthen the chromium-ligand bond. This parameter change enables the catalyst to maintain its structural integrity and selectivity even at elevated temperatures (above 80°C), allowing the reaction to proceed at higher rates without sacrificing 1-octene selectivity or promoting heavy oligomer formation.
3Ease of manufacture
If conventional diphosphine ligands are used, then catalyst synthesis is straightforward, but catalyst performance at elevated temperatures deteriorates with low activity and high polymer formation
Solution Approach 1:
The patent modifies the ligand synthesis parameters by using commercially available substituted aromatic compounds (such as fluorinated benzenes or methoxy-substituted benzenes) that can be readily converted to the required diphosphine ligands through standard organic synthesis procedures. These parameter changes in the starting materials and synthesis conditions maintain ease of manufacture while producing ligands with enhanced thermal stability and catalytic performance at elevated temperatures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The catalyst system achieves high activity, low polymer co-product formation, and improved selectivity towards 1-octene, maintaining effectiveness even at elevated temperatures, thereby addressing the limitations of existing systems.
Implementation Method 1
chromium-based catalyst systems with diphosphine ligands catalyse the selective conversion of ethylene to 1-hexene and/or 1-octene
Implementation Method 2
chromium(III) acetylacetonate and (1-benzofuran-7-yl)2PN(n-Hex)P(phenyl)2, a chromium complex of the ligand was generated in situ and used for the oligomerisation of ethylene
Data Source
AI summary
A process for the otigomerisation of ethylene to predominantly 1-hexene or 1-octene or mixtures of 1-hexene and 1-octene includes contacting ethylene with a catalyst under ethylene oligomerisation conditions. The catalyst comprises a source of chromium, a diphosphine ligating compound, and optionally an activator. The diphosphine ligating compound includes at least one optionally substituted fused cyclic structure including at least two rings, the optionally substituted fused cyclic structure including a 5- to 7- membered aromatic first ring bonded to a phosphorus atom, the aromatic first ring being fused to a 4- to 8-membered heterocyclic second ring, the heterocyclic second ring including a heteroatom which is separated by two ring atoms along the shortest connecting path from the phosphorous atom that is bonded to the first aromatic ring.