Chromium Catalyst Ligand Design for 1-Octene Selectivity
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Solution Overview
Problem
Current chromium-based catalyst systems for ethylene tetramerization suffer from low activity, high polymer co-product formation, and selectivity towards heavy oligomers, especially at elevated temperatures, which complicates the production of 1-octene and leads to polymer fouling and reactor issues.
Innovation Solution
A process using a chromium catalyst system with a diphosphine ligating compound featuring substituted aromatic rings and a specific linking group, which maintains catalyst stability and selectivity towards 1-octene even at higher temperatures, reducing polymer co-product 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 tetramerisation, then catalyst activity can be maintained, but polymer co-product formation increases and selectivity towards heavy oligomers worsens, especially at elevated temperatures
Solution Approach 1:
The patent modifies the chemical parameters of the ligand system by introducing specific substituted aromatic rings with electron-withdrawing groups and heteroatoms (O or S) at ortho positions. This changes the electronic and steric parameters of the catalyst, resulting in reduced polymer formation and improved selectivity towards 1-octene while maintaining catalyst activity.
Solution Approach 2:
The patent creates a composite catalyst system combining chromium with a specifically designed diphosphine ligand featuring substituted aromatic rings. This composite structure integrates multiple functional elements (chromium center, phosphine groups, substituted aromatic rings) that work synergistically to achieve high activity while suppressing polymer formation and heavy oligomer production.
2Productivity
If reaction temperature is elevated to improve process efficiency, then productivity increases, but catalyst stability decreases and selectivity towards heavy oligomers increases
Solution Approach 1:
The patent changes the thermal stability parameters of the catalyst system through the introduction of thermally robust ligand structures with substituted aromatic rings. These structural modifications enable the catalyst to maintain its stability and selectivity at elevated temperatures, allowing process operation at higher temperatures without sacrificing catalyst reliability.
3Productivity
If conventional PNP ligands are used for ethylene tetramerisation, then catalyst activity is maintained, but selectivity towards 1-octene decreases due to high heavy oligomer formation
Solution Approach 1:
The patent applies local quality modification by introducing specific substituents at particular positions (ortho positions) on the aromatic rings of the ligand. These localized structural changes at specific sites of the ligand molecule create the desired electronic and steric environment that enhances 1-octene selectivity while maintaining overall catalyst activity.
Solution Approach 2:
The patent modifies the chemical parameters of the ligand structure by incorporating electron-withdrawing groups and heteroatoms at specific positions, which changes the electronic distribution and steric properties of the catalyst active site. This leads to improved selectivity towards 1-octene by favoring the desired oligomerisation pathway over heavy oligomer formation.
4Manufacturing precision
If reaction temperature is increased to shift selectivity from 1-hexene to 1-octene, then 1-octene production improves, but polymer fouling increases
Solution Approach 1:
The patent changes the chemical parameters of the catalyst system to reduce its tendency to form polymer co-products. The modified ligand structure with substituted aromatic rings alters the catalyst's interaction with ethylene, reducing unwanted polymerisation reactions while maintaining the desired oligomerisation selectivity, thereby minimizing polymer fouling even 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 formation, and improved selectivity towards 1-octene, maintaining performance across a range of temperatures and pressures, thereby enhancing process efficiency and reducing reactor fouling.
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 catalyst with novel diphosphine ligands
Data Source
AI summary
A process for the oligomerisation, preferably the tetramerisation, 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 oiigomerisation conditions. The catalyst comprises a source of chromium, a diphosphine ligating compound, and optionally an activator. The diphosphine iigating compound includes at least one substituted aromatic ring bonded to a phosphorous atom. The substituted aromatic ring is substituted at a ring atom adjacent to the ring atom bonded to the respective phosphorous atom with a group Y, where Y is of the form -AREWG, A being O, S or NR5, where R5 is a hydrocarbyl, heterohydrocarbyl or organoheteryl group, and REWG is an electron withdrawing group.