Ligand-Based Chromium Catalyst for Ethylene Trimerization
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Solution Overview
Problem
The selective tetramerization of ethylene is challenging due to the poor structural stability of the CrC8 nine-membered ring intermediate, which hinders the industrial production of 1-octene with high selectivity and catalytic activity.
Innovation Solution
A ligand-based chromium catalyst with specific electronic and steric structural regulation is used to improve the catalytic ability for forming CrC6 and CrC8 cyclic transition states, enabling the selective trimerization and tetramerization of ethylene to produce 1-hexene and 1-octene with high selectivity and productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional metal catalysts (aluminum-based, titanium-based, nickel-based, zirconium-based, iron-based, or cobalt-based) are used for ethylene oligomerization, then the reaction can proceed, but the selectivity for 1-hexene and 1-octene is low and the product distribution follows Schulz-Flory or Poisson distribution
Solution Approach 1:
The patent applies parameter changes by modifying the electronic and steric parameters of the chromium catalyst through specific ligand design. The PNP-ligand with particular substituents (R1-R5) creates a catalyst system with optimized electronic properties that favor selective formation of CrC6 and CrC8 cyclic transition states, thereby improving selectivity for 1-hexene and 1-octene while maintaining high productivity
Solution Approach 2:
The patent employs composite materials by creating a chromium catalyst system composed of chromium trichloride combined with a specifically designed PNP-ligand and methylaluminoxane. This composite catalyst system leverages the synergistic effects of each component: chromium provides the catalytic center, the PNP-ligand provides electronic and steric control, and methylaluminoxane activates the system, together achieving high selectivity and activity
2Reliability
If selective tetramerization is attempted using conventional catalysts, then the reaction can occur, but the CrC8 nine-membered ring intermediate has poor structural stability, hindering high selectivity and catalytic activity
Solution Approach 1:
The patent applies parameter changes by optimizing the electronic parameters of the chromium catalyst through the PNP-ligand design. The ligand's electronic properties (controlled by substituents R1-R5) stabilize the CrC8 nine-membered ring intermediate by adjusting the electron density at the chromium center, thereby improving both the structural stability of the intermediate and the catalytic activity for tetramerization to 1-octene
Solution Approach 2:
The patent uses the PNP-ligand as an intermediary that mediates between the chromium center and the ethylene substrate. The ligand acts as a stabilizing intermediary for the CrC8 intermediate through its electronic and steric properties, protecting the unstable intermediate from decomposition while facilitating the reaction pathway to 1-octene with high selectivity and activity
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 ligand-based chromium catalyst significantly enhances the production of 1-hexene and 1-octene, achieving selectivity ranging from 81% to 87% and maintaining high catalytic activity, facilitating the industrial production of these linear alpha-olefins.
Implementation Method 1
A ligand-based chromium catalyst with specific electronic and steric structural regulation is used to improve the catalytic ability for forming CrC6 and CrC8 cyclic transition states
Data Source
AI summary
A ligand based chromium catalyst and application in catalyzing ethylene oligomerization are disclosed. The chromium catalyst is formed by a chromium compound and an organic ligand containing P and/or N. The substituents on N and P of the ligand can be replaced, whereby selective ethylene trimerization and tetramerization can be realized so as to produce 1-hexene and 1-octene at the same time.