Ethylene Oligomerization Mixed Ligand Selectivity
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Solution Overview
Problem
Current ethylene oligomerization processes using chromium catalysts with P-N-P ligands suffer from poor alpha selectivity, leading to the production of commercially valueless cyclic C6 molecules, which require additional energy-intensive separation steps, and catalyst activity decreases when optimized for high performance.
Innovation Solution
A mixed catalyst system comprising a chromium source, specific diphosphine ligands with bulky hydrocarbyl substituents, and an activator, such as alumoxanes, is used to achieve high catalyst activity and selectivity for octene and hexene production, maintaining high alpha selectivity even at elevated activity levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If chromium catalysts with P-N-P ligands are used for ethylene oligomerization, then catalyst activity is improved, but alpha selectivity deteriorates leading to poor hexene selectivity and formation of cyclic C6 molecules
Solution Approach 1:
The patent applies local quality by introducing a specific substituent (R) at the ortho position of the phenyl group in the P-N-P ligand structure. This localized structural modification at a specific position of the ligand creates a unique electronic and steric environment around the chromium catalyst center, thereby improving alpha selectivity for hexene production while maintaining high catalyst activity.
Solution Approach 2:
The patent employs parameter changes by modifying the chemical structure of the P-N-P ligand through the introduction of substituent R at the ortho position. This structural parameter change alters the electronic and steric properties of the catalyst, optimizing the balance between catalyst activity and alpha selectivity for hexene production.
2Productivity
If conventional P-N-P ligands are used, then catalyst activity is maintained, but additional separation steps are required due to poor alpha selectivity, increasing energy consumption
Solution Approach 1:
By introducing substituent R at the ortho position of the ligand, the patent creates a localized structural feature that enhances alpha selectivity. This local modification reduces the formation of cyclic C6 byproducts, thereby minimizing the need for additional separation steps and reducing energy consumption in the overall process.
Solution Approach 2:
The patent converts the potential harm of poor selectivity (which would require energy-intensive separation) into a benefit by designing a ligand structure that inherently promotes alpha selectivity. The ortho-substituted P-N-P ligand structure transforms the catalyst's interaction with ethylene to favor hexene production, eliminating the need for additional separation energy.
3Productivity
If process conditions are optimized for high catalyst activity, then productivity increases, but alpha selectivity of hexene decreases
Solution Approach 1:
The patent uses local quality by placing substituent R at the ortho position of the ligand structure. This localized structural feature maintains a stable catalyst geometry that preserves alpha selectivity even under process conditions optimized for high activity, unlike conventional ligands where activity optimization compromises selectivity.
Solution Approach 2:
The patent creates a composite catalyst system by combining chromium with the specifically designed ortho-substituted P-N-P ligand. This composite structure integrates the benefits of high chromium activity with the selectivity-enhancing features of the modified ligand, allowing simultaneous optimization of both activity and alpha selectivity under the same process conditions.
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 process ensures high alpha selectivity for hexene and octene production, reducing the formation of unwanted cyclic molecules and minimizing energy requirements for separation, while maintaining high catalyst activity, thus enhancing process efficiency and product value.
Implementation Method 1
contacting ethylene with an oligomerization catalyst comprising; 1) a source of chromium; 2.1) a first ligand defined by the formula: wherein R is isopropyl; 2.2) a second ligand defined by the formula: wherein R2
Data Source
AI summary
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.