In-situ Cr/P-N-P Catalyst Activation for Ethylene Oligomerization
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Solution Overview
Problem
Existing ethylene oligomerization processes using Cr catalysts with bridged diphosphine ligands face challenges in fouling and require high temperatures, which can lead to reduced catalyst stability and activity, and the need for precise catalyst preparation in the presence of ethylene.
Innovation Solution
A continuous flow process at low temperatures (30-45°C) involving in-situ activation of a Cr/P-N-P catalyst system with hydrogen, where the catalyst is prepared and activated in the absence of ethylene, significantly reducing fouling and optimizing activity by using a 'catalyst first' start-up protocol.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the Cr/P-N-P catalyst system is activated in the presence of ethylene at higher temperatures, then catalyst activity is improved, but reactor fouling increases and catalyst stability decreases
Solution Approach 1:
The catalyst system is activated in advance in the absence of ethylene at low temperatures (30-45°C) before ethylene is introduced. This preliminary activation step allows the catalyst to become fully active without the presence of ethylene, thereby preventing fouling while maintaining high catalyst activity for subsequent oligomerization reactions
2Productivity
If the Cr/P-N-P catalyst system is activated in the presence of ethylene at higher temperatures, then catalyst activity is improved, but catalyst stability decreases
Solution Approach 1:
The activation temperature is changed from conventional high temperatures to low temperatures (30-45°C). This parameter change allows the catalyst to achieve high activity while maintaining stability, as the low temperature prevents degradation and unwanted side reactions that would otherwise reduce catalyst stability
3Productivity
If precise catalyst preparation is performed in the presence of ethylene, then catalyst activity is optimized, but process complexity increases
Solution Approach 1:
The catalyst preparation and activation process is segmented into distinct stages: first activating the catalyst in the absence of ethylene, then introducing ethylene for oligomerization. This segmentation simplifies the overall process by eliminating the need for complex in-situ preparation procedures while maintaining high catalyst 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
This method achieves low fouling rates and high catalyst activity, producing hexene-1 and octene-1 with improved selectivity and stability, allowing for efficient continuous operation with reduced reactor fouling and increased productivity.
Implementation Method 1
a method for the preparation of an activated ethylene oligomerization catalyst under continuous flow conditions, said method comprising contacting: A) a continuous flow of a catalyst system comprising 1) a source of chromium; 2) a P-N-P ligand
Implementation Method 2
The process is operated at a low temperature; produces low levels of fouling and requires the use of hydrogen to optimize activity
Data Source
AI summary
The oligomerization of ethylene using a chromium (Cr) catalyst having a phosphorus-nitrogen-phosphorus (P-N-P) ligand is known. Reactor fouling with by-product polyethylene can be severe at operating temperatures of greater than 60°C. However, the activation of such catalysts in a continuous flow reactor at low temperatures can be difficult and activity can be low. We have now discovered that highly active Cr/P-N-P catalysts may be prepared and activated in-situ (i.e. directly in the polymerization reactor) at low temperatures (from about 30 to about 45°C) by combining the Cr; the P-N-P ligand and an aluminoxane in the process solvent in the presence of hydrogen. The use of hydrogen allows very high productivity (greater than 1 x 106 grams of ethylene conversion per gram of Cr) at low temperature. We have also observed reactor fouling rates as low as 2 to 10 parts per million of polyethylene per hour (based on total ethylene conversion) using this process.