Co-Supported Chromium and Group 4 Catalyst for Bimodal Polyethylene
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Solution Overview
Problem
Existing co-supported and mixed catalyst systems for polyethylene production, particularly those involving chromium and transition metal catalysts, face challenges in achieving bimodal polyethylene with reversed comonomer incorporation and improved mechanical properties, as they often result in deactivation or poisoning of catalyst components.
Innovation Solution
A catalyst system comprising a co-supported group 6 based chromium catalyst and a group 4 based organometallic catalyst, with the organometallic catalyst featuring phosphinimide or ketimide ligands, is immobilized on an inorganic oxide support, allowing for the production of broad or bimodal polyethylene with enhanced comonomer incorporation and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If chromium catalyst and group 4 transition metal catalyst are combined in co-supported or mixed catalyst formulations, then the molecular weight distribution broadens and mechanical properties improve, but the catalyst components deactivate each other
Solution Approach 1:
A silica support acts as an intermediary carrier that physically separates the chromium catalyst and group 4 transition metal catalyst components. The support provides distinct locations for each catalyst type, preventing direct harmful interactions while maintaining their individual activities. This mediator approach allows the beneficial effects of both catalysts to coexist without mutual deactivation.
Solution Approach 2:
The catalyst system is segmented into distinct chromium-based catalyst components and group 4 transition metal catalyst components, each supported separately on the silica carrier. This segmentation prevents the catalyst components from interacting in a way that causes deactivation, while still allowing them to work together in the polymerization process to achieve broad molecular weight distribution and improved mechanical properties.
2Productivity
If conventional chromium and metallocene catalysts are co-supported, then bimodal polyethylene is produced, but the metallocene catalyst is poisoned by chromium compounds
Solution Approach 1:
The silica support serves as an intermediary that carries both the chromium catalyst precursor and the metallocene catalyst separately. This physical separation through the support medium prevents the chromium compounds from poisoning the metallocene catalyst while still allowing both catalysts to function in the polymerization process to produce bimodal polyethylene.
Solution Approach 2:
The chromium catalyst precursor and metallocene catalyst are pre-supported on the silica carrier in a controlled manner before the polymerization reaction begins. This preliminary arrangement ensures that the catalysts are positioned and stabilized on the support, reducing the risk of harmful interactions during the reaction while maintaining their respective activities for producing the desired bimodal polymer structure.
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 effectively produces polyethylene with a bimodal molecular weight distribution and reversed comonomer incorporation, improving environmental stress cracking resistance and processability, while maintaining catalyst compatibility and activity.
Implementation Method 1
a catalyst system comprising a co-supported group 6 based polymerization catalyst and a group 4 based polymerization catalyst which do not significantly deactivate or poison one another when immobilized on a single support
Data Source
Figure 1~2
Figure 3
AI summary
Polyethylene is made by (co)polymerizing ethylene in a gas-phase reactor using a catalyst system comprising a chromium catalyst and a Group 4 transition metal catalyst, co-supported on an inorganic oxide support. The Group 4 transition metal catalyst is defined by the formula shown, wherein M is a Group 4 metal, P1 is a phosphinimide or ketimide ligand (shown), L is a monoanionic ligand which is a cyclopentadienyl or a bulky heteroatom type ligand, m is 1 or 2, n is 0 or 1, and p is an integer. The co-supported catalyst system gives access to polyethylene having a broad or bimodal molecular weight distribution. In the copolymerization of ethylene, reversed or partially reversed comonomer distribution is achieved: the Group 4 component provides polymer segments having higher molecular weight and also higher comonomer incorporation than polymer segments produced at the chromium sites. (Formulae I,II,III).