Polyethylene Copolymers via Multi-Catalyst Segmentation
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Solution Overview
Problem
There is a need for controlled techniques to produce polyethylene copolymers with broad orthogonal composition distribution (BOCD) to achieve improved physical properties such as stiffness, toughness, and processability, which are currently limited by the trade-offs between these attributes in traditional catalyst systems.
Innovation Solution
The use of a catalyst system comprising multiple pre-catalysts co-supported on a single support, such as bis(n-butyl, methyl cyclopentadienyl) zirconium and bis(1-ethylindenyl) zirconium, with a silica methylaluminoxane activator, allows for the adjustment of molecular weight distribution, short chain branch distribution, and long chain branching to achieve a broad orthogonal composition distribution, enabling the production of polymers with enhanced properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional Ziegler-Natta or chromium based catalysts are used, then broad short chain branch distribution (SCBD) is achieved, but the trade-off between stiffness, toughness, and processability cannot be optimized
Solution Approach 1:
The patent divides the single catalyst system into multiple distinct pre-catalysts (e.g., a first pre-catalyst and a second pre-catalyst with different metallocene structures). Each pre-catalyst contributes differently to polymer chain formation, enabling independent control over molecular weight distribution and short chain branch distribution. This segmentation allows simultaneous optimization of stiffness, toughness, and processability without being constrained by the uniform SCBD produced by traditional single-site catalysts.
2Manufacturing precision
If single site metallocene catalysts are used, then homogeneous copolymers with narrow molecular weight distribution are produced, but the ability to achieve broad orthogonal composition distribution is limited
Solution Approach 1:
The patent creates a composite catalyst system by combining multiple pre-catalysts with different metallocene structures (e.g., ansa-metallocene and non-ansa metallocene) on a single support. This composite approach allows the system to exhibit properties that neither catalyst alone could provide: the first pre-catalyst can control molecular weight distribution while the second pre-catalyst controls short chain branch distribution, achieving broad orthogonal composition distribution and superior polymer properties.
3Productivity
If reaction temperature is increased to increase production rates, then productivity improves, but molecular weight distribution narrowing occurs
Solution Approach 1:
The patent changes the fundamental parameter of catalyst structure from single-site to multi-site systems. By using multiple pre-catalysts with different thermal stabilities and activity characteristics, the system can maintain broad molecular weight distribution even at elevated temperatures. The different pre-catalysts respond differently to temperature changes, allowing one to compensate for the other and maintain MWD control while achieving high production rates.
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 approach enables the production of polyethylene copolymers with improved balance of stiffness, toughness, and processability, as demonstrated by the pilot plant runs, which show higher melt index ratio, dart impact strength, and absence of long chain branching, resulting in polymers with superior performance characteristics.
Implementation Method 1
catalyst system comprising multiple pre-catalysts co-supported on a single support, such as bis(n-butyl, methyl cyclopentadienyl) zirconium and bis(1-ethylindenyl) zirconium, with a silica methylaluminoxane activator
Data Source
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AI summary
Polymers, and systems and methods for making and using the same are described herein. A polymer includes ethylene and at least one alpha olefin having from 4 to 20 carbon atoms. The polymer has a melt index ratio (MIR) greater than about 40. The polymer also has a value for Mw1/Mw2 of at least about 2.0, wherein Mw1/Mw2 is a ratio of a weight average molecular weight (Mw) for a first half of a temperature rising elution (TREF) curve from a cross-fractionation (CFC) analysis to an Mw for a second half of the TREF curve. The polymer also has a value for Tw1 - Tw2 of less than about -15 °C, wherein Tw1 - Tw2 is a difference of a weight average elution temperature (Tw) for the first half of the TREF curve to a Tw for the second half of the TREF curve.