Fluorided Silica Catalyst for High-Density Polyethylene
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Solution Overview
Problem
There is a need for new and improved catalyst systems for the polymerization of olefins to achieve increased activity, specific polymer properties such as high melting point, higher density, high molecular weights, and altered comonomer distribution without compromising the polymer's properties.
Innovation Solution
A catalyst system comprising a fluorided silica support, an alkylalumoxane activator, and at least two metallocene catalyst compounds, where the first metallocene is a bridged monocyclopentadienyl group 4 transition metal compound and the second is a biscyclopentadientyl group 4 transition metal compound, used in a process that does not calcine the fluorided support at temperatures of 400° C. or more, to produce ethylene polymer compositions with specific molecular weight distributions and densities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a fluorided silica support is calcined at high temperatures (400°C or more), then the support structure is stabilized, but the polymerization activity and specific polymer properties (high density, high molecular weight) deteriorate
Solution Approach 1:
The patent applies parameter changes by controlling the calcination temperature of the fluorided silica support to be below 400°C. This temperature parameter optimization preserves the support's structural stability while maintaining its catalytic activity and ability to produce high-density polyethylene with high molecular weight, thus resolving the contradiction between support stability and polymerization productivity
2Device complexity
If traditional single metallocene catalysts are used, then the catalyst system is simple, but the polymer properties (molecular weight distribution, comonomer distribution, density) cannot be sufficiently optimized
Solution Approach 1:
The patent merges two different metallocene catalyst compounds into a single catalyst system. This combination enables precise control over polymer properties including molecular weight distribution, comonomer distribution, and density, while maintaining operational simplicity. The dual-catalyst system achieves superior polymer property control compared to single metallocene catalysts
3Strength
If catalyst systems are designed to produce high molecular weight polymers, then the polymer strength is improved, but the processing flexibility and comonomer incorporation are compromised
Solution Approach 1:
The patent applies local quality by using two different metallocene catalysts that each contribute specific properties to the final polymer. One catalyst primarily contributes to high molecular weight and strength, while the other enables comonomer incorporation and processing flexibility. This localized functional assignment within the catalyst system allows the polymer to simultaneously achieve high strength and processing adaptability
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 solution achieves ethylene polymer compositions with high density, improved strength, and flexibility, along with specific molecular weight distributions and comonomer incorporation, enhancing the commercial usefulness of the polymers produced.
Implementation Method 1
a fluorided support, where the fluorided support has not been calcined at a temperature of 400° C. or more
Implementation Method 2
an alkylalumoxane activator, and at least two metallocene catalyst compounds
Data Source
AI summary
This invention relates to ethylene polymers obtained using a catalyst system comprising fluorided silica, alkylalumoxane activator and at least two metallocene catalyst compounds (a bridged monocyclopentadienyl group 4 transition metal compound and a biscyclopentadientyl group 4 transition metal compound), where the fluorided support has not been calcined at a temperature of 400° C. or more, and is preferably produced using a wet mixing method, such as an aqueous method. The ethylene polymers have: 1) at least 50 mol % ethylene; 2) a reversed comonomer index, mol %, (RCI,m) of 85 or more; 3) a Comonomer Distribution Ratio-2 (CDR-2,m) of the percent comonomer at the z average molecular weight divided by the percent comonomer at the weight average molecular weight plus the number average molecular weight divided by 2 ([% comonomer at Mz]/[% comonomer at ((Mw+Mn)/2)] as determined by GPC of 2.3 or more; and 4) a density of 0.91 g/cc or more.