Polymerization catalysts for production of polyethylene with high molecular weight
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Solution Overview
Problem
Existing catalyst systems struggle to produce high molecular weight polymers efficiently at high polymerization temperatures (120°C to 250°C) while maintaining high reactivity.
Innovation Solution
A catalyst system comprising a heterogeneous procatalyst with a titanium species, an aluminum species, and a magnesium chloride component, combined with a hydrogenation procatalyst of the formula Cp2TiX2, where each Cp is cyclopentadienyl substituted with (C1-C10)alkyl and X is a halogen, is used to polymerize (C2-C12)α-olefins in solution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional catalyst systems are used at high polymerization temperatures (120°C to 250°C), then polymerization can proceed at high temperature, but the molecular weight of the produced polymer is low and catalyst efficiency decreases
Solution Approach 1:
The catalyst system is segmented into multiple functional components: a main group IV metal catalyst (Ti, Zr, or Hf) providing polymerization activity, an organometallic compound (Cp2TiX2) acting as a hydrogenation procatalyst, and an aluminum alkoxide compound serving as both cocatalyst and electron donor. This segmentation allows each component to perform its specific function optimally, with the hydrogenation procatalyst specifically targeting H2 removal to enable high molecular weight polymer production at elevated temperatures.
Solution Approach 2:
The invention employs a composite catalyst system combining multiple metal-based compounds with distinct functions. The combination of group IV metal catalyst, organometallic hydrogenation procatalyst, and aluminum alkoxide creates a synergistic system where the components work together to achieve high molecular weight polymerization at temperatures of 120°C to 250°C, overcoming the limitations of individual catalyst systems.
2Quantity of substance
If electron donors are added to increase the high density fraction (HDF), then the molecular weight of polymer increases, but the catalyst efficiency decreases
Solution Approach 1:
The invention changes the chemical parameters of the catalyst system by using specific organometallic compounds with controlled ligand structures (Cp2TiX2 where X is halogen or alkoxide) and specific aluminum alkoxide compounds. These parameter changes optimize the balance between producing high molecular weight polymer and maintaining catalyst efficiency, avoiding the efficiency loss typically associated with electron donor addition.
Solution Approach 2:
The aluminum alkoxide compound serves as an intermediary that facilitates the interaction between the main group IV metal catalyst and the organometallic hydrogenation procatalyst. It acts as both a cocatalyst activating the main catalyst and an electron donor enhancing HDF, while the organometallic compound specifically removes H2 to prevent chain termination. This intermediary role allows the system to achieve high molecular weight and high efficiency simultaneously.
3Productivity
If hydrogen is present in the catalyst system, then polymerization can proceed, but hydrogen terminates the polymerization chain limiting molecular weight increase
Solution Approach 1:
The invention converts the harmful effect of hydrogen (which terminates polymer chains and limits molecular weight) into a beneficial effect by using the organometallic compound Cp2TiX2 as a hydrogenation procatalyst. This procatalyst specifically removes H2 from the system through hydrogenation reactions, transforming hydrogen from a chain-terminating impurity into a controlled reactant that enables high molecular weight polymer production while maintaining polymerization 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
The catalyst system achieves high molecular weight polymers with increased efficiency and reactivity, even at elevated temperatures, by effectively removing hydrogen and enhancing polymer chain growth.
Implementation Method 1
a hydrogenation procatalyst... for removing H2 generated by the metallocene polymerization catalysts; and (2) in one reactor of a linked reactor system, for removing H2 carried over from a prior reactor
Implementation Method 2
The catalyst systems for producing ethylene-based polymers may typically comprise a chromium-based catalyst system, a Ziegler-Natta catalyst system, and/or a molecular (either metallocene or non-metallocene) catalyst system
Data Source
AI summary
The catalyst system includes a heterogeneous procatalyst, an electron donor, and a hydrogenation procatalyst. The heterogeneous procatalyst includes a titanium species, an aluminum species, and a magnesium chloride component. The hydrogenation procatalyst has the formula Cp2TiXnTiCp2 or Cp2TiXn. In formula Cp2TiXn, each Cp is a cyclopentadienyl substituted with at least one R1, wherein R1 is (C1-C10)alkyl; and each X is independently monoanionic or neutral, wherein each X is independently (C1-C40)hydrocarbon, (C1-C40)heterohydrocarbon, (C1-C40)hydrocarbyl, (C1-C40)heterohydrocarbyl, or a halogen atom.