Asymmetric Bridged Metallocene Catalysts for Polypropylene
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Solution Overview
Problem
Conventional catalyst systems for polypropylene production suffer from deactivation in the presence of higher alpha olefins and dienes, require costly separation of racemic isomers, and produce polypropylene with insufficient melt strength, necessitating post-reactor modifications and increased production costs.
Innovation Solution
Development of aromatic-solvent-free supported catalyst systems using asymmetric bridged metallocenes with indacenyl ligands, which allow for in-situ production of MAO within a metal oxide support, reducing production costs and avoiding the instability of low-temperature MAO formation processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional catalyst systems are used, then polypropylene production is achieved, but catalyst deactivation occurs in the presence of higher alpha olefins and dienes
Solution Approach 1:
The patent modifies the catalyst system by changing the ligand structure from conventional indenyl to indacenyl ligands, which fundamentally alters the electronic and steric properties of the catalyst. This parameter change enables the catalyst to maintain high activity while resisting deactivation by higher alpha olefins and dienes, directly resolving the contradiction between productivity and reliability.
Solution Approach 2:
The patent employs composite catalyst systems combining metallocene catalysts with specific supports and activators (such as methylalumoxane). This composite approach creates a synergistic effect where the support and activator components enhance the catalyst's resistance to deactivation while maintaining high polypropylene production rates.
2Productivity
If racemic isomers of bis-indenyl zirconocenes are used, then high activity and molecular weight capability are achieved, but separation of racemic isomers is required increasing production costs
Solution Approach 1:
The patent employs asymmetric indacenyl ligands that create chiral catalyst environments, enabling the production of isotactic polypropylene with high stereoregularity. This asymmetry in the ligand structure allows for high catalytic activity and molecular weight capability without requiring separation of racemic isomers, as the asymmetric ligand configuration inherently provides the desired stereocontrol, thereby reducing production costs.
3Productivity
If conventional catalyst systems are used, then polypropylene production is achieved, but melt strength is insufficient requiring post-reactor modifications
Solution Approach 1:
The patent enables continuous production of polypropylene with high melt strength properties directly during the polymerization process. By using indacenyl ligand catalysts that promote long-chain branching in-situ, the useful action of producing high-quality polymer continues uninterrupted without requiring separate post-reactor modification steps, thus maintaining productivity while achieving the desired strength properties.
Solution Approach 2:
The patent merges the polymerization function with the branching function into a single catalytic process. The catalyst system simultaneously performs chain growth and introduces long-chain branches during polymerization, combining what were previously separate processes (polymerization followed by post-reactor branching) into one integrated operation, thereby eliminating post-reactor modifications while maintaining high productivity.
4Ease of manufacture
If MAO is prepared by low temperature reaction of TMA and water in toluene, then catalyst activation is achieved, but the process is exothermic and requires special care with cold storage
Solution Approach 1:
The patent changes the temperature parameter of the MAO formation process from low temperature to higher temperatures, which fundamentally alters the reaction characteristics. At elevated temperatures, the reaction becomes more manageable with better heat control, eliminating the need for cold storage infrastructure while still producing the required catalyst activator, thus simplifying the overall process.
Solution Approach 2:
The patent converts the exothermic nature of the MAO formation reaction from a harmful effect (requiring cold storage and special care) into a beneficial feature. By controlling the reaction to occur at higher temperatures with appropriate heat management, the exothermicity becomes a source of reaction driving force and can be managed through standard thermal processing equipment, thereby simplifying the overall process requirements.
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 aromatic-solvent-free supported catalyst systems achieve higher activity and comonomer incorporation, producing polypropylene with enhanced properties such as high melting point, high molecular weight, and long chain branching without catalyst deactivation, even at high comonomer concentrations, thus reducing production costs and eliminating the need for post-reactor processing.
Implementation Method 1
catalyst systems for the polymerization of olefins
Implementation Method 2
MAO is typically formed from the low temperature reaction of trimethylaluminum (TMA) and water
Data Source
AI summary
The present disclosure provides aromatic-solvent-free supported catalyst compounds and catalyst systems comprising asymmetric bridged metallocenes containing a ligand having at least one saturated ring, catalyst systems including such compounds, and uses thereof. These supported catalyst compounds and catalyst systems can be used to prepare polymer comprising no aromatic solvent.