Supported Metallocene Catalyst Purification for Isotactic Polypropylene
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Solution Overview
Problem
Existing methods struggle to separate metallocene compounds of a racemic form from meso isomers effectively, leading to low yields and difficulty in producing high-purity isotactic polypropylene with desired properties.
Innovation Solution
A method involving the dissolution of a racemic form and meso isomer mixture in a solvent mixture of toluene and hexane, followed by controlled temperature and sequential addition, allows for the selective precipitation of the meso isomer, thereby increasing the purity of the racemic form, which is then supported on a carrier to create a high-purity metallocene catalyst.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If general recrystallization solvents are used to separate racemic form from meso isomer, then the separation process becomes simple, but the purity of racemic form cannot be achieved due to similar solubility
Solution Approach 1:
The patent changes the solvent parameters by using a specific mixed solvent system (toluene and n-hexane in a volume ratio of 1:4 to 1:9) instead of general recrystallization solvents. This parameter change creates a significant solubility difference between the racemic form and meso isomer, enabling effective separation while maintaining process simplicity.
Solution Approach 2:
The patent employs a composite solvent system combining toluene and n-hexane in specific proportions. This composite solvent approach leverages the complementary properties of both solvents to achieve selective dissolution and separation, resolving the contradiction between ease of manufacture and manufacturing precision.
2Productivity
If racemic form and meso isomer are produced simultaneously during ansa-metallocene catalyst preparation, then the catalyst preparation is efficient, but the subsequent separation becomes difficult
Solution Approach 1:
By changing the solvent parameters to a specific toluene-n-hexane mixed system, the patent enables simple filtration-based separation instead of complex chromatographic methods, thus reducing separation complexity while maintaining high productivity from simultaneous production of both isomers.
3Reliability
If Ziegler-Natta catalysts are used for polypropylene production, then the process is well-established, but the polymer has high xylene soluble content and broad molecular weight distribution
Solution Approach 1:
The patent extracts the active catalyst species into a supported metallocene catalyst system with defined single-site architecture. This extraction from the multi-site Ziegler-Natta system eliminates the broad molecular weight distribution and high xylene soluble content, achieving uniform polymer properties while maintaining process reliability.
Solution Approach 2:
The patent creates a composite catalyst system combining metallocene compound with solid support materials (such as silica or magnesium chloride). This composite structure provides both the single-site activity for uniform polymer properties and the mechanical stability for reliable industrial processing.
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 a high-purity racemic metallocene catalyst, facilitating the synthesis of isotactic polypropylene with low xylene soluble content and excellent catalytic activity.
Implementation Method 1
dissolving the mixture in a solvent including toluene and hexane, wherein concentrations of toluene and hexane are each independently 0.05 M or more
Implementation Method 2
the step of dissolving the mixture in the solvent including toluene and hexane includes the step of first adding toluene to the mixture to dissolve the mixture, and sequentially, adding hexane thereto to dissolve the mixture at a temperature lower than the dissolution temperature of toluene
Data Source
AI summary
Provided are a method of preparing a supported metallocene catalyst, and a method of preparing polypropylene using the catalyst prepared thereby. According to the present invention, provided is a supported metallocene catalyst capable of preparing an isotactic polypropylene polymer having a low xylene soluble content while having excellent catalytic activity.