Toluene-Free Supported Metallocene Catalyst via In-Situ Alumoxane
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Solution Overview
Problem
Commercially available methylalumoxane (MAO) catalyst systems for olefin polymerization are unstable and contain detectable amounts of aromatic solvents, which affect their performance and stability, and result in polyolefin products with residual solvent contamination, making them unsuitable for sensitive applications.
Innovation Solution
A method for preparing supported alumoxane catalyst systems using an aliphatic solvent, where a hydrocarbyl aluminum compound reacts with a non-hydrolytic active oxygen-containing compound to form a stable alumoxane precursor, which is then contacted with a catalyst compound, eliminating detectable aromatic solvent content and enhancing stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If commercially available MAO is used as a toluene solution to activate metallocene catalysts, then good catalytic activity and productivity are achieved, but aromatic solvent residues contaminate the polyolefin products and stability is reduced
Solution Approach 1:
The invention extracts and removes the harmful aromatic solvent (toluene) from the MAO solution by using an aliphatic solvent (hexane) as the medium. The MAO is prepared and maintained in hexane solution, which does not leave harmful residues in the polyolefin product, thereby eliminating contamination while preserving catalytic functionality.
Solution Approach 2:
The invention changes the solvent parameter from aromatic (toluene) to aliphatic (hexane). This parameter change eliminates the harmful aromatic residues in the product while maintaining the ability of the solvent to dissolve and stabilize MAO, thus preserving catalytic activity without the negative effects of aromatic contamination.
2Stability of the object's composition
If commercially available MAO in toluene solution is stored at cold temperatures to reduce gelation, then gelation is reduced, but the MAO becomes unstable and requires special handling with short shelf life
Solution Approach 1:
The invention changes the solvent parameter from aromatic to aliphatic, which fundamentally alters the stability characteristics of MAO. The aliphatic solvent (hexane) provides a more stable environment for MAO that does not require cold storage to prevent gelation, thereby improving shelf life and handling stability while maintaining compositional stability.
3Object-affected harmful factors
If aliphatic solvent is used instead of aromatic solvent to prepare MAO, then aromatic solvent residues are eliminated from polyolefin products, but MAO precipitation occurs reducing catalytic performance
Solution Approach 1:
The invention successfully uses aliphatic solvent (hexane) instead of aromatic solvent, changing the solvent parameter to eliminate aromatic residues. The key is that the MAO is freshly prepared in situ in the hexane solution and used immediately, which maintains its dissolved state and catalytic activity without the precipitation problems that would occur with stored solutions.
4Object-affected harmful factors
If MAO is prepared in situ in aliphatic solvent, then aromatic solvent contamination is eliminated and stability is improved, but additional preparation steps and process complexity are introduced
Solution Approach 1:
The invention performs preliminary preparation of the MAO in the aliphatic solvent (hexane) before the polymerization step. By preparing the activated catalyst system in advance in the desired solvent medium, the process ensures that no aromatic residues are introduced during polymerization, while the pre-prepared nature of the solution simplifies the overall process.
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 provides a stable catalyst system free from aromatic solvents, maintaining high productivity and operability, and producing polyolefins with negligible aromatic hydrocarbon residues, suitable for applications requiring low solvent contamination, such as food packaging.
Implementation Method 1
at least one hydrocarbyl aluminum compound and at least one non-hydrolytic active oxygen-containing compound to form a stable alumoxane precursor
Implementation Method 2
an aromatic solvent can dissolve MAO without causing any issue observed with other solvents... A homogeneous MAO solution is desired for MAO molecules to be evenly distributed in the pores of the a catalyst support material
Data Source
AI summary
The present disclosure provides methods for preparing a catalyst system comprising contacting in an aliphatic solvent at least one support material, at least one hydrocarbyl aluminum compound and at least one non-hydrolytic active oxygen-containing compound to form a supported alumoxane (catalyst system precursor) and contacting the supported alumoxane with at least one catalyst compound having a Group 3 through Group 12 metal atom or lanthanide metal atom. The supported alumoxane may be heated prior to contact with the catalyst compound.