Ethylene Oligomerization Activator Preparation
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Solution Overview
Problem
The use of methylaluminoxane (MAO) as an activator for ethylene oligomerization catalysts often results in high levels of by-product polymer, particularly when using modified MAO in aliphatic solvents, and the use of aromatic solvents poses toxicological and separation challenges.
Innovation Solution
A process involving the partial hydrolysis of trimethylaluminum in a non-aromatic solvent to prepare an activator, which is then used within 7 days with a chromium-based catalyst system containing a bridged diphosphine ligand for ethylene oligomerization, minimizing by-product polymer formation and avoiding aromatic solvent issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If modified MAO is used in aliphatic solvents to improve solubility, then solubility is improved, but by-product polymer formation increases
Solution Approach 1:
The invention changes the chemical composition parameters of the activator by using pure MAO instead of modified MAO, and by preparing it in a specific molar ratio range (0.4-1.6) of water to aluminum alkyl. This parameter optimization allows the system to achieve both good solubility in aliphatic solvents and reduced by-product polymer formation, resolving the contradiction between solubility improvement and harmful by-product reduction.
2Stability of the object's composition
If aromatic solvents are used to improve MAO solubility, then solubility is improved, but toxicological issues and separation challenges arise
Solution Approach 1:
The invention changes the solvent type parameter from aromatic to aliphatic, combined with optimizing the activator preparation parameters (water to aluminum alkyl molar ratio). This allows the system to achieve adequate solubility using safer aliphatic solvents, eliminating the toxicological and separation problems associated with aromatic solvents while maintaining process effectiveness.
3Object-generated harmful factors
If pure MAO is used instead of modified MAO to reduce by-product polymer, then by-product polymer formation is reduced, but solubility problems in aliphatic solvents occur
Solution Approach 1:
The invention optimizes the preparation parameters of pure MAO, specifically the molar ratio of water to aluminum alkyl (0.4-1.6) and the aluminum alkyl to chromium catalyst ratio (10-100). This parameter optimization enables pure MAO to achieve both reduced by-product polymer formation and adequate solubility in aliphatic solvents, resolving the contradiction between harmful by-product reduction and solubility maintenance.
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 reduces by-product polymer formation and eliminates the need for aromatic solvents, providing a safer and more efficient ethylene oligomerization process with lower levels of unwanted polymer products.
Implementation Method 1
an activator is prepared by the partial hydrolysis of a solution of an alkyl aluminum with water
Implementation Method 2
contacting: a) said activator; b) a catalyst comprising a source of chromium and a ligand defined by the formula (R1
Data Source
AI summary
The ohgomenzation of ethylene using a chromium catah st having a bridged diphosphine ligand can produce a selective product distribution to predominanth' hexene or predominanth' octene/hexene when activated with aluminoxane. When the aluminoxane is provided in a non-aromatic solvent, the oligomerization reaction also produces pohmer byproducts. The present invention mitigates this problem by the in situ preparation of the aluminoxane activator by partial hydrolysis with water of dilute (0.5 to 3 weight %) trimethylaluminum in the non-aromatic solvent.