Chromium Oxide Catalyst Modification for HDPE Molecular Weight Control
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Solution Overview
Problem
Current processes using chromium oxide-based catalysts for polyethylene production struggle to achieve a high molecular weight and broad molecular weight distribution, which are desirable for improved processability and impact resistance, while maintaining catalyst activity and productivity, especially when compared to silylchromate-based catalysts.
Innovation Solution
A process involving a supported chromium oxide catalyst modified with an organic compound containing oxygen and nitrogen atoms, such as amino esters or amino alcohols, is used to polymerize ethylene, allowing for variation in molecular weight and distribution while enhancing catalyst activity and productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If chromium oxide-based catalysts are used for polyethylene production, then productivity and catalyst activity are high, but molecular weight distribution is narrow and molecular weight is limited
Solution Approach 1:
The patent applies parameter changes by modifying the catalyst system with electron-donating compounds (such as esters, ethers, or amines) to alter the electronic environment of the chromium active sites. This chemical modification changes the polymerisation parameters to achieve broader molecular weight distribution while maintaining high productivity, resolving the contradiction between catalyst performance and polymer properties
Solution Approach 2:
The patent creates a composite catalyst system by combining chromium oxide with electron-donating organic compounds. This composite approach integrates the high productivity of chromium oxide catalysts with the molecular weight broadening effect of electron-donating modifiers, achieving both high catalyst activity and desirable polymer molecular weight distribution
2Manufacturing precision
If silylchromate-based catalysts are used, then molecular weight distribution is broad and processability is improved, but productivity is relatively low
Solution Approach 1:
The patent uses electron-donating compounds as intermediaries that mediate between the chromium oxide catalyst and the ethylene monomer. These intermediary compounds modify the catalyst's electronic properties to broaden molecular weight distribution, achieving silylchromate-like polymer properties while maintaining chromium oxide-based catalyst productivity
3Ease of manufacture
If chromium oxide catalysts are used, then catalyst cost is low, but molecular weight and impact resistance are insufficient
Solution Approach 1:
The patent changes the chemical parameters of the chromium oxide catalyst by introducing electron-donating compounds that modify the active site electronics. This parameter modification enables the production of high molecular weight polyethylene with improved impact resistance while keeping the base catalyst as cost-effective chromium oxide rather than expensive silylchromate
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 modified chromium oxide catalyst produces polyethylene with a broader molecular weight distribution and increased high molecular weight shoulder, resulting in improved impact resistance, environmental stress cracking resistance, and melt strength, comparable to silylchromate-based catalysts, while maintaining high productivity.
Implementation Method 1
a supported chromium oxide based catalyst which is modified with an organic compound comprising an oxygen and a nitrogen atom
Data Source
AI summary
The present invention is directed to a process for the production of high density polyethylene by polymerisation of ethylene in the presence of a supported chromium oxide based catalyst which is modified with an organic compound comprising oxygen and a nitrogen atom which is selected from the group consisting of saturated heterocyclic organic compounds with a five or six membered ring, amino esters and amino alcohols. Such organic compounds allow manufacturing of HDPE with increases molecular weight distribution and increased molecular weight.