Multi-reactor Slurry Polymerization with Ethylene Purification
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Solution Overview
Problem
In ethylene slurry polymerization processes, catalyst poisons such as oxygen-containing polar molecules degrade yields and selectivity, and there is a need to minimize their adverse effects while ensuring consistent polyethylene structure and composition across reactors.
Innovation Solution
A multi-reactor slurry polymerization process involving a cascade of reactors, where ethylene is purified to reduce impurities like carbon monoxide, carbon dioxide, oxygen, and water before being fed, and fresh aluminum alkyl is used in the first reactor, with subsequent reactors receiving recycled catalyst and diluent, maintaining specific temperature and pressure conditions to produce multimodal polyethylene.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If ethylene containing impurities is used in the polymerization process, then the process complexity is reduced, but catalyst yield and selectivity deteriorate due to poisoning by oxygen-containing polar molecules
Solution Approach 1:
The patent applies preliminary action by purifying the ethylene feedstock before it enters the polymerization reactors. An ethylene purification unit is positioned upstream to remove oxygen-containing polar molecules and other impurities from the ethylene stream before catalysis occurs, preventing catalyst poisoning in advance and maintaining high yield and selectivity
2Device complexity
If ethylene containing impurities is used in the polymerization process, then the process complexity is reduced, but catalyst selectivity deteriorates due to poisoning by oxygen-containing polar molecules
Solution Approach 1:
The purification unit is positioned upstream to remove impurities before they can affect catalyst selectivity. This preliminary removal of oxygen-containing polar molecules ensures that the catalyst maintains its intended selectivity for the desired polymerization reactions throughout the multi-reactor cascade
3Productivity
If ethylene is purified to reduce impurities before being fed to reactors, then catalyst yield and selectivity are improved, but process complexity increases due to addition of purification unit
Solution Approach 1:
The ethylene purification unit acts as an intermediary component between the ethylene feed source and the polymerization reactors. It mediates by selectively removing impurities from the ethylene stream while allowing the purified ethylene to pass through to the catalyst systems, thereby protecting the catalysts without requiring modification of the reactors themselves
4Manufacturing precision
If ethylene is purified to reduce impurities before being fed to reactors, then catalyst selectivity is improved, but process complexity increases due to addition of purification unit
Solution Approach 1:
By performing purification upstream before the ethylene enters the reactor cascade, the patent ensures that catalyst selectivity is maintained throughout the polymerization process. The purification unit is positioned to remove impurities in advance, preventing their interaction with the catalyst systems in the subsequent reactors
5Adaptability or versatility
If multi-reactor cascade process is used to produce multimodal polyethylene, then product versatility is improved, but process complexity increases due to multiple reactors and purification requirements
Solution Approach 1:
The patent applies segmentation by dividing the polymerization process into multiple separate reactors arranged in a cascade. Each reactor can be optimized for producing specific polyethylene characteristics, and the purification unit is positioned upstream to serve all reactors, thereby managing complexity through modular organization while maintaining product versatility
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 process enhances the yield and selectivity of polyethylene production by minimizing catalyst poisoning, ensuring consistent product structure and composition, and producing high-density polyethylene suitable for films, pipes, or blow-molded articles.
Implementation Method 1
before the ethylene is fed to the two or more polymerization reactors of the reactor cascade, the ethylene is passed through an ethylene purification unit and the concentration of the impurity is reduced
Implementation Method 2
Ziegler type catalysts have been used in ethylene polymerization processes. These catalysts use aluminum alkyl compounds as co-catalyst activators to activate titanium or vanadium sites on the catalyst
Implementation Method 3
The monomer(s) are polymerized with a catalyst
Data Source
AI summary
A slurry polymerization process for the preparation of polyethylene in a reactor cascade of two or more polymerization reactors including the steps of feeding to a polymerization reactor amounts of ethylene, of a Ziegler catalyst, of fresh aluminum alkyl and of a diluent; feeding the slurry product withdrawn from the polymerization reactor to a second polymerization reactor; and feeding additional amounts of ethylene and of diluent wherein the ethylene is first passed through an ethylene purification unit, which reduces at least the concentration of carbon monoxide, carbon dioxide, oxygen, acetylene and water contained in the ethylene, before it is fed to the two or more polymerization reactors of the reactor cascade.