Chromium Catalyst Reduction for Polyolefin Flow Index Control
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Solution Overview
Problem
Chromium-based catalysts used in polyolefin production often fail to achieve the desired flow index response, leading to inconsistent polymer properties and operational difficulties in polymerization reactors, as existing methods lack precise control over the catalyst's reduction process and drying temperature.
Innovation Solution
A method involving the controlled addition of a reducing agent to a chromium-based catalyst in a mix vessel, with a conduit extension directing the agent to a specific location within the vessel, combined with adjustable agitation and drying temperature, to achieve a desired flow index response and increase catalyst productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a chromium-based catalyst is activated by calcining in a non-reducing atmosphere to convert chromium to hexavalent state, then catalyst productivity and activity are improved, but the flow index response becomes inconsistent and polymer molecular weight distribution becomes narrower than desired
Solution Approach 1:
The patent applies preliminary action by performing a controlled reduction treatment of the hexavalent chromium catalyst before polymerization. The reducing agent is added in advance to convert excess Cr+6 to Cr+3, creating a pre-conditioned catalyst with optimized reduction state distribution. This preliminary reduction step ensures consistent flow index response and broader molecular weight distribution in the resulting polyolefin, while maintaining the high productivity achieved through initial hexavalent chromium activation.
2Productivity
If the reducing agent is added rapidly to the chromium-based catalyst, then the reduction process is faster and productivity increases, but the flow index response and molecular weight characteristics become inconsistent
Solution Approach 1:
The patent implements periodic action by adding the reducing agent in controlled stages rather than all at once. The addition occurs over a specified time period with intermittent mixing, allowing progressive reduction of Cr+6 to Cr+3. This staged approach ensures uniform distribution of reducing agent and consistent reduction state throughout the catalyst particles, resulting in reproducible flow index response and molecular weight characteristics while maintaining efficient reduction speed.
3Loss of time
If the catalyst is dried at higher temperature to remove solvent more quickly, then processing time is reduced and productivity increases, but the flow index response and catalyst activity become inconsistent
Solution Approach 1:
The patent applies parameter changes by optimizing the drying temperature to a specific range that balances solvent removal efficiency with catalyst consistency. The controlled drying process maintains temperature parameters that prevent overheating and ensure uniform solvent evaporation throughout the catalyst particles. This parameter optimization achieves adequate solvent removal within acceptable time frames while maintaining consistent flow index response and catalyst activity across production batches.
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 allows for tailored flow index response and increased productivity of the chromium-based catalyst, resulting in polyolefins with consistent molecular weight and improved processing characteristics, reducing operational issues in polymerization reactors.
Implementation Method 1
introducing a reducing agent into the mix vessel... to promote reaction of the reducing agent with the chromium-based catalyst to give a reduced chromium-based catalyst
Data Source
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Figure 3A~3B
AI summary
A method of preparing a chromium-based catalyst for the polymerization of an olefin into a polyolefin, the method comprising: feeding a chromium-based catalyst to a mix vessel; introducing a stream comprising a reducing agent into the mix vessel through a conduit extending into a nozzle of the mix vessel; and agitating a mixture of the chromium-based catalyst, the reducing agent, and a solvent in the mix vessel to promote contact of the reducing agent with the chromium-based catalyst to give a reduced chromium-based catalyst.