Metallocene Catalyst Transition in Gas Phase Polymerization Reactors
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Solution Overview
Problem
Transitioning between metallocene catalysts in gas phase polymerization reactors is inefficient due to issues like sheeting, fouling, and plugging, which require lengthy shutdowns and produce off-grade resin, and existing methods fail to effectively use water as a polymerization neutralizer without causing catastrophic events.
Innovation Solution
A method involving reducing superficial gas velocity, increasing the reactor bed height, and using a sequence of polymerization neutralizers, including carbon monoxide and water, to safely stop polymerization without interrupting fluidization, followed by purging with an inert gas and introducing the new metallocene catalyst.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional kill procedures are used to transition between metallocene catalysts, then the reactor can be purged and reloaded with new catalyst, but the process requires opening the reactor, producing off-grade resin, and allowing impurities to enter, resulting in time-consuming and expensive operations
Solution Approach 1:
The patent introduces a polymerization neutralizer as an intermediary substance to stop the polymerization reaction and neutralize the metallocene catalyst in situ, eliminating the need to open the reactor for catalyst deactivation. This mediator enables the transition process to be completed through chemical means rather than mechanical intervention, significantly reducing transition time and avoiding contamination from opening the reactor.
Solution Approach 2:
The patent maintains continuous operation of the reactor throughout the catalyst transition process by keeping the fluidized bed intact and avoiding shutdown. The neutralizer is introduced while the reactor remains operational, and the new catalyst is introduced without interrupting the fluidization, ensuring continuous useful action and eliminating the need for reactor opening and reloading.
2Reliability
If water is used as a polymerization neutralizer with metallocene catalysts, then neutralization is achieved, but catastrophic events occur due to unpredictable static tendencies and sheeting behavior
Solution Approach 1:
The patent uses carbon monoxide as an intermediary neutralizer that first stops the polymerization reaction without causing sheeting or static charge issues. This intermediate step prepares the system for subsequent water introduction by eliminating the metallocene catalyst activity in a controlled manner, preventing the catastrophic events that would occur if water were introduced directly.
Solution Approach 2:
The patent performs preliminary neutralization using carbon monoxide before introducing water as the neutralizer. This preliminary action removes the unpredictable static tendencies and sheeting behavior associated with metallocene catalysts, creating a safe condition for subsequent water introduction and eliminating the harmful effects that would otherwise occur.
3Reliability
If the reactor is opened for catalyst transition, then complete catalyst removal and replacement is achieved, but impurities such as moisture and air enter the reactor, necessitating additional time-consuming removal procedures
Solution Approach 1:
The patent uses a polymerization neutralizer as an intermediary chemical agent to deactivate and remove the metallocene catalyst in situ, eliminating the need to open the reactor for catalyst removal. This chemical mediation achieves complete catalyst deactivation while maintaining the sealed reactor environment, preventing impurity contamination.
Solution Approach 2:
The patent maintains the reactor in a closed, operational state throughout the entire catalyst transition process. The fluidized bed is never interrupted, and the reactor remains sealed, ensuring continuous useful action while preventing any impurity entry that would occur with opening the reactor.
4Adaptability or versatility
If metallocene catalysts are used during reactor shutdown or transition, then catalyst flexibility is maintained, but unpredictable static tendencies cause sheeting and fouling, forcing complete shutdowns
Solution Approach 1:
The patent introduces a polymerization neutralizer as an intermediary substance to control and neutralize the metallocene catalyst during transition. This mediator stabilizes the system by chemically deactivating the catalyst's unpredictable static tendencies, allowing flexible catalyst transitions while maintaining reactor operation stability and preventing sheeting and fouling.
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
Enables faster and more efficient transitions with reduced off-grade product formation by safely using water as a neutralizer, minimizing sheeting and fouling, and maintaining reactor efficiency.
Implementation Method 1
introducing a first polymerization neutralizer to the reactor... and then introducing a second polymerization neutralizer to the reactor
Data Source
AI summary
A method for transitioning a gas phase polymerization reactor between metallocene catalysts is provided. The method comprises first reducing the superficial gas velocity and increasing the height of the fluidized bed within the reactor prior to stopping a feed comprising a first metallocene catalyst. The method further comprises introducing a first polymerization neutralizer to the reactor, wherein the first polymerization reactor does not comprise water, and then introducing a second polymerization neutralizer to the reactor, wherein the second polymerization neutralizer is different from the first polymerization neutralizer. After this, the method comprises purging the reactor with an inert gas and then introducing a feed comprising a second metallocene catalyst to the reactor.