Continuous Ethylene Copolymer Transition Process
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Solution Overview
Problem
Current methods for transitioning between two ethylene copolymers with different comonomers in gas phase fluidised bed reactors result in significant production of off-grade material, hot spots, and agglomerates, and are inefficient due to high hydrocarbon release and labor-intensive processes.
Innovation Solution
A continuous transition process where both comonomers are present during the transition, maintaining a stable polymerization production rate, ethylene partial pressure, and catalyst activity, without deinventorying and using a catalyst killer, to produce ethylene copolymers with controlled melt index and density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional transition methods (gas inventory blow down, catalyst killer addition) are used to switch between copolymers with different comonomers, then the transition can be completed, but significant off-grade material is produced and hydrocarbon is released
Solution Approach 1:
The patent maintains continuous polymerization during the transition process by keeping the reactor bed inventory constant and avoiding complete gas inventory blow down. Both comonomers A and B are present simultaneously during the transition, allowing the reaction to continue producing polymer at a stable rate while the comonomer composition gradually shifts from A to B, eliminating the need to stop production and discard off-grade material
Solution Approach 2:
The patent controls the transition by gradually adjusting comonomer feed rates and partial pressures rather than making abrupt changes. The comonomer partial pressure ratio (comonomer B)/(comonomer A+B) is controlled to vary between 0.05-0.95 during transition, allowing smooth compositional changes that keep polymer properties within acceptable ranges and minimize off-grade production
2Loss of substance
If the reactor bed is deinventoried or gas inventory is blown down to reduce transition material, then off-grade production is reduced, but the process becomes less efficient and more complex
Solution Approach 1:
The patent maintains continuous polymerization during the transition process by keeping the reactor bed inventory constant and avoiding complete gas inventory blow down. Both comonomers A and B are present simultaneously during the transition, allowing the reaction to continue producing polymer at a stable rate while the comonomer composition gradually shifts from A to B, eliminating the need to stop production and discard off-grade material
Solution Approach 2:
The patent uses a transition period where both comonomers are present simultaneously as an intermediary state between producing copolymer with only comonomer A and copolymer with only comonomer B. This intermediate state allows gradual compositional change while maintaining stable polymerization conditions and continuous production of acceptable-grade material
3Reliability
If catalyst killer compounds are added to stop polymerization during transition, then the transition can be controlled, but the process becomes discontinuous and less efficient
Solution Approach 1:
The patent maintains continuous polymerization during the transition process by keeping the reactor bed inventory constant and avoiding complete gas inventory blow down. Both comonomers A and B are present simultaneously during the transition, allowing the reaction to continue producing polymer at a stable rate while the comonomer composition gradually shifts from A to B, eliminating the need to stop production and discard off-grade material
Solution Approach 2:
The patent employs control systems that monitor comonomer partial pressures, polymer composition, and reaction conditions during the transition. Based on this feedback, the system adjusts comonomer feed rates to maintain the comonomer partial pressure ratio within the specified range (0.05-0.95), ensuring reliable control without needing catalyst killer compounds
4Loss of time
If comonomer composition is changed rapidly to achieve quick transition, then transition time is reduced, but hot spots and agglomerates form reducing product quality
Solution Approach 1:
The patent controls the transition by gradually adjusting comonomer feed rates and partial pressures rather than making abrupt changes. The comonomer partial pressure ratio (comonomer B)/(comonomer A+B) is controlled to vary between 0.05-0.95 during transition, allowing smooth compositional changes that keep polymer properties within acceptable ranges and minimize off-grade production
Solution Approach 2:
The patent implements a dynamic transition process where comonomer feed rates and partial pressures are continuously adjusted during the transition period rather than using fixed step changes. This dynamic control allows the system to adapt to changing reaction conditions and maintain uniform polymer quality throughout the transition, preventing hot spots and agglomerate formation
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 reduces off-grade material production, minimizes hydrocarbon release, and maintains reactor stability, enabling efficient and environmentally friendly transitions between ethylene copolymers with different comonomers.
Implementation Method 1
the polymerization catalyst activity must remain within +−10% of its activity during the steady state production of the copolymer PE-A
Implementation Method 2
Gas phase polymerisation reactors
Data Source
AI summary
Process for the transition between an ethylene co-polymerization process in a polymerization reactor in the presence of a catalyst and of ethylene E and an olefin co-monomer A to produce an ethylene copolymer PEA into an ethylene co-polymerization process carried out in the same polymerization reactor in the presence of a catalyst and of ethylene E and an olefin co-monomer B to produce an ethylene copolymer PEB. Co-monomers A and B are different and are both present in the reactor during at least part of the transition from PEA to PEB. The transition is performed continuously by (i) starting the transition by stopping steady state production of ethylene copolymer PEA and (ii) ending the transition when steady state production of ethylene copolymer PEB is achieved.