Catalyst Transition in Gas Phase Fluidized Bed Reactors
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Solution Overview
Problem
Current processes for polyethylene production in gas phase reactors face challenges in continuously transitioning between different catalyst systems without shutting down the reactor, leading to production losses due to the need for reactor shutdowns.
Innovation Solution
A method involving the continuous feeding of a recycle stream and olefin monomer to a gas phase fluidized bed reactor, where the reactor operates in condensing mode, allowing for the transition from one catalyst system to another by maintaining a specific liquid phase percentage and adjusting antistatic agent amounts, enabling continuous operation without fresh catalyst introduction initially and then introducing the new catalyst system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the reactor is shut down to transition between catalyst systems, then the catalyst can be changed, but polyolefin production is lost
Solution Approach 1:
The patent applies preliminary action by introducing the new catalyst system before completely deactivating the old catalyst system. The transition is initiated while the reactor is still operating with the first catalyst, allowing the second catalyst to be introduced and activated in advance, so that when the first catalyst deactivates, the second catalyst is already ready to maintain continuous production without shutdown.
Solution Approach 2:
The patent ensures continuity of useful action by maintaining polymerization activity throughout the catalyst transition process. The reactor operates continuously with both catalyst systems present during the transition period, and the second catalyst is introduced in a manner that prevents complete cessation of production, thereby eliminating downtime between catalyst systems.
2Duration of action of stationary object
If the reactor operates in condensing mode with liquid phase recycle stream, then heat from polymerization is absorbed and continuous operation is enabled, but the process complexity increases
Solution Approach 1:
The patent utilizes phase transitions by employing a condensing mode where the recycle stream undergoes phase change from gas to liquid. The condenser section cools the recycle gas stream, causing condensation of heavier components, and the resulting liquid phase is separated and recycled back to the reactor. This phase transition mechanism enables heat absorption and continuous operation while managing the increased process complexity through established thermodynamic principles.
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 method allows for seamless transitions between catalyst systems in polyethylene production, reducing downtime and maintaining continuous production, thereby increasing on-stream time and productivity by preventing polymer agglomerate formation.
Implementation Method 1
upon being fed to the reactor the liquid phase of the recycle stream adsorbs a portion of the heat generated by the polymerization reaction and evaporates within the fluidized bed
Implementation Method 2
cooling at least a portion of the gaseous stream to condense a portion thereof and to form a cooled gaseous stream, wherein the cooled gaseous stream comprises a gas phase and a liquid phase
Implementation Method 3
a portion of the olefin monomer contacts the first catalyst in the fluidized bed of the reactor and undergoes an exothermic polymerization reaction
Data Source
AI summary
A method of transitioning from a first catalyst to a second catalyst in a gas phase fluidized bed reactor comprising continuously feeding the first catalyst and a recycle stream comprising olefin monomer to the reactor; wherein the monomer contacts the first catalyst in the fluidized bed and polymerizes; wherein the reactor is operating in condensing mode (withdrawing a gaseous stream comprising unreacted monomer from the reactor, cooling the gaseous stream to condense a portion thereof, and contacting the cooled gaseous stream with fresh monomer to form the recycle stream); and wherein a liquid phase of the recycle stream evaporates within the fluidized bed; discontinuing the first catalyst to the reactor while continuing to feed the recycle stream; maintaining the condensing mode in reactor at >3 wt. % liquid phase in recycle stream while no fresh catalyst is introduced to reactor; and introducing the second catalyst to the reactor operating in condensing mode.