Polymer Grade Transition Control for Off-Grade Reduction
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Solution Overview
Problem
Existing methods for transitioning from one polymer grade to another in gas phase polymerization reactors often result in the production of significant amounts of off-grade polymer material, leading to economic losses and reactor shutdowns, as they fail to effectively minimize off-grade material production during transitions.
Innovation Solution
A method is developed to determine initial conditions for a transition that minimizes off-grade product production by identifying a primary property causing the most off-grade material and optimizing its starting value and change time, while synchronizing non-primary properties to comply with target specifications at the same time, thereby reducing the amount of off-grade material produced during the transition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional transition methods are used to switch from one polymer grade to another, then the transition can be completed, but significant amounts of off-grade polymer material are produced
Solution Approach 1:
The patent applies preliminary action by determining optimal initial conditions (starting values of product properties and their time constants) before the transition begins. This pre-planning ensures that the transition follows an optimized trajectory that minimizes off-grade material production from the outset, rather than reacting to deviations during the transition process.
Solution Approach 2:
The patent employs parameter changes by systematically varying product properties (such as melt index and density) and their time constants during the transition. By controlling how these parameters change over time and coordinating their compliance times with target specifications, the method optimizes the transition path to reduce off-grade material while maintaining productivity.
2Loss of time
If transition speed is increased to reduce downtime, then reactor availability improves, but off-grade material production increases
Solution Approach 1:
The patent resolves this contradiction by changing the parameters of product properties and their time constants during transition. By optimizing these parameters, the method achieves a balanced transition speed that minimizes both downtime and off-grade material production, rather than simply increasing speed at the cost of quality.
Solution Approach 2:
The method uses feedback by continuously monitoring product properties during transition and adjusting control strategies based on how closely the properties are approaching target specifications. This coordinated control of multiple product properties ensures efficient transition timing while maintaining quality standards.
3Productivity
If multiple product properties are optimized simultaneously, then transition efficiency improves, but control complexity increases
Solution Approach 1:
The patent manages control complexity by systematically parameterizing product properties and their time constants. This structured approach allows multiple properties to be coordinated through defined relationships rather than independent control, improving transition efficiency while keeping the control framework manageable.
Data Source
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AI summary
A method for determining initial conditions for a transition from an initial reaction to a target reaction to minimize (or substantially minimize) the amount of off-grade material produced during the transition, and optionally also process control variables for implementing the transition. A product property that can cause production of more off-grade product during the transition than can any other of the properties is identified as a primary property, and process control variables for implementing the transition are determined so that the product produced during the transition goes off-grade due to the primary property, and due to each of at least one other product property, at the same or substantially the same time, and preferably also so that each non-primary property reaches a value compliant with the target specification set as late as possible but not later than the time the primary property reaches a value compliant with the target specification set.