Bimodal Polyethylene Comonomer Distribution via Cyclic Ratio Adjustment
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Solution Overview
Problem
There is a continuous need for new methods to produce bimodal polyethylenes with improved properties, particularly in achieving an increased distribution of comonomer across the high molecular weight portion of the polymer, which is desirable for reducing crack formation in polymer products.
Innovation Solution
A method involving a bimodal catalyst system and a trim solution is used in a single reactor, where the trim/catalyst ratio and 1-hexene/ethylene ratio are adjusted in cycles to achieve a relative maximum and minimum ratio, concurrently, to enhance the distribution of comonomer across the high molecular weight portion, utilizing a gas-phase polymerization process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single reactor with steady-state ratios is used for polymerization, then the manufacturing process is simple and easy to operate, but the distribution of comonomer across the high molecular weight portion is insufficient
Solution Approach 1:
The patent implements periodic cycling of the trim/catalyst ratio and 1-hexene/ethylene ratio in a single reactor. The ratios are adjusted in cycles where the trim/catalyst ratio increases to a relative maximum while the 1-hexene/ethylene ratio decreases to a relative minimum, then reverses. This periodic variation in reaction conditions during polymerization creates the desired bimodal molecular weight distribution with improved comonomer distribution across the high molecular weight portion.
2Manufacturing precision
If the trim/catalyst ratio is increased to improve comonomer distribution, then the comonomer incorporation improves, but the 1-hexene/ethylene ratio becomes unoptimized
Solution Approach 1:
The patent employs synchronized cyclic adjustment of both the trim/catalyst ratio and the 1-hexene/ethylene ratio. During each cycle, when the trim/catalyst ratio is increased to enhance comonomer distribution, the 1-hexene/ethylene ratio is concurrently decreased to a relative minimum, and vice versa. This coordinated periodic action allows both ratios to be dynamically optimized throughout the polymerization process, achieving improved comonomer distribution while maintaining proper 1-hexene/ethylene balance.
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 results in an improved distribution of comonomer across the high molecular weight portion, reducing crack formation and enhancing the properties of bimodal polyethylenes for various applications, such as films and molded articles.
Implementation Method 1
feeding a bimodal catalyst system and a trim solution to a single reactor
Implementation Method 2
feeding a bimodal catalyst system and a trim solution to a single reactor to establish an average steady-state trim/catalyst ratio
Data Source
AI summary
Embodiments are directed towards methods of making binodal polyethylenes, wherein the methods include a plurality of cycles of ratio adjustments.