Recycled Polyolefin Aldehyde Reduction via Gas Flow
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Solution Overview
Problem
Current recycling processes for polyolefin waste fail to effectively reduce the content of malodorous C7-C11 aldehydes, leading to unacceptable odors in recycled polyolefin pellets, which are energy-intensive and not applicable to a broad range of recycling streams.
Innovation Solution
A process involving a gas flow through a fixed bed reactor with a Reynolds number range of 35 to 1200, using air or nitrogen gas, to treat shredded polyolefins, reducing C7-C11 aldehyde content while maintaining reasonable energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a stirred bed with aeration is used to remove volatiles, then odor reduction is achieved, but energy consumption increases significantly
Solution Approach 1:
The patent replaces the mechanical stirring system with a gas flow-based removal mechanism. Instead of using mechanical agitation to facilitate mass transfer, the invention uses controlled gas flow through the extruder to carry away volatile odor-causing substances, thereby eliminating the need for energy-intensive stirring while maintaining odor reduction effectiveness
Solution Approach 2:
The invention employs pneumatic principles by introducing gas flow into the extrusion system. The gas flow carries volatile compounds from the polyolefin material through the extruder, enabling odor removal without mechanical stirring. This pneumatic approach is inherently more energy-efficient than mechanical aeration systems
2Loss of substance
If washing and drying steps are applied to shredded polyolefin, then soluble waste is removed, but malodorous substances remain in the material
Solution Approach 1:
The patent exploits phase transition principles by heating the polyolefin material during extrusion to a temperature where volatile odor-causing substances transition from the solid/liquid phase to the gas phase. This thermal treatment enables the release and removal of malodorous compounds through the gas flow, a mechanism that washing and drying cannot achieve
3Device complexity
If extrusion without degassing ports is used, then processing is simplified, but aldehyde content remains high
Solution Approach 1:
The invention implements continuous gas flow through the extrusion process to continuously remove volatile aldehydes and odor-causing substances. This continuous action integrates odor removal into the extrusion operation itself, eliminating the need for separate degassing ports or stages while maintaining simplified processing architecture
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
Significantly reduces the odor activity value of recycled polyolefins by minimizing the content of C7-C11 aldehydes and limonene, resulting in pellets with improved odor quality and broader applicability.
Implementation Method 1
the chips obtained shall be essentially free of odors... providing about 90 percent reduction in volatile impurities
Implementation Method 2
introducing the chips into a stirred bed with aeration... gas flow for an extended period of time
Data Source
AI summary
Disclosed is a process for treating plastic waste chips containing a blend of polypropylene and polyethylene in an amount of at least 83.0 wt.-% to less than 100 wt.-% and further containing C7 to C11 aldehydes in an amount of 8000 ppb to 20000 ppb and limonene in an amount of 5 ppm to 500 ppm, the process comprising subjecting said plastic waste chips, in a fixed bed without stirring under standard pressure or reduced pressure, to a gas flow for achieving a Reynolds number in the range of 35 to 1200 at a temperature in the range of 20° C. to a point 10° C. below the Vicat softening point (10N, ISO 306) of said plastic waste and recovering the treated plastic waste chips containing C7 to C11 aldehydes in a total amount of 50 ppb to less than 5000 ppb limonene in an amount of 0.5 to 5 ppm.