Purifying Polymer Streams by Dissolving PLA Contaminants
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Solution Overview
Problem
The presence of PLA contamination in conventional polymer streams disrupts the PET recycling process, leading to higher residue levels and impaired quality, as existing sorting techniques are not effective in distinguishing between PET and PLA, resulting in lower yields and contaminated PET products.
Innovation Solution
A process involving grinding the polymer stream, dissolving PLA in a lactic ester, and separating the dissolved PLA and impurities from the undissolved polymers, allowing the purified polymers to be treated via conventional recycling routes, with the lactic ester being recovered for further processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sorting techniques are used to separate PET and PLA, then the sorting process is simple, but the separation effectiveness is poor leading to contamination
Solution Approach 1:
The patent extracts PLA from the PET/PLA mixture by exploiting its solubility in lactic ester. The PLA is selectively dissolved in the lactic ester solvent, separating it from the insoluble PET polymer. This extraction method achieves complete separation even at low contamination levels (1-10% PLA), overcoming the limitations of conventional sorting techniques that fail to distinguish between these polymers.
Solution Approach 2:
The patent introduces lactic ester as an intermediary substance that selectively interacts with PLA. This intermediary solvent enables the separation process by dissolving PLA while leaving PET unchanged. The intermediary allows for effective separation without requiring complex sorting equipment or methods, simply by adding the selective solvent and performing liquid-liquid extraction.
2Manufacturing precision
If PLA contamination is present in PET stream, then the recycling process can be simplified, but the residue level increases and quality deteriorates
Solution Approach 1:
The patent applies preliminary action by treating the PET/PLA mixture with lactic ester solvent before the conventional recycling process. This pre-treatment step dissolves and removes PLA contamination, purifying the PET stream in advance. As a result, the subsequent conventional recycling process operates with clean material, achieving high residue levels (95-98% recovery) and maintaining excellent PET quality without disruption.
3Measurement precision
If optical sorting techniques are used to distinguish PET and PLA, then the separation is more accurate, but the installation and effectiveness are limited
Solution Approach 1:
The patent replaces complex optical sorting systems with a simple chemical extraction method. Instead of using sophisticated optical sensors and sorting machinery that are difficult to install and maintain, the invention uses the selective solubility of PLA in lactic ester to achieve separation. This substitution of mechanical/optical systems with a chemical process simplifies the overall system, making it easier to implement while achieving complete separation accuracy.
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 effectively removes PLA contamination, enabling the purified polymers to be reused in conventional recycling channels without disrupting the recycling process, thereby improving the quality and yield of recycled PET.
Implementation Method 1
suspending a mixture of polymers containing a weight fraction of at most 50% of poly (lactic acid) PLA in a lactic ester, with solubilization of the PLA fraction in the lactic ester
Implementation Method 2
The dissolved lactic ester, PLA and other impurities are then recovered for separate and further processing. The undissolved polymer is recovered for treatment via conventional recycling routes.
Data Source
AI summary
The invention relates to a method for purifying a conventional polymer flow (PE, PP, PET, PVC, etc.) contaminated with a maximum of 50% PLA, including the steps of suspending the polymer by solubilizing the PLA fraction, and of recovering the purified polymer after separation.