Polyester Recycling Process for Food Packaging Quality
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Solution Overview
Problem
Existing methods for recycling polyester materials, particularly for food packaging, are either simple and fail to meet quality standards or require complex and energy-intensive processes, often involving multiple apparatus and high operating costs.
Innovation Solution
A process involving the melting of washed old polyester with diol addition, mixing with fresh polyester melt, polycondensation under reduced pressure, underwater granulation, and dealdehyde treatment using purge air, which simplifies equipment and reduces costs while achieving high-quality polyester granules suitable for food packaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If simple melting and mixing of used polyester with fresh polyester is used, then the process is simple and low cost, but the product quality does not meet food packaging standards due to insufficient impurity removal and low viscosity
Solution Approach 1:
The patent applies parameter changes by controlling the polycondensation temperature (240-280°C), vacuum pressure (0.1-10 mbar), and residence time (30-120 minutes) in the finishing reactor to achieve the desired viscosity (0.6-1.2 dl/g) and impurity removal, transforming the simple mixing process into a controlled quality production process
Solution Approach 2:
The patent extracts and removes impurities and volatile substances from the polyester melt through vacuum degassing in the finishing reactor, separating harmful components (acetaldehyde, water, oligomers) from the polymer matrix to achieve food packaging quality standards
2Manufacturing precision
If complex processes with multiple apparatus and crystallization stages are used, then high-quality polyester for food packaging can be achieved, but the energy consumption and operating costs increase significantly
Solution Approach 1:
The patent merges the impurity removal, viscosity adjustment, and crystallization functions into a single finishing reactor by conducting polycondensation under vacuum at controlled temperature, eliminating the need for separate crystallization apparatus and reducing energy consumption while maintaining product quality
Solution Approach 2:
The finishing reactor performs multiple functions simultaneously: polycondensation to adjust viscosity, vacuum degassing to remove impurities, and crystallization to prevent sticking, making the device multi-functional and reducing the overall number of apparatus needed in the process
3Manufacturing precision
If vacuum degassing and repeated vacuum application are used, then impurities can be removed effectively, but the energy required to generate vacuum and the process time increase
Solution Approach 1:
The patent applies continuous vacuum degassing throughout the polycondensation process in the finishing reactor, maintaining constant removal of volatile substances rather than using repeated intermittent vacuum cycles, which reduces energy consumption while achieving effective impurity removal
4Stability of the object's composition
If hot air crystallization for several hours is used, then granules can be crystallized sufficiently, but large apparatus and great heating energy are required
Solution Approach 1:
The patent combines the crystallization process with the polycondensation process by maintaining the melt at polycondensation temperature (240-280°C) under vacuum, allowing crystallization to occur in-situ within the finishing reactor rather than requiring a separate crystallization apparatus
5Adaptability or versatility
If used polyester contains undefined impurities from various sources, then recycling flexibility is maintained, but the degree of polymerization cannot be controlled without complex process steps
Solution Approach 1:
The patent uses parameter changes (temperature, vacuum pressure, residence time) in the finishing reactor to control the degree of polymerization and adjust the viscosity of recycled polyester with undefined impurities, achieving consistent product quality without complex additional process steps
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
The process produces polyester granules with improved viscosity, reduced acetaldehyde content, and enhanced crystallization, meeting stringent requirements for food packaging without the need for additional additives or complex crystallization stages, resulting in a more economical and ecological recycling method.
Implementation Method 1
addition of diol to the melt of the old polyester in or after the melting device
Implementation Method 2
polycondensation of the melt mixture in a high-viscosity melt reactor under reduced pressure
Implementation Method 3
granulation of the polyester melt in an underwater granulator at a water temperature of between 90 and 99° C.
Implementation Method 4
treating the granules in the dealdehyde treatment tank by means of a purge air stream, the inlet temperature of the purge air stream being between 180° C. and 200° C.
Data Source
AI summary
The invention relates to a process for the manufacture of granulates from a mixture of old polyester and fresh polyester which meets the demands made of food packaging, whereby the old polyester is melted, diol for the melting of the old polyester is added, the melted mass of the old polyester is mixed with the melted mass of fresh polyester from a melting reactor and the melted mass mixture is polycondensated in a high-viscosity melting reactor. The polyester melted mass is then granulated in an underwater granulator and the granulate thus manufactured is treated with a cleansing air stream in a dealdehydising container.