Continuous Depolymerization Device for Multilayer Plastic Waste Recycling
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Solution Overview
Problem
Multilayer polymer-based composite materials, commonly used in food packaging and other applications, are difficult to recycle due to the challenge of separating different layers, leading to material loss as they are often thermally recycled or sent to landfills, with existing processes being uneconomical and limited in their ability to recover all recoverable ingredients.
Innovation Solution
A method and device that can comprehensively treat mixed plastic waste by categorizing feed streams based on their composition, using pretreatment, basic depolymerization, and acid depolymerization processes in a continuous twin-screw extruder and stirred reactor, respectively, to recover terephthalic acid, polyamides, and polycarbonates, allowing for the same device to handle different waste types with varying polyolefin content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If thermal recycling or landfilling is used for multilayer materials, then processing is simple, but material loss occurs and recycling efficiency is low
Solution Approach 1:
The multilayer waste is segmented into different components through sequential chemical treatment. The basic depolymerization separates polycondensates from polyolefins, and the acid depolymerization further separates polyamides from other materials, enabling individual recovery of each material type
Solution Approach 2:
Chemical reagents serve as intermediaries to facilitate separation. NaOH and alcohol act as intermediaries in basic depolymerization to extract polycondensates, while H2SO4 acts as an intermediary in acid depolymerization to dissolve polyamides, enabling systematic material recovery
2Loss of substance
If existing depolymerization processes are used, then some polycondensates can be recovered, but the process is limited to very selective wastes and cannot treat all multilayer materials
Solution Approach 1:
The device is designed with universal functionality to treat multiple waste types. By incorporating both basic and acid depolymerization units, the system can process Feedstream A (PAT-rich), Feedstream B (PA-rich), and Feedstream C (PC-containing), making it adaptable to diverse multilayer compositions
Solution Approach 2:
The process sequence is dynamically adjusted based on feedstream composition. The control unit determines whether to apply basic depolymerization first, acid depolymerization first, or both, optimizing the treatment pathway for each specific waste type
3Loss of substance
If high pressures and high temperatures are used for acid depolymerization, then terephthalic acid extraction is effective, but the process becomes uneconomical and operates as batch process rather than continuous
Solution Approach 1:
The acid depolymerization unit is designed as a continuous process where waste material and H2SO4 are continuously fed, reacted, and processed. The reactor maintains steady-state operation with continuous material flow, eliminating batch processing interruptions and improving productivity
Solution Approach 2:
The process uses moderate temperature and pressure parameters optimized for continuous operation. Rather than extreme conditions, the system employs controlled parameter ranges that enable sustained continuous processing while maintaining effective depolymerization and TPA extraction
4Adaptability or versatility
If the same device is used for different waste types, then device versatility is improved, but the process complexity increases due to different processing sequences
Solution Approach 1:
The device is segmented into independent functional units: basic depolymerization unit, acid depolymerization unit, and control unit. Each unit performs a specific function, and the control unit orchestrates their operation based on feedstream type, managing complexity through modular architecture
Solution Approach 2:
The control unit automatically determines the appropriate processing sequence based on the feedstream composition. The system self-regulates by selecting the correct treatment pathway (basic first, acid first, or both) without requiring manual intervention, simplifying operation despite process complexity
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
Enables the efficient recovery of raw materials from diverse multilayer waste streams, achieving high throughput and quality of recycled products while tolerating impurities, and allowing for the same device to process different waste types with varying polyolefin content, thereby reducing material loss and enhancing recycling efficiency.
Implementation Method 1
basic depolymerization with NaOH and the addition of an alcohol
Implementation Method 2
acid depolymerization...the filtrate is treated with a base to precipitate TPA
Implementation Method 3
The stirred reactor is designed to heat the waste material and facilitate chemical reactions
Data Source
Figure 1
AI summary
In order to devise a method and design a device for recycling waste essentially containing polyalkylene terephthalate, in particular polyethylene terephthalate and/or polybutylene terephthalate, and additionally containing polycondensate in a continuous process, according to the invention, acidic depolymerization and basic depolymerization are coupled.