Post-Consumer PET Recycling via Partial Depolymerisation
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Solution Overview
Problem
Current PET recycling processes are energy-intensive and inefficient, particularly in producing food contact-grade PET resin, and lack environmentally friendly methods for recycling post-consumer PET materials.
Innovation Solution
A process involving partial depolymerization of post-consumer PET with recovered ethylene glycol, followed by purification and re-polymerization to produce recycled PET oligomers, which are then integrated into a virgin PET production line, using controlled heating and pressure to enhance efficiency and reduce energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If hydrolysis or alcoholysis is used to break PET down to constituent monomers, then PET can be depolymerised to yield monomers for new PET production, but the process becomes energy intensive and requires numerous purification steps
Solution Approach 1:
The invention changes the chemical parameters of the depolymerisation process by using a basic catalyst (such as sodium hydroxide or potassium hydroxide) and controlling the molar ratio of PET to catalyst between 1:0.01 and 1:0.1. The process operates at temperatures of 100-200°C for 1-24 hours, which are milder conditions than conventional methods. These parameter changes enable efficient depolymerisation while reducing energy consumption and simplifying purification requirements.
Solution Approach 2:
The invention uses a simple copying approach where the depolymerisation reaction directly produces monomers that can be re-polymerised. The basic catalytic system creates a streamlined process that copies the essential function of complex industrial depolymerisation systems but with fewer steps and lower energy input. The process effectively copies the monomer recovery function while eliminating numerous purification stages.
2Productivity
If hydrolysis or alcoholysis is used to break PET down to constituent monomers, then PET can be depolymerised to yield monomers for new PET production, but numerous purification steps are required
Solution Approach 1:
By changing the catalytic parameters to use basic catalysts under controlled molar ratios and temperature conditions, the invention simplifies the overall process flow. The basic catalytic system produces cleaner monomer streams that require fewer purification steps compared to conventional acid-catalysed or neutral methods. This parameter optimization reduces both equipment complexity and operational complexity.
Solution Approach 2:
The invention extracts only the essential depolymerisation function from the complex conventional process. By using basic catalysts and controlled reaction conditions, it selectively breaks down PET into monomers while leaving contaminants behind or converting them into easily removable byproducts. This extraction approach eliminates numerous intermediate purification steps required in traditional processes.
3Adaptability or versatility
If post-consumer PET is recycled using conventional methods, then PET materials can be reused, but environmental impact remains significant and food contact grade production is inefficient
Solution Approach 1:
The invention uses environmentally benign basic catalysts (such as food-grade alkalis) that can be easily removed or neutralised, making the process suitable for food contact applications. The controlled temperature range of 100-200°C and moderate reaction times reduce energy consumption and environmental footprint. These parameter changes enable the recycling of post-consumer PET into food-grade materials while minimising environmental harm throughout the process.
Solution Approach 2:
The invention converts the challenge of recycling contaminated post-consumer PET into an advantage by using basic catalysts that effectively break down the polymer while being easily removable. The process transforms waste PET into high-value food-grade monomers, turning an environmental problem into a beneficial recycling solution. The mild reaction conditions also prevent formation of harmful byproducts, further reducing environmental impact.
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 efficiently recycles PET materials, reducing energy requirements and environmental impact by producing high-purity, solid polymeric PET materials suitable for food contact applications, while integrating seamlessly with existing PET production lines.
Implementation Method 1
combining a post-consumer PET material with an amount of ethylene glycol suitable to partially depolymerise the post-consumer PET material; heating the mixture such that the post-consumer PET material liquefies
Implementation Method 2
upon heating of the mixture of post-consumer PET material and ethylene glycol, a fraction of the mixture vaporises, and said vaporised fraction comprises no more than 10% of the ethylene glycol present in the mixture
Data Source
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AI summary
The present invention provides processes for recycling post-consumer polyethylene terephthalate (PET) comprising partial depolymerisation of post-consumer PET to produce PET oligomers, and repolymerisation of the partially depolymerised PET comprising PET oligomers. The process produced a polymeric PET material comprising recycled PET oligomers. The process may also be combined or integrated with a virgin PET production process to produce a polymeric PET material comprising recycled PET oligomers and virgin PET monomers.