PET Depolymerization Viscosity Reduction via Conditioning
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Solution Overview
Problem
Current processes for depolymerizing polyester, particularly polyethylene terephthalate (PET), face challenges in efficiently recycling PET containing high amounts of pigments and opaque materials due to clogging issues and adverse effects on mechanical properties, limiting the recycling of opaque PET beyond 10-15% in colored PET streams.
Innovation Solution
A process involving a conditioning step at 150-300°C to reduce viscosity, followed by glycolysis at 180-400°C with a diol, and subsequent separation and decolorization steps to produce purified monomers, allowing for effective homogenization and reduced stirring power requirements, enabling the recycling of PET with higher pigment content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If opaque PET containing pigments is included in PET for recycling, then the recycling scope is expanded, but the mechanical properties of recycled PET are adversely affected
Solution Approach 1:
The patent extracts pigments and impurities from opaque PET feedstock through a conditioning step involving heating to 150-300°C followed by glycolysis at 180-400°C with a diol. This separation removes the harmful pigmented components while retaining the valuable polyester chains, enabling the recycled material to achieve mechanical properties comparable to virgin PET despite accepting opaque PET with up to 95% homogenization in the process
Solution Approach 2:
The patent applies parameter changes by transforming the physical and chemical state of the PET feedstock through controlled heating and chemical reaction conditions. By adjusting temperature (150-300°C conditioning, 180-400°C glycolysis), pressure, and diol-to-PET ratio (1:1 to 10:1), the process converts opaque PET with pigments into purified monomers that can be repolymerized into high-quality recycled PET with restored mechanical properties
2Productivity
If a conditioning step is implemented to reduce viscosity, then homogenization efficiency is improved, but process complexity increases
Solution Approach 1:
The patent applies preliminary action by implementing a conditioning step before the main glycolysis reaction. This preliminary heating to 150-300°C reduces the viscosity of the PET feedstock and pre-mixes it with the diol, creating a more homogeneous reaction mixture that enters the glycolysis reactor with optimal flow characteristics. This preliminary preparation significantly improves homogenization efficiency during subsequent processing
Solution Approach 2:
The patent merges the conditioning and glycolysis operations into an integrated continuous process. The conditioning section and glycolysis reactor are connected in series, with the diol being introduced and mixed during the conditioning phase, then undergoing glycolysis in the subsequent reactor. This merging of operations improves efficiency while managing complexity through process integration rather than separate discrete 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 improves depolymerization efficiency, simplifies feedstock introduction, and allows for the recycling of PET with up to 95% homogenization, treating various types of PET waste, including opaque and multilayer PET, producing monomers that can be repolymerized into virgin-like PET.
Implementation Method 1
a conditioning step implementing at least one conditioning section to produce a stream of conditioned feedstock... said conditioning section is fed at least with said polyester feedstock and is implemented at a temperature of between 150 and 300° C.
Implementation Method 2
said mixing section is fed with said stream of conditioned feedstock obtained from the conditioning section and a diol effluent, and is operated in a static or dynamic mixer... with a residence time of between 0.5 second and 20 minutes
Implementation Method 3
improve the depolymerization efficiency, while at the same time reducing the stirring power required for this homogenization
Implementation Method 4
b) a step of depolymerization by glycolysis, fed at least with the mixed stream... performed at a temperature of between 180 and 400° C., and a residence time of between 0.1 and 10 hours
Implementation Method 5
decomposing the polyester recovered in the form of waste into monomers which can be used again as feedstock in a polymerization process
Implementation Method 6
c) a step of separating out the diol fed at least with the effluent from step b)... producing a diol effluent and an effluent rich in liquid monomers
Implementation Method 7
e) a step of decolourizing the pre-purified monomers effluent... in the presence of an adsorbent and producing a purified monomers effluent
Data Source
AI summary
The invention relates to a process for depolymerizing a polyester feedstock comprising PET, said process comprising, prior to the step of depolymerization by glycolysis and to the step of purification of the depolymerization effluent, an improved step of conditioning the feedstock in which the polyester feedstock is conditioned in terms of temperature and pressure and then mixed with a diol effluent in a static or dynamic mixer in order in particular to substantially reduce the viscosity of the feedstock.