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 to homogenize PET feedstock with recycled oligomer residue and diol effluent, followed by glycolysis depolymerization, diol separation, and decolorization, optimizing the mixing and separation conditions to reduce viscosity and prevent clogging, allowing for the recycling of PET with higher pigment content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If opaque PET containing pigments is collected with coloured PET for recycling, then the amount of plastic upgraded from waste increases, but the mechanical properties of recycled PET are adversely affected when opaque PET content exceeds 10-15%
Solution Approach 1:
The patent extracts and removes pigments from the PET recycling stream through a purification process involving filtration and adsorption. This allows opaque PET to be processed without the pigments that would otherwise degrade mechanical properties, enabling higher proportions of opaque PET (up to 30-50% or more) to be included in the feedstock while maintaining recycled PET quality.
Solution Approach 2:
The patent changes the chemical parameters of the recycling process by introducing specific purification treatments. The process modifies the feedstock composition by removing pigment contaminants, thereby changing the effective parameters of the recycling system to accommodate higher opaque PET content without compromising mechanical properties.
2Adaptability or versatility
If a depolymerization process treats PET with high pigment content, then recycling of opaque PET is enabled, but clogging issues occur in the process equipment
Solution Approach 1:
The patent applies preliminary purification actions before depolymerization, including filtration to remove macroscopic impurities and adsorption to remove pigments. This preliminary treatment prevents pigment particles from entering and clogging the depolymerization equipment, while still allowing the process to handle feedstock with high opaque PET content.
Solution Approach 2:
The patent introduces intermediary purification steps (filtration and adsorption) between the feedstock input and the depolymerization process. These intermediary treatments act as mediators that remove harmful pigment particles while allowing the depolymerization process to proceed with high opaque PET content feedstock without clogging.
3Ease of manufacture
If clear PET flakes undergo extrusion-filtration and solid state polymerization, then mechanical recycling produces reusable extrudates, but the process is limited to clear PET and cannot effectively handle coloured or opaque PET
Solution Approach 1:
The patent fundamentally changes the approach from mechanical recycling to chemical recycling through depolymerization. This parameter change in the recycling methodology enables the process to handle coloured and opaque PET that would be unsuitable for traditional mechanical recycling, while the added purification steps ensure the recycled material meets quality requirements.
Solution Approach 2:
The patent extracts pigments and colourants from the PET feedstock through purification processes before depolymerization. This extraction removes the limiting factor (pigments) that prevented clear PET mechanical recycling from handling coloured or opaque PET, thereby expanding the versatility of the recycling process.
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 effectively recycles PET with up to 95% homogenization, reduces stirring power requirements, and facilitates the recycling of diester oligomers, enabling the treatment of PET with high pigment content, 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 being fed at least with said polyester feedstock and being implemented at a temperature of between 150 and 300° C.
Implementation Method 2
said mixing section being at least fed with said stream of conditioned feedstock... and comprising at least one zone for mixing the polyester feedstock at a temperature of between 150 and 300° C.
Implementation Method 3
b) a step of depolymerization by glycolysis fed at least with the mixed stream... performed at a temperature of between 180 and 400° C.
Implementation Method 4
c) a step of separating out the diol fed at least with the effluent from step b)... performed at a temperature of between 100 and 250° C., at a pressure below that of step b)
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 at least with a recycled residue effluent and a diol effluent in particular in order to substantially reduce the viscosity of the feedstock.