Recycling Opaque PET via Glycolysis Depolymerization
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Solution Overview
Problem
The recycling of opaque PET is challenging due to the detrimental effect of pigments on mechanical properties and the difficulty in removing them, leading to suboptimal recycling outcomes and limited product applications.
Innovation Solution
A process integrating depolymerization and polymerization steps with optimized integration of diol streams, involving glycolysis at controlled temperatures and pressures, followed by separation, purification, and discolouration, to produce high-quality terephthalate polyester from recycled PET, including opaque varieties, without compromising mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If opaque PET containing pigments is recycled through conventional mechanical recycling, then the recycling rate increases, but the mechanical properties of the recycled PET are detrimentally affected
Solution Approach 1:
The patent applies chemical recycling through glycolysis to fundamentally change the processing parameters from mechanical to chemical methods. This allows complete depolymerization of PET into monomers, effectively removing pigment contamination and enabling the production of recycled PET with mechanical properties equivalent to virgin PET, thus resolving the contradiction between recycling rate and mechanical property preservation
Solution Approach 2:
The patent extracts and removes pigment contaminants from the recycling process by depolymerizing the PET into monomers that can be purified separately. The pigments are left behind as residues during the glycolysis process, allowing the recovery of high-purity PET monomers that can be repolymerized into material with excellent mechanical properties
2Quantity of substance
If opaque PET is included in the coloured PET stream, then the collection efficiency increases, but the mechanical properties of the recycled PET are detrimentally affected above 10-15% content
Solution Approach 1:
The patent changes the recycling parameter from mechanical processing to chemical glycolysis, which can handle any proportion of opaque PET without degrading mechanical properties. The chemical process completely breaks down the polymer structure, allowing pigments to be separated as residues while recovering pure PET monomers regardless of the initial opaque PET content in the feedstock
3Manufacturing precision
If a depolymerization process is integrated into the recycling process, then the quality of recycled polyester is improved, but the process complexity increases
Solution Approach 1:
The patent merges the depolymerization, purification, and repolymerization steps into an integrated continuous process. By combining these operations and optimizing the glycolysis conditions, the process achieves high-quality recycled polyester while managing complexity through process integration and standardized operational parameters
Solution Approach 2:
The patent implements a continuous recycling process where PET waste is continuously depolymerized, purified, and repolymerized without interruption. This continuous operation improves efficiency and quality consistency while reducing the practical complexity of batch processing, making the enhanced recycling process more industrially viable
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 process enables the production of polyester with properties similar to virgin polyester, reducing raw material consumption and energy use, while effectively recycling opaque PET, thus overcoming the limitations of existing recycling methods.
Implementation Method 1
a step of depolymerization of said feedstock of polyester to be recycled, comprising at least one reaction section fed with said feedstock of polyester to be recycled and with a glycol feedstock, wherein said reaction section is operated, at a temperature between 150°C. and 400°C., preferably between 180°C. and 300°C., preferably between 200°C. and 280°C.
Implementation Method 2
a separation step, comprising at least one separation section fed with said depolymerization reaction effluent obtained at the end of the depolymerization step a), in order to obtain at least one glycol effluent and one diester effluent
Implementation Method 3
a step for purifying the diester effluent obtained at the end of step b), comprising at least one separation section that is fed with said diester effluent obtained at the end of step b) and operated at a temperature below or equal to 250°C., at a pressure less than or equal to 0.001 MPa, with a liquid residence time per section of the less than equal to 10 min, then a discolouration section operated at a temperature between 100°C. and 250°C. and at a pressure of between 0.1 and 1.0 MPa, in the presence of an adsorbent
Implementation Method 4
a step for condensing said polymerization feedstock resulting from step d), in order to produce at least one condensation reaction effluent, one diol effluent and one aqueous effluent or one methanol effluent
Implementation Method 5
a step of polycondensation of said condensation reaction effluent obtained in step e) in order to obtain at least said terephthalate polyester and a diol effluent
Data Source
AI summary
The invention relates to a process for producing a terephthalate polyester from at least one feedstock of polyester to be recycled, integrating a process of depolymerization, advantageously by glycolysis, of the polyester to be recycled in order to produce a diester intermediate compatible with the specifications of the polymerization steps and comprising an optimized system for recycling the streams.