Opaque PET Depolymerisation via Glycolysis and Adsorption
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Solution Overview
Problem
Current recycling methods for polyesters, particularly opaque PET, face challenges due to the presence of pigments and dyes, which alter mechanical properties and clog filters, limiting the recycling of opaque PET beyond 10-15% in colored PET streams, preventing efficient fiber production and requiring complex and costly purification processes.
Innovation Solution
A method involving a conditioning step, followed by glycolysis depolymerization at 200-400°C with a controlled diol-to-diester ratio and residence time, diol separation, monomer separation, and decolorization using adsorbents to produce purified monomers suitable for repolymerization, effectively removing pigments and dyes, allowing for the recycling of opaque PET into virgin-like PET.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If opaque PET is collected together with colored PET in mechanical recycling, then the quantity of recovered plastic is maximized, but the mechanical properties of recycled PET are altered beyond 10-15% opaque PET content
Solution Approach 1:
The patent extracts pigments and dyes from the polyester through chemical depolymerization and purification processes. The glycolysis step breaks down the polyester into monomers, and subsequent filtration and distillation steps remove pigment particles and dye molecules, producing purified monomers suitable for repolymerization into high-quality recycled PET with restored mechanical properties
Solution Approach 2:
The patent changes the chemical state of the polyester by converting it from polymeric form to monomeric form through glycolysis at controlled temperatures (200-400°C) and pressures. This parameter change enables effective separation of pigments and dyes, and the purified monomers can be repolymerized to produce PET with mechanical properties comparable to virgin PET
2Manufacturing precision
If total elimination of pigments by filtration is attempted, then the purity of recycled PET is improved, but filter clogging occurs due to extremely fine pigment particles
Solution Approach 1:
The patent replaces the mechanical filtration system with a chemical depolymerization system. By breaking down the polyester into monomers through glycolysis, the process transforms solid pigment particles suspended in polymer matrix into a liquid mixture where pigments can be separated through phase separation, centrifugation, or distillation, avoiding the clogging issues of direct mechanical filtration
Solution Approach 2:
The patent changes the physical state and molecular weight of the polyester by depolymerizing it into monomers. This parameter change from high molecular weight polymer to low molecular weight monomers fundamentally alters the separation mechanism, allowing pigment removal through liquid-liquid separation or distillation rather than mechanical filtration, thus preventing filter clogging
3Ease of manufacture
If certain pigments are present during separation operations, then the recycling process can proceed, but polymerization reaction is catalyzed increasing risks of clogging
Solution Approach 1:
The patent performs preliminary depolymerization of the polyester into monomers before any separation or repolymerization steps. By converting the polyester to monomers first, the process eliminates the risk of premature polymerization during separation operations. The monomers are then purified and subsequently repolymerized under controlled conditions, preventing catalyst-induced clogging during intermediate processing steps
4Manufacturing precision
If complex purification processes are used to remove pigments and dyes, then the quality of recycled PET is improved, but the process cost and complexity increase
Solution Approach 1:
The patent combines multiple purification functions into an integrated chemical depolymerization process. The glycolysis reaction simultaneously breaks down the polyester, releases pigments and dyes, and produces soluble monomers that can be purified in one continuous process flow. This merging of depolymerization and purification steps reduces the need for multiple separate treatment units and complex process control systems
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 enables the treatment of polyesters with high pigment content, removing impurities and producing monomers that can be repolymerized into PET with properties indistinguishable from virgin PET, expanding recycling opportunities and overcoming the limitations of existing technologies.
Implementation Method 1
a step of depolymerization by glycolysis fed at least by the effluent from step a) and by an additional diol, carried out at a temperature between 200 and 400° C.
Implementation Method 2
a diol separation step fed at least by the effluent from step b), operated at a temperature between 100 and 250° C., at a pressure lower than that of step b)
Implementation Method 3
a stage of decolorization of the pre-purified monomer effluent, carried out at a temperature of between 100 and 250°C, and at a pressure of between 0.1 and 1.0 MPa in the presence of an adsorbent
Data Source
AI summary
The invention relates to a method for the depolymerisation of a polyester load comprising opaque PET, said method including at least conditioning, depolymerisation and diol-separation steps, a step of separating the liquid-monomer-rich effluent, and a subsequent discolouration step.