Purified BHET Monomer Production via Glycolysis and Adsorption
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current chemical recycling processes for polyethylene terephthalate (PET) struggle with effectively depolymerizing colored and opaque PET due to the presence of pigments, which affects the mechanical properties of recycled PET and is difficult to purify, leading to limited recycling options and product quality.
Innovation Solution
A process involving glycolysis depolymerization of PET, followed by a purification step that includes adsorption and crystallization, to produce a decolourized and purified diester monomer effluent, specifically bis(2-hydroxyethyl) terephthalate (BHET), achieving high purity and color neutrality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If mechanical recycling is used for colored and opaque PET, then processing is simpler, but the mechanical properties of recycled PET are adversely affected and recycling options are limited
Solution Approach 1:
The invention changes the chemical parameters of the PET through depolymerization and repolymerization processes. By breaking down the polymer into monomers and re-synthesizing it, the chemical structure is reset, eliminating the degradation that occurs in mechanical recycling and restoring mechanical properties to virgin-like levels.
Solution Approach 2:
The invention extracts and removes pigments and dyes from the PET recycling stream through chemical treatment during the depolymerization process. This separation of colorants from the polymer matrix enables the production of clear, high-quality recycled PET that maintains excellent mechanical properties.
2Adaptability or versatility
If opaque PET with high pigment content is included in recycling streams, then recycling scope is expanded, but purification becomes difficult and product quality deteriorates
Solution Approach 1:
The invention uses chemical parameter changes during depolymerization to transform the relationship between pigments and the polymer matrix. The chemical breakdown allows pigments to be separated from the regenerated polymer, enabling effective purification even from highly pigmented opaque PET materials.
3Manufacturing precision
If depolymerization by glycolysis is used, then pigment removal is improved, but process complexity and energy consumption increase
Solution Approach 1:
The glycolysis process serves multiple functions simultaneously: it depolymerizes the PET, removes pigments through chemical breakdown, and produces purified monomers for repolymerization. This multi-functionality consolidates what would otherwise require separate processing steps into a single integrated operation.
4Manufacturing precision
If depolymerization by glycolysis is used, then pigment removal is improved, but energy consumption increases
Solution Approach 1:
The invention optimizes the energy parameters of the glycolysis process by controlling temperature, pressure, and catalyst conditions. By carefully managing these parameters, the process achieves effective pigment removal while minimizing energy consumption through efficient heat transfer and optimized reaction conditions.
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 removes pigments and dyes, resulting in a purified BHET monomer that can be repolymerized into virgin-like PET, expanding recycling options and improving product quality by achieving high lightness and color parameters, with no significant absorption in visible wavelengths.
Implementation Method 1
step of depolymerization by glycolysis of a polyester feedstock
Implementation Method 2
a step of purification of the diester effluent comprising a step of adsorption
Implementation Method 3
followed by a step of crystallization of the diester monomer
Data Source
AI summary
The present invention relates to a process for depolymerization of a polyester feedstock comprising PET, comprising:a) a step for conditioning the polyester feedstock, to produce a conditioned feedstock stream;b) a step of depolymerization of the conditioned feedstock stream, at a temperature of between 150 and 300° C., in the presence of diol with a ratio by weight between the diol and the diester in the feedstock of between 0.3 and 8.0, to produce a reaction effluent;c) a step of separation of the diol from the reaction effluent, to produce at least a liquid monomers effluent;d) a step of separation of the liquid monomers effluent into a heavy impurities effluent and a prepurified monomers effluent; ande) a step of purification of the prepurified monomers effluent, comprising a substep e1) of adsorption at a temperature of between 50 and 200° C. and a crystallization substep e2), and producing at least one decolourized purified diester monomer effluent.