Efficient chemical recycling method for waste polyester fabrics
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Solution Overview
Problem
Conventional chemical recycling methods for waste polyester fabrics are costly and produce poor-quality products due to high temperatures, long depolymerization times, low selectivity, and a yellowish hue of the BHET monomer.
Innovation Solution
A chemical recycling method using a composite solvent comprising alcohol ether and phenyl ether for pre-treatment and depolymerization of waste polyester fabrics, eliminating the need for drying and reducing energy consumption and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional drying process is used to remove solvent from decolored PET fabric, then solvent residue is reduced below 1.0%, but energy consumption increases and equipment complexity increases
Solution Approach 1:
The patent extracts the solvent removal function from the drying process by using supercritical carbon dioxide to directly extract and remove the solvent from the fabric. This eliminates the need for thermal drying while achieving complete solvent removal, resolving the contradiction between solvent residue control and energy consumption
Solution Approach 2:
The patent changes the physical state parameters of carbon dioxide to supercritical state (temperature above 31.1°C and pressure above 73 atm), enabling it to act as an extraction medium that can penetrate fabric and remove solvent without requiring subsequent drying. This parameter change allows solvent removal without thermal energy input
2Productivity
If conventional BHET monomer chemical recovery process is used with high temperature depolymerization, then depolymerization can proceed, but depolymerization time increases and BHET selectivity decreases
Solution Approach 1:
The patent changes the temperature parameter from conventional high temperature (190-240°C) to moderate temperature (100-150°C) and introduces supercritical carbon dioxide as a new medium. This parameter change enables depolymerization to proceed efficiently without the time loss associated with conventional high-temperature processes
Solution Approach 2:
The patent introduces supercritical carbon dioxide as an intermediary medium that facilitates depolymerization at lower temperatures. The supercritical CO2 acts as both the extraction medium for solvent removal and the reaction medium for depolymerization, enabling the process to proceed faster and more selectively than conventional thermal methods
3Productivity
If conventional BHET monomer chemical recovery process is used, then depolymerization can proceed, but BHET product exhibits yellowish hue indicating poor quality
Solution Approach 1:
The patent uses supercritical carbon dioxide, an inert atmosphere, as the reaction medium for depolymerization. This inert environment prevents oxidation and other side reactions that cause yellowing of the BHET product, thereby maintaining high product quality while ensuring productive depolymerization
Solution Approach 2:
The patent changes the temperature parameter from high temperature (190-240°C) to moderate temperature (100-150°C) in the depolymerization process. This parameter change reduces thermal degradation and prevents yellowing of the BHET monomer, thereby improving product quality while maintaining production efficiency
4Loss of substance
If solvent recovery process is used to condense and recover evaporated solvent, then solvent can be recovered, but solvent leakage occurs and equipment complexity increases
Solution Approach 1:
The patent extracts the solvent from the fabric using supercritical carbon dioxide in a direct extraction process. The solvent is removed with the supercritical CO2 stream and can be recovered through simple depressurization, eliminating the need for complex condensation and recovery equipment that causes leakage in conventional processes
Solution Approach 2:
The patent replaces the thermal-mechanical solvent recovery system (evaporation-condensation equipment) with a supercritical fluid extraction system. The solvent is removed through pressure-controlled supercritical extraction and can be recovered by simple pressure release, eliminating mechanical complexity and leakage risks associated with conventional thermal recovery 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
The method achieves high selectivity of ethylene terephthalate monomers, improves the quality of recycled r-PET, and reduces energy consumption and costs by eliminating the need for drying and lowering depolymerization temperatures.
Implementation Method 1
The polyester fabric is extracted using a composite solvent and filtered to obtain a decolored polyester fabric. The composite solvent contains alcohol ether and phenyl ether
Implementation Method 2
Ethylene glycol is then added to the decolored polyester fabric to depolymerize into ethylene terephthalate monomers
Data Source
AI summary
The disclosure provides a chemical recycling method for polyester fabrics, which includes the following steps. The polyester fabric is extracted using a composite solvent and filtered to obtain a decolored polyester fabric. The composite solvent contains alcohol ether and phenyl ether, and the decolored polyester fabric contains the composite solvent. Ethylene glycol is then added to the decolored polyester fabric to depolymerize into ethylene terephthalate monomers.