Polyester Depolymerization Solvent System for High-Purity Terephthalic Acid
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Solution Overview
Problem
Existing methods for regenerating terephthalic acid from waste polyester are economically inefficient, environmentally unfriendly, and require excessive use of solvents and energy, with low purity and stability of the recovered product.
Innovation Solution
A method involving the use of an alkaline catalyst mixed with a basic hydrolysis solvent composed of an alkylated aromatic compound and a polarity adjusting compound to depolymerize polyester, followed by filtration, treatment with an organic solvent, and precipitation with an acidic solution to obtain high-purity terephthalic acid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If glycolysis is used to depolymerize polyester into BHET monomers, then the process is simple and easy to implement, but the reaction is very slow without catalysts and complete depolymerization cannot be achieved
Solution Approach 1:
The patent introduces a specific catalyst system (metal salts such as zinc acetate, calcium acetate, or magnesium acetate combined with organic acids) as an intermediary to mediate the glycolysis reaction. This catalyst system enables complete depolymerization of PET into BHET monomers by facilitating the ester bond cleavage, thereby resolving the contradiction between ease of implementation and reaction speed.
Solution Approach 2:
The patent optimizes reaction parameters including temperature (150-200°C), pressure, and catalyst concentration to achieve complete depolymerization. By adjusting these parameters, the reaction speed is significantly improved while maintaining the simplicity of the glycolysis process, resolving the contradiction between ease of manufacture and productivity.
2Manufacturing precision
If activated carbon is used extensively during purification to remove impurities, then purification efficiency is improved, but manufacturing cost increases significantly
Solution Approach 1:
The patent optimizes the amount and type of activated carbon used in purification, combining it with controlled precipitation conditions (pH adjustment, temperature control) to achieve high purity terephthalic acid with minimal carbon consumption. This reduces the quantity of expensive activated carbon required while maintaining product purity.
Solution Approach 2:
The patent employs a multi-stage purification approach where initial filtration removes bulk impurities, followed by controlled precipitation to separate terephthalic acid from dissolved contaminants. This reduces reliance on large amounts of activated carbon by using cheaper alternative purification methods.
3Manufacturing precision
If sublimation purification is performed at high temperature of 200°C or higher to purify DMT, then purification is achieved, but energy consumption increases and environmental impact worsens
Solution Approach 1:
The patent utilizes controlled precipitation from aqueous solution followed by filtration as an alternative to thermal sublimation. By adjusting pH and solubility conditions, terephthalic acid precipitates in high purity form that can be separated by filtration, avoiding the need for high-temperature sublimation and significantly reducing energy consumption.
Solution Approach 2:
The patent replaces the thermal field-based sublimation process with a chemical field-based precipitation process. Instead of using heat to purify the product, the method uses pH adjustment and solubility control to achieve purification through precipitation and filtration, thereby substituting a high-energy thermal process with a low-energy chemical process.
4Manufacturing precision
If large amounts of water and solvent are used in alkaline hydrolysis for purification, then terephthalic acid can be recovered, but manufacturing cost increases due to solvent recovery and disposal
Solution Approach 1:
The patent employs a precipitation method where terephthalic acid is recovered as a solid precipitate that can be filtered and washed with minimal solvent. The mother liquor containing dissolved salts and impurities is discarded or treated separately, avoiding the need for large-scale solvent recovery operations. This approach minimizes solvent loss while achieving high product purity.
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 a high conversion rate to terephthalic acid with minimal solvent use, reduced energy consumption, and stable solvent reuse, resulting in high-purity terephthalic acid with almost no impurities.
Implementation Method 1
The hydrolysis is a method of depolymerizing polyester into terephthalic acid and ethylene glycol through hydrolysis using water or a solvent and a catalyst
Implementation Method 2
isolating and purifying a precipitated solid crystal
Data Source
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AI summary
The present disclosure provides a method for producing high-purity regenerated terephthalic acid using polyester depolymerization and high-purity regenerated terephthalic acid produced thereby. An object to be achieved by the present disclosure is to provide a method for producing terephthalic acid capable of obtaining high-purity terephthalic acid from waste polyester, reducing the amount of solvent used for hydrolysis, solvent recovery energy, and manufacturing cost, and increasing the stability of the solvent.