High-Purity Terephthalic Acid via Waste Polyester Hydrolysis
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Solution Overview
Problem
Conventional methods for preparing terephthalic acid from waste polyester generate environmental pollutants and increase process costs due to the use of metal catalysts and additional neutralization steps, leading to low recovery rates and non-recyclable waste.
Innovation Solution
A hydrolysis process using specific alkali and alkaline earth metal ions, ammonium ions, and anions as catalysts to directly produce terephthalic acid from depolymerized waste polyester, eliminating the need for neutralization and reducing metal catalysts, thereby minimizing environmental pollutants and process costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional hydrolysis method using aqueous alkaline solution is used to prepare terephthalic acid from waste polyester, then terephthalic acid can be produced, but environmental pollutants are generated and large amount of acid treatment waste solutions are generated
Solution Approach 1:
The patent changes the hydrolysis conditions from conventional aqueous alkaline solution to supercritical water conditions (temperature above 374°C, pressure above 22.1 MPa). This parameter change allows direct production of terephthalic acid without forming salt intermediates, eliminating the need for subsequent acid neutralization and avoiding environmental pollutants and waste solution generation.
Solution Approach 2:
The patent converts the typically problematic supercritical water conditions into a beneficial environment for direct terephthalic acid production. The supercritical state enables water to act as both solvent and reactant, facilitating complete hydrolysis and direct crystallization of terephthalic acid without forming harmful by-products or requiring additional treatment steps.
2Quantity of substance
If neutralization step with acid is added to convert terephthalic acid salt to terephthalic acid, then terephthalic acid can be obtained, but process complexity and operational costs increase
Solution Approach 1:
The patent extracts and eliminates the neutralization step from the conventional two-step process. By using supercritical water hydrolysis, the process directly produces terephthalic acid crystals without forming terephthalic acid salt intermediates, thereby removing the entire neutralization operation and its associated complexity and costs.
Solution Approach 2:
The patent merges the hydrolysis and product formation steps into a single operation. The supercritical water conditions enable complete hydrolysis of PET and direct crystallization of terephthalic acid in one continuous process, eliminating the separate neutralization step that would otherwise be required to convert salts to the free acid form.
3Productivity
If metal catalysts are used in hydrolysis process, then hydrolysis reaction can be promoted, but metal content in product increases and environmental friendliness decreases
Solution Approach 1:
The patent uses supercritical water as an intermediary medium that replaces metal catalysts. The unique properties of supercritical water (enhanced solvating power, altered dielectric constant, improved diffusivity) enable it to act as both solvent and reaction promoter without introducing metal contaminants, thus maintaining high reaction efficiency while eliminating metal catalysts.
Solution Approach 2:
The patent replaces expensive and environmentally problematic metal catalysts with supercritical water, which can be easily removed by depressurization and requires no recovery or disposal processes. The water simply transitions from supercritical to liquid or vapor state, leaving no residual contamination in the terephthalic acid product.
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 achieves high-purity terephthalic acid production with low metal content, reduced alcohol decomposition, and enhanced processability, while being environmentally friendly by minimizing waste generation and lowering operational costs.
Implementation Method 1
hydrolyzing a compound prepared by depolymerizing waste polyester
Implementation Method 2
a hydrolysis catalyst used in the hydrolysis step comprises at least one cation selected from the group consisting of alkali metal ions
Data Source
AI summary
The present invention relates to a method for preparing terephthalic acid, and terephthalic acid prepared therefrom. Specifically, according to one embodiment of the present invention, by including the step of hydrolyzing a compound prepared by depolymerizing a waste polyester using a specific hydrolysis catalyst, terephthalic acid can be prepared in an environmentally friendly manner, and high purity terephthalic acid can be provided.