Continuous PET Hydrolysis for High-IV Terephthalic Acid Recovery
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Solution Overview
Problem
Existing methods for hydrolyzing polyethylene terephthalate (PET) with high polymerization degree (IV ≥ 0.75 dl/g) face challenges such as low reactivity, reactor clogging, and the use of toxic organic solvents, leading to incomplete decomposition and safety hazards.
Innovation Solution
A continuous hydrolysis process using a continuous reactor, where PET is heated and pressurized, mixed with an alkali-metal and ethylene glycol slurry, and reacted without an organic solvent, employing a staged introduction of alkali and weak acid salts to maintain reaction efficiency and purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If PET with high polymerization degree (IV ≥ 0.75 dl/g) is used, then product quality and mechanical strength are improved, but hydrolysis reactivity decreases and decomposition becomes incomplete
Solution Approach 1:
The patent applies parameter changes by systematically optimizing reaction conditions including temperature (200-280°C), pressure (0.1-10 MPa), residence time (1-60 minutes), and alkali-metal to PET ratio (1:0.1 to 1:5) to achieve complete hydrolysis of high-polymerization PET while maintaining productivity
Solution Approach 2:
The patent employs preliminary action through pre-mixing alkali-metal with weak acid salts (such as Na2CO3, K2CO3, NaHCO3, KHCO3) before introducing to the reactor, which prepares the catalytic system in advance to immediately activate hydrolysis upon contact with PET, overcoming the low reactivity of high-IV PET
2Productivity
If conventional hydrolysis methods are used, then some decomposition is achieved, but toxic organic solvents must be used and safety hazards increase
Solution Approach 1:
The patent applies the extraction principle by completely removing toxic organic solvents from the hydrolysis system and replacing them with water as the reaction medium, thereby eliminating solvent-related safety hazards while maintaining decomposition efficiency through optimized alkali-metal catalysis and process conditions
Solution Approach 2:
The patent creates a safe reaction environment by using water as the reaction medium and operating under controlled pressure conditions, effectively creating an inert-like environment that eliminates flammability and toxicity risks associated with organic solvents
3Productivity
If high-pressure and high-temperature conditions are applied to improve hydrolysis rate, then reaction speed increases, but energy consumption and operational complexity increase
Solution Approach 1:
The patent applies partial action by using moderate pressure (0.1-10 MPa) and temperature (200-280°C) conditions that are sufficient to achieve complete hydrolysis without requiring extreme conditions, thereby reducing energy consumption while maintaining high hydrolysis rates through effective alkali-metal catalysis
Solution Approach 2:
The patent employs continuous hydrolysis in a reactor system where PET and alkali-metal slurry are continuously fed, reacted, and discharged, maintaining steady-state operation that improves energy efficiency compared to batch processing while ensuring complete decomposition through continuous exposure to optimal reaction conditions
4Productivity
If alkali-metal is added to accelerate hydrolysis, then reaction efficiency improves, but impurity formation and purification difficulty increase
Solution Approach 1:
The patent introduces weak acid salts (Na2CO3, K2CO3, NaHCO3, KHCO3) as intermediary substances that work synergistically with alkali-metal to catalyze hydrolysis, helping to control the reaction pathway and reduce impurity formation while maintaining high reaction efficiency
Solution Approach 2:
The patent optimizes the ratio of alkali-metal to PET (1:0.1 to 1:5) and controls reaction parameters to achieve complete hydrolysis with minimal impurity formation, using precise parameter control to balance reaction efficiency and 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
This method achieves high-yield production of terephthalic acid with improved safety and reduced impurities, avoiding the use of toxic solvents and overcoming the limitations of high-polymerization PET.
Implementation Method 1
introducing high polymerization degree polyethylene terephthalate having an intrinsic viscosity of 0.75 dl/g or more into a continuous reactor, and then heating and pressurizing the same to prepare a fluidal polyethylene terephthalate
Implementation Method 2
implementing neat reaction of the fluidal polyethylene terephthalate with the mixed slurry in the continuous reactor to prepare alkali-metal terephthalate
Implementation Method 3
introducing a mixed slurry prepared by mixing alkali containing an alkali-metal, a weak acid salt of the alkali-metal and ethylene glycol together
Implementation Method 4
heating and pressurizing the same to prepare a fluidal polyethylene terephthalate
Data Source
AI summary
The present invention relates to a method for production of terephthalic acid using high polymerization degree polyethylene terephthalate, which includes: (i) introducing high polymerization degree polyethylene terephthalate having an intrinsic viscosity of 0.75 dl/g or more into a continuous reactor, and then heating and pressurizing the same to prepare a fluidal polyethylene terephthalate; (ii) introducing a mixed slurry prepared by mixing an alkaline material containing an alkali-metal, a weak acid salt of the alkali-metal and ethylene glycol together into an internal position of the continuous reactor, through which the fluidal polyethylene terephthalate passes, and implementing neat reaction of the fluidal polyethylene terephthalate with the mixed slurry in the continuous reactor to prepare alkali-metal terephthalate; and (iii) dissolving the prepared alkali-metal terephthalate in water, removing foreign substances through filtration and centrifugation, adding acid to the alkali-metal terephthalate dissolved in water and reacting the same, thereby producing terephthalic acid.