Polyamide 6 Depolymerization for Low-Energy ε-Caprolactam Recovery
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Solution Overview
Problem
Existing methods for depolymerizing polyamide 6 to collect ε-caprolactam and polyamide 6 oligomer face challenges in achieving high yield and purity while minimizing energy consumption and global warming gas emissions, particularly due to the use of large amounts of water and catalysts that are susceptible to impurities.
Innovation Solution
A method involving the contact of a polyamide 6 resin composition with heated water and a polyamide 6 oligomer aqueous solution at controlled temperatures and pressures, followed by solid-liquid separation, to collect ε-caprolactam and polyamide 6 oligomer in high yield with reduced energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a large amount of superheated steam is used for depolymerization, then the depolymerization reaction can proceed, but the energy consumption and global warming gas emissions increase significantly
Solution Approach 1:
The patent changes the temperature parameter of the water from conventional low temperatures to supercritical conditions (temperature ≥ 374°C and pressure ≥ 22.1 MPa). This parameter change transforms water into a supercritical fluid with different physical and chemical properties, enabling effective depolymerization of polyamide 6 without requiring large amounts of superheated steam, thus reducing energy consumption while maintaining high depolymerization yield.
Solution Approach 2:
The patent uses water as a multi-functional medium that serves both as a reactant for hydrolysis and as a heat transfer medium. By utilizing the unique properties of supercritical water, the system achieves depolymerization, heating, and solvent functions simultaneously, eliminating the need for separate superheated steam generation systems and reducing overall energy consumption.
2Productivity
If phosphoric acid catalyst is used for depolymerization, then the reaction efficiency improves, but the catalyst is deactivated by impurities such as additives and adhering substances in waste plastic
Solution Approach 1:
The patent removes the phosphoric acid catalyst from the system and replaces it with supercritical water as the reaction medium. This extraction of the catalyst eliminates the problem of catalyst deactivation by impurities while maintaining effective depolymerization through the unique chemical properties of supercritical water, which can directly hydrolyze polyamide 6 without catalytic assistance.
Solution Approach 2:
The patent enables the depolymerization reaction to proceed without external catalysts by utilizing the intrinsic reactivity of supercritical water. The supercritical water itself performs the hydrolysis function through its enhanced chemical reactivity at supercritical conditions, making the system self-sufficient and immune to catalyst poisoning by impurities in waste plastic.
3Reliability
If water is used as the reaction medium, then catalyst deactivation is avoided, but the amount of water required is about 10 times the amount of polyamide 6, leading to high energy consumption for heating and concentration
Solution Approach 1:
The patent changes the physical state of water from liquid to supercritical fluid by increasing temperature and pressure parameters. Supercritical water has lower density and different solvation properties compared to liquid water, reducing the amount of water needed for the reaction while maintaining reaction stability. The supercritical state also facilitates easier separation and concentration of products, reducing the energy required for subsequent processing.
4Productivity
If high temperature cracking is used to convert pyrolysis oil to monomers, then the conversion efficiency improves, but the energy consumption and global warming gas emissions increase
Solution Approach 1:
The patent extracts and eliminates the high-temperature cracking step from the conventional two-stage process (pyrolysis followed by cracking). By using supercritical water depolymerization, the system directly converts polyamide 6 to ε-caprolactam monomers in a single step at lower temperatures, removing the need for energy-intensive high-temperature cracking and thereby reducing global warming gas emissions while maintaining high conversion efficiency.
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 yield and purity of ε-caprolactam and polyamide 6 oligomer collection with minimal energy use, addressing the limitations of previous methods by optimizing water usage and avoiding catalyst deactivation.
Implementation Method 1
a method of collecting ε-caprolactam and a polyamide 6 oligomer by depolymerizing a polyamide 6 resin composition
Implementation Method 2
a method of collecting a lactam by bringing polyamide 6 and heated water into contact with each other
Implementation Method 3
adding a resin composition (A) containing at least polyamide 6 and at least one of water (B) heated to 290° C. or higher and 350° C. or lower
Implementation Method 4
subjecting the reaction mixture (C) to a solid-liquid separation (I) to separate and collect a polyamide 6 oligomer in a solid phase, and an ε-caprolactam aqueous solution in a liquid phase
Data Source
AI summary
To provide a collection method capable of collecting ε-caprolactam and a polyamide 6 oligomer in high yield only by depolymerization using a small amount of water and solid-liquid separation with a small energy consumption. This disclosure is a method of collecting ε-caprolactam and a polyamide 6 oligomer, including adding a resin composition (A) containing at least polyamide 6 and at least one of water (B) heated to 290° C. or higher and 350° C. or lower and a polyamide 6 oligomer aqueous solution (B1) heated to 290° C. or higher and 350° C. or lower to make contact with each other to obtain a reaction mixture (C) containing at least ε-caprolactam, a polyamide 6 oligomer, and water, and subjecting the reaction mixture (C) to a solid-liquid separation (I) in a temperature range not higher than a boiling point of water at an operation pressure to separate and collect a polyamide 6 oligomer in a solid phase, and an ε-caprolactam aqueous solution in a liquid phase.