Superheated Water Dechlorination for Chlorinated Plastic Recycling
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Solution Overview
Problem
Existing methods for dechlorinating chlorinated polymers in plastic waste, such as PVC, face challenges including high energy consumption, formation of corrosive gases, formation of chloride salts, incorporation of oxygen, and inefficiencies in recycling due to impurities and non-homogeneous mixtures, which hinder effective recycling and chloride recovery.
Innovation Solution
A method involving superheating an aqueous plastic mixture of chlorine-containing polymers to at least 210°C under acidic conditions, maintaining a pH of at most 4, which removes chlorine as hydrogen chloride without forming chloride salts and minimizing oxygen incorporation, allowing for efficient dechlorination and subsequent chloride recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If gasification or pyrolysis is used to break down polymer chains, then chlorine can be removed from the plastic material, but corrosive hydrogen chloride gas is released and chlorinated polycyclic aromatic hydrocarbons may form
Solution Approach 1:
Water serves as an intermediary medium in the hydrothermal treatment process. The superheated water facilitates chlorine removal from PVC while converting it into dissolved hydrogen chloride in the aqueous phase rather than gaseous HCl, thereby preventing corrosion and dioxin formation while achieving effective dechlorination
Solution Approach 2:
The process utilizes extreme temperature and pressure parameters to superheat water above its normal boiling point, creating a unique hydrothermal state where water remains liquid but exhibits enhanced solvent properties and reactivity, enabling chlorine to transfer from polymer to aqueous phase as dissolved HCl rather than gas
2Productivity
If alkaline base is used to accelerate dechlorination reaction, then chlorine removal is enhanced, but chloride salt is formed as a side product with minimal commercial value
Solution Approach 1:
Instead of using alkaline conditions that convert HCl into worthless chloride salts, the invention inverts the approach by maintaining acidic conditions where HCl remains in its molecular form dissolved in water, transforming the unwanted side product into a recoverable commodity chemical with significant commercial value
3Speed
If alkaline base is used for dechlorination, then reaction speed increases, but oxygen is incorporated into the dechlorinated product
Solution Approach 1:
The invention changes the pH parameter from alkaline to acidic conditions, which maintains fast reaction kinetics through acid-catalyzed dechlorination while preventing oxygen incorporation into the polymer structure, thereby preserving product quality and suitability for further processing
4Stability of the object's composition
If mechanical recycling is used to maintain polymer chains intact, then material structure is preserved, but the waste stream must be clean and homogeneous which is difficult to achieve
Solution Approach 1:
The hydrothermal treatment selectively extracts chlorine from the PVC polymer structure while leaving the polymer chains intact. This extraction approach allows processing of mixed, impure waste streams by removing the harmful chlorine component without requiring pre-sorting or cleaning, bridging the gap between mechanical and feedstock recycling
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
Achieves high chlorine removal rates (>80%) with low oxygen incorporation, producing dechlorinated plastic suitable for further processing and enabling efficient chloride recovery through ion exchange, reducing the need for post-treatment and energy-intensive processes.
Implementation Method 1
superheating the aqueous plastic mixture to a temperature of at least 210°C
Implementation Method 2
The chlorine is transferred from the plastic to an alkaline aqueous phase wherein the base is used to minimize corrosion and to accelerate the dechlorination reaction
Implementation Method 3
during the superheating, the pH of the water in the aqueous plastic mixture is maintained at at most 4
Implementation Method 4
enabling efficient chloride recovery through ion exchange
Data Source
AI summary
The invention is in the field of recycling plastic material. In particular, the invention is directed to a method for dechlorination of a chlorine-containing polymer comprised in plastic material using superheating. The invention is further directed to a dechlorinated polymer obtainable by the method. The method is performed in water, with a pH of at most 4 during the method.