Innovative Application of Tetrafluoroethylene in Environmental Protection: Degradation and Recycling Technology
1、 Environmental challenges of tetrafluoroethylene (TFE) related materials
Polytetrafluoroethylene (PTFE) and fluorinated copolymers (such as FEP and PFA) have strong chemical inertness and a natural degradation cycle of over 1000 years. Traditional landfill or incineration can lead to:
Microplastic pollution: Nano sized particles generated by wear and tear enter water bodies and soil, affecting ecosystems.
Toxic by-products: Hazardous substances such as hydrogen fluoride (Hf) and polyfluorodibenzodioxins (PFDs) are released during incineration.
Core contradiction: The conflict between high performance and difficult to degrade characteristics forces the industry to explore environmentally friendly degradation and recycling technologies.
2、 Innovation in degradation technology of tetrafluoroethylene based materials
1. Chemical degradation: a key breakthrough in breaking C-F bonds
(1) High temperature melt cracking method
Principle: In an inert atmosphere (such as N ₂), PTFE is heated to 600-800 ℃ and thermally cracked to produce TFE monomer, fluorinated olefins (such as C ₂ F ₄, C ∝ F ₆), and a small amount of carbon powder.
Innovation point:
Introducing transition metal catalysts (such as Ni/Al ₂ O3) to lower the cracking temperature to 450 ℃ and reduce energy consumption by 30%.
Supporting condensation adsorption system: using fluorocarbon solvents (such as FC-72) to recover TFE monomers with a purity of up to 99.5%, achieving closed-loop regeneration.
Application scenario: Large scale processing of industrial waste (such as waste seals and coating waste), with a monomer recovery rate of about 70%.
(2) Electrochemical degradation method
Principle: Using PTFE powder as the anode, apply a voltage of 1.5-2.0 V in a molten carbonate electrolyte (such as Li ₂ CO ∝ - Na ₂ CO ∝ - K ₂ CO ∝), and decompose C-F bonds through electrooxidation reaction
Advantages:
The reaction can be initiated at room temperature, with energy consumption only 1/5 of thermal cracking.
The products are CO ₂ and fluoride salts (such as KOF), which can be used to prepare chemical raw materials such as potassium fluoride (KF) without secondary pollution.
Laboratory progress: The degradation rate of 100 g PTFE sample reached 92% within 4 hours, and the fluoride ion recovery rate exceeded 95%.
(3) Biodegradation: Microbial synergy
Filtering direction:
Extreme microorganisms: strains of bacteria (such as Pseudomonas) capable of metabolizing fluorinated organic matter were isolated from the soil of fluoride factories and gradually deFluorined by secreting fluorinating enzymes.
Genetic engineering bacteria: The gene encoding C-F bond cleavage enzyme (such as FlDA) is introduced into Escherichia coli to construct an engineering bacterium that decomposes PTFE into F ⁻ and CO ₂ under anaerobic conditions.
Limitations: Currently, only low molecular weight fluoropolymers (such as CF ₂ Cl ₂) can be degraded, and the degradation efficiency of high molecular weight PTFE is less than 5%. Further optimization of metabolic pathways is needed.
2. Physical degradation: energy field assisted chain breaking
(1) Plasma technology
Low temperature plasma: Using radio frequency glow discharge to generate high-energy electrons (10-20 eV), which bombard the PTFE surface, breaking the C-F bond and generating free radicals such as CF ∝ and CF ₂, ultimately converting into gases such as COF ₂ and CF ₄.
Innovative applications:
Combined with microwave: In a 2.45 GHz microwave field, the degradation rate of PTFE is increased by three times compared to traditional plasma, making it suitable for thin film waste (such as waste FEP cable skin).
By product treatment: HF is removed by alkaline absorption (such as NaOH solution), and the gas products are catalytically reformed to produce CO and F ₂, which can be used to synthesize new fluorides.
(2) Ultrasound assisted degradation
Mechanism: Ultrasonic waves (20-100 kHz) generate cavitation bubbles in the liquid, and instantaneous high pressure (>100 MPa) and high temperature (>5000 K) cause mechanical shear and thermal decomposition of PTFE particles in synergy.
Optimize parameters:
By adding nano iron particles (50 nm) as catalysts, the degradation efficiency is increased by 40%, making it suitable for the remediation of microplastic contaminated water bodies (such as treating PTFE particles with a particle size<50 μ m).
3、 Innovation in Recycling Technology of Tetrafluoroethylene Materials
1. Mechanical recycling: from "downgraded utilization" to "high-value regeneration"
(1) Traditional crushing filling process
Process: Waste cleaning → Crushing (particle size<1 mm) → Blending with glass fiber (30%) and molybdenum disulfide (10%) → Compression molding.
Application: Recycled PTFE is used for low-end seals and bearings, with a performance retention rate of about 60-70% (tensile strength reduced from 20 MPa to 12 MPa).
(2) Supercritical fluid regeneration technology
workmanship
Immerse the waste material in supercritical CO ₂ (temperature 31.1 ℃, pressure 7.38 MPa) for swelling for 2 hours;
Add small molecule fluorides (such as CF ∝ COOH) as chain transfer agents and perform solid-phase polymerization at 150 ℃ to repair broken molecular chains.
Effect: The molecular weight distribution of regenerated PTFE is restored to 90% of the new material, and the tensile strength reaches 18 MPa, which can be directly used for medical device components.
2. Chemical recycling: monomer recycling and high-value utilization
(1) TFE monomer recycling loop
Technical route:
PTFE
pyrolysis
catalyst
TFE monomer
Suspension Polymerization
New PTFE
Case: A chemical enterprise has built a production line capable of processing 5000 tons of PTFE waste annually. The monomer recovery rate is 75%, and the cost of recycled materials is 40% lower than that of new materials. The line has been used to produce chemical pipelines.
(2) Upgrading and conversion of fluorocarbon compounds
Synthesis of Fluorinated Fine Chemicals:
Reacting the cracked product TFE with ethanol to prepare fluorinated ethers (such as CF ₂=CF-O-CH ₂ CH3) for the synthesis of novel fluorinated surfactants.
Through the telomerization reaction, TFE and HF are combined to form perfluorooctanoic acid (PFOA substitute), which is used for environment-friendly lotion polymerization.
3. Energy recovery: clean incineration and resource coupling
Efficient incineration system:
Using an oxygen rich incinerator (with an O ₂ concentration of 25-30%), the combustion temperature is controlled above 1200 ℃ to ensure complete decomposition of PTFE into HF and CO ₂.
Supporting dry defluorination technology: using CaO powder to adsorb HF, generating CaF ₂ (purity>98%), which can be used in the electrolytic aluminum industry (replacing fluorite).
Energy conversion: The thermal energy generated by incineration drives a steam turbine to generate electricity. One ton of PTFE waste can generate approximately 1500 kWh of electricity, achieving the triple benefits of "carbon reduction, electricity production, and solid waste utilization".