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Depolymerization of Nylon‑6 over a Supported Ruthenium Catalyst to ε‑Caprolactam
Prabin Dhakal1, Abdenour Achour1, Phuoc Hoang Ho1
1Chemical Engineering, Competence Centre for Catalysis, Chalmers University of Technology, Gothenburg 41296, Sweden.
ACS Environmental Au
|July 23, 2026
Summary
This study introduces a new catalytic process for recycling nylon-6 into its monomer, ε-caprolactam, achieving high yields and selectivity. The novel method utilizes ruthenium catalysts and activated hydrogen, offering a sustainable solution for plastic waste management.
Area of Science:
- Materials Science
- Chemical Engineering
- Environmental Science
Background:
- Plastic waste poses a significant environmental challenge, necessitating effective recycling strategies.
- Catalytic hydro-depolymerization is a promising plastic recycling method, but research on heteroatom-containing plastics like nylon-6 is limited.
- Developing efficient methods for nylon-6 recycling is crucial for establishing a circular economy in the plastics industry.
Purpose of the Study:
- To develop a novel heterogeneous catalytic process for the efficient hydro-depolymerization of nylon-6 into its monomer, ε-caprolactam.
- To investigate the catalytic activity and selectivity of ruthenium supported on zirconia with activated hydrogen for nylon-6 depolymerization.
- To understand the influence of catalyst properties, such as Ru particle size, and reaction conditions on the depolymerization efficiency.
Main Methods:
- Heterogeneous catalytic hydro-depolymerization of nylon-6 using ruthenium supported on zirconia and activated hydrogen.
- Optimization of reaction conditions including temperature (350 °C) and hydrogen pressure (30 bar).
- Characterization of the catalyst using techniques such as XPS and H2-TPR to analyze Ru particle size and reduction behavior.
Main Results:
- Achieved a 94% yield of ε-caprolactam from nylon-6 depolymerization with only 3.4% hexamethylenimine byproduct.
- Identified optimal catalyst conditions with 2.3 wt % Ru loading and a Ru particle size of 9.5 ± 2.3 nm for maximum efficiency.
- Demonstrated that water addition enhances selectivity to 100% and confirmed catalyst reusability and robustness against plasticizers and additives.
Conclusions:
- The developed ruthenium-catalyzed hydro-depolymerization process is highly effective for recycling nylon-6 into ε-caprolactam.
- Catalyst particle size and the synergistic effect between Ru and activated hydrogen are critical for efficient C-N bond cleavage and depolymerization.
- The process shows potential for industrial application due to its high efficiency, selectivity, robustness, and catalyst reusability, contributing to a circular economy for plastics.
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