Recovering Valuable Chemicals from Polypropylene Waste via a Mild Catalyst-Free Hydrothermal Process

• Published in: Environmental science & technology 2024-09, Vol.58 (37), p.16611-16620
• Main Authors: Xu, Qiongying, Wang, Qiandi, Yang, Jiaqi, Liu, Wenzong, Wang, Aijie
• Format: Article
• Language: English
• Subjects: Acetic acid; Addition polymerization; Atomic properties; Carbon; Carbonyl compounds; Carbonyl groups; Carbonyls; Catalysis; Catalysts; Chemical recovery; Circular economy; Cost analysis; Cyclotron resonance; Density functional theory; Economic analysis; Emission analysis; Fourier analysis; Fourier transforms; High temperature; Hydrogen peroxide; Hydrothermal treatment; Mass spectrometry; Mass spectroscopy; Oxidation; Oxidation-Reduction; Physico-Chemical Treatment and Resource Recovery; Plastic pollution; Polymers; Polypropylene; Polypropylenes - chemistry; Recovery; Recycling; Scale (corrosion); Spectral analysis; Spectrum analysis; Technology assessment
• ISSN: 0013-936X; 1520-5851; 1520-5851
• DOI: 10.1021/acs.est.4c04449

Waste polypropylene (PP) presents a significant environmental challenge, owing to its refractory nature and inert C–C backbone. In this study, we introduce a practical chemical recovery strategy from PP waste using a mild catalyst-free hydrothermal treatment (HT). The treatment converts 64.1% of the processed PP into dissolved organic products within 2 h in an air atmosphere at 160 °C. Higher temperatures increase the PP conversion efficiency. Distinct electron absorption and emission characteristics of the products are identified by spectral analysis. Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS) reveals the oxidative cracking of PP into shorter-chain homologues (10–50 carbon atoms) containing carboxylic and carbonyl groups. Density functional theory (DFT) calculations support a reaction pathway involving thermal C–H oxidation at the tertiary carbon sites in the polymer chain. The addition of 1% H2O2 further enhances the oxidation reaction to produce valuable short-chain acetic acids, enabling gram-scale recycling of both pure PP and disposable surgical masks from the real world. Techno-economic analysis (TEA) and environmental life cycle costing (E-LCC) analysis suggest that this hydrothermal oxidation recovery technology is financially viable, which shows significant potential in tackling the ongoing plastic pollution crisis and advancing plastic treatment methodologies toward a circular economy paradigm.