Valorization of packaging plastic waste by slow pyrolysis

Low and high-density polyethylene (LDPE and HDPE) and polypropylene (PP) are three most common polyolefins profusely used as packaging materials and abundantly found in the plastic waste stream. These plastic waste samples were collected from household waste and converted into plastic derived oil (PDO) by low temperature (300 °C to 400 °C) slow pyrolysis (long isothermal holding time) in a semi-batch reactor. The PDO samples obtained had shown variation in their compositions and fuel properties based on the pyrolysis temperature. PDO from the pyrolysis of PP has high octane number (∼92) and low viscosity. Noticeably, the PDO samples obtained at low temperature pyrolysis are lighter with low viscosity, high octane number and having high calorific values. 1H NMR analysis revealed that the oil samples mostly consist of paraffinic and olefinic hydrocarbons. Simulated distillation (SimDist) of PDO indicated that the liquid products resemble the characteristic closer to middle distillate of petroleum fraction having very low pour point and flash point. The temperature with long pyrolysis time also influenced the evolved gas composition and yield. Trace amount of hydrogen, carbon monoxide and carbon dioxide were present in the gaseous product along with various hydrocarbon gases ranging from C1–C5. The degradation mechanism follows end chain scission which produces monomer units whereas random scission results most of the hydrocarbon products. Subsequent reactions like radical recombination and inter or intra molecular hydrogen transfer results in the formation of most of the olefinic components.

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Recommended citation: P. Das and P. Tiwari, “Valorization of packaging plastic waste by slow pyrolysis,” Resources, Conservation and Recycling, vol. 128, pp. 69-77, 2018/01/01/ 2018.