Co-pyrolysis of mixed municipal solid waste components in a semi-pilot scale rotary kiln: synergistic effects on pyrolysis oil and biochar properties.

Sustainable valorisation of municipal solid waste (MSW) is essential to mitigate landfill pressures, reduce greenhouse gas emissions, and support the circular bioeconomy. This study investigates the sequential co-pyrolysis of wastepaper (WP), textiles (TW), mixed plastics (MP), and mustard husk (MH) in a semi-pilot-scale rotary kiln reactor at 500 °C. The individual feedstocks, binary (WP-MP), ternary (WP-MP-TW; PTP), and quaternary mixtures (PTP-MH; Mix-4) were pyrolysed to evaluate synergistic decomposition behaviour and product upgrading. Thermogravimetric analysis revealed primary devolatilization between 230-550 °C, with mixtures exhibiting shifted decomposition onset due to hydrogen-donor interactions and radical coupling between biomass and polymer-derived intermediates. Mixed plastics yielded the highest pyrolysis oil content (43 wt%) and the lowest char yield (16 wt%), whereas wastepaper produced the highest char (30-40 wt%). Furthermore, co-pyrolysis significantly enhanced product distribution, with PTP and Mix-4 achieving up to 37 wt% pyrolysis oil, 18-28 wt% char, and reduced gas formation compared to pure biomass. The quality of pyrolysis oil improved markedly with blending; calorific value increased from 18.41 MJ kg-1 (WP pyrolysis oil) to 34.67 MJ kg-1 (WP-MP) and 31.32 MJ kg-1 (Mix-4), accompanied by lower water content (1.22-7.00 wt%) and reduced pH (3.2-4.9). GC-MS results confirmed the formation of increased aromatic and aliphatic hydrocarbons in blended feeds, particularly benzene, toluene, xylene, and long-chain alkanes, indicating a synergistic effect of hydrogen transfer and deoxygenation. Finally, char samples exhibited carbon contents of 32.20-76.10 wt% with porous microstructures, supporting their suitability for energy and material applications. The co-pyrolysis enhances the quality of pyrolysis oil and char, offering a scalable pathway for mixed MSW utilisation, reduced preprocessing requirements, and improved resource recovery.