Co-pyrolysis characteristics of corn stalk mixed with oily sludge

This study explored co-pyrolysis of corn stalks and oily sludge as a sustainable waste valorization method using Response Surface Methodology with Box–Behnken design to evaluate four key parameters: material ratio, pyrolysis temperature, pyrolysis time, and nitrogen flow rate. And co-pyrolysis products were characterized for resource recovery potential. The results analysis showed material ratio most influenced pyrolysis-derived oil yield, followed by nitrogen flow rate, temperature, and time. For pyrolysis-derived carbon yield, nitrogen flow rate was most significant, then material ratio, pyrolysis temperature, and time. Optimal conditions (5:5 dry basis ratio, 650 °C, 90 min, 15 L/min nitrogen) yielded 28.42 wt% oil and 67.58 wt% carbon, with less than 5% error between predicted and experimental values. The carbon exhibited a surface area of 95.35 m²/g, with 71.75% micropores, micropore volume of 0.034 cm³/g, confirming a predominantly microporous architecture. Combustion performance showed favorable temperatures: ignition (378.34 °C), peak (491.32 °C), and burnout (684.02 °C), with a combustion index of 5.62 × 10⁻⁷ %/(min²·°C³), that compares favorably with those reported for other biomass-derived chars. Additionally, the oil was enriched with volatile methylsiloxanes and long-chain branched alkanes (C₂₆H₅₄), which contribute to higher heating value but may also increase viscosity, suggesting trade-offs in fuel applicability. Thus, it can be inferred that the energy generated from combusting the pyrolysis products could sufficient to support the endothermic demands of the pyrolysis process itself, highlighting the feasibility of internal thermal energy integration. This energy integration reduces external energy requirements and improves sustainability, offering economic and environmental benefits for scale-up.