Co-pyrolysis of waste tires and goat manure: Comprehensive analysis of thermal behavior, synergistic interactions, and kinetic mechanisms

Co-pyrolysis offers a promising strategy to leverage the complementary characteristics of different feedstocks for efficient utilization of waste resources. This study aims to investigate co-pyrolysis characteristics of waste tires (WT) and goat manure (GM) using a thermogravimetric analyzer, focusing on the effects of mixing ratio and heating rate, as well as synergistic interactions and reaction kinetics. Results show that pyrolysis occurs in two main stages, e.g., devolatilization and mineral decomposition stages, with the 1WT3GM blend exhibiting the best performance. Further kinetic analysis using three model-free methods, i.e., Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and Friedman (FR), revealed complex, multi-step reaction mechanisms. For WT pyrolysis, activation energy ( E α ) slowly increased during additive and natural rubber decomposition ( α = 0.05–0.30), sharply rose during synthetic rubber breakdown ( α = 0.30–0.65) with a peak at 607 kJ/mol, and then dropped during char formation. GM addition led to irregular E α trends and significantly reduced average E α values from 310.03 kJ/mol for 3WT1GM to 248.98 kJ/mol for 1WT3GM, corresponding to a 19.7% reduction, indicating enhanced reactivity and improved heat transfer via synergistic effects. Moreover, compensation effect analysis demonstrated a strong positive correlation between E α and ln A ( R 2 > 0.9), confirming the reliability of the kinetic models. Furthermore, XRD analysis revealed that the GM addition promotes the formation of stable mineral phases such as CaS. These findings underscore the potential of WT/GM co-pyrolysis for energy recovery and waste reduction, and provide mechanistic insights for developing efficient co-pyrolysis systems. • Co-pyrolysis characteristics of waste tire (WT) and goat manure (GM) was studied. • WT/GM co-pyrolysis includes devolatilization and mineral decomposition stages. • Kinetic analysis revealed synergistic interactions during WT/GM co-pyrolysis. • Compensation effect confirmed the strong reliability of the kinetic models. • GM addition promoted the formation of stable mineral phases such as CaS.