A review on pyrolysis of waste tires: mechanisms, products, and interconversions

The global accumulation of waste tires presents a serious environmental challenge, driving the development of sustainable recycling technologies. Pyrolysis, conducted under oxygen-free conditions, offers an effective route for recovering oil, gas, and char. This review provides an integrated and critical synthesis of waste tire pyrolysis (WTP) by linking reaction fundamentals with process engineering, with an emphasis on condition-resolved quantitative benchmarking across kinetic frameworks and reactor environments. Reported kinetic parameters are benchmarked across commonly used models, and reactor-/condition-specific oil/char/gas yields are compiled with statistical descriptors to enable more consistent comparisons. The degradation mechanisms and synergistic interactions of natural rubber (NR), styrene-butadiene rubber (SBR), and polybutadiene rubber (BR) are clarified, followed by a critical assessment of kinetic modeling approaches ranging from single-step models to advanced model-free methods. We further synthesize how operating severity and reactor-imposed environments jointly govern yields and quality, emphasizing the roles of heating intensity, effective vapor residence time, and vapor-solid disengagement/separation in driving secondary cracking/condensation and the observed yield scatter across studies. Future priorities include in-situ diagnostics, data-driven kinetic-reactor models, catalyst-reactor co-design, and sustainability assessment to support product-oriented optimization and scale-up of WTP toward circular resource utilization.