Chemical recycling of end-of-life tires by intermediate pyrolysis using a twin-auger reactor: Validation in a laboratory environment

This work deals with the chemical recycling of end-of-life tires (ELT) by means of intermediate pyrolysis to produce tire pyrolysis oil (TPO), raw recovered carbon black (rCB), and tire pyrolysis gas (TPG). Here, the operational features of a twin-auger pyrolyzer, as well as the characteristics of the resulting products were satisfactorily validated in a laboratory environment. Hence, the twin-auger pyrolyzer used in this work aligns with the characteristics associated with the fourth technology readiness level (TRL-4). In order to assure this statement, both the statistical repeatability of yields and, the consistency of the product's properties were assessed. As such, 27 experiments divided into 4 replicates were conducted at the conditions which maximized the TPO yield, while minimizing that of raw rCB: ELT mass flow rate of 1.16 kg/h, reactor temperature of 475 °C, solid residence time of 3.5 min, and N₂ flow rate of 300 mL/min. Thereafter, we explored the main physicochemical properties of different pyrolysis product samples, randomly selected throughout the experimental campaign. The TPO was characterized in terms of density, viscosity, total acid number (TAN), flash point, elemental composition, heating value, distillation characteristics, and contents of both water and carbon Conradson. The contents of saturates, aromatics, resins, and asphaltenes (SARA) were also determined. The raw rCB was characterized by proximate, elemental, and heating value analyses. Textural properties such as surface area (S_BET), total pore volume (V_T), micropore volume (V_Min), and mesopores volume (V_Meso), were identified as well, including SEM images analysis. Finally, the chemical composition of the TPG was measured by quantitative gas chromatography (H₂, CH₄, CO, CO₂, C₂H₆, C₂H₄, C₃H₈, H₂S). The analysis of variance (ANOVA) suggested that the twin-auger pyrolyzer is repeatable in terms of TPO, raw rCB, and TPG yields, with a reliability of 95 %. Likewise, the characterization of the products revealed that their properties remained quite stable across the experimental runs. These results demonstrate the stability and suitability of the experimental facility, which leads to the conclusion that the twin-auger reactor is a reliable and promising technology for the chemical recycling of ELT by means of intermediate pyrolysis.