Waste tire valorization by intermediate pyrolysis using a continuous twin-auger reactor: Operational features

Pyrolysis can be regarded as a roadmap towards a circular and sustainable economy for waste tires (WT). This work investigates the operational characteristics of a novel twin-auger reactor to transform WT by intermediate pyrolysis into tire pyrolysis oil (TPO), recovery carbon black (rCB), and tire pyrolysis gas (TPG). The influence of four operating parameters: reactor temperature (X₁), WT mass flow rate (X₂), solid residence time (X₃) and N₂ volumetric flow rate (X₄), was assessed in order to maximize the TPO yield (Y₁), while keeping the rCB one (Y₂) as low as possible. The experimental campaign was conducted based on central composite design (CCD). The analysis of variance (ANOVA) showed that X₁ and X₂ exhibit the highest statistical influence. An optimization of both responses resulted in TPO, rCB, and TPG yields of 45, 40 and 15 wt%, respectively, when the pyrolyzer is operated at 475 °C, 1.16 kg/h, 3.5 min and 300 mL/min. At these conditions, the resulting TPO showed contents of C, H, S, N and O around 88.2, 9.7, 1.3, 0.7 and <0.1 wt%, respectively, along with a heating value of 42.02 MJ/kg. The rCB is comprised of moisture, volatile matter, fixed carbon, and ash around 2.5, 3.7, 75.5, and 18.3 wt%, respectively; while the TPG was mainly composed of H₂ (23.7 vol%) and CH₄ (28.2 vol%). Overall, these results suggest that twin-auger pyrolyzers are well suited for valorizing WT by intermediate pyrolysis.