Pyrolysis of Waste Tires in a Twin-Auger Reactor Using CaO: Assessing the Physicochemical Properties of the Derived Products

This work assesses the effect of adding CaO during the pyrolysis of waste tires (WT) using a twin-auger reactor on the properties of the pyrolysis derived products. Pyrolysis was conducted in a lab-scale facility at a reactor temperature of 475 °C, solid residence time of 3.5 min, WT mass flow rate of 1.16 kg/h, and N2 flow rate of 300 mL/min. CaO was continuously fed at ratios of 10, 15, and 20 wt %, according to the WT mass flow rate, using two particle size ranges: fine (105-149 μm) and coarse (149-841 μm). The resulting tire pyrolysis oil (TPO) was initially characterized in terms of sulfur content, and the sample with the lowest sulfur content, named TPO[CaO], was further studied by different analytical techniques, including GC-MS and 1H NMR. The tire pyrolysis gas (TPG) and the tire pyrolysis solid (TPS) related to TPO[CaO], so-called TPG[CaO] and TPS[CaO], respectively, were also characterized by gas chromatography, and elemental, proximate, and XRF analyses, respectively. Lastly, an acid demineralization process was carried out to remove some of the inorganic elements in the TPS[CaO]. The addition of 15 wt % of coarse CaO during the pyrolysis of WT resulted in a sulfur reduction in TPO of 26.10%, while viscosity and water content were significantly reduced. The GC-MS analysis revealed a significant presence of benzene, toluene, xylene, and limonene in both TPO and TPO[CaO]. Likewise, 1H NMR suggested an increase of hydrogen atoms in aromatic, naphthenic, and olefin structures in the TPO[CaO], and a decrease of these atoms in paraffinic structures. Similarly, H2 and some CxHy compounds increased, while CO2, CO, and H2S decreased in TPG[CaO], which supports the hypothesis of the participation of CaO in several reactions during the pyrolysis of WT. Although the ash content in TPS[CaO] was significantly high after pyrolysis (57.5 wt %), the acid demineralization process was effective at removing 80% of its inorganic content, improving its surface area and porosity. The information presented in this work aims at providing some insights toward the advancement of in situ upgrading strategies for the resulting products derived from pyrolysis of WT.