A new pyrolysis model was developed to predict the individual product (noncondensable volatiles, condensable volatiles, and char) yield for Ecolomondo's industrial waste tire pyrolysis process. This novel predictive kinetics-based model couples product selectivity data obtained from thermogravimetric analysis experiments to a global single-step decomposition reaction term to reproduce the nonlinear relationship between product selectivity and temperature. A transient energy balance based on a lumped capacitance method was also used to calculate the tire shred temperature using the rotary drum wall temperature as an input. The kinetics model was compared to experimental oil production data from the industrial process as well as existing models in the literature. It is shown that the model can successfully predict the oil production of the industrial process and the model accuracy is greater for smooth operating conditions. On the other hand, other pyrolysis models from the literature failed to accurately predict the oil production.

The mechanisms of transfer of sulfur to the volatile phase and char phase during the pyrolysis of tires have been investigated by complementing the available literature data with TGA experiments. For isothermal experiments, the global selectivity expression could be simplified into an intrinsic form of sulfur loss selectivity, which is solely a function of temperature. Two other phenomena have been found to influence the intrinsic sulfur loss selectivity: solid matrix desulfurization and metals sulfidation. In the case where tires would contain no metals and pyrolysis was performed at a temperature of 400°C or higher, decomposition kinetics is limiting and the intrinsic sulfur loss selectivity would converge to the value of 1. Below 350 °C, mass transfer limitation will promote solid matrix desulfurization, producing sulfur loss selectivity greater than 1. Over 350 °C, if zinc and/or steel are present in tires, sulfidation will cluster sulfur in the solid phase and sulfur loss selectivity will become lower than 1. A developed form of sulfur loss selectivity could be obtained to account for these phenomena.

This study was motivated by the fact that differential scanning calorimetry (DSC)/differential thermal analysis (DTA) results in literature showed significant exothermic peaks while in overall, pyrolysis is an endothermic phenomenon. The specific heat of the decomposing tires has been determined with a new methodology: instead of assuming constant char properties throughout pyrolysis, the specific heat of evolving solids (char) was evaluated with increasing temperature and conversion. Measured specific heat values were observed to increase until pyrolysis was triggered at 250°C. Then, the specific heat of the solids decreased continuously until 400°C at which point they started to increase. This unexpected trend pointed out that the exothermic peak observed with DSC is an artefact generated by the control system of the apparatus. To overcome this limitation, the energy balance was performed over industrial data and the newly found heat capacity values. The enthalpy of pyrolysis was found to have a term dependent on the weight loss derivative, with a constant value of 410 kJ/kg tires. Two other terms for the enthalpy of pyrolysis have been identified, which were independent of weight loss. The first one is believed to correspond to the sulphur cross-link breakage at low temperature (65 kJ/kg), while the second one, at the final stage of pyrolysis, should correspond to charring reactions approaching the thermodynamic equilibrium (75 kJ/kg). Ultimately, this work proposes a new methodology to determine the enthalpy of pyrolysis with larger scale experimental data.

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