Effect of chlorine on zinc transformation during flue gas pyrolysis of waste tires with PVC: An experimental study and theoretical calculations

Abstract

Volatile ZnCl2 will be produced during the co-pyrolysis of waste tires (WT) and waste plastic (PVC), since WT contain a large amount of ZnO and PVC contain Cl. In this study, the release properties of Zn were investigated during high-temperature flue gas pyrolysis of WT and PVC mixture (WP). The addition of PVC reduced the relative enrichment (RE) of Zn in the solid product by about 42.4% at 850 °C. In addition, CaO and Al2O3 facilitated the Zn release while MgO and Fe2O3 had enrichment effects on Zn. Furthermore, the adsorption mechanisms of metal oxides to ZnCl2 were investigated in depth using density functional theory (DFT) calculations. It indicated that ZnCl2 was physisorbed by Al2O3, while it was chemisorbed by CaO, Fe2O3 and MgO. CaO had the highest adsorption energy (−147.9 kJ/mol) for ZnCl2. The DFT calculation results for CaO were opposite to the experimental results, due to the formation of CaCl2 which inhibited the adsorption. Importantly, Zn to O and Cl to metal atom bonds were the key mechanisms by which ZnCl2 was trapped by metal oxides.