Desulfurization and upgrade of pyrolytic oil and gas during waste tires pyrolysis: The role of metal oxides

Pyrolysis can effectively convert waste tires into high-value products. However, the sulfur-containing compounds in pyrolysis oil and gas would significantly reduce the environmental and economic feasibility of this technology. Here, the desulfurization and upgrade of waste tire pyrolysis oil and gas were performed by adding different metal oxides (Fe2O3, CuO, and CaO). Results showed that Fe2O3 exhibited the highest removal efficiency of 87.7 % for the sulfur-containing gas at 600 degrees C with an outstanding removal efficiency of 99.5 % for H2S. CuO and CaO were slightly inferior to Fe2O3, with desulfurization efficiencies of 75.9 % and 45.2 % in the gas when added at 5 %. Fe2O3 also demonstrated a notable efficacy in eliminating benzothiophene, the most abundant sulfur compound in pyrolysis oil, with a removal efficiency of 78.1 %. Molecular dynamics simulations and experiments showed that the desulfurization mechanism of Fe2O3 involved the bonding of Fe-S, the breakage of C-S, dehydrogenation and oxygen migration process, which promoted the conversion of Fe2O3 to FeO, FeS and Fe2(SO4)3. Meanwhile, Fe2O3 enhanced the cyclization and dehydrogenation reaction, facilitating the upgrade of oil and gas (monocyclic aromatics to 57.4 % and H2 to 22.3 %). This study may be helpful for the clean and high-value conversion of waste tires.