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

Abstract

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 °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.

Keywords: Metal oxide; Molecular dynamics simulation; Monoaromatic hydrocarbons; Volatile desulfurization; Waste tire pyrolysis.