Product characterization and sulfur transformation from waste tires valorization via fast pyrolysis in the presence of hydrogen

Fast pyrolysis in the presence of hydrogen is an advanced thermal decomposition process that enables the conversion of waste tires into value-added products while promoting sulfur transfer. In this study, waste tire pyrolysis experiments were performed in a laboratory-scale downdraft tubular reactor under varying hydrogen concentrations (0–15 vol.%) in the carrier gas. The mass balance of the three-phase products demonstrated an increased yield of gaseous products with hydrogen participation. A partial hydrogen proportion (5 vol.%) slightly enhanced the yield of tire pyrolysis oil (TPO) from 44.25 wt.% to 46.21 wt.%. However, further increases in hydrogen content led to a pronounced reduction in TPO yield, with a significant increase in gaseous products. The chemical composition of TPO was characterized using Fourier transform infrared spectroscopy (FTIR) and gas chromatography–mass spectrometry (GC–MS). The results revealed an increasing proportion of diolefins, predominantly d-limonene, accompanied by a decrease in aromatic compounds as the hydrogen concentration increased. Furthermore, iodometric titration, GC–MS, and X-ray photoelectron spectroscopy (XPS) were employed to quantify sulfur-containing species in the gaseous, liquid, and solid products. The findings indicate that hydrogen addition promotes the preliminary desulfurization of TPO and enhances the decomposition of organic sulfur species in pyrolysis carbon black (PCB). The interaction between sulfur radicals and hydrogen radicals facilitates the formation and release of H₂S, thereby promoting sulfur migration from condensed phases to the gas phase.