Formation of primary volatiles during fast pyrolysis of waste tyre in a wire mesh reactor

Abstract

This study investigates the formation of primary volatiles obtained from fast pyrolysis of waste tyre using a wire mesh reactor (WMR) at a temperature of 300‒600 °C and a heating rate of 1000 °C/s. The unique design of WMR allows the collection of primary volatiles with minimized secondary reactions in the vapour phase. Using a recently developed method, this study successfully quantified all major products in the primary volatiles (condensed as oil product) by gas chromatography-mass spectrometry (GC‒MS). The waste tyre pyrolysis can start at a low temperature of ∼250 °C, and the char yield reduces but the oil yield increases with pyrolysis temperature and holding time. At 600 °C, the char yield rapidly reaches a stable value of ∼35 % due to the presence of carbon black in the waste tyre. The oil yield at a holding time of 100 s increases from ∼20 % at 350 °C to a maximum of ∼47 % at 600 °C. The oil products mainly include limonene, isoprene, toluene, ethylbenzene, and p-xylene. Among these major products, limonene has the highest selectivity of ∼60‒65 % depending on the pyrolysis conditions, while isoprene, p-xylene, ethylbenzene, and toluene contribute to ∼9‒13 %, ∼7‒10 %, ∼6‒8 %, ∼6‒8 % of the oil products, respectively. The total selectivity of the quantified compounds in the oil products is about ∼94‒97 %, indicating that almost all compounds in the oil products are quantified. During pyrolysis, limonene and isoprene are mainly produced from natural rubber, while aromatic products such as toluene, p-xylene and ethylbenzene are more likely produced from synthetic rubber. The tyre sample exhibits melting behaviour at ≥400 °C, forming a molten liquid phase that may promote the secondary reactions of isoprene to form limonene via monomer recombination. Overall, these results provide new insights into the primary pyrolysis mechanism of waste tyre.