Novel photothermal pyrolysis on waste tire to generate high-yield limonene

Waste tire is a typical solid municipal waste with large production capacity. Developing new low carbon-emission method to pyrolyze waste tire and produce high-value limonene is promising. Herein, a novel photo-thermal pyrolysis system was successfully built, and waste tire was firstly pyrolyzed by photothermal at different temperatures (400 ?, 500 ?, 600 ?, and 700 ?). The photothermal pyrolysis can assist in achieving high yield of limonene, of which the yield can high up to 8.98 wt% at 600 ? and the relative peak areas of Gas Chromatography-Mass Spectrometer (GC-MS) results were all about 30 A.%. cis-1,4-polyisoprene in waste tire partly decomposed into some free radicals and they further reacted to generate limonene by intramolecular cyclization, dimerization, and isomerization. Parts of limonene aromatized to 1-methyl-4-(1-methylethenyl)-benzene and converted to triolefins that formed diene rings, the diene rings further aromatized to xylene and toluene, which were partly combined to generate 1,6,7-trimethyl-naphtalene. The photothermal pyrolysis mechanisms of waste tire were revealed: At higher pyrolysis temperature, waste tire partly decomposed and others polymerized to form amorphous carbons. The small aromatic rings and alkyl-aryl C-C bonds further polymerized to be large aromatic rings system. The pores in char further formed and limonene generation was strengthened, because the limonene formation/decomposition was mainly limited in the pores. Subsequently, some pores were blocked at 700 ?, the generation of limonene was thus inhibited.