Pyrolysis of waste tyres with zeolite USY and ZSM-5 catalysts

Abstract

Pyrolysis of waste tyres was carried out with a two-stage bed reactor. The waste tyres were first pyrolysed in a fixed bed reactor, and then the evolved pyrolysis gases were passed through a secondary catalytic reactor filled with two types of zeolite catalysts, which were ultrastable Y-type (USY) and ZSM-5 catalyst. The catalytic temperatures were examined to determine their influence on the yield of product from the pyrolysis–catalyst of waste tyres. The results indicated that with the increase of catalytic temperature, the gas yield increased at the expense of oil yield. The light fractions (<220°C) distilled from the derived oils with the two catalyst were analyzed by gas chromatography/mass spectrometry (GC/MS). It showed that there was a dramatic increase in the concentration of single ring aromatic compounds in the light fractions of the derived oils after catalysis. For example, toluene reached a value in the light fraction of 11.62wt%, benzene 1.6wt%, m/p-xylene 12.27wt% and o-xylene 4.42wt%, with the catalysis of USY catalyst, at the pyrolysis temperature, catalysis temperature and catalyst/tyre ratio of 500, 400°C and 0.5, where the light fraction was about 71wt% in the derived oil. The yield of aromatic hydrocarbons in the derived oils were related to the different properties of the two catalysts such as the pore size which influenced the selectivity, and the silica/alumina (Si/Al) ratio which influenced the number of active sites on the catalyst surface.