Aromatic chemicals from the catalytic pyrolysis of scrap tyres

Scrap tyres were pyrolysed in a fixed bed reactor and the evolved pyrolysis gases were passed through a secondary catalytic reactor. The main objective was to maximise the concentration of single ring aromatic compounds, which are of known higher commercial value. Three types of zeolite catalyst were examined of different surface acidity and pore size. The influence of catalyst to tyre ratio on the yield and composition of the derived oils was examined. The results showed that the influence of the catalyst was to reduce the yield of oil with a consequent increase in the gas yield. Coke formation on the catalyst amounted to approximately 4 wt.%. However, there was a dramatic increase in the concentration of certain single ring aromatic compounds in the derived oils after catalysis. For example, toluene reached a maximum value in the oil of 24 wt.%, benzene 5 wt.%, m/p-xylenes 20 wt.% and o-xylene 7 wt.%. The yield in terms of conversion of the mass of tyre to mass of individual chemical were 7.7 wt.% toluene, 1.4 wt.% benzene, 6.4 wt.% m/p-xylenes and 2.2 wt.% o-xylene, representing a very significant potential increase in the value of the derived oils. The yield of aromatic hydrocarbons in the derived oils were related to the different properties of the three catalysts such as pore size, which influenced selectivity, and the silica/alumina ratio which influenced the number of catalytically active sites on the catalyst surface.