Pyrolysis of scrap tyres

Cross-section samples (2–3 cm wide), representative of a whole car tyre, have been pyrolysed under nitrogen in a 3.5 dm3 autoclave at 300°C, 400°C, 500°C, 600°C and 700°C. The whole solid, liquid and gaseous products generated during each pyrolysis were collected and characterised. No significant influence of temperature on the amount and characteristics of pyrolysis products was observed over 500°C. Tyre-pyrolysis liquids are a complex mixture of C5–C20 organic compounds, with a great proportion of aromatics. They have high gross calorific values, GCV (∼42 MJ kg−1) and N and S contents (0.4% and 1.2%, respectively) within those specified for certain heating fuels. About 30 wt.% of such liquids is an easily distillable fraction with boiling points (70–210°C) in the range of commercial petrol, and about 60 wt.% of them have the boiling point range (150–370°C) typical of diesel oil. Pyrolysis gases are composed of hydrocarbons of which C1 and C4 are predominant, together with some CO, CO2 and SH2; they have very high gross calorific values (68–84 MJ m−3). Tyre-pyrolysis residues have equal dimensions as the original tyre portion and are easily disintegrable into black powder and steel cords. The black powder has surface areas comparable to those of commercial carbon blacks, but it has a great proportion of ash and impurities (∼12 wt.%), which are the inorganic fillers added to tyre rubber; it may have a potential use as semireinforcing or nonreinforcing carbon black.