High-value resource recovery products from waste tyres

A novel process has been developed which enables the production of high-value carbon nanotubes (CNTs) and hydrogen-rich syngas from the two-stage pyrolysis–catalysis of waste tyres. The waste tyre samples originated from truck tyres and from car tyres. In addition, three of the main rubber elastomers used in tyre manufacture, polybutadiene rubber, styrene–butadiene rubber and natural rubber, were also investigated. The waste car tyres produced a syngas yield of 30·2 wt%, which was composed largely of hydrogen (53·8 vol%) with a calorific value of 18·8 MJ/m3. Increasing the tyre:catalyst ratio increased the yield of hydrogen. The component rubber elastomers produced much higher yields of syngas and hydrogen gas concentration. The carbon deposited on the catalyst during reaction was found to be mostly composed of graphitic CNTs. Changing the process conditions in terms of tyre:catalyst ratio could increase the yield of the carbon deposited on the catalyst to up to 14 wt%.