Carbon nanotubes and hydrogen production from the pyrolysis catalysis or catalytic-steam reforming of waste tyres

A range of process conditions have been investigated to maximise the production of carbon nanotubes (CNTs) and/or hydrogen from waste tyres. A two-stage pyrolysis-catalytic reactor system was used and the influence of catalyst temperature (700, 800 and 900 °C), tyre: catalyst ratio (1:0.5, 1:1 and 1:2) and steam input (water injection 0, 2 and 5 ml h−1) to the second catalyst stage were investigated. The catalyst used was a Ni/Al2O3 catalyst prepared by a wetness impregnation technique. Carbon was deposited on the catalyst surface during pyrolysis-catalysis increasing with increasing catalyst temperature and also increasing as the tyre: catalyst ratio was raised. Examination of the carbon showed it to be composed of largely filamentous type carbons, producing 253.7 mg g−1 tyre of filamentous carbons at a tyre: catalyst ratio of 1:1 and catalyst temperature of 900 °C. A significant proportion of the deposited filamentous carbons were multi-walled carbon nanotubes as shown by transmission electron microscopy characterisation. The introduction of steam to the process enhanced hydrogen production, producing a maximum of 34.69 mmol g−1 tyre at a water injection rate of 5 ml h−1.