An Experimental Study of CO2 and Steam Activation of a Spent Tyre Pyrolysis Char

The activation of a spent tyre pyrolysis char using CO2 and steam was experimentally investigated. The pyrolysis char, produced in an industrial scale retort process operating in the absence of air at 550 °C, was ground and sieved to a particle size fraction <150 μm, and activated in a fixed bed reactor under CO2 and steam, respectively. The effect of temperature (750 to 1050 °C), reaction time (0.5 to 6h) and activation agent concentration (33.3 to 66.7 vol.% of CO2 or steam with N2 as carrier gas) on the burn-off was measured. The BET surface area, pore volume and average size of the activated chars were also determined using N2 adsorption. It was found that higher temperature and activation agent concentration, and longer reaction time led to higher burn-off. As the burn-off increased, the BET surface area initially increased and then decreased, reaching a maximum for both CO2 (434.5 m2g-1) and steam (666.6 m2g-1). The chars activated with steam showed about 20 – 50% higher BET surface areas than those activated with CO2 at the same burn-off. The total pore volume increased up to 0.55 cm3g-1 for CO2 and 1.07 cm3g-1 for steam at approximately 70 wt.% and 80 wt.% burn-off, respectively. Steam-activated chars displayed a similar total pore volume to CO2-activated chars until ca. 25 wt.% burn-off, above which the total pore volume was significantly higher for the steam-activated chars.