The activation of tyre char has been addressed using steam as activation agent. The char samples used in the activation have been obtained by continuous flash pyrolysis carried out in a conical spouted bed reactor described elsewhere [30,31]. Operating at 500 8C, char yield reaches 34%, which accounts for the total amount of carbon black contained in the tyre. Pyrolysis conditions are an important factor for porosity development during the activation process. Some authors [32] report that a reduction in secondary reactions and tar formation during the pyrolysis process improves the subsequent activation process.
Fig. 1 shows a schematic representation of the activation unit used in this study.
The unit’s main component is the fixed bed reactor where activation takes place.
The reactor is placed inside a radiant oven that provides the heat to operate at temperatures up to 1000 8C. The unit is provided with a pressure meter to ensure that pressure in the reactor during the activation reaction is not higher than 1.2 atm. Both the reactor and the oven are located in a hot box at 270 8C to ensure that water is vaporized before entering the reactor.
The heat in the hot box is supplied by two blowers provided with four cartridges. Nitrogen is fed into the reactor by means of a mass flowmeter.
The water flowrate is controlled by a high precision HPLC Gilson 307 pump. 2-g samples of tyre char have been used in each reaction. It is noteworthy that the char particles obtained in the conical spoutedbed are the same size as the original tyre particles used in the pyrolysis process, which are smaller than 1 mm.
Furthermore, the excellent gas–solid contact of the conical spouted bed (and the short gas residence time) avoids additional carbonaceous material deposition on the original carbon black of the tyre.
This is due to the fact that gas–particle circulation in this bed is countercurrent in the annular zone and co-current but highly turbulent in the spout, which allows for a very efficient contact.