Production of activated carbon by waste tire thermochemical degradation with CO₂

The thermochemical degradation of waste tires in a CO₂ atmosphere without previous treatment of devolatilization (pyrolysis) in order to obtain activated carbons with good textural properties such as surface area and porosity was studied. The operating variables studied were CO₂ flow rate (50 and 150 mL/min), temperature (800 and 900 °C) and reaction time (1, 1.5, 2, 2.5 and 3 h). Results show a considerable effect of the temperature and the reaction time in the porosity development. Kinetic measurements showed that the reactions involved in the thermochemical degradation of waste tire with CO₂, are similar to those developed in the pyrolysis process carried out under N₂ atmosphere and temperatures below 760 °C, for particles sizes of 500 μm and heating rate of 5 °C/min. For temperatures higher than 760 °C the CO₂ starts to oxidize the remaining carbon black. Activated carbon with a 414-m²/g surface area at 900 °C of temperature, 150 mL/min of CO₂ volumetric flow and 180 min of reaction time was obtained. In this work it is considering the no reactivity of CO₂ for devolatilization of the tires (up to 760 °C), and also the partial oxidation of residual char at high temperature for activation (>760 °C). It is confirmed that there are two consecutive stages (devolatilization and activation) developed from the same process.