Waste tire recycling process for production of steam activated carbon in a pilot plant

This work is focused on the production of activated carbon from waste tires by means of a two-steps process: steam gasification of starting material followed by steam activation of char. In particular the evaluation of the most appropriate hold time value for the activation step, in terms of quality and amount of activated carbons produced, and the energy balance of the overall process were performed. The hold time was choose as the best compromise between a high surface area of final product and a not excessively low burn-off value. Investigations were carried out through seven experimental tests on a pilot plant based on a rotary kiln reactor. Studies performed pointed out that, when other process parameters were kept constant (in steam gasification: temperature is 850 degrees C, steam to feed ratio is 1, mean residence time of material is 6 min, carrier flowrate of N-2 is 0.9 Nm(3)h(-1); in steam activation: temperature is 920 degrees C, steam to char ratio is 2, carrier flowrate of N-2 is 1 Nm(3)h(-1)), a hold time in activation step set to 3 h is the best choice, resulting in a surface area of 786 m(2).g(-1) and a burn-off value equal to 78.4%. Moreover, the energy balance of the overall process which goes from waste tires to activated carbon was performed: if 1 kg.h(-1) of waste tires are gasified and activated for three hours, an input power of 3.5 kW is requested. After the experimental tests, a theoretical model was developed, based on the Arrhenius equation whose parameters were determined from a sigmoidal regression of the experimental data. The theoretical model showed results in good agreement with the experimental data, especially for hold times greater than 2 h, and can represent a useful tool to make decision choices.