# Valorization of Waste Tires by Pyrolysis and Activation Processes
## 3 Results and Discussion
### Solid Fraction Characterization  
The chemical and physical activation had an effect on the solid fraction morphology, as can be seen in Figure 4. Carbon black particles have spherical shapes forming aggregates [43], and a rough surface and microporosity were observed in S2 and S4. In energy storage applications, a high surface area carbon electrode material provides a greater space for charge separation between the electrode and the ions in the electrolyte [15; 44]. Surface area and porosity varied between the different pyrolytic solids obtained. It was observed that chemical activation increases surface area, but not as much as physical activation (Table 3). Apparently, the increase in surface area is not related to pore size, which can be attributed to different pore morphologies or pore size distribution. \begin{table}
\begin{tabular}{c c c c c} \hline  & **Process** & **Solid (\%)** & **Liquid (\%)** & **Gas (\%) a** \\ \hline
1 & Pyrolysis & 34.69 \(\pm\) 2.54 & 65.79 & 1.32 \\
2 & Chemical activation and pyrolysis & 57.19 \(\pm\) 0.07 & 13.59 \(\pm\) 5.57 & 29.21 \(\pm\) 5.50 \\
3 & Pyrolysis and physical activation & 24.82 \(\pm\) 2.32 & 60.93 & 15.89 \\
4 & Chemical activation, pyrolysis, and physical activation & 52.22 \(\pm\) 1.58 & 9.1 \(\pm\) 1.10 & 38.7 \(\pm\) 0.48 \\ \hline \end{tabular} a Calculated by difference.  
\end{table} 
Table 2: Solid, gas, and liquid yields of each pyrolysis process expressed as a percentage of the weight of the sample fed into the pyrolysis reactor. Note: Average and standard deviation were calculated considering only experimentally reliable values. Figure 4: Scanning electron microscope images of solid fraction from the pyrolysis/activation processes performed. Note: Magnification is indicated in the columns and carbon black solid samples in the rows. The adsorption-desorption isotherms and the pore size distribution are presented in Figure 5. The activations performed before pyrolysis had an important effect on the pore size of the solid fraction. The Boudouard reaction that occurs during physical activation causes the development of micropores, mesopores, and macropores [39], which increases surface area. Apparently, chemical activation with H2 SO4 generates a more controlled porosity than physical activation, which can be seen in the pore size distribution plot (Figure 5b). The processes with chemical activation presented the formation of micropores. This may be due to the elimination of H2 SO3 and sulfur dioxide during carbonization, which previously occupied space. The conductivity results (Figure 6 and Table 3) indicate that morphological characteristics caused by the chemical activation of the solid fraction led to a higher conductivity value, which is valuable in energy storage applications as electrodes. An ANOVA test was performed to evaluate significant differences in conductivity among processes. A \(p\) value < 0.0001 indicated no equal means; therefore, at least one process is different from the rest; similarly, [PERSON]'s test showed that each of the solids are significantly different from one another. Figure 5: Plots of (a) adsorption–desorption isotherms and (b) pore size distribution for all pyrolysis solids. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Solid** & **Process** & **Surface Area** & **Pore Size (nm)** & **Pore Volume** & **Conductivity** \\
**Sample** & **Process** & **(m\({}^{2}\)/g)** & **Pore Size (nm)** & **(cm\({}^{3}\)/g)** & **(\(\Omega^{-1}\) m\({}^{-1}\))** \\ \hline S1 & Pyrolysis & 107.9 & 33.0 & 0.9 & 0.7 \(\pm\) 0.3 \\ S2 & Chemical activation and pyrolysis & 151.5 & 5.1 & 0.2 & 1.9 \(\pm\) 0.2 \\ S3 & Pyrolysis and physical activation & 313.4 & 13.4 & 1.0 & 1.3 \(\pm\) 0.1 \\ S4 & Chemical activation, pyrolysis, and physical activation & 339.1 & 3.6 & 0.3 & 2.4 \(\pm\) 0.1 \\ \hline \end{tabular}
\end{table} 
Table 3: Surface area, pore size, pore volume, and conductivity results of solid fraction from each process.