## 2 Materials and Methods
### Catalytic Pyrolysis
#### 3.3.3 Characterization of Solid Fraction  
Table 7 represents the elemental components, the C/N and C/H ratio, and _HHV_ of the biochars obtained by thermal and catalytic pyrolysis. In general, the results found are similar for all the biochar samples, which indicate that the use of the catalyst does not have an appreciable influence on the characteristics of the biochar. The _HHV_ values are, like the biochar, produced from plastics, such as HDPE [58] and PP [59], and are higher than biochar from municipal solid waste (MSW) mixture [60], plastic mix from MSW mixture [61] and lower than biochar from biomass [62,63]. Regarding elemental composition, a high carbon content was observed (from 50.0 to 70.9%), lower nitrogen (from 1.1 to 5.4%) lower hydrogen (from 3.1 to 9.4%), and no sulfur. Comparing thermal and catalytic pyrolysis, the most notable aspect is the decrease in hydrogen content for both \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Surgical Mask**} & \multicolumn{2}{c}{**FFP2 Mask**} \\ \cline{2-5}  & **Thermal** & **Catalytic-1 st Run** & **Thermal** & **Catalytic-1 st Run** \\ \hline Density 15 \({}^{\circ}\)C (kg/m\({}^{3}\)) & 810 & 790 & 850 & 830 \\ Viscosity (cSt) & 4.09 & 3.15 & 154.49 & 15.03 \\ pH value & 6.0 & 6.1 & 6.0 & 5.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Physicochemical characterization of liquid biooil. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{\multirow{2}{*}{**Type of Pyrolysis**}} & \multicolumn{2}{c}{**Chain Size**} & \multicolumn{1}{c}{\multirow{2}{*}{**Average MW of Biooil**}} \\ \cline{3-4} \multicolumn{1}{c}{} & **C 5-9** & **C 9-13** & **C +13** & **(g/mol)** \\ \hline \multirow{3}{*}{Surgical Mask} & Thermal & 27.4\% & 8.2\% & 64.4\% & 271.4 \\  & Catalytic-1 st run & 50.5\% & 12.1\% & 37.4\% & 186.8 \\  & Catalytic-2 nd run & 32.7\% & 11.0\% & 56.3\% & 230.9 \\  & Catalytic-3 rd run & 22.6\% & 12.3\% & 65.1\% & 259.3 \\ \hline \multirow{3}{*}{FFP2 Mask} & Thermal & 38.6\% & 15.4\% & 46.0\% & 211.8 \\  & Catalytic-1 st run & 42.8\% & 9.2\% & 48.1\% & 207.5 \\  & Catalytic-2 nd run & 38.5\% & 10.0\% & 51.4\% & 214.0 \\  & Catalytic-3 rd run & 32.3\% & 12.0\% & 55.7\% & 228.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Liquid biooil composition by chain size and average molecular weight. the FFP2 and surgical masks and the increase in the carbon content for the surgical masks, which could be attributed to a change in the reactions that can occur during the pyrolysis process due to the presence of the catalyst. Today, the applications of biochar solid are very limited; nevertheless, some emerging uses have been considered. The biochar can be used as low-quality fuel for combustion processes, as a precursor to obtain adsorbents, as additives in epoxy resins, or as crop nutrients, among others [64; 65; 66; 67; 68; 69]. The high heating values obtained in this work (Table 5) suggested that biochar can be a stronger candidate for mainly solid fuel use. Furthermore, the values of nitrogen content show the fitness of biochar as a soil enhancer and growth nutrient in crops. On the other hand, an application also investigated for biochar is its use as solid adsorbent. The potential of biochar for use as adsorbent is based primarily on its surface properties. In this sense, the surface properties of the obtained biochars have been determined. For the FFP2 mask, a BET surface area of 0.235 m\({}^{2}\)/g, a total pore volume of 0.011 cm\({}^{3}\)/g, and an average pore diameter of 191.6 nm were obtained. For the surgical mask, these values were 4.941 m\({}^{2}\)/g, 0.012 cm\({}^{3}\)/g, and 9.717 nm, respectively. The low BET surface area values of these biochars are justified by the fact that they have not been subjected to a subsequent activation process, so the presence of residual volatile matter can block the porosity of the biochars [70]. Other researchers also found low BET surface area values for the biochar obtained in the pyrolysis of different plastic waste [61; 71; 72; 73; 74].