# Biochar from Agro-Forest Residue: Application Perspective Based on Decision Support Analysis
## 3 Results and Discussion
### Kinetic Analysis  
Comprehensive kinetic analysis was carried out, applying the model described in Section 2.4, and considering two-staged combustion: biochar devolatilization (stage 2) and combustion (stage 3). Generally, all six types of biochar showed similar kinetic profiles. The calculated kinetic parameters and their corresponding correlation factors R\({}^{2}\) are given in Table 3.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Biochar** & **Colza** & **Cherry Stones** & **Peach Stones** & **Grape Pomace** & **Softwood** & **Sunflower Husks** \\ \hline \multicolumn{8}{c}{Heating rate 10 \({}^{\circ}\)C/min} \\ \hline Stage 2 & & & & & \\ \hline \(E\) (kJ/mol) & 95.21 & 111.9 & 119.2 & 125.2 & 131.7 & 94.1 \\ \(A\) (1/s) & \(1.44\times 10^{5}\) & \(2.69\times 10^{6}\) & \(6.06\times 10^{6}\) & \(1.19\times 10^{8}\) & \(8.92\times 10^{7}\) & \(9.1\times 10^{4}\) \\ R\({}^{2}\) & 0.9906 & 0.9934 & 0.9904 & 0.9900 & 0.9913 & 0.9848 \\ \hline Stage 3 & & & & & & \\ \hline \(E\) (kJ/mol) & 96.73 & 209.4 & 305.4 & 148.9 & 134.97 & 274.3 \\ \(A\) (1/s) & \(2.69\times 10^{6}\) & \(1.21\times 10^{16}\) & \(2.35\times 10^{19}\) & \(5.40\times 10^{8}\) & \(3.7\times 10^{7}\) & \(1.42\times 10^{11}\) \\ R\({}^{2}\) & 0.9782 & 0.9935 & 0.9868 & 0.9926 & 0.9543 & 0.9703 \\ \hline \multicolumn{8}{c}{Heating rate 20 \({}^{\circ}\)C/min} \\ \hline Stage 2 & & & & & \\ \hline \(E\) (kJ/mol) & 99.71 & 119.5 & 112.9 & 125.7 & 149.7 & 114.9 \\ \(A\) (1/s) & \(1.20\times 10^{6}\) & \(1.79\times 10^{7}\) & \(2.31\times 10^{6}\) & \(7.62\times 10^{7}\) & \(5.86\times 10^{9}\) & \(2.62\times 10^{7}\) \\ R\({}^{2}\) & 0.9907 & 0.9826 & 0.9911 & 0.9944 & 0.9928 & 0.9914 \\ \hline Stage 3 & & & & & \\ \hline \(E\) (kJ/mol) & 100.34 & 208.9 & 231.9 & 172.3 & 196.9 & 166.8 \\ \(A\) (1/s) & \(2.514\times 10^{5}\) & \(2.76\times 10^{12}\) & \(3.03\times 10^{13}\) & \(8.47\times 10^{9}\) & \(9.92\times 10^{11}\) & \(1.85\times 10^{10}\) \\ R\({}^{2}\) & 0.9833 & 0.9645 & 0.9684 & 0.9909 & 0.9931 & 0.9674 \\ \hline \multicolumn{8}{c}{Heating rate 30 \({}^{\circ}\)C/min} \\ \hline Stage 2 & & & & & \\ \hline \(E\) (kJ/mol) & 86.3 & 110.6 & 84.4 & 91.6 & 160.9 & 96.9 \\ \(A\) (1/s) & \(4.45\times 10^{4}\) & \(3.73\times 10^{6}\) & \(6.16\times 10^{3}\) & \(4.64\times 10^{4}\) & \(6.61\times 10^{10}\) & \(3.32\times 10^{5}\) \\ R\({}^{2}\) & 0.9976 & 0.9948 & 0.9862 & 0.9953 & 0.9929 & 0.9831 \\ \hline \end{tabular}
\end{table}
Table 3: Calculated kinetic parameters and correlation factor R\({}^{2}\).  
The oxidation of the currently examined biochar showed high \(E\) values, which resulted from the high thermal resistance of the feedstock's main constituents (hemicellulose, cellulose, and lignin). Limited numbers of references on biochar oxidation were found in the literature [38; 59; 60]. The presently obtained biochar oxidation kinetics were compared with literature data for the stage char oxidation of similar types of biomass, burnt under comparable experimental conditions. [PERSON] et al. [36] reported \(E\) of 126 kJ/mol to 167 kJ/mol at a heating rate between 10 and 40 \({}^{\circ}\)C/min in case of fir wood oxidation. In parallel to the current study, the authors used the Coats-Redfern method for first-order reaction. In the present experiment, the obtained \(E\) for softwood biochar oxidation was 134.97 and 562.9 kJ/mol at the same heating rates. Increasing the heating rate led to higher \(E\) in both studies. A similar trend was observed when comparing the present results with those reported by [PERSON] et al. [61]. The authors evaluate the combustion characteristics of raw and torrefied grape pomace (200-300 \({}^{\circ}\)C) in a thermogravimetric analyzer (using a heating rate of 10 \({}^{\circ}\)C/min) and in DTF, at 1100 \({}^{\circ}\)C. They report an apparent \(E\) of 84.9 and 85.2 kJ/mol for the devolatilization (assumed to resemble stage 2 of the present study), whereas the \(E\) values for the char oxidation (stage 3) were 137.5 and 109.2 kJ/mol for the raw and the torrefied grape pomace, respectively.