# Study of Cocoa Pod Husks Thermal Decomposition
## 3 Results and Discussion
### Kinetic Parameters  
The kinetic study of thermal decomposition of CPH was carried out in different reaction atmospheres and heating rates of 5, 10, 15 and 20 \({}^{\circ}\)C min\({}^{-1}\). First, the adjustment was made individually for each heating rate in a nitrogen atmosphere. Using this strategy, a very good fit was obtained for each experiment (Figure 2) and VC values are in the range 0.5-1.6%. Figure 2: Individual fit of CPH thermal decomposition experiments in inert atmosphere for each heating rate. (**a**) comparison of experimental and calculated data, (**b**) example of the four fractions obtained in the fitting at 15 \({}^{\circ}\)C min\({}^{-1}\), (**c**) variation of the \(w_{o}\) values, (**d**) variation of the \(log\ k_{o}\) values, (**e**) variation of the \(n\) values, (**f**) variation of the E/R values. As can be seen in Figure 2a, the kinetics fit is very good for all heating rates. The adjustment was achieved considering four biomass decomposition fractions, i.e., 4 independent reactions. According to the temperature ranges where the decomposition processes take place (Figure 2b), fractions 2, 3 and 4 are related to hemicellulose, cellulose and lignin, respectively, and fraction 1 is related to lighter extractives present in CPH, such as pectine. Furthermore, these fractions can also include the residues generated in the decomposition processes of hemicellulose, cellulose, lignin and extractives and that decompose more slowly. The variation of each kinetic parameter for each component as a function of the heating rate can be visualized in Figure 2c-f. The values shown, despite having been obtained from individual fittings, did not present a significant variation with the heating rate. With this background, the model proposed has been used to fit simultaneously the TG and DTG curves obtained at the 4 heating rates, reaching the kinetic parameters representative of the thermal decomposition of CPH under inert atmosphere. Figure 3 compares experimental and calculated curves and Table 2 shows the kinetic parameters obtained. In this case, the VC value is 2.7%. The adjustment in this case is less precise than the one obtained for each heating rate independently. This was expected due to the complexity of the overlapping decomposition processes and the increasing number of data fitted simultaneously. However, despite the above, the results obtained in the overall fit are good and the values of the kinetic parameters are similar to others previously obtained in biomass kinetic studies. [PERSON] et al. [31] summarize the information from several articles on biomass pyrolysis kinetics, where values of activation energy (E) from 36 to 192 kJ mol\({}^{-1}\) and frequency factor (\(k_{0}\)) up to \(1.7\times 10^{21}\) s\({}^{-1}\) are found. The same treatment was performed for the data obtained under oxidizing atmosphere and the results can be seen in Figure 4 and in Table 3. Similarly to the case of inert atmosphere, the VC value is 2.7%. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** & \(W_{1}\) & \(W_{2}\) & \(W_{3}\) & \(W_{4}\) \\ \hline \(k_{0}\) (s\({}^{-1}\)) & \(1.87\times 10^{9}\) & \(2.74\times 10^{13}\) & \(1.41\times 10^{40}\) & \(1.20\times 10^{7}\) \\ \(E/R\) & 12,527.41 & 19,130.53 & 54,889.86 & 15,032.63 \\ \(E\) (kJmol\({}^{-1}\)) & 104.16 & 159.06 & 456.38 & 124.99 \\ \(n\) & 4.20 & 2.80 & 8.40 & 2.64 \\ \(w_{0}\) & 0.18 & 0.37 & 0.32 & 0.14 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Kinetic parameters of CPH thermal decomposition experiments at inert atmosphere. Overall adjustments of the four heating rates. Figure 3: Fit of CPH thermal decomposition experiments under inert atmosphere. (**a**) DTG, (**b**) TG.