# Study of Cocoa Pod Husks Thermal Decomposition
## 3 Results and Discussion
### Analytical Pyrolysis EGA Analysis  
A series of experiments were carried out in EGA in order to determine the composition of volatiles generated under different conditions. On the one hand, a slow pyrolysis of CPH was carried out, determining the volatiles distribution at three different temperature ranges: 80-150 \({}^{\circ}\)C, 150-350 \({}^{\circ}\)C and 350-500 \({}^{\circ}\)C. On the other, flash pyrolysis at 400 \({}^{\circ}\)C was also performed, determining the composition of the volatiles obtained. As was expected, the presence of aromatics, phenol derivatives, furan and pyran derivatives, ketones, carboxylic acids as well as nitrogen compounds is detected in the volatiles obtained, but their percentage and distribution depend on the operating conditions, such as final temperature and heating rate. By analyzing the results of the slow pyrolysis, it is observed that the product distribution obtained is very different in the 3 ranges analyzed:  
1. 80-150 \({}^{\circ}\)C. Only water is detected in this range. The temperature is not high enough to release any other volatiles. 2. 150-350 \({}^{\circ}\)C. Besides water and CO\({}_{2}\), which are the main compounds detected, 3 other compounds clearly stand out among all: acetic acid, 2,6-dimethoxy-4-(2-propenyl)-phenol and 1-hydroxy-2-propanone. The presence of other ketones, phenol derivatives and organic acids is detected in lower percentages. 3. 350-500 \({}^{\circ}\)C. By increasing temperature, the number of volatiles formed increases. In fact, the total chromatographic area obtained in this range is 20% higher than the area  
Figure 4: Fit of CPH thermal decomposition experiments in oxidizing atmosphere. (**a**) DTG, (**b**) TG. \begin{table}
\begin{tabular}{c c c c c} \hline
**Parameter** & \(W_{1}\) & \(W_{2}\) & \(W_{3}\) & \(W_{4}\) \\ \hline \(k_{0}\) (s\({}^{-1}\)) & 2.95 \(\times\) 10\({}^{8}\) & 3.29 \(\times\) 10\({}^{7}\) & 4.77 \(\times\) 10\({}^{49}\) & 9.39 \(\times\) 10\({}^{6}\) \\ \(E/R\) & 13,333.08 & 16,066.52 & 85,362.67 & 18,950.29 \\ \(E\) (kJmol\({}^{-1}\)) & 110.86 & 133.58 & 709.75 & 157.56 \\ \(n\) & 2.49 & 1.13 & 0.65 & 1.37 \\ \(w_{0}\) & 0.61 & 0.33 & 0.02 & 0.04 \\ \hline \end{tabular}
\end{table} 
Table 3: Kinetic parameters of CPH thermal decomposition experiments in oxidizing atmosphere. Overall adjustments of the four heating rates. obtained in the previous one. Water and CO\({}_{2}\) continue to be the main compounds, but a greater number of volatiles, more than 200, is detected. The yields of all of them are more similar and, unlike the previous temperature range, the compounds with higher percentages do not stand out too much from the rest. The increase in temperature has increased the generation of compounds but has decreased the selectivity of the process, i.e., many more compounds with lower yield. The 3 compounds with the highest area percentage are 2-methoxy-phenol, toluene and 2-methyl-furan. Many other phenol derivatives (4-methyl-phenol, 2,3-dimethyl-phenol, 2-methoxy-4-propyl-phenol, 2,6-dimethoxy-4-(2-propyl)-phenol), aromatics (benzene, ethylbenzene, xylene, naphthalene derivatives), organic acids (C16, C18) and other functional groups are also identified. The differences in the type of compounds obtained from one temperature range to another reveal the fraction of the biomass which is decomposing in each interval. Thus, between 150-350 \({}^{\circ}\)C, hemicellulose has been totally degraded, generating the highest yields of acetic acid [32; 33]. However, phenol derivatives and other aromatics show their maximum percentage at higher temperatures, in the range 350-500 \({}^{\circ}\)C, when the lignin fraction has reached a high degradation level [32; 34]. Table 4 shows the area percentage of the volatiles identified with a percentage greater than 1%, for both temperature ranges. The values have been calculated with respect to the total area excluding CO\({}_{2}\), i.e., the area related to condensable volatiles, except for the value of this compound which has been referred to the total area.