# A Thermogravimetric Analysis of Biomass Conversion to Biochar: Experimental and Kinetic Modeling
## 3 Results and Discussion
### Thermal Decomposition of Biomass Waste
#### 3.1.2 Thermogravimetric Profile of the Biomass Waste Samples  
The thermal stability of the biomass waste was evaluated by thermogravimetric analysis. The evolution of biomass residue thermal decomposition is presented in Figure 2 in terms of TG curves and Figure 3 in terms of DTG curves, both for apple peel (A) and potato peel (B). Also, the most important peak temperatures as well as the residue amount after decomposition are given in Table 2. Even if at first sight the two biomasses have similar decomposition pathways, there are some differences that can be evidenced from DTG curves. The degradation of biomass samples was studied between 25 and 800 \({}^{\circ}\)C at \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{6}{c}{**Proximate Analysis (wt\%)**} \\ \cline{2-9}  & **Moisture * & **Volatile Content * & **Fixed Carbon * & **Ash * & **Protein** & **Lipids** & **Carbohydrate** \\ \hline Apple peel & 5.48 & 76.73 & 17.23 & 0.56 & 4.31 \({}^{\text{a}}\) & 3.48 \({}^{\text{a}}\) & 63.84 \({}^{\text{a}}\) \\ \hline Potato peel & 2.11 & 75.79 & 18.35 & 5.88 & 11 \({}^{\text{b}}\) & 1.75 \({}^{\text{b}}\) & 62.4 \({}^{\text{b}}\) \\ \hline \hline \end{tabular}  
* \({}^{*}\) From this study; \({}^{\text{a}}\) [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] [45]; \({}^{\text{b}}\) [PERSON] et al. [48].  
\end{table} 
Table 1: Proximate analysis of biomass waste samples. different heat rates (5, 10, 20, and 30 \({}^{\circ}\)C/min). The weight range of the samples studied was 9-11 mg. Region I from these curves (Figure 3) can be ascribed to the moisture release from the biomass structure. The recorded weight loss in this region for each biomass sample is almost 5% of the initial weight. As heating rate increases, the determined weight loss values for apple peel were 5.76%/min, 5.25%/min, 4.52%/min, and 3.17%/min at 5, 10, 20, and 30 \({}^{\circ}\)C/min, whereas for potato peel the weight loss values were 4.95%/min, 1.81%/min, 1.51%/min, and 2.58%/min for the same heating rates. The second stage of degradation corresponding to devolatilization differs slightly due to the composition of the analyzed sample. Apple and potato peels, which consist mostly of carbohydrates such as disaccharides and starch, exhibit distinct thermal degradation characteristics as evidenced by the DGT curves. Therefore, the potato peel showed a sharp second weight loss in the range 205-375 \({}^{\circ}\)C of 50%, with the maximum decomposition temperature at 297 \({}^{\circ}\)C, which was associated with starch pyrolysis [48]. The weight loss around 10% over 355 \({}^{\circ}\)C was associated with the decomposition of cellulose present in potato peel [52]. The apple peel devolatilization degradation takes place in two stages (region II and III), emphasizing that this biomass is a heterogeneous mixture, in a temperature range of 150-400 \({}^{\circ}\)C, similar with the one reported by [PERSON], et al. [53]. The first peak from 150 to 300 \({}^{\circ}\)C (maximum around 220 \({}^{\circ}\)C), with a weight loss of 38%, is caused by simple carbohydrates [45] such as fructose, glucose and sucrose [54], meanwhile, the second peak  
Figure 3: DTG curves for apple (**A**) and potato (**B**) peel at different heating rates (where I to IV are decomposition regions/stages referred in the paper). Figure 2: TG curves for apple (**A**) and potato (**B**) peel at different heating rates. between 280 and 380 \({}^{\circ}\)C with a maximum at 330 \({}^{\circ}\)C has a weight loss of approximately 24% attributed to non-starch polysaccharide degradation. The broad peak that starts at temperatures above 375 \({}^{\circ}\)C is attributed to lignin degradation [45] that occurs over a wide temperature range. These features are in accordance with literature studies [55].