# A Thermogravimetric Analysis of Biomass Conversion to Biochar: Experimental and Kinetic Modeling
## 4 Conclusions  
This study investigated the impact of pyrolysis temperature on the kinetic parameters, physicochemical characteristics, and structural properties of apple and potato peels to be used as adsorbents. The thermal stability of the biomass waste was evaluated by thermogravimetric analysis. The proximate analysis of apple and potato peel waste indicated high volatile matter content and low ash content of the fixed carbon, suggesting good potential to produce high yields of biochar. The degradation of biomass samples was studied between 25 and 800 \({}^{\circ}\)C at different heating rates (5, 10, 20, and 30 \({}^{\circ}\)C/min). The results showed that moisture content of the biomass sample is almost 5% of the initial weight. The second stage of degradation corresponding to devolatilization differs slightly due to the composition of the analyzed sample. The potato peel showed one degradation peak in the range 205-375 \({}^{\circ}\)C, with 50% weight loss, associated with starch pyrolysis. The \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Adsorbent** & **Experiment Condition** & **Niltrate Efficiency Removal (\%)** & **References** \\ \hline Magnetic biochar at 550 \({}^{\circ}\)C & 300 ppm NO3\({}^{-}\), 0.25 g biochar, & 71.46 & [87] \\  & 120 min, pH 7, & & \\ \hline Thermally treated black tea & 300 ppm NO3\({}^{-}\), 0.2 g & 73.71 & [32] \\ waste at 400 \({}^{\circ}\)C & adsorbent, 90 min, pH 6.5, & & \\ \hline Black tea waste, at 105 \({}^{\circ}\)C & 300 ppm NO3\({}^{-}\), 0.2 g & 79.25 & [32] \\ adsorbent, 90 min, pH 6.5, & & & \\ \hline Apple peel at 250 \({}^{\circ}\)C & 300 ppm NO3\({}^{-}\), 0.2 g & 68.54 & This study \\ adsorbent, 90 min, pH 6.5, & & & \\ \hline Apple peel at 800 \({}^{\circ}\)C & 300 ppm NO3\({}^{-}\), 0.2 g & 52.78 & This study \\ adsorbent, 90 min, pH 6.5, & & & \\ \hline Potato peel at 250 \({}^{\circ}\)C & 300 ppm NO3\({}^{-}\), 0.2 g & 64.10 & This study \\ adsorbent, 90 min, pH 6.5, & & & \\ \hline Potato peel at 800 \({}^{\circ}\)C & 300 ppm NO3\({}^{-}\), 0.2 g & 45.46 & This study \\ adsorbent, 90 min, pH 6.5, & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The comparison of the nitrate sorption efficiency of various biochar data. weight loss of around 10% over 355 \({}^{\circ}\)C was attributed to the decomposition of cellulose and lignin derivatives present in potato peel. Apple peel devolatilization degradation takes place in two stages: one with a weight loss of 38% and maximum around 220 \({}^{\circ}\)C, caused by degradation of simple carbohydrates, and the second peak between 280 and 380 \({}^{\circ}\)C with a maximum at 330 \({}^{\circ}\)C and a weight loss of approximately 24%, which is attributed to cellulose degradation. The broad peak that starts at a temperature above 375 \({}^{\circ}\)C is attributed to lignin degradation that occurs over a wide temperature range. The decomposition kinetics were analyzed using thermal data collected under non-isothermal conditions with a constant heating rate based on both model-free and model-fit approaches. The results showed values of the activation energies in agreement with those from other biomass decomposition studies. The effect of temperature on biomass waste surface structure showed that the surface morphologies of both samples are influenced by the pyrolysis temperature. Pyrolysis of apple and potato peels at 250 \({}^{\circ}\)C produced a smooth surface with minimal visible pores; meanwhile, at a temperature of 800 \({}^{\circ}\)C, the biochar exhibited deep porous channels with cavity diameters measuring less than 40 \(\upmu\)m for the potato peel and less than 30 \(\upmu\)m for the apple peel. These observations are also supported by the FTIR analysis, which indicates the disappearance of the bands characteristic of the hydroxyl, aliphatic, ether, and ester functional groups. The elemental analysis also confirms the loss of functional groups due to dehydration and deoxygenation reactions, indicating a carbon percentage of 66.52 and 77.78% for potato and apple peel, respectively.