# Granular Activated Carbon from Grape Seeds Hydrothermal Char
## 3 Results and Discussion
### Thermal Stability  
Figure 3 reports the DTG curves that are relevant to all samples. The derivative mass loss is plotted versus temperature in the temperature range 110-900 \({}^{\circ}\)C. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample ID**} & \multicolumn{2}{c}{**VM**} & \multicolumn{2}{c}{**FC**} & \multicolumn{2}{c}{**Ash**} & \multicolumn{2}{c}{**Elemental Analysis (wt \% daf.b.)**} \\ \cline{3-8}  & **(wt \% d.b.)** & **(wt \% d.b.)** & **(wt \% d.b.)** & **C** & **H** & **N** & **O * \\ \hline
**Grapeseed** & 69.8 & 29.2 & 1.1 & 57.7 & 6.1 & 1.5 & 34.7 \\
**H180** & 67.9 & 30.3 & 1.8 & 65.3 & 6.5 & 1.4 & 26.8 \\
**H180K025** & 31.9 & 59.6 & 8.5 & 83.7 & 1.1 & 1.4 & 13.9 \\
**H180K050** & 35.5 & 58.8 & 5.7 & 78.1 & 1.0 & 1.2 & 19.7 \\
**H180K100** & 34.3 & 62.8 & 3.0 & 66.3 & 2.6 & 0.9 & 30.2 \\
**H220** & 69.5 & 28.3 & 2.2 & 68.1 & 6.6 & 1.7 & 23.5 \\
**H220K025** & 26.6 & 66.7 & 6.7 & 80.7 & 1.6 & 1.7 & 16.0 \\
**H220K050** & 33.9 & 61.5 & 4.5 & 75.6 & 1.7 & 1.5 & 21.1 \\
**H220K100** & 30.9 & 65.9 & 3.2 & 77.9 & 1.4 & 1.5 & 19.3 \\
**H250** & 57.4 & 41.6 & 1.0 & 69.1 & 6.2 & 1.9 & 22.8 \\
**H250K025** & 31.3 & 54.2 & 14.5 & 76.4 & 2.0 & 2.1 & 19.6 \\
**H250K050** & 27.5 & 67.3 & 5.3 & 84.5 & 0.8 & 1.8 & 12.9 \\
**H250K100** & 36.4 & 59.4 & 4.2 & 76.9 & 1.5 & 2.2 & 19.4 \\ \hline \hline \end{tabular}  
* VM = volatile matter; FC = fixed carbon; ash =ashes; d.b. = dry basis; daf.b. = dry and ash free basis;
* calculated by difference; ultimate analysis performed in duplicate: average values are shown (Er < 2.1%).  
\end{table} 
Table 3: Proximate and ultimate analyses of the hydrochar and grape seeds activated carbon (GSAC) samples. In Figure 3a raw grape seeds, the three different hydrochloric samples and one selected GSAC (H250K050) are compared. Raw biomass and all of the three hydrochars show much more evident weight losses than the activated carbon sample. In particular, grape seeds present three evident peaks, namely at about 290 \({}^{\circ}\)C, 350 \({}^{\circ}\)C, and 425 \({}^{\circ}\)C, the last with a shoulder at 465 \({}^{\circ}\)C. The different peaks could be ascribed to the degradation and volatilization of grape seeds main constituents: the oil fraction (grape seeds contains 10-15% oil [44]), hemicellulose and cellulose, lignin. The increment of the HTC temperature results in a progressive disappearance of such peaks. Sample H180 maintains the peak at about 350 \({}^{\circ}\)C, and it presents a second large peak centered at about 450 \({}^{\circ}\)C. For sample H220, the peak at 350 \({}^{\circ}\)C is reduced, while the peaks at 425-465 \({}^{\circ}\)C increase in intensity. The hydrochar that is produced at 250 \({}^{\circ}\)C only presents a single wide peak at around 450 \({}^{\circ}\)C. The behavior shown by such samples is evident: the HTC treatment makes the less thermally stable constituents to disappear, and/or transforms them into much more stable matter. Importantly, the subsequent activation treatment makes the difference with regard to sample thermal stability. In Figure 3a, the DTG curve of GSAC sample H250K050 evidences this: it appears quite flat when compared to the DTG curves of hydrochars and raw biomass. Raw grape seeds and sample H180 present DTG values as low as \(-6\)%/min, samples H220 and H250 reach DTG values of about \(-4\)%/min. For sample H250K050, the DTG curve does not decrease below \(-0.6\)%/min. Figure 3b-d evidence that all nine GSAC samples share a similar thermal stability. After the activation treatment, the derivative weight losses are far more contained, never lower than \(-1\)%/min in all of the temperature range for all the GSACs samples. In accordance with the previous discussion on proximate analysis data, GSACs do not show clear trends of thermal stability based on the amount of activator or on the HTC temperature. All of the GSAC samples, regardless their production conditions, show quite contained weight losses during TGA in N\({}_{2}\).