## 3 Results and Discussion
### Activated Carbons by Chemical Activation of Hydrochars  
Previous works have proven that hydrochars can be more effective adsorbents than thermal (pyrolytic) biochars due to their diverse structures and surface functional groups [54]. Looking at the characteristics of the hydrochars, the GS-220-40 was selected for further activation to achieve a well-developed porosity typical of a carbon-based adsorbent. In previous works [23] HTCs obtained at 180-240 \({}^{\circ}\)C were more prone to yield a better developed porosity upon KOH-activation than those obtained above 260 \({}^{\circ}\)C, although from fairly different precursors than in the current work. Table 3 summarizes the porous textures of the activated carbons. Representative N\({}_{2}\) adsorption-desorption isotherms are depicted in Figure 2. All of them correspond to essentially microporous solids; there was a higher contribution of mesoporous in the case of H\({}_{3}\)PO\({}_{4}\)-activation. The rest of isotherms are given as Supplementary Material (Figures S1-S3). KOH was by far the activating agent allowing the highest porosity development, with BET surface area values up to ca. 2200 m\({}^{2}\):g\({}^{-1}\). These carbons were essentially microporous with increased mesoporousity at increasing KOH to hydrochar mass ratio. The activated carbon prepared at 4:1 mass ratio had almost 1800 m\({}^{2}\):g\({}^{-1}\) BET surface area in spite of its high ash content (38.2%), mostly due to the remaining inorganic matter derived from the activating agent. In fact, its BET surface area represented as much as ca. 2900 m\({}^{2}\):g\({}^{-1}\) on an ash-free basis. The lowest surface area development occurred with FeCl\({}_{3}\) as activating agent, due in part to the very high ash content of the resulting activated carbons. The highest BET surface area of these carbons on an ash-free basis was 770 m\({}^{2}\):g\({}^{-1}\), only slightly more than one-quarter that of the abovementioned KOH-activated carbon. FeCl\({}_{3}\)-activation can be addressed to the preparation of carbon-supported Fe catalysts. [PERSON] et al. [44] and [PERSON] et al. [55] prepared this type of catalyst, and tested theirs in catalytic wet peroxide oxidation (CWPO), from FeCl\({}_{3}\)-activation of sewage sludge. Activation with H\({}_{3}\)PO\({}_{4}\) gave rise to microporous carbons but with much higher relative contribution of mesoporousity, showing Type IV isotherms of the IUPAC classification. The BET surface area values are relatively low compared to the obtained by the same method with other precursors. The ash content was significantly lower than by the two other activation procedures. Increasing the H\({}_{3}\)PO\({}_{4}\) to HC ratio decreased the BET surface area, affecting mostly, the mesopore contribution. \begin{table}
\begin{tabular}{c c c c} \hline
**Sample** & **HHV (MJ\(\cdot\)kg\({}^{-1}\))** & **Energy Density** & **Energy Recovery Efficiency 1** \\ \hline GS & 23.6 & - & - \\ GS-180-40 & 24.5 & 1.04 & 0.78 \\ GS-200-40 & 26.8 & 1.14 & 0.87 \\ GS-220-40 & 27.6 & 1.17 & 0.69 \\ GS-240-40 & 29.1 & 1.23 & 0.73 \\ GS-260-40 & 30.3 & 1.29 & 0.81 \\ GS-280-40 & 30.9 & 1.31 & 0.81 \\ GS-300-40 & 31.4 & 1.33 & 0.64 \\ \hline \end{tabular} 1  
\end{table} 
Table 2: Energy properties of raw grape seeds and hydrochars. Figure 3 shows SEM images of the grape seeds, hydrocarbons and activated carbons. The raw GSs exhibited a well-defined morphological structure in three different layers, while in the hydrochar image shows some partial degradation of the structure occurred, although the morphology was still preserved in great part, which indicates good thermomechanical stability for the GSs. This allows obtaining granular activating carbons from this starting material. KOH activation produced a spongy-like structure with many holes. In the case of FeCl\({}_{3}\)-activation, the formation of microspheres was visible; after the activation with H\({}_{3}\)PO\({}_{4}\), prismatic particles can be seen.