# Granular Activated Carbon from Grape Seeds Hydrothermal Char
## 3 Results and Discussion
### Proximate and Ultimate Analysis  
Table 3 reports the proximate and ultimate analyses of the hydrochar and GSAC samples. The hydrothermal treatment at mild conditions (180-220 \({}^{\circ}\)C) did not imply significant changes in the proximate composition, when compared with the raw feedstock. Conversely, when carbonization was conducted at 250 \({}^{\circ}\)C, FC increased significantly, from 29.2% to 41.6%. HTC determines a diminution of the oxygen content and an increase in the carbon content, as it is well-known in the literature: the data of Table 3 confirms that the higher is the HTC temperature, the higher is the C content and the lower is the O content.  
After the activation treatment, VM is definitely reduced, dropping from a value of 64.9% \(\pm\) 6.6% (standard deviation) for the three hydrocarbons to a value of 32.0% \(\pm\) 3.4% for the nine GSACs. Correspondingly, FC increases to a value of 61.8% \(\pm\) 4.3% for the GSACs. It is worth noticing that the amount of activator does not determine a trend in the values of VM. This is consistent with the yield data reported in Table 2. A large reduction in VM already occurs with relatively low amounts of activator: higher quantities of KOH do not cause evident changes in VM and FC.  
Ashes show an interesting trend. Indeed, GSACs show much higher ash contents than the corresponding hydrochar samples, which could be only partially caused by their concentration due to the overall mass loss occurring during activation. The ash content diminishes when increasing the activator amount. It could be thus hypothesized that the activation step produces ash constituents whose removal during the acid washing phase occurs only partially (see Section 2). The clear trends observed for the ash content versus KOH amount most likely depend on the combination of activator amount and washing step. Interestingly, the higher the amount of ashes, the higher the pH\({}_{\text{PZC}}\) of the GSACs (Table 2).  
As far as the elemental composition is concerned, it is remarkable that the amount of hydrogen drops considerably from 6.4% \(\pm\) 0.2% for the three hydrochars to 1.5% \(\pm\) 0.5% for the nine GSACs. The H contents of the GSACs found here is in good agreement with literature data relevant to GSACs obtained by means of (one stage) chemical activation [22]. Such behavior can be attributed to reactions occurring during the activation procedure, such as reactions (4), (5) and (6) above. The same reactions may lead to a decrease in the oxygen content of the GSACs, which reduces from 24.4% \(\pm\) 2.1% (values for the hydrochars) to 19.1% \(\pm\) 5.1% for the GSACs. However, the O content is highly variable for the various GSACs, and in one case (sample H180K100), it is even higher than for the parent hydrochar. No trend of the O content with respect to the amount of activator can be seen. A similar reasoning can be made regarding the carbon content of the various samples. C content moves from 57.7% for the raw grape seeds to 67.5% \(\pm\) 1.9% for the three hydrochars to 77.8% \(\pm\) 5.3% for the nine GSACs, without a trend with respect to the amount of KOH. Nitrogen content slightly increases with the increase in HTC temperature, both for hydrochars and GSACs.