# Granular Activated Carbon from Grape Seeds Hydrothermal Char
## 4 Conclusions  
A two-stage process was successfully developed to produce high surface granular activated carbon from grape seeds (GSAC), by using HTC, followed by low temperature activation with relatively small amounts of KOH. The overall final yields were around 35%, in line with (or even higher than) those that were obtained in other works and based on a single-stage process. Very high surface areas can be obtained, with most of the pores falling in the micro-pore range. When compared to single-stage processes, milder reaction conditions can be adopted to obtain similar surface areas. Additionally,  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Pretreatment to** & **Activating Agent:** & **Carbonization** & **Max SBT** & **Optimum** & & \\
**Activation** & **wt. Ratio Range** & **Method** & **(m\({}^{2}\)/g)** & **Activation** & **Y\({}_{\text{ov}}\) (\%)** & **Ref.** \\ \hline Oil removal by & & & & & & \\ H\({}_{2}\)SO\({}_{4}\) & H\({}_{3}\)PO\({}_{4}\); 1–4 & 1 stage & 1139 & 500 & 50 & [2] \\ \hline Grinding & K\({}_{2}\)CO\({}_{3}\) & 1 stage & 1238 & 800 & 26 & \\ KOH; 0.25–1 & 1 stage & 1222 & 800 & 31 & [22] \\ \hline Grinding & ZnCl\({}_{2}\), n.s. & 1 stage & 916 & 550 & n.s. & [8] \\ \hline Drying & KOH; 0.25–1 & HTC & 1018 * & 600 & 35 & This study \\ \hline \hline \end{tabular}
1 stage: one stage process; n.s. not specified; * sample H250K050.  
\end{table}
Table 4: Comparison of grape seeds activated carbon properties of the “optimum samples” from a selection of studies.  
the obtained surface was quite clean from functional groups and the GSACs that resulted were quite thermally stable.  
The best results in terms of material quality were obtained at the highest HTC temperature (250 \({}^{\circ}\)C) with the intermediate KOH:hydrochar ratio of 0.5: surface area higher than 1000 m\({}^{2}\)/g and micro-pore-volume accounting for 90% of total pore volume (0.4857 cc/g). Actually, in a wide range of operating conditions, the higher were the HTC temperature and the KOH:hydrochar ratio, the higher was the surface area of the GSAC. But, at the highest values tested for both process parameters (HTC temperature: 250 \({}^{\circ}\)C, KOH:hydrochar ratio equal to 1), the whole process resulted too severe: a portion of micro-pores collapsed and larger pores formed, causing surface area reduction. In any case, also low HTC temperatures and the intermediate KOH:hydrochar ratio allowed for producing GSACs with relatively high surface areas (\(\approx\) 600 m\({}^{2}\)/g) and well developed micro-porosity. Actually, the two-stage process can be very advantageous, owing to such a high grade of flexibility. It can be thus a concrete path for the valorization of grape seeds as well as other agro-industrial waste, with high value creation and improved sustainability.  
We greatly appreciate financial support from International Mobility Program Erasmus Mundus Action 2 AREAS+ project 2014, funded by the European Commission with Grant Agreement N. 2013-2543/001-001. The authors thanks Ms [PERSON] of the University of Trento for her great care in executing extensive TGA runs till the last working day before Christmas holidays.  
[PERSON] and [PERSON] conceived and designed the experiments; [PERSON] performed the experiments; the analytical work was carried out by [PERSON] and [PERSON]; all the authors analyzed the data and contributed in writing the paper.  
The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.