# Granular Activated Carbon from Grape Seeds Hydrothermal Char
## 1 Introduction  
Biomass residues arise from nearly all agricultural and agro-industrial productions. Such kind of waste requires proper disposal, in accordance to law requirements. Therefore, it represents a cost to producers and local communities as a whole. Owing to that, policies are currently oriented towards the valorization of such waste materials, as a source for both new materials and (renewable) energy. Between these two alternatives, valorization to produce new valued materials is preferred [1]. In the present study, grape seeds are utilized as a secondary raw material to produce granular activated carbon, with potential utilization as an adsorbent or catalyst support. Grape seeds arise from winemaking process, and they contribute up to 15% of the total solid waste that is generated by the process [2]. Nowadays, when not disposed of as a waste, grape seeds are mostly utilized for the extraction of grape seed oil [3], which is universally recognized for its valuable properties, as it contains a number of noble compounds [4]. Such oil is thus utilized for food and nutraceutical applications. Grape seeds can be also used in animal feed mixture [5], although this is a lower added-value application. The production of activated carbon from biomass residues is getting popular recently due to the abundant availability of such feedstock and its very low cost. Almost all sorts of biomass waste have been investigated as activated carbon precursors, such as wood [6], seeds [2; 7], shells [8; 9; 10], stones [11; 12], straw [13], husk or hulls [6; 13; 14], sawdust [14], and even ashes [15; 16; 17]. However, not every substrate can be considered as a potential candidate for activated carbon production. Indeed, in order to move from research applications to actual industrial production, continuous supply of the chosen biomass should be ensured. If a mere agricultural residue (e.g., rice husk, date stone, and durian shell) is taken into account, it should be collected over very wide areas to obtain the amounts and the continuity required by industrial operations. This would be detrimental for the economic feasibility of the waste biomass valorization path. It would be more practical if the considered feedstocks were accumulated in an industry as a side product of an existing agro-industrial process, so that the steadiness of the supply could be assured. Potential candidates could be palm kernel shells from palm oil industries [9], bagasse fly ashes from sugarcane industries [17], potato peels from food industry [18], Jatropha shells from biodiesel production facilities [19], and grape seeds from winemaking industries. Some experimental works reported the possibility to use grape seeds as precursor for activated carbon [2; 8; 20; 21; 22]. The highest surface area (S\({}_{\text{BET}}\)) of 1339 m\({}^{2}\)/g was obtained by a laborious method of cyclic oxygen chemisorption-desorption activation [21], while the conventional chemical impregnation followed by thermal activation method was able to reach a surface area of 1238 m\({}^{2}\)/g using 50 wt % potassium carbonate (K\({}_{2}\)CO\({}_{3}\)) at 800 \({}^{\circ}\)C [22]. Most of the grape seeds activated carbons showing high-surface area (S\({}_{\text{BET}}\) > 1000 m\({}^{2}\)/g) possesses a large volume fraction of micro-pores with low development of larger pores, which may limit the application for liquid adsorption, except for ZnCl\({}_{2}\) activated samples [8]. As a drawback, the cyclic method seems ill-suited to further industrial development due to its laborious and time-consuming procedure. In these previous studies, except for the cyclic activation method, the activated carbon is prepared by means of a single stage process, i.e., chemical activation, where carbonization and activation occur simultaneously. Such a method requires a single high-temperature reactor, and carbonization and activation steps necessarily take place at the same reaction conditions.