## 3 Results and Discussion  
### Thermal Degradation and Kinetic Analysis of Sargassum spp. The thermogravimetric (TGA) and derivative analysis (DTG) curves of the _Sargassum_ spp. are shown in Figure 2. The TGA curve is divided into three main zones (I-III) to coincide with the results of various analyses of the pyrolysis of diverse kinds of marine biomass, including _Sargassum_ spp. [41; 42; 43; 44]. Zone I shows a very low percentage of loss of mass (\(\approx\)15%) due to dehydration; that is, the elimination of water and some slightly volatile substances from _Sargassum_ spp. This zone is represented by an approximate temperature range of 300-460 K. The following stage (zone II) takes place between 460 and 870 K and displays the largest, most significant mass degradation (\(\approx\)50%), due to the elimination of diverse amounts of biopolymers from the algae [45]. This zone is characterized by complex chemical reactions fostered by decarbonization and the degradation of important polymers, such as cellulose and hemicellulose [46]. The third zone of mass degradation occurs between 870 and 1150 K.  
The right panel of Figure 2 shows the degradation velocity (DTG), or first derivative of TGA. As a result of the temperature increase, a series of peaks appeared, which that became more pronounced as the temperature rose. According to the literature, the second peak of the DTG graph usually occurs in the range of 460-580 K and represents, principally, the thermal degradation of carbohydrates due to depolymerization and cracking [46]. Following the curve, a third peak appears in the interval between 580 and 625 K. This peak represents the decomposition of the proteins of _Sargassum_ spp. [47; 48]. Other authors have observed that these two peaks appear in the opposite order, as in the case of _Saccharina japonica_ (_S. japonica_) [49], where the third peak was seen to be higher, indicating differences primarily in carbohydrate content. In this regard, and compared to _S. japonica_, the _Sargassum_ spp. Figure 2: Thermogravimetric (TGA-left \(y\)-axis) and derivative analysis (DTG-right \(y\)-axis) curves of _Sargassum_ spp. collected on the Mexican Caribbean coast. analyzed in the present study presents a second peak that is higher than the third one, suggesting that they contain a larger amount of carbohydrates. Another interesting aspect of the second peak of the DTG of the _Sargassum_ spp. marine biomass (Figure 2) is that its temperature at the point of maximum heating velocity is lower than that of terrestrial biomass [50]. One example of this is the cellulose of lignocellulosic materials such as pine trees, which during their initial stage of degradation generally present a larger temperature range after the second DTG peak [51]. This phenomenon can be explained by comparing the degree of devolatilization and primary composition of terrestrial biomass (cellulose, hemicellulose, lignin), which pyrolyzes at a higher temperature than the main components of marine biomass (soluble carbohydrates in H\({}_{2}\)O, lipids, proteins), which degrade thermally at a lower temperature [50]. As Figure 2 shows, Zone III becomes visible at around 850 K with a fourth peak that begins at a temperature above 900 K and ends at approximately 1050 K. According to the graph, this transformation occurs at a very low heating velocity. The degradation in Zone III is due mainly to the degradation of inorganic material, such as the thermal transformation of some carbonates and the elimination of certain metals contained in _Sargassum_ spp. [47]. To determine the kinetic parameters of _Sargassum_ spp., we analyzed the TGA-DTG data in Figure 2. It is well-known that the most important kinetic parameters are activation energy (\(E_{a}\)), reaction order (\(n\)), and the frequency factor (\(Z\)).