## 2 Materials and Methods
### Characterization
#### 2.1.1 Thermogravimetric and Kinetic Analyses  
A thermogravimetric analysis [24; 25; 26; 27] was conducted to determine (i) physical-chemical changes in _Sargassum_ spp. at different temperatures, (ii) the kinetics of the pyrolithic process of this material, and (iii) its kinetic parameters. To eliminate the moisture, _Sargassum_ spp. samples were oven dried at, a temperature of 25 \({}^{\circ}\)C for five days. Once dry, the samples were ground in an agate mortar to a particle size of approximately 400 microns, and dried again at 115 \({}^{\circ}\)C, until they reached a constant weight. All the samples remained in storage in the oven until analyses were conducted. The thermal degradation (TGA-DTG) of the _Sargassum_ spp. was determined in a PerkinElmer STA 6000 thermogravimetric analyzer. To perform the thermal process and protect the samples from oxidation, a relative grade inert gas (nitrogen) was utilized at a purity of 99.99% and a flow rate of 20 mL/min. The samples were heated from room temperature (25 \({}^{\circ}\)C) to a maximum of 900 \({}^{\circ}\)C. For the thermal process, we considered non-isothermal conditions at a heating velocity of 10 \({}^{\circ}\)C/min. To reduce errors, complete pyrolysis was performed in three time. Each sample used had an approximate weight of \(30\pm 5\) mg. The TGA analysis allowed us to calculate such key parameters as activation energy (\(E_{a}\)), frequency factor (Z), and reaction order (\(n\)). Diverse mathematical models have been proposed for studying the kinetics of thermogravimetric processes based on Arrhenius' equation. It is important to note that existing models are of two types: a function of the degree of advance, represented by \(\alpha\); and a function of heating velocity, represented by \(\beta\). The present study analyzed the pyrolysis of _Sargassum_ spp. by considering an inert nitrogen atmosphere using [PERSON]'s method, based on the degree of advance (\(\alpha\)) to determine the aforementioned kinetic parameters. Figure 1: Processing of _Sargassum_ spp. (**a**) collection; (**b**) washing; (**c**) open-air drying; (**d**) grinding. According to various researchers, the complete thermal process of biomass can be simplified as a global mechanism [28; 29; 30]. If we consider that the decomposition of the biomass can be obtained in only one step, then the conversion velocity can be represented as a function of \(k(T)\)[31; 32; 33] as follows:  
\[\frac{d\alpha}{dt}=k(T)*f(\alpha) \tag{1}\]  
Once the degree of conversion is defined, applying [PERSON] expression makes it possible to proceed with the kinetic analysis. If we consider the initial and final mass (\(m_{i}\), \(m_{f}\)) as the mass in the sample-holder of the TGA apparatus (aluminum crucible), and the residual mass at the end of the pyrolithic process, respectively, then the degree of conversion, or degree of advance (\(\alpha\)), of any mass (\(m\)) in the entire temperature range (\(T\)), is expressed as:  
\[\alpha=\frac{m_{i}-m}{m_{i}-m_{f}} \tag{2}\]  
As Equation (3) shows, and considering the \(k(T)\) term of Equation (1), dependence with respect to temperature can be described as a function of [PERSON] expression as follows:  
\[\textit{Velocity constant}[k(T)]=pre-exponential\textit{ factor}\left(A\right)*e^{\frac{-activation\textit{ energy}\left(E_{a}\right)}{\textit{pos constant}\left(k\right)\textit{Temperature}\left(k\right)}} \tag{3}\]  
The appropriate kinetic analysis is fundamental for the goals of evaluating pyrolysis and optimizing the thermal transformation of _Sargassum_ spp., that is, to obtain the most important parameters of the thermal process. The Horowitz-Metzger method is a simplified form of [PERSON]'s integral method and, provides an excellent approach towards a straight line, so it is utilized to calculate such kinetic parameters as activation energy (\(E_{a}\)) by analyzing a slope that is obtained by representing a function of the degree of conversion (\(\alpha\)) with respect to the temperature of the thermal degradation process [34].