## 2 Materials and Methods
### TG Analysis  
The thermogravimetric analysis (TG) was carried out by using a thermobalance (NETZSCH STA 449F5 Jupiter, Germany), located in the Cork, Wood and Charcoal Institute belonging to CICYTEX. Different samples from each residue were selected, with variable weights from 30 to 38 mg in an aluminum crucible (Al2O3), undergoing temperatures between 30 to 900 \({}^{\circ}\)C with a temperature ramp of 20 \({}^{\circ}\)C/min in argon atmosphere, and a gas flow of 50 mL/min, and an air atmosphere (80/20) with a gas flow of 50 mL/min. The protective gas was argon (20 mL/min). To conduct properly the thermogravimetric analysis the Difference Thermogravitometry curve (DTG) has been calculated, corresponding to the first derivative of the DT curve. All the samples were done in triplicate in order to assure a suitable reproducibility of results. In order to determine the different temperature events during pyrolysis, under inert atmosphere (argon), and combustion, under air atmosphere, the tangent method [7,27,28], has been selected, which is shown in Figure 2.  
Concerning combustion, the temperature at which combustion or burning ended was considered when the residual mass was 1% of the original mass [28, 29, 30]. In the case of pyrolysis, the main characteristic temperatures of the process were determined, such as the starting temperature of fast pyrolysis \(T_{m}\) (corresponding to the starting temperature of the thermal process according to the tangent method), the end temperature of pyrolysis, \(T_{f}\) (corresponding to the end temperature of the thermal process according to the tangent method), and the peak temperature \(T_{p}\) (the temperature at which the maximum weight loss rate took place). Moreover, the pyrolysis index, \(P_{i}\), was calculated, which is defined as the easiness to start the process, and the end of pyrolysis index, \(P_{f}\), which is useful to assess the yield of pyrolysis in biomass, was also obtained [31]:  
\[P_{i}=\frac{DTG_{max}}{t_{p}t_{m}} \tag{1}\]  
\[P_{f}=\frac{DTG_{max}}{\Delta t_{1/2}t_{p}t_{f}} \tag{2}\]  
Figure 2: Tangent method. where \(DTG_{max}\) (%/min) denotes the maximum pyrolysis rate; \(t_{p}\) (min) is the corresponding time of the maximum pyrolysis rate; \(\Delta t_{1/2}\) (min) represents the time range that corresponds to \(DTG/DTG_{max}=\frac{1}{2}\); and \(t_{m}\) (min) and \(t_{f}\) (min) is the time associated with \(T_{m}\) and \(T_{f}\), respectively. The pyrolysis characteristic index \(P\) was calculated, which shows the energy required to pyrolyze a fuel [31]:  
\[P=\frac{DTG_{max}DTG_{mean}}{T_{m}^{2}T_{f}} \tag{3}\]  
where \(DTG_{mean}\) (%/min) represents the mean pyrolysis rate. Regarding combustion, the ignition temperature, \(T_{i}\) (corresponding to the starting temperature of the thermal process according to the tangent method), the burnout temperature, \(T_{f}\), and peak temperature, \(T_{p}\), (the temperature at which the maximum weight loss rate was observed) were determined. Moreover, the ignition index, \(D_{i}\), and the burnout index, \(D_{f}\), were calculated to describe the ignition and burnout characteristics of the residues [29]:  
\[D_{i}=\frac{DTG_{max}}{t_{p}t_{i}} \tag{4}\]  
\[D_{f}=\frac{DTG_{max}}{\Delta t_{1/2}t_{p}t_{f}} \tag{5}\]  
where \(DTG_{max}\) (%/min) denotes the maximum combustion rate; \(t_{p}\) (min) is the corresponding time of the maximum combustion rate; \(\Delta t_{1/2}\) (min) represents the time range that corresponds to \(DTG/DTG_{max}=\frac{1}{2}\); and \(t_{i}\) (min) and \(t_{f}\) (min) represent the ignition time and burnout time, respectively. The devolatilization index \(D\) and the combustion characteristic index \(S\) were calculated.