## 2 Experimental Part
### Analytical Methods  
The basic properties of biomasses, such as proximate and ultimate analyses and calorific values, were determined. The proximate and ultimate analyses of dry samples were performed as described in our previous papers [52; 69] and are represented by the equations below (Equations (5)-(8)) [7].  
\[\text{MC (wt.\%)}= \left(\frac{\text{A}-\text{B}}{\text{A}-\text{C}}\right)\cdot 100, \tag{5}\] \[\text{AC (wt.\%)}= \left(\frac{\text{B}-\text{C}}{\text{A}-\text{C}}\right)\cdot 100,\] (6) \[\text{VM (wt.\%)}= \frac{\left(\text{A}-\text{B}\right)-\left(\text{MC }\cdot\left(\text{A}-\text{C}\right)\right)}{\left(\text{A}-\text{C}\right) \cdot\left(100-\text{MC}\right)}\cdot 100,\] (7) \[\text{FC (wt.\%)}= 100-\text{MC}-\text{AC}-\text{VM}, \tag{8}\]  
where AC is ash, TC is fixed carbon, Vm is volatile matter, MC is moisture content, A is the sum of the crucible mass and sample mass, B is the sum of the crucible mass and sample mass after drying, and C is the sum of the empty crucible mass.  
Standard procedure was applied for the determination of quantities in Equations (5)-(7) following refs. [70; 71; 72]. The weight percentage of O was calculated using Equation (9):  
\[\text{O (wt.\%)}= 100\ -\ \text{C (wt.\%)}\ -\ \text{H (wt.\%)}\ -\ \text{N (wt.\%)}\ -\ \text{S (wt.\%)}\ -\ \text{AC (wt.\%)}. \tag{9}\]  
Figure 1: Schematic diagram of the experiment.  
Figure 2: Torrefaction setup.  
Higher heating values (HHV) were detected by a bomb calorimeter (IKA C6000 Isoperibol (Staufen, Germany) following the UNI EN 14918. To ensure the measurement quality, all analyzers were calibrated at regular intervals. For each analysis, up to 20 mg of each biomass material was used. The method was carried out in triplicate in order to calculate the standard deviation.  
To investigate the thermal degradation characteristics of biomasses, thermogravimetric (TGA) and derivative thermogravimetric (DTG) analyses of the samples were conducted on raw and torrefied biomass samples using the thermogravimetric analysis described above in Section 2.2. The samples were heated at the constant heating rate, 25 \({}^{\circ}\)C/min under a nitrogen medium (25 \({}^{\circ}\)C, 20 mL/min), from 30 \({}^{\circ}\)C until they reached the final torrefaction temperature. With each biomass sample, three identical experiments were performed to verify repeatability, and the results show that the absolute differences between the three identical experiments are less than 8%. Lastly, the chemical functionalities of the biomass materials (i.e., the raw and torrefied samples) were characterized by a Fourier transform infrared (FTIR) spectrometer, Thermo Scientific, Nicolet iS50 FTIR (Waltham, MA, USA), with an attenuated total reflectance (ATR) sampling technique. The spectra were recorded between 400 and 4000 cm\({}^{-1}\) by averaging 16 scans with a spectral resolution of 4 cm\({}^{-1}\). The most severe torrefaction conditions (350 \({}^{\circ}\)C, 60 min) were selected for comparison purposes in both TGA and FTIR analyses.  
The torrefaction severity index (TSI) introduced in this work is defined as shown in Equation (10):  
\[\text{TSI}= \frac{\text{WL}_{\text{T},\text{t}}}{\text{WL}_{\text{350 }^{\circ}\text{C, 60 min}}}=\frac{100\ -\ \text{MY}_{\text{T},\text{t}}}{100\ -\ \text{MY}_{\text{350 }^{\circ}\text{C, 60 min}}}, \tag{10}\]  
where WL represents the weight loss of the torrefied biomass at the specific torrefaction temperature (T) and time (t), and MY represents the mass yield.