# Use of Invasive Acacia Biomass to Produce Biochar and Solid Biofuels
## 2 Materials and Methods  
Solid biofuels and biochar were elaborated from biomass of invasive _A. dealbata_ and _A. melanogaster_. Materials of these exotic species were collected in a natural area named _Canones del Sil_ (Northwestern Spain, WGS84 coordinate: N 42.411024749820186, E \(-\)7.632084153695484), within the Natura 2000 protected area. This preserved space gains significance when addressing the management of invasive species, particularly the acacias, whose proliferation is fueled by climate change and anthropogenic pressure. The material was obtained from trees of both species with normal diameters below 10 cm and heights of 4 m.  
To adjust this study, four clearly distinguishable types of biomasses were separated: small branches and leaves (phyllodes) called \"branch/leaf\" (Figure 1a); woody and trunk biomass fraction of higher volume called \"wood\" (Figure 1b); and these original types of biomasses were ground (Figure 1c) to subsequently elaborate briquettes, pellets, and biochar (Figure 1d-f) that were then analyzed. Figure 1: (**a**) “Branch/leaf” original biomass of phyllodes of _A. dealbata_. (**b**) “Wood” original biomass of trunks of _A. dealbata_. (**c**) Original biomass ground for analysis and characterization of \(\leq 1\) mm (**d**) briquettes (**e**) pellets and (**f**) biochar. For the characterization of the original biomass, solid biofuels, and biochar, different methodologies were employed: UNE-EN ISO 18134-3 for moisture content (%) [36], UNE-EN ISO 17828 for density (kg/m\({}^{3}\)) [37], UNE-EN ISO 18123 for volatile matter (%) [38], UNE-EN ISO 18122 for ash (%) [39], and UNE-EN 13037 for pH (%) [40]. Pellets were elaborated using a Euro-Tolds device, with a flat matrix system of 300 mm and 6 mm pellet diameter, by traditional pelletization [41]. To elaborate the briquettes, a TI device with a double-head and bi-directional hydraulic system was used with 14.71 MPa pressure and 80 mm briquette diameter. The size of the evaluated briquettes and pellets was 80 \(\times\) 100 mm and 6 \(\times\) 3 mm, respectively, and all characterization tests were carried out in triplicates. To develop the biochar, a simple mobile double-chamber reactor (of internal chamber of 50 L) on a laboratory scale was employed. The system was discontinuous and autonomous. The previous residual temperature within a slow pyrolysis system was used, concatenating successive processes. Additionally, the syn-gas produced was redirected to the heating process, thereby avoiding loss of energy and emission into the atmosphere. This also prevented the oven from cooling down between processes; thus residual heat was used. The aim of this method is to achieve simple manufacturing using low-cost-effective materials and easy operation, with a mobile format, in order to employ it near the biomass source. The heating process does not require energy from electricity or fossil sources, since it is heated by the temperature generated by the biomass itself [32]. This system increases the temperature using waste biomass in the pyrolysis chamber up to between 300 and 600 \({}^{\circ}\)C. The temperature is generated through a co-fuel process involving biomass waste. Temperature profiles were constant with a FT-data logger and measured with 4 K thermocouples. In the reactor, as soon as the pyrolysis chamber reached a temperature of \(\geq\)300 \({}^{\circ}\)C, the power of the biomass chamber was sustained, and the combustion of the pyrolysis gas was redirected inside the biomass chamber. Figure 2 represents the temperatures recorded in each of the chambers and at the gas outlet of the pyrolization chamber for a time process of 120 min. The process used for wood fraction biomass began with the cold reactor. For the branch/leaf biomass fraction, the thermal process started with the residual heat of the previous process, making use of certain thermal inertia and initial heating conditions.