# Use of Invasive Acacia Biomass to Produce Biochar and Solid Biofuels
## 1 Introduction
As a result of this, there are several parameters in the process that have physicochemical influences on the final properties of biochar, with the most relevant being the characteristics of the original raw material, reaction temperature, heating rate, residence time, and reaction atmosphere [21; 22]. Different waste materials were processed with adequate results using slow pyrolysis under low-moderate temperatures (400-500 \({}^{\circ}\)C) with long residence time (2-3 h) [23; 24]. By using different agricultural and forest wastes, as well as pine chip and cork, biochar with good properties can be obtained [20; 25; 26]. Utilizing acacia wood in a slow pyrolysis process (temperatures mainly in the range of 300-500 \({}^{\circ}\)C), the authors of [24] obtained satisfactory results, with an optimum temperature of 435 \({}^{\circ}\)C for 1 h using a laboratory electrical furnace. New applications of biochar, in addition to the known use as energy, have acquired special relevance, not only in the agriculture and livestock sector, where it is used to improve the physical and chemical properties of the soil [27], but also as domestic and industrial products (filters, animal feed, cosmetics, etc.). The use of biochar in soil can be beneficial as it can increase the amount of organic matter, it is a fertility enhancer, it contributes to carbon sequestration, it is a nutrient leaching preventer, and it is an acidity modifier (pH). Due to its porous structure, biochar is also used as an additive in low rainfall areas, where it has been proved to stabilize the level of moisture in the soil [28], or as a structuring agent and base for nutrients during the composting process, where it has optimized the degradation of organic matter while reducing emissions of ammonia and greenhouse gasses [29]. It has been shown to be effective in reducing the absorption of heavy metals and helps to sequester solid carbon in agricultural fields for hundreds and even thousands of years [30]. The market viability of certain types of biochar and solid biofuels has been demonstrated, primarily due to their low production costs--attributable to the use of low-cost feedstocks, often derived from waste--and their scalability for large-scale production [31]. This study developed densified solid biofuel and biochar from two invasive plants biomass material and compared their parameters with those of original biomass. The production of biochar in this environment aligns with various sustainability goals, principles of circular economy, and the achievement of the Sustainable Development Goals (SDGs). Through the application of thermochemical conversion processes, slow pyrolysis, using a mobile straightforward double-grade reactor [32], the initial biomass could be transformedinto a biochar with high-fixed-carbon. These principles fit into the guidelines for sustainable biochar production issued by the European for Biochar Foundation (EBC) [33]. With fast pyrolysis, high-fixed-carbon contents are usually not achieved, and with gasification, generally biochar with higher carbon content is produced, although its quality may not be sufficient for different applications, mainly due to the fact that it still contains harmful substances such as polycyclic aromatic hydrocarbons [34]. In these two processes, biochar is a low-yield byproduct, whereas higher yields are achieved in oil and gas production. In this work, slow pyrolysis was used, as it is a methodology with a foreseeable commercial relevance, without an excessively advanced technique, suitable for simpler use, and able to achieve an adequate release of volatile components and a relatively high-fixed-carbon content of the solid [35].