Electron Microscopy Characterization of Persea americana Mill Residues for Application in Solid Biofuels in Agro-Industrial Regions of Michoacán

The increase in human activities has led to a rise in energy use, which has resulted in excessive dependence on fossil fuel consumption, generating environmental impacts such as climate change due to excessive greenhouse gas emissions. In addition, these resources are becoming increasingly expensive and scarce. In this context, the use of solid biofuels derived from biomass residues has become a viable alternative due to factors such as the abundance and low cost of this type of residue, and is projected to be an important energy source in the coming years [1,2]. Wood represents the majority of solid biofuels used in Mexico, through its combustion for cooking or heating water in rural areas, which directly contributes to deforestation. For this reason, alternatives such as the use of agro-industrial residues are being explored; for example, the use of avocado pruning waste, residues that are mostly wood and whose utilization may contribute to reducing the use of firewood [3,4]. This research presents an energy analysis based on agro-industrial residues of Persea americana Mill. (avocado) generated in the state of Michoacán. Avocado is the most relevant crop in the state, since Michoacán is the largest producer nationwide, with an approximate cultivated area of 186,713 hectares and an estimated production of 2,252,783 tons of avocado, from which approximately 145,636 tons of residues are obtained. Approximately 15 kg of sample were collected directly from the cultivation areas (Figure 1a). After collection, a dehydration phase of the residues was carried out using an efficient solar drying system (Figure 1b). The samples were subjected to a mechanical grinding process in order to obtain homogeneous particle sizes (Figure 1c). A morphological analysis was performed using a Scanning Electron Microscope (SEM), employing a Bruker field emission instrument, model Jeol JSM 7600F. A calorific value analysis was also conducted in accordance with the guidelines established by the UNE-EN 14918 (2011) standard [5], using a LECO AC600 calorimeter calibrated with 1 g of benzoic acid, and using 0.100 g of anhydrous sample. The calorific value reported for this residue was 19.8 MJ/kg, similar to the values reported in other studies, which range from 19.2 to 20.1 MJ/kg [3,6]. The use of this residue can be directed toward the generation of solid fuels in order to meet local energy needs, due to its excellent calorific value and availability. Figures 1 (d) and (e) show the SEM characterization, which made it possible to determine the morphology of this residue, suggesting the presence of polymeric compounds associated with lignocellulosic materials, which are positively associated with a high calorific performance of the material. If all avocado residues generated in the state of Michoacán were utilized, the approximate energy potential that could be obtained is 2,894 PJ/year, which could meet the energy demand of various rural communities in the state, representing an attractive energy alternative. Avocado waste generation process: (a) collected avocado samples (b) avocado drying (c) pulverized avocado samples (d, e) morphology of avocado samples.