Biomassa residual do coco babaçu: potencial de uso bioenergético nas regiões norte e nordeste do Brasil

Abstract

Traditionally, biomass is directly used as a source of bioenergy through the complete combustion or for the production of charcoal for domestic use, as well as for use in the steel industry. However, in recent years, research has been developed aiming for the use of lignocellulosic residues for this purpose, because these plant materials also feature organic compounds that can be oxidized and generate energy in a sustainable and efficient manner. Moreover, these residues are generally available in large quantities in production areas. Thus, the objective of this study was to evaluate the potential of babassu nut residues (epicarp, mesocarp and endocarp) for bioenergy use, especially considering the direct combustion and charcoal production for the steel industry. The material was collected in the rural area of the municipality of Sítio Novo do Tocantins, in the state of Tocantins, Brazil, and is obtained from the extractive exploitation by local communities. Initially, it was sought to characterize the fresh biomass and, due to this fact, the analyzes were performed considering jointly the three layers that make up the babassu nut shell. The following chemical characterizations were performed: molecular (lignin, total extractives and holocellulose), elemental (C, H, N, S and O), immediate (fixed carbon, volatiles and ash), energy (higher heating value and lower heating value), physical (basic density and energy density) and thermal, in nitrogen atmosphere and synthetic air (thermogravimetry, differential thermal analysis and differential scanning calorimetry), besides the morphological characterization by scanning electron microscopy. The babassu nut shell was carbonized in an electric furnace (muffle) at the following final temperatures: 450ºC, 550°C, 650°C, 750°C and 850°C, considering a heating rate of 100°C h-1. Mass and energy balance of the carbonizations were performed, and the charcoals produced were evaluated by apparent relative density, energy densities and fixed carbon stock; immediate and elemental analyses were also performed, as well as thermal analyses in synthetic air atmosphere (thermogravimetry and differential thermal analysis) and determination of heating values. Babassu nut residues showed a high bioenergy potential, mainly due to its high energy density. The use of this biomass as a source of bioenergy can be highly feasible, given its chemical and thermal characteristics, allied to a low ash content and excellent performance in combustion. The charcoal in babassu nut shell showed high values of apparent density and energy density, besides a suitable chemical composition for industrial use, and can be considered as a potential replacement for coal in the steel industry. The effect of the final carbonization temperature was pronounced for all characteristics evaluated in charcoal, except for the nitrogen content, and significantly affected its combustibility.