Efeito de pré-tratamentos químicos nas propriedades de um resíduo da colheita do milho visando sua conversão energética

Abstract

The petroleum crisis of the 1970s highlighted the urgency of adopting renewable sources, such as biomass, to replace fossil fuels. This substitution brings benefits such as waste management, pollution reduction and the transition for cleaner sources such as alcohol, biogas and biodiesel. Brazil has a vast production of corn, generating significant waste, including stalks, straw, husks and corncobs, which account for around 50% of the harvest. As collectors of solar energy, plants store chemical energy that can be accessed through thermochemical routes such as combustion, gasification and pyrolysis. Bio-oil (a biofuel) and biochar (used as an adsorbent to remove heavy metals and colorants from effluents) are produced during pyrolysis, an oxygen-free process. To optimize pyrolysis, chemical pre-treatments can be applied on biomass to alter its structure and remove components, improving the quality of the products and catalyzing reactions. Studies on the application of these treatments for pyrolysis are scarce, so there is significant interest in exploring how they affect the reuse of residues such as those from corn harvest. Therefore, in this work, the characterization of the untreated corn harvest residue, treated with salt and treated with acid was carried out through the proximate and lignocellulosic analyses to verify the impact of these treatments on the properties of the residue and how this would affect the thermal conversion processes. Thermogravimetric analysis of the residue was also carried out. The acid treatment removed minerals from the biomass and resulted in a reduction in ash, from 1.48% to 0.61%. This reduction is beneficial, as low ash levels improve the efficiency of the process by preventing accumulations in the equipment and improve the efficiency of the thermochemical process. In addition, there was an increase in volatiles, from 78.88% to 84.35%, indicating greater energy potential, making acid treatment a promising option for improving the properties of the waste, favoring its conversion into a more efficient source of energy. The low moisture content of all the samples also contributes to more efficient thermal conversions. As for the lignocellulose analysis, the acid treatment led to a considerable reduction in the extractive and hemicellulose contents, with the hemicellulose being hydrolyzed by the acid and the extractives being removed and the extractives removed for having few chemical bonds with the biomass fibers. The salt treatment proved to be as efficient at removing hemicellulose and extractives as the acid treatment, but removed a lower percentage of hemicellulose and a slightly higher percentage of extractives. From the DTG analysis, it was possible to verify, through comparisons in the literature, that corn residue has great potential for use in thermal conversion, as its components degrade more quickly than the study in comparison, increasing the reaction rate.