Produção de biocombustíveis e oligossacarídeos prebióticos a partir de resíduos agrícolas ligno(hemi)celulósicos

Abstract

Bioethanol and other cellulosic fuels are energy commodities derived from renewable sources of phytobiomasses with the potential to replace petroleum-based fuels. One of the most contemporary ways of obtaining bioethanol is by using ligno(hemi)cellulosic residues as feedstock. One good source of these materials are the residual agricultural phytobiomasses (e.g. wheat husk, soybean hull, cane bagasse and chemically similar) found in abundance in Brazil due to the extent and economic influence of the agricultural practice in the country. In order to use these materials – such as the wheat husks and the soybean hulls – to produce biofuels, it is required a pretreatment process, preferably of the milder acid class, to seize the carbohydrates of the two dominant fractions: Cellulose and hemicellulose. In this final paper, preference was given to dilute phosphoric pretreatment (H3PO4 at pH effective in the pH range of 2 to 3 and therefore 5 - 25 mmol / L) - phosphoric hydrolysis, combined with moderate thermopressurization (159 - 180 ° C = 5 to 9 atm). This range allows not only to adhere to the complete hydrolysis or to optimize the release of hemicellulose pentoses but also to direct it in the direction of xylos oligosaccharides, already, per se, with prebiotic properties; and it also allows in parallel to solubilize the lignin, consequently benefiting the enzymatic hydrolysis of the residual cellulose. The methodology analytical baseline was the chromatography, in both thin layer (CCD) and high performance liquid (HPLC). The best pretreatment conditions with O-phosphoric acid in order to increase the saccharification power of the biomasses and thus the ethanol production for the wheat husk was of 7 atm and pH 3, obtaining a high content of hydrolysis percentage of 36.8%; For soybean hulls of 5 atm in the three pH (2, 2,5 and 3), obtaining on average 50 - 55%. However, for a high release of oligosaccharides in the soluble fraction, the best condition was 7 atm and pH 3, with the wheat husk being an agricultural residue with a higher concentration compared to soybean hulls. For the alcoholic fermentation, the Saccharomyces cerevisiae strain was more efficient in the production of ethanol in less time of experiment, in the best conditions, in the range of 8 μL/mL, compared to the strain of Pichia stipitis.