Fermentação de açúcares liberados de biomassas lignocelulósicas pré-tratadas com líquidos iônicos para a produção de etanol

Abstract

Fossil fuels, such as gasoline, diesel and coal, are the main sources of energy nowadays. In addition to generate problems, from the emission of greenhouse gases to the increase in fuel prices, these energy sources are likely to be depleted in the next 40 to 50 years. A widely used alternative to fossil fuels is first-generation ethanol, produced mainly from corn and sugarcane. Although ethanol is considered a clean source of energy because it does not emit polluting gases and helps in carbon sequestration, it is linked to a decrease in food supply and the consequent rise in food prices. Therefore, new studies on renewable energy sources, such as second-generation ethanol from feedstock and other lignocellulosic residues, are commonly found in the literature. In this context, this study aimed to evaluate the production of secondgeneration ethanol from the following lignocellulosic residues: sugarcane bagasse, elephant grass, Pinus sp. sawdust and Eucalyptus sp. sawdust, pretreated separately with the ionic liquids 1-ethyl-3-methylimidazolium acetate and 1-butyl-3-methylimidazolium acetate. Hydrolysis of lignocellulosic biomass with enzymes from Penicillium echinulatum was carried out after the pretreatment. Saccharomyces cerevisiae, Schizosaccharomyces pombe Y 698 and the bacterium Geobacillus thermoglucosidasius were used for the fermentation of sugars released during hydrolysis. The highest concentrations of reducing sugars obtained after enzymatic hydrolysis were 681.89 mg. g -1 for sugarcane bagasse, 474.30 mg.g -1 for elephant grass, 237.84 mg.g -1 for Eucalyptus sp. sawdust and 233.62 mg. g -1 for Pinus sp. sawdust, all pretreated with 1-ethyl-3- methylimidazolium acetate. S. cerevisiae was the microorganism with the highest efficiency in the consumption of reducing sugars. However, the highest ethanol yield (96 mg.g -1) was obtained for sugarcane bagasse pretreated with 1- butyl-3-methylimidazolium acetate and fermented by S. pombe. G. thermoglucosidasius showed potential for the simultaneous consumption of xylose and glucose, but ethanol production was low (21 mg.g -1 for sugarcane bagasse). These data contribute to expand the knowledge about the effects of ionic liquid pretreatments for the production of secondgeneration ethanol.