Produção de etanol de segunda geração

Abstract

The techniques of alcohol production in antiquity, only restricted to natural or spontaneous fermentation of some plant components such as sugars, began to expand from the development of the distillation process. The development of technologies to produce ethanol from lignocellulosic materials is promising due to several advantages of the use of residual biomass for second generation ethanol. Thus, it can be a technological alternative, because the sugar cane bagasse, the main lignocellulosic material in tropical countries, has enormous energy potential. The sugar cane bagasse is a byproduct of the sugar industry, as well as straw. Bagasse can serve as feedstock for ethanol production, being subjected to acid or enzymatic hydrolysis, in which the cellulose and hemicellulose fractions are converted to hexoses and pentoses that can be fermented to ethanol. There are two main processes for producing lignocellulosic or second generation. Ethanol first, the pulp is subjected to an enzymatic hydrolysis process, using enzymes called cellulases. There is also the acid hydrolysis, taken with concentrated or diluted hydrochloric or sulfuric acid. Both processes produce a hydrolyzate rich in glucose which is then fermented to ethanol with a view to improving the potential of hemicellulose hydrolyzates, richin pentoses, for use in a subsequent conversion processes. Various treatments have been used to remove or reduce the concentrations of toxic compounds present in the fermentation media, aiming to overcome the negative effect of these inhibitors in the hydrolyzates. The knowledge about yeast species which ferment pentoses is limited. Four new species of D-xylose-fermenting yeasts from the clade Spathaspora are found in northern Brazil. These species are described as Spathaspora brasiliensis, Spathaspora suhii, Spathaspora roraimanensis, Spathaspora xylofermentans. All of these species are able to ferment D-xylose during aerobic growth, albeit with different efficiencies. Among other D- xylose-fermenting species are: Pachysolen tannophilus, Scheffersomyces stipitis, Scheffersomyces shehatae, Candida tenuis, Brettanomyces naardenensis and Scheffersomyces segobiensis. Native strains of the yeast Saccharomyces cerevisiae, the main organism used in the production of ethanol from fermentative processes were unable to metabolize, D -xylose originating from the hemicellulose fraction. Aiming to move forward and make the production of second generation ethanol more efficient, its recommended the incorporation of molecular biology techniques in order to provide the S. cerevisiae strains used to be able to ferment D -xylose.