Estudo das etapas de pré-tratamento e hidrólise enzimática de palha de cana-de-açúcar visando a produção de etanol de segunda geração.

Abstract

Environmental concerns have encouraged the search for greenhouse gas reduction and interest in the development of biofuels that can replace fossil fuels. As a result, ethanol production from renewable biomass such as sugarcane straw has become a potential raw material because it is abundant, available and its use does not compromise food security. The present work had as objective the study of the pretreatment and enzymatic hydrolysis of sugarcane straw in order the production of second generation ethanol. In the first stage of the work, the sugarcane straw was pretreated with dilute sulfuric acid, carried out according to factorial design, in which the following variables were analyzed: H2SO4 concentration (0.1 M, 0.2 M and 0.3 M), temperature (60, 80 and 100 ° C) and time (20, 40 and 60 minutes). In the second stage, enzymatic hydrolysis was performed using the commercial enzyme Cellulase Blend (SAE 0020) from Sigma- Aldrich® under the following conditions: 50 °C, with 150 rpm in a rotatory shaker, pH 4.8 in sodium citrate buffer. In the study of enzymatic hydrolysis were evaluated the influences of substrate (pretreated straw) and enzyme concentrations. The hydrolysis was performed according a factorial design 22, with three central points, totaling 7 experiments. In the hydrolysis study, the solid fraction obtained from the pretreatment in the condition of 0.3 M H2SO4, 60 minutes and 100 ºC was used as substrate (condition that released the highest concentration of reducing sugar and presented greater modifications when analyzed by the FTIR method). In relation to the pretreatment, it was observed that the concentration reducing sugar (RA) ranged from 2.90 to 15.90 g/L. Statistical analysis of the results using the Statistica software (Statsoft 7.0) showed that the coded model representing RA release was statistically significant at 95 % confidence. Solubilization of the straw components increased with the process severity, that is, with the highest acid concentration and higher temperature and time. In the case of enzymatic hydrolysis, it was observed that the concentrations of released reducing sugars were practically constant between 48 and 72 hours, so it was decided to evaluate their efficiency as a function of released reducing sugars in 48 hours. The results showed that the highest concentrations of reducing sugars were 12.84 and 15.51 g/L, corresponding to the conditions in which a higher solid fraction load (substrate) was used, being 10 % (w/v). Statistical analysis showed that substrate concentration and interaction between substrate concentration and enzyme concentration were the statistically significant factors at 95% confidence. The first-order model represents the RA concentration, was predictive and significant.