Pré-tratamento alcalino e hidrólise enzimática da palha de cana-de-açúcar.

Abstract

The reasons for the interest in biofuels vary among the different countries due its environmental, social and economic benefits, being its use gradually emphasized nowadays. Brazil is one of the countries with the greatest technological potential for the production of biofuels. Currently, ethanol has a high commercial demand, but the country has been facing a growing deficit in the supply of this fuel. In order to fix the problem of the demand on the supply of Brazilian ethanol in the market, researches on the use of lignocellulosic biomass appears as an alternative for the second ethanol generation. The difference of the conventional process is only the separation of the lignocellulosic biomass fractions (lignin, hemicellulose and cellulose) followed by additional steps as pretreatment and hydrolysis. Lignocellulosic residues, such as sugarcane straw, can be used to produce second generation ethanol. The main goal of this work was the study of the pretreatment of sugarcane straw with sodium hydroxide, in different concentrations and different application times, in order to find the best conditions regarding the solubilization of the macromolecular components that may favor the access of the enzymes to the cellulose, in the stage of enzymatic hydrolysis. The work was carried out in three main steps. Firstly, the straw was sieved, washed and dried in order to obtain a homogeneous sample of 20 mesh. In the second stage, the straw was subjected to a pretreatment according to an experimental planning, named 22, whose main variables studied were NaOH concentration (1 - 4%, w/v) and the time of application (10-30 min). All pretreatment tests were carried in autoclave at 121 ° C, keeping a solid feed in 10% (w/v). The efficiency of the pretreatments was verified first of all, by the determination of the solubilization of the macromolecular components and followed by the release of the reducing sugars in the enzymatic hydrolysis step. In the third part of this work, the solid straw fractions, obtained in each pretreatment, were submitted to enzymatic hydrolysis, in duplicate, at 50 ºC, and pH 4.8 (buffer solution of sodium citrate), under constant stirring of 150 rpm, applying then a load of 15 FPU/gstraw of an enzyme from the Cellulase Complex (Novozymes), during 72 hours. The pretreatment with NaOH 4% (w/v), during 10 and 30 minutes, presented the highest solubilization of macromolecular components, 55.06 and 56.54%, respectively. Regarding the release of reducing sugars, after the step of enzymatic hydrolysis, values were obtained from 7.19 to 19.33 g/L, among the highest concentrations of 15, 61 and 19.33 g/L, and application times of 10 and 30 minutes, respectively, under 4% NaOH concentration (w/v). Those conditions were the most severe ones applied in this study. The results were statistically analyzed using the software Statistica 10.0. The coded models for the solubilization of the macromolecular components (Scm) to the reducing sugars released in the enzymatic hydrolysis (ARHE) were significant, presenting 95% confidence. Therefore, there is evidence that alkaline pretreatment and enzymatic hydrolysis are alternatives to ethanol production from sugarcane straw.