Otimização do pré-tratamento da palha da cana-de-açúcar com ácido sulfúrico e hidrólise enzimática para obtenção de açúcares fermentescíveis

Abstract

The present work proposes the optimization of acid pretreatment followed by enzymatic hydrolysis of sugarcane straw for a second generation of second generation ethanol. For this, pretreatment of the lignocellulosic material was performed with a liquid solid ratio of 0.5: 10 in dilute solution of sulfuric acid. In the proposed experimental design - a rotational composite central delineation (RCCD) 2² where four tests were included in the axial conditions and three repetitions in the central point, the factors evaluated in the optimization were: sulfuric acid solution concentration (0.10 - 2, 90 % m/v) and pretreatment time performed in a vertical autoclave at 120 ° C and 1 Kgf/cm² for 14-55 minutes. The response variables defined for the optimization were: the glucose mass released as a function of the initial sugar cane straw mass of the pre-treatment, and the concentration of soluble solids released measured in degrees Brix (°B). The results showed that the optimized condition for the release of glucose and also soluble solids was the condition of sulfuric acid at 2.0 % w/v concentration with time of 40 minutes in autoclave, where a concentration of 0.194 g glucose/g sugar cane straw and 3.2 °B. Statistical analysis showed that the concentration of sulfuric acid (linear and quadratic) and autoclave time (linear and quadratic) were statistically significant (by p-value analysis) in a 95 % confidence interval for the mass response variable glucose per sugarcane straw mass; while for the soluble solids concentration variable, only the concentration of sulfuric acid (linear and quadratic) was statistically significant. In addition, the ANOVA (analysis of variance) analysis showed that the predicted model is statistically significant with R² of 96.77 % for the variable mass response of glucose by sugar cane straw mass, and 92.59 % for the soluble solids concentration variable. It was also observed that the calculated F for the two response variables is larger than the table F, confirming in both cases the significance of the proposed mathematical models. In the enzymatic hydrolysis carried out with the commercial enzyme Celluclast® 1,5L with a load of 15 FPU/g of biomass, a digestibility of 68.71 % of the sugarcane straw cellulose used was verified, whereas 35.59 % of the biomass total cellulose was converted to glucose. Thus, it was concluded that the sulfuric acid concentration is the factor with the greatest impact on the conversion of sugarcane straw to fermentable sugars and also on the release of soluble solids in the pre-treatment stage. In enzymatic hydrolysis, the overall yield of cellulose to glucose obtained was 35.59 % due to the low concentration of β-glycosidases in the enzyme used.