Pré-tratamento organossolve do bagaço da cana-de-açúcar com glicerina bruta para obtenção de açúcares fermentescíveis

Abstract

As a result of the decrease in dependence on fossil fuels, lignocellulosic biomass is one of the main alternatives for the diversification of the world energy matrix. Among biomasses, sugarcane bagasse has become attractive due to the growing scenario of sugarcane production and its potential to be converted into fermentable sugars for the production of second generation ethanol (2G). In this work, the organosolve pretreatment with crude glycerol, as a solvent for the delignification of the sugarcane bagasse and the obtaining of fermentable sugars by enzymatic hydrolysis, aiming at the production of 2G ethanol was evaluated. Experimental conditions were defined by Doehlert (23) experimental design, with three independent variables: temperature (°C), time (min) and solid-liquid ratio (RSL) (mL/g). A total of 15 experiments were performed, with three replicates of the central point. Pretreatment reactions were performed using a 80:20 crude water-glycerol mixture (80 mL glycerol / 20 mL water) as solvent in a stainless steel tubular reactor (autoclave type) under different temperatures (150 , 160, 170, 180, 190, 200 and 210° C), time (30, 60, 90, 120 and 150 min) and solid-liquid ratio (6, 8 and 10). The efficiency of the pretreatment was evaluated through the morphological and chemical characterization of the solid fraction obtained, enzymatic hydrolysis by the quantification of total reducing sugars (ART), as well as the quantification of fermentable sugars such as xylose and glucose via High Efficiency Liquid Chromatography (CLAE). The solid fraction was characterized as the final yield after pretreatment and in relation to the delignification content, removal of hemicelluloses and obtaining cellulose. The best delignification condition 210°C/60 min/8(mL/g) was for sample 9 which had 79.02% of delignification and glucose concentration of 59.49 g/L. The pretreatment condition that obtained the highest percentage of cellulose, 82.49%, was for sample 1, pretreated under the following conditions: 180 ° C/150 min / 8 (mL / g), sample that achieved the highest enzymatic conversion, 412.35 (mg / mL) of total reducing sugars (ART), using the relatively low enzyme loading 10FPU / g cellulose. Other samples pre-treated under different conditions established in the planning also achieved satisfactory conversion of total reducing sugars. When analyzed fermentable sugars such as glucose, samples 9 and 10 presented the best glucose concentration corresponding to 59.49 g/L and 59.75 g/L, respectively. In general, pre-treatment with crude glycerol favored the enzymatic hydrolysis of the pretreated substrate, the SEM and X-ray (XRD) analyzes showed that pretreatment removed lignin and hemicelluloses from the plant fiber of sugarcane bagasse, opening up the highly recalcitrant structure of biomass.