Acid hydrolysis of lignocellulosic materials for the production of second generation ethanol

Brazil is one of the countries with the largest agricultural production in the world, consequently, it generates large amounts of agro-industrial residues that are used as biomass in the production of second-generation ethanol, a renewable energy alternative capable of replacing fossil fuels. The objective of this work was to study the effect of diluted acid hydrolysis in different types of lignocellulosic residues and the production of 2G ethanol from these hydrolysates using different fermenting microorganisms. The hydrolysis experiment was carried out with different concentrations of sulfuric acid (0-5%) submitted to different heating times in an autoclave (10-15 min.). Analyzes of total reducing sugars and phenolic compounds were performed before fermentation by the microorganisms produced ethanol. Fermentation ocured for 24 hours at 30 ºC, with tests of different agitation of the fermented broth. The acid hydrolysis condition that released the highest amount of fermentable sugars was 5.0% sulfuric acid and the contact time with the biomass was 15 min. heating in an autoclave at 121 °C. The material that showed the highest release of sugars after acid hydrolysis was cassava residue, with 131.09 g.L-1 of reducing sugars. The fermentations were carried out with microorganisms individually and in consortium. The largest production of 2G ethanol was from the hydrolyzate of soybean hulls, from 47.70 g.L-1 of ethanol with a productivity of 5.96 g.L-1.h-1 by the consortium of Zymomonas mobilis and Candida tropicalis, during 8 h of fermentation. The hydrolyzed lignocellulosic materials released fermentable sugars that resulted in the production of second-generation ethanol.