Abstract
As the main component of lignocelluloses materials, cellulose is a biopolymer consisting of many glucose units connected through ß-1,4-glycosidic bonds. The breakage of the ß-1,4-glycosidic bonds by acids leads to the hydrolysis of cellulose polymers, resulting in the sugar molecule glucose or oligosaccharides. Mineral acids, such as HCl and H2SO4, have been used in the hydrolysis of cellulose. The lignocellulosic materials usually require a first step of pretreatment due to the association between the three major components of plant cell wall (cellulose and hemicelluloses fractions and lignin) in order to make available the monomeric sugars found in these fractions, for fermentation to ethanol. Different procedures have been employed, for example, acid hydrolysis, alkali hydrolysis, steam explosion, among others. The pretreatment using dilute sulfuric acid (acid hydrolysis) is the most widely used for having high efficiency in the separating process of cell wall components resulting in hemicellulose hydrolysate and cellulignin. A second step for obtaining the cellulose present in the cellulignin, studies have shown a need for delignification stage using sodium hydroxide as catalyst. The cellulose is submitted to acid or enzymatic hydrolysis to solubilize the glucose (cellulose hydrolyzate). Regardless of intense research on cellulose hydrolysis process by enzymatic way, the amount of hydrolyzate obtained in this process is still less than the amount required for subsequent studies on the fermentation of these hydrolysates which opens the option of research for the use of chemical hydrolysis. In order to use sugarcane bagasse as a substrate for ethanol production, optimum conditions for acid hydrolysis of cellulose fraction were investigated. A 23 full factorial Central Composite Design (CCD), including three replications at the center point was applied to evaluate the effect of temperature, acid concentration and reaction time on extraction efficiency. In this study, the hydrolysis of cellulose conditions varied in terms of sulfuric acid (H2SO4) concentration (2-6 %, w/v), reaction time (10-30 min) and incubation temperature (155-175 °C). The experiments were carried out using a 200-ml stainless-steel container (19 x 7 cm), which was tightly sealed and immersed in a silicone bath provided with electrical heating. The maximum extraction efficiency (E) was 71 % under the conditions of 2 % of H2SO4 at 155 °C for 10 min, which the main components (in g L-1) in the hydrolysate were glucose, 22.74; 5-hydroxymethylfurfural, 0.206; furfural, 0.145 and no xylose, arabinose and acetic acid formation was detected. Experiments will be performed to evaluate the fermentability of this hydrolysate to ethanol by Scheffersomyces stipitis.
