2-23: Reducing the chemical loads in alkaline-sulfite pretreatment for sugarcane bagasse from experimental hybrid plants containing reduced lignin content

Alkaline-sulfite pretreatment of lignocellulose is efficient in increasing enzymatic digestibility of the pretreated material with minimal removal of lignin and hemicellulose. Residual lignin remains partially sulfonated, increasing the hydrophilicity and swelling of the fibers. Negatively charged lignin may additionally lead to less unproductive adsorption of cellulases.  In prior research, it was demonstrated that selected plants with reduced lignin content can take advantage of this pretreatment process. This work reports the alkaline-sulfite pretreatment of bagasse recovered from sugar cane hybrids selected for low lignin content. Varied loads of sodium hydroxide (2.5%, 3.75% e 5%) and sodium sulphite (5%, 7,5% e 10%) were used. Reactions with alkaline sulphite at 120 ^oC for 2h proved efficient in dissolving part of the lignin and hemicellulose resulting in a pretreated material susceptible to efficient enzymatic hydrolysis. Maximum hydrolysis efficiencies were 92 and 77% for cellulose and xylan conversions, respectively. Although reference samples and experimental hybrids with low lignin content gave similar efficiencies in enzymatic hydrolysis, the hybrids with less original lignin presented increased initial hydrolysis rates. Furthermore, the hybrids with originally less lignin required lower chemical loads in the pretreatment to achieve a defined level of cellulose conversion. Compiled data indicated that alkaline-sulfite pretreatment was efficient to increase the enzymatic saccharification of the sugar cane bagasse samples. The hybrid raw-materials with reduced lignin content required lower dosages of chemicals during the pretreatment step and also provided increased hydrolysis rates.