In this work, in natura sugar cane bagasse - SCB (39.0% cellulose, 30.0% hemicellulose and 21.6% lignin), donated by Centro de Tecnologia Canavieira (Piracicaba, Brazil), was pretreated with NaOH. The influence of sodium hydroxide concentration (1.0-7.0% w/v) and of residence time (15-90 min) was investigated using factorial design. Treatments were performed in an autoclave at 121 oC/2.0 bar). Samples were taken before and after the pretreatments, and characterized chemically and using SEM.
The selected pretreatment condition was 7.0% of NaOH and residence time of 30 minutes. In this condition, the loss of cellulose was 1.2%, with 81.3% removal of lignin and 83.9% of hemicellulose. A higher normality of the alkaline solution seems to be advantageous in the present case. This is actually an optimization problem: the amount of acid released by the hydrotreatment in the autoclave must be enough to make soluble the hemicellulose fraction, but not so high to attack and degrade the cellulosic glucose.
The pretreated SCB material was hydrolyzed employing 10% of solid loading and 20 FPU/g-cellulose (Accellerase 1500, Genencor). The experiments were carried out in 250 mL Erlenmeyer flasks (200 rpm, pH 4.8, 50 oC). A yield of ca. 75% was obtained in all assays.
Fermentation experiments were carried out in shake flasks (commercial Saccharomyces cerevisiae, 250 rpm, 30 oC). In all experiments around 90% of the theoretical fermentation yield was reached.