Monday, April 30, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Alkaline sulfite pretreatment has been used to enhance the enzymatic hydrolysis of sugar cane bagasse. The main effect of this process is a selective lignin removal with minimal hemicellulose and cellulose solubilization. The introduction of sulfonic groups in the of the bagasse fibers is also an important way for increasing the fiber swelling, making cellulose microfibrils more accessible to the enzymes. This study has analyzed the microstructure and composition of sugar cane bagasse treated at 121oC with sodium hydroxide (5%) and sulfite sodium (10%) at cooking times varying from 30 to 120 min. Pretreated samples were mechanically disintegrate and hydrolyzed with commercial cellulases. The structure changes caused in the fibers were analyzed by Scanning Electron Microscopy (SEM) and Light Microscopic, which revealed the swelling of the fiber after the pretreatment. Energy Dispersive X-ray Spectrometry (EDS) showed that the sulfur contents increased in the fiber surfaces. The sulfur contents in the surfaces were proportional to the total sulfonic groups determined by conductometric titration. Under enzymatic digestion, the samples treated for 30, 60 and 90 min presented similar residual lignin contents (approximately 11%) but differed in the contents of sulfonic groups. Accordingly, the levels of enzymatic saccarification of these materials were proportional to the contents of sulfonic groups in the samples. Compiled data suggested that, despite lignin removal, the alkaline sulfite pretreatment also facilitates the subsequent enzymatic hydrolysis by providing a residual lignin that is less hydrophobic owing the presence of sulfonic groups.