ACID-HYDROLYSIS OF SUGAR-BEET PULP AS PRETREATMENT FOR FERMENTATION

Substrate pretreatment is a cost-sensitive operation in the production of ethanol from lignocellulosic materials. The general purpose of thi s work is to optimize substrate pretreatment by selectively solubilizi ng the hemicellulose fraction to render a cellulose-enriched fraction for further fermentation or enzyme hydrolysis. Hemicellulose hydrolyza te, usually a waste stream, is proposed to be fermented by the pentose -utilizing yeast Pichia stipitis. Sugar beet pulp (SBP) was chosen as a substrate due to its low lignin content which makes substrate pretre atment simpler and less expensive. Hemicellulose utilization is very i mportant in the case of SBP, whose hemicellulose content is as high as 50%. Conditions for SBP pretreatment by acid hydrolysis were optimize d, SBP and acid (HCl and H2SO4) concentrations, agitation, temperature and particle size were analyzed as key variables. Experiments were pl anned according to a factorial design, the objective function to be op timized being the percentage ratio of hydrolyzed hemicellulose to hydr olyzed cellulose. SBP concentration was always more than 50 g/l to obt ain a high sugar concentration in the hydrolyzate. The best conditions for SBP pretreatment were: 55 g/l of 32-50 mesh SBP, 1.1 g H2SO4/g SB P, 90 min at 80 degrees C and 400 rpm. Under such conditions, 86.3% an d 7.8% of cellulose and hemicellulose hydrolysis, respectively, were o btained.