Pretreatment and hydrolysis conditioning process of cellulosic material for bioethanol production

Abstract

Sweet sorghum straw is lignocellulosic material that is promoted as an alternative feedstock for ethanol production because it is available and inexpensive. Due to its composition of cellulose and hemicelluloses, that could be hydrolyzed into fermentable sugars. The composition of sweet sorghum straw used in this study consists of 44.51% cellulose, 38.12% hemicelluloses and 6.18% lignin. Conversion of this potential feedstock requires a pretreatment step to alter the microscopic size and structure of the lignocelluloses. This research was studied in order to find the optimum conditions on hydrolysis of sweet sorghum straw. The biomass was mixed with dilute sulfuric acid (0-3%v/v) with solid loading of 10% w/v and then pretreatment at high temperatures (120-190°C) for 10-30 min of pretreated times. The maximum vield of glucose and xylose from sweet sorghum straw was 0.234 g glucose/g dry substrate and 0.208 g xylose/g dry substrate, respectively, at the pretreatment condition: 120°C, 3%H2So4 for 10 min. After chemical pretreatment, the pretreated sweet sorghum straw was hydrolyzed with commercial cellulose. Four variables of saccharification condition were investigated; a substrate concentration (1-7%), cellulose concentration (Celluclast 1.5, Novozyme) (15-35 FPU/g substrate), a temperature (30-70°C) and a pH (3-7). The optimum conditions were 1% of substrate concentration, 15 FPU/g-substrate of cellulose, at temperature 40°C and pH of 5. Obviously, glucose was the only monosugar detectable with the yield of 0.344 g glucose/g dry solid under this saccharification condition. Monosugars liberated from the pretreated sweet sorghum straw and the saccharified pretreated sweet sorghum straw was used as carbon source for ethanol fermentation by Saccharomyces cerevisiae. Fermentation condition was at 30°C, pH 5.5 and agitation rate of 150 rpm. The high yield of ethanol concentration, of 15.40 g-ethanol/100 g-total sugars after 12 h of cultivation was obtained when using monosugar liberated from the saccharified acid pretreated sweet sorghum straw as substrate.