Abstract
Sorghum, a starch-containing plant, is a potential valuable bioenergy crop because of its drought tolerance, limited growth needs, and limited use as a feedstock. Production of ethanol from sorghum needs optimization to yield a maximum amount of bioethanol at a minimum energy cost. The hydrolysis pretreatment includes liquefaction and saccharification, resulting in glucose, a substrate for fermentation. A maximized glucose yield from hydrolysis should lead to a maximized ethanol yield from the entire process.
In this work biomass concentration and hydrolysis temperature were examined, and the resultant glucose yield was determined. Initial experiments used 28% (w/v) sorghum in water in a 500-mL, three-necked reactor vessel placed directly on a hotplate. This setup produced a bottom-up heating gradient that resulted in low glucose yields. This was improved by including an oil bath that allowed temperature regulation within 1°C. Liquefaction of a 28% (w/v) aqueous sorghum slurry at 85°C, using the oil bath resulted in 26.6 g/L glucose compared to 11.8 g/L glucose, when the hotplate was used. Previous methods using the same experimental setup but without the oil bath had only a 0.062 g/g (glucose/sorghum) yield whereas the oil bath methodology yielded 0.088 g/g, an approximately 42% increase in glucose yield per batch reaction. Because each liquefaction requires approximately 81.5 kJ for a two-hour incubation at 85°C, maximizing glucose yield per batch reaction is an important task for making bioethanol production less energy intensive.