Production of fuel ethanol with diluted phosphoric acid steam explosion pretreated sweet sorghum

Sweet sorghum was considered as raw material for ethanol production. In this work, sugars from the lignocellulosic material were released by steam explosion of dilute-phosphoric-acid-soaked sweet sorghum. The pretreatment conditions used were 190°C, 0.5% (w/w) phosphoric acid (on a dry weight basis), and 5 min residence time. Following pretreatment, a 6 h liquefaction step was carried out using the commercial enzymes Cellic CTec2^® from Novozyme.  After liquefaction, the whole slurry was transferred to the fermentation vessel, where it was inoculated using the ethanologenic strain Escherichia coli SL100.  Results show that total sugars obtained from pretreatment reached some 50 g/L, with xylose as the main sugar. During fermentation, glucose was completely consumed within 24 h and xylose within 48 h. The maximum ethanol titer obtained was 22.5 g/L after 48 h. The process was successfully scaled up to an 80 L fermentation. To conclude, sweet sorghum can be considered a viable feedstock for ethanol production. Further studies will focus on process optimization.