Response surface optimization of corn stover pretreatment using dilute phosphoric acid for enzymatic hydrolysis and ethanol production

Dilute H3PO4 (0.0–2.0%, v/v) was used to pretreat corn stover (10%, w/w) for conversion to ethanol. Pretreatment conditions were optimized for temperature, acid loading, and time using central composite design. Optimal pretreatment conditions were chosen to promote sugar yields following enzymatic digestion while minimizing formation of furans, which are potent inhibitors of fermentation. The maximum glucose yield (85%) was obtained after enzymatic hydrolysis of corn stover pretreated with 0.5% (v/v) acid at 180 °C for 15 min while highest yield for xylose (91.4%) was observed from corn stover pretreated with 1% (v/v) acid at 160 °C for 10 min. About 26.4 ± 0.1 g ethanol was produced per L by recombinant Escherichia coli strain FBR5 from 55.1 ± 1.0 g sugars generated from enzymatically hydrolyzed corn stover (10%, w/w) pretreated under a balanced optimized condition (161.81 °C, 0.78% acid, 9.78 min) where only 0.4 ± 0.0 g furfural and 0.1 ± 0.0 hydroxylmethyl furfural were produced.