Dilute sulphuric acid pretreatment and enzymatic hydrolysis of Jatropha curcas fruit shells for ethanol production

• Dilute-acid pretreatment of Jatropha curcas shells for enzymatic hydrolysis was assessed.
• Cellulose conversions above 80% were achieved in the enzymatic hydrolysis.
• Optimal conversion was predicted for pretreatment at 136 °C, 30 min and 1.5% H2SO4.
• Water extraction prior to pretreatment was found to further improve the enzymatic conversion.

Jatropha curcas is a promising source of oil for the biodiesel industry, and the shells of its fruits could be considered for ethanol production. In this work, the composition of J. curcas shells is investigated, and the potential of dilute-sulphuric acid pretreatment for improving the enzymatic hydrolysis of cellulose is evaluated. A Box–Behnken experimental design was used for assessing the effect of temperature (110–150 °C), H2SO4 concentration (0.5–2.5%) and pretreatment time (15–45 min) on the formation of sugars during pretreatment and on the enzymatic conversion of cellulose. Cellulose conversions above 80% were achieved both in the separated enzymatic hydrolysis and in the simultaneous saccharification and fermentation of the pretreated materials. Optimal SSF conversions were predicted for pretreatments at low temperature (136 °C) and moderate acid concentrations (1.5%) and reaction time (30 min). The inclusion of an extraction step prior to the pretreatment revealed a further improvement of the enzymatic conversion of cellulose.