Dilute sulfuric acid pretreatment of cardoon for ethanol production

Cardoon (Cynara cardunculus L.) is an herbaceous species originating in the Mediterranean area that can be considered as a potential lignocellulosic feedstock for biofuels and high added value products.In this work, cardoon biomass (stems and leaves) was pretreated with dilute sulfuric acid in a batch reactor. The effect of temperature (160–200 °C), acid loading (0–0.2%, w/w) and solid/liquid ratio (5–10%, w/v) on overall sugar yields was studied using a response surface method according to a Box–Behnken experimental design. Overall xylose yield reaches a maximum of 90% of the content in raw material at 180 °C and 0.1% (w/v) acid addition and 7.5% (w/v) solid concentration. Regarding overall glucose yield, best results were achieved at 200 °C, 0.2% (w/w) acid loading and 7.5% (w/v) solid concentration. According to statistical optimization used optima conditions to maximize both overall glucose and xylose yield were 184.5 °C and 0.15% (w/v) acid concentration. At these conditions, 70% and 93% of glucose and xylose, respectively, could be recovered. The highest simultaneous saccharification and fermentation (SSF) yields are obtained when biomass was pretreated at 200 °C with 0.2% sulfuric acid reaching values close to 65% of theoretical.