Desirability function for optimization of Dilute Acid pretreatment of sugarcane straw for ethanol production and preliminary economic analysis based in three fermentation configurations

Sugarcane straw is a lignocellulosic residue accumulated during the harvest of sugarcane and is a potential feedstock for second generation biofuel. This work covers the optimization of pretreatment step in the ethanol production using a complete factorial design (23), where the analyzed factors were temperature, acid concentration and time in the Dilute Acid pretreatment. Desirability function was applied in this stage to maximize sugar yields and minimize inhibitor concentrations, resulting in overall sugars yield ∼60% and furfural concentration of 0.5 g/L. An enzymatic hydrolysis stage was done to increase sugar release. The fermentation stage was studied through three different configurations, such as Separate Hydrolysis and Fermentation (SHF), Simultaneous Saccharification and Fermentation (SSF) and Presaccharification and Simultaneous Saccharification and Fermentation (PSSF). The most promising alternative turned out to be PSSF due its higher ethanol concentration, with a value of 14.8 g/100 g dry weight (DW) biomass, equivalent to 187 L/tonne DW using C6-sugars. The economic analysis revealed that the integration between enzymatic hydrolysis and fermentation in the ethanol production affected the total capital cost. The cost of raw materials (sugarcane straw and enzymes) had the most significant impact on the total production cost and accounted between 35.66 and 25.88% of the total cost of the ethanol plant from sugarcane straw.