Optimization of FeSO4-assisted sulfuric acid hydrolysis for improved sugar yield from sugarcane bagasse

Abstract

Sugarcane bagasse (SB) consists of two major sugar polymers (cellulose and hemicelluloses) connected to lignin. Due to the recalcitrant nature of SB, pretreatment is considered a crucial process step before it can be converted to biomolecules. Raw SB consists of cellulose (40.4 wt%), hemicellulose (23.8wt%), lignin (27.2wt%), ash (3.0wt%) and extractives (4.4wt%). After pretreatment of SB with 8% sodium hydroxide at room temperature, the cellulosic fraction increased to 61.9wt%, while hemicellulose and lignin fraction decreased to 17.1wt% and 10.8 wt%, respectively. Design of experiment was employed to optimize FeSO4-assisted sulfuric acid hydrolysis conditions. The experimental results and predicted values showed strong agreement with high R2 value of 0.995. The highest glucose yield of 90.04% was obtained with 1.5% sulfuric acid, 40mmol/L FeSO4 and 120min, corresponding to predicted value of 88.98%. The optimum glucose yield was attained at high levels of FeSO4 and hydrolysis time, and a low level of sulfuric acid. After validation, the experimental and predicted values of glucose yield were 88.67% and 86.55% respectively, thus confirming the success of the optimization process. Also, the hydrolysates obtained were found to contain low amounts of inhibitory compounds (furfural and 5-hydroxymethylfurfural). Saccharomyces cerevisiae IQAr/ 45-1 efficiently converted the sugar present in the hydrolysate to achieve 82.2% of theoretical ethanol yield. Thus, this process, which involved the use of cheap chemical reagents to overcome SB recalcitrance and liberate fermentable sugars, could potentially support a biorefinery.