Evaluation of an organosolv-based biorefinery process to fractionate wheat straw into ethanol and co-products

In this study, organosolv pre-extraction of wheat straw (WS) was conducted to extract lignin for understanding the effect of silica on enzymatic hydrolysis of carbohydrates. The results showed that the presence of silica in the WS substrate was associated with a decreased conversion of carbohydrates into monomeric sugars during enzymatic hydrolysis. Then, a sequential two-stage pretreatment process comprising ethanol pre-extraction and alkaline pretreatment was investigated to convert WS carbohydrates into bioethanol and recover lignin and silica. The results demonstrated that the pre-extraction with ethanol at 160 °C for 50 min followed by alkaline treatment with 11% sodium carbonate (Na2CO3) was sufficient to generate a highly digestible substrate. 85.7% of the original sugars in the raw feedstock was recovered by two-stage pretreatment followed by enzymatic hydrolysis with an enzyme loading of 12 FPU/g glucan. Fermentation with Saccharomyces cerevisiae SR8 u strain consumed 97.8% sugars in the hydrolysate to reach 6.5% w/v ethanol titer. With this proposed process, about 89.1% silica and 62.5% lignin were recovered at high levels of purity.