Liquefaction of lignocellulosic biomass through biochemical conversion pathway: A strategic approach to achieve an industrial titer of bioethanol

Abstract

Owing to fossil fuel depletion, the conversion of lignocellulosic biomass into bioethanol has gained momentum in the field of transportation sector. In the present study, liquefaction of sorghum stalks has been performed for the production of fermentable sugars and their subsequent conversion into bioethanol. Pretreatment, delignification, enzymatic hydrolysis are three sequential steps involved in the liquefaction process. About 82% of hemicellulose hydrolysis was attained by the pretreatment of sorghum stalks at 121 °C with 0.2 M sulfuric acid for 120 min. Further, the pretreated residue was de-lignified with 1–5% (w/v) sodium hydroxide which resulted in 85–98.7% removal of lignin. Subsequently, around 65–99.6% of cellulose hydrolysis was attained at an optimum enzyme loading of 30 mg protein/g of glucan. The optimum liquefaction condition of sorghum stalks was achieved by performing the pretreatment process at 121 °C with 0.2 M sulfuric acid for 120 min, delignification at 121 °C with 2% NaOH for 20 min and enzymatic hydrolysis at 50 °C with 30 mg protein/g of glucan for 72 h. Furthermore, 18.4 g/L and 74.7 g/L xylulosic and cellulosic ethanol was produced from pretreatment and enzymatic hydrolysis derived hydrolysates, respectively. Finally, 97.7% of sorghum stalks liquefaction was achieved, in which 84% of holocellulose (cellulose and hemicellulose) converted into 494 g of fermentable sugars which is further converted into 225 g or 285 mL ethanol per kg of sorghum stalks (equivalent to 285 L ethanol per ton of biomass).