Lignocellulosic Agroresidual Waste Materials to Liquid Biofuels – A Green Technology Process

Abstract

Lignocellulosic biomass is the most abundant biomass available in the world. The recalcitrant cell wall of lignocellulosic biomass makes pretreatment a necessary action. Efficient pretreatment results in production of maximum sugars from enzymatic hydrolysis and minimize their loss. Various solvents have been developed for the pretreatment of lignocellulosic biomass viz. ionic liquids, DES and natural deep eutectic solvents (NADES). Recently, research on NADES is considered to be a new subject in chemistry and is rapidly gaining interest. Besides environmental friendly, employing NADES in advancement of the existing biorefinery seems to be a promising approach for clean fractionation or pretreatment of the lignocellulosic biomass residues. Production of cellulosic ethanol was carried out by lactic acid and choline chloride (LA-CC) mixture based NADES pretreated ricestraw through separate saccharification and fermentation process. Also, comprehensive evaluation on solvent recovery and its reusability, extraction of high purity lignin and xylan, and reducing sugars production were performed. Pretreatment at 5% and 10% solid loadings using LA-CC mixture at molar ratio of 9:1 and subsequent enzymatic saccharification at 10% and 25% biomass loadings produced maximum glucose yields of 38.1±1.2 g/L and 90.2±2.3 g/L with glucan conversion efficiency of 40.3 % and 31.4 %, respectively. Further fermentation of produced reducing sugars with Clavispora NRRL Y-50464 at 9 % glucose concentration produced maximum ethanol yield of 37.1 g/L in 36 h with 80.8% conversion efficiency. Besides, NADES pretreatment of ricestraw solubilised 72-75 % of biomass bound lignin from which nearly 86 – 90 % lignin was recovered from the liquid spent wash extract. Moreover, nearly 99% of the treated NADES reagent was recovered and reused in three consecutive biomass pretreatment cycles with no loss in both pretreatment efficiency and production of reducing sugar yields. This clearly indicates a promising integrated process of green technology for cellulosic ethanol production from ricestraw.