Highly Efficient Fractionation of Cornstalk into Noncondensed Lignin, Xylose, and Cellulose in Formic Acid

Traditional pretreatment of lignocellulose is usually conducted under higher acidic and high temperature conditions, which leads to both the degradation of sugar and the condensation of lignin, hindering the subsequent conversion. An effective approach to fractionate lignocellulose into 93.9% of noncondensed lignin, 99.4% of cellulose, 17.8% of xylose, and 66.7% of xylooligosaccharides under mild conditions was developed using the formic acid solution at 80 °C for 100 min. The β-O-4 bond content of lignin fractionated with formic acid (54.6 per 100 C9 units) was higher than dioxasolv lignin (48.4 per 100 C9 units), indicating that formic acid pretreatment well protected the ether bonds in lignin. Therefore, the hydrogenolysis of fractionated lignin contributed to 28.0% of aromatic monomer yield, which was comparable to dioxasolv lignin. As cellulose possesses a large amount of porosity because lignin was separated from lignocellulose, the hydrolysis of fractionated cellulose by molten salt hydrates gave a 96.4% of glucose yield.