Mild and efficient two-step pretreatment of lignocellulose using formic acid solvent followed by alkaline salt

An efficient fractionation of three main components of corn cob and a good delignification effect were reported with formic acid (88%) pretreatment at 80 °C for 3 h. The pretreated substrate demonstrated a poor enzymatic digestibility with a mere 9.1% hydrolysis yield. Subsequently, various post-treatment processes after pretreatment were conducted and the mechanisms behind the effect on the hydrolysis were investigated. During pretreatment, formic acid adsorption occurred, which resulted in a significant inhibiting effect for the hydrolysis of the pretreated substrate. Mild post-treatment quickly removed the easily desorbed formic acid in the solid and cellulose accessibility was found to be increased greatly along with the decrease of formic content. After hot water and alkaline salt post-treatment, the hydrolysis yield increased to 81.2% and 98.5%, respectively. Meanwhile, the formic acid content of the substrate decreased by 15.9% and 61.4%. The restarted hydrolysis performance indicated that the factor associated with the nature of substrate, such as formic acid content, cellulose accessibility, and the existence of ester bonds, should be responsible for the enzymatic digestibility of the substrate. Herein, the proposed two-step pretreatment with formic acid (88%) followed by alkaline salt solution at room temperature demonstrates a remarkable effect on the conversion of lignocellulose material and has high feasibility for industrial application since it is mild to environment and requires low energy.