Acid hydrotropic fractionation of switchgrass at atmospheric pressure using maleic acid in comparison with p-TsOH: Advantages of lignin esterification

Abstract Switchgrass was fractionated using maleic acid (MA) as an acid hydrotrope in comparison with p-toluenesulfonic acid (p-TsOH) at atmospheric pressure. MA achieved more rapid and greater maximal dissolution of lignin and hemicelluloses (88 % and 63 %, respectively) than did p-TsOH (73 % and 55 %, respectively). MA esterified (carboxylated) the dissolved acid hydrotropic lignin (AHL) as evidenced by 2D 1H-13C HSQC NMR analysis, which improved AHL antioxidant ability compared with AHL from p-TsOH that is not carboxylated. MA also carboxylated the lignin and cellulose in the fractionated cellulosic water-insoluble solids (WIS), which significantly improved WIS enzymatic digestiblity for sugar production than did p-TsOH with the same level of delignification. It also improved the lignin lubrication effect to facilitate mechanical fibrillation of WIS into lignocellulosic nanofibrils. MA is an FDA-approved indirect food additive (21CFR175-177) with lower acidity and solubility than p-TsOH, which substantially benefits recycling and decreasing environmental impacts to achieve sustainability.