A facile ionic liquid and p-toluenesulfonic acid pretreatment of herb residues: Enzymatic hydrolysis and lignin valorization

This study aimed to develop a promising biorefinery technology for the value-added utilization of herb residues by using ionic liquid (IL) assisted by aromatic acid (p-toluenesulfonic acid, TsOH) pretreatment. The result showed that the addition of low concentration of TsOH into IL could effectively deconstruct the recalcitrant intercellular structure of herb residues and rapidly extract the lignin fraction. Under the optimum conditions (79% IL, 1.0% TsOH, and 20% H2O at 130 °C and 2 h), the highest cellulose recovery yield of 96.4%, the lignin removal rate of 79.9% and ideal saccharification yield of 98.9% were achieved. Moreover, the main byproduct lignin exhibited comparable yield, high purity, and thermal stability, suggesting the potential application in the conversion of bio-based chemicals and materials. Furthermore, the IL was successfully recycled three times and the recovery rate was at least 95% each time. High saccharification yields and lignin recovery were maintained during all cycles. The hemicellulose-derived saccharides were the main impurities detected in the recycled IL. Overall, this work presents a novel green pretreatment process that can effectively utilize herb residues.