Rapid and efficient separation of eucalyptus hemicellulose by synergistic catalysis of acid and ketone in α-ketoglutaric acid pretreatment.

The efficient catalytic hydrolysis and mitigation of unstable structural transitions in lignin are essential for the commercialization of organic acid pretreatment. A novel binary carboxylic acid pretreatment utilizing α-ketoglutaric acid (AKA) was developed, which exploits a distinctive ion-pair biomimetic catalytic mechanism along with the activation of the ketone group. Under optimal AKA pretreatment conditions (5 % acid concentration, 150 °C, 45 min), the hemicellulose separation yield reached 85.21 %. The rapid and efficient separation of eucalyptus hemicellulose results from the low pKa value and the ion-pair biomimetic catalytic mechanism of AKA. The lignin structure exhibited greater integrity (β-O-4: 47.45 %) and a higher phenolic hydroxyl content (1.82 mmol·g-1) compared to conventional binary carboxylic acid pretreatments (maleic and oxalic acids). These findings indicated that the recondensation of lignin, which occurs after the cleavage of aryl-ether bonds during acidic catalysis, was inhibited by the activation of ketone groups during AKA pretreatment. This study introduces an innovative methodology for developing efficient binary carboxylic acid pretreatment procedures focused on selective hemicellulose separation, emphasizing effective catalytic hydrolysis and the maintenance of lignin reactivity.