Rapid and mild fractionation of hemicellulose through recyclable mandelic acid pretreatment

[Display omitted] •A new organic acid, mandelic acid pretreatment method was discovered.•Rapid and efficient separation of hemicellulose was realized.•The good reuse performance of mandelic acid pretreatment was proved.•Lignin, rich in phenolic hydroxyl groups, was retained in the residual solids. The development of organic acid pretreatments from biological sources is essential to facilitate the progress of green and sustainable chemistry. In this study, the effectiveness of mandelic acid pretreatment (MAP) was analyzed for eucalyptus hemicellulose separation. 83.66% of xylose was separated under optimal conditions (temperature: 150 °C; concentration: 6.0 wt%; time: 80 min). The hemicellulose separation selectivity is higher than acetic acid pretreatment (AAP). The stable and effective separation efficiency (56.55%) is observed even after six reuses of the hydrolysate. Higher thermal stability, larger crystallinity index and optimized surface element distribution in the samples were demonstrated by MAP. Lignin condensation is effectively inhibited through MAP, as determined from the structural of different lignin. In particular, the demethoxylation of lignin by MA was found. These results open up a new way to construct a novel organic acid pretreatment for separating hemicellulose with high efficiency.