Direct separation of acetate and furfural from xylose by nanofiltration of birch pretreated liquor: Effect of process conditions and separation mechanism

•Nanofiltration as simple and effective way to separate monosaccharides from PTL.•Over 99% of xylose purity was achieved after three diafiltration rounds.•Increasing pressure caused compression, which changed separation mechanism.•Charge density and electrostatic repulsion increased at increasing pH.•Cake-layer formation was identified as the main fouling mechanism.