Sequential Ion-Exchange Polishing of Oil Palm Trunk-Derived XOS-Containing Liquor: Effects of Holding Time and Water Washing on Sugar Recovery and Impurity Removal

High Resolution Image Download MS PowerPoint Slide Downstream purification of lignocellulosic XOS-containing hydrolyzates requires effective impurity removal while minimizing the loss of the sugar-containing fraction. In this study, oil palm trunk (OPT)-derived XOS-containing liquor was purified by activated carbon pre̵-purification followed by sequential anion- and cation-exchange treatment, with emphasis on the effects of ion-exchange holding time and post-elution water washing on reducing sugar recovery and impurity removal. Activated carbon acted as the primary cleanup step, whereas ion exchange served as a polishing step for the partially purified fraction. In the ion-exchange study, holding time markedly affected recovery, with 10 min giving the highest reducing sugar recovery after both anion exchange (57.92%) and cation exchange (14.20%) while maintaining high impurity removal. Under this optimized holding time, post-elution washing with 1 L distilled water further increased recovery to 94.03% after anion exchange and 92.26% after cation exchange, while preserving substantial removal of furfural, acid-soluble lignin (ASL), and hydroxymethylfurfural (HMF). Application of the optimized downstream sequence at larger scale retained 72.18% of the reducing sugars and achieved final furfural, ASL, and HMF removals of 98.03, 98.73, and 98.76%, respectively. However, HPLC analysis showed that the final purified fraction remained xylose-dominant rather than DP2–DP6 XOS-dominant, indicating that downstream polishing improved cleanup and sugar recovery but could not overcome the saccharide profile generated during upstream hydrolysis. These findings establish a recovery-conscious polishing strategy for OPT-derived XOS-containing liquor and highlight the need to couple downstream purification with upstream hydrolysis control to improve final XOS selectivity.