Extraction of xylan from sugarcane bagasse through mild hydrothermal treatment with phosphoric acid-based porous geopolymers

The conventional acid extraction of xylan is inevitably accompanied by serious water pollution. This paper presented a sustainable treatment process for extracting xylan from sugarcane bagasse by phosphoric acid-based porous geopolymers containing sodium (Na-PAG) under mild hydrothermal conditions. The experimental investigation showed that the maximum xylan relative extraction rate reached 25.9% when the hydrothermal reaction time was 4 h, the hydrothermal temperature was 150 °C, the pH was 2, the mass ratio of bagasse fiber to Na-PAG was 3, the mass ratio of water to bagasse fiber was 8, and the bagasse fiber meshes were 40–80. Compared to the difference in hemicellulose content before and after the reaction using the Van Soest method, the selectivity of Na-PAG for hemicellulose was as high as 89.32%. The high acidity required for hemicellulose depolymerization was reduced by the “acid slow-release” property of Na-PAG. The black liquor obtained after separating xylan and Na-PAG can also be used for repeated experiments. The treatment process enables the reuse of solid and liquid waste, which is crucial for sugar-paper co-production and clean production.