Formation of organic acids during cellobiose decomposition in hot-compressed water

•Major organic acids produced from cellobiose decomposition were quantified.•Saccharinic acid has the highest yield and selectivity on a carbon basis.•Formic acid contributes the largest to the hydrogen ion in the liquid product.•Reaction pathways for organic acids production are summarised. This paper systematically reports the major organic acids produced during cellobiose decomposition in hot-compressed water (HCW) at 200–275 °C and a residence time of 8–66 s. Saccharinic, formic, lactic and glycolic acids are identified and quantified using high-performance anion exchange chromatography with conductivity detection and mass spectrometry (HPAEC-CD-MS). Among the identified organic acids, saccharinic acid, which is reported for the first time in the field under non-catalytic conditions, has the highest yield (i.e., ∼5.8% at 275 °C and ∼66 s) on a carbon basis, but formic acid has the highest contribution to total hydrogen ion in the liquid product due to its high molar concentration and high dissociation constant. The results also show that the hydrogen ion concentrations contributed by the identified organic acids agree well with those calculated from the measured pH of the solutions after the reaction, especially at cellobiose conversions