Formation of Soluble Furanic and Carbocyclic Oxy-Organics during the Hydrothermal Carbonization of Glucose

In this study, the water-soluble products formed during the hydrothermal carbonization of glucose were analyzed by liquid chromatography (LC)–mass spectrometry (MS) and LC–MS² to determine the formulas and the possible structures of the main compounds. In addition to the well-known compounds of 3-deoxyglucosone, 5-hydroxymethylfurfural, and levulinic acid, the furanic compounds and the carbocyclic oxy-organics containing hydroxy group and carbonyl group with a molecular mass range between 170 and 260 Da were also identified. Both C–C coupling reaction and C–C cleavage reaction were proved to be involved during the formation of these carbocyclic oxy-organics, so they were proposed to be released via C–C cleavage of the primary polymers, which were formed by aldol condensation of the primary precursors formed during the degradation of glucose. The identification of these carbocyclic oxy-organics was indirect evidence that aldol condensation played a crucial role during the formation of hydrochar from carbonization of glucose.