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

Abstract

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.

Characterization of the Soluble Products Formed during the Hydrothermal Conversion of Biomass-Derived Furanic Compounds by Using LC–MS/MS

“… 27 Here, the (H-2O)/C values of these carbocyclic compounds were all higher than 0, indicating that these compounds should be the byproducts released during the formation of hydrochar. 30 …”

Identification of the Soluble Byproducts Formed during the Hydrothermal Conversion of Cellulose Catalyzed by Solid Tungstated Alumina

“…The C atoms of these detected compounds were in the range of 3–12, and the O atoms were in the range of 3–6, quite similar to the soluble compounds formed during the hydrothermal carbonization of glucose. 22 , 28 …”

“…On the other hand, our previous studies suggested that the hydrochar and carbocyclic compounds were also formed by condensation/polymerization of the α-carbonyl aldehydes. 19 , 20 , 28 Thus, α-carbonyl aldehydes were proposed to be the key intermediate for the formation of the carboxylic acids, the carbocyclic compounds, and the hydrochar.…”

“…Then, those formed α-carbonyl aldehydes could be converted through three main routes: (1) the α-carbonyl aldehydes could undergo a Cannizaro reaction to generate C 3 -C 6 α-hydroxy acids, such as lactic acid and 2,5,6-trihydroxyhex-3-enoic acid; (2) the α-carbonyl aldehydes could undergo hydrolytic C–C cleavage to release carboxylic acid; (3) the α-carbonyl aldehydes could undergo aldol condensation to generate initial polymers, which then further undergo polymerization/condensation to hydrochar or undergo a C–C cleavage reaction to release some carbocyclic compounds containing hydroxy groups and carbonyl groups. 28 …”

“…The corresponding ion formula of the ion peaks in the MS and MS 2 spectra were determined by software developed in our lab, and the core structures and the functional groups of the detected compounds were determined through the ion formula. 28 The corresponding formulas of ions with m / z at 95.01, 97.03, 107.01, 123.01, and 125.02 were [C 5 H 3 O 2 ], [C 5 H 5 O 2 ], [C 6 H 3 O 2 ], [C 6 H 3 O 3 ], and [C 6 H 5 O 3 ], respectively, all of which were proposed to contain furanic structures because the DBEs of these ions were no less than 3 and the number of oxygen atoms of those ions was no less than 2. The formulas of ions with m / z at 79.05, 91.05, 93.07, 95.05, 105.07, 107.05, 133.06, and 147.08 were [C 6 H 7 ], [C 7 H 7 ], [C 7 H 9 ], [C 6 H 7 O], [C 8 H 9 ], [C 7 H 7 O], [C 9 H 9 O], and [C 10 H 11 O], respectively, all of which were proposed to contain carbocyclic structures because the DBEs of those ions were no less than 3 and the number of oxygen atoms of those ions was no more than 1.…”