Hydrothermal carbonization of cellulose, lignin, D-xylose (substitute for hemicellulose), and wood meal (WM) was experimentally conducted between 225 and 265 °C, and the chemical and structural properties of the hydrochars were investigated. The hydrochar yield is between 45 and 60%, and the yield trend of the feedstock is lignin > WM > cellulose > Dxylose. The hydrochars seem stable below 300 °C, and aromatic structure is formed in all of these hydrochars. The C content, C recovery, energy recovery, ratio of C/O, and ratio of C/H in all of these hydrochars are among 63−75%, 80−87%, 78−89%, 2.3− 4.1, and 12−15, respectively. The higher heating value (HHV) of the hydrochars is among 24−30 MJ/kg, with an increase of 45−91% compared with the corresponding feedstock. The carbonization mechanism is proposed, and furfural is found to be an important intermediate product during D-xylose hydrochar production, while lignin hydrothermal carbonization products are made of polyaromatic hydrochar and phenolic hydrochar. The formation of microspheres on the surface of cellulose and WM hydrochars is discussed, and transformation of the hemicellulose should be the reaction for WM microsphere production.

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Amorphous carbon-based sulfonated catalysts were generated from four kinds of biomass (lignin, cellulose, wood meal and D-xylose) by hydrothermal carbonization at various temperatures (225, 245 and 265 uC) followed by sulfonation, with a yield of 36-56%. All of these catalysts showed aromatic structure, hydroxyl and carboxyl groups, with a density of SO 3 H groups between 0.56 and 0.87 mmol g 21 . 5-Hydroxymethylfurfural (HMF) was produced from inulin in ionic liquids (ILs) in one step with the addition of carbon-based sulfonated catalysts, with a factual yield of 47-65% at 100 uC, 60 min. Moderate extension of reaction time (from 30 to 90 min) and increase of temperature (from 80 to 120 uC) promoted HMF production. Ethyl acetate was used as extractant, and about 39-55% of HMF can be recovered from ILs. One problem with these carbon-based sulfonated catalysts was that they would be partly deactivated in ILs for separate reuse, however, they can be easily regenerated by dilute sulfuric acid treatment. The carbon-based sulfonated catalysts exhibited good catalytic activity compared with traditional solid acid catalysts, and the carbon-based sulfonated catalyst/ILs reaction system showed high reusability. In consideration of the renewable as well as the high catalytic activity abilities, these biomass derived carbonbased sulfonated catalysts would be promising for industrial application.

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