关键词: 水热碳化, 碳微球, 固体酸, 水解, 纤维素

Hydrolysis of cellulose plays a key role in the biomass utilization. As a commonly used solid acid in cellulose hydrolysis, sulfated activated carbon normally prepared from the impregnation of activated carbon by sulfuric acid does not meet the principles of green chemistry and leads to environmental issues. In this work, carbonaceous microshperes bearing COOH, OH groups were synthesized by hydrothermal carbonization of fructose at 150 ℃ for 4 h, and the obtained carbonaceous material could be used directly for the catalytic hydrolysis of cellulose without any post-modification or in-situ functionalization, where a reducing sugar yield of 45.6% was obtained at 130 ℃ in 3 h in ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]). To improve the catalytic activity of the carbonaceous solid acid catalyst, sulfonic groups were grafted onto the carbonaceous microspheres by one-step hydrothermal carbonization of fructose in the presence of sulfosalicylic acid as co-monomer. The effects of reaction temperature, reaction time, catalyst dosage, water content and initial cellulose concentration on the hydrolysis of cellulose were systematically investigated in the presence of the as-prepared sulfonated carbonaceous solid acid catalyst, and the reducing sugar yield for cellulose hydrolysis was improved to 60.7% at 130 ℃ in 90 min in [BMIM][Cl]. An appropriate water content of around 1% in the ionic liquid could promote the formation of the reducing sugars, whereas a water content of greater than 1% lead to a decrease in the yield of reducing sugars. No large decrease in the yield of reducing sugars could be observed for initial cellulose concentration (w) of up to 10%. The catalyst could be reused and exhibited constant stability for at least five successive trials. The method developed offers a new way for the preparation and in-situ functionalization of carbonaceous solid acid catalysts, and provides a renewable strategy for the sustainable biomass utilization.

Key words: hydrothermal carbonization, carbonaceous microspheres, solid acid, hydrolysis, cellulose