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[摘要]：Depolymerization of cellulose is a significant part of the challenge in converting lignocellulosic biomass to valuable products such as monomeric sugars. Aiming to develop a new approach for efficient depolymerization of cellulose, we explored a sequential combination of organic acid (oxalic acid, OA) and base (tetramethylammonium hydroxide, TMAH). In hydrolysis reactions of cellulose at 150 degrees C, we demonstrated the enhancing effect of a sequential combination on its conversion. In two-step experiments, the highest conversion (73.0%) was achieved when the reaction with acid was followed by that with base (OA-TMAH sequence), which is greater than the prolonged treatment with either acid or base alone. In the residue after the reaction with OA, a more disordered, amorphous-like structure was present compared to raw cellulose and the sample after that with TMAH alone, as evidenced by C-13 cross-polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) and powder X-ray diffraction (XRD) measurements. Such structural change in the first OA treatment step can be the main cause of high conversion of cellulose in OA-TMAH treatment sequence. Analysis of liquid products clearly indicated that OA and TMAH both promote depolymerization of cellulose by cleaving the glycosidic bonds but generated distinctly different products: glucose and ketogluconic acid, respectively. Reactions of cellulose with conventional mineral acid (H2SO4) and base (NaOH) were also examined, and the relative orders of conversions and the liquid products were similar to those from reactions with organic acid and base. The selectivities to glucose and ketogluconic acid in organic acid and base treatments, respectively, were better than those with their inorganic counterparts. |
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