The supercritical water gasification of xylose, a model substrate for hemicellulose, was carried out at 400 and 450 °C and at a constant pressure of 25 MPa in the presence of acetic acid using a continuous flow reactor. More specifically, we aimed to compare the reaction rate constants of xylose decomposition in both the presence and absence of acetic acid. Upon the application of a residence time of 0.5–5 s, a xylose concentration of 1.5 wt %, and an acetic acid concentration of 1.5 wt %, we successfully elucidated the effect of acetic acid on each reaction within the reaction network for the first time. In the presence of acetic acid, the retro-aldol reactions and carbon gasification production (i.e., the radical reactions) were suppressed, while the acetic-acid-catalyzed dehydration of xylulose to furfural (i.e., an ionic reaction) was enhanced by 2 orders of magnitude. As such, reaction control through the addition of chemical species to either stabilize ions or react with radicals appears possible.

中文翻译：

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乙酸添加对超临界水中木糖分解的影响

使用连续流反应器，在乙酸存在下，于400和450℃，在25 MPa的恒压下，对木糖（半纤维素的模型底物）进行超临界水气化。更具体地说，我们旨在比较在有乙酸和无乙酸的情况下木糖分解的反应速率常数。在停留时间为0.5-5 s，木糖浓度为1.5 wt％，乙酸浓度为1.5 wt％的情况下，我们首次成功阐明了乙酸对反应网络中每个反应的影响。在乙酸的存在下，逆醛醇缩合反应和碳气化产物（即自由基反应）被抑制，而乙酸催化的木酮糖脱水成糠醛（即，离子反应）提高了2个数量级。这样，通过添加化学物质以稳定离子或与自由基反应的反应控制看来是可能的。