Dissolution and hydrolysis of cellulose in subcritical and supercritical water
Dissolution and hydrolysis of cellulose in subcritical and supercritical water
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DOI：
10.1021/ie990690j
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发表时间：
2000-08-01
影响因子：
4.2
通讯作者：
Arai, K
中科院分区：
文献类型：
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作者：
Sasaki, M;Fang, Z;Arai, K
微晶纤维素在亚临界和超临界水(25 Mpa，320-400℃，0.05-10.0 S)中进行了分解实验。在400℃时，主要是水解物，而在320-350℃的水中，主要是葡萄糖的水分解产物。在此条件下对纤维素、纤维二糖和葡萄糖的动力学研究表明，在350℃以下，纤维素的分解速度慢于葡萄糖和纤维二糖的分解速度，而在350℃以上，纤维素的水解率急剧增加，并高于葡萄糖和纤维二糖的分解速度。用钻石顶压室(DAC)直接观察高温水中高压条件下的纤维素反应，结果表明，在280℃以下，随着反应时间的延长，纤维素颗粒逐渐变小，但在高温(300-320℃)，纤维素颗粒随着透明度的增加而消失，并且比较低温度结果的预期要快得多。这些结果表明，纤维素在高温下的水解是在水中溶解的。这可能是由于纤维素晶体中分子内和分子间氢键的断裂所致。因此，在超临界水中形成了均匀的大气，导致纤维素在350摄氏度以上的分解速度急剧增加。
Decomposition experiments of microcrystalline cellulose were conducted in subcritical and supercritical water (25 MPa, 320-400 degrees C, and 0.05-10.0 s). At 400 degrees C hydrolysis products were mainly obtained, while in 320-350 degrees C water, aqueous decomposition products of glucose were the main products. Kinetic studies of cellulose, cellobiose, and glucose at these conditions showed that below 350 degrees C the cellulose decomposition rate was slower than the glucose and cellobiose decomposition rates, while above 350 degrees C, the cellulose hydrolysis rate drastically increased and became higher than the glucose and cellobiose decomposition rates. Direct observation of the cellulose reaction in high-temperature water at high-pressure conditions by using a diamond anvil cell (DAC) showed that, below 280 degrees C, cellulose particles became gradually smaller with increasing reaction time but, at high temperatures (300-320 degrees C), cellulose particles disappeared with increasing transparency and much more rapidly than expected from the lower temperature results. These results suggest that cellulose hydrolysis at high temperature takes place with dissolution in water. This is probably because of the cleavage of intra- and intermolecular hydrogen linkages in the cellulose crystal. Thus, a homogeneous atmosphere is formed in supercritical water, and this results in the drastic increase of the cellulose decomposition rate above 350 degrees C.