Crystal Structure Change and Recrystalization of Cellulose in Supercritical Water

1)金刚石砧座原位观察将纤维素粉装入装有蒸馏水的金刚石砧座中，以10ﾟC的升温速率加热至400ﾟC，在280ﾟC以下，纤维素颗粒的粒径随时间的延长而减小。然而，在300ﾟC到320ﾟC的温度范围内，纤维素颗粒立即消失，而不改变颗粒的大小和形状。这一现象表明，纤维素在300ﾟC以上的热压缩水中溶解。用流动型装置测定了纤维素在亚临界或超临界水中的水解率。我们发现，在350ﾟC左右，纤维素的水解率急剧增加，其中一个原因可能是纤维素在热水中的溶解。2)沉淀物的分析发现，几个小时后，液体流出物中就有白色的沉淀物出来。用FTIR对该沉淀物进行了分析，鉴定为类纤维素物质。废水中沉淀物的收集量随反应时间的延长而增加，在400ﾟC时达到最大值。

1) In-situ observation using diamond anvil cell (DAC)Cellulose powders were loaded in a diamond anvil cell (DAC) with distilled water and heated up to 400 ﾟC at a heating rate of 10ﾟC.Below 280ﾟC, cellulose particle size decreased generally with time. However, at a temperature range from 300ﾟC to 320ﾟC, the cellulose particles disappeared immediately without changing particle size and shape. This phenomenon suggests that cellulose dissolves into hot compressed water above 300ﾟC.The hydrolysis rate of cellulose in sub- or supercritical water was measured by using a flow type apparatus. We found that the drastic increase of the rate at around 350ﾟC.The one of the reason of the drastic increase of the hydrolysis rate of cellulose might be the dissolution of cellulose in hot water.2) Analysis of precipitatesWe found that white precipitates in the liquid effluent came out after few hours. This precipitate was analyzed by FTIR and identified as a cellulose-like material. The collected amount of precipitate in the liquid effluent increased with the reaction time and shows maximum at 400ﾟC.XRD analysis of the precipitate shows the cellulose crystal structure.