Mechanisms of sequential dissolution and hydrolysis for lignocellulosic waste using a multilevel hydrothermal process
Mechanisms of sequential dissolution and hydrolysis for lignocellulosic waste using a multilevel hydrothermal process
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使用多级水热过程连续溶解和水解木质纤维素废物的机制
DOI：
10.1016/j.cej.2015.03.042
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发表时间：
2015-08
影响因子：
15.1
通讯作者：
Jiajun Chen
中科院分区：
文献类型：
--
作者：
Yan Zhao;Siyuan Zhang;Jiajun Chen
水热转化过程中，木质纤维素的溶解和水解同时进行，导致可发酵糖的分解和抑制剂的积累。采用多级水热法对木质纤维素废弃物进行连续溶解和水解，并对溶解机理进行了研究。随着温度从190 °C增加到220 °C，反应时间从5分钟增加到40分钟，处理过的玉米秸秆的结晶度从43.1%增加到72.5%。在这些条件下的FT-IR分析表明，逐渐半纤维素消失和纤维素保留。对于纤维素溶解，高于240 °C的温度呈现结晶度和聚合度的显著降低。随着温度的升高，分子间和分子内氢键断裂，糖苷键保留到260 ℃。因此，木质素和半纤维素的无定形结构以及纤维素的结晶结构可以分别在190 °C和240 °C左右依次溶解。动力学分析表明，在190 °C以上的温度下，木质纤维素的溶解反应不符合表面反应速率方程，这是由于木质纤维素结构中的高溶解速率和相互作用。与此相对，在试验水热条件下，纤维素溶解的反应动力学没有急剧变化，根据所得到的反应速率常数，计算出活化能为189.8 ± 8.6 kJ mol− 1。这些发现大大提高了对机理的理解，并为使用多级水热过程的木质纤维素废物的顺序溶解和水解提供了证据。
Hydrothermal conversion normally results in fermentable sugar decomposition and inhibitor accumulation through dissolving and hydrolyzing lignocellulose synchronously. A multilevel hydrothermal process was applied to sequentially dissolve and hydrolyze lignocellulosic waste, and the dissolution mechanisms were investigated. The crystallinity of treated corn stalks increased from 43.1% to 72.5% with temperatures increasing from 190 to 220 °C and reaction times from 5 to 40 min. FT-IR analysis under these conditions showed gradual hemicellulose disappearance and cellulose retention. For cellulose dissolution, temperatures above 240 °C presented significant reductions in crystallinity and degrees of polymerization. Intermolecular and intramolecular H-bonds were broken with the increase in temperature, and glycosidic bonds remained until 260 °C. Thus, the amorphous structures of lignin and hemicellulose, as well as crystalline structure of cellulose, could be sequentially dissolved around 190 °C and 240 °C, respectively. Kinetic analysis revealed that the lignocellulosic dissolution reaction above 190 °C did not agree with the surface reaction rate equation because of the high dissolution rate and interaction in the lignocellulosic structure. By contrast, the reaction kinetics of cellulose dissolution did not exhibit a sudden change in the test hydrothermal conditions, and the activation energy was calculated as 189.8 ± 8.6 kJ mol−1according to the obtained reaction rate constants. These findings significantly enhance the understanding of the mechanism, and provide evidence for the sequential dissolution and hydrolysis of lignocellulosic waste using a multilevel hydrothermal process.
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