纤维素二聚体模型物热裂解的热力学性质研究  

Theoretical Study on Thermodynamic Properties of Pyrolysis of Cellulose Dimer Model Compound

作　　者：蒋原野 于海珠[2] 傅尧[1] 

机构地区：[1]中国科学技术大学化学系,合肥230026 [2]北京科技大学高分子科学与工程系,北京100083

出　　处：《化学学报》2013年第12期1611-1619,共9页Acta Chimica Sinica

基　　金：国家自然科学基金(Nos.21172209;21272223;21202006);高等学校博士学科点专项科研基金资助课题(No.20123402110051);中央高校基本科研业务费专项资金(No.WK2060190008;FRF-TP-13-023A);中国科学院基金(No.KJCX2-EW-J02)资助~~

摘　　要：纤维素是生产生物质燃料,精细化工品的重要原料.热解是由纤维素解聚的重要手段之一.了解纤维素热解的反应机理对发展高效的生物质转化技术具有重要意义.我们利用密度泛函理论方法,以纤维素二聚体为模型,详细研究了其发生键均裂过程的热力学能量变化.发现糖苷键和侧链C—C键的均裂相对于C—OH键和O—H键均裂在热力学上更优.此外,我们发现不同物种的热力学稳定性与其在纤维素快速热解实验产物中的比例无关.最后我们发现温度对反应能否自发发生具有重要的影响,为通过调节温度来改变不同类型反应的选择性提供了一条思路.Cellulose is an important material for production of biofuel and refined chemicals. Pyrolysis is one of the most promising approaches for cellulose de-polymerization. Understanding the mechanism of cellulose pyrolysis is essential for development of efficient biomass conversion technologies. In this study, the thermodynamic energy change of cellulose pyrolysis through homolytic bond cleavage was studied with the aid of density functional theory method by using cellulose dimer as a model compound. The free energy changes of various homolytic bond dissociation of cellulose dimer were studied by the method of M06-2x at the temperature of 800 ℃. To compare with experiment results of cellulose pyrolysis reported recently by Huber et al., the free energy changes of reaction pathways studied by Auerbach group via Car-Parrinello molecu- lar dynamics calculations were also studied. Calculated results show that the free energy changes ofhomolytic dissociation of glucosidic bond varies in the range of 45- 51 kcal/mol. The free energy changes of homolytic bond dissociation of C--OH bond vary in the range of 62-70 kcal/mol. The free energy changes of homolytic bond dissociation of O---H bond vary in the range of 82-95 kcal/mol. The free energy changes of homolytic bond dissociation of C---C bond vary around 46 kcal/mol. Furthermore, thermodynamic stabilities of products were found to be irrelevant to the ratios of them in Huber et al.＇s fast pyrolysis experiments no matter at a high temperature （800 K） or a mild temperature （298 K）. Finally, we found that temperature have a significant influence on whether a reaction can occur spontaneously or not. At relatively high temperature, the reactions having significant increase of entropy are favored, e.g. dehydration. The free energy of reactions with small entropy changes are less sensitive to the change of temperature. This foundation provides an inspiration for controlling chemical selectivity of different types of reactions by temperature regulation.

关 键 词：纤维素二聚体 热裂解 密度泛函理论方法 

分 类 号：TK16[动力工程及工程热物理—热能工程] TK6