纤维素单体热解机理的热力学研究

Thermodynamic Studies of Pyrolysis Mechanism of Cellulose Monomer

为了了解纤维素热解机理,结合相关实验结果对纤维素单体(β-D-吡喃葡萄糖)的热解设计了四种热解反应途径.利用Gaussian 03程序,采用密度泛函理论(DFT),在UB3LYP/6-31G(d)水平上,对各反应物和产物的几何结构进行了能量梯度法全优化,计算了不同温度下各反应路径的热力学参数.计算结果表明:所有反应均为吸热反应;当温度在550K以上时,所有反应都能自发进行.从热力学的角度分析,热解更有利于发生开环反应而形成乙醇醛、1-羟基-2-丙酮、CO等小分子产物.

For understanding the pyrolysis mechanism of cellulose, four kinds of paths of pyrolytic reaction were designed for the thermal decomposition of the cellulose monomer （namely β-D-glucopyranose） according to related experimental results. At the UB3LYP/6-31G（d） level of density functional theory, the equilibrium geometries of the reactants and products were optimized and the standard thermodynamic parameters of every reaction path in different temperature ranges were calculated by the help of Gaussian 03 package. The thermodynamic calculation results show that all above reactions are endothermic processes and can take place spontaneously when temperature of reaction exceeds 550 K. According to thermodynamic points of view, the pyrolysis of cellulose monomers favors to produce low molecular weight products, e.g. hydroxyacetaldehyde, acetol and carbon monoxide.