基于量子化学的玉米秸秆热解机理的模拟计算

Theoretical study on pyrolysis mechanism of corn stalk based on quantum chemistry

建立了玉米秸秆的分子模型,并以此为研究对象,采用密度泛函理论B3LYP方法,在6～31g基组水平上,对其进行了热解反应机理研究。设计了玉米秸秆热解过程的4条初反应路径,并在分析初反应结果的基础上设计了14条次反应路径,对每条反应路径的反应物,过渡态,中间体以及产物均进行了结构优化和频率计算。计算结果表明:玉米秸秆热解初期半纤维素开始热解,木质素侧链轻微热解;初反应R1,R4反应焓变较小,分别为395. 77 kJ/mol和104. 70 k J/mol,认为玉米秸秆热解主反应路径以TS2及TS8次反应路径为主,其热解产物包括呋喃类,吡喃类,烷烯烃和芳香族化合物。

The molecular model of corn stalk was established and chosen as a research object in this paper.The corn stalk molecular model were theoretically calculated by using density functional theory methods B3LYP at 6~31g level.Four initial reaction were designed,and then fourteen secondary reaction were designed according to the analysis of the initial reaction results.The reactants,transition states,intermediates and products in every reaction path were optimized and their frequency were calculated.The calculation results show that hemicellulose is pyrolysed earliest in the initial stage of corn stalk pyrolysis,the side chains of lignin also begin to pyrolyze slightly at the same time;the enthalpy changes of R1 and R4 in the initial reaction are 395.77kJ/mol and 104.70kJ/mol respectively,which proves that the mainly pyrolysis reaction paths for corn stalk are the secondary reaction of TS2 and TS8.The pyrolysis products of corn stalk include furan,pyran,alkanes and aromatic compounds.