Theoretical study on pyrolysis and product selectivity of β-O-4 type lignin dimer model

doi:10.16085/j.issn.1000-6613.2017-0553

Abstract

Abstract: Lignin,as the second most available cellulose in botanic field,it is of great economic and environmental significance to convert it into targeted platform compounds. To understand the pyrolysis mechanism of lignin,the 1-methoxy-2-(2-phenylpropoxy) benzene was selected as a lignin dimer model compound of β-O-4-linkage. The pyrolysis of this dimer was investigated using density functional theory B3LYP methods at 6-31G(d,p)level. Eight possible pyrolysis pathways (mainly the homolytic cleavage of C-O bond) were proposed according to bond dissociation energies of lignin dimer model,then the activation energies for each reaction pathway were calculated. The calculation results showed that the bond dissociation energy of C_β-O was the lowest,and that of O-CH₃ the second lowest. The order of all kinds of bond dissociation energy is C_β-O < O-CH₃ < C_α-C_β < C_α-C_γ < C_aromatic-O < C_α-C_aromatic < C_aromatic-OCH₃. It could be deduced that the dimer was mainly decomposed through the cleavage of the C_β-O linkage. And major pyrolytic products of phenol and alkene compounds were formed in this process.Thus,the optimum pathway1 can be determined based on its thermodynamic parameters and lowest energy barrier of 44.73kJ/mol.

Key words: lignin, β-O-4 linkage dimer, density functional theory, pyrolysis mechanism, product selectivity

摘要： 木质素作为含量仅次于纤维素的天然可再生资源，将其转化为高附加值的平台化合物具有重大的经济以及环境意义。本文针对具有β-O-4典型连接方式的木质素二聚体模型化合物[2-甲氧基（2'-甲基-2'-苯基乙基）苯醚]，利用密度泛函理论方法B3LYP，在6-31G（d，p）基组水平上对其热解反应机理以及产物形成选择性进行理论研究，分析了二聚体中各化学键的解离能及Mulliken布居数，设计并计算了8条后续可能反应路径的标准热力学参数。研究结果表明，该木质素二聚体模型化合物的初次热裂解路径主要为C_β—O键均裂的反应；热解的主要产物是酚类化合物如苯、苯酚、邻苯二酚以及烃类化合物如烯烃等；其中路径1是热力学支持的最优路径，其能垒为44.73kJ/mol。

关键词: 木质素, &beta, -O-4型二聚体, 密度泛函理论, 热解机理, 产物选择性

CLC Number:

FAN Di, XIE Xin'an, LI Lu, LI Yan, LI Wei, WEI Xing, SUN Jiao. Theoretical study on pyrolysis and product selectivity of β-O-4 type lignin dimer model[J]. Chemical Industry and Engineering Progress, 2017, 36(12): 4436-4444.

樊荻, 解新安, 李璐, 李雁, 黎巍, 魏星, 孙娇. β-O-4型木质素二聚体模型化合物热解机理及产物选择性理论[J]. 化工进展, 2017, 36(12): 4436-4444.

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