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Reaction Mechanisms in Pyrolysis of Hardwood, Softwood, and Kraft Lignin Revealed by ReaxFF MD Simulations
Energy & Fuels ( IF 5.2 ) Pub Date : 2019-11-08 , DOI: 10.1021/acs.energyfuels.9b02843 Tingting Zhang 1, 2 , Xiaoxia Li 1, 2 , Li Guo 1, 2 , Xin Guo 3
Energy & Fuels ( IF 5.2 ) Pub Date : 2019-11-08 , DOI: 10.1021/acs.energyfuels.9b02843 Tingting Zhang 1, 2 , Xiaoxia Li 1, 2 , Li Guo 1, 2 , Xin Guo 3
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Reactions of linkages and monomer rings in hardwood, softwood, and kraft lignin pyrolysis were investigated using reactive force field (ReaxFF) molecular dynamics (MD) simulations. Four large lignin models with diverse linkages and oxygen-containing groups were constructed on the basis of the two-dimensional lignin models proposed by Adler and Freudenberg for softwood lignin, by Nimz for hardwood lignin, and by Marton for kraft lignin. Large-scale ReaxFF MD simulations were performed using the GMD-Reax code and analyzed with the VARxMD code. The breaking of Cα/Cβ–O bonds in α/β–O–4 linkages is the dominant pathway to convert the source lignin molecules into smaller fragments. Differences in pyrolyzate evolution and linkage behavior among hardwood, softwood, and kraft lignin can be attributed to different reactions of linkages and their linked monomers induced by their varied oxygen-containing substituents. The consumption evolution of β–O–4 linkages can be promoted by their active substituents (Cα═O and Cα–O–4). The conversion of β–β_γ–O−α linkages and their linked monomer rings can be accelerated by the Cα═O substituent on the β–β_γ–O−α linkages and by the substituents of Cα–O–4 and OCH3 on the monomer ring. The different evolution profiles of the softwood, hardwood, and kraft lignin models are caused by the differences in the inherent structures (mainly linkage and oxygen-containing functional groups) of lignin from different tree species or isolation methods. Despite distinct differences in the pyrolyzate evolutions and linkage behaviors, the ring substructure evolutions of five- to seven-membered rings are similar for the four lignin models. This work demonstrates a useful alternative approach for investigating the pyrolysis reaction mechanism of lignin from varied sources.
中文翻译：
ReaxFF MD模拟揭示硬木，软木和牛皮纸木质素热解的反应机理
使用反作用力场（ReaxFF）分子动力学（MD）模拟研究了硬木，软木和牛皮纸木质素热解过程中的键和单体环的反应。在Adler和Freudenberg提出的用于软木木质素的二维木质素模型，Nimz提出的硬木木质素和Marton提出的硫酸盐木质素的二维木质素模型的基础上，构建了四个具有不同键和含氧基团的大型木质素模型。使用GMD-Reax代码执行了大规模的ReaxFF MD仿真，并使用VARxMD代码进行了分析。Cα / Cβ的破坏α/ β–O–4键中的–O键是将源木质素分子转化为较小片段的主要途径。硬木，软木和牛皮纸木质素之间热解产物的演化和键合行为的差异可归因于键合及其连接的单体因其不同的含氧取代基而引起的不同反应。β-O-4键的消费进化可以通过它们的活性的取代基（C促进α = O和C α -O-4）。β-β_γ-O-α键和它们的相连的单体的环的转化可以由C来加速α对β-β_γ-O-α键= O取代基，被C的取代基α -O-4和OCH 3在单体环上。软木，硬木和牛皮纸木质素模型的不同演变特征是由于来自不同树种或分离方法的木质素固有结构（主要是键合和含氧官能团）的差异引起的。尽管在热解产物的演化和键合行为上有明显的不同，但是对于四个木质素模型，五元至七元环的环亚结构演化是相似的。这项工作表明了一种有用的替代方法，用于研究来自各种来源的木质素的热解反应机理。
更新日期：2019-11-11
中文翻译：
ReaxFF MD模拟揭示硬木，软木和牛皮纸木质素热解的反应机理
使用反作用力场（ReaxFF）分子动力学（MD）模拟研究了硬木，软木和牛皮纸木质素热解过程中的键和单体环的反应。在Adler和Freudenberg提出的用于软木木质素的二维木质素模型，Nimz提出的硬木木质素和Marton提出的硫酸盐木质素的二维木质素模型的基础上，构建了四个具有不同键和含氧基团的大型木质素模型。使用GMD-Reax代码执行了大规模的ReaxFF MD仿真，并使用VARxMD代码进行了分析。Cα / Cβ的破坏α/ β–O–4键中的–O键是将源木质素分子转化为较小片段的主要途径。硬木，软木和牛皮纸木质素之间热解产物的演化和键合行为的差异可归因于键合及其连接的单体因其不同的含氧取代基而引起的不同反应。β-O-4键的消费进化可以通过它们的活性的取代基（C促进α = O和C α -O-4）。β-β_γ-O-α键和它们的相连的单体的环的转化可以由C来加速α对β-β_γ-O-α键= O取代基，被C的取代基α -O-4和OCH 3在单体环上。软木，硬木和牛皮纸木质素模型的不同演变特征是由于来自不同树种或分离方法的木质素固有结构（主要是键合和含氧官能团）的差异引起的。尽管在热解产物的演化和键合行为上有明显的不同，但是对于四个木质素模型，五元至七元环的环亚结构演化是相似的。这项工作表明了一种有用的替代方法，用于研究来自各种来源的木质素的热解反应机理。
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