Elucidating Biomass-Derived Pyrolytic Lignin Structures from Demethylation Reactions through Density Functional Theory Calculations
Elucidating Biomass-Derived Pyrolytic Lignin Structures from Demethylation Reactions through Density Functional Theory Calculations
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DOI：
10.1021/acs.energyfuels.2c04292
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发表时间：
2023-03
期刊：
影响因子：
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通讯作者：
Raiza Manrique;Evan Terrell;Pavlo Kostetskyy;F. Chejne;Mariefel V. Olarte;L. Broadbelt;M. García-Pérez-M.-García-P
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作者：
Raiza Manrique;Evan Terrell;Pavlo Kostetskyy;F. Chejne;Mariefel V. Olarte;L. Broadbelt;M. García-Pérez-M.-García-P
热解木质素是热解油的一部分，其含有广泛的酚类化合物，可用作生产燃料和化学品的中间体。然而，由于木质素结构的特殊性，很难建立木质素的热解机理和确定木质素的热解结构。本研究提出了二聚体，三聚体和四聚体结构的基础上，其相对热力学稳定性的硬木木质素模型在热解。通过电子结构计算，研究了愈创木基（G）和异戊二烯基（S）单元以及βO4和β5键在硬木模型木质素中的位置对低聚物构型的影响。假定βO4键发生均裂并产生两个自由基片段。这些可以通过在热喷射之前的中间液体（路径1）形成期间吸收可能在溶液中的氢自由基来稳定。当自由基使用分子内氢时，可能会发生另一种途径（途径2），将其自身转化为稳定的产物。随后，可以发生脱甲基化反应，从而产生甲烷分子和新的低聚木质素衍生分子。研究了最可能的结果结构。我们使用选定的模型化合物的FTIR和NMR光谱来评估我们的计算方法。热物理性质使用基团贡献法计算。这些结果使我们深入了解木质素低聚物的结构以及这些分子是如何形成的。为裂解油分离和改质设备的设计提供了有益的参考。
Pyrolytic lignin is a fraction of pyrolysis oil that contains a wide range of phenolic compounds that can be used as intermediates to produce fuels and chemicals. However, the characteristics of the raw lignin structure make it difficult to establish a pyrolysis mechanism and determine pyrolytic lignin structures. This study proposes dimer, trimer, and tetramer structures based on their relative thermodynamic stability for a hardwood lignin model in pyrolysis. Different configurations of oligomers were evaluated by varying the positions of the guaiacyl (G) and syringyl (S) units and the bonds βO4 and β5 in the hardwood model lignin through electronic structure calculations. The homolytic cleavage of βO4 bonds is assumed to occur and generate two free radical fragments. These can stabilize by taking hydrogen radicals that may be in solution during the intermediate liquid (pathway 1) formation before the thermal ejection. An alternative pathway (pathway 2) could occur when the radicals use intramolecular hydrogen, turning themselves into stable products. Subsequently, a demethylation reaction can take place, thus generating a methane molecule and new oligomeric lignin-derived molecules. The most probable resulting structures were studied. We used FTIR and NMR spectra of selected model compounds to evaluate our calculation approach. Thermophysical properties were calculated using group contribution methods. The results give insights into the lignin oligomer structures and how these molecules are formed. They also provide helpful information for the design of pyrolysis oil separation and upgrading equipment.