Elucidation of Structure and Physical Properties of Pyrolytic Sugar Oligomers Derived from Cellulose Depolymerization/Dehydration Reactions: A Density Functional Theory Study
Elucidation of Structure and Physical Properties of Pyrolytic Sugar Oligomers Derived from Cellulose Depolymerization/Dehydration Reactions: A Density Functional Theory Study
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DOI：
10.1021/acs.energyfuels.3c00641
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发表时间：
2023-05
期刊：
影响因子：
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通讯作者：
M. Denson;Evan Terrell;Pavlo Kostetskyy;Mariefel V. Olarte;L. Broadbelt;M. García-Pérez
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文献类型：
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作者：
M. Denson;Evan Terrell;Pavlo Kostetskyy;Mariefel V. Olarte;L. Broadbelt;M. García-Pérez
木质纤维素材料的快速热解是一个很有前途的研究领域，以生产可再生燃料和化学品。已知脱水是纤维素热解过程中最重要的反应家族之一;水是最重要的产物。与水一起，脱水反应还形成一系列分子大小不同的鲜为人知的低聚物物质，通常作为生物油水溶性（WS）级分的一部分收集。在这项工作中，我们使用电子结构计算，以评估几个低聚物物种的相对热力学稳定性从纤维素解聚中间体经历三个连续的脱水事件。编译了一个化学上有利的候选分子结构库。结果表明，大部分的水分子从非还原端被消除，形成在化学上更稳定的共轭化合物。这与文献中报道的结果一致，其中脱水反应优选发生在低聚物的非还原末端。这些糖低聚物的理论傅里叶变换红外光谱和核磁共振光谱定性地符合热解糖的实验结果。了解它们的化学结构可以帮助制定合理的策略来减少焦炭的形成，因为糖通常被认为是生物油精炼过程中焦炭形成的原因。估计的物理化学性质（沸点、熔点、生成吉布斯自由能、生成焓和溶解度参数等）也是进行第一原理工程计算以设计和分析新的热解反应器和生物油升级单元的基础。
Fast pyrolysis of lignocellulosic materials is a promising research area to produce renewable fuels and chemicals. Dehydration is known to be among the most important reaction families during cellulose pyrolysis; water is the most important product. Together with water, dehydration reactions also form a range of poorly known oligomer species of varying molecular sizes, often collected as part of the bio-oil water-soluble (WS) fraction. In this work, we used electronic structure calculations to evaluate the relative thermodynamic stabilities of several oligomer species from cellulose depolymerization intermediates undergoing three consecutive dehydration events. A library of the thermodynamically favored candidate molecular structures was compiled. Results revealed that most of the water molecules are eliminated from the non-reducing end, forming thermodynamically more stable conjugated compounds. This is consistent with results reported in literature where dehydration reactions occur preferably at the non-reducing ends of oligomers. The theoretical Fourier-Transform Infrared Spectroscopy and NMR spectra of these proposed sugar oligomers conform qualitatively to the experimental result of pyrolytic sugars. Understanding their chemical structure could help to develop rational strategies to mitigate coke formation as sugars are often blamed to cause coke formation during bio-oil refining. The estimated physical–chemical properties (boiling point, melting point, Gibbs free energy of formation, enthalpy of formation, and solubility parameters among others) are also fundamental to conducting first-principles engineering calculations to design and analyze new pyrolysis reactors and bio-oil up-grading units.