丁香酚气相热解的实验和动力学研究,Energy & Fuels

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丁香酚气相热解的实验和动力学研究
Energy & Fuels ( IF 5.2 ) Pub Date : 2023-05-04 , DOI: 10.1021/acs.energyfuels.3c00573
Liang Li ₁ , Ruben Van de Vijver ₁ , Kevin M. Van Geem ₁

Affiliation

丁香基（3,5-二甲氧基-4-羟基苯基）单元在硬木木质素中含量丰富，这解释了从这些饲料中提取的生物油中存在大量丁香醇的原因。为了提高对这些丁香基单元的分解化学的理解，在典型的快速热解条件下，对丁香醇的气相热解动力学进行了实验和理论研究。实验是在 673–923 K 的微型热解器装置中进行的，该装置与气相色谱 (GC) × 气相色谱-火焰电离检测/飞行时间质谱法和定制的气相色谱仪联用，可以检测和量化产品沸点高达 823 K，仅次于永久性气体和水。新获得的实验数据表明，2,3-二羟基苯甲醛是最重要的酚类产品，并形成大量热解水。丁香醇对这两种产品的拟议分解途径显示出两个新特征：(1) 2,3-二羟基苯甲醛是由丁香醇的单分子分解形成的，没有任何稳定的中间体，以及 (2) 这两种途径都导致 2,3-二羟基苯甲醛和水涉及更多的 H 原子迁移步骤以形成更稳定的自由基。CBS-QB3 理论水平的势能面计算表明新特征在动力学上是有利的。此外，还构建了包含 361 个反应和 93 个物种的丁香酚热解的详细动力学模型。重要物质的热力学数据和关键反应的动力学是通过 CBS-QB3 理论水平的从头计算确定的。该模型很好地预测了丁香醇的转化和主要产物的形成。生产率分析表明，新提出的途径是丁香醇的主要分解途径。这些发现为丁香基物种的热解和氧化化学提供了新的思路。

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Experimental and Kinetic Study on the Gas-Phase Pyrolysis of Syringol

Syringyl (3,5-dimethoxy-4-hydroxyphenyl) units are abundant in hardwood lignin, which explains the large amount of syringol present in bio-oils derived from these feeds. To improve understanding of the decomposition chemistry of these syringyl units, the gas-phase pyrolysis kinetics of syringol have been studied experimentally and theoretically under typical fast pyrolysis conditions. The experiments were performed at 673–923 K in a micropyrolyzer unit hyphenated with a gas chromatography (GC) × gas chromatography-flame ionization detection/time-of-flight mass spectrometry and a customized gas chromatograph, which allows to detect and quantify products with boiling points up to 823 K next to permanent gases and water. New obtained experimental data show that 2,3-dihydroxybenzaldehyde is the most important phenolic product, and a large amount of pyrolytic water was formed. The proposed decomposition pathways of syringol to these two products show two new features: (1) 2,3-dihydroxybenzaldehyde is formed from a unimolecular decomposition of syringol without any stable intermediates and (2) both pathways leading to 2,3-dihydroxybenzaldehyde and water involve one more H-atom migration step to form the more stable radicals. Potential energy surface calculations at the CBS-QB3 level of theory indicate that the new features are kinetically favorable. Furthermore, a detailed kinetic model for syringol pyrolysis including 361 reactions and 93 species was constructed. Thermodynamic data for important species and kinetics for crucial reactions were determined with ab initio calculations at the CBS-QB3 level of theory. The model predicts well the conversion of syringol and the formation of major products. A rate of production analysis shows that the new proposed pathway is the major decomposition pathway of syringol. These findings shed new light on the pyrolysis and oxidation chemistry of syringyl species.

更新日期：2023-05-04

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