Molecular Products and Radicals from Pyrolysis of Lignin
Molecular Products and Radicals from Pyrolysis of Lignin
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DOI：
10.1021/es302942c
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发表时间：
2012-12-04
影响因子：
11.4
通讯作者：
Dellinger, B.
中科院分区：
文献类型：
--
作者：
Kibet, J.;Khachatryan, L.;Dellinger, B.
在管式等温流动反应器中研究了木质素在2 0 0~90 0℃温度范围内、停留时间为0.2 S的两种反应模式(在氮气中的热解和在氮气中的4%O-2氧化热解)下的热降解.采用了两种实验方案：(1)部分热解，即同一木质素样品在每个温度下连续热解；(2)常规热解，即在每个热解温度下热解新的木质素.结果确定了两种实验模式之间的共同关系，以及一些不同之处。部分热解的大部分产物在300-500℃之间达到峰值，而常规热解反应的产物在400-500℃之间达到峰值。主要产物是丁香酚(2，6-二甲氧基苯酚)、愈创木酚(2-甲氧基苯酚)、苯酚和邻苯二酚。在所分析的化合物类别中，酚类化合物含量最丰富，占所检测化合物总数的40%以上。苯、苯乙烯和对二甲苯在整个温度范围内都有大量生成。有趣的是，在部分热解过程中形成了6个环状多环芳烃。氧化热解与热解没有太大的区别，主要产物仍然是丁香酚、愈创木酚和苯酚，唯一显著的区别是产物分布在200~400℃之间。首次成功地将低温基质隔离电子顺磁共振与热解反应器对接，解释了不稳定反应中间产物的结构。EPR结果表明，甲氧基、苯氧基和取代苯氧基是形成主要产物的前体，如辛香酚、愈创木酚、酚和取代酚。
Thermal degradation of lignin under two reaction regimes (pyrolysis in N-2 and oxidative pyrolysis in 4% O-2 in N-2) has been investigated in a tubular, isothermal, flow-reactor over the temperature range 200-900 degrees C at a residence time of 0.2 s. Two experimental protocols were adopted: (1) Partial pyrolysis in which the same lignin sample was continuously pyrolyzed at each temperature and (2) conventional pyrolysis, in which new lignin samples were pyrolyzed at each pyrolysis temperature. The results identified common relationships between the two modes of experiments, as well as some differences. The majority of products from partial pyrolysis peaked between 300 and 500 degrees C, whereas for conventional pyrolysis reaction products peaked between 400 and 500 degrees C. The principal products were syringol (2,6-dimethoxy phenol), guaiacol (2-methoxy phenol), phenol, and catechol. Of the classes of compounds analyzed, the phenolic compounds were the most abundant, contributing over 40% of the total compounds detected. Benzene, styrene, and p-xylene were formed in significant amounts throughout the entire temperature range. Interestingly, six ringed polycyclic aromatic hydrocarbons were formed during partial pyrolysis.Oxidative pyrolysis did not result in large differences from pyrolysis; the main products still were syringol, guaiacol, phenol, the only significant difference being the product distribution peaked between 200 and 400 degrees C.For the first time, low temperature matrix isolation electron paramagnetic resonance was successfully interfaced with the pyrolysis reactor to elucidate the structures of the labile reaction intermediates. The EPR results suggested the presence of methoxyl, phenoxy, and substituted phenoxy radicals as precursors for formation of major products; syringol, guaiacol, phenols, and substituted phenols.