Low-pressure two-stage catalytic hydropyrolysis of lignin and lignin-derived phenolic monomers using zeolite-based bifunctional catalysts
Low-pressure two-stage catalytic hydropyrolysis of lignin and lignin-derived phenolic monomers using zeolite-based bifunctional catalysts
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DOI：
10.1016/j.jaap.2020.104779
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发表时间：
2020-03
影响因子：
6
通讯作者：
Yuan Xue;Ashokkumar M. Sharma;Jiajie Huo;Wangda Qu;Xianglan Bai
中科院分区：
文献类型：
--
作者：
Yuan Xue;Ashokkumar M. Sharma;Jiajie Huo;Wangda Qu;Xianglan Bai
以玉米秸秆、火炬松和红橡树为原料，以HZSM-5、MoO3/ZSM-5和Ni/ZSM-5为催化剂，研究了木质素的两段催化加氢热解。与惰性气体催化热解相比，常压氢气的存在显著促进了木质素的碳氢生成，同时显著降低了焦炭收率。与HZSM-5相比，MoO3/ZSM-5增加了芳烃的生成，而Ni/ZSM-5增加了脂肪族烃的生成。MoO3/ZSM-5和Ni/ZSM-5均降低了焦炭收率，抑制了多芳的生成，提高了对单环芳烃的选择性。玉米秸秆木质素的芳烃产率最高，火炬松木质素次之，红橡木木质素次之。其中，MoO3/ZSM-5可使玉米秸秆木质素转化为芳烃和脂肪烃，转化率高达42.24℃。本研究以苯酚、愈创木酚和丁香酚为模型化合物，进一步研究了木质素衍生热解蒸汽在催化加氢热解过程中的反应途径。结果表明，脱甲氧基化后，甲氧基自由基加氢脱氧，酚环烷基化生成甲酚，中间产物二甲基苯酚再加氢脱氧生成苯和烷基化苯。MoO3/ZSM-5具有较强的脱甲氧基和加氢脱氧能力。相比之下，Ni/ZSM-5对酚羟基的去除能力要差得多。根据木质素和模型化合物的转化结果，发现木质素的芳烃总产率与木质素衍生热解蒸气中酚甲氧基的丰度呈负相关。研究还发现，简单H、G、S基单体的热解蒸汽比由相应H、G、S基的更复杂单体和低聚物组成的蒸汽更容易产生芳香烃。然而，G基单体和低聚物的产率差异不显著。
In the present study, a two-stage catalytic hydropyrolysis of lignin was investigated by converting lignin extracted from corn stover, loblolly pine and red oak using HZSM-5, MoO3/ZSM-5 and Ni/ZSM-5 as catalysts. Compared to the catalytic pyrolysis with inert gas, the presence of atmospheric-pressure hydrogen significantly enhanced the formation of hydrocarbon from lignin whereas dramatically reducing coke yield. In comparison to HZSM-5, MoO3/ZSM-5 increased the production of aromatic hydrocarbons, while Ni/ZSM-5 enhanced the formation of aliphatic hydrocarbons. Coke yields decreased with both MoO3/ZSM-5 and Ni/ZSM-5, which corresponds to the suppression of polyaromatic formation and increased selectivity to single ring aromatics. Corn stover lignin produced the highest yield of aromatic hydrocarbons with all three catalysts, followed by loblolly pine and red oak lignins. Particularly, up to 42.24 C% of corn stover lignin was converted into aromatic and aliphatic hydrocarbons with MoO3/ZSM-5. In this study, reaction pathways of lignin-derived pyrolysis vapor during catalytic hydropyrolysis were further studied using phenol, guaiacol, and syringol as the model compounds. Results suggest that demethoxylation followed by the hydrodeoxygenation of methoxyl radicals and subsequent alkylation of the phenolic ring to produce cresol, and dimethyl phenol as intermediates prior to the intermediate phenolics were further hydrodeoxygenated to produce benzene and alkylated benzene. MoO3/ZSM-5 showed strong ability for both demethoxylation and hydrodeoxygenation. In comparison, the ability of Ni/ZSM-5 for phenolic-hydroxyl removal was much inferior. Based on the results obtained from the conversions of lignin and the model compounds, a negative correlation between the total yields of aromatic hydrocarbons from lignin and the abundancy of phenolic methoxyls in the lignin-derived pyrolysis vapor was found. It was also found that the pyrolysis vapors of simple H, G, or S-based monomers tend to produce more aromatic hydrocarbons than the vapors composed of more complex monomers and oligomers from their corresponding H, G or S group. However, the yield differences were less significant among G and S-based monomers and oligomers.