木质素在超临界甲醇和乙醇溶剂中液化过程分析

doi:10.16085/j.issn.1000-6613.2018-1644

摘要/Abstract

摘要：

通过研究木质素分别在超临界甲醇和乙醇溶剂中的液化过程，分析反应温度（260～340℃）及反应时间（0～120min）对木质素在两种溶剂中的转化率、生物油收率及其组分差异的影响。实验表明，木质素在超临界乙醇中的转化率及产物收率均高于甲醇。当反应温度340℃，反应时间60min，木质素在超临界乙醇中的转化率和生物油收率比在甲醇中分别提高了16.23%和11.54%，残渣收率降低了16.23%。通过GC-MS和FTIR对生物油和残渣分析，发现生物油组分中芳香族化合物相对含量较高，在甲醇和乙醇溶剂中分别达到66.13%和58.84%；随着反应时间的延长，甲醇溶剂中残渣的醚键官能团逐渐增强，而在乙醇溶剂中则先增强后减弱。分析认为在木质素降解过程中，超临界乙醇和甲醇均可产生氢自由基作为供氢体，攻击木质素及其大分子片段中的官能团，同时使液化产物中的活性片段减活，减弱重聚合反应，从而更利于芳烃产物的生成。而甲醇在液化过程中容易与木质素断键产生的苯酚中间体发生脱氢缩合反应，通过醚键聚合产生长链芳香族化合物，形成残渣，降低生物油收率。

关键词: 木质素, 液化, 超临界流体, 小分子醇, 芳香族化合物

Abstract:

The effect of reaction temperature (260—340℃) and reaction time (0—120min) were explored in the liquefaction in supercritical methanol and ethanol solvent, respectively. The difference were analyzed between feedstock conversion, bio-oil yield and component in the process. Results showed the conversion and yield of lignin were higher in ethanol than those in methanol. The conversion and bio-oil yield in ethanol were 16.23% and 11.54% higher than those in methanol, respectively. The residue yield was lower 16.23%, when reaction at 340℃ lasted 60min. GC-MS and FTIR characterization revealed the aromatic content in bio-oil was very high, reached 66.13% and 58.84%, respectively in methanol and ethanol solvent. And the ether-bond functional group of residue in methanol gradually increased with the extension of reaction time, while it was enhanced firstly and then weakened in the ethanol solvent. In the process of lignin degradation, ethanol and methanol could produce hydrogen free radicals as hydrogen donors firstly, then attack lignin and its group bonding in macromolecular fragments. At the same time, it could inactivate the active fragments in the liquefied products, weaken the heavy polymerization reaction, and facilitate the generation of aromatic products. However, the methanol could easily undergo de-hydro-condensation reaction with phenol intermediates, which were produced in the process of liquefaction. Long-chain aromatic compounds could be produced through ether bond polymerization, forming residues, and reducing bio-oil yield.

Key words: lignin, liquefaction, supercritical fluid, alcohol, aromatic compounds

中图分类号:

廖玮婷, 解新安, 李璐, 李雁, 樊荻, 孙娇, 王鑫. 木质素在超临界甲醇和乙醇溶剂中液化过程分析[J]. 化工进展, 2019, 38(05): 2205-2211.

Weiting LIAO, Xin’an XIE, Lu LI, Yan LI, Di FAN, Jiao SUN, Xin WANG. Lignin liquefaction in supercritical methanol and ethanol solvent[J]. Chemical Industry and Engineering Progress, 2019, 38(05): 2205-2211.

图/表 11

表1 木质素元素分析

元素	质量分数/%
C_ad	57.48
H_ad	5.60
O_ad	34.49
N_ad	0.08

图1 木素原料热解的TG/DTG曲线图

图2 木质素液化与产物分离流程

图3 不同反应温度下木质素在超临界乙醇中液化产物收率及木质素转化率

图4 不同反应温度下木质素在超临界甲醇中液化产物收率及木质素转化率

图5 反应时间对木质素在超临界乙醇溶剂中液化产物收率及转化率的影响

图6 反应时间对木质素在超临界甲醇溶剂中液化产物收率及转化率的影响

图7 反应时间对甲醇液化生物油中主要化合物相对含量影响

图8 反应时间对乙醇液化生物油中主要化合物相对含量影响

图9 反应时间对甲醇液化木质素生成的固体残渣FTIR分析

图10 反应时间对乙醇液化木质素生成的固体残渣FTIR分析

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