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摘要: 采用微型高温高压反应釜，在超/亚临界乙醇体系，进行麦草碱木质素的解聚实验，通过扫描电子显微镜（SEM）、气相色谱/质谱联用仪（GC/MS）及红外光谱仪（FT-IR）对解聚产物进行分析，探讨大分子结构的解聚机理。结果表明，碱木质素在乙醇临界点条件（240℃，7.2 MPa）解聚获得最低残焦得率，数值为16.5%。碱木质素在亚临界乙醇体系解聚过程，碱木质素熔融形成直径1.0-2.0 μm的微球分散于乙醇中，结构单体间少量醚键和苯环侧链Cα均裂断裂，形成酚类、酯类、酮类和酸类产物；碱木质素在超临界乙醇体系解聚过程，熔融微球直径明显缩小，解聚时发生大量结构单体间醚键、苯环侧链Cα断裂及酯类产物的二次分解反应，解聚产物中酯类产物含量（11.94%）降低，酚类产物得率（52.14%）提高。Abstract: The depolymerization process of wheat straw alkali lignin in sub- and supercritical ethanol was investigated with a micro autoclave reactor. The degraded product properties and the depolymerization mechanism of lignin structure were studied by scanning electron microscopy (SEM), gas chromatography/mass spectrometry (GC/MS) and infrared spectroscopy (FT-IR). The experimental results show that the minimum residual char yield (16.5%) is obtained at the condition of ethanol supercritical point (240℃, 7.2 MPa). Under subcritical ethanol conditions, alkali lignin firstly melts and disperses in ethanol as 1.0-2.0 μm diameter of microspheres, then a small amount of ether linkages and benzene ring side chain Cα are broken to form phenols, esters, ketones and acids products. Under supercritical ethanol conditions, the diameter of molten microsphere is significantly reduced, and plenty of ether linkages and benzene ring side chain Cα are continuously broken, meanwhile, the lipid products are subjected to secondary decomposition reaction. The yield of lipid is decreased (11.94%), while the yield of phenolic products from depolymerization is increased (52.14%).
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Key words:
- alkali lignin /
- sub- and supercritical ethanol /
- depolymerization
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图 1 碱木质素超/亚临界乙醇体系解聚残焦得率
Figure 1 Analysis depolymerization char yield of alkali lignin in sub-and supercritical ethanol system
图 2 碱木质素和碱木质素超/亚临界乙醇解聚残焦的SEM照片
Figure 2 Char SEM micrographs of alkali lignin and alkali lignin depolymerization in sub-and supercritical ethanol
(a): alkali lignin; (b): 180 ℃ and 4 h char; (c): 240 ℃and 4 h char; (d): 300 ℃ and 4 h char
图 3 碱木质素在超临界乙醇体系解聚残焦EDS图残焦； 240 ℃/4 h半焦
Figure 3 Char EDS micrographs of alkali lignin depolymerization in supercritical ethanol; 240 ℃ and 4 h char
图 4 碱木质素和碱木质素亚/超临界醇解聚残焦FT-IR谱图
Figure 4 Char FT-IR spectra of alkali lignin and alkali lignin depolymerization in sub-and supercritical ethanol
图 5 碱木质素超/亚临界乙醇解聚液相产物GC/MS总离子流图
Figure 5 Oil GC/MS chromatogram of alkali lignin depolymerization in sub-and supercritical ethanol
图 6 碱木质素超/亚临界乙醇体系解聚过程断键方式示意图
Figure 6 Broken bond mechanism of alkali lignin depolymerization in sub-and supercritical ethanol system
表 1 实验原料的工业分析和元素分析
Table 1 Ultimate and proximate analyses of the materials
Materials Proximate analysis w/% Ultimate analysis w/% Na/10-6 A V FC C H O* N Alkali lignin 0.22 54.18 45.60 56.01 8.54 35.34 0.08 - *: by difference 
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表 2 碱木质素超/亚临界乙醇解聚液相产物组成的GC/MS分析
Table 2 Oil GC/MS of alkali lignin depolymerization in sub-and supercritical ethanol
Retention time t/min Products name Molecular formula Content w/% 180 ℃ 210 ℃ 240 ℃ 270 ℃ 300 ℃ 12.41 phenol 
- 2.89 2.97 0.46 5.65 15.47 phenol, 2-methoxy- - 8.54 10.77 13.06 12.82 18.32 phenol, 4-ethyl- - - 1.77 2.79 6.63 18.62 1, 4-benzenediol, 2, 5-dimethyl- - - - - 3.41 18.74 2-methoxy-4-methylphenol - 3.77 5.74 7.45 8.22 20.54 1, 2-benzenediol, 3-methoxy- - - 4.17 - - 20.98 phenol, 2-ethyl-4-methyl- - - - - 2.26 21.23 phenol, 4-ethyl-2-methoxy- - 5.73 7.47 10.10 10.87 22.34 phenol, 5-methyl-2-(1-methylethyl)- - - - - 2.08 23.28 phenol, 2, 6-dimethoxy - 15.77 17.62 19.81 7.29 23.48 t-butylhydroquinone - - - - 3.18 23.68 phenol, 2-methoxy-4-propyl- - - 1.63 2.49 3.45 25.55 benzoic acid, 4-hydroxy-3-methoxy- - 5.11 9.10 9.64 6.49 26.63 4-hydroxy-3-methoxyacetophenone - 3.50 1.94 - - 27.70 benzene, 1, 2, 3-trimrthoxy-5-methyl- - 6.94 7.14 9.14 6.38 27.84 2-propanone, 1-(4-hydroxy-3-methoxyphenyl)- - 2.83 2.98 2.87 - 28.16 4-hydroxy-benzoicaciethylester 
- 8.03 4.12 - - 29.29 benzoic acid, 4-hydroxy-3-methoxy-, ethyl ester - 8.15 3.24 2.71 - 29.31 diethyl suberate - - - - 4.58 29.71 2, 4, 6-trimethoxy benzaldehyde - - - - 2.70 30.51 4-hydroxy-3-methoxyphenylacetic acid, ethyl ester - 7.59 4.58 4.19 1.28 31.62 decanedioic acid, dimethyl ester - - - - 9.69 32.54 ethanone, 1-(4-hydroxy-3, 5-dimethoxyphenyl)- 100 10.30 4.75 3.17 - 32.90 ethyl-β-(4-hydroxy-3-methoxy-phenyl)-propionate - 2.77 5.95 4.97 3.01 33.05 3, 5-domethoxy-4-hydroxyphenylacetic acid - 1.45 4.05 4.05 - 35.59 acetic acid, diphenyl-, ethyl ester - 6.64 - 3.11 -
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