Study on the transformation characteristics of microstructure in Shengli lignite during low-temperature oxidation
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摘要: 选用内蒙古的胜利褐煤作为研究对象，通过固定床反应装置对褐煤进行不同温度（200-300 ℃）下的低温氧化，利用FT-IR、Raman和XPS等方法对氧化处理后煤样的结构进行了表征，考察了不同温度下低温氧化对褐煤微结构和质量变化的影响，并利用热重分析仪研究了氧化后煤样的燃烧反应性能。结果表明，温度对低温氧化过程中胜利褐煤的质量变化率影响较大，低于220 ℃时，褐煤的质量变化率很小，高于220 ℃时，质量变化率有明显的改变。特别在220-230 ℃，煤样的质量变化率由5.80%（220 ℃）突变为42.55%（230 ℃）。FT-IR/Raman/XPS表征结果显示，220 ℃氧化后的煤样中有明显的苯醌类结构形成，此结构的形成使苯环骨架C=C的伸缩振动吸收峰发生红移，且Raman谱图中D峰位置偏移，D峰和G峰两峰间距增大。氧化温度低于220 ℃的煤样表面C-O-和C=O的含量均增加，推测煤样在220-230 ℃质量变化率的突变主要与苯醌类结构的氧化分解有关。Abstract: A Shengli lignite from Inner Mongolia was selected as the research object, with which the low-temperature oxidation experiments were carried out at different temperatures (200-300℃) in a fixed bed reactor. The structure of coal samples after oxidation treatment was characterized by FT-IR, Raman and XPS. The effects of low-temperature oxidation at different temperatures on the microstructure and mass change of lignite were investigated and the combustion performance was determined by TGA. The results show that the temperature has a significant influence on mass change rate of Shengli lignite during low-temperature oxidation. The mass change rate of lignite is very limited when temperature is below 220℃ and it changes obviously when the temperature is higher than 220℃. Especially at 220-230℃, the mass change rate of coal samples is changed from 5.80% (220℃) to 42.55% (230℃). The FT-IR/Raman/XPS characterization results show that the analogous benzoquinone structure forms after oxidized at 220℃, and these lead to the stretching vibration absorption peak of the aromatic C=C shift to lower wavenumber. In Raman spectra, the position of the D peak shifts, and the distance between the peaks of D and G increases. The content of C-O-and C=O on the surface of coal samples increases at oxidation temperature lower than 220℃. It is speculated that the jump of mass change rate of coal samples at 220-230℃ is mainly related to the oxidative decomposition of analogous benzoquinone structure.
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图 1 实验装置示意图
Figure 1 Schematic diagram of the experimental installation
1: reaction carried gas; 2: gas chromatography; 3: mass flowmeter; 4: temperature thermocouple; 5: thermo detector; 6: temperature controlled thermocouple; 7: temperature control meter; 8: reactor; 9: ice-bath; 10: cold hydrazine; 11: treater; 12: back pressure meter; 13: six-way valve; 14: gas chromatography
图 2 不同温度低温氧化煤样的质量变化率
Figure 2 Mass change rate of coal samples after low-temperature oxidation at different temperatures
图 3 SL及不同温度低温氧化煤样的FT-IR谱图
Figure 3 FT-IR spectra of SL and coal samples after low-temperature oxidation at different temperatures
图 4 SL及不同温度低温氧化煤样的Raman光谱谱图
Figure 4 Raman spectra of SL and coal samples after low-temperature oxidation at different temperatures
图 5 煤样XPS C 1s谱图(a)与SL拟合图(b)
Figure 5 XPS C 1s peaks of the coal samples (a) and the fitting curves of SL (b)
图 6 SL及不同温度低温氧化煤样燃烧的TG/DTG曲线
Figure 6 TG/DTG curves of SL and coal samples after low-temperature oxidation at different temperatures
图 7 胜利褐煤低温氧化过程可能的机理分析示意图
Figure 7 Possible mechanism schematic of Shengli lignite during low-temperature oxidation
表 1 SL的工业分析和元素分析
Table 1 Proximate and ultimate analyses of SL
Sample Proximate analysis wad/% Ultimate analysis w/% M A V FC C H S N & O SL 3.21 12.43 37.90 46.46 57.60 3.53 1.51 24.93 note: ad: air dried; M: moisture; A: ash content; V: volatile; FC: fixed carbon 
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表 2 SL及不同温度低温氧化煤样Raman光谱图中峰位置和峰间距
Table 2 Peak locations and spacing distances in the Raman spectra of SL and coal samples after low-temperature oxidation at different temperatures
Sample F(D) /cm-1 F(G) /cm-1 d(G-D)/cm-1 SL 1371 1594 223 SL-T (200, 210) 1371 1588 217 SL-220 1358 1588 230 SL-T (230, 240, 250, 300) 1371 1585 214
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表 3 煤样中碳元素键合比例的分析
Table 3 Analysis for the content of carbon bonding forms in coal samples
Sample Carbon form (content w/%) C-C/C-H C*-C* C-O- C=O COO- SL 76.06 6.82 8.02 4.67 4.43 SL-200 76.28 6.14 8.36 4.72 4.50 SL-210 76.12 5.95 8.30 5.11 4.52 SL-220 76.34 5.13 8.46 5.40 4.67 SL-230 77.89 3.88 8.31 5.35 4.57 SL-240 78.68 3.74 7.73 5.32 4.53 SL-250 79.27 3.59 7.43 5.20 4.51 SL-300 78.51 3.58 7.97 5.31 4.63
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