Functional groups of sequential extracts and corresponding residues from Hefeng sub-bituminous coal based on FT-IR analysis
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摘要: 以酸洗和丰次烟煤为研究对象，依次采用石油醚、二硫化碳、甲醇、丙酮和丙酮/二硫化碳对煤样进行超声五级萃取，每级萃取物和萃余物分别记为Ei和Ri（i=1、2、3、4、5）。通过对Ei及Ri进行FT-IR表征，借助分段分峰拟合手段分析了萃取产物的分子结构。结果表明，五级萃取物的羟基氢键结构均以自缔合羟基氢键为主；在脂肪类物质中，除第三级萃取物E3以脂肪族−CH3和不对称的−CH2伸缩振动为主之外，其余几级萃取物均以对称和不对称的−CH2伸缩振动为主；E1主要以脂肪链末端−CH3的对称弯曲振动和−CH3、−CH2的不对称变形振动为主，说明石油醚主要将煤样中易于解离的化学键断裂；五级萃取中CS2溶解了更大比例的含脂肪侧链的芳香结构。各级萃余物所含官能团种类相同，说明煤样主体结构并未因逐级萃取而发生改变。萃取对残渣中芳香结构和羟基氢键结构影响较大。其中，酸洗煤样以苯环二取代为主，而萃取后以苯环四取代为主。萃取前，酸洗煤样中羟基氢键结构以羟基醚氢键为主，而萃取后转变成以自缔合羟基氢键为主。另外，分级萃取对含氧官能团和脂肪类官能团影响较小。对比红外结构参数发现，E1、E3及R5有较高的芳环缩合度，E4的脂肪直链较长、支链较少。Abstract: Petroleum ether, carbon disulfide, methanol, acetone, and acetone/carbon disulfide were selected as solvents for ultrasonic-assisted extraction of acid-washed Hefeng sub-bituminous coal. The extract and residue were identified as Ei and Ri (i = 1, 2, 3, 4, 5) for each stage. By FT-IR characterization of Ei and Ri, molecular structure of the extracted product was analyzed by means of segmented peak fitting. The results show that the hydroxy hydrogen bond in the fifth-order extract is dominated by self-associating hydroxy hydrogen bond; in aliphatic substances, only E3 was dominated by aliphatic −CH3 and asymmetric −CH2 stretching vibration, while the other extracts were dominated by symmetric and asymmetric −CH2 stretching vibration. E1 is dominated by symmetric bending vibration of aliphatic chain terminal −CH3 and asymmetric deformation vibration of −CH3 and −CH2, indicating that petroleum ether mainly break the easily dissociated chemical bonds in coal samples; CS2 dissolve a higher proportion of aromatic structure containing aliphatic side chains. The functional groups contained in the five residues are the same, indicating that the main structure of the coal sample is not changed due to the stepwise extraction. Extraction has an obvious influence on aromatic structure and hydroxy hydrogen bond in the residue. Aromatic structures change from di-substituted benzene dominant to tetra-substituted benzene dominant. Before extraction, the hydroxyl hydrogen bond in the acid-washed coal sample was dominated by hydroxyl ether hydrogen bonds, and after extraction, it was transformed into self-associated hydroxyl ones. In addition, sequential extraction has little effect on oxygen-containing functional groups and aliphatic functional groups. By comparing structural parameters, it is found that E1, E3, and R5 has a higher degree of aromatic condensation, and E4 has a longer straight-chain and less branched chain.
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Key words:
- coal structure /
- FT-IR spectroscopy /
- functional groups /
- extract residue
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图 3 700−900 cm−1段萃取物的红外分峰谱图
Figure 3 FT-IR curve-fitting results of the extracts (700−900 cm−1)
图 4 1000−1800 cm−1段萃取物的红外分峰谱图
Figure 4 FT-IR curve-fitting results of extracts (1000−1800 cm−1)
图 5 2800−3000 cm−1段萃取物的红外分峰谱图
Figure 5 FT-IR curve-fitting results of extracts (2800−3000 cm−1)
图 6 3100−3600 cm−1段萃取物的红外分峰谱图
Figure 6 FT-IR curve-fitting results of extracts (3100−3600 cm−1)
图 8 700−900 cm−1段萃余物的红外分峰谱图
Figure 8 FT-IR curve-fitting results of the extraction residue (700−900 cm−1)
图 9 1000−1800 cm−1段萃余物的红外分峰谱图
Figure 9 FT-IR curve-fitting results of the extracts residues (1000−1800 cm−1)
图 10 2800−3000 cm−1段萃余物的红外分峰谱图
Figure 10 FT-IR curve-fitting results of the extraction residue (2800−3000 cm−1)
图 11 3100−3600 cm−1段萃余物的红外分峰谱图
Figure 11 FT-IR curve-fitting results of the extraction residue (3100−3600 cm−1)
表 1 煤样的工业分析和元素分析
Table 1 Proximate and ultimate analyses of the coal samples
Sample Proximate analysis w/% Ultimate analysis wdaf/% H/C Mad Ad Vdaf FCdaf C H N S O* HF 5.88 21.18 42.81 57.19 74.91 5.65 1.50 0.37 17.57 0.91 HFAC 1.52 1.84 44.37 55.63 73.05 5.33 1.50 0.38 19.74 0.88 
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表 2 五种样品红外光谱分峰拟合各吸收峰面积比例
Table 2 Parameters of FT-IR spectrum for five samples by curve-fitting
Band position/cm−1 Functional groups Area percentage/% E1 E2 E3 E4 E5 900−860 five adjacent H deformation 10.13 10.95 0 21.24 8.28 860−810 four adjacent H deformations 22.54 57.05 17.21 40.56 36.04 810−750 three adjacent H deformations 39.22 24.24 56.95 16.18 8.10 750−720 two adjacent H deformations 28.11 7.77 25.84 22.03 47.59 1710 carboxylic acids C=O 11.48 21.61 13.59 12.78 19.54 1650 conjugated C=O 4.73 14.48 10.34 21.51 15.39 1500 aromatic C=C 1.26 2.86 4.21 8.46 9.67 1436 asymmetric −CH3, −CH2 36.56 20.20 3.18 14.56 13.01 1371 CH3-Ar, R 16.80 11.88 3.55 10.00 9.75 1269 symmetric deformation −CH3 8.95 12.32 15.45 10.61 13.30 1165 C−O phenols 2.54 8.37 25.91 9.43 8.07 1110 grease C−O 9.53 5.19 20.94 8.39 6.12 1035 alkyl ethers 7.84 3.09 2.84 4.26 5.16 2950 aliphatic −CH3 22.56 24.16 31.67 14.42 23.15 2920 asymmetric aliphatic −CH2 29.12 26.21 34.80 39.21 37.34 2890 aliphatic −CH 20.06 20.65 18.36 17.99 16.40 2850 symmetric aliphatic −CH2 28.27 28.98 15.17 28.39 23.10 3600−3500 OH−π 17.43 16.20 14.86 33.78 9.41 3500−3350 self-associated OH 53.67 39.40 55.80 40.73 44.94 3350−3260 OH-ether O 13.72 31.07 18.41 19.25 38.44 3260−3170 cyclic OH 15.19 13.33 10.93 6.24 7.21
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表 3 五级萃取物的结构参数
Table 3 Structural parameters of five samples derived from the FT-IR spectrum
Sample DOC A(CH2)/A(CH3) E1 16.19 1.28 E2 3.24 1.08 E3 13.03 1.06 E4 0.90 2.71 E5 0.34 1.61
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表 4 六种样品红外光谱分峰拟合各吸收峰面积比例
Table 4 Parameters of FT-IR spectrum for six samples by curve-fitting
Band position/cm−1 Functional groups Area percentage/% HFAC R1 R2 R3 R4 R5 900−860 five adjacent H deformation 5.41 19.88 19.19 21.66 15.01 19.02 860−810 four adjacent H deformations 11.52 43.34 43.82 44.84 38.78 41.66 810−750 three adjacent H deformations 18.73 18.51 13.08 15.62 8.81 16.81 750−720 two adjacent H deformations 64.34 18.27 23.91 17.89 37.4 22.51 1710 carboxylic acids C=O 15.94 11.49 11.57 12.56 16.96 14.68 1650 conjugated C=O 19.67 23.57 22.66 23.98 21.41 22.85 1500 aromatic C=C 6.54 9.96 8.65 7.48 6.40 9.00 1436 asymmetric −CH3, −CH2 12.18 14.95 14.89 15.64 15.12 14.14 1371 CH3-Ar, R 7.98 9.2 9.51 9.21 9.26 9.27 1269 symmetric deformation −CH3 9.33 10.75 11.14 11.07 11.90 9.35 1165 C−O phenols 9.05 8.93 9.48 8.71 8.43 8.42 1110 grease C−O 15.69 7.55 7.91 8.36 6.39 8.14 1035 alkyl ethers 3.62 3.61 4.19 2.99 4.13 4.13 2950 aliphatic −CH3 19.06 15.68 15.71 17.99 21.61 15.06 2920 asymmetric aliphatic −CH2 35.83 39.69 39.00 40.82 37.31 38.15 2890 aliphatic −CH 24.95 18.11 18.60 15.59 17.04 18.34 2850 symmetric aliphatic −CH2 20.16 26.51 26.69 25.61 24.04 28.44 3600−3500 OH−π 30.53 29.18 26.76 26.23 7.42 31.85 3500−3350 self-associated OH 36.26 40.13 34.76 31.00 41.18 38.01 3350−3260 OH-ether O 20.06 18.75 22.95 24.68 42.82 18.08 3260−3170 cyclic OH 13.15 11.94 15.53 18.09 8.58 12.06
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表 5 酸洗煤及五级萃余物的结构参数
Table 5 Structural parameters of six samples derived from the FT-IR spectrum
Sample I DOC A(CH2)/A(CH3) $ 'C' $ HFAC 0.17 0.09 2.53 0.84 R1 0.30 0.08 2.54 0.81 R2 0.46 0.11 2.49 0.82 R3 0.35 0.11 2.28 0.84 R4 0.19 0.10 1.72 0.86 R5 0.60 0.14 2.55 0.83
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