Separation and characterization of C5-asphaltene from low temperature coal tar
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摘要: 从低温煤焦油中蒸馏提取出大于350℃的常渣，以正戊烷、正戊烷+5%乙醇、正戊烷+5%异丙醇三种溶剂沉淀沥青质。通过1H-NMR、13C-NMR、傅里叶变换离子回旋共振质谱仪（FT-ICR MS）、元素分析和相对分子量测定等手段对重组分沥青质的结构参数、杂原子化合物的分布等方面进行了分析，构建含杂原子的平均分子结构模型。结果表明，乙醇和异丙醇的加入可以显著降低C5-沥青质的收率，所得沥青质的芳香性增强，平均分子量增大，为更高缩合度的具有较短侧链的结构；极性溶剂的加入没有改变沥青质中杂原子化合物的类型，但是O1和O2中一部分低缩合度的化合物转移到可溶质中，O3-O6化合物的相对丰度增大，表明混合溶剂有利于萃取低缩合度的化合物。Abstract: The asphaltene was obtained from the low temperature coal tar heavy fraction by solvent precipitation with three kinds of solvents; n-pentane, n-pentane with 5% ethanol and n-pentane with 5% isopropanol. The properties such as structure parameters and hetero atom distribution were analyzed by 1H-NMR, 13C-NMR, FT-ICR MS, elemental analysis and average molecular weight determination (GPC). Some possible average molecular structures containing hetero atoms were constructed and discussed. The results show that after adding polar solvent, the yield of C5-asphaltene is significantly reduced, while the aromaticity and average molecule weight are enhanced. The average molecular structure of the C5-asphaltene exhibits shorter side-chains and higher condensation degree. Though the type of heteroatom compounds in the asphaltene is barely changed by the addition of polar solvents, the relative abundance of O3-O6 class species is increased. Meanwhile, some O1-O2 class species with low condensation degree are transferred into maltene, indicating that the mixed solvent has a larger solubility with these compounds.
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图 3 不同沥青质的负离子ESI FT-ICR MS谱图
Figure 3 Negative-ion ESI FT-ICR MS spectrum of different asphaltenes
图 4 不同沥青质的杂原子分布
Figure 4 Heteroatom class and type distribution of different asphaltenes
图 5 不同沥青质的O1类DBE及碳数分布
Figure 5 DBE number vs the carbon number for O1 class in different asphaltenes
图 6 不同沥青质的O2类DBE及碳数分布
Figure 6 DBE number vs the carbon number for O2 class in different asphaltenes
图 7 不同沥青质的O3-O6类DBE及碳数分布
Figure 7 DBE number vs the carbon number for O3-O6 class in different asphaltenes
图 8 不同沥青质的N1O1类DBE及碳数分布
Figure 8 DBE number vs the carbon number for N1O1 class in different asphaltenes
表 1 原料油的基本性质
Table 1 Main properties of the raw maeterial
wCCR/% ρ20/(g·cm-3) η100/(mPa·s) Mn w(C7 asphaltene)/% w(oxygen)/% H/C (atomic ratio) 17.73 1.103 590.20 339 26.58 7.80 1.14 
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表 2 溶剂的物性参数
Table 2 Physical parameters of several solvents
Solvent Boiling point t/℃ Polarity Molecular weight n-pentane 36.1 0 72.15 Ethanol 78.3 4.3 46.07 iso-propanol 82.4 3.9 60.06
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表 3 煤焦油重组分沥青质元素分析和分子量
Table 3 Elemental analysis and molecular weights of coal tar asphaltene
Sample Element analysis w/% H/C (atomic ratio) Mn Mw Polydispersitya Mw/Mn C H N S O C5 83.73 7.46 0.81 0.20 7.00 1.07 398 708 1.78 C5+C2 77.94 6.11 1.18 0.30 6.92 0.94 541 1 046 1.93 C5+C3 82.43 6.06 1.42 0.30 8.60 0.88 523 1 020 1.95
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表 4 两种算法计算1H-NMR谱图的氢分布
Table 4 Calculated numbers of hydrogen atoms from 1H-NMR by two methods
H type C5 C5+C2 C5+C3 Method 1 HA 8.26 13.40 11.77 Hα 8.64 10.50 10.71 Hβ 9.81 6.97 7.09 Hγ 2.73 1.97 1.87 Method 2 HA 9.53 13.22 12.77 Hα 7.21 11.20 10.78 Hβ 9.42 6.16 6.19 Hγ 3.29 2.21 1.71
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表 5 两种算法计算1H-NMR芳碳率和13C-NMR芳碳率相对误差
Table 5 Relative error of fA calculation by two methods
C5 C5+C2 C5+C3 13C-NMR fA 0.67 0.70 0.74 1H-NMR fA method 1 0.62 0.72 0.72 method 2 0.66 0.73 0.75 Relative method 1 7.46 2.68 2.70 error/% method 2 1.49 4.28 1.35
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表 6 沥青质的平均分子结构参数
Table 6 Average structure parameters of coal tar asphaltene
Structure parameter C5 C5+C2 C5+C3 CA 18.27 25.62 26.78 CN 3.97 7.50 7.42 CP 5.51 1.98 1.69 fA 0.66 0.73 0.75 fN 0.14 0.21 0.21 fP 0.20 0.06 0.05 RT 4.89 6.90 7.79 RA 3.56 4.40 5.31 RN 1.32 2.50 2.47 RA/RN 2.70 1.76 2.15 HAU/CA 0.82 0.83 0.79 σ 0.36 0.37 0.39 n 1 1 1 L 5.03 2.70 2.97 Average molecular Formula C28H32 N0.23O1.74 C35H32 N0.45O2.33 C36H31 N0.53O2.81
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