| 高磁场固态碳13核磁共振法研究干酪根的热降解成烃机理 |
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| 引用本文： | 秦匡宗,吴肖令.高磁场固态碳13核磁共振法研究干酪根的热降解成烃机理[J].沉积学报,1990,8(1):19-27. |
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| 作者姓名： | 秦匡宗 吴肖令 |
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| 作者单位： | 1.华东石油学院北京研究生部; |
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| 基金项目： | 国家自然科学基金委员会研究项目 |
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| 摘 要： | 用高磁场(75.46MHZ)固态碳13核磁共振(NMR)波谱仪研究了抚顺油页岩在热降解模拟试验中干酪根的化学结构变化.为了消除旋转边带的干扰,在应用交叉极化与魔角自旋(CP/MAS)技术的同时,采用了Dixon TOSS技术,从而得到高分辨的波谱图。据此测定了热降解过程中干酪根各种碳结构组成的变化,计算了芳碳率、亚甲基基团平均碳原子数、环缩合指数等一系列干酪根的结构参数,并与干酪根的相对产油潜力相关联.发现干酪根的产油潜力直接与亚甲基基团的含量有关,而芳碳以及与芳碳相连的甲基碳则贡献甚微.文中还对干酪根的热降解成烃机理作了探讨。
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| 关 键 词： | 干酪根 核磁共振 产油潜力 |
| 收稿时间： | 1987-12-07 |
MECHANISM OF HYDROCARBON FORMATION FROM OIL SHALE KEROGEN VIEWED BY HIGH MAGNETIC FIELD SOLID STATE C-13 NMR SPECTROSCOPY |
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| Institution: | 1.Beijing Graduate School, China Petroleum University;2.Physics Department, East China Normal University |
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| Abstract: | Fushun oil shale was pyrolysed in Fischer Assay with heating rate of 5℃ / mm to different final temperatures ranged from 400 to 510℃ .The raw oil shale and the pyrolyzed solid residues were extracted by chloroform and demineralized by hydrochloric acid and hydrofluoric acid. The chemical structure of these kerogen concentrates was investigated using the high field (75.46 MHz) solid state C- 13 NMR spectroscopy with cross polarization and magic angle spinning. The Dixon TOSS technique combined with rotor spinning rate of 4 KHz suppressed the aromatic carbon spinning side-bands and provided satisfactory spectra of high resolution and low distortion. In the aliphatic carbon region, the peaks assigned to the terminal methyl carbons ( 14-16 ppm), the aromatic bonded methyl carbons ( 18-20 ppm), the ethelene carbons (28-30 ppm) and the shoulder (35-40 ppm) likely assigned to the alpha methelene or methine carbons bonded to the aromatic rings, are founded to be distinguished distinctly. The resolution of the aromatic carbon region is limited perhaps due to the anisotropy of the aromatic structure. Generally, the high field solid state C-13 NMR (CP / MAS+TOSS) spectroscopy provided a direct method for detecting and measuring the carbon distribution of kerogen. The aliphatic termimal methyl carbon is weakened graduately as the final temperature of degradation is increased, that implies it takes an active part in the oil and gas formation. On the contrary, the aromatic methyl carbons grow up from a shoulder in the original kerogen NMR spectra to a main peak of residue aliphatic carbons for the kerogens which had experienced the high degree thermal degradation. It supports the hypothesis that the beta bond scission is one of the essential reactions in the thermal degradation process. The most dominant resonance band of the original kerogen is the methelene carbons, which consume quickly throughout the process of oil and gas formation, and were depleted as the genaration of oil had finished. The broad band of aromatic carbons becomes a dominent peak in the spectrum as the process is going on. It is found that the yield of aromatic carbon in the whole process of degradation is kept nearly constant. Since the aromatic cluster of the original kerogen had been recognized in the previous studies to be primary composed of 3-5 kata-condensed rings, yet most aromatic components of shale oil have only single and double rings, it reasonable to assume that as the simple aromatics were formed by aromatization of aliphatics, they are rather easy to migrate as components of oil, and merely the intrinsical aromatic carbons were left in the degradated kerogens. It sounds to be an answer that why the conservation of aromatic carbon is not an individual feature in many thermal degradation experiments for different types of kerogens. In general, the aomatic carbons contribute little to the generation of hydrocarbons. Based on the NMR and ultimate analysis data of kerogens, a series of chemical structural parameters had been derived, including apparent carbon aromaticity, average carbon number of methelene groups and ring condensation index. They are correlated with the kelative oil yields of the derogens where the original kerogen oil yield was taken as unit. A straight line is plotted to show the relation between relative oil yields and apparent aliphatic carbon fractions. It intersects with the axis of aliphatic carbon fraction at 0.17, indicates that this portion of aliphatic carbon have not taken part with oil generation. Another straight line plotted with the sum of methelene and terminal methyl carbon fractions instead of the aliphatic carbon fraction reaches the origin point. It means that they are the exact matrix of oil.The relation of relative oil yields and average number of carbon atoms in methelene groups of carbon number larger than 5 possess of high potential in generating oil, and those of less than 3 are insignificant to the oil formation. The curve of ring condensation index evolution path depicts different reaction stages of |
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