Vitrinites In Typical Coal-bearing Basins Of China: The Molecular Characterization And Their Kinetic Studies On The Hydrocarbon Generation And Carbon Isotope Fractionation

The certain oil and gas pertained to coals and coaly mudstones have been found in the Jurassic coal-bearing basins in NW China. But little oil has been found in any Carboniferous-Permian coal-bearing basins. Vitrinite is the most dominant maceral in coals. And HI of coals shows good correlation with proportion of desmocollinite or summation of liptinite and desmocollinite. Therefore, it's meaningful to study structure of different vitrinites for understanding formation of coal-generated oils. The main conclusions of this study are followings:1. Jurassic and Carboniferous-Permian coal used for this study is obtained from Jungger, Turpan-Hami, Ordos and other basins of China. Flash pyrolysis-gas chromatography/ mass spectra (Py-GC/MS) have been applied to the quantitative determination of different groups of hydrocarbons and non-hydrocarbons presented in pyrolysates of hand purified vitrinites isolated from coals.Aliphatics, phenols, alkylbenzenes and other aromatic hydrocarbons are the mayor components in pyrolysates of vitrinites. Long chain aliphatics are more abundant in pyrolysates of hydrogen-rich desmocollinites while phenols are more abundant in pyrolysates of telocollinites. And aliphatics are the most abundant components in pyrolysates of Jurassic hydrogen-rich desmocollinite of Xinjiang Area. However, similar phenol distributions are presented in pyrolysates of vitrinites at the same maturation level. And this indicates pheols may be originated from diagenetically altered lignins.Flash pyrolysis at different temperatures point and step pyrolysis have been applied to study variation of production ratio and relative proportion of major components in pyrolysates. Relative abundance of n-alkanes reaches the highest in pyrosates generated at 350℃, and then shows decreasing trend with increasing temperature while relative abundance of alke-1-nes, phenols and alkylbenzenes show contrary variation.Flash pyrolysis in the presence of tetramethylammonium hydroxide (TMAH) has been employed for the characterization of polar components that cannot be detected using normal pyrolysis GC-MS. And large quantity of carboxylic acid methyl esters is determined.2. 13C NMR spectra, which provide direct measurements of the chemical structure of organic matter, have been obtained for vitrinites. The oil-prone carbons, such as methylene carbon, are relatively rich in spectra of desmocollinites, and the gas-prone carbons, such as methyl carbon and methoxyl carbons, are relatively rich in spectra oftelocoUinites. Converted into numerical parameters, the spectra show differences relate to vitrinite type and rank. NMR parameters, fa, Sox, fCO2H and fCOH, are examined for characterization of macromolecular structure of vitrinites. Result shows Sox is sensitive to rank of coals.3. The depositional environment of vitrinites has been discussed based on the characterization of vitrinite structure. It shows Jurassic hydrogen-rich desmocollinites has been deposited in running water swamp and telocoUinites has been deposited in moist forest swamp. Several isolated lipid macerals have been subject to perform flash pyrolysis-GC/MS for comparison between desmocollinites and lipids, and the result shows that aliphatics in desmocollinite may be originated from lipid parts of high plants.4. Hydrocarbon generation kinetics study of vitrinites based on pyrolysis of gold tube closed system shows: Activation energies of methane generated from telocollinite are higher than that from desmocollinite due to macromolecular structure differences. But carbon isotope distributions of generated methane in pyrolysates of vitrinites are similar. Carbon isotope ratio of methane decreases in the early stage of gas generation and increases in later stages. At higher temperature, δ13C1 decrease slightly or almost keep stable with increasing temperature. Decreasing trend of δ 13C, in the early stage may be caused by heterogeneous structure or differences of activation energies between 12C-12C and 12C-13C are not strictly constant at different range of activation energy area.5. Aliphatics, especially long chain n-alkanes are more abundant in liquid fraction originated from Zhunji-1 desmocollinite than that from Tujun-1 telocollinite in gold tube pyrolysis. And distribution of n-alkanes in liquid fraction shows even to odd predominance that indicates anhydrous gold tube pyrolysis is not suitable for the simulation of oil generation.