一种解释高-过成熟烷烃气碳同位素系列倒转的新观点:芳香烃脱甲基作用

A New Interpretation of Carbon Isotope Series Reverse of Highly-Over Mature Alkane Gases:Demethylation of Aromatic Hydrocarbons

天然气成因机理复杂,鉴于在高-过成熟阶段烷烃气碳同位素系列倒转普遍存在,而高-过成熟阶段有机质中常富含芳环结构,利用芳香烃(甲苯)热裂解实验探讨高-过成熟阶段烷烃气碳同位素系列倒转成因.甲苯热裂解实验表明随着模拟温度的增加,烷烃气产率逐渐增大;模拟产物中H2产率也随着模拟温度的增加而增加.甲苯裂解产物中δ13C1、δ13C2和δ13C3分布区间分别为-31.8‰^-27.7‰,-31.0‰^-20.4‰和-31.0‰^-20.4‰.在甲苯热模拟实验450°C时,出现了烷烃气碳同位素系列的部分倒转(δ13C1>δ13C2<δ13C3).发现无论是煤成气还是油型气,在高-过成熟阶段都会出现烷烃气碳同位素系列的倒转,结合本次模拟实验结果,认为芳香烃脱甲基作用可能是烷烃气高-过成熟阶段出现碳同位素系列倒转的一个重要原因.

The genetic mechanism of natural gas is complex.In view of the fact that carbon isotope series reverse of alkane gas exists generally in the highly-over mature stage,and the organic matter in the highly-over mature stage is often rich in aromatic ring structure,the carbon isotope series reverse of alkane gas in the highly-over mature stage is discussed by means of pyrolysis experiments of aromatic hydrocarbons(toluene).The pyrolysis of toluene shows that the yield of alkane gas increases with the increase of simulated temperature,and the yield of H2 in the product increases with the increase of simulated temperature.The distribution ranges ofδ13C1,δ13C2 andδ13C3 in toluene pyrolysis products are-31.8‰to-27.7‰,-31.0‰to-20.4‰and-31.0‰to-20.4‰,respectively.In the toluene thermal simulation experiment at 450°C,partial reversal of carbon isotope series of alkanes occurred(δ13C1>δ13C2<δ13C3).It is found that carbon isotope series reversal occurs in both coal type gas and oil type gas at highly-over mature stage.Combining with the simulation results,it is considered that aromatic hydrocarbon demethylation may be an important reason for carbon isotope series reversal in highly-over mature stage of alkane gas.