低阶煤热解结构演化及与烷烃气碳同位素相关性的红外光谱

为了阐释煤热解过程中结构演化与烷烃气碳同位素的关系，进行了低阶煤在高压釜密闭体系下热解实验，分析热解烷烃气碳同位素组成；借助傅里叶红外光谱(FTIR)精细剖析了煤结构演化规律，构建了烷烃气碳同位素组成与结构演化的关系模型，揭示了热解烷烃气碳同位素变化的原因。结果显示在R_{o, max}＜1.3%之前的阶段，煤中脂链轻碳同位素被分馏出去而重碳同位素被留在长链中；当1.3%＜R_{o, max}＜2.0%时, 具有相对较重碳同位素组成脂链再进一步的断裂分解仍主导了烷烃气碳同位素变化，也即是R_{o, max}在2.0%之前的阶段，煤中脂链倾向性的裂解方式是烷烃气碳同位素变化的主要因素；此后(R_{o, max}＞2.0%)由于芳环缩聚和解体进程的加剧使得环内重碳物质得以释放进入烷烃气中，而导致其碳同位素组成迅速变重。热解烷烃气中甲烷和乙烷碳同位素组成与煤脂链结构演化呈现同步性特征，δ13C_CH4和δ13C_C2H6值可以作为煤脂链结构演化的敏感性指标。R_{o, max}=1.3%和2.0%是煤热解结构演化与烷烃气碳同位素组成关联性的重要节点。研究成果对探索煤生烃与结构演化的耦合关系及二次生烃机理有理论意义。

Infrared Spectroscopic Study on the Structure Evolution of Low Rank Coal and Its Correlation with Carbon Isotope of Alkane Gas in Pyrolysis Process

In order to elucidate the relationship between structure evolution and carbon isotope of alkane gas in coal pyrolysis process, we selected low rank coal to carry out pyrolysis experiments in autoclave closed system. The carbon isotopic composition of alkane gas was analyzed, and the evolution of coal structure was studied using Fourier transform infrared spectroscopy (FTIR). The relationship model between carbon isotope composition of alkane gas and structure evolution was established. Moreover, the reasons for changes in carbon isotope of alkane gas were revealed. The results showed that light carbon isotopes fractionation of lipid chains cause heavy carbon isotopes to be retained in long chains when R_{o, max}＜1.3%. The materials within the loop, containing heavy carbon isotopes, are not fractionated out heavily when 1.3%＜R_{o, max}＜2.0%, and carbon isotope of alkane gas still depends on the further fractionation from lipid chains. Namely, the changes in carbon isotope of alkane gas are mainly caused by lipid chain orientation fracture when R_{o, max}＜2.0%. Since then (R_{o, max}＞2.0%), due to the intensification of aromatic condensation and disintegration, the heavy carbon in the loop can be released into the alkane gas, and its carbon isotopic composition rapidly becomes heavier. There is a synchronization phenomenon between carbon isotope composition of methane and ethane and structure evolution of lipid chain, and the values of δ13C_CH4 and δ13C_C2H6 can be used as the sensitivity index of structure evolution of lipid chain. In addition, it was pointed out that R_{o, max}=1.3% and 2.0% are important nodes in the relationship between structure evolution of coal and carbon isotopic composition of alkane gas in pyrolysis process. The research results have theoretical significance in exploring the coupling relationship between hydrocarbon generation of coal and structure evolution and mechanism of secondary hydrocarbon generation.