陕南地区中煤阶煤分子结构演化特征

Molecular evolution of medium rank coal in Southern Shaanxi

为研究陕南地区中煤阶煤结构中官能团的变化,以北秦岭商洛煤产地和上扬子镇巴煤产地的8个中等变质程度煤样为研究对象,采用X射线衍射和傅里叶红外光谱对煤结构进行表征,结合分峰拟合来获取官能团的相对含量及结构参数。结果表明:随着镜质体反射率增大,芳环层面网间距逐渐减小,堆砌度与延展度逐渐增大,芳香度在反射率为1.30%时出现拐点;中煤阶煤芳香结构中苯环取代方式以三取代和二取代为主,随着变质程度的增高,苯环二取代的比例升高,脂肪族结构逐渐脱落导致相对比例降低,含氧官能团的吸收峰强度逐渐减弱,其中在反射率为1.3%时羰基相对含量最低;自缔合羟基、醚氧羟基和环羟基的相对含量均呈先减小后增大的趋势,煤分子结构中链状结构的环化使环状羟基相对含量在反射率为1.30%后增大,环化作用增强导致甲基含量减少,分子结构空间排列紧密,自缔合羟基相对含量增加;红外结构参数芳碳率、芳香性、芳香环缩聚程度和CH _(2)/CH_(3)等随反射率的增大而增大,成熟度的变化与醚氧或酚羟基的转化相关。总体上芳香结构相对含量增大,脂族结构减少,缩聚程度增加,生烃潜力随反射率增大,反映煤结构的生烃潜力降低。

In order to study the changes of functional groups in the structure of medium rank coal in southern Shaanxi,8 medium rank coal samples from Shangluo coal district in northern Qinling and Zhenba coal district in upper Yangtze were taken as the research objects.The coal structure was characterized by X-ray diffraction and FTIR,and the relative content and structural parameters of functional groups were obtained by peak fitting.The results show:with the increase of vitrinite reflectance,the distance between aromatic ring layers gradually decreases while the stacking degree and ductility gradually increase,and aromaticity displays a turning point at a reflectance of 1.30%.The benzene ring substitution in the aromatic structure of medium rank coal is mainly trisubstituted and disubstituted.With the increase of metamorphic grade,the proportion of benzene ring disubstituted increases.The gradual shedding of the aliphatic structure leads to a decrease in the relative proportion;the intensity of the absorption peak of the oxygen-containing functional group gradually weakens,and the relative content of the carbonyl group is the lowest when the reflectivity is 1.30%.The relative content of self-associated hydroxyl group,ether oxygen hydroxyl group and ring hydroxyl group see a trend of first decreasing and then increasing.The cyclization of chain like structure in coal molecular structure increases the relative content of ring hydroxyl group after the reflectivity is 1.30%.The enhancement of cyclization leads to the decrease of methyl content,the spatial arrangement of molecular structure is close,and the relative content of self-associated hydroxyl group increases.The infrared structural parameters such as aromatic carbon ratio,aromaticity,aromatic ring polycondensation degree and CH_(2)/CH_(3) increase with the increasing reflectivity.The change of maturity is related to the conversion of ether oxygen or phenolic hydroxyl group.Overall,the relative content of aromatic structure increases,the aliphatic structure decreases,the degree of condensation increases,and the hydrocarbon generation potential increases with reflectivity,reflecting a decrease in the hydrocarbon generation potential of coal structure.