FTIR和Raman技术在煤结构分析中的应用研究

Investigation of Different Structures of Coals Through FTIR and Raman Techniques

为明确不同煤种大分子结构特征的异同,采用傅里叶变换红外光谱(FTIR)和拉曼光谱(Raman)分析技术,对五种烟煤(HY,HJ,BL,DJ和HK)进行系统表征,为后续煤及类煤材料结构和性能的研究提供可靠指导。在FTIR光谱特征曲线上,波数3200~3600 cm^(-1)范围有明显的吸收区,其中样品HJ相较于其他4种样品更明显,主要是由于—OH官能团和N—H结构振动引起,但该波段容易受到自由水或结晶水的影响,从而造成判断误差。在2923 cm^(-1)处可以观察到CH_(2)反对称伸缩振动峰值都明显高于其对称伸缩振动,产生这一现象的原因是烟煤中存在大量脂肪族CH_(2)碳链结构,后续将其液化加工再应用的潜力较大。而在1000~1800 cm^(-1)的含氧官能团波数范围内,主要包含了羟基(醇羟基和酚羟基)、羧基、羰基等。为了更清晰的表征煤结构,定量分析了煤的表观芳香度fa(FTIR),(R/C)_(u),H_(al)/H,A_(ar)/A_(al)和H/C原子比之间的关系,可以看出随着煤质水平的提高,煤中芳香族氢含量增加,脂肪族氢含量降低。另外比较了各个结构参数发现fa(FTIR),(R/C)_(u)和H/C原子比之间存在线性关系,能够更加准确的表征煤阶。Raman光谱特征曲线通过Origin 2018进行分峰拟合,采用去卷积方法将频谱划分为十个峰,分别为G,G_(R),V_(L),V_(R),D,S,G_(L),S_(L),S_(R)和R。对比不同波段峰面积比例及主峰半高宽和H/C原子比的关系,发现随着H/C原子比的增加,A_(D)/A_(G)值总体呈下降趋势。从而说明煤样基本结构中单元核的芳香环数量随着煤化作用及其石墨化程度的增加而增加,该结果与FTIR光谱分析一致。通过上述研究结果的对比可证明FTIR和Raman光谱技术是煤中大分子结构特征研究的可靠方法。最后基于两种分析技术提供的结构参数,建立了简单的煤分子模型,为煤化学研究中基础分子构建提供参考。

In order to understand the structure and performance of coal further,the Fourier transform infrared spectroscopy(FTIR),and Raman spectroscopy was used to analyze the structure of five kinds of bituminous coals(HY,HJ,BL,DJ and HK)in detail.It was expected that the results obtained by infrared and Raman technology research would bring a deeper understanding of spectral characterization of coals and also provided reliable guide for the subsequent research of coal and coal-like materials.It could be seen that there are obvious absorption regions in the wavenumber range of 3200~3600 cm^(-1) through the infrared spectroscopy,in which the sample HJ was more obvious than the other four coals,mainly due to the effect of the—OH functional group and some N—H vibrations.However,due to the influence of free water or crystal water on this band,the judgment error would not be discussed here.At the band of 2923 cm^(-1),it could be observed that the peak of CH_(2) antisymmetric stretching vibration was significantly higher than its symmetric stretching vibration.The reason that resulted in this phenomenon was there existeda large amount of aliphatic CH_(2) carbon chain structure,then the potential of hydrogen liquefaction and application in the subsequent research of coal was huge.In the range of 1000 to 1800 cm^(-1),oxygen-containing functional groups mainly included hydroxyl groups(alcohol hydroxyl groups and phenolic hydroxyl groups),carboxyl groups,carbonyl groups,etc.In order to characterize the coal structure more clearly,the relationship between the apparent aromaticity f a(FTIR),(R/C)_(u),H_(al)/H,A_(ar)/A_(al) and H/C atomic ratios of coal was studied.According to the calculation parameters,with the coal quality level increases,the aromatic hydrogen content in the coal increased,and the aliphatic hydrogen content decreased.In addition,comparing various structural parameters,found a linear relationship between f a(FTIR),(R/C)_(u) and H/C atomic ratios,which could more accurately characterize coal rank.Raman spectroscopy was fitted by Origin 2018,and the deconvolution method was used to divide the spectrum into ten peaks,namely G,G R+V L+V R,D,S,G_(L),S_(L),S_(R) and R.The relationship between the ratio of the peak area in different bands and the half-height width of the main peak with H/C atomic ratio were studied.The comparison showed that with the increase of the H/C atomic ratio,the A_(D)/A_(G) value generally shows a downward trend.It was indicated that the number of aromatic rings of the unit core in the basic structure of the coal sample increased with coalification and the degree of graphitization,which was consistent with the result of infrared spectroscopy.The comparison of the above results could prove that infrared and Raman spectroscopy were reliable methods for structure research of coal.On the basis of the above,a simple coal molecular model was constructed from them,which could provide a reference for the construction of coal molecular for simulation calculation.