低QI含量的软沥青（SCTP）是制备煤系针状焦的优选原料, 研究其在液相碳化成焦阶段（350～550 ℃）的结构变化有助于高品质针状焦的研制。 利用样品的红外光谱, 通过分峰拟合对谱图中3 100～2 800 cm-1区的C—H伸缩振动峰和900～700 cm-1区的芳香C—H弯曲振动峰进行了详细辨析, 接着基于标准物质的相应C—H振动峰的校正因子, 定量出SCTP在不同碳化温度（400, 500, 600和800 ℃）下的各类型芳香氢（Hsolo, Hduo, Htrio和Hquarto）和脂肪氢（HCH3, HCH2和HCH）的质量百分含量; 进一步计算了样品的SP2杂化碳（SP2C）和SP3杂化碳（SP3C）的含量以及H/C原子比、 芳香性指数（Iar）、 芳香邻位取代指数（Ios）和支链化指数（CH3/CH2）等结构参数, 讨论了SCTP在液相碳化成焦过程中芳香结构的变化情况。 结果表明, 煤系针状焦原料SCTP主要由低环数少侧链的芳烃构成, Iar为0.77, 其82%左右的芳香氢分布在含有三/四个相邻芳香C—H的结构中, 而其脂肪氢主要分布在环烷的CH2结构中。 随着碳化温度升高, SCTP的脂肪氢或SP3C几乎呈直线下降, 到400 ℃时损失约50%, 这主要归因于轻组分的失去和环烷结构的脱氢, 在500 ℃形成半焦时仅有0.15 Wt.%的脂肪氢和0.88 Wt%的SP3C, 600 ℃时已检测不到脂肪氢的存在。 然而, 由于环烷结构转变为芳环, 导致芳香氢在400 ℃之前从原料的3.89 Wt%轻微增加至4.5 Wt%。 随温度进一步升高, 芳香氢则迅速减少, 到500 ℃时仅为1.14 Wt%, 表明在400～500 ℃中间相形成阶段沥青芳烃分子间发生了激烈的脱氢缩合反应, 大量质子化SP2C转化为非质子化SP2C也证实了这点。 在500 ℃后芳香氢继续减少, 到800 ℃时已检测不到它们的存在。 另外, 发现芳烃的C—H面外弯曲振动比其面内伸缩振动对红外光更灵敏。 Iar的增加以及H/C原子比、 Ios和CH3/CH2等参数的减小, 说明SCTP在成焦过程中其芳烃分子在逐步缩合长大, 芳香性提高。 利用红外光谱对各类型氢的快速定量, 可及时了解成焦过程中沥青芳烃分子的结构变化, 有助于针状焦的生产。

Soft coal tar pitch (SCTP) with low QI content is the preferred raw material for preparing coal-based needle coke, the study on its structure changes in the stage of liquid-phase carbonization into coke (350~550 ℃) is helpful to prepare high-quality needle coke. In this paper, a detailed analysis on the C—H stretching vibration peaks in the range of 3 100～2 800 cm-1 and the aromatic C—H bending vibration peaks in the range of 900～700 cm-1 has been carried by the peak-fitting technique using the infrared spectra of the sample. And then based on the calibration factors of the corresponding C—H vibration peaks for the standard substances, the mass percentages of the different types of aromatic hydrogen (Hsolo, Hduo, Htrio and Hquarto) and aliphatic hydrogen (HCH3, HCH2 and HCH) of SCTP were quantitated at different carbonization temperatures (400, 500, 600 and 800 ℃). Furthermore, the contents of SP2 hybridized Carbon (SP2C) and SP3 hybridized Carbon (SP3C) as well as these structural parameters such as H/C atomic ratio, aromatic index (Iar), aromatic ortho-substitution index (Ios) and branched index (CH3/CH2) were calculated, and the changes of aromatic structure of SCTP during the coking process were also discussed. The results showed that the coal-based needle coke raw material SCTP is mainly composed of aromatic hydrocarbons with a low number of the ring and few side chains, its Iar is 0.77, and about 82% of its aromatic hydrogen is distributed in the structure containing three/four adjacent aromatic C—H, while its aliphatic hydrogens are mainly distributed in the CH2 of naphthenic structures. With the increase of carbonization temperature, the aliphatic hydrogen or SP3C of SCTP decreased almost linearly, losing about 50% at 400 ℃, which was mainly attributed to the loss of light components and the dehydrogenation of naphthenic structures. The green coke formed at 500 ℃ had Only 0.15 Wt.% aliphatic hydrogen and 0.88 Wt.% SP3C, and the presence of aliphatic hydrogen was not detected at 600 ℃. However, the aromatic hydrogen increased slightly from 3.89 Wt.% of the raw material to 4.5 Wt.% before 400 ℃ because of the conversion of the naphthenic structuresinto aromatic rings. As the temperature increases further, aromatic hydrogen decreases rapidly, reaching only 1.14 Wt.% when the temperature reaches 500 ℃, indicating that the aromatic hydrocarbon molecules undergo intense dehydrogenation condensation reaction during the mesophase formation stage at 400~500 ℃, which was also confirmed by the conversion of a large number of protonated SP2C into unprotonated SP2C. Aromatic hydrogen continued to decrease after 500 ℃, and their presence was not detected at 800 ℃. In addition, it was found that the out-of-planebending vibration of aromatic C—H is more sensitive to infrared light than its in-plane stretching vibration. The increase of Iarand the decrease of these parameters such as H/C atomic ratio, Ios, CH3/CH2 indicated that the aromatic molecules in the SCTP are gradually grown up by their condensation, and its aromaticity increased in the coking process. The fast quantification of various types of hydrogen by infrared spectrum can timely understand the structural changes of aromatic hydrocarbon molecules of the pitch in the coking process, which is helpful to the production of needle coke.