准东次烟煤难溶组分的热失重行为与热解产物分布

Weight loss behavior and pyrolysis products distribution of the insoluble portion from Zhundong sub-bituminous coal

  • 摘要: 以准东次烟煤(Zhundong Sub-bituminous Coal, ZSBC)及其萃余残渣(Extraction Residue, ER)为研究对象,采用扫描电子显微镜(SEM)、傅里叶变换红外光谱(FTIR)、热重分析(TGA)和热解−气相色谱/质谱联用(Py-GC/MS)技术,系统考察了ER的热失重行为与热解产物分布。SEM分析表明:ER表面形貌较ZSBC更光滑,颗粒分布更均匀,证实了萃取过程主要脱除煤中游离的可溶有机质。FTIR光谱显示:ER的脂肪族—CH2伸缩振动峰强度减弱,而芳环和含氧官能团特征峰保留完整,表明常温超声萃取未破坏煤的大分子骨架结构。TG-DTG分析发现,ER与原煤具有相似的3阶段热解行为,但随着升温速率提高,ER的热解特征温度向高温区偏移,且失重率从66.63%降至63.11%,表明升温速率的增加促进了挥发分的生成,有利于ER热解过程的进行。通过Friedmann、OFW和KAS这3种动力学方法计算ER的热解活化能(Ea),发现转化率(α)在0.2~0.8范围内所得Ea分别为39.07~654.82、29.60~662.67 和34.76~675.73 kJ/mol,表明热解过程从易断裂的弱键逐步过渡到需高能量的芳环缩聚过程。热力学参数(ΔH、ΔG、ΔS)进一步证实ER热解为吸热、熵减的非自发反应。Py-GC/MS分析表明:700 ℃时ER热解产物的芳烃含量较450 ℃显著增加,而酚类减少,主要归因于醚键断裂引发的芳构化反应及二次裂解作用。基于产物分布,提出了包含初级热解和二次反应的多路径热解机制。综上所述,揭示了萃余残渣热解过程中结构和动力学特征及其与热解产物分布的关系,为准东煤的分级转化提供了理论依据。

     

    Abstract: With Zhundong sub-bituminous coal (ZSBC) and its extraction residue (ER) as the research objects, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) were used to systematically investigate the thermogravimetric behavior and pyrolysis products distribution of ER. SEM analysis showed that the surface morphology of ER was smoother than that of ZSBC, and the particle distribution was uniform, which confirmed that the extraction process mainly removed the free soluble organic matter from the coal. FTIR spectra showed that the intensity of the aliphatic —CH2 stretching vibration peak of ER was weakened, while the characteristic peaks of aromatic ring and oxygen-containing functional groups were intact, indicating that the macromolecular skeleton structure of the coal was not damaged by ultrasonic extraction at room temperature. TG-DTG analysis showed that ER presented similar three-stage pyrolysis behavior to raw coal, while with the increase of heating rate, the pyrolysis characteristic temperature of ER shifted to high temperature region, and the coke yield decreased from 66.63% to 63.11%, indicating that the increase of heating rate promoted the formation of volatiles, which was conducive to the pyrolysis process of ER. The pyrolysis activation energy (Ea) of ER was calculated by Friedmann, OFW and KAS kinetic methods, and it was found that, with the conversion rate (α) increased from 0.2 to 0.8, the value of Ea was 39.07−654.82, 29.60−662.67, and 34.76−675.73 kJ/mol, respectively. The results show that the pyrolysis process gradually transitions from weak bonds that are easy to break to polycondensation of aromatic rings that require high energy. Thermodynamic parameters (ΔH, ΔG, and ΔS) confirmed that the pyrolysis of ER was a non-spontaneous reaction with endothermy and entropy reduction. Py-GC/MS analysis showed that the aromatic hydrocarbon content in ER pyrolysis products increased significantly at 700 ℃ compared with 450 ℃, while phenols decreased, which was mainly attributed to the aromatization reaction and secondary cleavage caused by ether bond cleavage. Based on the product distribution, a multipath pyrolysis mechanism including primary pyrolysis and secondary reaction was proposed. In summary, the research reveals the characteristics of the structure and pyrolysis kinetics of ER, and the relationship between the characteristics and the pyrolysis products, and thus provides a theoretical basis for the sequential conversion of ZSBC.

     

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