The open system pyrolysis characteristics of 7 low rank coals and the evolution kinetics of H_2 and its relation to the first coalification jump were determined using a thermogravimetric analyzer coupled to a quadrupole mass spectrometer (TG/MS). Results showed that both the coal pyrolysis characteristics and the evolution kinetics of H_2 are strongly related to the first coalification jump, which is demonstrated by three aspects: the weight loss rate indicates an abrupt change at C_(daf)=80% (R_(max)~0=0.60%) (C_(daf) is carbon content (mass fraction) of sample in dry-ash-free basis, R°max is the maximum reflectance of vitrinite in coal); the characteristic temperatures and kinetic parameters of H_2 exhibit a minimum value at C_(daf)=80% (R_(max)~0=0.60%); the total yield of hydrogen had a maximum value at C_(daf)=80% (R_(max)~0=0.60%) and this is consistent with the initial point of the first coalification jump. These aspects indicate that the derived parameters can reveal the first coalification jump. Combined with the structural characterization of the coals by FTIR, a mechanism that explains the results was determined using the following three factors: (1) the evolution characteristics of aliphatic oxygen-containing functional groups; (2) the retrogressive reaction of soluble organic matter and (3) the "polarization" of organic matter.%用开放体系的热重.质谱联用仪(TG/MS)研究了7种低煤级煤的热解特征、H_2的生成动力学特征以及它们与第一次煤化作用跃变的关系.结果显示,煤热解失重率在碳含量(C_(daf))为80%(质量分数)和镜质组最大反射率(R_(max)~0)为0.60%附近发生转折;氢气生成的特征温度参数以及动力学参数均在C_(daf)为80%(R_(max)~0为0.60%)左右表现为最低;氢气的总产率在此处最大.这些特征参数的极值点刚好与第一次煤化作用跃变点一致,说明这些参数可以反映第一次煤化作用跃变的发生.结合傅立叶变换红外(FHR)光谱法获得的煤结构特征.对影响机制进行了分析解释,认为是由以下3个方面的原因导致的:(1)煤中脂肪类含氧官能团的演化特征;(2)可溶有机质的低温热缩聚作用;(3)有机质的"两极分化"作用.
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