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摘要: 以中国特殊显微组分树皮体作为研究对象,并与镜质体和树皮煤进行比较,通过热重实验分析了树皮体的热行为特性,并运用原位加热透射电镜(HRTEM)研究了树皮体在线受热后其化学结构变化特征,并进一步分析了树皮体热性质特性的原因。研究表明,相比于镜质体和树皮煤,树皮体在受热过程中的失重总量和热解最大速率均高,而三个样品的热解最大速率温度接近。在350 ℃之后,树皮体和镜质体的化学结构均具有定向性,且随着温度的升高,其定向性越明显。树皮体和镜质体分别在400和450 ℃时,呈现芳香层片堆积。同一温度条件下比较发现,树皮体和镜质体化学结构中以萘、2×2和3×3条纹为主;其次是4×4和5×5条纹。相比较而言,树皮体的萘含量高于镜质体,而镜质体中的3×3、4×4和5×5条纹的含量高于树皮体。在350-500 ℃,随着温度的逐渐升高,树皮体和镜质体中的萘含量增加,在450 ℃时,其萘的含量达到最高。树皮体的热解行为特性与其加热过程中化学结构特征变化有关,尤其是萘的含量变化。Abstract: Barkinite, one of Chinese special maceral, was chosen to study its peculiar thermal characteristics based on thermogravimetric analysis and Rock-eval analysis by comparing vitrinite with bark coal. The changes of chemical structure by heat-treatment of barkinite were discussed by HRTEM. The distribution of functional group of barkinite was studied by Micro-FTIR method. The results show that barkinite has the highest mass loss and the maximum rate of mass loss among these three samples. Barkinite and vitrinite have both orientated layers after temperature above 350℃. With the increasing of temperature, the orientation in aromatic layer is obviously improved and some layers in stacks increase. At the same temperature, for barkinite and vitrinite, three fringes show the greatest abundance, namely, naphthalene, 2×2, and 3×3 fringes, following by 4×4 and 5×5 fringes. Barkinite has a higher abundance of naphthalene than vitrinite and has lower abundances of larger aromatic fringes than vitrinite, for instance, 3×3, 4×4, and 5×5 fringes. With the increasing of temperature, the content of naphthalene in barkinite and vitrinite is increased. Their abundance reaches the highest at 450℃ that is also the temperature of the maximum mass loss rate of barkinite, which indicates that the thermal characteristics of barkinite is related to the abundance of naphthalene in the chemical structure of barkinite.
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Key words:
- barkinite /
- thermogravimetric analysis /
- HRTEM /
- chemical structure
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表 1 样品的基本性质
Table 1 Basic characteristics of coal samples used
Sample Ro
w/%Proximate analysis
w/%Ultimate analysis
wdaf/%H/C
atomic
ratioMaceral
φ/%Mad Ad Vdaf C H O* N St,d V Ba OL+I Bark coal 0.67 1.02 8.15 52.80 73.27 5.64 10.54 1.42 0.98 0.92 24 68 8 Barkinite - 0.84 0.39 69.93 - - - - 1.01 - 3 96 1 Vitrinite - 1.20 6.09 45.74 81.45 5.24 10.73 1.26 1.31 0.77 87 12 1 note: Ro: the mean maximum vitrinite reflectance; M: moisture; A: ash; V: volatile matter; ad: air-dry basis; d: dry basis; daf: dry-ash-free; V: vitrinite; Ba: barkinite; I: inertinite; OL: other liptinites; *: by difference; -: no determined 表 2 样品的热重参数和部分岩石热解
Table 2 TGA parameters analysis and Rock-Eval data of samples used
Sample Thermogravimetric analysis Rock-Eval[25] tmax/
℃MR/
(%·℃-1)S2/
(mg·g-1)S1+S2/
(mg·g-1)HI/
(mg·g-1)Bark coal 450 0.40 234 242 343 Vitrinite 453 0.40 237 244 296 Barkinite 454 1.08 461 472 611 note: tmax: temperature of maximum volatiles loss; MR: the maximum rate of mass loss; S1: amount of free hydrocarbons exposed before pyrolysis at 300 ℃ (mg (HC)/g (rock)); S2: amount of hydrocarbons exposed by the thermal cracking during programmed temperature increments above 300 ℃ in pyrolysis (mg (HC)/g (rock)); HI: hydrogen index 表 3 HRTEM晶格条纹归属分类
Table 3 Assignment of parallelogram-shaped aromatic fringes from the HRTEM fringe data
Aromatic sheet Minimum values
/nmMaximum values /nm Mean length
/nmGrouping
/nmNaphthalene 0.28 0.49 0.39 0.30-0.54 2×2 0.49 0.71 0.60 0.55-0.74 3×3 0.74 1.13 0.93 0.75-1.14 4×4 0.98 1.56 1.27 1.15-1.44 5×5 1.23 1.98 1.60 1.45-1.74 6×6 1.47 2.41 1.94 1.75-2.04 7×7 1.72 2.84 2.28 2.05-2.44 8×8 1.96 3.26 2.61 2.45-2.84 -
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