The distribution and variation of aromatic nuclei in the pyrolysis products of Naomaohu coal
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摘要: 本研究利用固定床反应器在不同温度下进行新疆淖毛湖(NMH)煤热解实验,并利用多种表征方法研究了煤热解过程半焦和焦油芳核大小分布变化规律。结果表明,随着温度升高,半焦芳碳含量增加,石墨化程度和晶格条纹有序度增加;焦油中芳核结构主要以一或二环为主,含有少量三环及以上芳核;不同热解温度下焦油同步荧光谱图变化不大,虽然焦油产率随温度升高先增加后减少(550 ℃时最大),但焦油中芳核大小分布变化较小,焦油没有发生显著的缩聚反应,同时表明不同大小芳核受到桥链束缚数量,以及桥链裂解活性相对均一。随热解温度升高,热解半焦及焦油中,1 × 1芳核含量降低;终温在500−600 ℃时,缩聚反应主要以1 × 1芳核向2 × 2和3 × 3芳核的转变为主;终温高于650 ℃,缩聚反应以4 × 4及更大芳核的生成为主。Abstract: The size distribution of aromatic nuclei in coal influences the composition of tar and char during pyrolysis. Pyrolytic experiments of Naomaohu (NMH) coal from Xinjiang in China were carried out in a fixed-bed reactor at different temperatures to study the size distribution of aromatic nuclei during coal pyrolysis. With the increase of pyrolysis temperature, the aromaticity of char, the graphitization degree, and the order degree of aromatic layers increase. The tar is mainly composed of aromatic clusters with 1−2 rings and contains a small amount of aromatic clusters with 3 or more rings. The tar yield increases first and then decreases with increasing temperature (maximum at 550 ℃). However, the changes in the synchronous fluorescence spectra of the tars with increasing temperature are not significant, indicating that the size distribution of aromatic nuclei in tar changes little with no significant condensation polymerization, and also indicating that the number of bridged bonds and the cracking activity distribution of these bridge chains in different size aromatic rings are relatively uniform. With the increase of pyrolysis temperature, the content of 1 × 1 aromatic layers in the pyrolysis products (char and tar) decreases gradually. When the pyrolysis temperature is at between 500 and 600 ℃, the 1 × 1 aromatic layers are mainly transformed into 2 × 2 and 3 × 3 aromatic layers. When the temperature is higher than 650 ℃, the formation of aromatic layers with the size of 4 × 4 and above takes the main part of condensation polymerization.
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Key words:
- coal pyrolysis /
- char /
- aromatic structure /
- size distribution /
- HRTEM
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表 1 煤样的工业分析和元素分析
Table 1 Proximate and ultimate analyses of NMH coal sample
Proximate analysis w/% Ultimate analysis wdaf/% Mad Ad Vdaf C H N S O* 3.54 5.22 52.23 71.64 6.01 0.85 0.42 21.08 *: by difference δ/cm−1 Reflected structural information Vibration type of key GL 1710 carbonyl group C=O sp2 G 1590 aromatic ring quadrant breathing; alkene C=C sp2 GR 1540 aromatic with 3−5 rings; amorphous
carbon structuressp2,sp3 VL 1506 VR 1430 D 1370 C−C between aromatic rings and aromatics with not less than 6 rings sp2 SL 1290 aryl-alkyl ether; para-aromatics sp2,sp3 S 1180 Caromatic−Calkyl; aromatic (aliphatic) ethers; C−C on hydroaromatic rings; hexagonal diamond carbon sp3; C−H on aromatic rings sp2,sp3 SR 1065 C−H on aromatic rings; benzene (ortho-di-substituted) ring sp2 R 800−960 C−C on alkanes and cyclic alkanes; C−C on aromatic rings sp2,sp3 Aromatic sheet Min L/
ÅMa × L/
ÅMean/
ÅGrouping/
Å1 × 1 2.8 4.9 3.9 3.0−5.4 2 × 2 4.9 7.1 6.0 5.5−7.4 3 × 3 7.4 11.3 9.3 7.5−11.4 4 × 4 9.8 15.6 12.7 11.5−14.4 5 × 5 12.3 19.8 16.0 14.5−17.4 6 × 6 14.7 24.1 19.4 17.5−20.4 7 × 7 17.2 28.4 22.8 20.5−24.4 8 × 8 19.6 32.6 26.1 24.5−28.4 -
[1] 谢克昌. 以煤为主格局决定能源转型立足点和首要任务[N]. 中国科学报, 2019, 007: 1−2.Xie Ke-chang. The coal-based pattern determines the foothold and primary task of the energy transition[N]. Chin Sci Daily, 2019, 007: 1−2. [2] SOLOMON P R, FLETCHER T H. Impact of coal pyrolysis on combustion[J]. Symp Comb,1994,25(1):463−474. doi: 10.1016/S0082-0784(06)80675-2 [3] SHURTZ R C, KOLSTE K K, FLETCHER T H. Coal swelling model for high heating rate pyrolysis applications[J]. Energy Fuels,2011,26(5):3612−3627. [4] SHURTZ R C, HOGGE J W, FOWERS K C, SORENSEN G S, FLETCHER T H. Coal swelling model for pressurized high particle heating rate pyrolysis applications[J]. Energy Fuels,2012,26(6):3612−3627. doi: 10.1021/ef300442r [5] WANG C A, WATSON J K, LOUW E, MATHEWS J P. Construction strategy for atomistic models of coal chars capturing stacking diversity and pore size distribution[J]. Energy Fuels,2015,29(8):4814−4826. doi: 10.1021/acs.energyfuels.5b00816 [6] ZHANG H X, LIU Z Y, LIU I Y. Case study of quantification of aromatic ring structures in lignite using sequential oxidation[J]. Energy Fuels,2016,30(3):2005−2011. doi: 10.1021/acs.energyfuels.5b02617 [7] SHUI H F, ZHU W W, WANG W W, PAN C X, WANG Z C, LEI Z P, REN S B, KANG S G. Thermal dissolution of lignite and liquefaction behaviors of its thermal dissolution soluble fractions[J]. Fuel,2015,139(1):515−522. [8] JIANG J, YANG W, CHENG Y, LIU Z, ZHAO K. Molecular structure characterization of middle-high rank coal via XRD, Raman and FTIR spectroscopy: Implications for coalification[J]. Fuel,2019,239:559−572. doi: 10.1016/j.fuel.2018.11.057 [9] TAKAGI H, MARUYAMA K, YOSHIZAWA N, YAMADA Y, SATO Y. XRD analysis of carbon stacking structure in coal during heat treatment[J]. Fuel,2004,83(17/18):2427−2433. doi: 10.1016/j.fuel.2004.06.019 [10] FOLEY H. Structural characterization of Nigerian coals by X-ray diffraction, Raman and FTIR spectroscopy[J]. Energy,2010,35:5347−5353. doi: 10.1016/j.energy.2010.07.025 [11] ZHANG S X. Structure of the organic crystallite unit in coal as determined by X-ray diffraction[J]. Int J Min Sci Technol,2011,21:667−671. [12] 张小蕊, 邹冲, 赵俊学, 马成, 胡冰, 刘诗薇, 何江永. XRD和Raman法评估热解气氛中H2和CO对半焦化学结构的影响[J]. 燃料化学学报.,2019,47(11):1288−1297.ZHANG Xiao-rui, ZHOU Chong, ZHAO Jun-xue, MA Cheng, HU Bing, LIU Shi-wei, HE Jiang-yong. Effect of H2 and CO as pyrolysis atmosphere on chemical structure of char by XRD and Raman methods[J]. J Fuel Chem Technol,2019,47(11):1288−1297. [13] RONG L, YANG Y, LI D, WANG X, JIA F, WANG J. Effect of rare earth oxides on the formation of semi-char from low-rank coal pyrolysis: a comparative study based on X-ray diffraction and Raman analysis[J]. Energy source Part A,2020,1−14. [14] GUEDES A, VALENTIM B, PRIETO A C, NORONHA F. Raman spectroscopy of coal macerals and fluidized bed char morphotypes[J]. Fuel,2012,97:443−449. doi: 10.1016/j.fuel.2012.02.054 [15] 苏现波, 司青, 宋金星. 煤的拉曼光谱特征[J]. 煤炭学报,2016,41(5):1197−1202.SU Xian-bo, SI Qing, SONG Jin-xing. Characteristics of coal Raman spectrum[J]. J China Coal Soc,2016,41(5):1197−1202. [16] 李霞, 曾凡桂, 王威, 董夔. 低中煤级煤结构演化的拉曼光谱表征[J]. 煤炭学报,2016,41(9):2298−2304.LI Xia, ZENG Fan-gui, WANG Wei, DONG Kui. Raman characterization of structural evolution in the low-middle rank coals[J]. J China Coal Soc,2016,41(9):2298−2304. [17] MENG D, YUE C, WANG T, CHEN X. Evolution of carbon structure and functional group during Shenmu lump coal pyrolysis[J]. Fuel,2020,287(38):119538. [18] SHENG C. Char structure characterised by Raman spectroscopy and its correlations with combustion reactivity[J]. Fuel,2007,86(15):2316−2324. doi: 10.1016/j.fuel.2007.01.029 [19] SONG Q, ZHAO H, JIA J, YANG L, LV W, GU Q, SHU X. Effects of demineralization on the surface morphology, microcrystalline and thermal transformation characteristics of coal[J]. J Anal Appl Pyrolysis,2020,145:104711−104716. [20] WANG S, CHEN H, ZHANG X. Transformation of aromatic structure of vitrinite with different coal ranks by HRTEM in situ heating[J]. Fuel,2020,260:116309. doi: 10.1016/j.fuel.2019.116309 [21] SHARMA A, KYOTANI T, TOMITA A. A new quantitative approach for microstructural analysis of coal char using HRTEM images[J]. Fuel,1999,78(10):1203−1212. doi: 10.1016/S0016-2361(99)00046-0 [22] NIEKERK D V, MATHEWS J P. Molecular representations of Permian-aged vitrinite-rich and inertinite-rich South African coals[J]. Fuel,2010,89(1):73−82. doi: 10.1016/j.fuel.2009.07.020 [23] MATHEWS J P, FERNANDEZ-ALSO V, DANIEL J A, SCHOBERT H H. Determining the molecular weight distribution of Pocahontas No. 3 low-volatile bituminous coal utilizing HRTEM and laser desorption ionization mass spectra data[J]. Fuel,2010,89:1461−1469. doi: 10.1016/j.fuel.2009.10.014 [24] SONG Y, JIANG B, LI M, HOU C, MATHEWS J P. Macromolecular transformations for tectonically-deformed high volatile bituminous via HRTEM and XRD analyses[J]. Fuel,2019,263:116756. [25] FERNANDEZ-ALSO V, WATSON J K, WAL R V, MATHEWS J P. Soot and char molecular representations generated directly from HRTEM lattice fringe images using Fringe3D[J]. Combust Flame,2011,158(9):1807−1813. doi: 10.1016/j.combustflame.2011.01.003 [26] CHEN H, WANG S Q, TANG Y G, ZENG F G, HAROLD H. Aromatic cluster and graphite-like structure distinguished by HRTEM in thermally altered coal and their genesis[J]. Fuel,2021,292(8):120373. [27] 赵洪宇, 李玉环, 舒元锋, 宋强, 吕俊鑫, 王子民, 曾鸣, 舒新前. CaO对褐煤和无烟煤热解产物分布及煤焦结构的影响[J]. 煤炭科学技术,2016,44(3):177−183.ZHAO Hong-yu, LI Yu-huan, SHU Yuan-feng, SONG Qiang, LV Jun-xin, WANG Zi-min, ZENG Ming, SHU xin-qian. Effect of calcium oxide on pyrolysis products distribution and char structure of lignite and anthracite[J]. Coal Soc Technol,2016,44(3):177−183. [28] 邱海鹏, 郭全贵, 宋永忠, 翟更太, 宋进仁, 刘朗. 石墨材料导热性能与微晶参数关系的研究[J]. 新型炭材料,2002,17(1):36−40.Qiu Hai-peng, Guo Quan-gui, Song Yong-zhong, zhai Geng-tai, song jin-ren, liu lang. Study of the relationship between thermal conductivity and microcrystalline parameters of bulk graphite[J]. New Carbon Mater,2002,17(1):36−40. [29] XU J, SU S, SUN Z, QING M, XIONG Z, WANG Y, JIANG L, HU S, XIANG J. Effects of steam and CO2 on the characteristics of chars during devolatilization in oxy-steam combustion process[J]. Appl Energy,2016,182:20−28. doi: 10.1016/j.apenergy.2016.08.121 [30] SONG Y, FENG W, LI N, LI Y, ZHI K, TENG Y, HE R, ZHOU H, LIU Q. Effects of demineralization on the structure and combustion properties of Shengli lignite[J]. Fuel,2016,183(1):659−667. [31] MATHEWS J P, SHARMA A. The structural alignment of coal and the analogous case of Argonne Upper Freeport coal[J]. Fuel,2012,95:19−24. doi: 10.1016/j.fuel.2011.12.046 [32] XIONG Y, JIN L, YANG H, LI Y, HU H. Insight into the aromatic ring structures of a low-rank coal by step-wise oxidation degradation[J]. Fuel Process Technol,2020,210:106563. doi: 10.1016/j.fuproc.2020.106563 [33] KERSHAW J R, SATHE C, HAYASHI J I, LI C Z, CHIBA T. Fluorescence spectroscopic analysis of tars from the pyrolysis of a Victorian Brown Coal in a Wire-Mesh Reactor[J]. Energy Fuels,2000,14:476−482. doi: 10.1021/ef990181u