Catalytic microwave pyrolysis of low-rank pulverized coal for preparation of high value-added modified bluecoke powders containing carbon nanotubes

doi:10.11949/0438-1157.20230132

Abstract

Abstract:

The limitation of large-scale utilization of bluecoke powders in industrial production due to their small particle size and low volatiles, and their preparation through high value-added modification therefore is an attractive and promising research subject for now. In this study, the high value-added modified bluecoke powders containing carbon nanotubes were prepared by KOH-assisted microwave pyrolysis of low-rank pulverized coal. The effects of KOH addition (alkali-carbon ratio) on the morphological structure, graphitization, microcrystalline structure and carbon nanotubes content of the modified bluecoke powders were investigated, and the generation mechanism of carbon nanotubes in the modified bluecoke powders was speculated. The results showed that carbon nanotubes with diameters of 30—50 nm and lengths of several tens of micrometers were produced in the modified bluecoke powders at the alkali-carbon ratio of 1.0, and the content was about 3.01%(mass). With the increment of the alkali-carbon ratio, the formation of carbon nanotubes was promoted by the etching of K and Fe₃C produced from minerals in the raw coal, meanwhile the ordering of modified bluecoke powders and the interaction of graphite layer spacing were enhanced. The characteristic peak G' in the Raman spectra of carbon nanotubes was found that indicated the high value-added modified bluecoke powders containing carbon nanotubes were successfully produced. In addition, the intensities of C—C, C—H and ether bonded C—O—C structures in FT-IR spectra of the modified bluecoke powders were significantly weakened. This phenomenon was caused by two potential reasons. On the one hand, these carbon structures became the direct solid-phase carbon source of carbon nanotube with the presence of catalysts. On the other hand, the thermal decomposition of these carbon structures released CO and CH₄, which could be used as the gas-phase carbon source for carbon nanotubes. The formation of carbon nanotubes in the high value-added modified bluecoke powders may be the result of the joint action of the “top formation” model and the “particle-wire-tube formation” model.

Key words: carbon nanotubes, growth mechanism, catalytic microwave pyrolysis, modified bluecoke powders, low-rank pulverized coal

摘要：

由于兰炭末粒径小、挥发分低等原因限制了其在工业生产中大规模利用。因此，兰炭末高附加值改性制备是当前极具吸引力和前景的研究课题。通过KOH协助微波热解低阶粉煤制备了含有碳纳米管的高附加值改性兰炭末，研究了KOH添加量（碱碳比）对改性兰炭末的形貌和结构、石墨化度、微晶结构和碳纳米管（CNTs）含量的影响，推测了改性兰炭末中碳纳米管的生成机制。结果表明：当碱碳比为1.0时，改性兰炭末中生成了直径在30~50 nm，长度约为几十微米的碳纳米管，其含量为3.01%（质量）。随着碱碳比增加，K的刻蚀和原煤所含矿物质产生的Fe₃C对碳纳米管的生成具有促进作用，改性兰炭末的有序性有所增强，石墨层间距的交互作用增强，Raman光谱中出现碳纳米管的标志特征峰G′，表明生成了含有碳纳米管的高附加值改性兰炭末。此外，FT-IR光谱中改性兰炭末中的C—C、C—H和醚键C—O—C结构强度明显减弱。这种现象的产生可能有两方面原因：一是这些碳结构在催化剂的作用下成为了碳纳米管直接生成的固相碳源；二是这些碳结构热分解释放出CO和CH₄，这些气体可作为碳纳米管的气相碳源。高附加值改性兰炭末中碳纳米管的生成可能是 “顶端生成”模型和“粒-线-管生成”模型共同作用的结果。

关键词: 碳纳米管, 生长机制, 催化微波热解, 改性兰炭末, 低阶粉煤

CLC Number:

TQ 536.9

Lei WU, Jiao LIU, Changcong LI, Jun ZHOU, Gan YE, Tiantian LIU, Ruiyu ZHU, Qiuli ZHANG, Yonghui SONG. Catalytic microwave pyrolysis of low-rank pulverized coal for preparation of high value-added modified bluecoke powders containing carbon nanotubes[J]. CIESC Journal, 2023, 74(9): 3956-3967.

吴雷, 刘姣, 李长聪, 周军, 叶干, 刘田田, 朱瑞玉, 张秋利, 宋永辉. 低阶粉煤催化微波热解制备含碳纳米管的高附加值改性兰炭末[J]. 化工学报, 2023, 74(9): 3956-3967.

Figures/Tables 12

Table 1 Proximate and elemental analysis of raw coal

Sample	Industrial analysis/%(mass)				Elemental analysis/%(mass)
Sample	FC_ad.	M_ad.	A_ad.	V_daf.	C_daf.	H_daf.	O_daf.	N_daf.	S_daf.
coal	54.68	6.71	10.85	34.26	81.84	4.23	9.87	0.95	3.11

Table 2 Ash analysis of raw coal

Composition	Content/%(mass)
Fe₂O₃	29.89
Al₂O₃	7.25
CaO	25.29
MgO	1.36
SiO₂	12.01
K₂O	0.08
Na₂O	0.12

Fig.1 Schematic diagram of the preparation of carbon nanotube-rich bluecoke powders using microwave pyrolysis of low-rank coal

Fig.2 Microscopic morphology of modified bluecoke powders at different alkali-carbon ratios (SEM)

Fig.3 TEM images of modified bluecoke powders SC-1.0 (TEM)

Fig.4 XRD patterns of modified bluecoke powders at different alkali-carbon ratio

Fig.5 FT-IR spectra of modified bluecoke powders at different alkali-carbon ratio

Fig.6 Raman spectra of modified bluecoke powders at different alkali-carbon ratio

Fig.7 Splitting results of Raman spectra for modified bluecoke powders at different alkali-carbon ratios

Table 3 Raman spectral fitting parameters for modified bluecoke powders at different alkali-carbon ratios

Samples	I_D1/I_G	I_D2/I_G	I_D3/I_G	I_D4/I_G	I_G/I_All
SC-0	2.145	0.284	1.519	0.543	0.151
SC-0.4	2.206	0.215	1.489	0.434	0.130
SC-0.6	1.228	0.252	1.884	0.352	0.168
SC-0.8	1.156	0.174	1.279	0.774	0.245
SC-1.0	1.152	0.135	0.791	0.324	0.247
SC-1.2	1.181	0.230	0.829	0.274	0.222
CNT	1.150	0.154	1.390	0.266	0.240

Fig.8 Thermal mass loss diagram of modified bluecoke powders at different alkali-carbon ratios

Fig.9 Generation mechanism of carbon nanotube in bluecoke powders obtained by KOH-assisted microwave pyrolysis of low-rank coal

References 33

34	Minutolo P, Commodo M, Santamaria A, et al. Characterization of flame-generated 2-D carbon nano-disks[J]. Carbon, 2014, 68: 138-148.
35	Brubaker Z E, Langford J J, Kapsimalis R J, et al. Quantitative analysis of Raman spectral parameters for carbon fibers: practical considerations and connection to mechanical properties[J]. Journal of Materials Science, 2021, 56(27): 15087-15121.
36	Beyssac O, Goffé B, Petitet J P, et al. On the characterization of disordered and heterogeneous carbonaceous materials by Raman spectroscopy[J]. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2003, 59(10): 2267-2276.
37	Meng D X, Yue C Y, Wang T, et al. Evolution of carbon structure and functional group during Shenmu lump coal pyrolysis[J]. Fuel, 2021, 287: 119538.
38	Zhang T K, Zhang Y F, Wang Q, et al. Mechanism of K-catalyzed transformation of solid carbon structure into carbon nanotubes in coal[J]. Fuel Processing Technology, 2020, 204: 106409.
39	Zhang T K, Wang Q, Li G Q, et al. Formation of carbon nanotubes from potassium catalyzed pyrolysis of bituminous coal[J]. Fuel, 2019, 239: 230-238.
40	He R Z, Deng J, Deng X L, et al. Effects of alkali and alkaline earth metals of inherent minerals on Fe-catalyzed coal pyrolysis[J]. Energy, 2022, 238: 121985.
41	Wang Z P, Ogata H, Morimoto S, et al. Nanocarbons from rice husk by microwave plasma irradiation: from graphene and carbon nanotubes to graphenated carbon nanotube hybrids[J]. Carbon, 2015, 94: 479-484.
42	Sun Y, Wang Y J, Ma H J, et al. Fe₃C nanocrystals encapsulated in N-doped carbon nanofibers as high-efficient microwave absorbers with superior oxidation/corrosion resistance[J]. Carbon, 2021, 178: 515-527.
43	He L M, Hu S, Jiang L, et al. Carbon nanotubes formation and its influence on steam reforming of toluene over Ni/Al₂O₃ catalysts: roles of catalyst supports[J]. Fuel Processing Technology, 2018, 176: 7-14.
44	Lv X M, Zhang Y F, Wang Y, et al. Formation of coal-based carbon nanotubes by Fe-K catalyst[J]. Journal of Analytical and Applied Pyrolysis, 2022, 161: 105400.
45	Yuan J C, Wang Y, Tang M F, et al. Preparation of N, O co-doped carbon nanotubes and activated carbon composites with hierarchical porous structure for CO₂ adsorption by coal pyrolysis[J]. Fuel, 2023, 333: 126465.
46	Zhou J, Wu L, Zhou J J, et al. Advances in coal catalytic microwave pyrolysis and its carbon-based absorbing microwave catalysts[J]. Chemical Industry and Engineering Progress, 2019, 38(9): 4060-4074.
47	Zhang P, Wu M D, Liang C, et al. In-situ exsolution of Fe-Ni alloy catalysts for H₂ and carbon nanotube production from microwave plasma-initiated decomposition of plastic wastes[J]. Journal of Hazardous Materials, 2023, 445: 130609.
1	Jorschick H, Preuster P, Bösmann A, et al. Hydrogenation of aromatic and heteroaromatic compounds—a key process for future logistics of green hydrogen using liquid organic hydrogen carrier systems[J]. Sustainable Energy & Fuels, 2021, 5(5): 1311-1346.
2	Yang R R, Zhou J, Wu L, et al. Understanding effects of potassium activator on the porous structure and adsorption performance of bluecoke-based porous powder during microwave heating[J]. Journal of Molecular Liquids, 2022, 366: 120249.
3	Wu L, Liu J, Reddy B R, et al. Preparation of coal-based carbon nanotubes using catalytical pyrolysis: a brief review[J]. Fuel Processing Technology, 2022, 229: 107171.
4	Yang R R, Zhou J, Wu L, et al. Fabrication of developed porous carbon derived from bluecoke powder by microwave-assisted KOH activation for simulative organic wastewater treatment[J]. Diamond and Related Materials, 2022, 124: 108929.
5	Zhang X Y, Sun B K, Fan X, et al. Hierarchical porous carbon derived from coal and biomass for high performance supercapacitors[J]. Fuel, 2022, 311: 122552.
6	Ma M Y, Chai W C, Cao Y J. Structure and electrochemical property of coal-based activated carbon modified by nitric acid[C]//TMS 2021 150th Annual Meeting & Exhibition Supplemental Proceedings. Cham: Springer, 2021: 15-24.
7	Im U S, Kim J, Lee S H, et al. Preparation of activated carbon from needle coke via two-stage steam activation process[J]. Materials Letters, 2019, 237: 22-25.
8	Zhang G J, Qu J W, Du Y N, et al. Hydrogen production from CO₂ reforming of methane over high pressure H₂O₂ modified different semi-cokes[J]. Journal of Industrial and Engineering Chemistry, 2014, 20(5): 2948-2957.
9	Reddy B R, Ashok I, Vinu R. Preparation of carbon nanostructures from medium and high ash Indian coals via microwave-assisted pyrolysis[J]. Advanced Powder Technology, 2020, 31(3): 1229-1240.
10	Shen X, Zhao Z, Li H, et al. Microwave-assisted pyrolysis of plastics with iron-based catalysts for hydrogen and carbon nanotubes production[J]. Materials Today Chemistry, 2022, 26: 101166.
11	Das T, Saikia B K, Baruah B P. Formation of carbon nano-balls and carbon nano-tubes from northeast Indian Tertiary coal: value added products from low grade coal[J]. Gondwana Research, 2016, 31: 295-304.
12	Deng H, Li G X, Yang H B, et al. Preparation of activated carbons from cotton stalk by microwave assisted KOH and K₂CO₃ activation[J]. Chemical Engineering Journal, 2010, 163(3): 373-381.
13	Ashok A, Kumar A, Ponraj J, et al. Synthesis and growth mechanism of bamboo like N-doped CNT/graphene nanostructure incorporated with hybrid metal nanoparticles for overall water splitting[J]. Carbon, 2020, 170: 452-463.
14	Nie H R, Cui M M, Russell T P. A route to rapid carbon nanotube growth[J]. Chemical Communications, 2013, 49(45): 5159-5161.
15	Bajpai R, Wagner H D. Fast growth of carbon nanotubes using a microwave oven[J]. Carbon, 2015, 82: 327-336.
16	Mahmood A, Muhmood T, Ahmad F. Carbon nanotubes heterojunction with graphene like carbon nitride for the enhancement of electrochemical and photocatalytic activity[J]. Materials Chemistry and Physics, 2022, 278: 125640.
17	Botas J A, Serrano D P, Guil-López R, et al. Methane catalytic decomposition over ordered mesoporous carbons: a promising route for hydrogen production[J]. International Journal of Hydrogen Energy, 2010, 35(18): 9788-9794.
18	Qiu J S, Wang Z Y, Zhao Z B, et al. Synthesis of double-walled carbon nanotubes from coal in hydrogen-free atmosphere[J]. Fuel, 2007, 86(1/2): 282-286.
19	Zhao Y, Liu L, Qiu P H, et al. Impacts of chemical fractionation on Zhundong coal’s chemical structure and pyrolysis reactivity[J]. Fuel Processing Technology, 2017, 155: 144-152.
20	Zhao J Y, Deng J, Chen L, et al. Correlation analysis of the functional groups and exothermic characteristics of bituminous coal molecules during high-temperature oxidation[J]. Energy, 2019, 181: 136-147.
21	Zhang J B, Jin L J, Cheng J, et al. Hierarchical porous carbons prepared from direct coal liquefaction residue and coal for supercapacitor electrodes[J]. Carbon, 2013, 55: 221-232.
22	Widayat, Satriadi H, Wibawa L P, et al. Oil and gas characteristics of coal with pyrolysis process[C]//AIP Conference Proceedings. AIP Publishing LLC, 2022, 2453(1): 020077.
23	Liu H P, Zhang L Y, Chen T P, et al. Experimental study on the fluidization behaviors of the superfine particles[J]. Chemical Engineering Journal, 2015, 262: 579-587.
24	Xia H Y, Wang K, Yang S H, et al. Formation of graphene flowers during high temperature activation of mesocarbon microbeads with KOH[J]. Microporous and Mesoporous Materials, 2016, 234: 384-391.
25	Bai Y, Yue H, Wang J, et al. Super-durable ultralong carbon nanotubes[J]. Science, 2020, 369(6507): 1104-1106.
26	Lin X C, Wang C H, Ideta K, et al. Insights into the functional group transformation of a Chinese brown coal during slow pyrolysis by combining various experiments[J]. Fuel, 2014, 118: 257-264.
27	Osswald S, Flahaut E, Gogotsi Y. In situ Raman spectroscopy study of oxidation of double-and single-wall carbon nanotubes[J]. Chemistry of Materials, 2006, 18(6): 1525-1533.
28	Xu L, Liu H Y, Jin Y, et al. Structural order and dielectric properties of coal chars[J]. Fuel, 2014, 137: 164-171.
29	Mohammadi S, Kolahdouz Z, Mohajerzadeh S. Hydrogenation-assisted unzipping of carbon nanotubes to realize graphene nano-sheets[J]. Journal of Materials Chemistry C, 2013, 1(7): 1309-1316.
30	Yao L S, Yi B K, Zhao X Q, et al. Microwave-assisted decomposition of waste plastic over Fe/FeAl₂O₄ to produce hydrogen and carbon nanotubes[J]. Journal of Analytical and Applied Pyrolysis, 2022, 165: 105577.
31	Lee S H, Park J, Kim H R, et al. Synthesis of carbon nanotube fibers using the direct spinning process based on design of experiment (DOE)[J]. Carbon, 2016, 100: 647-655.
32	Liu X H, Zheng Y, Liu Z H, et al. Study on the evolution of the char structure during hydrogasification process using Raman spectroscopy[J]. Fuel, 2015, 157: 97-106.
33	Sheng C D. Char structure characterised by Raman spectroscopy and its correlations with combustion reactivity[J]. Fuel, 2007, 86(15): 2316-2324.

[1]	Haoyu XIAO, Haiping YANG, Xiong ZHANG, Yingquan CHEN, Xianhua WANG, Hanping CHEN. Recent progress of catalytic pyrolysis of plastics to produce high value-added products [J]. CIESC Journal, 2022, 73(8): 3461-3471.
[2]	Chuyue CAI, Xiaoming FANG, Zhengguo ZHANG, Ziye LING. Enhancing heat dissipation performance of paraffin/silicone rubber phase change thermal pad by introducing carbon nanotubes [J]. CIESC Journal, 2022, 73(7): 2874-2884.
[3]	Xue’an LIU, Liyi TANG, Jian QIN, Dajiang TANG, Zhangfa TONG, Huiying QU. Preparation of carbon nanotube bridged porous carbon by Ni/Co-ZIF-8 pyrolysis and its application to supercapacitors [J]. CIESC Journal, 2022, 73(7): 3287-3297.
[4]	Xingda SHI, Huayan CHEN, Yanan GE, Chunrui WU, Hongyou JIA, Xiaolong LYU. Construction of three-dimensional network by modified MWCNT and AlN fillings in PVDF to improve the thermal conductivity [J]. CIESC Journal, 2022, 73(5): 2262-2269.
[5]	Xue HAN, Shengwang GAO, Guoying WANG, Xunfeng XIA. Research of enhanced carbon nanotubes activated peroxymonosulfate by cerium doping [J]. CIESC Journal, 2022, 73(4): 1743-1753.
[6]	Shide WU, Feng YI, Dan PING, Yifei ZHANG, Jian HAO, Guoji LIU, Shaoming FANG. NH₄Cl assisted preparation of Ni-N-CNTs catalyst and its performance for electrochemical CO₂ reduction [J]. CIESC Journal, 2022, 73(10): 4484-4497.
[7]	Lu ZHAO, Guoqing NING, Xingxun LI. S-doped carbon nanotubes used as conductive additives to improve the electrochemical performance of LMFP [J]. CIESC Journal, 2021, 72(12): 6388-6398.
[8]	SHI Xiaofei, JIANG Qinyuan, LI Run, CUI Yiming, LIU Qingxiong, WEI Fei, ZHANG Rufan. Synthesis and structure control of horizontally aligned carbon nanotubes: progress and perspectives [J]. CIESC Journal, 2021, 72(1): 86-115.
[9]	Huizhong ZHAO, Min LEI, Tianhou HUANG, Tao LIU, Min ZHANG. Water vapor adsorption performance of composite adsorbent MWCNT/MgCl₂ [J]. CIESC Journal, 2020, 71(S1): 272-281.
[10]	ZHOU Feng, HUANG Huimin, QIAN Feiyue, SHEN Yaoliang, ZHOU Xiaoji, LI Xin, XIA Xue. Effects of carbon nanotubes mats structure on rejection performance of composite membranes [J]. CIESC Journal, 2018, 69(5): 2318-2326.
[11]	MA Yanbing, LIU Hui'e, CHEN Shuang, DING Chuanqin. Facile synthesis of carbon nanotubes-graphene aerogels and its adsorption property for emulsified oil in water [J]. CIESC Journal, 2018, 69(4): 1508-1517.
[12]	LIU Zhuang, WANG Wei, JU Xiaojie, XIE Rui, CHU Liangyin. Carbon-based membranes with confinement effect for mass transport: from carbon nano-tube membranes to graphene membranes [J]. CIESC Journal, 2018, 69(1): 166-174.
[13]	LI Chenyang, FENG Miao, CUI Haifeng, CAO Guiping, LÜ Hui, CHEN Rongqi. Preparation of carbon nanotube catalyst on structure-modified cordierite monolith for polystyrene hydrogenation [J]. CIESC Journal, 2017, 68(7): 2746-2754.
[14]	SUN Yingying, CHEN Lin, XU Hongfei, LIN Jun, DU Xiaoze. Derivation of thermal conductive equation of hybrid filled composites [J]. CIESC Journal, 2015, 66(S1): 359-364.
[15]	WANG Haiyang, DU Yanni, LI Zhenfang, SONG Xiaopeng, TAN Duanming, GONG Junbo. Crystallization process and growth mechanism for spherical products of clopidogrel sulfate [J]. CIESC Journal, 2015, 66(9): 3633-3639.