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Influence of cross-linking modification of coal tar pitch on carbon structure

2024 No. 02
303
121
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Authors:
CHENG Junxia
MAN Mengyao
CHU Hongyu
WU Qiuping
SONG Shuaichao
WEN Xiliang
ZHU Yaming
ZHAO Xuefei
Unit:
College of Chemical Engineering,University of Science and Technology
Abstract:

The microstructure of pitch-based carbon products is highly dependent on the properties of precursor pitch. While using chemical cross-linking to modify asphalt, although all the reaction mechanism of chemical cross-linking operates via electrophilic substitutionreaction, the degree of such modification fluctuates based on the type of cross-linking agent and catalyst utilized, which in turn impactsthe structure of resulting carbon products. Using medium and low temperature coal tar pitch as raw materials, the effects of three crosslinking agents: terephthalyl alcohol(PXG), benzaldehyde (BA), p-phenylenediamine chloride (TPC), coupled with five catalysts: ptoluenesulfonic acid, concentrated sulfuric acid, concentrated nitric acid, concentrated hydrochloric acid, and boric acid on the structureof carbon products after asphalt crosslinking modification were explored. The thermal stability and functional group changes of cross-linking modified pitch through TG-DTG and FT-IR were studied. XRD and Raman were used to characterizethe microstructural differencesof modified pitch carbon products. The results show that the presence of cross-linking agents and catalysts facilitate occurrence of molecular crosslinking in pitch, effectively curbing the volatilization of light components during thermal conversion, and substantially enhancingpitch′s coking value, softening point, and thermal stability among other metrics. When PXG serves as a cross-linking agent, the methylene H on the branched chain within the cross-linked product is not easily replaced. Conversely, when boric acid functions as the catalyst,the methyl H at the branch chain′s end is more prone to replacement. Utilizing BA as cross-linking agent,the position of hydrogen substitution predominantly occurs on the aromatic ring. When TPC is used as the cross-linking agent and concentrated sulfuric acid is used asthe catalyst, the content of C==O functional groups in the cross-linked product increases, indicating that TPC participates more in the reaction under this combination. Irrespective of the cross-linking agent used, when concentrated hydrochloric acid is employed as a catalyst,the crosslinking reaction substantially promotes the substitution of C—H bonds on the benzene ring and branch chains. After cross-linking modification, the strong π - π interactions among molecules in pitch′s carbonization process are weakened, effectively hindering theformation of ordered carbon structures, thereby increasing ID / IG values. Simultaneously, the interlayer spacing d002 of carbon microcrystalssignificantly expands, while the Lc value demonstrates a declining trend and the number of aromatic layers reduces, indicating that chemical cross-linking not only disrupts the arrangement of ordered carbon structures, but also restrains the development of carbon microcrystals. When boric acid isused as a catalyst, the catalytic effect is more ideal. The resultant carbon product′s d002 exhibits the highest performance amongst its group. When PXG and boric acid collectively cross-link with pitch, the d002 of the achieved carbon material extendsto 0.377 nm. In conclusion, this study lays a robust practical basis for the further targeted regulation and construction of pitch-based carbon materials.

Keywords:
mid-low temperature coal tar pitch
cross-linking modification
catalyzer
carbon microstructure
layer-spacing
Citation format:
程俊霞(1982—),女,河南商丘人,副教授,硕士生导师,博士。E-mail:cheng.anshan@163.com.
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Citation format:
CHENG Junxia,MAN Mengyao,CHU Hongyu,et al.Influence of cross-linking modification of coal tar pitch on carbonstructure[J].Clean Coal Technology,2024,30(2):93-101.

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    SHI Yixiang
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