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• HTP hydrolyzes ether bonds to form phenolic hydroxyl groups. • SSP breaks hydrogen bonds and dissolves small molecule compounds. • Destruction of ether bonds facilitates the release of aromatic C C and light tar. • Destruction of hydrogen bond reduces the pyrolysis activation energy of oxygen-containing groups. Coal pyrolysis is one of the methods of clean and efficient utilization of coal. Coal has a complex structure, which has an important influence on its pyrolysis characteristics. In order to further explore the structure–activity relationship between the structure and pyrolysis characteristics of coal, the structure of coal can be artificially changed to investigate the influence of structural changes on its pyrolysis characteristics. In this study, hydrothermal pretreatment (HTP) and solvent swelling pretreatment (SSP) were used to artificially change the structure of Shengli (SL) lignite. The influence of each pretreatment on the physicochemical structure was analysed by Fourier-transform infrared (FT-IR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The evolution of functional groups and the pyrolysis characteristics of the SL/pretreated coal were investigated by using an in-situ FT-IR device and a fluidised bed reactor, respectively. The results showed: HTP could remove some oxygen-containing functional groups and aliphatic side chains, hydrolyze ether bonds and generate phenolic hydroxyl groups, thus destroying the cross-linking structure, promote the release of aromatic C C, the yield of pyrolysis tar increased from 9.4% to 10.6%, and the content of light tar increases from 43.1% to 49.1%. SSP mainly weakening the cross-linking structure by destroying hydrogen bonds and dissolving part of oxygen-containing functional groups, which reduces the pyrolysis activation energy of oxygen-containing functional groups and aliphatic groups, promotes the generation of tar. Accordingly, the yield of tar increases from 9.4% to 11.1%, and the content of light tar increases from 43.1 % to 49.8%. In particular, this research work reveals the structure–activity relationship between the structural changes of coal and the pyrolysis characteristics, which provides a theoretical basis for the directional pyrolysis of lignite. [ABSTRACT FROM AUTHOR]

• The content of phenolic hydroxyl increased during hydrothermal pretreatment. • OH-ether O hydrogen bonds were newly formed during THF swelling pretreatment. • Reactions during methane thermal pretreatment were bond breaking and re-bonding. • Structure-activity relationship between coal structure and pyrolysis was revealed. Studying the relationship between the structure and pyrolysis of coal is useful for understanding the coal pyrolysis mechanism. In this study, three typical pretreatment methods (viz. hydrothermal pretreatment, tetrahydrofuran swelling pretreatment, and methane thermal pretreatment) were selected to artificially change the structure and composition of Shendong coal. Subsequently, the physicochemical structure and pyrolysis characteristics of the pretreated coals were systematically investigated. The results indicate that the three pretreatment methods had different influences on the pore modification and evolution of the functional groups in coal, thereby destroying the cross-linking structure in different ways. Correspondingly, these changes eventually altered the distribution and composition of the pyrolysis products. Based on these findings, the different mechanisms underlying the pyrolysis behavior, involving alteration of the structure and composition, were analyzed, and the structure–activity relationship between the coal structure and the pyrolysis characteristics was explored. [ABSTRACT FROM AUTHOR]