This study conducted Tetrahydrofuran Soxhlet extraction experiments and multiple test technologies (including gas chromatography/mass spectrometry (GC/MS), Fourier-transform infrared spectroscopy (FTIR), microcalorimeter) to examine the the organic chemical composition, molecular structure, and gas adsorption behaviors in different metamorphic deformed coals. Then, the microscopic control mechanism was revealed by clarifying the relationships between chemical composition and structure and the adsorption heat. The results show that oxygen-containing and aliphatic compounds from low molecular weight compounds(LMWCs) occupy a more obvious position in high rank coals, but aromatic compounds with low aromatic condensation degree only appear in medium rank coals. While a greater variety of LMWCs, especially oxygen-containing and other heteroatom-containing compounds, are released under tectonic deformation and failure effects. Then, on the basis of functional group characteristics, it finds that tectonic stresses not only cause the detachment effect in high rank coals to form short-chain aliphatic structures, but also induce the cyclization effect in medium rank coals to form alicyclic structures. Additionally, tectonic heat generation can promote the reduction or disappearance of unstable oxygen-containing functional groups. And the advanced evolution feature of the molecular structure for tectonically deformed coals is more pronounced under the high metamorphic stage. Further, combined with the adsorption heat results, both oxygen-containing functional groups and aromatic structures can strengthen gas adsorption, but long-chain aliphatic structures exhibit more obvious negative correlation to weaken gas adsorption. Meanwhile, tectonically deformed coals consistently manifest a stronger adsorption capacity than intact coal before and after LMWCs dissolution. However, affected by adsorption sites and pore spaces, medium and high rank coals exhibit an inverse adsorption heat response following LMWCs dissolution. ● Abundant low molecular weight compounds are released under tectonic deformation. ● Tectonic stress can induce detachment and cyclization in coal molecular structure. ● Advanced evolution of chemical structure is more pronounced in TDC with high rank. ● Long-chain aliphatic structures can weaken gas adsorption in coal. ● Low molecular weight compounds tend to affect gas adsorption in different rank coals.
Zhang et al. (2026) studied this question.