Gas Generation Characteristics and Mechanisms of Medium-Rank Bituminous Coal Under Rotational Shear

Clarifying whether tectonic stress directly induces coal macromolecular structural evolution and gas generation plays a key role in elucidating deep coal gas sources and coal-gas outburst mechanisms. Existing studies pay insufficient attention to medium-rank bituminous coal, which is abundant in aliphatic side chains and active functional groups, and its stress-responsive gas generation mechanism remains unclear. Rotational shear experiments were conducted on coal from Pingdingshan No.10 Mine under 12.5 MPa axial pressure at 25 °C and 80 °C with three shear rates. Notably, no replicate samples were set for each experimental condition. Gas generation characteristics and structural evolution were characterized via FTIR, ¹³C NMR and GC-MS analyses. Results show that 25 °C shearing only causes physical fragmentation, with CO₂ as the sole product. Under 80 °C thermo-mechanical coupling, low shear rate preferentially cleaves aliphatic side chains, yielding the highest CH₄ and promoting aromatic polycondensation. High shear rate fragments aromatic skeletons, suppressing hydrocarbon generation and dominating CO₂ production. This study verifies the stress-temperature coupling chemical effect of medium-rank bituminous coal and reveals the shear-rate-regulated differential gas generation mechanism, providing direct experimental evidence for tectonic stress-induced coalification and gas generation.