High-pressure pyrolysis mechanism of tar-rich coal in Taiyuan Formation, Ordos Basin

Poor fluidity and difficult extraction of coal tar pose critical challenges for in-situ tar-rich coal development. However, the influence of temperature-pressure variations on pyrolysis products remains unclear. This study explores pressure's dual regulatory mechanisms on pyrolysis kinetics and product distribution via pressurized thermogravimetric and pyrolysis experiments. Thermogravimetric analysis shows 24.1 % thermal weight loss at atmospheric pressure; at 8 MPa, this decreases by 6.97 %, with decomposition activation energy increasing by 20.9 % due to enhanced organic matter interactions promoting small-molecule and coke formation. At 8 MPa, 500–700 °C condensation converts high-viscosity heavy tar to lighter tar and residual carbon. Coal tar analysis reveals pressure boosts light hydrocarbons (max. 61.6 %). High-pressure environments promote the cleavage of macromolecular Cal-Cal and Car-CH₃ bonds, thereby facilitating the generation of CH₄: 550 °C/8 MPa yields 33.45 % CH₄ (five times atmospheric), favoring methane-rich syngas. At 550 °C, kerogen fully cracks, with residues (TOC >40 %) providing energy via oxidation-coupled exothermic reactions. This work demonstrates improved tar fluidity, supporting optimized in-situ conversion sweet spot theory.