Research on the nanopore characteristics during the pyrolysis of typical tar-rich coals from shaanxi province

Tar-rich coal pyrolysis offers a practical route to bolster domestic oil supply, yet pore structures in Shaanxi coals respond differently to temperature and systematic comparisons remain limited. Here, tar-rich coals from the Zhangjiamao, Caojiatan, Yuanzigou, and Dafosi mines were heated to 400, 450, 500, and 550 °C, and low-temperature N₂ adsorption was used to track temperature-driven pore-structure evolution. At room temperature, pore-volume distributions fall into two categories: Type-Ⅰ, dominated by micropores, and Type-Ⅱ, concentrated near the mesopore–macropore boundary. From 400 to 450 °C, mesopores respond most strongly, showing the largest volume increase and the fastest mass-loss rate, indicating progressive opening of previously closed pores and their linkage with native mesopores to form new pore networks. Above 450 °C, pyrolysis intensifies: newly generated micro- and macropores dominate, fracture connectivity grows, and thermal rupture drives mesopore collapse, together yielding rapid increases in micro/macropore volumes and enhanced connectivity that favor more complete pyrolysis. Fractal analysis further shows that, for Type-Ⅰ, pore-surface oxidation between 400 and 450 °C markedly increases pore complexity, whereas above 450 °C new micro/macropores control structural change; Type-Ⅱ exhibits opposite trends over the same window, governed by distinct thermal responses. These results identify 400–450 °C as a critical interval for internal pore transformation and provide guidance for efficient utilization of tar-rich coal resources.