Research on the pore structure of bituminous coal on the basis of different degassing temperature and particle size

The coal seam gas adsorption capacity increases with the specific surface area of the coal. However, the optimum experimental particle size and degassing temperature have not been given for Low-temperature N₂ adsorption (LTNA) test which is commonly used for specific surface area measurement of porous media. To evaluate the effects of particle size and temperature on coal pore structure, fat coal from Pingdingshan Eighth Mine and coking coal from Pingdingshan Eleventh Mine were characterized by thermogravimetry-mass spectrometry (TG-MS), LTAN, and scanning electron microscopy (SEM). Research shows that: (1) Optimal degassing temperature is 150°C, with 200–300 mesh as the best particle size. (2) When the particle size is reduced to 200 mesh, the pore structure parameters of hard coal increase sharply. The impact on pore area distribution is most evident in pores < 2 nm and 10–100 nm, while the effect on pore volume is more prominent in pores > 10 nm. (3) According to the results of SEM, the surface impurities of coal sample decrease obviously when the degassing temperature is 150°C. As the degassing temperature increases, the pore structure is distorted. The results can be used to evaluate coalbed methane (CBM) resources more accurately, enhance gas extraction technology, and develop more efficient coal-based adsorption materials.