Effect of heating temperature on pore structure of briquette coal using SEM, NMR, N2/CH4 adsorption-desorption analyses

The development of briquettes capable of effectively replacing raw coal samples in physical simulation experiments is crucial for coal mine gas disaster prevention. We invented a new method for preparing briquette coal (BC), and studied how the heating temperature changed its pore structures using scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), the low temperature liquid nitrogen adsorption test (LTNAT), and the CH₄ adsorption-desorption test. We found that with an increase in heating temperature, SEM analysis showed that the surface roughness of the coal body increased, and the pores gradually changed from non-developed to large pores. NMR analysis showed that the content of briquette micropores decreased, and that of the macropores increased. Furthermore, at 300 °C, the cumulative total porosity of the BC was less than that of other coal samples. In the LNLDT test, all coal samples had inverted "S" type and IV type isothermal adsorption curves, with the minimization of peak values of pore volume and specific surface area occurring at 600 °C; D₁ gradually decreased, and D₂ gradually increased. The CH₄ adsorption-desorption test showed that a higher preparation temperature during the adsorption process resulted in a greater adsorption capacity of briquette to CH₄. A Langmuir model was used to fit the adsorption data, where the adsorption constant "a" of coal increased and "b" decreased. Our results provide a reference for studying similar materials and can be used in physical simulation experiments for the prevention and control of coal and gas outbursts.