Capillary Condensation and Melting/Freezing Transitions for Methane in Slit Coal Pores

Grand canonical Monte Carlo method has been applied to study the adsorption behavior of methane in slit coal micropores for pore widths from 1.5 to 4.5 nm at temperatures 111–300 K. The adsorbent surface is considered to be inhomogeneous with C, N, S, O and H atoms, as well as vacancies, taken into account. The effect of surface microstructure on mechanism of the pore filling and saturation pressure is found to be more pronounced at relatively low and moderate strength of the adsorption field. It is also shown that irregular impurities and defects at the adsorbent surface contribute to the lowering of the freezing temperature and can change qualitively its dependence on the pore width.