Study of the effect of H2S on the diffusion and displacement of CH4 in coal

In order to address the issue of safe and efficient extraction of coalbed methane in H2S-containing coal mines, this study explored the impact of H2S on CH4 diffusion and displacement within coal. The molecular structure model of Guizhou Linhua (LH) coal was obtained based on the structural physical characterization experiment of coal such as 13C NMR, FTIR, XPS, we investigated the diffusion coefficient of CH4 in coal under different fixed adsorption amounts of H2S and examined the corresponding adsorption curves of mixed gas (H2S, CH4, CO2) under varying component proportions using the molecular simulation software Materials Studio. The results indicate that when H2S is present in the adsorption system, lower levels of absorbed H2S content by coal correspond to higher CH4 diffusion coefficients and improved diffusion effects. In other words, the presence of H2S inhibits CH4 diffusion within coal. Under identical temperature and pressure conditions, the adsorption capacity of coal for CH4, H2S, and CO2 follows this order: H2S > CO2 > CH4. When the mixture n(CO2)/n(CH4) is in the range of 0–150 % and there is H2S influence in the system, there is a significant reduction in CH4 adsorption capacity compared to two-component coals containing CO2/CH4, it becomes evident that H2S has an inhibitory effect on CO2 displacing CH4 within coal.