Comparison of methane adsorption and diffusion characteristics in soft and hard coal

Adsorption and diffusion in soft and hard coal determine the abundance and seepage rule of coal-bed gas, we can facilitate the identification of the function of gas in coal and gas outburst and improve the coal seam gas recovery rate and drainage rate in mining through researching the adsorption and diffusion, so the research on adsorption and diffusion is of important significance. Using the experimental device designed by us, we studied the characteristics of adsorption and diffusion of samples, these samples came from Xin'an mine and NO.1 mine of Pingdingshan and were divided into two groups, and each group was divided into soft coal and hard coal, the comparison of absorption amount and Langmuir coefficient was studied under same absorption pressure, the control factors of coal surface energy were analyzed and the diffusion coefficient in initial desorption time was examined. The research results indicate that the coal surface energy is not apparently different in soft coal and hard coal, the Langmuir adsorption volume of soft coal is bigger than that of the hard coal in the same coal seam, the absorption amount is related with pressure and strength of coal body, the diffusion coefficient of the hard coal is bigger than that of the soft coal, and whether hard or soft coal, the diffusion coefficient tends to decrease with the desorption time and pressure, but the diffusion coefficient of the soft coal is bigger than that of the hard coal during short period of diffusion. The results are important for increasing recovery ratio in mines and studying the mechanism of coal and gas outburst.