Author(s)

Dongmin Ma^1,2, Jianchang Zhang¹, Jianping Bai², Hui Zhang¹

¹Xi’an University of Science and Technology, Xi’an, China.
²National Key Laboratory of Coal and CBM Co-Mining Technology, Jincheng, China.

A series of methane adsorption-desorption isotherm experiments on anthracite of No. 3 Sihe coal mine were conducted at 20°C, 25°C, 30°C, 35°C and 40°C respectively. Based on Clausius-Clapeyron equation, isosteric heat of adsorption and maximum heat of adsorption has been calculated. These calculations indicate that the maximum heat of adsorption in process of elevated pressure (adsorption) and lowered stress (desorption) is 23.31 KJ/mol and 24.02 KJ/mol, so it belongs to physical adsorption. However, the latter is higher than the former. From the point of view of thermodynamics, in the adsorption-desorption equilibrium system, dropping pressure alone does not lead to desorption, but it improves adsorption of water vapor molecules on the surface of the coal pores. The adsorption heat of water vapor molecules is greater than 40 KJ/mol, so the methane on the surface of coal pores will be easily replaced by water vapor, and the desorption of methane occurs eventually. Thus, the gas production in coalbed methane well by pressure reduction is consistent with the negative pressure for gas extraction.

Methane, Adsorption, Desorption, Thermodynamics

Ma, D. , Zhang, J. , Bai, J. and Zhang, H. (2014) Thermodynamic Characteristics of Adsorption-Desorption of Methane in 3^# Coal Seam of Sihe. Natural Resources, 5, 782-794. doi: 10.4236/nr.2014.512067.