Influence of high and low rank coal wettability and methane adsorption/desorption characteristics

In order to study the influence of different ranks of coal wettability on the adsorption/desorption of coalbed methane(CBM), Sihe No.3 coal and Dafosi No.4 coal samples were collected, which were used to perform the contact angle measurements and adsorption/desorption experiments, and analyzed the thermal characteristics of the isosteric adsorption heat through thermodynamic calculation. The results show that the water-wettability of Dafosi No.4 coal is far better than Sihe No.3 coal resulting from Dafosi No.4 coal is low metamorphic (CY) coal and the number of oxygen containing functional groups such as carboxyl group, hydroxyl group and so on. Meanwhile, Dafosi No. four coal has the hydrophilic property of the material component and the advantage of the development of the pore and crack. The coal moisture content is influenced by the wettability of coal, and which indirectly influences the adsorption/desorption characteristics of CBM. The relationships among wettability, moisture content, desorption rate and recovery efficiency from Dafosi No. 4 coal and Sihe No.3 coal is complicated, which is restricted by the critical water content and there is a critical point of temperature. By comparing the isosteric adsorption heat, found that the hydrophilic property of coal is not conducive to the adsorption of CBM. CBM adsorption heat release is much less than desorption heat absorption, there is the significant desorption hysteresis, and it decreased with increasing adsorption/desorption capacity and low rank coal's weakening trend gets more obvious.