Desorption hysteresis of CO2 and CH4 in different coals with cyclic desorption experiments

The gas adsorption/desorption experiments in coal are important contents in the research of coalbed methane (CBM) recovery and CO2 sequestration. However, the curve of gas desorption often lags behind the adsorption curve, which is called desorption hysteresis. Desorption hysteresis is a common phenomenon that has a significant impact on the prediction of CBM recovery. In this paper, the characteristics of CH4 and CO2 desorption were examined using an experimental apparatus. The parameters of the Langmuir model were obtained from the desorption data. It can be concluded that the desorption isotherm of an initial pressure chosen according to the in situ coal seam pressure is more appropriate for the prediction of CBM recovery. The ratio of desorption hysteresis for CO2 is weaker than that for CH4 in different ranks coal. The desorption hysteresis is more likely to happen in low rank coal. The results of pore structure show that the average pore width of coal sample after CO2 cyclic desorption experiments is changed. The pore deformation is not the primary factor that causes desorption hysteresis, and the solution phase of gas could be another factor. The findings of this study can help for better understanding of the process of CBM recovery, the production of CBM and the CO2 storage in coal seams.