CO2 isothermal adsorption models of coal in the Haishiwan Coalfield

Since the capacity of CO2 adsorption of coal is a key factor in coal and CO2 outbursts, an experimental study was carried out on CO2 isothermal adsorption with high-pressure volumetry with dry coal samples from the No.2 coal seam in the Haishiwan Coalfield. Four different equations (Langmuir, BET, D-R and D-A) were used to fit the experimental data. We discuss adsorption mechanisms. The results show that the amount of CO2 adsorption increases rapidly under low relative pressure, i.e., the ratio of equilibrium pressure and saturated vapor pressure, which indicates that molecular layer adsorption or micropore filling may occur in coal. No clear equilibrium state was observed on the isothermal adsorption curves under relative pressure (P/P0) ranging from 0 to 0.8. The fitted results show that the accuracy of the D-A equation is highest with n=1. Micropores are more developed in coal by comparing the BET equation with a pressure mercury injection method on the surface area. The D-A equation (n=1) provides the best fit. By comparing the calculated specific surface area of the BET equation and the mercury intrusion method, it is found that micropore adsorption of CO2 occupies a dominant position. © 2010 China University of Mining and Technology.