Isothermal adsorption kinetics properties of carbon dioxide in crushed coal

Abstract

Understanding the dynamic response of coal to carbon dioxide sorption is crucial for optimizing carbon dioxide sequestration in unmineable coal seams and enhanced coalbed methane recovery. In order to explore the adsorption kinetics of carbon dioxide in coal, 15 isothermal adsorption tests were conducted on bituminous and sub-bituminous coals at 50°C for increasing equilibrium pressures (up to 4 MPa). The pseudo-second order (PSO) model is introduced to approximate the carbon dioxide sorption kinetics in coal, and the kinetics properties are then investigated via the PSO model. The linear relationship between (t/q) and (t) is validated and confirmed with a high correlation coefficient (>99%). The kinetics parameter, k2, decreases with both increasing equilibrium sorption pressure and increasing pressure difference. The sorption equilibrium content, Qe, in each sorption stage depends on both the final equilibrium pressure and the pressure difference. Based on the relationship between sorption content and time, the sorption content for different pressure ranges is predicted using different time intervals. The analysis indicates that the adsorption process for carbon dioxide in coal is a combination of both bulk diffusion-controlled and surface interaction-controlled processes; the former dominates the initial stage while the latter controls the majority of the overall process. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd