Roles of adsorption potential and surface free energy on pure CH4 and CO2 adsorption under different temperatures

Abstract

To fill the knowledge of adsorption characteristics of CH 4 and CO 2 associated with equilibrium and thermodynamics, adsorption equilibrium tests of pure gas on a coal were conducted under the different temperatures (35 °C, 50 °C, and 65 °C by the static volumetric method. The equilibrium data were well matched by the SLD-PR model. The influence of some significant factors including temperature, pressure, adsorption potential and surface free energy on gas adsorption capacity were discussed. The results showed that the higher temperature (gas pressure) corresponds to the smaller (larger) adsorption capacity and the larger adsorption potential is, the smaller adsorption capacity is. Taking CH 4 as adsorbent, the modified Langmuir equation can well match the SLD-PR model. However, when the adsorption medium is CO 2 , modified Freundlich equation is better. Using the two modified equations, we study further the relationship among the variation of surface free energy, its reduction rate and gas adsorption capacity. It can be concluded the larger the gas adsorption capacity is, the greater the reduction of surface free energy is, and the smaller the reduction rate of surface free energy is.