Study on the adsorption of CH4, CO2 and various CH4/CO2 mixture gases on shale

Abstract

The isothermal sorption experiments of CH4, CO2 and CH4/CO2 mixture gases on shale were performed. The sorption affinities of CH4, CO2 and CH4/CO2 mixture gases were compared using Henry’s coefficient (KH). The thermodynamics of sorption of CH4, CO2 and their mixture were discussed based on surface potential (Ω), entropy loss (ΔS) and change of Gibbs free energy (ΔG). It is shown that the uptakes of CO2 is largest, followed by CH4/CO2 mixture gases and CH4 in sequence. The introduction of a small amount of CO2 into mixture gases can significantly enhance the adsorption quantity of mixture gases and suppress the adsorption of CH4. The lower pressure and the smaller CO2 mole fraction in bulk phase (yCO2) improve separation factor and boost the displacement of adsorbed CH4 by CO2. KH, Ω and ΔS for CO2 are higher than those for CH4, and KH, Ω and ΔS for CH4/CO2 mixture gases are between those for CH4 and CO2. Increasing yCO2 increases KH, Ω and ΔS. ΔG of CO2 and CH4/CO2 mixture gases are bigger than that of CH4. CO2 adsorption is more spontaneous and the introduction of CO2 enlarges the spontaneity degree of adsorption of mixture gases.

Keywords

• Competitive adsorption
• Shale gas
• Carbon dioxide
• Entropy loss
• Adsorption affinity