Studies on the competitive sorption of CO2 and CH4 on hard coal

•The competitive sorption of CO2 and CH4 on hard coal where measured.•The value of the effective diffusion coefficient grew along with the content of CO2.•An increase of CO2 adsorbate concentration worsens the fit of the Langmuir isotherm model.•Competitive sorption of CO2−CH4 on coal causes a small change of pore structure.