| Abstract
| - Adsorption isotherms of methane and carbon dioxide on two kinds of Australian coals have been measuredat three temperatures up to pressures of 20 MPa. The adsorption behavior is described by three isothermequations: extended three-parameter, Langmuir, and Toth. Among these, the Toth equation is found to be themost suitable, yielding the most realistic values of pore volume of the coals and the adsorbed phase density.Also, the surface area of coals obtained from CO2 adsorption at 273 K is found to be the meaningful parameterwhich captures the CO2 adsorption capacity. A maximum in the excess amount adsorbed of each gas appearsat a lower pressure with a decrease in temperature. For carbon dioxide, after the appearance of the maximum,an inflection point in the excess amount adsorbed is observed close to the critical density at each temperature,indicating that the decrease in the gas-phase density change with pressure influences the behavior of the excessamount adsorbed. In the context of CO2 sequestration, it is found that CO2 injection pressures of lower than10 MPa may be desirable for the CH4 recovery process and CO2-holding capacity.
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