Competitive CO2/CH4 adsorption and desorption in Powder River Basin coals: Implications for carbon storage

Adsorption of carbon dioxide (CO2) and methane (CH4) recovery within coalbeds are competitive processes driven by adsorption/desorption phenomena. Understanding these processes is crucial for assessing carbon storage potential in coalbeds to achieve carbon neutrality. This study introduces a novel sequential gas injection method to investigate competitive CH4/CO2 sorption behaviors on two Powder River Basin (PRB) coals: Canyon and Felix. The ability of PRB coals to adsorb CO2 competitively in CH4–rich environments and the effects of moisture content on the isotherms were examined. The evaluated moisture content for Canyon and Felix coals was 31.09 % and 34.25 %, respectively. The average gravimetric adsorption amounts of CO2 and CH4 under dry conditions were 0.025 g/g and 0.006 g/g for Canyon and 0.023 g/g and 0.005 g/g for Felix coal, respectively, while it decreased to 0.016 g/g and 0.004 g/g and 0.016 g/g and 0.0039 g/g, under moist conditions. Both coals showed that moisture content has a significant impact on CO2 adsorption than on CH4, with reductions in adsorption ranging from 43.75 % to 56.25 % for CO2 and 46.15 %–50 % for CH4. Competitive isothermal experiments revealed that CO2 adsorbs over four times more than CH4, while CH4 desorbs more rapidly than CO2. A Langmuir extended model provided an excellent fit for both coals with higher correlation coefficients (R2 values > 0.98). These findings suggest that PRB coals are viable candidates for CO2 storage, as they can effectively adsorb CO2 in the presence of substantial amounts of CH4.