Comparative study on different coals from the Lorraine basin (France) by sorption isotherms, thermogravimetric analysis and breakthrough curves for CO2-ECBM recovery

The enhanced coalbed methane recovery using CO₂ injection (CO₂-ECBM) is widely proposed as a way of achieving the energy transition and reducing atmospheric CO₂ in areas such as the Lorrain basin in France, where heavy industry is responsible for huge CO₂ emissions and coal mines have been closed for more than a decade. This paper deals with the feasibility of extracting methane from the Lorraine basin using CO₂-ECBM by comparing data from sorption isotherms, thermogravimetric analyses and breakthrough curves for two coal samples. One is bituminous (Box 18), from Folschviller (France) and is compared with another sub-bituminous (TH01) from La Houve (France), which is used as a reference because it was identified as a good candidate for CO₂-ECBM in a previous research program. The quantities of adsorbed gases (CO₂/CH₄) obtained by sorption isotherms, thermogravimetry and CO₂ breakthrough curves showed that Box 18 adsorbs more CO₂ and CH₄ than TH01 due to its higher porosity and good affinity for gases (CO₂/CH₄). Tόth model fits the experimental CH₄ and CO₂ adsorption isotherms better, reflecting the fact that the adsorption surface of the coals studied is heterogeneous. Adsorption enthalpies obtained by calorimetry indicated physisorption for gas-coal interactions, with higher values for CO₂ than for CH₄. Thermogravimetric analyses and breakthrough curves carried out at up to 50% relative humidity showed that the adsorption capacity of CO₂ decreases with increasing temperature and the presence of water, respectively. The compilation of these experimental data explained the adsorption process of the studied coals and revealed their advantages for CO₂-ECBM.