Methane/CO2 binary gas interaction on some moist, high–volatile bituminous Indian coals: 2. Pure-/mixed-gas adsorption modelling

The pure and mixed methane and CO2 excess experimental adsorption of three moist, high-volatile bituminous Indian coal samples at 40 °C and up to a pressure of ∼6500 kPa, were tested for the applicability of the adsorption models. For pure gas, Langmuir and Dubinin-Astakhov (DA) models were used and it was observed both Langmuir and DA models were matching with experimental data, although the fit with DA model was better. For mixed gas, Extended Langmuir (EL) and Ideal Adsorbed Solutions (IAS) theory were considered for model prediction. Later, the IAS theory was also combined with the Langmuir, DA equation for their applicability on mixed gas modelling. It was observed that none of the models were suitable for predicting the mixed gas adsorption. Although, EL-model show the maximum match for fitting experimental data at lower pressure, the deviation was increased at higher pressures. In general, the experimental CO2 separation factor was observed to decrease with an increase in pressure and CO2 gas concentration. However, the model prediction of CO2 separation factor was only validated by IAS-DA, other models showed inconsistent results.