Density functional theory-based adsorption isotherms for pure and flue gas mixtures on Mg-MOF-74. Application in CO₂ capture swing adsorption processes

A simplified model is applied for the prediction of gas/solid adsorption isotherms of pure gases (i.e., CO₂, N₂, SO₂) on the metal-organic framework Mg-MOF-74 and then applied to flue gas mixtures with small amounts of SO₂ in the range 0.001-1% in weight. The model is based on periodic density functional theory (DFT) calculations and a dual-site Langmuir approach (DFT/DSL), using a mean-field approximation for the inclusion of the lateral interactions. This model not only provides reliable adsorption isotherms (P ≤ 1 atm, 293 ≤ T ≤ 373 K) but also isosteric heats of adsorption in good agreement with both available experimental data and more refined previous models. Moreover, the effect of SO₂ in the efficiency of adsorption of the other components of the mixture has been evaluated by showing that a very low presence of SO₂ is enough to poison the Mg-MOF-74 structure. Finally, several swing adsorption techniques have been analyzed at different operative conditions to quantify the impact of SO₂ poisoning in the CO₂ adsorption.