Molecular simulations of the adsorption and separation of hydrogen sulfide, carbon dioxide, methane, and nitrogen and their binary mixtures (H2S/CH4), (CO2/CH4) on NUM-3a metal-organic frameworks

Removal of hydrogen sulfide from a binary mixture with methane gas, using IRMOF-1: a theoretical investigation

The natural gas is mainly composed by methane, ethane, propane, and contaminants. Among these contaminants, the H₂S gas has some specific characteristics such as its toxicity and corrosion, besides reducing the combustion power efficiency of natural gas. In this context, metal-organic frameworks appear as promising materials for purification of natural gas by adsorption, due to their large surface area and pore volume. In this work, Grand Canonical Monte Carlo method was used to study the adsorption and separation of CH₄:H₂S mixture by IRMOF-1. The adsorption isotherms were computed for the pure components, and at different compositions of binary mixture (90:10, 75:25, 50:50, 25:75, and 10:90). Interaction energy obtained with the semiempirical method confirmed that the inorganic unit is the preferred site for CH₄ and H₂S adsorption. Moreover, in a gas mixture with 50:50 proportion of CH₄:H₂S mixture, methane adsorbs preferentially in the inorganic unit only at pressures close to 20 bar. Non-covalent interaction (NCI) analyses indicated that the interactions involving H₂S are more effective than that for CH₄, due to an electrostatic character in the H₂S interaction. The simulations also showed that the separation of gases occurs in all compositions and pressures studied, suggesting that IRMOF-1 has a promising potential for this application.