Adsorption of H₂S from Hydrocarbon Gas Using Doped Bentonite: A Molecular Simulation Study

Hydrogen sulfide is a commonly occurring impurity in hydrocarbon gases such as natural gas or landfill gas. Apart from its toxicity, H₂S can cause problems in downstream processing because of corrosion of piping in the presence of moisture. Removing this contaminant using a cost-effective and energy-efficient technique such as adsorption using commonly occurring adsorbents would be beneficial both for processing and refinement of hydrocarbon gases and for their use as an energy source. In this work, grand canonical Monte Carlo simulations were performed using an ab initio forcefield to predict adsorption isotherms for methane, hydrogen sulfide, and nitrogen in bentonite doped with K⁺, Li⁺, and Na⁺ cations with a view to aiding the development of low-cost pressure-swing adsorption systems for the targeted removal of H₂S from landfill gas or natural gas. Pure species simulations were done, in addition to considering mixtures at conditions approximating real-world natural gas fields. Highly selective targeted adsorption of hydrogen sulfide was achieved for all three doped bentonites, with the adsorbed phase consisting of almost pure H₂S, although the volume of gas adsorbed differed between adsorbents. The results suggest the following ranking for the three doped bentonite adsorbents in terms of their overall performance: K⁺ > Li⁺ > Na⁺. By considering both the composition of the adsorbed phase and the total quantity of adsorbed gas, there may be an interplay between the gas-gas and gas-solid interactions that becomes somewhat noticeable at low pressures.