Study on the Separation of H₂ from CO₂ Using a ZIF-8 Membrane by Molecular Simulation and Maxwell-Stefan Model

The purification of H₂-rich streams using membranes represents an important separation process, particularly important in the viewpoint of pre-combustion CO₂ capture. In this study, the separation of H₂ from a mixture containing H₂ and CO₂ using a zeolitic imidazolate framework (ZIF)-8 membrane is proposed from a theoretical point of view. For this purpose, the adsorption and diffusion coefficients of H₂ and CO₂ were considered by molecular simulation. The adsorption of these gases followed the Langmuir model, and the diffusion coefficient of H₂ was much higher than that of CO₂. Then, using the Maxwell-Stefan model, the H₂ and CO₂ permeances and H₂/CO₂ permselectivities in the H₂-CO₂ mixtures were evaluated. Despite the fact that adsorption of CO₂ was higher than H₂, owing to the simultaneous interference of adsorption and diffusion processes in the membrane, H₂ permeation was more pronounced than CO₂. The modeling results showed that, for a ZIF-8 membrane, the H₂/CO₂ permselectivity for the H₂-CO₂ binary mixture 80/20 ranges between 28 and 32 at ambient temperature.