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

The purification of H-2-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 H-2 from a mixture containing H-2 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 H-2 and CO2 were considered by molecular simulation. The adsorption of these gases followed the Langmuir model, and the diffusion coefficient of H-2 was much higher than that of CO2. Then, using the Maxwell-Stefan model, the H-2 and CO2 permeances and H-2/CO2 permselectivities in the H-2-CO2 mixtures were evaluated. Despite the fact that adsorption of CO2 was higher than H-2, owing to the simultaneous interference of adsorption and diffusion processes in the membrane, H-2 permeation was more pronounced than CO2. The modeling results showed that, for a ZIF-8 membrane, the H-2/CO2 permselectivity for the H-2-CO2 binary mixture 80/20 ranges between 28 and 32 at ambient temperature.