Study on the Separation of H(2) from CO(2) 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 CO(2) capture. In this study, the separation of H(2) from a mixture containing H(2) and CO(2) 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 CO(2) 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 CO(2). Then, using the Maxwell–Stefan model, the H(2) and CO(2) permeances and H(2)/CO(2) permselectivities in the H(2)–CO(2) mixtures were evaluated. Despite the fact that adsorption of CO(2) 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 CO(2). The modeling results showed that, for a ZIF-8 membrane, the H(2)/CO(2) permselectivity for the H(2)–CO(2) binary mixture 80/20 ranges between 28 and 32 at ambient temperature.