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

Area of Science:

• Materials Science
• Chemical Engineering
• Separation Science

Background:

• Membrane-based purification of hydrogen (H₂)-rich streams is vital for pre-combustion carbon dioxide (CO₂) capture.
• Zeolitic imidazolate frameworks (ZIFs) offer promising properties for gas separation membranes.

Purpose of the Study:

• To theoretically investigate the separation of H₂ from H₂/CO₂ mixtures using a ZIF-8 membrane.
• To evaluate the performance of ZIF-8 membranes for H₂ purification via molecular simulation.

Main Methods:

• Molecular simulations were employed to determine adsorption and diffusion coefficients of H₂ and CO₂.
• The Langmuir model described gas adsorption, while the Maxwell-Stefan model evaluated permeance and permselectivity.
• Analysis focused on the interplay between adsorption and diffusion phenomena within the ZIF-8 membrane.

Main Results:

• H₂ exhibited a significantly higher diffusion coefficient than CO₂ in the ZIF-8 membrane.
• Despite higher CO₂ adsorption, H₂ permeation was more pronounced due to combined adsorption-diffusion effects.
• The ZIF-8 membrane demonstrated an H₂/CO₂ permselectivity between 28 and 32 for an 80/20 H₂/CO₂ mixture at ambient temperature.

Conclusions:

• ZIF-8 membranes show excellent potential for selective H₂ purification from CO₂-containing streams.
• The theoretical model confirms the viability of ZIF-8 membranes for pre-combustion CO₂ capture.
• Understanding adsorption-diffusion interplay is key to optimizing membrane performance for gas separations.