CO2/H2 separation using a highly permeable polyurethane membrane: Molecular dynamics simulation

• Investigation of a novel type of biodegradable polyurethane for CO2/H2 separation.
• Effect of temperature and the presence of H2O and CO on transport properties of syngas components.
• The membrane morphological investigation by XRD, FFV, RDF, free volume distribution.
• Significant performance of CO2/H2 separation achieved in the simulated membrane.
• Indication of two unknown behaviors of CO2 movement through the simulated membrane.

In this study, Molecular Dynamics (MD) and Grand Canonical Monte Carlo (GCMC) simulations were conducted to investigate the diffusivity, solubility, and permeability of CO2, CO, H2, and H2O in a polyurethane membrane at three different temperatures. The characterization of the simulated structures was carried out using XRD, FFV, Tg and density calculation, and cavity size distribution. The obtained results were within the expectations reported data in the literature based on the experimental approach, indicating the authenticity of approached in this work. The results showed that the highest diffusivity and permeability coefficients were observed for H2; while the highest values of solubility coefficient were found for H2O and CO2 gases. The increase of operating temperature from 298 K to 318 K has a positive effect on the permeation of all gases and a corresponding negative effect on the selectivity of the gas pair CO2/H2. Also, the results vividly showed that CO2 and H2O gases have a profound affinity with hard phase of polyurethane, while H2 and CO were conversely adsorbed by soft one. Moreover, the enhancement of permeability and permselectivity of CO2/H2 pair confirmed using Robeson Upper-Bond graph showed its good capacity for CO2/H2 separation application.