Mixed matrix membranes incorporated with cubic-MOF-5 for improved polyetherimide gas separation membranes: Theory and experiment

Cubic metal-organic framework 5 (C-MOF-5) nanocrystals with a high surface area (2387 m2/g) were successfully synthesized. The structure of C-MOF-5 nanocrystals was characterized by XRD, FTIR, particle size analysis, and N2 adsorption techniques. Novel mixed matrix membranes (MMMs) containing C-MOF-5 inside an polyetherimide (PEI) matrix were prepared using solution casting method and characterized by SEM, FTIR, and single gas permeation analyses. The SEM images of the MMM cross-sections revealed that C-MOF-5 particles have changed the morphology of polymer matrix. In addition, it has attained the proper distribution of filler as well as good compatibility between the filler and the polymer. The results showed that the C-MOF-5 nanocrystals facilitated the gas transport along the membranes and for all gases (H2, CO2, CH4, and N2), permeabilities, diffusivities, and solubilities of the MMMs were increased with increasing the loading of C-MOF-5 nanocrystals at ambient temperature and pressure of 6 bar. Incorporation of 5 wt.% of C-MOF-5 into pure PEI resulted in ∼40% increase in H2 permeability and the separation factor (αi,jP) of H2/CO2, H2/CH4, CO2/CH4, and CH4/N2 was changed from 5.99, 111.89, 18.67, 0.9 to 6.13, 117.42, 19.17, and 0.92, respectively. For high loadings of C-MOF-5s (15 and 25 wt.%), the mentioned separation factors (αi,jP) were increased except for H2/CO2. CO2 and CH4 permeability was strongly affected by the solubility coefficient and less affected by the diffusion coefficient. On the other hand, N2 permeability was strongly affected by the diffusion coefficient and less affected by the solubility coefficient. The experimental gas permeations through C-MOF-5/PEI nanocomposite with different filler loadings were fitted well on Higuchi model.