Flux Equations for Osmotically Moderated Sorption–Diffusion Transport in Rigid Microporous Membranes
The development of non-aqueous reverse osmosis separations via the use of rigid microporous membrane materials suggests that flux equations originally developed for swellable polymeric membranes should be revisited. This paper demonstrates that the gradient of fractional occupancy of penetrant molecules within the micropores of the membrane is the driving force for permeation without requiring assumptions about pressure within the membrane. Flux equations are derived using both Fickian and Maxwell-Stefan approaches, and different behavior in the permeate flux versus upstream hydraulic pressure relationship is shown to arise as a result of differences in the loading dependence of the single component Maxwell-Stefan diffusivity. Molecular modeling results available in the literature and experimental data obtained from carbon molecular sieve (CMS) membranes showcase that these loading-dependent changes in the Maxwell-Stefan diffusivity are possible. This loading dependence is separated into three regimes: so-called “weak confinement” diffusion and “strong confinement” diffusion, both of which have been discussed at length in the literature, and a new “hybrid confinement” diffusion, which is introduced here. Furthermore, the separation mechanism of solvent molecules through a rigid bimodally microporous membrane is studied using xylene molecules passing through CMS membranes fabricated under different conditions as examples. Altogether, this study provides fundamental insight and guidance into osmotically-moderated sorption-diffusion transport of solvent molecules through rigid microporous membranes.
- Research Organization:
- Georgia Tech Research Corp., Atlanta, GA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
- Grant/Contract Number:
- SC0019182
- OSTI ID:
- 1593887
- Journal Information:
- Industrial and Engineering Chemistry Research, Journal Name: Industrial and Engineering Chemistry Research Journal Issue: 12 Vol. 59; ISSN 0888-5885
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Similar Records
Understanding and controlling water-organic co-transport in amorphous microporous materials
Co-transport of water and p-xylene through carbon molecular sieve membranes