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Pulsed field gradient (PFG) NMR was used in combination with single crystal IR microscopy (IRM) to study diffusion of ethane inside crystals of a mixed linker zeolitic imidazolate framework (ZIF) of the type ZIF-7-8 under comparable experimental conditions. These crystals contain 2-methylimidazolate (ZIF-8 linker) and benzimidazolate (ZIF-7 linker). It was observed that the PFG NMR attenuation curves measured for ethane in ZIF-7-8 exhibit deviations from the monoexponential behaviour, thereby indicating that the ethane self-diffusivity in different crystals of a crystal bed can be different. Measurements of the ethane uptake curves performed by IRM under the same conditions in different ZIF-7-8 crystals of the bed yield different transport diffusivities thus confirming that the rate of ethane diffusion is different in different ZIF-7-8 crystals. The IRM observation that the fractions of ZIF-8 and ZIF-7 linkers are different in different ZIF-7-8 crystals allowed attributing the observed heterogeneity in diffusivities to the heterogeneity in the linker fraction. The quantitative comparison of the average ethane self-diffusivities measured by PFG NMR in ZIF-7-8 with the corresponding data on corrected diffusivities from IRM measurements revealed a good agreement between the results obtained by the two techniques. In agreement with the expectation of smaller aperture sizes in ZIF-7-8 than in ZIF-8, the average ethane self-diffusivities in ZIF-7-8 were found to be significantly lower than the corresponding self-diffusivities in ZIF-8.
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Induction vacuum swing adsorption over magnetic sorbent monoliths and extrudates for ethylene/ethane separation
Abstract Electrification of adsorption processes is emerging as an adaptable solution for future gas separations. This study develops magnetic sorbent structures for use in induction vacuum swing adsorption (IVSA) process specifically designed for olefin/paraffin separation. Two sorbents, namely Fe3O4/ZIF‐7 (ethane‐selective) and Fe3O4/13X (ethylene‐selective) were developed and formulated into extrudates (Fe20/ZIF‐7‐P) and monoliths (Fe20/13X‐M), and tested under different regeneration scenarios, including simultaneous and subsequent induction‐evacuation, induction only, and evacuation only. The dynamic adsorption results demonstrated that regeneration under subsequent induction‐evacuation improves desorption rate and capability. Under this regeneration scenario, Fe20/ZIF‐7‐P achieved an ethane desorption rate of 0.24 mmol/g.min, representing a remarkable 37.5% enhancement over the induction‐only scenario. Similarly, Fe20/13X‐M exhibited an ethylene desorption rate of 0.35 mmol/g.min, indicative of a 34.2% enhancement. Moreover, the IVSA cyclic runs highlighted the excellent regeneration capability and stability of both Fe20/ZIF‐7‐P and Fe20/13X‐M with Fe20/13X‐M exhibiting ethylene purity, recovery, and productivity of 99.4%, 99.6%, and 39.9 mol/kg.h, respectively. Overall, these findings underscore the potential of the hybrid induction/vacuum process as an effective technique for achieving efficient regeneration of sorbents in olefin/paraffin separation.
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- Award ID(s):
- 2431601
- PAR ID:
- 10513898
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- AIChE Journal
- Volume:
- 70
- Issue:
- 7
- ISSN:
- 0001-1541
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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