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Asymmetric pore windows in MOF membranes for natural gas valorization

Abstract

To use natural gas as a feedstock alternative to coal and oil, its main constituent, methane, needs to be isolated with high purity1. In particular, nitrogen dilutes the heating value of natural gas and is, therefore, of prime importance for removal2. However, the inertness of nitrogen and its similarities to methane in terms of kinetic size, polarizability and boiling point pose particular challenges for the development of energy-efficient nitrogen-removing processes3. Here we report a mixed-linker metal–organic framework (MOF) membrane based on fumarate (fum) and mesaconate (mes) linkers, Zr-fum67-mes33-fcu-MOF, with a pore aperture shape specific for effective nitrogen removal from natural gas. The deliberate introduction of asymmetry in the parent trefoil-shaped pore aperture induces a shape irregularity, blocking the transport of tetrahedral methane while allowing linear nitrogen to permeate. Zr-fum67-mes33-fcu-MOF membranes exhibit record-high nitrogen/methane selectivity and nitrogen permeance under practical pressures up to 50 bar, removing both carbon dioxide and nitrogen from natural gas. Techno-economic analysis shows that our membranes offer the potential to reduce methane purification costs by about 66% for nitrogen rejection and about 73% for simultaneous removal of carbon dioxide and nitrogen, relative to cryogenic distillation and amine-based carbon dioxide capture.

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Fig. 1: Schematic illustrations of pore-aperture editing and shape-mismatch-induced separation based on shape difference.
Fig. 2: Synthetic guide and characterization of pore-aperture-edited Zr-fum(100−x)-mesx-fcu-MOF membranes.
Fig. 3: Separation performances of Zr-fum(100−x)-mesx-fcu-MOF membranes and diffusion energy barriers.
Fig. 4: Comprehensive evaluations of N2/CH4 separation performance of Zr-fum67-mes33-fcu-MOF membranes under practical conditions and techno-economic comparison of distillation system with membrane or hybrid membrane–distillation system.

Data availability

The datasets analysed and generated during the current study are included in the paper and its Supplementary InformationSource data are provided with this paper.

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Acknowledgements

We gratefully acknowledge funding from King Abdullah University of Science and Technology and the CCF programme 1972. This work was also granted access to the HPC resources of CINES under the allocation A0100907613 made by GENCI.

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Authors and Affiliations

Authors

Contributions

S.Z. and M.E. conceived the idea and designed the experiments. S.Z. synthesized the materials and carried out most of the characterization. S.Z. and O.S. analysed the results. J.L. performed the gas adsorption experiments. P.M.B. contributed to the high-pressure adsorption experiments and H2S-related measurements. E.A.-H., J.J. and Z.H. contributed to the NMR characterization. H.J. contributed to the structure simulation. T.J. contributed to the element distribution mapping. P.L. and G.M. performed and analysed the molecular simulations. A.R. and J.G. contributed to the techno-economic analysis. S.Z., O.S. and M.E. wrote the manuscript. All the authors contributed to the revision of the manuscript.

Corresponding author

Correspondence to Mohamed Eddaoudi.

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Nature thanks Juergen Caro and Alexander Knebel for their contribution to the peer review of this work.

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This file includes: Supplementary Figures 1–31; Supplementary Tables 1–4; and Supplementary Notes 1 and 2.

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Zhou, S., Shekhah, O., Ramírez, A. et al. Asymmetric pore windows in MOF membranes for natural gas valorization. Nature 606, 706–712 (2022). https://doi.org/10.1038/s41586-022-04763-5

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