**5. Conclusions**

This investigation reports the effective separation of propyne (C3H4) and propylene (C3H6) using the fluorinated metal organic framework, SIFSIX-3-Ni. The SIFSIX MOF showed a better adsorption capacity compared to another pyrazine based MOF (NbOFFIVE-1-Ni) under the same experimental conditions. Characterization of the adsorbents showed developed micropores and a stable structure with a BET area of around 248 m<sup>2</sup> g<sup>−</sup>1. The maximum uptake recorded for the SIFSIX was in excess of 3.2 mmol g<sup>−</sup><sup>1</sup> for C3H4 compared to 2.99 mmol g<sup>−</sup><sup>1</sup> for C3H6. Size sieving and thermodynamic interactions were thought to be the main separation mechanisms, as indicated by the high isosteric heat of adsorption towards propyne on SIFSIX. The selectivity of propyne over propylene on the used metal organic frameworks can be attributed to kinetic (size exclusion) and thermodynamic (pore and surface interactions) combination. Isotherm models fitted the Toth model well for all combinations of solid metal organic frameworks and gases at the full applied range of temperatures. The smaller kinetic diameter of propyne and the strong interactions make its adsorption easier on SIFSIX-3-Ni and facilitate its possible application in the separation of propyne and propylene binary mixtures. A 10-min time difference between the breakthrough of C3H6 and the lighter C3H4 was evident from the dynamic breakthrough curves, indicating grea<sup>t</sup> potential for the application of SISFIX-3-Ni for propyne/propylene separation.

**Author Contributions:** Conceptualization, M.K. and G.W.; methodology, M.K. and F.A.; software, M.K.; validation, M.K. and F.A.; formal analysis, M.K.; investigation, M.K.; data curation, M.K.; writing—original draft preparation, M.K.; writing—review and editing, G.W. and F.A.; visualization, M.K.; supervision, M.K.; project administration, M.K. and F.A.; funding acquisition, M.K. and G.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** Qatar National Research Fund under the National Priorities Research Program award number NPRP10-0107-170119.

**Acknowledgments:** The work was made possible by a gran<sup>t</sup> from the Qatar National Research Fund under the National Priorities Research Program award number NPRP10-0107-170119. Its content are solely the responsibility of the authors and do not necessarily represent the official views of QNRF. The authors acknowledge the CLU unit at Qatar University for helping in sample analysis.

**Conflicts of Interest:** The authors declare no conflict of interest.
