Understanding ethane/ethylene adsorption selectivity in ethane-selective microporous materials

Adsorption selectivity for ethane/ethylene (C2H6/C2H4) mixture determines to a large extent the separation quality in practical applications. Understanding and improving the adsorption selectivity is important to address this changeling separation process. GCMC simulations were used to study the effects of pore size and shape on C2H6/C2H4 selectivity in C2H6-selective microporous materials, which were constructed by adding 4,4′-bipyridine pillars in slit pores to mimic MOFs. The introduction of pillars in slit pores showed both positive and negative effects on the adsorption selectivity, depending on the spacing between pillars. The highest selectivity was obtained for the material 7.5-10.0-9.0 with slightly smaller pores than those where the transition from one to two adsorbed layers occurred. The simulation model used in this work successfully predicted the selectivity in many C2H6-selective adsorbents, which also exhibited stronger van der Waals interactions than other interactions. Furthermore, we showed that high selectivity on MOFs with very small pores could be explained by the presence of strong electric field gradients within the pores, which makes the adsorption of ethylene unfavourable.