(350b) On-Surface Synthesis and Grafting of Ionic Liquid Functionalities on Mesoporous Silica Adsorbents to Induce Reverse Selectivity for Removal of Ethane from Ethylene

Developing cost-effective ethane-selective adsorbents for pressure-swing adsorptive separation of ethane from ethylene as an alternative to energy-intensive cryogenic distillation is a challenging task. In addition to inducing paraffin-selectivity, regeneration of such adsorbents is challenging as well, due to the relatively high heat of adsorption of the adsorbate gases¹. Herein, we present highly surface-functionalized mesoporous silica exhibiting reverse selectivity with ultra-low enthalpy of adsorption. These novel adsorbents were designed by controlled grafting of a paraffin-selective ionic liquid (IL) onto the silica surface by silanization resulting in switching the selectivity of the adsorbents from being olefin- to becoming paraffin-selective. Gravimetric adsorption experiments validated the reverse selectivity which was due to the enhanced van der Waal’s forces between the six hydrogen atoms of the C₂H₆ molecule and the fluorine atoms (C–H···F interactions). We further evaluated the effect of key parameters such as the amount of IL loading and types of IL anion and IL cation on the selectivity. The isosteric heat of adsorption was as low as 12 kJ/mol for ethane, revealing industrially relevant regeneration potential.

Acknowledgments
Financial support by the Center for Catalysis and Separations (CeCaS) of Khalifa University (Award No. RC2-2018-024) is greatly acknowledged.

Reference

1. Anwar, F.; Khaleel, M.; Wang, K.; Karanikolos, G. N. Selectivity Tuning of Adsorbents for Ethane/Ethylene Separation : A Review. Ind. Eng. Chem. Res. 2022, 61, 34, 12269–12293.