Ionic Liquid - Grafted Mesoporous Silica Exhibiting Reverse Selectivity for Ethane/Ethylene Separation

Development of paraffin-selective adsorbents for the separation of ethane/ethylene mixtures, as an alternative technology to the energy-intensive cryogenic distillation, is challenging. Herein, we report surface-functionalized mesoporous silica adsorbents exhibiting reverse selectivity prepared by controlled in-situ synthesis of paraffin-selective ionic liquids (ILs) onto the pre-silanized surface of MCM-41 mesoporous silica. The surface modification switched the selectivity of the adsorbents from being inherently olefin-selective to becoming paraffin-selective, due to the enhanced van der Waal’s interactions between the grafted IL functionalities and the ethane molecules. A range of silica-based adsorbents functionalized with ILs of different loadings and anion and cation types were synthesized, characterized and investigated for their ethane/ethylene adsorption behavior. In addition to reversing the selectivity yielding values of up to 3.4 for ethane over ethylene, the adsorbents exhibited low isosteric heat of adsorption, indicatively 12 kJ/mol for ethane, while their performance was stable upon pressure swing adsorption and breakthrough cyclic testing. Dynamic packed bed experiments with ethane/ethylene mixtures demonstrated a breakthrough ethylene productivity of up to 1.2 mmol/g with a breakthrough selectivity of 2.4.