Electrostatically driven kinetic inverse CO2/C2H2 separation in LTA-type zeolites

Abstract

The identical molecular size and similar physical properties of carbon dioxide (CO₂) and acetylene (C₂H₂) make their adsorptive separation extremely challenging to achieve with most adsorbents. Reports on the separation of CO₂ and C₂H₂ mixtures by zeolites are even rarer with the mechanism of adsorptive separation requiring further exploration. In this paper, we report that ion modulation of zeolite 5A promotes the difference in kinetic diffusion of CO₂ and C₂H₂, realizing the inverse separation of zeolite from selective adsorption of C₂H₂ to selective adsorption of CO₂. Creating a compact pore space restricting the orientation of gas molecules enables charge recognition. The positive electrostatic potential at the pore openings was utilized to hinder the diffusion of C₂H₂ between the cages while ensuring the transfer of CO₂, increasing their diffusion differences in pore channels and leading to the CO₂/C₂H₂ kinetic selectivity of 31.97. Grand canonical Monte Carlo (GCMC) simulation demonstrates that the CO₂ distribution in K-5A-β is significantly higher than that of C₂H₂. Dynamic breakthrough experiments verify the excellent performance of material in practical CO₂/C₂H₂ separation, for CO₂/C₂H₂ (50/50 and 1/99, V/V) mixtures can be separated in one step, thus directly generating high purity C₂H₂ (> 99.95%), which provides a promising thought for the zeolite-based separation of CO₂ and C₂H₂.