Controllable inverse C2H2/CO2 separation in ultra-stable Zn-organic frameworks for efficient removal of trace CO2 from acetylene

Abstract

It is of great challenge to produce highly pure C₂H₂ from the CO₂/C₂H₂ mixture because of their similar physical properties. Metal–organic frameworks (MOFs) have shown great potential in purifying C₂H₂ by virtue of their versatile pore environment with excellent tunability. However, the rational exploration of ideal MOF adsorbents with CO₂-preferred CO₂/C₂H₂ separation performance (also called inverse C₂H₂/CO₂ separation) is extremely difficult. In this work, we demonstrate a new Zn-MOF family (SNNU-334–336) with special CO₂-preferred CO₂/C₂H₂ separation performance, which can be rationally controlled by functional groups as well as temperature. Notably, SNNU-334–336 MOFs show extremely high stability, and SNNU-336 can maintain a stable structure even after 7 days in boiling water and 30 days in air, which is unprecedented for all Zn-based MOF materials. Different to common MOF adsorbents, the adsorption isotherms of SNNU-334–336 MOFs for C₂H₂ and CO₂ under the same temperature all have an intersection point (we called the inverse point), which gradually moves to the high-pressure region with the increase of temperature and changes with the pore environment variation. So, SNNU-334–336 MOFs can be rationally controlled from C₂H₂-selective to CO₂-selective CO₂/C₂H₂ adsorption separation adsorbents. IAST selectivity calculation indicates that a very high CO₂ over C₂H₂ selectivity (3595.4) can be achieved, which nearly surpasses those of all reported MOFs with CO₂-preferred CO₂/C₂H₂ separation performance. Fixed-bed column breakthrough experiments further prove that SNNU-334–336 MOFs all have controllable inverse CO₂/C₂H₂ separation ability and can produce C₂H₂ with extra-high purity (>99.9%) from the CO₂/C₂H₂ (1/99) mixture.