Basic Zeolites as Efficient Adsorbents for Removing Trace Amounts of Acetylene from Ethylene

Abstract

Adsorptive separation of acetylene (C2H2) from ethylene (C2H4) using porous materials has emerged as an energy-efficient process for obtaining polymer-grade C2H4. Numerous microporous organometallic and organic materials have recently been developed to selectively adsorb C2H2 over C2H4. In contrast, zeolites, widely used commercial adsorbents due to their stability and synthesis scalability, have rarely been explored for C2H2/C2H4 separation. In this study, we synthesized faujasite (FAU) zeolite adsorbents with different basic properties by controlling Si/Al ratios, charge-balancing cations (Na+ and K+), and the amount of excess alkali oxides and investigated their performance in the C2H2/C2H4 separation. The results demonstrate that zeolites with higher basicity (or with more negatively charged O atoms) exhibit a stronger interaction with C2H2 through C delta--H delta+<middle dot><middle dot><middle dot>O delta- Lewis acid-base interactions. Meanwhile, larger K+ extraframework cations located in more accessible supercages provide additional interactions with the abundant pi-electrons of C2H2. Therefore, the KX zeolite supported with 3 wt % K2O clusters within its micropore (3K(2)O/KX) exhibited a high IAST C2H2/C2H4 selectivity of 20.2 as well as a remarkable dynamic selectivity of 121.8 at 298 K and 1 bar for a 1/99 (v/v) C2H2/C2H4 mixture. The adsorbent enabled the efficient production of high-purity C2H4 (>99.9995%) from a mixture of C2H2/C2H4 (1/99) with a high productivity (758.2 L kg(-1)). These findings hold promise for the development of efficient, stable, and scalable inorganic adsorbents in C2H2/C2H4 separation.