Design of Olefin-Phobic Zeolites for Efficient Ethane and Ethylene Separation

Abstract

Selective adsorption of ethane from a mixture of ethane (C2H6) and ethylene (C2H4) has emerged as an energy-efficient process for obtaining high-purity ethylene. Recently, it has been reported that some novel microporous organometallic and organic adsorbents can preferentially adsorb C2H6 over C2H4. Conversely, zeolite adsorbents, which are widely used in industry due to their high stability and low material cost, generally prefer C2H4 adsorption ("olefin-philic"). In this study, we carefully investigated the effects of chemical composition (Si/ Al ratio), silanol defect, and pore topology (BEA, CHA, and MFI) of zeolites to develop efficient "olefin-phobic" adsorbents. The results showed that the Si-O-(Na+)-Al (weak Lewis acid) and isolated Si- OH (weak Bronsted acid) groups in the zeolite frameworks undesirably increased the affinity for C2H4 (Lewis base). Consequently, defect-free pure silica zeolites exhibited promising C2H6/C2H4 selectivities (1.98-2.25), which were superior to those of Al-containing zeolites (0.26) and pure silica zeolites with abundant silanols (1.50), at 298 K and 1 bar. In particular, defect-free pure silica BEA exhibited the highest C2H6/C2H4 selectivity (2.25), large C2H6 uptake (2.27 mmol g-1), and facile regeneration at 298 K. The adsorbent enabled the efficient separation of high-purity C2H4 (>99.95%) from a mixture of C2H6/C2H4 with high productivity (22.98 L L-1). The productivity was comparable or even superior to that of recently reported C2H6-selective adsorbents. The present results provide hope for the development of efficient, stable, and scalable inorganic adsorbents for the selective C2H6 adsorption.