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

Selective adsorption of ethane from a mixture of ethane (C 2 H 6 ) and ethylene (C 2 H 4 ) 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 C 2 H 6 over C 2 H 4 . Conversely, zeolite adsorbents, which are widely used in industry due to their high stability and low material cost, generally prefer C 2 H 4 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 Brønsted acid) groups in the zeolite frameworks undesirably increased the affinity for C 2 H 4 (Lewis base). Consequently, defect-free pure silica zeolites exhibited promising C 2 H 6 /C 2 H 4 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 C 2 H 6 /C 2 H 4 selectivity (2.25), large C 2 H 6 uptake (2.27 mmol g –1 ), and facile regeneration at 298 K. The adsorbent enabled the efficient separation of high-purity C 2 H 4 (>99.95%) from a mixture of C 2 H 6 /C 2 H 4 with high productivity (22.98 L L –1 ). The productivity was comparable or even superior to that of recently reported C 2 H 6 -selective adsorbents. The present results provide hope for the development of efficient, stable, and scalable inorganic adsorbents for the selective C 2 H 6 adsorption.