Gate-tailoring with protons and metal cations in a flexible zeolite for high-efficiency ethylene/ethane separation

The separation of ethylene (C2H4) from ethane (C2H6) is a critical yet energy-intensive process in the chemical industry, demanding energy-efficient and cost-effective solutions. Here, we report a Li+-exchanged silicoaluminophosphate RHO zeolite (Li-SAPO-RHO) with unprecedented selectivity for C2H4 over C2H6. This exceptional performance is attributed to the synergy between H+ and Li+ ions strategically positioned at the flexible eight-membered ring (8MR) gates of the zeolite. These ions effectively modulate the transport barriers for C2H4 and C2H6, significantly enhancing separation efficiency. Li-SAPO-RHO exhibits an Ideal Adsorbed Solution Theory selectivity exceeding 20,000 and enables the production of polymer-grade C2H4 (>99.9%) from refinery dry gas, with a productivity of up to 238.6 mmol/L. This performance surpasses that of all existing zeolite and metal-organic framework-based benchmark adsorbents. The H+-Li+ synergistic gating effect has been investigated using advanced characterization techniques, such as electron diffraction and neutron powder diffraction, along with ab initio molecular dynamics simulations. In addition to its exceptional selectivity and productivity, Li-SAPO-RHO offers advantages of low-cost synthesis, ultrahigh stability, and excellent cyclic performance, making it a highly promising candidate for industrial-scale light olefin separations.