The distortion of the 8MRs caused by Li + ions creates a tightly fitting environment for C2H4, further facilitating its diffusion. The optimized Li + -loaded SAPO-RHO adsorbent (Li-2-SAPO-RHO) achieved an unprecedented IAST selectivity exceeding 20,000 for C2H4 over C2H6. It also delivered polymer-grade C2H4 (> 99.9%) with a separation productivity of up to 238.6 mmol/L from refinery dry gas and a high C2H4 capture capacity of 1.50 mmol/g under dynamic conditions. The Li-2-SAPO-RHO adsorbent offers several practical advantages. It features a straightforward synthesis process using the low-cost OSDA, diethylamine (DEA) followed by direct solid-phase ion exchange. Its production is scalable, environmentally friendly, and exhibits excellent stability under humid and hydrothermal conditions. These properties make Li-2-SAPO-RHO a highly promising candidate for industrial-scale C2H4/C2H6 separation.