One-Step Purification of C ₂ H ₄ from CO ₂ /C ₂ H ₄ by Polyethylenimine-Modified Mesoporous Carbon Adsorbents

Although the separation of CO 2 from C 2 H 4 is critical for emerging syngas/CO 2 -to-olefin processes, it remains a great challenge due to the similar molecular dimensions of them and the tendency of conventional adsorbents to preferentially trap C 2 H 4 . In this study, a polyethylenimine (PEI)-functionalized mesoporous carbon adsorbent (UMC@PEI30) was fabricated via an ultrasonic-assisted impregnation strategy, which achieved high PEI dispersion and created micropores of 0.6–0.8 nm. This approach reduced the amine blocking ratio (ABR) from 60% to 4% compared to that of conventional impregnation methods. An optimal PEI loading of 30 wt % was identified to maximize the synergistic physisorption-chemisorption effect. Physical adsorption dominated at low temperatures, and chemical adsorption of CO 2 became dominant at higher temperatures, with an isosteric adsorption heat of approximately 47 kJ/mol. Dynamic breakthrough experiments demonstrated a separation window of 21.47 min for preferentially trapping CO 2 (and directly releasing C 2 H 4 ) when treating a CO 2 /C 2 H 4 (50/50) mixture at 298 K. The purity of the released C 2 H 4 ranged from 99.91% to 99.98%, and the adsorbent performance remained nearly constant over 10 adsorption–desorption cycles. This work provides a scalable and effective strategy for preferential CO 2 adsorption over C 2 H 4 and establishes a promising advance for industrial C 2 H 4 /CO 2 separation technology.