One-Step Purification of C₂H₄ from CO₂/C₂H₄ by Polyethylenimine-Modified Mesoporous Carbon Adsorbents

Although the separation of CO₂ from C₂H₄ is critical for emerging syngas/CO₂-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 C₂H₄. 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 CO₂ 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 CO₂ (and directly releasing C₂H₄) when treating a CO₂/C₂H₄ (50/50) mixture at 298 K. The purity of the released C₂H₄ 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 CO₂ adsorption over C₂H₄ and establishes a promising advance for industrial C₂H₄/CO₂ separation technology.