Benchmarking selective capture of trace CO₂ from C₂H₂ using an amine-functionalized adsorbent

Purifying C₂H₂ by removing trace CO₂ is critically needed yet challenged by their analogous physical properties. Herein, we report a commercial resin adsorbent HP20 (Diaion® HP-20 Resin) loaded with polyethyleneimine (PEI@HP20) which selectively captures trace CO₂ and excludes C₂H₂. PEI@HP20 possesses a high CO₂ adsorption capacity (4.35 mmol/g) at 100 kPa and 298 K and a record CO₂/C₂H₂ uptake ratio compared with all reported CO₂-selective adsorbents. The ideal adsorbed solution theory selectivity reaches 1.33×10⁷. The pilot-scale pressure-temperature swing adsorption on 2 kg PEI@HP20 further validated that it can obtain >99.99% purity C₂H₂ from CO₂/C₂H₂(1/99, v/v) mixtures with a high yield of 344.7 g per cycle. The combination of multinuclear solid-state Nuclear Magnetic Resonance, Fourier Transform infrared spectroscopy and density functional theory calculations reveal that the performance of PEI@HP20 relies on a dual chemisorption/physisorption mechanism. This work highlights a promising method to develop green, low cost, high efficiency, and readily scalable CO₂-selective adsorbent.