Ethylene (C₂H₄) is the highest volume product in the petrochemical industry, which is generally produced from the steam cracking of hydrocarbons or partial combustion of natural gas, inevitably resulting in extra gases including acetylene (C₂H₂) and carbon dioxide (CO₂). 

Deeply removing C₂H₂ and CO₂ to produce polymer-grade (99.95% purity) C₂H₄ is important in industry. At present, one-step purification of C₂H₄ from ternary CO₂/C₂H₂/C₂H₄ mixture is still a challenge in the chemical industry, since few materials have both high C₂H₂/C₂H₄ and top-level CO₂/C₂H₄ selectivity simultaneously.

In a study published in Angewandte Chemie International Edition, Prof. WU Mingyan and Prof. CHEN Qihui from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences reported an ultramicroporous material FJI-H38 with adaptive pores and abundant N/O binding sites, realizing one-step C₂H₄ purification from C₂H₂/C₂H₄/CO₂ mixture.

Researchers found that the abundance of aromatic rings and the high-density carboxylate oxygen atoms distributed on the pore surface of FJI-H38 provides the preferred environment for C₂H₂ and CO₂ simultaneously. Adsorption experiment revealed that FJI-H38 shows excellent trace C₂H₂ and CO₂ trapping capability at 0.01 bar and 298 K. Therefore, FJI-H38 has top-level C₂H₂/C₂H₄ selectivity and highest CO₂/C₂H₄ simultaneously.

Dynamic breakthrough experiment confirmed that polymer-grade C₂H₄ (99.95%) with record-high productivity can be obtained in one step from ternary C₂H₂/CO₂/C₂H₄ mixture under various conditions. Even at 318K, the separation performance of FJI-H38 had no obvious decrease, which had never been seen in previously reported materials.

Gas-loaded single-crystal X-ray diffraction experiments demonstrated that such excellent separation performance is due to the adaptive recognition of C₂H₂ and CO₂ by FJI-H38 through the synergistic effect of appropriate pore size and the match of electrostatic potentials, where C₂H₂ and CO₂ can be anchored by the O/N and aromatic hydrocarbons sites. In contrast, the C₂H₄ molecular can’t be tightly captured by FJI-H38 because its molecular size is too big.

This study represents a step forward toward one-step C₂H₄ purification from the multi-component mixture. The synergistic effect of appropriate pore size and the match of electrostatic potentials will facilitate the designed synthesis of porous materials for challenging energy-saving gas separation.