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 greatly important in industry since the extra gases can reduce the quality of polyethylene commodities and a trace amount of C₂H₂ can poison the Ziegler-Natta catalyst. At present one-step purification of C₂H₄ from ternary CO₂/C₂H₂/C₂H₄ mixture is still a great 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, 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.

The researchers found that the abundance of aromatic rings and the high-density carboxylate oxygen atoms distributed on the pore surface of FJI-H38, which provide C₂H₂ and CO₂ preferred environment simultaneously. The adsorption experiment shows that FJI-H38 shows excellent trace C₂H₂ (54.03 cm³cm^-3) and CO₂ (76.77 cm³cm^-3) trapping capability at 0.01 bar and 298 K. Therefore, FJI-H38 exhibits top-level C₂H₂/C₂H₄ selectivity and highest CO₂/C₂H₄ simultaneously.

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

Gas-loaded single-crystal X-ray diffraction experiments demonstrate 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, since the molecular size of C₂H₄ is too big to perfectly match with the pore size and the electrostatic potentials, the C₂H₄ molecular can’t be tightly captured by FJI-H38.

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

A flexible metal-organic framework possesses appropriate pore size and the match of electrostatic potentials on its pore surface, realizing one-step C₂H₄ purification from C₂H₂/CO₂/C₂H₄ mixture.(Image by Prof. WU’s group)

Contact:

Prof. WU Mingyan

Fujian Institute of Research on the Structure of Matter

Chinese Academy of Sciences

Email: wumy@fjirsm.ac.cn

Keywords: Ethylene purification, ternary mixture, metal-organic frameworks, one step separation

Published Paper Title:One-Step Ethylene Purification from Ternary Mixture with Adaptive Recognition Sites

Link:https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.202423496