Removing trace amounts of acetylene (C₂H₂) from ethylene (C₂H₄)-rich gas mixtures is vital for the supply of high purity C₂H₄ to the chemical industry and plastics sector. However, selective removal of C₂H₂ is challenging due to the similar physical and chemical properties of C₂H₂ and C₂H₄. Cryogenic distillation (also known as low-temperature rectification) is a widely used commercial separation process involving liquefying gas mixtures at very low temperatures (183-258 K with 7-28 bar) and then selectively distilling a specific gas component at its boiling point, which is expensive and energy intensive.

Dr. Wang’s team from North China Electric Power University has developed a new method for dynamic removal of trace amounts of C₂H₂ from C₂H₄-rich gas mixtures. The “single-molecule traps” strategy that tunes the electrostatic interactions between the one-dimensional (1D) channel of a covalent organic framework (denoted as COF-1) and C₂H₂ molecules greatly improve the adsorption selectivity of C₂H₂ over C₂H₄. C₂H₂ molecules are preferentially located in single-molecule traps in COF-1 adsorbent, comprising an ideal microenvironment formed by the O atom of a C=O group, N atom of a C≡N group, and H atom of a phenyl ring in the 1D channels. COF-1 delivered a high affinity for C₂H₂ at ultralow pressures, which is relevant to the practical challenges of purifying C₂H₄ feedstocks in industry.

Image: The strategy of “single-molecule traps” in molecular level explanation.

By providing a clear illustration of the structure-separation performance relationship, which relies on the differing adsorption affinity of COF-1 for C₂H₂ and C₂H₄ at a molecular level, this study guides the rational development of COF-based adsorbents for removing trace C₂H₂ from industrial produced C₂H₄, thus delivering high-purity C₂H₄ gas.

Tag: Advanced Manufacturing

Sources: https://spj.science.org/doi/10.34133/research.0458