Inverse CO₂ /C₂ H₂ Separation with MFU-4 and Selectivity Reversal via Postsynthetic Ligand Exchange

Area of Science:

• Materials Science
• Chemical Engineering
• Separation Science

Background:

• Selective adsorption of acetylene (C2H2) over carbon dioxide (CO2) is crucial for industrial gas separation.
• While many porous materials favor C2H2 adsorption, CO2-selective sorbents are less common, posing a challenge for inverse separation.

Purpose of the Study:

• To report the performance of MFU-4 (Zn5Cl4(bbta)3) for inverse CO2/C2H2 separation.
• To investigate the mechanism of kinetic separation in MFU-4 and explore modifications for altered selectivity.

Main Methods:

• Synthesis and characterization of MFU-4 and its analogue MFU-4-F.
• Dynamic breakthrough experiments for gas separation performance evaluation.
• Adsorption kinetics measurements and computational studies to elucidate separation mechanisms.
• Postsynthetic F-/Cl- ligand exchange for tuning pore aperture and selectivity.

Main Results:

• MFU-4 demonstrated remarkable kinetic separation of CO2 from C2H2, yielding high-purity C2H2 (>98%) in dynamic breakthrough experiments.
• Computational studies and adsorption kinetics revealed that narrow pore windows in MFU-4, formed by Zn-Cl groups, exclude C2H2.
• MFU-4-F, synthesized via ligand exchange, exhibited reversed selectivity for equilibrium C2H2/CO2 separation and high C2H2 adsorption capacity (6.7 mmol g-1).

Conclusions:

• MFU-4 is an effective material for kinetic inverse CO2/C2H2 separation, enabling high-purity acetylene generation.
• Postsynthetic modification of MFU-4 can tune its pore structure and switch selectivity from kinetic to equilibrium-based separation.
• MFU-4-F shows potential for harvesting fuel-grade acetylene from mixtures via room temperature desorption.