Breaking the trade-off between selectivity and adsorption capacity for gas separation

Area of Science:

• Materials Science
• Chemical Engineering
• Separation Science

Background:

• The energy-intensive nature of gas separation technologies is a significant environmental concern.
• Porous materials often face a trade-off between selectivity and adsorption capacity, hindering efficient gas separations.
• Acetylene (C₂H₂) removal from carbon dioxide (CO₂) is crucial for various industrial processes.

Purpose of the Study:

• To systematically investigate hybrid ultramicroporous materials (HUMs) for selective C₂H₂ removal from CO₂.
• To explore the impact of crystal engineering on the separation performance of HUMs.
• To develop a sorbent with both high selectivity and high adsorption capacity for C₂H₂/CO₂ separation.

Main Methods:

• Synthesis of six isostructural HUMs with a pcu topology using a common organic linker (pypz) and varying inorganic pillar ligands and metal cations.
• Characterization of the binding affinities of the synthesized HUMs for C₂H₂ and CO₂.
• Performance evaluation using fixed-bed dynamic column breakthrough experiments with equimolar C₂H₂/CO₂ mixtures.

Main Results:

• All synthesized HUMs demonstrated preferential binding of C₂H₂ over CO₂.
• Crystal engineering allowed tuning of pore size and chemistry, leading to enhanced separation performance.
• SIFSIX-21-Ni achieved a record C₂H₂/CO₂ separation selectivity of 27.7 and a high adsorption capacity of 4 mmol·g⁻¹.

Conclusions:

• The developed HUMs offer a promising solution for energy-efficient gas separation.
• SIFSIX-21-Ni represents a breakthrough in C₂H₂ selective sorbents, overcoming the selectivity-capacity trade-off.
• This work demonstrates the power of crystal engineering in designing advanced porous materials for targeted gas separations.