Noncryogenic Air Separation Using Aluminum Formate Al(HCOO)₃ (ALF)

Area of Science:

• Materials Science
• Chemical Engineering
• Separation Science

Background:

• Oxygen-enriched gas production is vital for industrial and medical applications.
• Current separation technologies are energy-intensive, relying on cryogenics or less efficient nitrogen adsorption.
• Direct oxygen adsorption methods offer improved efficiency but require suitable materials.

Purpose of the Study:

• To investigate the potential of the metal-organic framework Al(HCOO)3 (ALF) for efficient oxygen separation from air.
• To evaluate ALF's O2/N2 selectivity and adsorption capacity at low temperatures.
• To explore synthetic modifications for enhancing ALF's performance.

Main Methods:

• Gas adsorption isotherms and breakthrough experiments.
• Neutron and synchrotron X-ray powder diffraction.
• Raman spectroscopy and computational studies.
• Co-adsorption experiments to verify selectivity.

Main Results:

• ALF demonstrates substantial O2 adsorption (≈1.7 mmol/g at 190 K) and high O2/N2 selectivity (50-125).
• Effective O2 adsorption was observed at relevant temperatures (190 K and 250 K).
• Initial O2 adsorption kinetics are fast, suggesting viability for temperature-swing applications.

Conclusions:

• ALF is a low-cost, easily prepared material with excellent O2/N2 selectivity for air separation.
• Its performance at low temperatures makes it a promising candidate for cost-effective air separation.
• Synthetic strategies, such as Al/Fe solid solutions, can further improve kinetics.