Adaptive Pore Opening to Form Tailored Adsorption Sites in a Cooperatively Flexible Framework Enables Record Inverse...

Area of Science:

• Materials Science
• Chemical Engineering
• Separation Science

Background:

• Traditional cryogenic distillation for alkane/alkene separation is energy-intensive.
• Existing porous adsorbents often show preferential uptake of the desired alkene, necessitating frequent regeneration.
• A need exists for adsorbents with inverse selectivity for alkanes to enable direct alkene purification and reduce energy costs.

Purpose of the Study:

• To develop a low-energy separation method for propane and propylene using porous adsorbents.
• To discover materials exhibiting inverse selectivity for propane over propylene.
• To achieve direct purification of reagent-grade propylene with reduced energy consumption.

Main Methods:

• Synthesis and characterization of the structurally responsive metal-organic framework CdIF-13.
• Powder synchrotron X-ray diffraction and first-principles calculations to elucidate the mechanism of pore adaptation and adsorbate interactions.
• Dynamic column breakthrough measurements to evaluate separation performance under industrially relevant conditions.

Main Results:

• CdIF-13 exhibits inverse selectivity for propane over propylene due to adaptive pore size and shape changes.
• Record-setting separation performance with a selectivity factor of approximately 3 for a 95:5 propylene:propane mixture at 298 K and 1 bar.
• Demonstrated direct purification of propylene when CdIF-13 is combined with a rigid adsorbent.

Conclusions:

• Structurally responsive materials like CdIF-13 can achieve unprecedented separation factors through cooperative flexibility.
• The induced-fit mechanism of adsorbate-specific pore adaptation is key to the material's inverse selectivity.
• This approach offers a viable, energy-efficient alternative for industrial-scale alkene purification.