Polycatenated Molecular Cage-Based Propane Trap for Propylene Purification with Recorded Selectivity

Area of Science:

• Materials Science
• Chemical Engineering
• Separation Science

Background:

• Propane (C3H8)-selective adsorption is crucial for energy-efficient production of high-purity propylene (C3H6).
• Existing methods often require multiple adsorption-desorption cycles, increasing energy consumption.
• Developing advanced materials with enhanced selectivity and capacity is essential.

Purpose of the Study:

• To develop a novel strategy for preferential propane adsorption using a unique molecular cage structure.
• To investigate the adsorption mechanism, including multiple interactions and shape selectivity.
• To demonstrate the direct production of high-purity propylene via column breakthrough experiments.

Main Methods:

• Synthesis of a polycatenated molecular cage within a microporous framework: [Ni(bpe)2(WO4)] (bpe = 1,2-bis(4-pyridyl)ethylene).
• Characterization of adsorption properties, including selectivity and adsorption enthalpy.
• Computational modeling to understand the interaction and shape selectivity mechanisms.
• Column breakthrough experiments for propylene purification.

Main Results:

• The [Ni(bpe)2(WO4)] framework exhibited preferential C3H8 adsorption with C3H8/C3H6 selectivity ranging from 1.62 to 2.75.
• High adsorption enthalpy (around 42 kJ mol-1) was observed, indicating strong interactions.
• Dense electronegative binding sites within the cage facilitated multiple Cδ−-Hδ+···Cδ− interactions with propane.
• Shape selectivity favored the oblate propane molecule over the planar propylene molecule.
• Direct production of 99.6% purity propylene was achieved in a single column breakthrough experiment.

Conclusions:

• The novel polycatenated molecular cage demonstrates significant potential for energy-efficient propane/propylene separation.
• The combination of multiple interactions and shape selectivity is key to achieving high C3H8 adsorption.
• This technology offers a direct pathway to high-purity propylene, reducing energy consumption and process complexity.