Introducing halogen-bonded gates into zeolitic frameworks for efficient benzene/cyclohexene/cyclohexane separation

Area of Science:

• Materials Science
• Chemical Engineering
• Supramolecular Chemistry

Background:

• Separating C6 cyclic hydrocarbons like benzene, cyclohexene, and cyclohexane is a critical yet challenging process in the petrochemical industry.
• Existing separation methods often lack efficiency and selectivity for these closely related compounds.

Purpose of the Study:

• To design and synthesize a novel metal azolate framework (MAF) capable of selective C6 cyclic hydrocarbon separation.
• To investigate the mechanism of guest-dependent adsorption and aperture gating behavior within the MAF.
• To achieve high-purity benzene separation from its mixtures with cyclohexene and cyclohexane.

Main Methods:

• Synthesis of a new SOD-topology metal azolate framework (MAF).
• Characterization of the MAF's adsorption properties using temperature- and guest-dependent studies.
• Single-crystal X-ray diffraction analysis to elucidate structural features.
• Computational simulations to understand the role of halogen bonds in gating and diffusion.

Main Results:

• The synthesized MAF exhibits distinct, controllable adsorption behaviors for benzene, cyclohexene, and cyclohexane.
• The framework demonstrates efficient benzene purification from binary and ternary mixtures, achieving selectivity up to 113 ± 2 and purity over 98%.
• This represents the highest reported performance for benzene/cyclohexane/cyclohexene separation to date.

Conclusions:

• The novel MAF, controlled by C-Br⋯N halogen bonds, effectively separates C6 cyclic hydrocarbons.
• Halogen bonding is identified as a critical factor in the gating mechanism, enabling highly efficient adsorptive separation.
• This work presents the first example of halogen-bonding controlled gating for advanced adsorptive separation applications.