(682f) Framework Flexibility Driven Adsorptive Separation of C8 Aromatic Isomers in Metal Organic Frameworks: A Computational Exploration

Separation of xylene isomers from mixtures of C₈ aromatic compounds using metal organic frameworks is of potential interest for practical production of these species. In this work, we have used computational methods to explore adsorption of xylenes in several MOFs. It was found that use of rigid framework approximation in molecular simulations to describe adsorption in MOFs gives drastically different results than experiments. To address this issue, new methods combining ab-initio and MD calculations were developed to study the flexibility of these materials and its effect on adsorption of C₈ aromatic compounds in MOFs. In addition to the well-known structural transitions that can occur for materials like MIL-53, rotation of organic linkers and changes in torsion angle between metal-oxygen bonds have strong influence on the highest capacity and selectivity of adsorbates. We have applied these methods to C₈ aromatic adsorbates in MIL-53 series to address the question of how much significant the effect of flexibility in these MOFs are.