Alkyl-Selective Metal-Organic Framework with Engineered Aliphatic Slots for Benchmark One-Step Para-Xylene Purification from C8 Aromatic Isomers

Abstract

The separation of para-xylene (PX) from C8 aromatic isomers remains a critical challenge in the chemical industry, given the structural similarities of these compounds. Herein, the study presents a metal-organic framework (MOF), CMOM-7, designed with aliphatic slots tailored to selectively trap non-para-alkyl groups of C8 aromatics, facilitating the one-step purification of PX. The framework features 1D channels that enhance diffusion kinetics, while the confined aliphatic slots exhibit a high affinity for ortho-xylene (OX), meta-xylene (MX), and ethylbenzene (EB). Breakthrough experiments demonstrate the exceptional selectivity of CMOM-7, achieving a PX purity of 99.5% with a yield of 264 mg/g. Single-crystal X-ray diffraction and density functional theory (DFT) calculations reveal that the selective adsorption is driven by the strong interactions between the aliphatic slots and the alkyl groups of OX, MX, and EB, while PX remains unbound within the channels. This study introduces CMOM-7 as a highly effective and energy-efficient adsorbent for the simultaneous separation of OX, MX, and EB from PX, offering a promising solution to one of the most challenging separations in industrial chemistry.