Structural functionalization in robust metal–organic frameworks for p-xylene separation with superior adsorption capacity

The subtle differences between the xylene isomers make the separation of p-xylene/m-xylene/o-xylene mixtures one of the most challenging tasks in the petrochemical industry. In this study, CAU-1 was used as a platform compound to construct functionalized pore environment with high stability for selective PX adsorption and separation. Single-component adsorption tests and liquid-phase multicomponent adsorption experiments showed that a series of functionalized scaffolds exhibited PX selective adsorption compared to the other two isomers, among them functional groups optimized CAU-1-OH ([Al8(OH)4(OCH3)8(BDC-OH)6])(BDC = 1,4-benzenedicarboxylate) showed ultra-high PX adsorption capacity (460 mg/g), superior to most reported MOFs. And the PX/MX selectivity of functionalized CAU-1-OH was improved by 18% compared to the original CAU-1. Furthermore, vapor breakthrough experiments on CAU-1-OH showed that it can effectively extract PX from ternary PX/MX/OX mixtures. The fundamental PX selective adsorption mechanism was also visually illustrated using grand canonical Monte Carlo simulation. In addition, the stability of the adsorbent was investigated under different conditions (RH = 40% and 80%, pH = 1–11, different solvents, and high temperatures), and the unchanged PXRD and BET curves indicate that the adsorbent has excellent structural stability. As thus, the large PX adsorption capacity, ultra-high structural stability, and excellent isomer separation performance make these materials good candidates for industrial PX purification from xylene isomers mixture.