Metal-organic framework MIL-53(Cr) as a superior adsorbent: Highly efficient separation of xylene isomers in liquid phase

Selective adsorption and separation of three xylene isomers of seven stable metal-organic frameworks (MOFs) were investigated, where MIL-53(Cr) manifested the highest adsorption capacity and apparent preference for o-xylene. Further detailed studies with MIL-53(Cr) showed that pseudo-second-order model fit best with adsorption kinetics of xylene isomers, and the isotherms were perfectly fitted by Langmuir isotherm model. The adsorption was proved to be a quick process, and both the changes of entropy and enthalpy contributed to the o-xylene selectivity, but which mainly resulted from the entropy effect. The adsorption capacity of preferable isomer o-xylene, on account of better packing efficiency, was record-breaking 8.19 mmol/g, and selectivity of OX/PX, OX/MX and MX/PX were 13.75, 8.01 and 1.72, respectively. Both the adsorption capacity and OX selectivity on MIL-53(Cr) in liquid phase adsorption and breakthrough experiments were super high, which discriminated it from zeolites and other materials reported so far. Combined with extremely short equilibrium time and high stability, MIL-53(Cr) can be a promising adsorbent for separation of xylenes in industrial process.