Study on thermodynamics, dynamics and reverse shape separation selectivity of mesoporous UiO-66 for nHEP/MCH

UiO-66-Z with uniform mesopores using 2-aminoterephthalic acid and terephthalic acid as mixed ligands was synthesized by hydrothermal method in this paper. Thermodynamic and dynamic properties of UiO-66-Z were discussed. Dynamic separation performance and adsorption selectivity of UiO-66-Z for the equimolar n-heptane/methylcyclohexane (nHEP/MCH) binary mixture were investigated. Results show that UiO-66-Z has complete tetrahedral cages with uniform mesopores of 38 angstrom. Adsorption rate constant of MCH on UiO-66-Z (14.5 x 10(-3) s(-1)) is twice that of UiO-66 (6.7 x 10(-3) s(-1)), while nHEP does not significantly change at 323K with the pressure of 0.05-0.1 kPa. Effective adsorption diffusion coefficient of nHEP and MCH on the UiO-66-Z is about 25 times higher than that on the UiO-66. Compared with UiO-66, the desorption activation energy (Ed(1)) of the first desorption peak of nHEP and MCH on the UiO-66-Z is reduced by 53.75% and 76.66%, respectively. The separation selectivity of MCH to nHEP on the UiO-66-Z reaches up to 3.13 at 473 K. Results indicate that the introduction of mesopores in the UiO-66-Z can enhance mass transfer of nHEP and MCH in the pores, especially which is more obvious mass transfer effect for MCH with a larger molecular dynamics diameter under low partial pressure. The retention of most tetrahedral cages in the UiO-66-Z is conducive to improving its inverse shape separation selectivity for MCH/nHEP. Compared with UiO-66, nHEP and MCH have higher desorption efficiency on UiO-66-Z at the same temperature and time.

Automated summary

In this paper, UiO-66-Z with uniform mesopores was synthesized using a hydrothermal method, showing better adsorption performance compared to UiO-66, especially in terms of the adsorption rate of MCH.