Adsorption Equilibrium and Kinetics of CO2 on Chromium Terephthalate MIL-101

Abstract

In this work, isotherm and kinetics of CO 2 adsorption on a chromium-based metal organic framework MIL-101 sample were studied. The MIL-101 crystal cubes were synthesized by the microwave irradiation method and then characterized. The isotherms and kinetic curves of CO 2 adsorption on the MIL-101 sample were separately measured at 298, 308, 318, and 328 K within a pressure range of 0−30 bar by a gravimetric method. The mass-transfer constants and diffusion activation energy E a of CO 2 adsorption on the MIL-101 crystals were estimated separately. Results showed that the maximum uptake of CO 2 on MIL-101 was 22.9 mmol/g at 298 K and 30 bar and that isotherms of CO 2 adsorption were well-fitted with the Freundlich model. The isosteric adsorption heat of CO 2 on MIL-101 was in the range of 4.0−28.6 kJ/mol. It depended upon the amount of CO 2 uptake and decreased with the loading of CO 2 . The adsorption kinetics of CO 2 on the MIL-101 crystals was described by the linear driving force (LDF) model. With the increase of the temperature, the mass-transfer constants of CO 2 adsorption on MIL-101 increased. The diffusion coefficients of CO 2 were in the range from 4.11 × 10 −11 to 2.54 × 10 −10 cm 2 /s. The coefficients increased with the temperature and decreased with the pressure. The diffusion activation energies E a of CO 2 on MIL-101 were in the range of 2.62−4.24 kJ/mol, which decreased with the pressure.