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

摘要

In this work, isotherm and kinetics of CO2 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 CO2 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 CO2 adsorption on the MIL-101 crystals were estimated separately. Results showed that the maximum uptake of CO2 on MIL-101 was 22.9mmol/g at 298 K and 30 bar and that isotherms ofCO2 adsorption were well-fitted with the Freundlich model. The isosteric adsorption heat of CO2 on MIL-101 was in the range of 4.0-28.6 kJ/ mol. It depended upon the amount of CO2 uptake and decreased with the loading of CO2. The adsorption kinetics of CO2 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 CO2 adsorption on MIL-101 increased. The diffusion coefficients of CO2 were in the range from 4.11 x 10~(-11) to 2.54 x 10~(-10) cm~2/s. The coefficients increased with the temperature and decreased with the pressure. The diffusion activation energies E_a of CO2 on MIL-101 were in the range of 2.62-4.24 kJ/mol, which decreased with the pressure.