A comparative study of CO2 diffusion from adsorption kinetic measurements on microporous materials at low pressures and temperatures

• Adsorption kinetics of CO2 on several microporous materials at 273–293 K and up to 100 kPa.
• Isothermal and non-isothermal models used to calculate diffusion coefficients.
• Darken equation and a structural model used to study the pressure-dependence.
• Differences between diffusion time constant related to the activation energy.

The equilibrium adsorption and kinetics of CO2 on several microporous materials has been studied at 273, 283 and 293 K and gas pressures of up to 100 kPa. The porous materials used in this work were two zeolites (5A and 13X), two metal–organic frameworks (Basolite A100 and Basolite Z1200), an activated carbon and two pillared clays (Al-PILC and Zr-PILC). The isothermal and non-isothermal diffusion models were applied to calculate the diffusion time constants (D0/rc2) from the uptake curves. The non-isothermal model was found to fit the experimental data well over the whole range of adsorption rates. The values found for the zeolites, which ranged from 0.020 to 0.043 s−1, were lower than those for the metal–organic frameworks and pillared clays, which ranged from 0.036 to 0.081 s−1, in the same interval of temperatures. Furthermore, the values of the diffusion time constants were found to depend on gas pressure. The pressure-dependence of the diffusion time constants was studied using the Darken equation. Finally, activation energy values were estimated from the temperature-dependence for all materials and it was found to increase in the order: Z1200 < Al-PILC < 13X < AC < Zr-PILC < 5A; A100.

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