A novel adsorption differential volumetric apparatus to measure mass transfer in nanoporous materials

Abstract

A novel adsorption differential volumetric apparatus was developed for the determination of diffusional time constants in nanoporous materials and applied to diffusion of nitrogen and argon in commercial pellets of 4A zeolite. The system is designed for high rates of data acquisition allowing to determine mass transfer time constants of seconds over the pressure range from vacuum to 130 kPa. Diffusion of N2 and Ar on a single pellet and fragments obtained from the pellet are studied between –10 °C and 35 °C and 0.8 to 55 kPa. These systems are chosen as representing weak adsorption to demonstrate the sensitivity of the apparatus that gives a good signal-to-noise ratio even with a single pellet in the entire pressure range. The systems studied confirm micropore diffusion control and an isothermal diffusion model was shown to reproduce accurately the observed kinetics using reduced pressure plots. As the crystal size in the pellet is not known accurately, the resulting activation energies and the ratio of diffusional time constants of N2 and Ar were used to validate the results against known literature values.