Knudsen Diffusion and Viscous Flow Dusty-Gas Coefficients for Pelletised Zeolites from Kinetic Uptake Experiments

Abstract

A simple volumetric uptake apparatus was used to determine uptake data of N 2 on a sample of LiLSX zeolite for two different particle sizes, two temperatures, and a variety of different dosing pressure levels. Using a mass and energy conservation model for the dosing and sample volumes and the Dusty Gas Model + viscous flow for the mass transfer description at the pellet level, the Knudsen and viscous flow structural parameters were derived. Our analysis gave structural coefficients C K = 0.0827 ± 0.018 and C v = 0.0608 ± 0.026 which gave good agreement across all of the experimental runs conducted for both particle sizes and all pressure ranges. From these, tortuosity coefficients for Knudsen and viscous flow were derived and gave τ K = ε P,macro /C K = 3.7 ± 0.8 and τ v = ε P,macro /C v = 5.1 ± 2.2 respectively. These are in good agreement with reported values. The apparatus and procedure is not very sensitive to the viscous flow coefficient but is sensitive to the Knudsen coefficient. All other parameters of the model were measured or determined by calibration experiments. This study suggests that the apparatus may be useful for determination of some of the fundamental structural coefficients employed in the Dusty Gas Model.

Molecular transport in nanopores: a theoretical perspective

“…However, in the majority of applications both models require empirical specification of the transport parameters to fit the experimental or molecular simulation results. Examples include: Hejtma´nek et al 131 on transport of binary and ternary mixtures of light gases in mesoporous commercial catalysts; Moon et al 132 on separation analysis of H 2 /CO mixtures in mesoporous silica/alumina membranes; Chang and Lee 133 on the determination of DGM parameters for diffusion of light gases in silica by MD; or Todd et al 134 on the determination of DGM and structural parameters through uptake experiments in zeolites; interpretations of experimental data through the Lightfoot model have been carried out by Keurentjes et al 135 in the study of dialysis membranes using water/2-propanol solutions and Scattergood and Lightfoot 136 in ion-exchange membranes. In summary, the need to resort to empirical parameters, in addition to their algebraic equivalence, makes these two approaches equally convenient (with the same strengths and weaknesses) for the interpretation of experiments.…”

Macropore diffusion dusty-gas coefficient for pelletised zeolites from breakthrough experiments in the O2/N2 system

“…Time integration was performed with the integrator DVODE (Brown et al, 1989). Todd et al (2005) used a pure gas to reduce the intrapellet flux equation for the VF + DGM to a particularly simple form equivalent to Ficks first law of diffusion. In the present study we are using binary gas mixtures in breakthrough experiments.…”

Mass‐transfer models for rapid pressure swing adsorption simulation

“…With numerical valve coefficients controlled to achieve end of step pressure and purity targets, no fitting parameters remain to match experimental data. Equilibrium isotherm parameters,19 intrapellet structural parameters,29, 30 and pressure drop coefficients18 were determined independently. The isotherm for N 2 and O 2 on LiLSX was measured and correlated using the Dual‐Site Langmuir Equation.…”