Diffusion measurements through embedded zeolite crystals

Using temporal analysis of products and flux response technology to determine diffusion coefficients in catalytic monoliths

“…The FRT data compares well with other reported values for the diffusivity of propane in silicalite (Sun et al, 1996). Therein, a diffusion coefficient between 4-6 x 10 -10 m 2 s -1 was determined over the temperature range of 30-70 °C which may be compared with values of 4-10 x 10 -10 m 2 s -1 between 25-80 °C from the present study.…”

“…These changes may be associated with the macroscopic techniques observing other effects such as desorption during measurements as well as the actual diffusion of the molecules in the micropores. These additional effects have been shown to strongly influence the diffusivities observed (Crank 1979;Ruthven, 1988b andVan den Begin et al, 1989;Heink et al, 1992;Jobic et al, 1992;Hufton and Danner, 1993;Silva and Rodrigues, 1996;Sun et al, 1996;Cavalcante et al, 1997;Nijhuis et al, 1999;Loos 2000;Ruthven and Brandani 2000;Gobin 2006;Gunadi and Brandani 2006;Richardson et al, 2008;Karge et al, 2008;Guimarães et al, 2010).…”

“…Table 4 gives the activation energies for diffusion determined by other techniques to compare with this study. A large variation between the methods is observed dependant on whether the technique is microscopic or macroscopic in nature (Eic and Ruthven, 1988b;Heink et al, 1992;Sun et al, 1996;Karge et al, 2008). The microscopic techniques generally result in high diffusivities and low activation energies for diffusion.…”

Diffusion in Confinement: Agreement between Experiments Better than Expected

“…Figure 2 shows our recent simulation results for the diffusion of methane in MFI-type silica as a function of the adsorbate loading, 15 together with results obtained by several other groups through simulation 2-6 and experiment. 1,[7][8][9][10] Note that the potential parameters used in the simulations have been fitted to adsorption data, not diffusion data. 19 The experimental data (black symbols) are self-diffusion coefficients, except those obtained by single-crystal membrane (SCM) measurements, which should be corrected diffusivities.…”

“…Although there are over 130 different known zeolite topologies, most groups focus on the understanding of the diffusion in silicalite (MFI) because this material is very well characterized and the MFI structure is used in many industrial applications. [1][2][3][4][5][6][7][8][9][10][11][12] Talu et al 1 made a comparison of the various techniques used to measure diffusion in confinement. Figure 1 is based on their results.…”