Restrictive diffusion in aluminas

Abstract

The effect of the ratio of solute molecular diameter to the substrate pore diameter on the diffusion of polyaromatic compounds in four different pore sizes of amorphous gamma-aluminas was studied at atmospheric pressure and ambient temperature. Diffusion rates of the polyaromatic compounds in the aluminas decreased as the ratio of solute molecular diameter to pore diameter increased. Empirical correlations between the apparent reduction in solute effective diffusivity and the ratio of molecular diameter to pore diameter were obtained.< coronene < octaethylporphyrin = tetra-phenylporphyrin for a given alumina.Effective diffusivities at ambient temperature and pressure were determined by applying a pore diffusion model with a Freundlich isotherm to diffusion run data.

Configurational diffusion of asphaltenes in fresh and aged catalyst extrudates. Final technical report, September 20, 1991--September 30, 1996

“…As shown by Massoth and coworkers (Chantong and Massoth, 1983;Tsai et al, 1991), these different empirical or semiempirical expressions are basically the same. Furthermore, hindered diffusion behavior in alumina is different from that in membranes.…”

“…Most of the investigators tried to correlate their diffusion data with the theoretical models developed for membranes. Some studies showed that their data could be well represented by the Renkin equation (Chantong and Massoth, 1983;Limbach and Wei, 1990;Tsai et al, 1991;Rhee and Guin, 1994), while others observed the agreement of their results with the Beck and Schultz's power law of different z values ranging from 3.5 to 5.2 (Chantong and Massoth, 1983;Spry and Sawyer, 1975;Cheng et al, 1990;Tsai et al, 1991;Lee et al, 1991;1991a). Guo et al (1990) On the other hand, due to the different pore structures between membranes and porous alumina and silica, some different results have been observed, and different hindered diffusion concepts were proposed.…”

“…They suggested the following empirical equation (Prasher and Ma, 1977;Prasher et al, 1978) (2.28) where a and b are constants obtained from the best fit of the experimental data. Chantong and Massoth(1983) where T is the absolute temperature.…”

“…From above literature review, it can be seen that several hindered diffusion models have been suggested for both alumina and membranes in terms of the Davidson and Deen, 1988;Beck and Schultz, 1972;Bohrer et al, 1984;Cannel1 and Rondelez, 1980;Bohrer et al, 1987;Malone and Anderson, 1978. alumina, silica Hg porosimetry Cheng et al, 1990;Guo et al, 1990;Tsai et al, 1991;Colton et a1.,1975;Satterfield et al, 1978;Lee et al, 1991a;Chantong andMassoth, 1983. Satterfield et al, 1973.…”

“…Satterfield et al, 1973;Guin, 1994. Tsai et al, 1991;Lee et al, 1991;1991a;Chantong andMassoth, 1983. Davidson andDeen, 1988;Bohrer et al, 1984;Cannel1 and Rondelez, 1980.…”