Restrictive diffusion under catalytic hydroprocessing conditions

Abstract

The effect of the ratio of reactant molecular diameter to catalyst pore diameter on the restrictive diffusion of reactants in catalysts under catalytic hydroprocessing conditions was studied. Hydrogenation of four nitrogen-containing heterocyclic model compounds dissolved in decalin was carried out in a batch-mode operation at 623 K and 5.27 MPa of hydrogen partial pressure over three Ni-Mo/alumina catalysts encompassing a range of molecular to pore sizes of 0.03 to 0.35. An empirical correlation for restrictive diffusion under realistic processing conditions was developed. The correlation shows that the effective diffusivity is strongly influenced by the ratio of the reactant molecular size to the average micropore size, taking into account changes in pore sizes due to coke deposition. The restrictive effect under reaction conditions was found to be larger than the theoretical prediction for nonreactive conditions.

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

“…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.…”

“…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.…”

“…Many investigators have observed intrapore diffusion effects, and several mathematical diffusion models have been applied to describe the diffusion process (Guin et al, 1986;Lee et al, 1991;Limback and Wei, 1990;Haynes, 1988). Hindered diffusion effects include both stearic exclusion and hydrodynamic restriction phenomena (Deen, 1987).…”

Hindered diffusion of residue narrow cuts through polycarbonate membranes

“…The following power-law relationship is one which has been used in hindered diffusion studies. 10,17 FðkÞ ¼ ð1 À kÞ m :…”

Effectiveness factors for continuous mixtures

“…Lee et al (1991) estimated the effect of restricted diffusion in catalytic hydroprocessing. Limbach and Wei (1990) studied restricted diffusion of porphyrins in porous particles, and showed how best to estimate average pore and molecular sizes.…”