Restricted diffusion of liquids in microporous catalysts

Abstract

NOTATION c = concentration, mole/cm3 DJ E E A = activation energy, Joule/mole F R pj T = temperature, O K X = axial distance, cm a = transfer coefficient c = electrochemical effectiveness factor = diffusivity of species J, cm2/s = electrode potential vs, N.H.E., Volts -S-1 = gas constant, Joule/mole O K = reaction rate of species J, mole/cm2*s =--(-) 1 d s J h' dX" xr=o B Subscripts g J = species J 00 = intrinsic or bulk solution value = dimensionless concentration (= CJC,.)= observed value, Equation (6)

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

“…This assumption, motivated by experimental results to be discussed in the following chapters, results in an effective diffusivity which is also a function of radial position inside the catalyst particle. Thus, the model presented here is somewhat more general than previously used models which assumed constant average values for catalyst properties and a resulting constant effective diffusivity (Guin et al, 1986;Chantong and Massoth, 1983;Zhang et al, 1995;Stiegel et al, 1982;Stephens and Stohl, 1984;Johnson et al, 1986;Prasher et al, 1978;Butt et al , 1975).…”

“…where the factor K, included both partition and surface adsorption coefficient, and f(rm, rp) was some function of the solute radius rm and pore radius r,. 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.…”

“…Johnson et al (1986) studied the changes in effective diffusivity on resid deactivated HDS catalysts and found that the deactivation process lowered the De values by a factor of over 500 resulted from a wedge-type deposit of both the coke and metals. Prasher et al (1978) showed that the hindered diffusion in alumina based catalysts was enhanced during the hydrocracking of residuum process. They explained the reduction in effective diffusivity by the increase in pore constrictivity and decrease in pore connectivity due to the coke and metal deposits.…”

“…Additionally, during the catalyst usage the pore size of the catalyst is reduced or even plugged due to the deposition of carbonaceous and/or metals (Guin et al, 1986;Haynes and h u n g , 1984;Johnson et al, 1986;Prasher et al, 1978), which further enhances the diffusional limitation. Finally, since alumina, silica and supported porous catalysts are usually made as powders or extrudates of some shapes, direct measurements of effective diffusivities were usually performed in a finite diffusion cell containing a particle holding basket with either solute uptake or desorption (Guin et al, 1986;Prasher and Ma, 1977;Satterfield et al, 1973;Rhee and Guin, 1994;Chantong and Massoth, 1983;Tsai et al, 1991), whereas hindered diffusion studies with membranes were normally conducted in a diaphragm diffusion cell (Malone and Anderson, 1978;Conlon and Craven, 1972;Bohrer et al, 1987;Kathawalla and Anderson, 1988;Guillot et al, 1985;Cannel1 and Rondelez, 1980;Beck and Schultz, 1972;Davidson and Deen, 19,88).…”

“…This basic technique has been used by a number 'of investigators (Guin et al ,. 1986;Stephens and Stohl, 1984;Johnson and Massoth, 1986;Prasher et al, 1978). In some experiments, catalyst extrudates were crushed or broken in order to obtain particles of different radii.…”