Chromatographic intraparticle diffusivities

Arve and Liapis [34] suggest estimating the parameters characterizing the intraparticle diffusion and the adsorption-desorption step mechanisms of affinity chromatography from the experimental data obtained in a batch system. The numerical simulations of the chromatographic process will use the values of the parameters of the adsorption isotherm and those of the effective pore diffusion as determined from stirred tank experiments together with the film mass transfer coefficients calculated from chemical engineering expressions found in the literature. 

In conclusion, the particle size distribution may significantly affect the shape of intraparticle diffusion-controlled chromatographic curves, particularly if this distribution is strongly skewed toward the large partide diameters. 

Fludized bed chromatography (FBC) indirectly measures the intraparticle diffusion under liquid. Breakthrough curves from the chromatograph from fixed beds of either ion-exchange resin or solids are fit to mathematical models in order to dednce snrface diffusion parameters from chromatographic peaks from pulse responses [98Kohl]. 

When there is a size distribution in the particles packed in a chromatographic column, the distribution does not change the first moment of the elution peak while it may affect peak broadening through the contribution not only of intraparticle diffusion but also of other transport processes such as axial dispersion. The evaluation of the latter effect is not clear but it is possible to make a prediction of the effect of particle size distribution on the intraparticle diffusion contribution, 8i. This was done by Chihara, Suzuki and Kawazoe (1977) for several typical distribution functions. The effeevt of the particle size distribution can be accounted for by introducing a correction factor, F, into the expression of 6d. 

Chromatographic columns packed with conventional porous particles meet these requirements only to a limited extent. Slow diffusion of large molecules limits the speed of the separation due to the low rate of intraparticle mass transfer [7]. New approaches have been introduced to overcome this problem including ... 

Meyers, J.J., Liapis, A.I. Network modeling of the intraparticle convection and diffusion of molecules in porous particles packed in a chromatographic column, J. Chromatogr. A, 1998, 827, 197-213. 

Coming back to the effect of intraparticle convection on the measured value of the effective diffusivity let us mention two experimental examples.The first one deals with a dynamic chromatographic method in a SPSR.The characteristics of the catalyst and reactor are listed below [9J. 

One should be careful when using a measured value of the effective diffusivity by a dynamic chromatographic method for reactor design.As said before we get at a given Reynolds number an apparent effective diffusivity D (as a result of a model which does not include convective transport inside the pellet).How will the reactor design be affected by using this value for 5 instead of that of the true effective diffusivity and the intraparticle Peclet number for convection In order to answer this question let us define a quantity... 

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