Network modeling of the intraparticle convection and diffusion of molecules in porous particles packed in a chromatographic column

A pore network model (cubic lattice network) is constructed to represent the porous structure in a column packed with porous chromatographic particles. Expressions are developed and used to determine, through the utilization of the pore network model, the intraparticle interstitial fluid velocity and pore diffusivity of a solute as the pore connectivity, n(T), of the porous medium is varied from 2.6 to 6.0. The results show that the intraparticle interstitial velocity and the pore diffusivity increase significantly as the value of the pore connectivity, n(T), increases, and clearly indicate that the pore connectivity, n(T), plays a key role in determining the mass transport properties of a porous medium and, therefore, it is an extremely important parameter in the characterization and construction of porous particles. Furthermore, the results show that the intraparticle interstitial fluid velocity, upsilon(p,i) is many times larger than the diffusion velocity, upsilon(DA), of the solute within the porous medium, and the ratio upsilon(p,i)/upsilon(DA) increases significantly as the pore connectivity, n(T), increases. The results of this work indicate that the pore network model could allow one, for a given porous medium, solute and interstitial column fluid velocity, to determine the values of the intraparticle interstitial fluid velocity, upsilon(p,i), and pore diffusivity, D-p, of the solute in an a priori manner. The values of upsilon(p,i) and D-p could then be employed in the macroscopic models that describe the dynamic behavior of chromatographic separations in columns packed with porous particles. (C) 1998 Elsevier Science B.V. All rights reserved.