Pore network modelling of the behaviour of a solute in chromatography media: transient and steady-state diffusion properties

A pore network model is presented, that is a geometrical simplification of a porous medium. The network consists of pore chambers interconnected by pore throats. A recursive algorithm for the simulation of mercury intrusion porosimetry in the network is presented. Calculations indicate that it is possible to fit simulated mercury intrusion data to experimental data, and thereby obtain parameters of the pore size distribution and pore topology (pore connectivity). A time-dependent material balance equation for diffusion on the pore level is set up and solved for the pore network. By calculating the concentration evolution in the network, the transient diffusivity and the steady-state diffusivity are found. When the network is well connected, those two diffusivities are equal, but for poorly-connected networks they differ. For migrating solutes that are non-negligibly small compared to the pore throats, considerable differences between the transient and steady-state diffusivities were found.