Percolation models of adsorption–desorption equilibria and kinetics for systems with hysteresis

Abstract

Characterisation of internal structure of porous adsorbents was made using simplified 2D and 3D lattices of spherical pore sites and cylindrical pore connections based on primary adsorption and primary desorption equilibrium data. Two basic models of adsorption–desorption hysteresis in porous sorbents, i.e. the independent pore model and the pore blocking model, were developed and tested. Very good agreement with experimental equilibrium data for the systems Vycor glass–nitrogen was obtained by simultaneous optimisation of the lattice size and the lattice connectivity and by incorporating the pore-blocking assumption into the 3D percolation model. The pore blocking model predicts correctly also the equilibrium scanning curves and cycles inside the hysteresis loop. Evaluated connectivity and size distributions for both, the pore sites and the pore connections, were subsequently used also for reconstruction of the lattices and for modelling of adsorption–desorption kinetics of the same experimental system. Theoretical models predict correctly main qualitative features observed experimentally, i.e. maxima and minima of the mass transfer coefficient.