Effects of pore sizes of porous silica gels on desorption activation energy of water vapour

In this work, the effects of pore sizes of silica gel on desorption activation energy and adsorption kinetics of water vapour on the silica gels were studied. The isotherms and adsorption kinetic curves of water vapour on three kinds of silica gels with average pore diameters of 2.0 nm, 5.28 nm and 10.65 nm, respectively, were measured by the method of static adsorption, the desorption activation energies of water vapour on silica gels were estimated by using the TPD technique, and the effects of pore sizes of silica gel on adsorption kinetics and desorption activation energy were discussed. Results showed that the isotherm of water vapour on the A-type silica gel with the average pore diameter of 2 nm was of type I, which can be well described by the Langmuir model; the isotherms of water vapour on the B-type and the C-type mesoporous silica gels with the average pore diameters of 5.28 nm and 10.65 nm, respectively, were of type V; and at lower RH, the smaller the average pore size of the silica gel was, the smaller the adsorption rate constant was due to the diffusion resistance in the pores of the silica gels, while at a higher RH, the smaller the average pore size of the silica gel was, the larger the adsorption rate constant was. The desorption activation energies of water on the A-type, the B-type and the C-type silica gels were respectively 35.54 kJ/mol, 31.41 kJ/mol and 26.16 kJ/mol, which suggested that the desorption activation energy of water on the silica gels increased as the pore sizes of the silica gels decreased.