Water adsorption kinetics of silica based porous desiccants by volumetric method

Abstract

The adsorption kinetics of solid desiccants is critical for the design and optimal operation of air-conditioning systems. However, owing to the complex combination of diffusion processes in the interparticle layer and intraparticle mesopores/micropores, adequately illustrating the adsorption kinetics of solid desiccants is difficult. In this study, the adsorption kinetics of a microsphere silica gel bead was investigated using the volumetric method in a limited batch adsorption system. An analytical solution was adopted for the biporous diffusion model to obtain the effective mesopore diffusivity. A comprehensive diffusion model was developed based on the initial estimation by the analytical solution. The model, i.e., the triple diffusion resistance model that includes three transport resistances, viz., interparticle, mesopore, and micropore resistance was subsequently validated through an experiment. The results show that the rate-limiting step in the entire diffusion and adsorption process changes from intraparticle to interparticle diffusion with increasing sample mass. The proposed model considering the effect of interparticle diffusion successfully determines the effective mesopore diffusivity for each sample mass.