External mass transfer and hindered diffusion of organic compounds in the adsorption on activated carbon cloth

The overall rate of adsorption of organic compounds on activated carbon cloth (ACC) was interpreted with a diffusional model which takes into account external mass transfer and intrafiber diffusion. It was assumed that the intrafiber diffusion was solely due to pore volume diffusion (Fick diffusion). The effect of molecular size of the organic compounds on the overall rate of adsorption was studied using pyridine (0.49 nm), phenol (0.53 nm), naphthalenesulfonic acid (NAS) (0.85 nm), pentachlorophenol (PCP) (0.87 nm) and methylene blue (MB) (1.03 nm). The experimental concentration decay data were obtained in a differential column batch adsorber. The overall adsorption rate of pyridine and phenol was controlled by the external mass transfer whereas the intrafiber diffusion was the controlling mechanism in the adsorption rate of NSA, PCP and MB. Additionally, the intrafiber diffusion of NSA, PCP and MB was substantially reduced by hindered diffusion, which was due to steric exclusion, wall drag effects and obstruction caused by the molecules adsorbed on the pore walls. The controlling mechanism in the adsorption rate on ACC is a function of the molecular size of the organic compound.

► Adsorption rate on ACCs was reasonably interpreted with a diffusional model.
► Solute size played a significant role on adsorption rate on ACCs.
► External mass transfer and intrafiber diffusion were the controlling mechanisms.
► Intrafiber diffusion in ACCs was greatly reduced by restricted diffusion.