Intraparticle Mass Transport Mechanism in Activated Carbon Adsorption of Phenols

Abstract

Two parallel diffusion mechanisms, pore and surface, can control the rate of contaminant adsorption. The two mechanisms are different functions of temperature and adsorbate concentration. To develop a mechanistic design model for adsorption processes, the two mechanisms must be evaluated separately. In this paper, we show that the mechanisms can be separated accurately using a stepwise linearization technique. The technique can easily be incorporated in adsorption diffusion modeling. Two phenolic compounds were used in this study: p-chlorophenol (PCP) and p-nitrophenol (PNP). The application of the linearization technique is illustrated using two types of reactors: a completely mixed batch reactor and a differential reactor. The study results show that pore and surface diffusivity can be determined accurately using the linearization technique. Furthermore, the tortuosity for the absorbent can be estimated from the pore diffusivity. For PCP that is strongly adsorbed by the adsorbent, surface diffusion is the dominant mechanism controlling the intraparticle transport. For weakly adsorbed PNP, neither surface nor pore diffusion is dominant.