INTRAPARTICLE MASS-TRANSPORT MECHANISM IN ACTIVATED CARBON ADSORPTIONOF PHENOLS

Two parallel diffusion mechanisms, pore and surface, can control the r ate of contaminant adsorption. The two mechanisms are different functi ons of temperature and adsorbate concentration. To develop a mechanist ic design model for adsorption processes, the two mechanisms must be e valuated separately. In this paper, we show that the mechanisms can be separated accurately using a stepwise linearization technique. The te chnique can easily be incorporated in adsorption diffusion modeling. T wo phenolic compounds were used in this study: p-chlorophenol (PCP) an d p-nitrophenol (PNP). The application of the linearization technique is illustrated using two types of reactors: a completely mixed batch r eactor and a differential reactor. The study results show that pore an d surface diffusivity can be determined accurately using the lineariza tion technique. Furthermore, the tortuosity for the absorbent can be e stimated from the pore diffusivity. For PCP that is strongly adsorbed by the adsorbent, surface diffusion is the dominant mechanism controll ing the intraparticle transport. For weakly adsorbed PNP, neither surf ace nor pore diffusion is dominant.