Adsorption of pentachlorophenol (PCP) by activated carbon in fixed beds: application of homogeneous surface diffusion model

The adsorption of pentachlorophenol (PCP) from aqueous solutions was investigated using fixed beds of activated carbon. The equilibrium behaviour was shown to fit a Freundlich isotherm with the values of parameters K and l/n of 95 and 0.180 respectively, which are comparable to those of other substituted phenolics. The surface diffusion coefficient was evaluated from batch kinetic adsorption experiments and was found to be 2.26 × 10⁻⁹ cm²s⁻¹. The film transfer coefficient in the fixed beds was estimated using Gnielinski’s correlation. A Homogeneous Surface Diffusion Model (HSDM) was proposed to predict the PCP adsorption breakthrough curves in the fixed beds. The diffusion and convection equations were integrated using a combination of orthogonal collocation and Runge-Kutta techniques. The experimental results on the adsorption of PCP in activated carbon columns proved that the HSDM can predict the column performance satisfactorily and therefore can be used in the design of fixed beds for removal of PCP.