title: Continuous cephalosporin C purification: dynamic modelling and parameter validation.
abstract: A mathematical kinetic model for the adsorption and desorption of cephalosporin C on Amberlite XAD-2 resin is proposed. The model can represent Langmuir, Freundlich or linear isotherms at equilibrium. The intrinsic kinetic parameters and adsorption isotherms as well as physical parameters such as the effective diffusivity and the external mass transfer coefficient were obtained at different temperatures and ethanol concentrations. An unfavourable cephalosporin C adsorption occurred when ethanol was present in the solution. It has been shown that at 25 degrees C the ethanol, at concentrations from 1.5% to 2.5%, decreases the cephalosporin C adsorption. However, this behaviour was not observed at 10 degrees C. The kinetic model fitted the experimental data well under different conditions. The model was validated in a continuous process of cephalosporin C purification using the same resin. The model with the validated parameters is able to predict the behaviour of the reactor system. The continuous process is composed of two stirred tank reactors with adsorber recycle. The adsorption occurs in the first stage, and elution of the product takes place in the second stage with ethanol as eluent. The dynamic behaviour of the process was described using the following parameters: hydraulic residence time for the first (theta(h1)) and second stage (theta(h2)), solid residence time (theta(s)), initial concentration of CPC (C(0)), inlet ethanol concentration (C(ET0)) and kinetics parameters.