Fixed-bed ion exchange columns operating under non-equilibrium conditions: Estimation of mass transfer properties via non-equilibrium modeling

The present work describes a new technique for the estimation of particle film mass transfer coefficients, kf and homogeneous solid diffusivity, Dhs for resins in fixed-bed ion exchange columns under non-linear adsorption isotherm conditions. The experimental set-up is composed of a fixed-bed ion exchange column operating under recycling flow, and a reservoir. The experiments are carried out with custom made para-magnetic composite ion exchange resin filled columns. The single pass non-equilibrium packed-bed adsorption model is adapted to the present recirculation system and the model equations are numerically solved by the implicit schemes of the finite differences technique for predicting the mass transfer parameters. In order to find the kf values, model predicted reservoir concentration profiles for early-time data are generated, and different kf values were substituted into the model until the predicted and the experimental reservoir vs. time profiles agree. Once kf is known, a second version of the model is used by substituting different Dhs values where no time constraint is made. When the model output and the experimental reservoir concentration profiles agree, the corresponding Dhs value is taken as the homogeneous solid diffusion coefficient. The present methodology allows the experimental determination of kf and Dhs values for fixed-bed ion exchange columns through a simple recirculation system.