Sorption Equilibria and Rate Studies on Resinous Retardation Beads. 2. Rate Studies

Abstract

Dispersive forces which tend to limit mass transfer rates in sorption processes are studied singly and as a combined dissipation effect. Batch experiments are reported which demonstrate that solid phase diffusion within the resin is expected to be the rate-controlling step, taking values ranging from 0.34 X 10 to 3.7 X 10- cm/s for temperature ranging from 10 to 50 °C, respectively. The activation energy for solid phase diffusion in the washed resin was found to be somewhat high, taking a value of 10.5 kcal/mol. Axial dispersion was determined independently using packed beds of inert particles equivalent in size to the active resin material. It is shown that axial dispersion coefficient varies linearly with velocity and is independent of temperature (50 °C). Steady-state sorption experiments on a fixed bed are presented which confirm the contention that solid-phase diffusion is the rate-controlling step. It is demonstrated that axial dispersion does not influence the rate actually observed. Considering three simultaneous dissipation effects (dispersion, film transfer, and solid diffusion), it is shown that greater than 98% of the total resistance is attributable to solid-phase diffusion.