Document Type


Date of Award


Degree Name

Master of Science in Chemical Engineering - (M.S.)


Chemical Engineering

First Advisor

George C. Keeffe

Second Advisor

Joseph Joffe

Third Advisor

C. L. Mantell


In this investigation the rates of trivalent-univalent cation exchange in a stirred batch reactor for the chromic ion-Dovex 50 system have been measured. The progress of the reaction has been followed continuously by measuring the change in hydrogen ion concentration of the bulk solution as a function of time with a Beckman pH Meter having external electrodes immersed in the reaction mixture.

This work has been undertaken to determine the rate-controlling mechanism of the reaction, and the influence of agitator speed, particle size, and solution concentration on the rate of exchange. Agitator speed. studied, as limited by the equipment, are from 400 to 800 rpm. Screened resin size fractions from -16 +20 to -170 +200 have been used. The initial chromium ion concentration has been varied from .00422 to .10 normal.

The results show for the range of variables studied that diffusion through the liquid film surrounding the particles is the rate-controlling step. Increased rates are observed as the stirrer speed is increased. These higher exchange rates are shown to be the direct result of the increased speed of agitation shearing off a portion of the film, thus decreasing the resistance to mass transfer.

Film thicknesses have been calculated for all particle sizes and stirrer speeds. For a given concentration and speed the film thickness is shown to be the same for all particle sizes. The equation of Reichenberg (10) used to calculate film thicknesses is shown to fail for particle sizes below 80 mesh for this system. This is the first investigation of this type to show that for a given agitator speed the film thickness is the same for all particle sizes studied.

It has been verified that for a film diffusion mechanism the initial exchange rats per ml. of resin is directly proportional to the initial chromium concentration and inversely proportional to the particle radius.

The rate of exchange is described by the standard equation for steady-state unidirectional diffusion. Thus

dQ/dt = A2 DAC/Δr

where dQ/dt is the exchange rate (meq. Cr/sac), A2 is the effective area normal to diffusion calculated at the mid-point of the film, D is the diffusion coefficient of the chromic ion in aqueous solutions, Δr is the effective film thickness, ΔC is the concentration gradient across the film.



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