Date of Award
Master of Science in Chemical Engineering - (M.S.)
George C. Keeffe
Jerome J. Salamone
Saul I. Kreps
This investigation was directed toward the extension of data on the kinetics of monovalent - trivalent cation exchange and to establish data on the relationship between temperature and total capacity of an ion exchange resin. In order to compare the present study to a previous investigation by Klosowski (2), the capacity of the resin used for ferric and chromic ions was also measured.
In the kinetic study, the ferric ion-hydrogen ion exchange using Dowex 50 X-8 resin was studied in an agitated vessel. A two-bladed marine type propellor was used and the agitator speed was varied from 400 to 800 rpm. The exchange rates were measured for seven different particle size ranges from -16 mesh to +200 mesh.
The results of the kinetic study shows that within the range of variables studied, the exchange rate is film diffusional controlled for this system. The exchange rate varied directly with the agitator speed and inversely with the particle size range. The equation proposed by Reichenberg (6) for the calculation of film thickness gave results which agree with the experimental data for particle sizes from -16 to +60 mesh but failed for particle sizes below 70 mesh.
At 400, 600, and 800 rpm the average film thicknesses calculated for the ferric ion Dowex 50 system are within 6%, 1%, and exactly equal to the corresponding values of the chromic ion Dowex 50 system. Since the diffusion coefficients for the ferric and chromic ion systems are 0.57x10-5 and 0.642x10-5 cm2/sec. respectively, the agreement on the values of the film thicknesses are as expected. In view of this agreement, the experimental procedure used in this thesis with a modified form of the Reiohenberg Equation is proposed as a method for the determination of diffusion coefficients. In applying this method one would determine the rate of ion exchange at 600 rpm for a screened Dowex 50 resin fraction and then substitute the data taken in the equation shown below.
D = 0.0051 r/(Co) dØ/dt
D - Diffusion coefficient
r - Average particle radius
Co - Initial concentration in the bulk solution
dØ/dt - Exchange rate per unit volume
This method would greatly simplify the determination of these coefficients but would be subject to the assumptions given in the section on Calculations. The principal assumptions are that the exchange process is film diffusional controlled and that the process is carried out in dilute aqueous solutions in view of possible viscosity changes.
The results of the kinetic study can also be successfully applied to increase the efficiency of various methods which have been proposed for continuous ion exchange. In the mixer settler method proposed by Hiester (13), the present study indicates that optimum mixer conditions could be selected for any system based on the relationship between film thickness and agitator speed. From this relationship it would be possible to establish an optimum agitator speed. Once this speed was established, the exchange rate could be calculated using the Reichenberg Equation and the film thickness given in this study.
In the capacity vs temperature phase of this investigation, the amount of sodium ion hydrogen ion exchange was measured at temperatures from 0° to 100°C. using Dowex 50 X-8 and X-2 resin. The effect of regeneration temperature was also tested.
No change in the total resin capacity was found by variation in the loading temperature for either Dowex 50 X-8 or X-2 ion exchange resins. Some change in total capacity was effected, however, by variation in the regeneration temperature from ambient to 65°C.
The capacity of Dowex 50 X-8 ion exchange resin as determined for ferrie ion and chromic ion was 13.2 and 9.89 meq. per gram of dry resin respectively. Manufacturer's specification for this resin for monovalent ions is 5.0 +/- 0.3 meq. per dry gram. No data on the capacities for di and trivalent ions are available.
Hoerrner, Alfred George, "Ion exchange technology in the sodium and ferric ion-dowex 50 systems" (1958). Theses. 1533.