Effect of some operating variables on citrate recovery from model solutions by electrodialysis
The effect of pH and temperature (straight theta) on the overall performance indicators (i.e., solute recovery, rho, and Faraday, eta, efficiencies; specific energy consumption, epsilon, solute, JS, and water, JW, fluxes) of batch electrodialytic recovery of citric acid from model solutions was assessed at different values of feed solute concentration (cSf) and electric current density (j). Regardless of the initial feed concentration used, rho and JS were found to be independent of straight theta; eta and JW exhibited a positive trend with respect to straight theta, while epsilon a negative one. At the maximum temperature tested (33 degrees C), as the pH of the feed solution was varied from 3 to 7, rho increased from 0.90 +/- 0.08 to 0.97 +/- 0.02, eta grew from 0.09 +/- 0.02 to 0.50 +/- 0.01, JS practically doubled, epsilon reduced about 8 times, but JW increased from 3 to 4 times. So, the optimal conditions for this technique are to be determined by balancing the savings in the investment and maintenance costs against the energy costs. Copyright John Wiley & Sons, Inc.
Electrodialysis applications in the food industry.
Publisher Summary This chapter reviews the current and potential electrodialysis (ED) applications that appear to be of particular interest for the food and drinks sector in the short-medium term, as well as the basic mass transport equations that might help ED unit design or optimization. Electrodialysis (ED) is a unit operation for the separation or concentration of ions in solutions based on their selective electromigration through semipermeable membranes under the influence of a potential gradient. The current largest area of application for ED is in the desalination of brackish water for the production of potable water and de-ashing of milk whey to obtain valuable raw materials for baby foods. However, ED applications are still in their infancy and ED-processing potentialities have not been completely exploited probably because of the high specific electromembrane costs or their short lifetime.
Determination du courant limite d'electrodialyse par conductivite pour les faibles nombres de reynolds. Cas des solutions de tartrate acide de potassium
In the case of an electrodialysis operation, it is possible to obtain the limiting current by measuring the conductivity of the solution undergoing dilution. Starting from the equation of the constant flux of matter, when the concentration at the membrane falls to zero, (i/σd)crit = δ relates the current density i and the conductivity of the diluate σd. The critical value of (i/σd) is easily obtained from the drawing of σ dvs the potential applied to the apparatus. Experiments carried on aqueous solutions of KHC4H4O6 at 8 g/l show that (i/σd)crit) is well related to the Reynold's number by the relation αReβ. It is then possible to calculate the thickness δ of the diffusion layer as a function of the Reynold's number.