Studies on fluidized-bed electrode

In recent years, the application of chemical engineering techniques in the analysis and design of electrochemical processes, finds use extensively. Among the electrochemical processes only chlor-alkali process has attained on advanced stage with perfect improvements in the design of electrolyser and its components. In the electroorganic synthesis, where we have to employ low current density not many developments in cell technology has taken place, the main reason being the requirement of very large electrode surface area. The three dimensional electrode systems such as fluid bed, porous and packed bed electrodes came into existence to overcome the above said electrodes with some disadvantages like nonuniform potential concentration, existence of bipolarity. The development of fluid bed electrode reactor will help in the scale up, construction of the reactors and automation of the process. The purpose of the present work is to study the polarization characteristics of fluid bed electrode and compare the results with (1) solid electrode and having forced circulation of the electrolyte (2) solid electrode in the presence of inert fluid bed. The electrochemical reaction chosen for this purpose is the carbolic reduction of maleic acid to succinic acid in the presence of large amount of dilute H2SO4 as supporting electrolyte. Polarisation data were collected for the annulus at various Reynolds number (dcuP)/µ the mass transfer co-efficients ‘KL’ was calculated and the mass transfer data were correlated using the following dimensionless equation. Sh : 4.92 (Re. Sc. De/L)0.3 Similar correlation was made after obtaining mass transfer data for the solid electrode in the presence of inert fluid bed. The Reynolds number was modified as duP/µ(1-є) and the dimensionless equation JDє : 0.062 (Re)-0.10 (de/L)(1/3) It is possible to use much higher current then the normal system in the above two systems. For the active bed, the potential distribution in the solution and metal phases across the radial direction of the bed was measured for five expansions, ie 10, 20, 30, 40 and 50%. It was found that at very low current densities the bed was under uniform potential and effective thickness of the bed is a narrow region near the fedder. Based on the one dimensional model for porous electrode by Newman, Tobias and Fleischmann for plane parallel fluid bed electrode a malbemalical model was deduced. The values obtained using the model, Pm ie. The resistivity f metal phases and Ps, the resistivity of solution phase and the experimental values were compared and the optimum bed expansion was obtained, i.e. a maximum of 30% expansion is desirable for uniform potential distributio