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This work concerns the use of vibrating screens as electrodes in building electrochemical reactors, i.e., (i) the effect of superimposed flow on the mass-transfer coefficient at vibrated screens; and (it) factors affecting the relation between the mass-transfer coefficient and mechanical power consumed in vibrating the screen electrode. Superimposed solution flow using superficial velocity in the range of 0.7 to 5.4 cm/s enhanced the mass-transfer coefficient at relatively low vibration intensities, and at high vibration intensities superimposed solution flow decreases the mass-transfer coefficient. Power consumption calculations have shown that the efficiency of power utilization in enhancing the rate of mass transfer at vibrating screens is a function of the screen mesh number and the number of screens per bed. For vibrating screen beds, the mass-transfer coefficient increases with power consumption to a certain limit and then becomes insensitive to power consumption.Continuous electrochemical reactors using high liquid flow rates to enhance the rate of mass transfer in the reactor suffer from low residence times and consequently a low degree of conversion per pass. To overcome this problem, the continuous reactor is operated at a relatively low solution flow rate while the rate of mass transfer is enhanced using methods such as gas sparging, turbulence promoters, electrode rotation, or electrode vibration. Although turbulence promoters, gas stirring, and electrode rotation are used widely in practice, 1-3 the use of mechanical vibration is still limited even though vibratory agitation is more economical than rotary agitation. 4 In an earlier study, ~ the mass-transfer behavior of vibrating screens in a batch reactor was investigated with the object of developing a high space-time-yield reactor. The rate of mass transfer at a single horizontal vibrating screen of different mesh number was given by the equation J = 0.122 Re 0.6~ (Rjdw)l.7~ [1] where J is the mass-transfer J factor; Re is the vibrational Reynolds number; Rh is the hydraulic radius of the screen and dw is the screen wire diameter.Vibrating stacks of screens deviated from the above equation by 10 to 70 % depending on the number of screens per stack and the mesh number. Our object is: (i) to test the effect of low solution flow rates on the mass-transfer behavior of vibrating screens; such a study would assist in the development of a continuous electrochemical reactor based on vibrating screens; and (it) to study the effect of some operating variables on the power consumed in vibrating the screens; this study would assist in the economic evaluation of using vibrated screens in building electrochemical reactors. All previous studies on the effect of vibration on the rate of mass transfer were conducted in a nonflow batch reactor, 5-1~ and no work has been reported on the combined effect of solution flow and electrode vibration on the rate of mass transfer. Experimental TechniqueThe apparatus used here (Fig. 1) is similar to the apparatus used before ...

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