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The effect of impeller geometry on the rate of liquid-solid mass transfer at the wall of the stirred tank reactor was studied by measuring the rate of the diffusion-controlled disintegration of copper in acidified dichromate. Factors examined were rotation speed of impeller and its geometry, drag reducing polymer concentration, solution physical properties and baffles effect. The mass transfer data in the blank solution were correlated by dimensionless correlations. Radial flow impellers produced higher rates of mass transfer than axial flow impellers under the same conditions. For a given set of conditions the presence of baffles was found to increase the rate of mass transfer more than unbaffled reactors. Drag reducing polymer was found to decrease the mass transfer rate by an amount ranging from 3.5 to 38.5% depending on rotation speed of impeller, polymer concentration and impeller geometry. Implication of the present results for stirred tank biochemical reactors which use drag reducing polymer to control solution viscosity and decrease the shear stress between the moving solution and the vessel wall as to protect immobilized enzyme or cells fixed to the wall against mechanical damage were discussed. The present results would help in evaluating the financial possibility of utilizing drag reducing polymers in working biochemical stirred tank reactors. [ABSTRACT FROM AUTHOR]

The liquid–solid mass transfer behavior of 8 cylindrical blade impeller it can act as electrode or catalyst support in a new stirred tank reactor was studied in relation to catalytic and electrochemical reactor design by the electrochemical technique which involved measuring the limiting current of the cathodic reduction of K 3 Fe(CN) 6 . Variables studied were blade length, impeller rotation speed, physical properties of the solution, effect of baffles, effect of immiscible liquids, effect of superimposed solution flow (continuous operation), effect of the distance between successive impellers in case of multi-impeller reactor and the effect of drag reducing polymers. The mass transfer data for single rotating impeller were found to fit the following equation: S h = 0.429     S c 0.33     R e 0.42 Superimposed solution flow and impeller separation were found to have little effect on the rate of mass transfer, baffles were found to increase the rate of mass transfer while the presence of immiscible liquid decreases the rate of mass transfer. Addition of drag reducing polymers (Polyox WSR-301) was found to reduce the rate of mass transfer at single impeller by a maximum of 15.8%. Examination of heavy metal removal from dilute solutions revealed that the rate of metal deposition agrees fairly with the prediction of the equation despite the presence of surface roughness and H 2 evolution. The advantages of this reactor in conducting diffusion controlled catalytic and electrochemical liquid–solid reactions and liquid–solid reactions involving sparingly soluble reactants that to be dispersed such as gases, solid particles and immiscible liquids were highlighted. [ABSTRACT FROM AUTHOR]

Abstract: The effect of vertical plate electrode pulsation on the rate of cathodic copper deposition and anodic oxidation of ferrous sulphate was studied in a divided cell. Electrode oscillation was found to enhance the rate of diffusion controlled copper deposition and ferrous sulphate anodic oxidation by a factor ranging from 1.9 to 7.8 compared to the natural convection value depending on the vibration velocity. Electrode pulsation was found to increase the current efficiency of copper deposition from 52% to 98%, while the current efficiency of anodic oxidation of FeSO4 increased from 35% to 92% depending on the vibration velocity. Also, electrode vibration was found to decrease electrical energy consumption of copper deposition from 4 to 1.56kWh/kg; for anodic oxidation of FeSO4 electrode vibration reduces energy consumption from 3.35 to 1.25kWh/kg depending on vibration velocity. The importance of the present results for treating dilute solutions containing copper and ferrous ions such as printed circuit etching solution, pickling waste solutions, chemical machining waste solution, mine drainage water, leaching liquor obtained by leaching low grade copper sulphide ore by ferric salts was highlighted. The present technique has the advantage of recovering a precious metal and recycling a valuable chemical in one step, this satisfies the policy of zero discharge industry. [ABSTRACT FROM AUTHOR]