Mass Transfer and Chemical Reaction in Liquid-Liquid Agitation Systems

Abstract

In liquid-liquid systems, the effects of agitation for promoting mass transfer are set forth as follows:(1) Increase in the interfacial area.(2) Diminution of diffusional resistance in continuous phase.(3) Improvement in the mixing of the inner part of droplets.The authors measured the interfacial area and the over-all reaction rate for various liquid-liquid systems in agitation, and obtained the following conclusions.(1) For a liquid-liquid system whose density difference is zero and where simple physical dissolution of dispersed phase or diffusion-controlling reaction takes place, the increase in the rate of mass transfer is proportional to the increase in the interfacial area caused by the increase in agitator speed. Therefore the mass transfer resistance in the outer-side diffusional film of droplets is constant regardless of the agitator speed.(2) For a system where density difference is zero and where diffusion-controlling reaction takes place, the increase in agitator speed is slightly effectivc for the diminution of the outer-side diffusional resistance of droplets. However, as the density difference in liquid-liquid system is very small, the purpose of agitation is chiefly to increase the inter-facial area and to diminish, only slightly, the diffusional resistance.(3) For the system where density difference is zero and the diffusional and reaction resistance are comparable in magnitude, the over-all rate of reaction is, in the range of lower agitator speed, proportional to the increase in the interfacial area caused by the intensification of agitation.At a higher agitation speed, the concentration of dissolved and unreacted reactant in the continuous phase increases gradually with the increase in agitator speed, but the increase in the interfacial area is not accompanied by the increase in the over-all rate of reaction. Finally, the continuous phase is to be in saturated condition and the over-all reaction rate is to be controlling, if the overall rate is to be independent of agitator speed. Thus in liquid-liquid reaction system, there is sometimes an upper limit to effective agitator speed.