Mass transfer in liquid-liquid dispersion in a stirred tank extractor was investigated experimentally for several particular cases. Since the mass transfer resistance inside the drop depends on internal circulation condition, the mass transfer rate can be predicted from the modified rigid sphere model with the internal circulation correlation factor R. Experimental results show that R is nearly 1, which means that drops are internally stagnant in a stirred tank extractor within the experimental ranges.
The ratio of the resistances in the dispersed and the continuous phases was obtained from the proposed equations which were proven to be applicable to calculate the mass transfer coefficients in a stirred tank extractor. The limit conditions in which one of the resistances of the two phases can be ignored were fully discussed. Extraction efficiencies and drop size distributions for the various experimental conditions were predicted and they were well fitted with those obtained from experiments.
In order to estimate an extraction performance in a multistage agitated extraction column, a dispersed phase was regarded as ploy-dispersed drops by the application of simulation technique in a stirred tank extractor, and the effect of interactions between drops on the extraction performance was investigated.
The flow in the continuous phase was represented by a plug flow and a circulation flow, and then backmixing of the continuous phase was described according to the degree of the circulation flow. Each drop's moving velocity and direction were determined by its terminal velocity and the velocity (forward and backward) of surrounding continuous phase. Hence, in this model, it was possible to express forward mixing and back mixing of the dispersed phase (drops) simultaneously. It is confirmed that terminal velocity of drop in an agitated extraction column can be expressed by Gal-Or/Waslo's equation or by Stokes' equation depending on its size.
Measured concentrations of each phase in a 5-stage agitated extraction column were consistent with those calculated by simulation program, MAEC1, within 6% deviation.
