Modeling Mass Transfer During Single Organic Droplet Formation and Rise

Esko Lahdenpera

doi:10.4172/2157-7048.1000378

Abstract

Copper reactive extraction from ambient aqueous solution to organic droplets using single droplet experiments was performed. Extractant was Agorca M5640 hydroxyoxime in Exxsol D80. An image analysis based method was used to determine droplet concentration directly after droplet formation and rise. Mass transfer during formation is correlated using literature. Level Set interface tracking method was used to find formation hydrodynamics and as a result the assumption of non-circular velocity field could be validated. This was also supported by the circulation criteria based on needle Reynolds number. A model to estimate extraction rate as function of droplet Fourier number was based on a literature correlation and it was found that a model where the interface effect was described using interface mobility parameter was able to predict satisfactorily mass transfer. For a rising droplet stagnant cap model was used. Stagnant cap volumes were estimated from droplet images. A CFD model of a non-deforming rising droplet with rigid interface was used to fit interfacial reaction kinetic constant. Fitted value was much lower than experimentally determined by high a shear reactor. Mass transfer coefficients calculated from CFD model and estimated using literature correlations agreed well. By applying a two-film model it was shown that major part of the resistance is located at the interface between the phases.

Highlights

Single droplet experiment is a common method to determine mass transfer rates between the feeds in liquid-liquid extraction (LLE)
The surface velocity correction factor kH,R was determined with this model to take into account the drag increasing effect of surface active agents, local mass transfer coefficients Kcu and kCuA2 of Cu transfer in continuous phase and in droplet and the overall mass transfer coefficient KD
Droplet average formation times tF were estimated by dividing the average droplet volume with a feed rate: for the 0.8 mm needle 16, 5, 3 and 2 seconds and for the 0.4 mm needle 21, 4 and 3 seconds

Summary

Introduction

Single droplet experiment is a common method to determine mass transfer rates between the feeds in liquid-liquid extraction (LLE). In traditional experiments a droplet concentration are measured before formation and after coalescence and this provides an overall mass transfer rates for all stages. By using suitable experimental arrangements the effect of coalescence can be minimized but the droplet formation stage is often substantial [2,3,4,5] and by using several different droplet rise times the effect of formation is found by extrapolation of results into zero rise time This indirect method to determine the amount mass transfer during formation has some drawbacks. Diameter de is volume equivalent sphere diameter after droplet formation Those correlations assume that mass transfer inside the droplet is purely diffusion based. Fractional mass transfer resistances were calculated from the film model

Experiments

Results and Discussion

Conclusion