Mass Transfer During Droplet Formation – A Measuring Technique Study

Abstract

In liquid-liquid extraction processes, the mass transfer coefficient is one of the key design parameters. In the present study, the impact on mass transfer during droplet formation in a quiescent continuous phase is investigated analytically. Therefore, confocal Raman spectroscopy in a novel measurement cell combined with interfacial tension measurements are applied. It could be shown, that Marangoni effects in the system toluene-acetonitrile-water (mass transfer direction from the dispersed to the continuous phase) lead to 50 % of mass transferred in the first 5 s when 90 % is transferred in 1 min.

Visualization of Mass Transfer during Droplet Formation

“…), a central plume occurs, which can result in droplet detachment. At high solute concentrations, mass transfer is markedly enhanced in the first seconds of droplet formation by Marangoni eruptions, as already described in literature , , .…”

“…Interfacial flows inducted by interfacial tension gradients ( σ 1 : zone of lower interfacial tension, σ h : zone of higher interfacial tension .…”

Local analysis of Marangoni effects during and after droplet formation

“…A precision syringe pump (PSD/3-Mini module, Hamilton) is used to generate droplets of a well-defined volume in a newly designed measurement cell, as already described elsewhere. [34] It is made of stainless steel with the inner dimensions of 23 × 33 × 33 mm (H × W × Di) and a capillary height of 2 mm. The The highest starting concentration (c ACN,0 = 10 wt%) leads to the fastest mass transfer (T = 4).…”

Liquid‐Liquid Equilibrium and Interfacial Properties of the System Water + Hexylacetate + 1‐Hexanol

“…The longtime challenges in the development of new processes or in the optimization of already existing processes and apparatus are the improvement of the mass transport across the interface between the coexisting liquid phases as well as the understanding of droplet breakage and coalescence . The process efficiency and product quality in technical separation processes are substantially influenced by the specific interfacial area, which depends on droplet formation and the mutual effects of droplet breakage and coalescence . Thus, the correct prediction of droplet phenomena, respectively, a detailed knowledge of the droplet size distribution in space and time is a vital requirement for precise process design.…”