Surfactant-enhanced liquid–liquid extraction in microfluidic channels with inline electric-field enhanced coalescence

Abstract

Continuous microfluidic liquid-liquid extraction is realized in a microfluidic device by generating emulsions with large interfacial areas for mass transfer, and subsequently breaking these emulsions using electric fields into easily separated segments of immiscible liquids (plugs). The microfluidic device employs insulated electrodes in a potassium hydroxide-etched channel to create large electric fields (100 kV m(-1)) that drive coalescence of the emulsion phase. The result is a transition from disperse to slug flow that can then readily be separated by gravity. Extractions of phenol and p-nitrophenol from an aqueous to hexane-surfactant solution serve as model systems. In addition to the increased surface area in the emulsion, extraction efficiency is enhanced by reverse micelles resulting from the presence of surfactants. The surfactant concentration is varied approximately 1-10 wt% and a general two-parameter model is developed to quantify the extraction behavior and demonstrate the effectiveness of reverse micelle enhanced extraction.

Surface patterning of bonded microfluidic channels

“…Embedding metal or metal oxide electrodes in microfluidic devices can be achieved using standard photolithography, [74][75][76] providing a suitable platform for postbonding surface modification by electrochemical means. However, to date, only a few examples of postbonding channel patterning using this method have been published.…”

A Microfluidic Platform for the Rapid Determination of Distribution Coefficients by Gravity-Assisted Droplet-Based Liquid–Liquid Extraction

“…Droplet-based microfluidic systems are in fact closely related to the shake-flask method, where phase agitation causes emulsification prior to phase separation by allowing the mixture to re-equilibrate using gravity. Microfluidic droplet-based systems however tend to use surfactants to stabilise droplets 15 and hence require complicated techniques to drive de-emulsification for phase separation, such as the use of strong electric fields, 12 or require complicated detection methods to perform in-droplet measurements, such as laser-induced fluorescence.…”

“…3 However, microfluidic platforms have not become de rigueur for distribution coefficient measurements due to factors related to the material used for fabrication, phase control and overall system complexity. For example, microfluidic platforms presented in the literature have been fabricated in materials that scale poorly or are too expensive for commercial scale production, such as PDMS, 4-7 glass, [8][9][10] silicon, 11,12 and polymers (such as thiolene, 13 SIFEL 13 or NOA81 14 ) or require surface modification 5 prior to use. Both these characteristics make commercial application of such platforms unfeasible.…”

Microflow Systems for Chemical Synthesis and Analysis: Approaches to Full Integration of Chemical Process

“…Yager et al have developed diffusion-based extraction of miscible solutions and realized separation dependent on diffusion rates [59,60]. Recently, microsegmented flows of immiscible solutions were used for microchemical processes [57,[61][62][63]. Although microsegmented flows are advantageous for mixing and rapid molecular transport, phase separation and more than three-phase contact are difficult.…”