Integrated continuous microfluidic liquid-liquid extraction

We describe continuous flow liquid-liquid phase separation in microfluidic devices based on capillary forces and selective wetting surfaces. Effective liquid-liquid phase separation is achieved by using a thin porous fluoropolymer membrane that selectively wets non-aqueous solvents, has average pore sizes in the 0.1-1 mu m range, and has a high pore density for high separation throughput. Pressure drops throughout the microfluidic network are modelled and operating regimes for the membrane phase separator are determined based on hydrodynamic pressure drops and capillary forces. A microfluidic extraction device integrating mixing and phase separation is realized by using silicon micromachining. Modeling of the phase separator establishes the operating limits. The device is capable of completely separating several organic-aqueous and fluorous-aqueous liquid-liquid systems, even with high fractions of partially miscible compounds. In each case, extraction is equivalent to one equilibrium extraction stage.