Comparison of liquid-liquid extraction in batch systems and micro-channels

• Comparison of extraction in batch and micro-channels under similar conditions.
• Lumped and distributed modeling with a non-linear equilibrium relationship.
• 100 fold increase in mass transfer coefficient in slug flow regime.
• 100% extraction efficiency obtained in slug flow at residence time of about 3 s.

Liquid-liquid extraction is an important mass transfer operation in the chemical, food processing and pharmaceutical industries. Our work focuses on experimentally quantifying mass transfer performance in a well stirred batch vessel and in stratified flow and slug flow in micro-channels. Extraction of propionic acid from toluene to water is chosen as a test system. The distribution of propionic acid in toluene and water at equilibrium was found to be non-linear. The batch experiments were carried out both with a flat interface and as a well-mixed dispersed system. The continuous experiments were carried out in micro-channels with a square cross-section. A lumped parameter model was used to quantify the mass transfer coefficient in batch mode. A lumped (distributed) model was used to describe the extraction in a slug (stratified) flow in a micro-channel. The overall extraction performance is characterized as a function of residence time of the phases and the hydrodynamics. It was found that the micro-channel gives a superior extraction performance in the slug flow regime as compared to the well mixed batch system although both have comparable sizes of the dispersed phase. This is attributed to the strong internal circulations induced by shear in the slug flow regime.

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