Effective interfacial area for mass transfer in the liquid–liquid slug flow capillary microreactors

Abstract

Liquid–liquid biphasic reactions play an important role in the chemical and pharmaceutical industries. The liquid–liquid slug flow capillary microreactor offers considerable potential benefits over the conventional liquid–liquid contactors. Though the hydrodynamics and mass transfer have been investigated for this reactor concept, so far the effective interfacial area available for mass transfer has not been experimentally quantified. Despite the well-defined flow patterns arising in the capillary microreactor, the wetting behaviour of the liquids at the capillary wall is inadequately integrated into the models and thus, the true interfacial area being used for mass transfer is uncertain. In the present work, experiments were carried out to determine the mass transfer rates and effective interfacial area using physical and chemical methods. The effective interfacial areas measured by physical and chemical methods were compared and it confirms the presence of the previously conjectured organic wall film, which provides a much higher interfacial area including both, the ends and sides of the non-wetting slugs. Overall volumetric mass transfer coefficients were obtained by physical extraction and compared to the chemical method. The organic wall film is visualised by a light induced fluorescence method, which shows the organic phase completely covering the hydrophobic capillary wall, indicating that the effective interfacial area for mass transfer in this reactor concept can significantly differ from the physical interfacial area.