Gas-Liquid Flow and Interphase Mass Transfer in LL Microreactors

Arturo Macchi,Frederic Morin,Jan B Haelssig,Dominique M Roberge,Brendon J Doyle

doi:10.3390/fluids5040223

Arturo Macchi, Frederic Morin + Show 3 more

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https://doi.org/10.3390/fluids5040223

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Abstract

This work investigates the impact of fluid (CO2(g), water) flow rates, channel geometry, and the presence of a surfactant (ethanol) on the resulting gas–liquid flow regime (bubble, slug, annular), pressure drop, and interphase mass transfer coefficient (kla) in the FlowPlateTM LL (liquid-liquid) microreactor, which was originally designed for immiscible liquid systems. The flow regime map generated by the complex mixer geometry is compared to that obtained in straight channels of a similar characteristic length, while the pressure drop is fitted to the separated flows model of Lockhart–Martinelli, and the kla in the bubble flow regime is fitted to a power dissipation model based on isotropic turbulent bubble breakup. The LL-Rhombus configuration yielded higher kla values for an equivalent pressure drop when compared to the LL-Triangle geometry. The Lockhart–Martinelli model provided good pressure drop predictions for the entire range of experimental data (AARE < 8.1%), but the fitting parameters are dependent on the mixing unit geometry and fluid phase properties. The correlation of kla with the energy dissipation rate provided a good fit for the experimental data in the bubble flow regime (AARE < 13.9%). The presented experimental data and correlations further characterize LL microreactors, which are part of a toolbox for fine chemical synthesis involving immiscible fluids for applications involving reactive gas–liquid flows.

Highlights

Process intensification via miniaturization is a method of rendering reactors more efficient, economical, environmentally friendly, and safer through a reduction in volume
The gas and liquid were fed continuously into the microreactor system via a BronkhorstTM mini CORI-FLOWTM M12V10I mass flow controller (MFC) with an accuracy of ± 0.5% of flow rate and a HiTec Zang SyrDosTM 2 syringe pump equipped with 25 mL DURANTM borosilicate glass syringes, respectively
Regimes are shownsince in Figure and were identified theuntil flow the regime theoffirst few mixers were ignored, flow 3 typically does not as one of the following based on distinct criteria: bubble flow, where gas bubbles are nearly spherical develop fully until the end of the first row of mixers

Summary

Introduction

Process intensification via miniaturization is a method of rendering reactors more efficient, economical, environmentally friendly, and safer through a reduction in volume. The smaller length scales enhance heat and mass transfer rates by providing greater vessel specific areas and reducing transport distances. These improvements in transport rates, as well as the smaller working volumes, allow highly exothermic reactions to be run safely with less dilution and better yields [1]. Continuously operated micro- and milli-scale reactors offer these advantages at production rates relevant to the pharmaceutical industry, which are typically less than 600 g/min [2]. Small reactor dimensions have the added benefit of creating more consistent dispersions (e.g., segmented flow) and higher interfacial areas, which yield higher and more predictable mass transfer rates [3].

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