Patrick Plouffe

Enhancement of Interphase Transport in Mini-/Microscale Applications Using Passive Mixing

Structured mini-/microscale reactors continue to receive attention from both industry and academia due to their low pressure drop, high heat and mass transfer rates, and ease of scale-up relative to conventional reactor technology. Commonly considered for reactions such as hydrogenations, hydrodesulfurization, oxidations, and Fischer–Tropsch synthesis, the performance of these systems is highly dependent on mixing and the interfacial area between phases. While existing literature describes the initial flow patterns generated by a broad range of two-phase contactors, few studies explore the dynamic impacts of downstream passive mixing elements. Experimental and computational methodologies for characterizing two-phase flow pattern transitions, pressure drop, and heat and mass transfer are discussed, with relevant examples for serpentine and Venturi-based passive mixing designs. The efficacies of these two configurations are explored in the context of pressure drop, conditions leading to significant interface renewal, and design considerations for optimizing mass transfer. Challenges associate with the characterization of multiphase flow through these systems are highlighted, and strategies suggested for both experimental and computational analysis of dynamic flow patterns and fluid–fluid interactions.

Transport Phenomena in Two-Phase Liquid-Liquid Micro-Reactors

Micro-reactors offer distinct advantages over batch reactors currently used within the pharmaceutical and fine chemical industries. Their high surface area-to-volume ratios allow for increased heat and mass transfer, which is important for controlling reaction selectivity. In addition, micro-reactors are compatible with continuous processing technology, circumventing the time delays inherent to batch systems. Rapid mixing of reactants within micro-reactors is, however, limited by the inherent difficulty of generating turbulence at reduced geometry scales. Several different passive mixing strategies have been proposed in order to produce eddy-based secondary flows and chaotic mixing. This study examines the effectiveness of these strategies by comparing the energy-density normalized heat and mass transfer coefficients for a selection of industrial micro-reactors. First single, then two-phase liquid-liquid experiments were conducted. Pressure drop measurements were obtained to calculate friction factors and to verify the presence of eddy-based secondary flows. A hot heat exchange fluid and temperature measurements were used to estimate the internal convective heat transfer coefficients within each structure. Volumetric mass transfer coefficients were also determined for the mutual extraction of partially miscible n-butanol and water. Semi-empirical correlations for the reactors’ friction factor and Nusselt number as well as a description of the overall mass transfer coefficient based on energy dissipation are presented.Copyright

Local and overall heat transfer of exothermic reactions in microreactor systems

Non-reactive and reactive heat transfer experiments were performed in the FlowPlate® system manufactured by Ehrfeld Mikrotechnik, which is composed of alternating reactor and heat transfer fluid plates within a rack. The non-reactive model system studied a rectangular serpentine channel with Reynolds numbers ranging from 400–2000, and a Gnielinski-type model was fit to the internal Nusselt number. A silver-based thermal paste was shown to reduce the external resistance to heat transfer between the reactor and heat transfer fluid plates by ∼70%, leading to overall heat transfer coefficients of ∼2200 W m−2 K−1. In the reactive system, the synthesis of methyl 2-oxobutanoate, using dimethyl-oxalate and the Grignard reagent ethylmagnesium chloride, was highlighted as a test reaction to differentiate localized heat transfer characteristics across different reactors. The Grignard reaction was used to compare the impact of various micro-mixer geometries, materials, injection ports, and scales on hotspot formation in the reactors. Finally, an analysis of four case studies that can be extended to any micro-reactor system with known overall heat transfer coefficients was presented using the fourth Damkohler number to determine a maximum channel diameter that would remove energy sufficiently quick to avoid hotspot formation.

Enhancement of Inter-Phase Transport in Mini/Micro-Scale Applications Using Passive Mixing

Structured mini/micro-scale reactors continue to receive attention from both industry and academia due to their low pressure drop, high mass transfer rates and ease of scale-up when compared to conventional reactor technology. Commonly considered for heat and mass transfer limited reactions such as hydrogenations, hydrodesulphurization, oxidations and Fischer-Tropsch synthesis, the performance of these systems is highly dependent on mixing and the interfacial area between phases. While existing literature describes the initial flow patterns generated by a broad range of two-phase contactors, few studies explore the dynamic impacts of downstream passive mixing elements. Experimental and computational methodologies for characterizing two-phase flow pattern transitions, pressure drop, mixing and mass transfer are discussed, with relevant examples for serpentine and venturi-based passive mixing designs. The efficacy of these two configurations are explored in the context of pressure drop, conditions leading to significant interface renewal, and design considerations for optimizing mass transfer. Challenges associate with the characterization of multiphase flow through these systems are highlighted, and strategies suggested for both experimental and computational analysis of dynamic flow patterns and fluid-fluid interactions.Copyright