(456c) Mixing Time and Fluid Flow Profiles in Asymmetric Flow Jet Mixing Reactors

Microreactors/mixers offer promise for nanomanufacturing through scale-out versus scale-up options. Microreactors have been employed by the pharmaceutical industry for production of drug delivery vehicles, and most notably Covid mRNA vaccines. A common microreactor design involves impingement of jets with each other or with a crossflow stream. Many of these reactor designs necessitate equal jet flow rates to prevent asymmetries in the impingement zone that can lead to undesired flow patterns. However, asymmetric flow (unequal inlet flow rates) may be desired for a variety of reasons, such as use of delicate or expensive cargoes, to reduce toxicity and optimize safety of selected reactants, or to control supersaturation and solvent quality to maximize product quality.

Here, we examined mixing times and flow patterns in a jet mixing reactor under asymmetric flow conditions. The jet mixing reactor explored was originally developed for gas phase synthesis and demonstrated recently for synthesis of zeolites¹. The reactor has a crossflow geometry, consisting of a main line onto which two opposing jets impinge. The resulting product line exits the reactor as a continuation of the main line. This reactor has recently been used for manufacturing of Ag@Au nanoparticles, polymer nanostructures, quantum dots, and copper nanoparticles, demonstrating its versatility. Mixing time was experimental evaluated using the Villermaux-Dushman reaction², which consists of competing reaction sets with fast and slow kinetics whose products can be characterized using UV-Visible absorbance spectroscopy. The ratio of these products can be correlated to the mixing time through known equations³. Flow in the reactor was observed using dye streams. These results were corroborated and expanded upon using COMSOL simulations of the flow field. Mixing time in simulations was estimated by evaluating the point at which concentration reached 80% of the expected equilibrium value.

Concordance between experimental and theoretical data sets was high. Under symmetric flow, mixing times ranged from ~ 5-40 ms depending on reactor geometry (Channel diameters: 0.01-0.04”) and operational flow rate (5-32 ml/min). Under asymmetric flow, mixing times were increased relative to symmetric mixing conditions, and at ratios of 5:1 for the jet: main line flow rates homogenous kinetics for polymer nanoparticle precipitation could no longer be obtained and mixing time was insensitive to flow rate for total inlet flow rates > 35 ml/min. In more detailed examination of flow fields within these reactors, it was determined that mixing was enhanced by rotational vortices formed in the direction perpendicular to flow of the existing fluid downstream of the impingement zone. At high jet: main line flow ratios (i.e., ~ 5-10), back flow emerges into the main line that limits mixing. These data suggest that operation in asymmetric conditions is possible, but that there is an upper limit to operation without additional design improvements.

1. A. Parulkar and N. A. Brunelli, Industrial and Engineering Chemistry Research, 2017, 56, 10384-10392.
2. J. Commenge and F. Laurent, Chem. Eng. Process., 2011, 50, 979-990.
3. E. Arian and W. Pauer, Chem. Eng. Res. Des., 2021, 175, 296-308.