Mixing dynamics characterization of jet mixing reactor for controlled nanoparticle synthesis
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Date
2021-04
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Abstract
Purpose: Nanoparticle-based technologies offer an exciting new approach for various applications including biomedical, optoelectronics, and catalysis. Nanoparticles are of particular interest because they can exhibit size-dependent properties that are different from those of bulk materials. Nanoparticles produced using nanoprecipitation provide a facile and rapid approach for lab-scale synthesis. As the name suggests, nanoprecipitation is a precipitation-based process that offers the ability to control precipitate size at the nanoscale. However, nanoprecipitation processes are relatively fast, progressing on the order of milliseconds. Translating nanoprecipitation processes to sub-pilot stirred batch vessels introduces mixing limitations. As the reactor length scale increases, achieving uniform concentration in shorter timescales becomes exceedingly difficult. Concentration gradients give rise to differential precipitation kinetics, resulting in a wide distribution of nanoparticle sizes. A polydisperse population compromises the uniformity of size-dependent properties. Microreactors offer a promising approach to overcome mixing limitations by reducing reactor length scale. However, many two-inlet microreactor designs including, T-mixer, Y-mixer, and confined impinging jet reactor require equal inlet fluid flow rates for efficient mixing. This significantly restricts exploration of reaction parameters such as the degree of supersaturation achieved in nanoprecipitation. Here, we present a three-inlet jet mixing microreactor (JMR) that enables effective mixing in milliseconds and offers an opportunity to circumvent equal flow requirements of conventional microreactor systems. The JMR consist of two jet streams impinging on a single main line fluid stream at right angles, developing mixing in both axial and longitudinal directions. The proposed JMR is about the size of a dollar coin with inlet diameters ranging 0.5-2 mm, allowing for shorter mixing times due to smaller length scales. The presence of a third inlet stream in the JMR enables investigation of asymmetric flow, thereby providing access to wider design space. The competitiveness of JMR over conventional stirred batch vessels and two-inlet microreactors was assessed through mixing time characterization, and model block copolymer nanoparticle synthesis, with nanoparticle size and particle size distribution serving as evaluation criterion.
Research method: Mixing in the JMR was characterized using a competitive chemical reaction set, known as the Villermaux-Dushman reaction. This set consists of two parallel reactions that compete for a common limiting reagent.
A + B ---> P1 (Fast reaction)
C + B ---> P2 (Relatively slower reaction)
Depending on the amount of product formed from slower reaction (P2), fluid mixing time can be estimated using established correlations. Flow dynamics were also estimated using computational fluid dynamics, with simulations on ANSYS. Mixing dependence on different factors was explored, including dependence on fluid stream velocities, inlet diameters, main to jet fluid stream mixing ratio, and fluid viscosity.
Poly(butyl acrylate) – Poly(acrylic acid) (PBA – PAA; 7500 – 7500 Da) served as the model block copolymer system. PBA-PAA (1 mg/mL) dissolved in methanol was precipitated using water as antisolvent. Nanoparticles were purified using centrifugal filters and assessed for size using dynamic light scattering and transmission electron microscopy.
Findings and Implications: Mixing time data suggest that the JMR provides rapid mixing in range of 0.5 – 100 milliseconds, dependent on geometry, fluid velocity, and viscosity. Different fluid mixing ratios were examined to explore the effect of supersaturation, an experiment not achievable with current two-inlet microreactor systems. Model polymer nanoparticle studies indicate lower particle size and polydispersity achieved using the JMR. Rapid mixing resulted in focused nanoparticle size (lower polydispersity), with significantly higher reproducibility compared to stirred batch vessels. Thus, JMR designs hold promise to achieve a greater size and polydispersity control in rapid nanoprecipitation processes over batch stirred vessels and allows greater flexibility over two-inlet microreactor systems.
Description
Poster Division: Engineering: 1st Place (The Ohio State University Edward F. Hayes Graduate Research Forum)
Keywords
Jet mixing reactor, Villermaux-Dushman mixing study, Block copolymer nanoparticles, Transverse jet mixers, Microreactor