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Common cross-currently illuminated photochemical reactors lack energy efficiency to make them competitive in industry. The use of co- and counter-current illumination was previously proven to increase reactor performance, but these approaches made use of a collimated LED module whereby the used LED module itself having a lower than typical optical efficiency. In this paper, we study the use of non-collimated LEDs for the use in co- and counter-currently illuminated reactors. A ray tracing model was implemented in COMSOL and was validated using experimental data. Via these experimental data, the regime of no kinetic limitations was observed as conversion is not hampered by increasing light flux. Via the model results, it was determined that the most suitable light source for optimal light absorption by the reagent was the most collimated LED possible, in this case with a total viewing angle of 10°. The optimal reactor set-up uses the most reflective material, preferably aluminium or silver, to recuperate diverging light rays of the used wavelength. Furthermore, the wall thickness of the glass reactor must not be excessively thick, with an optimum at 1.5 mm wall thickness for this case. Regarding reagents and absorbance, it is best to use a higher concentration and reduce reactor length as this increases reactor performance under the condition that quantum yield is stable. Via the use of non-collimated light, it was determined that the entrance efficiency can be increased compared to a fully collimated light source, at the cost of reflection losses that increase with path length.

Determination of the experimental nucleation rate for crystallization in solution has been acknowledged as an important topic for a long time, as it improves the design and control of industrial cr...

The introduction of patterns on a membrane-solute interface has been suggested as an effective method to tackle the reduced flux and fouling issues. Herein, the effectiveness of using spray-modified non-solvent induced phase separation (s-NIPS) to create a variety of micrometer-level structured interfaces is now studied. Circular, triangular and rectangular patterns with different dimensions were successfully created on polyacrylonitrile membranes. The rectangular pattern height was varied from 500 to 1500 µm, which resulted in a proportional increase in clean water permeance from 590 ± 47 L m−2 h−1 bar−1 to 1345 ± 108 L m−2 h−1 bar−1 respectively. This coincided with some BSA rejection loss for the highest patterns, indicating the fragile nature of these tall features. No significant rejection losses were found for the smaller pattern heights (145–250 µm) as compared to flat membranes, while fluxes more than doubled still. The critical pressure was also increased substantially for patterned membranes and showed a proportionality with the pattern height. These experimental findings were correlated with the reduced foulant adhesion due to a shear-induced slip boundary layer at the membrane-solution interface. Computational fluid dynamics simulations further showed higher shear stress values due to flow constriction within the membrane’s valley regions. These findings indicate the high potential of s-NIPS patterned membranes in long-term industrial applications by requiring less membrane area for a given application and reducing cleaning interventions.

Nucleation kinetics play a fundamental role in the design and control of crystallization processes. Understanding how crystallization conditions impact different nucleation mechanisms and the overall nucleation kinetics will lead to improved control over the nucleation process. Herein, a comparative study of the nucleation kinetics for primary, secondary and ultrasound-induced paracetamol crystallization in stirred microvials is presented. The results are evaluated using the classical nucleation theory by assessing the influence of the nucleation mechanism on the kinetic and thermodynamic nucleation parameter. Primary nucleation is promoted by the presence of impurities and exogeneous surfaces. It is also shown that seeding a single crystal into the solution lowers the thermodynamic threshold for nucleation, even without fragmentation of the parental crystal. The addition of ultrasound to the crystallization process on the other hand affects the kinetic part of the nucleation process.

A modular multiphase flow crystallizer set-up for the continuous crystallization of paracetamol with an in-line nuclei generator has been developed. Gas bubbles are introduced in a capillary to provide heterogeneous nucleation sites and enhance the nucleation rate. Taking advantage of the separate nucleation and growth sections, control over crystal size distribution is achieved without compromising its span. Comparison with batch growth showed smaller crystal sizes as well as narrower span for the continuous growth. Different configurations of the setup were investigated with regard to the presence of the gas in nucleation and growth sections. Reproducible results were only obtained when gas is present both in the nucleation section (as microbubbles) and in the growth section (as gas slugs). Yields of up to 71% were obtained. Taking the growth time and temperature as varying parameters, the mean crystal size could be manipulated.

This study addresses the scalability of in-house designed, and 3D printed structured porous reactors for liquid-liquid reactions. The base structure of these porous reactors consists of cylindrical fibres in defined geometrical arrangements. Their scale-up was realized by increasing the reactor diameter by a factor of 1.5 and 2 respectively while keeping the fibre dimensions constant. Also, the effect of altering the fibre dimensions in proportion to the scale-up factor was assessed. The reactors were characterized in terms of their biphasic heat and mass transfer properties. In stratified flow, the scaled-up structured porous reactors exhibited high interfacial mass transfer coefficients (kLa) at residence times

Ultrasonic microreactors are increasingly applied to particle synthesis, crystallization processes, or organic synthesis involving solids because of the clogging prevention offered by ultrasound ir...

Continuous flow reactor technology has a proven track record in enabling photochemical transformations. However, transfer of a photochemical batch process to a flow protocol often remains elusive, ...

Herein, the control of enhanced protein nucleation in microdroplets under high supersaturation ratios is discussed, where lysozyme is used as a model protein. This study is conducted to evaluate the influence of droplet volume on the size and number of crystals through isothermal and double-pulse temperature experiments performed in a droplet-based microreactor. Lysozyme concentration is estimated during and at the end of the crystallization experiments, based on analytical and experimental results, respectively. Furthermore, nucleation rate in microdroplets is calculated following a Poisson distribution, and crystal growth is assumed to be diffusion-controlled. Controlled and enhanced lysozyme nucleation is achieved in smaller droplet volumes and under certain double-pulse temperature conditions. The droplet volume effect becomes more important at lower supersaturation ratios as the crystal number follows the droplet volume increase, while at higher supersaturation ratios, the crystal number does not considerably vary with the droplet volume. Finally, the proposed analysis can be adopted as an experimental design tool and extended to the crystallization of other macromolecules.

The handling of solids in microreactors represents a challenging task. In this paper, we present an acoustophoretic microreactor developed to manage particles in flow and to control the material synthesis process. The reactor was designed as a layered resonator with an actuation frequency of 1.21 MHz, in which a standing acoustic wave is generated in both the depth and width direction of the microchannel. The acoustophoretic force exerted by the standing wave on the particles focuses them to the channel center. A parametric study of the effect of flow rate, particle size and ultrasound conditions on the focusing efficiency was performed. Furthermore, the reactive precipitation of calcium carbonate and barium sulfate was chosen as a model system for material synthesis. The acoustophoretic focusing effect avoids solid deposition on the channel walls and thereby minimizes reactor fouling and thus prevents clogging. Both the average particle size and the span of the particle size distribution of the synthesized particles are reduced by applying high-frequency ultrasound. The developed reactor has the potential to control a wide range of material synthesis processes. ispartof: Lab On A Chip vol:19 issue:2 pages:316-327 ispartof: location:England status: published

Weakly-supported electrolyses are frequently encountered in organic electrosynthesis in small scale flow reactors. Sometimes “self-supported” electrolyses are reported where no supporting electrolyte is deliberately added at all. To interpret the steady-state and transient behavior of these electrochemical micro- and millireactors, an orthogonal collocation method based on Chebyshev polynomials was developed for calculating the concentration and current distributions in parallel plate and annular geometries. This method takes into account diffusion, migration, and convection in unidirectional flow for an arbitrary number of dilute ionic species. In particular, the method is flexible with regard to the electrode and homogenous reactions so that intricate reaction schemes are conveniently simulated. As a case study, the effect of the supporting electrolyte concentration and the stability of the generated reactive intermediate ions on a generic paired electrosynthesis is investigated. The numerically calculated concentration profiles and current responses are then compared with asymptotic approximations. This reveals that fundamentally different operating regimes exist for a self-supported paired electrolysis compared to more conventional electrolyses where an excess of supporting electrolyte is added. The Matlab code and a detailed user guide is freely available via the Supplementary Information. ispartof: Electrochimica Acta vol:292 pages:914-934 status: published

When immiscible liquids are subjected to an ultrasonic field, they form emulsions. This principle has been used to improve the mass transfer characteristics of a liquid-liquid extraction process in microreactor systems. The formation of emulsion and its characteristics are prominently dependent on the properties of the liquids used and this also holds true for emulsion brought about by ultrasound. This paper focuses on the properties of fluids that are reported to have an influence on the cavitation behaviour, namely viscosity, interfacial tension and vapour pressure. These properties were examined by changing the solvent of the organic phase in the hydrolysis of p-nitrophenyl acetate. The study is performed by comparing pairs of solvents that are different in one property but similar in the other two. The pairs selected are toluene – chlorobenzene for viscosity, toluene – methyl Isobutyl ketone for interfacial tension and methyl isobutyl ketone – 2-Methyl tetrahydrofuran for vapour pressure effects. A qualitative study was performed with a high-speed camera in flow to understand the emulsification initiation mechanisms and behaviours. These findings were further explored by performing the sonicated emulsion in a batch-sonicated reactor. The quantitative analysis of the fluid properties was evaluated and compared based on the relative percentage increase in yield upon sonication with respect to their individual silent conditions. The quantitative results were further supported by the quantification of the emulsion performed with an FBRM probe. The results indicate a two times improvement in yield with solvent of lower viscosity as 2 times more droplets were formed in the emulsion. Both the solvent systems with higher interfacial tension and vapour pressure had an improved yield of 1.4 times owing to larger number of droplets formed.

Computer-aided fabrication technologies combined with simulation and data processing approaches are changing our way of manufacturing and designing functional objects. Also in the field of catalytic technology and chemical engineering the impact of additive manufacturing, also referred to as 3D printing, is steadily increasing thanks to a rapidly decreasing equipment threshold. Although still in an early stage, the rapid and seamless transition between digital data and physical objects enabled by these fabrication tools will benefit both research and manufacture of reactors and structured catalysts. Additive manufacturing closes the gap between theory and experiment, by enabling accurate fabrication of geometries optimized through computational fluid dynamics and the experimental evaluation of their properties. This review highlights the research using 3D printing and computational modeling as digital tools for the design and fabrication of reactors and structured catalysts. The goal of this contribution is to stimulate interactions at the crossroads of chemistry and materials science on the one hand and digital fabrication and computational modeling on the other. ispartof: Chemical Society Reviews vol:47 issue:1 pages:209-230 ispartof: location:England status: published

This work aims at constructing a design which integrates a direct (solid) contact method with temperature control for chemical process applications. To realise this integration a two-step approach is proposed. Firstly, temperature control is achieved by suspending the tubing in a temperature controlled and sonicated liquid medium (indirect contact). Secondly, direct contact elements are introduced at regular intervals along the tubing. Therefore, this design is termed the hybrid contact reactor, as it incorporates both direct and indirect approaches of ultrasound transfer. Furthermore, two possible configurations, open and closed interval connection to the tubing, were assessed. Both hybrid reactors performed better than the indirect contact reactor (20-27% increase in yield) for residence times of less than 45 s and similar for residence times above. Even though the performance of the two hybrid designs was similar the closed interval resulted in more reproducible and distinct yields. This configuration was then scaled up 10 times in internal volume using a 2 mm ID tube. This design showed a relative performance similar to the interval contact design which gave the highest yields thus far for the same operating conditions. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no NMP2-SL-2012-309874 (ALTEREGO).

The increasing academic and industrial interest in flow chemistry resulted in the development of various micro- and milliflow reactors for a wide range of reactions. Owing,to this variety in flow reactors, it is vital to select the correct type benefiting the considered chemical reaction. This decision can be based on two fundamental reactor characterization techniques, namely, the residence time distribution (RTD) and the Viffermaux-Dtshman protocol. The first technique highlights deviations from ideal plug flow while the latter is a reaction based, characterization-technique to,quantify the efficiency of micromixing., This, paper compares the performance of classical tube reactors,with internal diameters ranging from 0:4 to 4.8 mm and commercial chip reactors from Little Things Factory and chemtrix (KiloFlow and Labtrix): The reactor characterization serves as an aid for the reaction selection, dependent on the kinetics of the studied reaction. The suitability of a reactor for very fast reactions (reaction half-life

Ortho-aminobenzoic acid (o-ABA) has three polymorphs from which form-I is the most stable and forms-II and III are meta–stable ones at 25 °C. In flow crystallization, the meta-stable form-II is quite persistent and prevents nucleation of the stable form-I. This is contrary to batch crystallization and possibly a result of high local supersaturation. In this work, seeded, anti-solvent crystallization of o-ABA was conducted to overcome nucleation of the meta-stable form and obtain a high yield of form-I. Experiments were conducted in a tubular flow crystallizer under silent and sonicated conditions. Seeding was effective in producing pure form-I only when ultrasound was applied. Under silent conditions, poor dispersion of seeds and heterogeneous wall nucleation led to the growth of form - II. Ultrasound improved dispersion and reduced nucleation on walls and thus a pure form-I product was obtained. Particle sizes and SEM images showed evidence of secondary nucleation as the mechanism for form-I occurring in seeded, sonicated experiments rather than seed growth. A high yield, 48% by mass and 85% of maximum crystallizable mass, could be achieved. Ultrasound increased the potential of the flow crystallization system by combining high yield with polymorph control. ispartof: Chemical Engineering Journal vol:408 status: published

Measuring mass mixing in batch reactors is of great interest to prevent yield losses during scale-up of reactions. In this work, we present a novel tool to accomplish this: the heat pulse method. This is a thermal-based technique consisting of a local heat pulse, applied electrically or by a hot liquid injection, during 10 s at a power of 5-15 W and subsequent measurement of temperature increase at locations of interest. The 95% mixing time from corrected and smoothed temperature profile characterizes heat mixing. A heat mixing model identifies the contributions of thermal conduction and convection and hereby relates local heat and mass mixing in a 800 mL in a 1 L batch reactor with a 45 degrees 4 blade downward pitched turbine. The heat pulse method is applicable on different reactors, solvent independent and non-destructive. Experiments are repeatable and mixing at reactive circumstances can be mimicked. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Ultrasonic small scale flow reactors have found increasing popularity among researchers as they serve as a very useful platform for studying and controlling ultrasound mechanisms and effects. This has led to the use of these reactors for not only research purposes, but also various applications in biological, pharmaceutical and chemical processes mostly on laboratory and, in some cases, pilot scale. This review summarizes the state of the art of ultrasonic flow reactors and provides a guideline towards their design, characterization and application. Particular examples for ultrasound enhanced multiphase processes, spanning from immiscible fluid-fluid to fluid-solid systems, are provided. To conclude, challenges such as reactor efficiency and scalability are addressed. ispartof: Materials vol:13 issue:2 ispartof: location:Switzerland status: published

© 2018, The Author(s). A catalytic membrane reactor with a Au–Pd catalyst, impregnated at the inner side of the membrane, was studied in the catalytic oxidation of benzyl alcohol in flow. The reactor comprised of four concentric sections. The liquid substrate flowed in the annulus created by an inner tube and the membrane. The membrane consisted of 3 layers of α-alumina and a titania top layer with 5 nm average pore size. Oxygen was fed on the outer side of the membrane, and its use allowed the controlled contact of the liquid and the gas phase. Experiments revealed excellent stability of the impregnated membrane and selectivities to benzaldehyde were on average > 95%. Increasing the pressure of the gas phase and decreasing liquid flowrates and benzyl alcohol concentration resulted in an increased conversion, while selectivities to benzaldehyde remained constant and in excess of 95%. ispartof: TOPICS IN CATALYSIS vol:62 issue:17-20 pages:1126-1131 ispartof: location:ENGLAND, Abingdon status: published

The hydrodynamics and mass transfer characteristics in liquid-liquid flow through various structured and well-defined porous reactors are characterized using laser based optical measurements (PIV and PLIF) in combination with chemical extraction methods. We investigate both high and low interfacial tension fluid systems (toluene-water and n-butanol-water), and we have identified that depending on the fluid properties different design parameters of the porous structures play a crucial role in determining the overall mass transfer performance. In general, the porous reactors enhance slug breakup, resulting in lower mean slug lengths for both phases compared to an empty tube and an associated enhancement in surface renewal velocities. The designed porous milli-scale reactors provide enhanced mass transfer performance, with an order of magnitude reduced energy dissipation compared to conventional milli-scale packed bed reactors. We thank Adriaan Spierings (inspire AG - innovation center for additive manufacturing, Switzerland) for manufacturing the custom designed porous reactors. S. K. acknowledges funding from Marie Curie CIG and FWO-Odysseus II.

We developed a numerical tool to investigate the phenomena of aggregation and clogging of rigid microparticles suspended in a Newtonian fluid transported through a straight microchannel. In a first step, we implement a time-dependent one-way coupling Discrete Element Method (DEM) technique to simulate the movement and effect of adhesion on rigid microparticles in two- and three-dimensional computational domains. The Johnson–Kendall–Roberts (JKR) theory of adhesion is applied to investigate the contact mechanics of particle–particle and particle–wall interactions. Using the one-way coupled solver, the agglomeration, aggregation and deposition behavior of the microparticles is studied by varying the Reynolds number and the particle adhesion. In a second step, we apply a two-way coupling CFD–DEM approach, which solves the equation of motion for each particle, and transfers the force field corresponding to particle–fluid interactions to the CFD toolbox OpenFOAM. Results for the one-way (DEM) and two-way (CFD–DEM) coupling techniques are compared in terms of aggregate size, aggregate percentages, spatial and temporal evaluation of aggregates in 2D and 3D. We conclude that two-way coupling is the more realistic approach, which can accurately capture the particle–fluid dynamics in microfluidic applications.

Controlling the pore architecture in macroporous scaffolds has important implications for their use as reactor packings and as catalyst supports. We report the preparation of a macroporous structure, where the pore walls are perforated by holes. These materials are prepared by modification of the ice-templating protocol developed in our group. We freeze a dispersion of colloidal silica, polymer and cross-linker in a water/acetonitrile medium and allow crosslinking to proceed in the frozen state. The presence of a small fraction of acetonitrile (varying between 1.6% to 6.4%) results in the formation of holes in the pore walls. Increasing the acetonitrile concentration changes the pore size distribution, and produces smaller pores on average. This also results in an increasing fraction of the wall area being covered by small pores, of the order of a few microns in size. Perforation of the walls by pores does not change the overall porosity or modulus of the scaffolds. However, the introduction of pores leads to a drastic reduction in the pressure drop required to pump liquid through the scaffolds. The observed residence time distribution (RTD) in the scaffolds is represented by two plug flow reactors (PFRs) in parallel. The RTD results indicate that increasing the hole fraction in the pore walls results in increased channelling which explains the aforementioned decreased pressure drop during pressure driven flow. ispartof: RSC Advances vol:8 issue:44 pages:24731-24739 ispartof: location:England status: published

We present a novel technique to quantify interfacial mass transfer in gas–liquid flows in capillaries. A model was developed which allowed the relationship between absorption fluxes and bubble size changes to be established. Depending on the observed absorption rate, two limiting and simplifying cases for low and high absorption rates were suggested. For both cases, the flux was viewed as an input function which optimally tracked the observed bubble velocity, bubble volume, and unit cell volume change. For the case of low absorption rates, the mass transfer coefficient can be assumed to be constant and the model was fitted to experimental data by adjusting the value of this mass transfer coefficient. The bubble velocities were extracted from flow images using the cross-correlation between measured signal intensities for nearby pixels. Bubble and unit cell volumes were not determined by individual tracking, but a probability density function was estimated for each location in the capillary which contains the bubble and unit cell sizes of all bubbles passed. This allows the model to be fitted to an ensemble of bubbles making the procedure more robust. The developed model was validated for CO2 absorption in a buffer solution, and then applied to CO2 absorption using the ionic liquid 1-ethyl-3-methylimidazolium acetate ([Emim][Ac]), which exhibits high absorption rates and less known thermophysical properties. The developed technique is able to quantify interfacial fluxes for a wide range of gas and liquid flow rates.

© 2015 American Chemical Society. The hydrodynamics of the G1 fluidic module of the Corning Advanced-Flow reactor (AFR) was characterized using particle image velocimetry. Two series of experiments, single-phase flow with liquid flow rates of 10-40 mL/min and two-phase flow with an identical overall flow rate range and gas volume transport fractions ranging from 0.125 to 0.50, were performed. From the instantaneous velocity vector maps, the mean and the root-mean-square velocities were computed, which allowed a systematic investigation of the single- and two-phase flow hydrodynamics and transport processes in the AFR. In single-phase flow, the velocity field is symmetric in the heart-shaped cells, and their particular design results in a stagnation zone that limits momentum exchange in each cell. The addition of the gas phase greatly increases the momentum exchange in the heart-shaped cells, which leads to a more uniform distribution of velocity fluctuations and increased transport processes within the AFR. ispartof: Industrial & Engineering Chemistry Research vol:54 issue:30 pages:7554-7564 status: published

Injecting a stream of microbubbles and thereby introducing a heterogeneous interface is proposed for enhancing nucleation and controlling particle formation in continuous microfluidic devices. Different gas and liquid flow rates were investigated to establish the two-phase flow regime map and to identify the optimum characteristics for microbubble flow. Subsequently, the effect of microbubbles was studied for the cooling crystallization of paracetamol. An enhanced nucleation rate compared to that in the operation without bubbles was observed and the presence of microbubbles results in the formation of more crystals, which indicates that nucleation is faster than that in operation without bubbles, i.e., the metastable zone width is reduced. Determining the crystal yield confirmed that a larger mass of crystals is obtained in a two-phase flow with microbubbles. Furthermore, results showed that the presence of microbubbles allows crystallizing continuously without clogging of the microreactor. ispartof: Langmuir vol:35 issue:1 pages:60-69 ispartof: location:United States status: published

This work reports a cheap and easy-to-use droplet-based microfluidic platform for the study of protein crystallization, offering the possibility to characterize the protein phase behaviour, and the effect of volumetric and interfacial phenomena on the crystallization mechanism. We conducted a parametric study supported by comparison with literature data, to quantify the influence of the droplet volume on the thermodynamic (solubility data) and kinetic (metastability data) parameters, using lysozyme as a model protein. Experiments were performed in a tubular microreactor at low Capillary numbers (4.1 × 10-5 2.3 × 10-4), resulting in a broad range of droplet sizes. The droplet formation in a flow-focussing geometry was also numerically studied using CFD and a correlation for the droplet size was developed. Subsequently, the lysozyme phase behaviour and the possible mechanisms associated with the nucleation process were evaluated. While crystallization in small volume droplets is usually characterized by a low nucleation probability and correspondingly low number of crystals, we did not observe this in our experiments. A potential explanation for this is the complex and stochastic mechanism of nucleation, including the competition between monomers and oligomers in solution., S.K. acknowledges funding from the European Research Council under the ERC Starting Grant Agreement no. 677169–MicroParticleControl. F.C acknowledges FCT (postdoctoral fellowship [SFRH/BPD/96132/2013]) under the project POCI-01-0145-FEDER-006939 (Laboratory for Process Engineering, Environment, Biotechnology and Energy – UID/EQU/00511/2013) funded by the European Regional Development Fund (ERDF), through COMPETE2020 – Programa Operacional Competitividade e Internacionalização (POCI) and by national funds, through FCT – Fundação para a Ciência e a Tecnologia. We thank OpenFoam developers and contributors for the use of their codes, especially Kevin van As from the Transport Phenomena Group (TU Delft). We also thank Vahid Kazemi Kamyab, Milad Mottaghi and Khurram Shazad for all the suggestions and discussions on the simulations., info:eu-repo/semantics/publishedVersion

Coupling photochemistry with flow microreactors enables novel synthesis strategies with higher efficiencies compared to batch systems. Improving the reproducibility and understanding of the photochemical reaction mechanisms requires quantitative tools such as chemical actinometry. However, the choice of actinometric systems which can be applied in microreactors is limited, due to their short optical pathlength in combination with a large received photon flux. Furthermore, actinometers for the characterization of reactions driven by visible light between 500 and 600 nm (e.g. photosensitized oxidations) are largely missing. In this paper, we propose a new visible-light actinometer which can be applied in flow microreactors between 480 and 620 nm. This actinometric system is based on the photoisomerization reaction of a diarylethene derivative from its closed to the open form. The experimental protocol for actinometric measurements is facile and characterized by excellent reproducibility and we also present an analytical estimation to calculate the photon flux. Furthermore, we propose an experimental methodology to determine the average pathlength in microreactors using actinometric measurements. In the context of a growing research interest on using flow microreactors for photochemical reactions, the proposed visible-light actinometer facilitates the determination of the received photon flux and average pathlength in confined geometries. ispartof: SCIENTIFIC REPORTS vol:8 issue:1 ispartof: location:England status: published

A novel reactor was developed for ultrasound-assisted liquid-liquid extraction. This reactor design entails introducing short contact intervals for the nlicrochannel tubing along the reactor plate channel to have a more focused transmission of the ultrasound. The non-contacted parts of the tubing are still under the influence of the ultrasound as a result of the pseudo-sonicated zone created by the adjacent intervals. The effect of introduction of these elements was first studied by compating the thermal profiles with and without the presence of intervals and it was found that the maximum intensities along the channel become focused at these intervals. The influence of the intervals on a sonicated two-phase flow was also studied and revealed a repetitive splitting (at the intervals) and coalescence (downstream from the interval) of the emulsified aqueous phase. This dynamic change in the size of the emulsified aqueous phase introduces additional interfacial area and improves the mass transfer between the phases. The number of intervals was varied between three, five and seven. The five intervals showed the best performance. On comparing the five-interval design with a direct-contact design it was shown that the interval design gave the best improvement in yield for the process conditions studied. (C) 2016 Elsevier B.V. All rights reserved. The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/ 2007-2013) under grant agreement no NMP2-SL-2012-309874 (ALTEREGO).

This paper describes the continuous-flow precipitation of hydroxyapatite Ca[subscript 5](PO[subscript 4])[subscript 3]OH (HAp) in two ultrasonic microreactors using diluted aqueous solutions of calcium and phosphate at 37°C. Precipitation of HAp was first carried out in a tubular microreactor immersed in an ultrasonic bath, where single-phase (laminar) flow and segmented gas-liquid flow were both evaluated. The single-phase flow study was then conducted in a novel microfluidic device developed at MIT. It consists of a Teflon stack microreactor with an integrated piezoelectric element (Teflon microreactor), thereby allowing the direct transmission of ultrasound to the reactor. Both microsystems produce single-phased calcium-deficient carbonated HAp under near-physiological conditions of temperature and pH. In addition, particle aggregation and primary particle size were significantly reduced in the segmented-flow tubular microreactor and in the Teflon microreactor. The as-prepared particles mostly consisted of rod-like shape nanoparticles with dimensions below 100nm in length and around 20nm in width. Further, the microreactors used yielded HAp particles with improved characteristics, namely higher crystallinity and less carbonate contamination, when compared to the HAp particles produced in a stirred tank batch reactor. Keywords: microfluidics; ultrasound; nanoparticles; hydroxyapatite; aggregation, Portuguese Foundation for Science and Technology (SFRH/BD/42992/2008)

© 2018 The Royal Society of Chemistry. Molecular oxygen is without doubt the greenest oxidant for redox reactions, yet aerobic oxidation is one of the most challenging to perform with good chemoselectivity, particularly on an industrial scale. This collaborative review (between teams of chemists and chemical engineers) describes the current scientific and operational hurdles that prevent the utilisation of aerobic oxidation reactions for the production of speciality chemicals and active pharmaceutical ingredients (APIs). The safety aspects of these reactions are discussed, followed by an overview of (continuous flow) reactors suitable for aerobic oxidation reactions that can be applied on scale. Some examples of how these reactions are currently performed in the industrial laboratory (in batch and in flow) are presented, with particular focus on the scale-up strategy. Last but not least, further challenges and future perspectives are presented in the concluding remarks. crosscheck: This document is CrossCheck deposited identifier: Simon Kuhn (ORCID) copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: This article is freely available. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (CC BY 3.0) history: Received 30 August 2016; Accepted 13 September 2016; Advance Article published 22 September 2016; Version of Record published 22 November 2016 ispartof: Reaction Chemistry & Engineering vol:1 issue:6 pages:595-612 status: published

A compact snapshot of the current convergence of novel developments relevant to chemical engineering is given. Process intensification concepts are analysed through the lens of microfluidics and sonochemistry. Economical drivers and their influence on scientific activities are mentioned, including innovation opportunities towards deployment into society. We focus on the control of cavitation as a means to improve the energy efficiency of sonochemical reactors, as well as in the solids handling with ultrasound; both are considered the most difficult hurdles for its adoption in a practical and industrial sense. Particular examples for microfluidic clogging prevention, numbering-up and scaling-up strategies are given. To conclude, an outlook of possible new directions of this active and promising combination of technologies is hinted. ispartof: Topics in Current Chemistry vol:374 issue:5 ispartof: location:Switzerland status: published

We describe fluoropolymer modification of silicon microreactors for control of wetting properties in chemical synthesis applications and characterize the impact of the coating on liquid-liquid multiphase flows of solvents and water. Annular flow of nitrogen gas and a Teflon AF (DuPont) dispersion enable controlled evaporation of fluoropolymer solvent, which in turn brings about three-dimensional polymer deposition on microchannel walls. Consequently, the wetting behavior is switched from hydrophilic to hydrophobic. Analysis of microreactors reveals that the polymer layer thickness increases down the length of the reactor from ∼1 to ∼13 μm with an average thickness of ∼7 μm. Similarly, we show that microreactor surfaces can be modified with poly(tetrafluoroethylene) (PTFE). These PTFE-coated microreactors are further characterized by measuring residence time distributions in segmented liquid-liquid multiphase flows, which display reduced axial dispersion for the coated microreactors. Applying particle image velocimetry, changes in segment shape and velocity fluctuations are observed resulting in reduced axial dispersion. Furthermore, the segment size distribution is narrowed for the hydrophobic microreactors, enabling further control of residence distributions for synthesis and screening applications.

© 2016 Elsevier B.V. A new method to apply ultrasound to a microchannel for liquid-liquid extraction was explored. The microchannel tubes are subjected to the ultrasound by direct contact with the transducer without the presence of a liquid medium. The design was constructed with the objectives of reproducibility, proper control of the ultrasound parameters and visibility of the behaviour of the two phase flow under the influence of ultrasound throughout the length of the channel. Two mechanisms of emulsion formation were observed. The effectiveness of the system under the influence of various operating and design parameters was quantified by calculating the yields of the two phase hydrolysis reaction of p-nitrophenyl acetate. The behaviour under various frequencies and amplitude was explored. At a frequency of 20.3. kHz, amplitude of 840. mV and flow rate of 0.1. ml/min the highest increase in yield was observed, which was almost 2.5 times that of the silent condition. A comparison was also made against silent batch and flow conditions to determine the actual effectiveness of the system. To obtain an identical yield of 75% the required residence time could be reduced by a factor of 20 in the sonicated flow condition compared to the silent batch condition. publisher: Elsevier articletitle: Ultrasound assisted liquid–liquid extraction in microchannels—A direct contact method journaltitle: Chemical Engineering and Processing: Process Intensification articlelink: http://dx.doi.org/10.1016/j.cep.2016.01.003 content_type: article copyright: Copyright © 2016 Elsevier B.V. All rights reserved. ispartof: Chemical Engineering and Processing vol:102 pages:37-46 status: published

Precipitation processes are widely used in industry for the production of particulate solids. Efficient mixing of the reagents is of major importance for the chemical and physical nature of the synthesized particles. Recently, microreactors have been studied to overcome homogeneity problems found when using stirred tank batch reactors. The present work investigated an ultrasonic tubular microreactor for the continuous-flow precipitation of hydroxyapatite (HAp), both in single-phase flow (SPF) and in gas-liquid flow (GLF). HAp nanoparticles were yielded for both configurations under near-physiological conditions of pH and temperature. The as-prepared particles, especially those that were prepared under GLF, show improved characteristics compared to commercial powder or powder obtained in a stirred tank batch reactor. Primary particles are smaller, particle shape is more homogeneous, and the aggregation degree of the particles is lower. © 2013 Elsevier Ltd.

We present a general inexpensive method for realizing a Teflon stack microreactor with an integrated piezoelectric actuator for conducting chemical synthesis with solid products. The microreactors are demonstrated with palladium-catalyzed C–N cross-coupling reactions, which are prone to clogging microchannels by forming insoluble salts as by-products. Investigations of the ultrasonic waveform applied by the piezoelectric actuator reveal an optimal value of 50 kHz at a load power of 30 W. Operating the system at these conditions, the newly developed Teflon microreactor handles the insoluble solids formed and no clogging is observed. The investigated reactions reach full conversion in very short reaction times and high isolated yields are obtained (>95% yield).

Ultrasound-assisted nucleation is a promising method of controlling the crystal length within a narrow range in antisolvent crystallization. This article proposes novel model equations representing crystal nucleation and growth under ultrasound application in the antisolvent system of ethanol (solvent), water (antisolvent), and aspirin (pharmaceutical ingredient). The model considers the enhancement of nucleation by ultrasound, and also accounts for the heat generated from both the application of ultrasound and the mixing of solvent and antisolvent. We further employ a global sensitivity analysis to determine the parameters that have the most significant impact on model outputs before validating multiple experimental case studies that represent crystal growth for different antisolvent contents and initial supersaturation ratios. The model successfully captures the effect of the ultrasound, which is a function of temperature and supersaturation ratio, and has a strong impact on the refinement and the quant...

Droplet microfluidics allows a higher degree of control over the crystallization conditions than conventional methodologies. To extend this approach, this work explores the synergistic effect of low-frequency pulsed ultrasound on lysozyme crystallization in microdroplets. Pulsed actuation allows control of the crystallization temperature, while the ultrasound effect significantly reduces the induction time and crystal size. Therefore, protein nucleation is enhanced by pulsed sonication without causing precipitation, resulting in uniform crystal size. Finally, the initial supersaturation ratio has a crucial contribution to the crystal size for silent experiments, while a threshold for induction time is observed in ultrasonic crystallization.

Ultrasonic micro-reactors are frequently applied to prevent micro-channel clogging in the presence of solid materials. Continuous sonication will lead to a sizeable energy input resulting in a temperature increase in the fluidic channels and concerns regarding microchannel degradation. In this paper, we investigate the application of pulsed ultrasound as a less invasive approach to prevent micro-channel clogging, while also controlling the temperature increase. The inorganic precipitation of barium sulfate particles was studied, and the impact of the effective ultrasonic treatment ratio, frequency and load power on the particle size distribution, pressure and temperature was quantified in comparison to non-sonicated experiments. The precipitation reactions were performed in a continuous reactor consisting of a micro-reactor chip attached to a Langevin-type transducer. It was found that adjusting the pulsed ultrasound conditions prevented microchannel clogging by reducing the particle size to the same magnitude as observed for continuous sonication. Furthermore, reducing the effective treatment ratio from 100 to 12.5% decreases the temperature rise from 7 to 1 °C. ispartof: Ultrasonics Sonochemistry vol:55 pages:67-74 ispartof: location:FRANCE, Univ Bourgogne Franche Comte, Besancon status: published

ispartof: CHEMICAL ENGINEERING & TECHNOLOGY vol:42 issue:10 pages:2105-2112 ispartof: location:GERMANY, Karlsruhe status: published

Highlights • Acoustic resonance within a liquid slug in gas–liquid Taylor flow was demonstrated. • Intense atomization was observed with slug resonance. • Visual evidence of the cavitation-wave hypothesis was provided., It is shown that a liquid slug in gas–liquid segmented flow in microchannels can act as an acoustic resonator to disperse large amounts of small liquid droplets, commonly referred to as atomization, into the gas phase. We investigate the principles of acoustic resonance within a liquid slug through experimental analysis and numerical simulation. A mechanism of atomization in the confined channels and a hypothesis based on high-speed image analysis that links acoustic resonance within a liquid slug with the observed atomization is proposed. The observed phenomenon provides a novel source of confined micro sprays and could be an avenue, amongst others, to overcome mass transfer limitations for gas–liquid processes in flow.

Ultrasound (US) is a promising method to address clogging and mixing issues in microreactors (MR). So far, low frequency US (LFUS), pulsed LFUS and high frequency US (HFUS) have been used independently in MR for particle synthesis to achieve narrow particle size distributions (PSD). In this work, we critically assess the advantages and disadvantages of each US application method for the case study of calcium carbonate synthesis in an ultrasonic microreactor (USMR) setup operating at both LFUS (61.7 kHz, 8 W) and HFUS (1.24 MHz, 1.6 W). Furthermore, we have developed a novel approach to switch between LFUS and HFUS in an alternating manner, allowing us to quantify the synergistic effect of performing particle synthesis under two different US conditions. The reactor was fabricated by gluing a piezoelectric plate transducer to a silicon microfluidic chip. The results show that independently applying HFUS and LFUS produces a narrower PSD compared to silent conditions. However, at lower flow rates HFUS leads to agglomerate formation, while the reaction conversion is not enhanced due to weak mixing effects. LFUS on the other hand eliminates particle agglomerates and increases the conversion due to the strong cavitation effect. However, the required larger power input leads to a steep temperature rise in the reactor and the risk of reactor damage for long-term operation. While pulsed LFUS reduces the temperature rise, this application mode leads again to the formation of particle agglomerates, especially at low LFUS percentage. The proposed application mode of switching between LFUS and HFUS is proven to combine the advantages of both LFUS and HFUS, and results in particles with a unimodal narrow PSD (one order of magnitude reduction in the average size and span compared to silent conditions) and negligible rise of the reactor temperature. ispartof: Ultrasonics Sonochemistry vol:60 ispartof: location:Netherlands status: published