Search

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...

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.

Continuous-flow simplified electrochemically mediated atom transfer radical polymerization (seATRP) was achieved for the first time without supporting electrolytes (self-supported) using a novel sonicated tubular microreactor. Polymerizations of different acrylic monomers were carried out under different applied currents. The reaction was fast with 75% conversion achieved at ambient temperature in less than 27 minutes. Results also showed good evolution of molecular weight and maintained narrow molecular weight distribution. The reaction rate can be further manipulated by tuning the applied current. Sonication under proper conditions was found to be able to significantly improve both reaction rate and controllability. Self-supported reactions also enable more environmentally friendly and cost-effective operations. ispartof: CHEMICAL SCIENCE vol:13 issue:42 pages:12326-12331 ispartof: location:England status: published

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

ispartof: Chemical Engineering And Processing-Process Intensification vol:181 status: accepted

Continuous-flow microreactor technology has been embraced by researchers in academia and industry due to its excellent transport properties and the increased safety and control over challenging chemical transformations. Despite its popularity, scaling the benefits associated with the microenvironment has proven to be a daunting challenge. This review provides an up-to-date overview concerning the different scale-up approaches of micro/milli-reactors, including numbering up (both internal and external), sizing up (increasing length, geometry similarity and constant pressure drop strategies) and a combination of numbering up and sizing up. The strategies, design principles and applications of each approach have been discussed in detail. Each scale-up approach has its merits and limitations. However, scale-up factors, that are required in the fine chemical and pharmaceutical industry, are within reach when different scale-up approaches are combined.

Summarization: Ultrasound-assisted crystallization is a promising process for the production of crystals within a size distribution width. Toward the direction of attaining high-quality crystals, this article proposes and assesses a theoretical feedback control scheme that can be applied in a continuous tubular crystallizer. In this crystallizer, the antisolvent crystallization of aspirin (a pharmaceutical ingredient) in water (an antisolvent) and ethanol (a solvent) takes place under ultrasound. Initially, a dynamic model is developed and includes the aspirin concentration variations while also taking into account temperature modifications in the inlet. After model validation, a PI control scheme is finely tuned, implemented theoretically, and critically assessed at the (i) trajectory control of the crystal length (average size), (ii) alleviation of suddenly emerged disturbances (e.g., solvent flow rate, inlet temperature), and (iii) a combination of worst-case operating scenarios. As identified, the proposed controller can offer a practical platform that can be readily applied to different scales and geometries in continuous tubular crystallizers operating with ultrasound. During all simulations, the produced crystals maintained high quality. Presented on: Industrial & Engineering Chemistry Research

Ultrasound is frequently applied in crystallization to enhance nucleation and achieve crystal sizes within a narrow range. In this work, a mathematical model is developed, which couples the acousti...

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 objective of this work is to establish an experimental approach to scale-up the production of melamine formaldehyde (MF) microcapsules from a batch lab-scale to a pilot-scale inline rotor stator mixer (RSM). The inline RSM is operated in a continuous recycle mode, allowing multiple passes of the emulsion through the intensive mixing zone during continuous production. The liquid is continuously recirculated directly to the RSM, without a holding vessel, as is the case in conventional batch recirculation emulsification. The setup is operated at feed flow rates of 0.24 kg/h - 20 kg/h. Parameters including the Weber number, tip speed and energy density are investigated to correlate the mean capsule size of the batch and flow process. Rotational speeds range from 3000 to 26,000 rpm. The dimensionless maximum diameter correlated well with the Weber number to the power -0.4, for both devices operated at the same residence time. Volume and number based mean diameters showed little influence of the feed flow rate in the continuous recycle mode of operation. This inline RSM setup is therefore an ideal tool to optimize emulsification processes at lab scale and increase production by increasing the feed flow rate, while maintaining rotor-stator geometry.

© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Milli-scale reactors with an integrated microstructure offer a promising scale-up approach for conventional microreactors. This study applies 3D-printed structured porous millireactors to industrially relevant liquid-liquid reactions. The underlying transport mechanisms are identified by quantifying interfacial heat and mass transfer. The structured reactors perform limited in Taylor flow compared to a packed-bed reactor due to limited interfacial mass transfer. However, in stratified flow, their productivity increases significantly at a fraction of the pressure drop of a packed bed. ispartof: CHEMIE INGENIEUR TECHNIK vol:91 issue:5 pages:592-601 status: Published online

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

The mass transfer coefficient, k L α , is often used to benchmark the liquid–liquid mass transfer performance in a microfluidic reactors. Cobalt(II) was extracted with an undiluted, highly viscous, ionic liquid from an aqueous phase in a microfluidic reactor (1 mm ID) and k L α values were determined (0.0002–0.033 s−1). It is concluded that the high viscosity of the ionic liquid causes two-phase slip, greatly reducing the efficiency of the microfluidic reactor. Furthermore, deviations (or non-idealities) from the assumptions related to mass transfer calculations (e.g., no reaction effects) can have a drastic impact on the measured k L α values. This work reports deviations between −25 and +40%. In general, it is shown how several non-idealities (i.e., a high continuous phase viscosity, non-linear equilibrium behavior and concentration effects) can affect the calculated mass transfer coefficient.

Knowledge and control of mixing in batch processes can prevent yield losses during scale-up. Therefore, in this study, a new heat-mixing model based ono the measurement of the heat distribution after an applied heat pulse, is proposed. The model was developed to predict mesomixing and support scale-up, scale-down, and design and optimisation of batch reactors. The proposed model considers the influences of rotational speed, stirrer type, solvent, stirrer-to-tank diameter, liquid-height-to-tank diameter, injection time, and pumping number. A strong correlation between the mixing time of the heat pulse method and the mass-transfer coefficient of the mixing-sensitive Bechamp reaction was observed.

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).

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.

© 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

A flat Teflon AF-2400 membrane microchannel reactor was experimentally and theoretically investigated for aerobic oxidation of benzyl alcohol on a 5 wt% Ru/Al2O3 catalyst. The reactor consisted of gas and liquid channels (75 mm (L) × 3 mm (W) × 1 mm (D)), separated by a 0.07 mm thick semipermeable Teflon AF-2400 flat membrane, which allowed continuous supply of oxygen during the reaction and imultaneously avoided direct mixing of gaseous oxygen with organic reactants. A catalyst stability test was first carried out, and the experimental data obtained were used to estimate the kinetics of benzyl alcohol oxidation with a 2D reactor model. Using these kinetics, predictions from the 2D reactor model agreed well with the experimental data obtained at different liquid flow rates and oxygen pressures. The mass transfer and catalytic reaction in the membrane microchannel reactor were then theoretically studied by changing the membrane thickness, the liquid channel depth, and the reaction rate coefficient. Oxygen transverse mass transport in the catalyst bed was found to be the controlling process for the system investigated, and decreasing the liquid channel depth is suggested to improve the oxygen supply and enhance the benzyl alcohol conversion in the membrane reactor.

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

© 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

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

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)

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 present a pH-sensitive laser-induced fluorescence (LIF) technique to investigate mass transfer in reactive flows. As a fluorescent dye, we used 5-(and-6)-carboxy SNARF-1, which, when excited with a pulsed Nd:YAG laser at 532 nm, provides good sensitivity in the range 4 ≤ pH ≤ 12. For validation, we first applied the dye to single-phase reactive flows by investigating the neutralization of sodium hydroxide with hydrochloric acid. Comparison to the classical passive mixing case showed that this dye was able to capture the reaction progress and to quantify the mass transport. Next, we investigated the absorption of CO2 in an alkaline solution using gas–liquid flow and found that the LIF technique is able to quantify the local mass-transfer rate in microfluidic systems. Results for different microchannel geometries highlight the strong connection between local mass transfer and secondary flow structures in gas–liquid Taylor flow.

We present a dynamic large eddy simulation of flow in a periodic open-cell structure in the turbulent regime. The flow domain is represented by a tube with inner diameter of 7 mm with integrated highly porous media. Simulations were performed for three different Reynolds numbers ranging from 1200 to 4500 based on the empty tube diameter. The obtained results were compared to experimental data for which measurements were performed downstream of the same periodic geometry manufactured from a transparent material by stereolithography. The measured pressure drop and turbulence statistics compare well to the results of the large eddy simulations. The numerical results give an insight into the forced convection mechanism within the porous media and enhance the understanding of flow through foamlike structures. Furthermore specific geometric details like the influence of the ligament shape of the porous material can be investigated applying this technique.

We present an investigation on species mass transfer in a milli-scale plug flow reactor using metal foams to enhance the mixing process. In the current design the reactor consists of a pipe with an inner diameter of 7 mm and metal foam inserts with different pore sizes of 20, 30 and 45 ppi. Simultaneous PIV and LIF measurements were performed in orthogonal planes normal to the radial and axial direction downstream of a foam element of 50 mm length. The investigated Reynolds numbers range from 600 to 7600 defined with the empty tube diameter and the bulk velocity. We discuss the influence of the pore sizes on the scalar mixing efficiency and compare the results to the reference empty tube case. A strongly intermittent flow caused by the metal foam was observed over the whole range of Reynolds numbers. The increased radial velocities lead to an enhanced mixing performance. Coefficients of Variation in the order of 0.1 were achieved.

© 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

© 2015 American Chemical Society. A Teflon AF-2400 tube-in-tube microreactor is investigated for the continuous, solvent-free, catalytic oxidation of benzyl alcohol with oxygen. The semipermeable Teflon AF-2400 tube acts as the interface between the gaseous oxidant and the liquid substrate. Because of the inherent safety of this contacting method, the use of pure oxygen is possible. The semipermeable tube was packed with 1 wt % Au-Pd/TiO2 catalyst particles and placed inside a PTFE tube to provide an annular region which was pressurized with pure oxygen. This design allowed continuous penetration of oxygen through the inner tube during the reaction, resulting in higher oxygen concentration in the catalyst bed and significantly improved conversion compared to a reactor operating with an oxygen presaturated feed. The amount of oxygen available for reaction in the tube-in-tube microreactor was 2 orders of magnitude higher than that in a nonpermeable reactor with oxygen presaturated feed. The semipermeable tube reactor performance in terms of both conversion and selectivity was enhanced by increasing the gas pressure, the catalyst contact time and by dilution of the catalyst. The highest conversion of benzyl alcohol obtained for the range of conditions investigated was 44.1%, with 73.0% selectivity to benzaldehyde, at 120 °C; catalyst contact time, 115 gcat·s/galcohol; and catalyst dilution factor, 4. ispartof: Industrial & Engineering Chemistry Research vol:54 issue:16 pages:4183-4189 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.

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

ispartof: CHEMICAL ENGINEERING JOURNAL vol:452 status: published