Multiphase Microreactor Research Articles

Microsensor Electrodes for 3D Inline Process Monitoring in Multiphase Microreactors

We present an electrochemical microsensor for the monitoring of hydrogen peroxide direct synthesis in a membrane microreactor environment by measuring the hydrogen peroxide and oxygen concentrations. In prior work, for the first time, we performed in situ measurements with electrochemical microsensors in a microreactor setup. However, the sensors used were only able to measure at the bottom of the microchannel. Therefore, only a limited assessment of the gas distribution and concentration change over the reaction channel dimensions was possible because the dissolved gases entered the reactor through a membrane at the top of the channel. In this work, we developed a new fabrication process to allow the sensor wires, with electrodes at the tip, to protrude from the sensor housing into the reactor channel. This enables measurements not only at the channel bottom, but also along the vertical axis within the channel, between the channel wall and membrane. The new sensor design was integrated into a multiphase microreactor and calibrated for oxygen and hydrogen peroxide measurements. The importance of measurements in three dimensions was demonstrated by the detection of strongly increased gas concentrations towards the membrane, in contrast to measurements at the channel bottom. These findings allow a better understanding of the analyte distribution and diffusion processes in the microreactor channel as the basis for process control of the synthesis reaction.

Design, Fundamental Principles of Fabrication and Applications of Microreactors

This study highlights the development of small-scale reactors, in the form of microstructures with microchannel networking. Microreactors have achieved an impressive reputation, regarding chemical synthesis ability and their applications in the engineering, pharmaceutical, and biological fields. This review elaborates on the fabrication, construction, and schematic fundamentals in the design of the microreactors and microchannels. The materials used in the fabrication or construction of the microreactors include silicon, polymer, and glass. A general review of the application of microreactors in medical, biological, and engineering fields is carried out and significant improvements in these areas are reported. Finally, we highlight the flow patterns, mixing, and scaling-up of multiphase microreactor developments, with emphasis on the more significant industrial applications.

Three-Dimensional VOF-DEM Model for Simulating Particle Dynamics in the Liquid Slugs of a Vertical Gas–Liquid–Solid Taylor Flow Microreactor

It proves challenging to analyze the particle dynamics experimentally, particularly in a multiphase microreactor. A numerical model based on volume of fluid (VOF) coupled with discrete element meth...

Correction to: Application of a multiphase microreactor chemostat for the determination of reaction kinetics of Staphylococcus carnosus.

Unfortunately, in the "How to Cite as" section, the given and the family name of the author was incorrectly published, the correct name is Lladó Maldonado. S.

Application of a multiphase microreactor chemostat for the determination of reaction kinetics of Staphylococcus carnosus.

Bioreactors at the microliter scale offer a promising approach to accelerate bioprocess development. Advantages of such microbioreactors include a reduction in the use of expensive reagents. In this study, a chemostat operation mode of a cuvette-based microbubble column bioreactor made of polystyrene (working volume of 550 µL) was demonstrated. Aeration occurs through a nozzle (Ø ≤ 100µm) and supports submerged whole-cell cultivation of Staphylococcus carnosus. Stationary concentrations of biomass and glucose were determined in the dilution rate regime ranging from 0.12 to 0.80 1/h with a glucose feed concentration of 1g/L. For the first time, reaction kinetics of S. carnosus were estimated from data obtained from continuous cultivation. The maximal specific growth rate (µmax = 0.824 1/h), Monod constant (KS = 34×10- 3gS/L), substrate-related biomass yield coefficient (YX/S = 0.315 gCDW/gS), and maintenance coefficient (mS = 0.0035 gS/(gCDW·h)) were determined. These parameters are now available for further studies in the field of synthetic biology.

Analysis of reaction kinetics during chemostat cultivation of Saccharomyces cerevisiae using a multiphase microreactor

This paper presents the determination of reaction kinetic parameters and the kinetic analysis of a chemostat cultivation performed using a multiphase microreactor (mMR). Saccharomyces cerevisiae was cultivated aerobically in continuous chemostat mode using an mMR. Steady-state biomass, substrate and ethanol concentrations were determined at dilution rates between 0.14≤D≤0.42h−1 with a glucose-feed concentration of 10gL−1. Modelling the aerobic chemostat culture was based on stationary balance equations. Maximal specific growth rate and Monod constant were determined using different linearization methods. The aerobic yeast metabolism was considered using two validity ranges of the model: (a) with purely oxidative metabolism in which glucose was converted into biomass or was used for maintenance metabolism, and no ethanol was generated; (b) with oxido-reductive metabolism employing an active Crabtree effect, in which ethanol was generated at the expense of biomass production. The different yield coefficients could be determined using the plots of the specific substrate consumption rate qS=f(D) and the specific product formation rate qP=f(D), respectively. Using this model, the reaction kinetic parameters were determined from the stationary concentrations of the biomass, glucose and ethanol that were determined during aerobic cultivation in the mMR. Finally, the kinetic parameters were compared with those reported in the literature that had been obtained using laboratory-scale reactors.

Electrochemical Multiphase Microreactor as Fast, Selective, and Portable Chemical Sensor of Trace Toxic Vapors

A novel type of gas chemical sensor is fabricated by combining microfabrication techniques and electrochemical transducer. The microchannel sensor we built is composed of liquid/gas microchannels separated by a nanoporous membrane. When oxime chemistry is adapted into it, the microchannel sensor gives response of hundreds of mV to trace vapor (10 ppb) of acetylcholine simulant within s. Double microchannel design further reduces potential drift and simplifies the sensor setup.

High Temperature Preparation of Core and Core/Shell Composite Nanocrystals in a Multiphase Microreactor

Microreactors can be used for continuous operation and precise control of heating conditions in chemical synthesis. Therefore, microreactors are expected to offer a more efficient strategy for obtaining homogeneous nanocrystals and easier of size control than the general batch reaction system. CdSe nanocrystals can be turned into emission color by controlling the size of nanocrystals. In this study, we synthesized CdSe nanocrystals by a multiphase microreactor. The CdSe nanocrystals were coated with ZnSe and ZnS by using the multiphase microreactor. The nanocrystals are coated on their surface with a shell of a larger band gap semiconductor, which can improve luminescence efficiency. Furthermore, we investigated the residence time in relation to size of nanocrystals and optimized the coating layer thickness.

Microfabricated Multiphase Reactors for the Direct Synthesis of Hydrogen Peroxide from Hydrogen and Oxygen

Hydrogen peroxide synthesis is demonstrated by direct combination of hydrogen and oxygen over supported palladium catalysts in a microchemical reactor. The direct combination process is chemically simple and environmentally benign for producing hydrogen peroxide, but the risk of handling the explosive gas mixture of hydrogen and oxygen over an active palladium catalyst limits implementation. By using a multichannel microchemical reactor with packed-bed catalyst, we realize the direct reaction of hydrogen and oxygen at hydrogen/oxygen ratios in the explosive regime at pressures of 2−3 MPa. As long as millimeter-sized void spaces are avoided, the microchannel structure and catalyst packaging effectively promote the heterogeneous reaction over the homogeneous free radical branching reactions that otherwise would lead to an explosion. Among the Pd/Al2O3, Pd/SiO2, and Pd/C catalysts investigated, Pd/C selectively yields hydrogen peroxide. The decomposition of peroxide is shown to be suppressed by the addition of bromide. Analysis of the microreactor data reveals significantly enhanced mass transfer relative to conventional reactors, consistent with previous multiphase microreactor studies.

Effect of Aromatics on Deep Hydrodesulfurization of Dibenzothiophene and 4,6-Dimethyldibenzothiophene over NiMo/Al2O3 Catalyst

The influence of different aromatics on the deep hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) over a commercial NiMo/γ-Al2O3 hydrotreating catalyst was investigated in a fixed-bed multiphase microreactor under designed conditions. Both the sulfur-containing compounds and the aromatic compounds in feeds and hydrotreated products were identified and quantified by GC−AED. Catalyst deactivation was observed, and a simple model for it was established. The kinetic behavior of these model compounds was studied with an assumption of pseudo-first-order reaction kinetics. The rate constants and the corresponding activation energies were determined, and the heat of adsorption for each compound on the catalyst surface was computed by density functional theory using the Material Studio software. The HDS rate for 4,6-DMDBT was much lower than that for DBT, which is attributed to the steric hindrance of the methyl groups at the 4 and 6 positions. The apparent activati...

Scaling down trickle bed reactors

The scaling down of trickle bed reactors for catalyst testing in deep hydrodesulphurisation (HDS) is evaluated. A multiphase micro-reactor system has been built specifically for HDS, consisting of a set of six 2 mm diameter packed beds with particles of approximately 100 μm. To confirm plug-flow behaviour (for integral conversion) and to guarantee the measurement of true kinetics, the hydrodynamics have to be investigated. For this purpose, a ‘cold-flow’ set-up of the same dimensions as the HDS reactors, has been built. A liquid feed with a dye tracer pulse as well as gas are fed to a glass column, packed with glass particles. From the recorded outlet concentration, the influence of the gas- and liquid-flow rate on the mean residence time and residence-time distribution (RTD) have been determined. This hydrodynamics investigation describes the deviation from plug flow in micro-scale packed beds. The results show that the deviations from plug flow are minimal. The effect of the gas-flow rate on the liquid-residence time is more pronounced in micro-packed beds than that in trickle beds with larger particles. The RTD study presented here provides valuable insight into the behaviour of scaled-down kinetic-test facilities.

Simulation and Design of a Non-adiabatic Multiphase Microreactor

We have identified a novel, multiphase microreactor configuration for the direct fluorination of toluene. With this reactor the fluorine and toluene are separated by a macroporous membrane impregnated with a solid Lewis acid catalyst, which influences the fluorine directly when being absorbed into the liquid phase. Reaction occurs in the membrane adjacent to the gas-phase. According to the literature fluorine is turned into an electrophile in the presence of acidic catalysts improving the selectivity towards monofluorinated products. The direct fluorination of toluene is a very fast and exothermic reaction and therefore heat management is of great importance to avoid thermal runaway. Also, the selectivity of the process deteriorates at elevated temperatures due to increasing radical reactions.To address this issue a detailed model of the heat and mass transfer has been developed. The catalytic membrane is modelled as an idealised system and the porosity, tortuosity and catalytic activity are parameters in a sensitivity analysis to obtain bench-mark values for the reactor performance and the membrane design. The software package FEMLAB has been employed to solve the partial differential equations simultaneously by means of the finite element technique.The performance of the membrane reactor configuration is compared to a falling film microreactor. It is shown that the membrane reactor has great potential to improve the selectivity of the direct fluorination reaction towards mono-fluorinated products by means of a thin solid acid catalyst layer. The influence of the reactor size and the aspect ratio on the temperature in the reaction plane and hot spot formation is studied. With the falling film reactor rising channel size results in increasingly prominent hot spot formation and the selectivity towards monofluorinated products deteriorates. The membrane supports the heat removal because the reaction plane is located inside the solid grid. In this manner the membrane catalyst increases the selectivity of the process and also shifts the optimal operation temperature to higher values towards room temperature. Higher production rate per channel can be achieved requiring less cooling.

The intensification of rapid reactions in multiphase systems using slug flow in capillaries

A multiphase microreactor based upon the use of slug flow through a narrow channel has been developed. The internal circulation, which is stimulated within the slugs by their passage along the channel, is responsible for a large enhancement in the interfacial mass transfer and the reaction rate. Mass transfer performance data has been obtained for a glass chip-based reactor in a 380 microm wide channel by monitoring the extraction of acetic acid from kerosene slugs as they moved along the reactor channel. Finally, the data was compared with that provided from other inter-phase contacting techniques.