Segmented Flow Microreactor Research Articles

Impinging Flow Reactor as a New Approach to Scaling-Up Microreactors for Enhanced Extraction and Separation of Zinc from Cadmium and Manganese

ABSTRACT Despite significant progress in microreactor research, limited throughput hinders their industrial application. The impinging flow method offers a novel approach to scaling up microreactors. In this study, a T-shaped impinging flow reactor was used to investigate the improvement of the throughput of micro-scale devices for the enhanced extraction and separation of zinc from cadmium and manganese using the impinging flow method. Computational fluid dynamics (CFD) simulations were performed to analyze the velocity fields and concentration distributions and gain a better understanding of the mixing and mass transfer phenomena. A comparison of experimental and simulation results under the same conditions was then carried out. Results revealed that decreasing mass transfer efficiency with increased inner diameter, though higher inlet flow rates partially offset this, however beyond a certain threshold, larger channel sizes significantly decrease efficiency. The study also demonstrated that impinging flow reactors exhibit superior volumetric mass transfer coefficients compared to segmented flow microreactors. By increasing the volumetric flow rate and channel inner diameter simultaneously, the millimeter impinging flow reactor achieved the same extraction efficiency as the micrometer segmented flow reactor with a scale-up factor of 1312.5, which indicates a significant increase in device capacity. Overall, this study demonstrates the potential for significant scale-up in device capacity using impinging flow reactors.

Experimental and numerical studies of separation intensification in segmented flow microreactors

Process intensification studies have already been well-established in continuous operations, particularly achieved by using microreactors. Separation intensification benefits from the application of process intensification and shows great potential, yet it is still not sufficiently studied. In this work, liquid-liquid two-phase segmented flow capillary microreactors and simulation models based on finite element method were used to perform experimental and numerical studies on the extractive separation intensification of the Zn-Cd-Mn system, respectively. The influence of hydrodynamics including metal ion concentration, plug velocity, and initial pH of the aqueous phase on the separation factor was explored. By regulating the hydrodynamic conditions, higher separation factors are obtained in shorter times to achieve separation intensification. The Damkhler number (Da) was introduced to clarify the rate-determining step and elaborate the separation mechanism. During the simulations, the results obtained from the model based on the finite element method agree well with the experimental ones. Taking advantage of the strong complementarity between numerical and experimental studies, separation intensification can be more deeply understood.

Segmented flow capillary microreactors for determination of kinetic rate constants of reactive zinc extraction system

Conventional techniques for kinetic rate constant acquisition are limited by diffusive transport, which can be well addressed by microfluidic techniques. Segmented flow capillary microreactors were used for the first time in this study to obtain kinetic rate constants for a reactive zinc extraction system. The influences of initial zinc ion concentration, total flow velocity, pH of the aqueous phase, and ionic strength on the kinetic rate constant determination were investigated. The control regimes were determined with the ratio of reaction to total resistance R, and the Hatta number. The kinetic rate constants obtained at low initial zinc concentrations, low acidity and high flow velocities exhibited minor deviations, indicating that the zinc sulfate/D2EHPA system could be under the kinetic control regime with the capillary microreactors, which also demonstrated the viability of the segmented flow approach. The kinetic rate constant data obtained with the segmented flow capillary microreactor from this work were much higher than those obtained from previous studies, which may be attributed to the fact that the microreactor minimizes the influence of diffusive transport. The purpose of this work was to provide reliable kinetic data of the reactive zinc extraction system and to verify the efficiency and superiority of the segmented flow microreactor approach over other techniques.

Simulations and analysis of multiphase transport and reaction in segmented flow microreactors

We present volume-of-fluid (VOF) based simulations of coupled transport and reaction processes in microscale segmented flow microreactors. The simulations implemented in OpenFOAM accurately capture the circulation patterns and micron-scale wetting film of the segmented flow. The accurate prediction of the interfacial concentration discontinuity is shown to depend on the local Peclet number. The integrated computational fluid dynamics (CFD) and mass transfer simulations provide complete spatial and temporal information about the concentration field within the reactor, which enable quantification of the mass transfer coefficient kLa as a function of time and operating condition. Mass transport in the segmented flow system is shown to be a two-regime process, dominated first by convection and then by diffusion. Scaling analysis provide a means for estimating mass transfer coefficients and give insights into how to select optimal operating conditions in segmented flow reactors. Finally, we predict mass transfer in segmented flow with reaction, specifically, the mass transfer enhancement as a function of the Damköhler number.

Epoxidation of methyl oleate with molecular oxygen: Implementation of Mukaiyama reaction in flow

Continuous‐flow technology with channel dimension in the millimeter region found widespread applications in numerous applications. The epoxidation of methyl oleate with molecular oxygen using an aldehyde as sacrificial reductant (Mukaiyama reaction) was implemented in a segmented flow microreactor. The effect of aldehyde structure and aldehyde/methyl oleate molar ratio on the conversion to epoxides was studied. Total conversion of methyl oleate (0.67 M in heptane) with a selectivity higher than 99% and a cis/trans ratio ∼75/25 was reach in less than 4 min, at room temperature, using three equivalents of 2‐ethylhexanal, 100 ppm of Mn(II) as catalyst and five bar of oxygen.Practical applications: As the result of the small reactor volumes, very high surface‐to‐volume ratio and high heat exchange efficiency compared to classical batch reactors, the overall safety of oxidation processes is significantly improved using continuous‐flow technology. Microreactors also provide better mass transfer, and thus, improve the productivity of the aerobic epoxidation of methyl oleate using aldehyde as sacrificial reductant while maintaining the high selectivity of the process.(i) Epoxidation of methyl oleate with molecular oxygen is performed safely using continuous‐flow technology. (ii) Total conversion is obtained in 4 min at r.t. using 100 ppm of Mn(II) and a sacrificial reductant. (iii) The selectivity and cis/trans ratio are comparable to batch.

A peculiar segmented flow microfluidics for isoquercitrin biosynthesis based on coupling of reaction and separation

A segmented flow containing a buffer-ionic liquid/solvent in a micro-channel reactor was applied to synthesize isoquercitrin by the hesperidinase-catalyzed selective hydrolysis of rutin, based on a novel system of reaction coupling with separation. Within the developed microchannel reactor with one T-shaped inlet and outlet, the maximum isoquercitrin yield (101.7±2.6%) was achieved in 20min at 30°C and 4μL/min. Compared with a continuous-flow reactor, reaction rate was increased 4-fold due to a glycine–sodium hydroxide:[Bmim][BF4]/glycerol triacetate (1:1, v/v) system that formed a slug flow in microchannel and significantly increased mass transfer rates. The mass transfer coefficient significantly increased and exhibited a linear relationship with the flow rate. Hesperidinase could be efficiently reused at least 5 times, without losing any activity. The bonding mechanism and secondary structure of hesperidinase indicated that hesperidinase had a greater affinity to rutin at a production rate of 4μL/min in this segmented flow microreactor.

Biocatalytic Production of Catechols Using a High Pressure Tube-in-Tube Segmented Flow Microreactor

This study reports the synthesis of 3-phenylcatechol at the preparative scale using a continuous segmented flow tube-in-tube reactor (TiTR). 2-Hydroxybiphenyl 3-monooxygenase (HbpA) was applied as a biocatalyst for the hydroxylation reaction, which is dependent on the substrate 2-hydroxybiphenyl, NADH, and oxygen. While the regeneration of the cofactor NADH was guaranteed by formate dehydrogenase (FDH), oxygen was supplied via the membrane surface from the outside of the reactor system. The oxygen transfer rate through the membrane of the TiTR was determined to be 24 μmol O2 min–1 mL–1 emphasizing the potential of the TiTR as promising technology for realizing gas-dependent enzymatic reactions. Residence time and total turnover number have been identified as key limiting parameters. It was possible to scale-up this system by extending the TiTR by additional residence time units. This allowed synthesis of 1 g of 3-phenylcatechol at a high space time yield of 14.5 g L–1 h–1.

Organic Electronics

This is the Second Edition of the Advanced Materials Organic Electronics Special Issues, focussing on a review and perspective of the progress, challenges, and opportunities of the research driving the current and future applications for this field. We have solicited a broad range of invited contributions that highlight the excitement and diversity of this multidisciplinary area. We showcase the spectrum of research and development offering a state-of-the-art review and current status. The field of organic electronics has recently experienced hugely impressive progress in the performance of both materials and devices. For example, it is now highly conceivable that transistors fabricated using organic semiconductors can be employed to drive even high-resolution OLED pixels. Both small-molecule and even polymer semiconductor thin films, processed from solution, have demonstrated charge carrier mobilities in excess of 5 cm2V−1s−1 in the last year or so. This is particularly remarkable in the case of polymer semiconductors, where the conventional paradigm of thin-film microstructures comprising highly crystalline π-stacked lamellar domains, optimally oriented and co-aligned with respect to the transport direction, has been challenged by new classes of less-ordered, dipolar polymers. In this case a one-dimensional transport mode along the polymer backbone is speculated to be preferred, leading to very high charge-carrier mobilities. An excellent example of this is a series of polymers based on the diketopyrrolopyrrole repeat unit, as reviewed in this special edition. Here the off axis dipole may facilitate close intermolecular interactions, while side chain functionality ensures the polymers have sufficient solubility for processing. The combination of polymer conformation modelling, synthesis, and microstructure characterisation has been compellingly employed on the morphology and charge transport properties of a well-known donor-acceptor copolymer, cyclopentabithiophene-co-benzothiadiazole (CDT-BTZ). The supramolecular structure of CDT-BTZ was modeled and compared with grazing incidence wide angle X-ray scattering (GIWAXS) measurements of thin films from the synthesised polymer. Subtle but important differences in the intermolecular packing as well as the side chain orientation arrangements were revealed and discussed, with significant implications for general semiconducting polymer molecular design principles. The concept of molecular and longer length-scale dimensionality and its critical influence on the charge transport properties of semiconducting materials is explicitly explored by Skabara, Garlin, and Geerts in this issue. Drawing from examples illustrating non-covalent intermolecular bonding and the role of molecular conformations in achieving higher order architectures, it is clear to see the influence on electrical properties. The choice of dielectric layer employed in the transistor architecture remains essential to high device performance. One exciting class of dielectric materials that have been demonstrated, particularly in low voltage applications, are electrolytes and have been reviewed in this edition by Frisbie and co-workers. It is also clear that conventional materials design and multistep, batch synthetic processing may not ultimately be feasible or scalable for the next generation of organic electronics devices and applications. With this in mind, the report by deMello and Nightingale demonstrates the possibility of new nanomaterials production from segmented flow microreactors. These systems, where the reagent phase is dispersed in an immiscible fluid non-solvent, have potential applications in the controlled synthesis of nanocrystals, and the challenges associated with mainstream production are addressed. Organic photovoltaic devices continue to improve rapidly, with efficiencies of single cell devices now routinely reported in excess of 7% and up to 10% in some instances. Janssen and Nelson dissect the fundamental theoretical limitations of organic solar cells, and evaluate the empirical approaches from both a thermodynamic and kinetic perspective that are employed to estimate the maximum efficiencies that can be expected to be achieved in practical devices. They optimistically suggest that limits of 20–24% may be theoretically reachable in single junction cells, thus raising the bar considerably for materials performance expectations. Measurements of transient current or voltage in dye sensitized solar cells following an optical perturbation gives useful information about charge concentration, transport and recombination in the devices. The theory and practice of a wide range of these measurements illustrated with numerous examples in the report by Barnes, O'Regan, and co-workers in this issue. The use of cutting edge metrology accelerates improvements in devices. For example, the observation of phase separation and crystallization during the spin-coating process of the bulk heterojunction layer of an organic solar cell has now been demonstrated by Amassian and co-workers in this issue. In particular, the role of polymer crystallization in driving phase separation during film formation is evaluated. Understanding the photophysical processes that determine charge separation and polaron pair recombination in organic solar cells is critical to optimize free carrier formation and boost device efficiency. A copper phthalocyanine small-molecule-based system was studied by Monkman and co-workers and concluded that intersystem crossing is the rate-limiting step for polaron-pair recombination and is driven by spin-orbit coupling.

Segmented Flow Reactors for Nanocrystal Synthesis

In the past decade microreactors have emerged as a compelling technology for the highly controlled synthesis of colloidal nanocrystals, offering multiple advantages over conventional batch synthesis methods (including improved levels of control, reproducibility, and automation). Initial work in the field employed simple continuous phase reactors that manipulate miscible streams of a single reagent phase. Recently, however, there has been increasing interest in segmented flow reactors that use an immiscible fluid to divide the reagent phase into discrete slugs or droplets. Key advantages of segmented flow include the elimination of velocity dispersion (a significant cause of polydispersity) and greatly reduced susceptibility to reactor fouling. In this progress report we review the operation of segmented flow microreactors, their application to the controlled synthesis of nanocrystals, and some of the principal challenges that must be addressed before they can become a mainstream technology for the controlled production of nanomaterials.

Partial wetting gas–liquid segmented flow microreactor

A microfluidic reactor strategy for reducing plug-to-plug transport in gas-liquid segmented flow microfluidic reactors is presented. The segmented flow is generated in a wetting portion of the chip that transitions downstream to a partially wetting reaction channel that serves to disconnect the liquid plugs. The resulting residence time distributions show little dependence on channel length, and over 60% narrowing in residence time distribution as compared to an otherwise similar reactor. This partial wetting strategy mitigates a central limitation (plug-to-plug dispersion) while preserving the many attractive features of gas-liquid segmented flow reactors.