A monolithic and flexible fluoropolymer film microreactor for organic synthesis applications

A photocurable and viscous fluoropolymer with chemical stability is a highly desirable material for fabrication of microchemical devices. Lack of a reliable fabrication method, however, limits actual applications for organic reactions. Herein, we report fabrication of a monolithic and flexible fluoropolymer film microreactor and its use as a new microfluidic platform. The fabrication involves facile soft lithography techniques that enable partial curing of thin laminates, which can be readily bonded by conformal contact without any external forces. We demonstrate fabrication of various functional channels (similar to 300 mu m thick) such as those embedded with either a herringbone micromixer pattern or a droplet generator. Organic reactions under strongly acidic and basic conditions can be carried out in this film microreactor even at elevated temperature with excellent reproducibility. In particular, the transparent film microreactor with good deformability could be wrapped around a light-emitting lamp for close contact with the light source for efficient photochemical reactions with visible light, which demonstrates easy integration with optical components for functional miniaturized systems.open1112Ysciescopu

Design of LTCC-based Ceramic Structure for Chemical Microreactor

The design of ceramic chemical microreactor for the production of hydrogen needed in portable polymer-electrolyte membrane (PEM) fuel cells is presented. The microreactor was developed for the steam reforming of liquid fuels with water into hydrogen. The complex three-dimensional ceramic structure of the microreactor includes evaporator(s), mixer(s), reformer and combustor. Low-temperature co-fired ceramic (LTCC) technology was used to fabricate the ceramic structures with buried cavities and channels, and thick-film technology was used to make electrical heaters, temperature sensors and pressure sensors. The final 3D ceramic structure consists of 45 LTCC tapes. The dimensions of the structure are 75 × 41 × 9 mm3 and the weight is about 73 g

Photochemical synthesis of a “cage” compound in a microreactor: Rigorous comparison with a batch photoreactor

An intramolecular [2 + 2] photocycloaddition is performed in a microphotoreactor (0.81 mL) built by winding FEP tubing around a commercially available Pyrex immersion well in which a medium pressure mercury lamp is inserted. A rigorous comparison with a batch photoreactor (225 mL) is proposed by means of a simple model coupling the reaction kinetics with the mass, momentum and radiative transfer equations. This serves as a basis to explain why the chemical conversion and the irradiation time are respectively increased and reduced in the microphotoreactor relative to those in the batch photoreactor. Through this simple model reaction, some criteria for transposing photochemical synthesis from a batch photoreactor to a continuous microphotoreactor are defined

Design and optimization of electrochemical microreactors for continuous electrosynthesis

The study focuses on the design and construction, as well as the theoretical and experimental optimization of electrochemical filter press microreactors for the electrosynthesis of molecules with a high added value. The main characteristics of these devices are firstly a high-specific electrochemical area to increase conversion and selectivity, and secondly the shape and size of themicrochannels designed for a uniform residence time distribution of the fluid. A heat exchanger is integrated into the microstructured electrode to rapidly remove (or supply) the heat required in exo- or endothermic reactions. The microreactors designed are used to perform-specific electrosynthesis reactions such as thermodynamically unfavorable reactions (continuous NADH regeneration), or reactions with high enthalpy changes

Sonoluminescence and sonochemiluminescence from a microreactor

Micromachined pits on a substrate can be used to nucleate and stabilize microbubbles in a liquid exposed to an ultrasonic field. Under suitable conditions, the collapse of these bubbles can result in light emission (sonoluminescence, SL). Hydroxyl radicals (OH*) generated during bubble collapse can react with luminol to produce light (sonochemiluminescence, SCL). SL and SCL intensities were recorded for several regimes related to the pressure amplitude (low and high acoustic power levels) at a given ultrasonic frequency (200 kHz) for pure water, and aqueous luminol and propanol solutions. Various arrangements of pits were studied, with the number of pits ranging from no pits (comparable to a classic ultrasound reactor), to three-pits. Where there was more than one pit present, in the high pressure regime the ejected microbubbles combined into linear (two-pits) or triangular (three-pits) bubble clouds (streamers). In all situations where a pit was present on the substrate, the SL was intensified and increased with the number of pits at both low and high power levels. For imaging SL emitting regions, Argon (Ar) saturated water was used under similar conditions. SL emission from aqueous propanol solution (50 mM) provided evidence of transient bubble cavitation. Solutions containing 0.1 mM luminol were also used to demonstrate the radical production by attaining the SCL emission regions.Comment: http://www.sciencedirect.com/science/article/pii/S1350417712000855; ISSN 1350-417

Preparation of highly active phosphated TiO2 catalysts via continuous sol–gel synthesis in a microreactor

Microreactors, featuring μm-sized tubes, offer greater flexibility and precise control of chemical processes compared to conventional large-scale reactors, due to their elevated surface-to-volume ratio and modular construction. However, their application in catalyst production has been largely neglected. Herein, we present the development of a microreactor process for the one-step sol–gel preparation of phosphated TiO2 – a catalyst which has been recently demonstrated to be an eco-friendly material for the selective synthesis of the platform chemical 5-hydroxymethylfurfural (5-HMF) from bio-derived glucose. In order to establish catalyst preparation–property–performance relationships, 18 samples were prepared according to a D-optimal experimental plan with a central point. The key properties of these samples (porosity, crystallite size, mole bulk fraction of P) were correlated, using quadratic and interaction models, with the catalytic performance (conversion, selectivity, reaction rate) of 5-HMF synthesis as a test reaction. The optimal calculated catalyst features were set as target parameters to optimise catalyst synthesis applying quadratic correlation functions. An optimal catalyst was obtained, validating the models employed, with a yield of almost 100% and a space–time yield of ca. 3 orders of magnitude higher than that of a conventional batch process. The high yield could be mainly attributed to the optimal hydrolysis ratio and temperature. Controlling the TiO2 crystallite size and surface acidity in conjunction with fine-tuning of the porous properties in the microreactor led to increased glucose conversion, surface based formation rates of 5-HMF, and selectivity towards 5-HMF of the optimal catalyst in relation to the batch-prepared material

Online monitoring of vinyl chloride polymerization in a microreactor using raman spectroscopy

A novel capillary-based microfluidic device has been designed to follow the vinyl chloride polymerization reaction. The use of a co-flow generation system enabled obtaining monodisperse vinyl chloride droplets within 200 µm in diameter, each one being considered as a polymerization reactor. During polymerization VCM droplets were visualized with a high speed camera. At the end of the reaction PVC grains were observed with a Scanning Electron Microscopy technique. Real-time non-invasive Raman measurement has been performed on stationary vinyl chloride monomer droplets and has provided values of effective reaction orders n and effective rate constants k. This microdevice allowed the investigation in difficult conditions (pressure, temperature) with a minimal amount of reagents and consequently under safe conditions

Optimal design of multi-channel microreactor for uniform residence time distribution

Multi-channel microreactors can be used for various applications that require chemical or electrochemical reactions in either liquid, gaseous or multi phase. For an optimal control of the chemical reactions, one key parameter for the design of such microreactors is the residence time distribution of the fluid, which should be as uniform as possible in the series of microchannels that make up the core of the reactor. Based on simplifying assumptions, an analytical model is proposed for optimizing the design of the collecting and distributing channels which supply the series of rectangular microchannels of the reactor, in the case of liquid flows. The accuracy of this analytical approach is discussed after comparison with CFD simulations and hybrid analytical-CFD calculations that allow an improved refinement of the meshing in the most complex zones of the flow. The analytical model is then extended to the case of microchannels with other cross-sections (trapezoidal or circular segment) and to gaseous flows, in the continuum and slip flow regimes. In the latter case, the model is based on second-order slip flow boundary conditions, and takes into account the compressibility as well as the rarefaction of the gas flow

Accelerated gas-liquid visible light photoredox catalysis with continuous-flow photochemical microreactors

In this protocol, we describe the construction and use of an operationally simple photochemical microreactor for gas-liquid photoredox catalysis using visible light. The general procedure includes details on how to set up the microreactor appropriately with inlets for gaseous reagents and organic starting materials, and it includes examples of how to use it to achieve continuous-flow preparation of disulfides or trifluoromethylated heterocycles and thiols. The reported photomicroreactors are modular, inexpensive and can be prepared rapidly from commercially available parts within 1 h even by nonspecialists. Interestingly, typical reaction times of gas-liquid visible light photocatalytic reactions performed in microflow are lower (in the minute range) than comparable reactions performed as a batch process (in the hour range). This can be attributed to the improved irradiation efficiency of the reaction mixture and the enhanced gas-liquid mass transfer in the segmented gas-liquid flow regime