Fabrication Of Microreactor Research Articles

Fabrication of micro-reactors by a self-assembly of cationic surfactants to mediate NHPI/Co catalyzed selective aerobic oxidation of cumene to cumyl hydroperoxide

A highly efficient transformation from cumene to cumyl hydroperoxide (CHP) is pursued industrially. Herein, didodecyl dimethyl ammonium bromide (DDAB) as a phase transfer catalyst was found an outstanding role for aerobic oxidation of cumene to CHP with a conversion of 99.5 % and a selectivity of 83.5 % at near room temperature. The promotion can partially be attributed to the formation of the reversed multilamellar vesicles (MLVs) as micro-reactors via a self-assembly. The vesicles promoted the enrichments of cumene on the outer surface due to their outward hydrophobic chains (didodecyl), and enhanced the concentrations of NHPI and cobaltous ions in the MLVs malls for the inward head groups, leading to close contacts between the catalyst and the substrate and a highly efficient transformation from cumene to CHP. Cumyl, cumyl oxyl, cumyl peroxyl, methyl, phthalimide N-oxyl (PINO) radicals and dicumyl, dicumyl peroxide (DCP) were well confirmed, demonstrating an intact propagation chain of from cumene to CHP.

Superstructures of Zeolitic Imidazolate Frameworks to Single- and Multiatom Sites for Electrochemical Energy Conversion.

The exploration of electrocatalysts with high catalytic activity and long-term stability for electrochemical energy conversion is significant yet remains challenging. Zeolitic imidazolate framework (ZIF)-derived superstructures are a source of atomic-site-containing electrocatalysts. These atomic sites anchor the guest encapsulation and self-assembly of aspheric polyhedral particles produced using microreactor fabrication. This review provides an overview of ZIF-derived superstructures by highlighting some of the key structural types, such as open carbon cages, 1D superstructures, hollow structures, and the interconversion of superstructures. The fundamentals and representative structures are outlined to demonstrate the role of superstructures in the construction of materials with atomic sites, such as single- and dual-atom materials. Then, the roles of ZIF-derived single-atom sites for the electroreduction of CO2 and electrochemical synthesis of H2 O2 are discussed, and their electrochemical performance for energy conversion is outlined. Finally, the perspective on advancing single- and dual-atom electrode-based electrochemical processes with enhanced redox activity and a low-impedance charge-transfer pathway for cathodes is provided. The challenges associated with ZIF-derived superstructures for electrochemical energy conversion are discussed.

Anodic bonding of mid-infrared transparent germanate glasses for high pressure - high temperature microfluidic applications

ABSTRACT High pressure/high-temperature microreactors based on silicon-Pyrex® microfabrication technologies have attracted increasing interest in various applications providing optical access in high-pressure flow processes. However, they cannot be coupled to infrared spectroscopy due to the limited optical transparency (up to ~2.7 μm in the infrared region) of the Pyrex® glass substrate employed in the microreactor fabrication. To address this limitation, the alternative approach proposed in this work consists in replacing the Pyrex® glass in the microreactor by a mid-infrared transparent glass with thermal and mechanical properties as close as possible or even better to those of the Pyrex®, including its ability for silicon-wafers coupling by the anodic bonding process. Glasses based on germanate GeO2, known for their excellent transmission in the mid-infrared range and thermal/thermo-mechanical properties, have been thus evaluated and developed for this purpose. The optical, mechanical, thermal and electrical conductivity properties of adapted glass compositions belonging to five vitreous systems have been systemically investigated. The glass composition 70GeO2-15Al2O3-10La2O3-5Na2O (mol.%) was defined as the best candidate and produced in large plates of 50 mm diameter and 1 mm thickness. Anodic bonding tests with Si-wafers have been then successfully conducted, paving the way for the development of fully mid-infrared transparent silicon-glass microreactors.

Cost and Environmental Impact Assessment of Stainless Steel Microreactor Plates using Binder Jetting and Metal Injection Molding Processes

Modular chemical process intensification provides a platform for down-scaling chemical process equipment and reducing the number of chemical process steps through increased surface area-to-volume ratios and increased heat and mass transfer rates. In turn, these improvements reduce capital investment and operating costs, facility size, feedstock consumption, and emissions from chemical processing. However, conventional microreactor fabrication has employed inefficient material removal and bonding processes to create devices formed of layers of metal shim stock. This research investigates the relative costs and environmental impacts of metal additive manufacturing and powder metallurgy processes for making microreactor components for a range of market sizes. Binder jetting additive technology and metal injection molding were studied for producing two plates for a microscale chemical reactor used in dimethyl ether production. The manufacturing process design method was applied to quantify the cost of goods sold, and life cycle assessment was applied to model environmental impacts. The manufacturing process design analysis showed that metal injection molding would have better cost performance than binder jetting for a greenfield facility due to lower capital tooling cost and shorter cycle time in making the green part. However, the life cycle assessment indicated, at lower annual production volumes, metal injection molding would have higher cumulative energy demand, global warming potential, and other impacts due to the mold plates and solvent use. While this work reports on model development and a single use case, it motivates a focus on validating analysis results for a range of part sizes and geometries, as well as alternative production routes. This future work would provide design and manufacturing decision makers with richer information regarding process capabilities, production costs, and product environmental impacts for a range of product complexities.

Review—Through-Mask Electrochemical Micromachining

Through-mask electrochemical micromachining (TMEMM) is a versatile microfabrication technique, which combines anodic metal-shaping and -finishing steps in a single operation for the purpose of microstructuring a wide range of electrically conductive materials. It has been extensively utilized for the manufacture of precision-engineered components in microsystems, such as microlenses, microprobes, microactuators, microchannels and microvalves. This is because TMEMM is able to mass-produce parts; it is applicable to difficult-to-etch materials and operable under polishing conditions. This review provides an in-depth summary of the current state of TMEMM and presents key concepts relevant to its application. To this end, the interplay between the current distribution, mass-transfer effects and surface-film formation is discussed, and its effect on the machining rate, shape profile and surface finish is highlighted. Also, past incarnations of TMEMM are reviewed in terms of their masking method, substrate material, electrolyte composition and technical application. Techno-economic aspects of TMEMM are debated in relation to potential rival techniques, taking microreactor fabrication as an example for a novel area of application. This is followed by an overview of process variations and recent developments.

Catalytic microreactor with electrodeposited hierarchically nanostructured nickel coatings for gas-phase fluorination reactions

The fabrication of a catalytic microreactor for the reaction of undiluted carbonyl difluoride and elemental fluorine to synthesize trifluoromethyl hypofluorite, CF3OF, on CsF catalyst supported on F2-passivated nanosctructured Ni coating was studied. The nanosctructured Ni support for catalyst immobilization was electrodeposited by a two-step procedure, consisting of a low current density step followed by a brief high current density one, for a hierarchical differentiation of structural features. An aqueous solution of NiCl2 with diethanolamine, as crystal modifier, and sodium lauryl sulphate, as anti-pitting agent, was used as electrolyte. Constant-pH Ni electrocrystallization was performed on H2SO4-etched Cu substrates in a range of pH from 1 to 4 via a HCl/H3BO3 based buffer. Passivation was carried out under up to 300mbar of undiluted F2. XRD, XPS, SEM, AFM, and static contact angle measurements were performed. Ni coatings obtained from pH 3 electrolytes were selected for microreactor fabrication on the basis of characterization data, due to the reproducibility and homogeneity of the structured Ni layers. The catalytic microreactor allowed the quantitative production of CF3OF from pure reactants, on demand, and removing any criticality relative to thermal and safety control of the synthesis. The CF3O-group selective transfer ability of the synthetized hypofluorite has raised interest in pharmaceutical and agrochemical industries in recent years.

Recent Advances in Fabrication of Photocatalytic Micro-Reactor

Microfluidic technology has been increasingly applied in field of photo catalytic reactor because of the large surface to volume ratio, shorter diffusion distance of the reactant solution, higher mixing efficiency and lower cost. This article reviews the detail progress in fabrication of micro-reactor for degradation of dye in waste water. Importantly, dye degradation required uniform UV light exposure which could be resolved by carrying out degradation in a micro-reactor. This paper discussed several of potential and commercial photocatalytic micro-reactor fabrication and configurations, in particular, the polydimethyl siloxane (PDMS) photocatalytic reactors.

Electroless plating of ultrathin palladium films: self-initiated deposition and application in microreactor fabrication

We present new electroless palladium plating reactions, which can be applied to complex-shaped substrates and lead to homogeneous, dense and conformal palladium films consisting of small nanoparticles. Notably, autocatalytic and surface-selective metal deposition could be achieved on a wide range of materials without sensitization and activation pretreatments. This provides a facile and competitive route to directly deposit well-defined palladium nanofilms on e.g. carbon, paper, polymers or glass substrates. The reactions proceed at mild conditions and are based on easily accessible chemicals (reducing agent: hydrazine; metal source: PdCl2; ligands: ethylenediaminetetraacetic acid (EDTA), acetylacetone). Additionally, the water-soluble capping agent 4-dimethylaminopyridine (DMAP) is employed to increase the bath stability, to ensure the formation of small particles and to improve the film conformity. The great potential of the outlined reactions for micro- and nanofabrication is demonstrated by coating an ion-track etched polycarbonate membrane with a uniform Pd film of approximately 20 nm thickness. The as-prepared membrane is then employed as a highly miniaturized flow reactor, using the reduction of 4-nitrophenol with NaBH4 as a model reaction.

Gas Sensors Based on Locally Heated Multiwall Carbon Nanotubes Decorated with Metal Nanoparticles

We report the design and fabrication of microreactors and sensors based on metal nanoparticle-decorated carbon nanotubes. Titanium adhesion layers and gold films were sputtered onto Si/SiO2substrates for obtaining the electrical contacts. The gold layers were electrochemically thickened until 1 μm and the electrodes were patterned using photolithography and wet chemical etching. Before the dielectrophoretic deposition of the nanotubes, a gap 1 μm wide and 5 μm deep was milled in the middle of the metallic line by focused ion beam, allowing the fabrication of sensors based on suspended nanotubes bridging the electrodes. Subsequently, the sputtering technique was used for decorating the nanotubes with metallic nanoparticles. In order to test the as-obtained sensors, microreactors (100 μL volume) were machined from a single Kovar piece, being equipped with electrical connections and 1/4′′ Swagelok-compatible gas inlet and outlets for controlling the atmosphere in the testing chamber. The sensors, electrically connected to the contact pins by wire-bonding, were tested in the 10−5to 10−2 W working power interval using oxygen as target gas. The small chamber volume allowed the measurement of fast characteristic times (response/recovery), with the sensors showing good sensitivity.

Design, fabrication and analysis of stagnation flow microreactors used to study hypergolic reactions.

A novel method to study the condensed phase reactions that occur during the ignition of hypergolic propellants (very fast liquid reactions) using microreactors is presented. Planar counterflow microreactors are used to isolate liquid-phase reactions and diffusion from secondary gas-phase chemical and transport processes that often occur concurrently during the overall ignition process. The counterflow microreactor has made it possible to achieve valuable insight into the preignition mechanisms of hypergolic propellants hitherto not possible using conventional drop or impinging jet tests. In the present paper, the microreactor fabrication, flow field characterization, and reactivity of 2-dimethylaminoethylazide and nitric acid as hypergols are presented. Particle image velocimetry and numerical simulations were conducted to characterize the laminar velocity flow-field from which stagnation point strain rates and contact residence times along the centerline of the microreactor were evaluated. Temperature measurements at the exit of the reactor (as well as at the stagnation point) were used as a measure for the extent of the reaction or the heat released from the reaction. For the hypergols, an increase in reactant flow (or equivalently strain rate at the stagnation point) was found to initially increase reactivity, but eventually resulted in a decrease in temperature, revealing a maxima in temperature and reactivity. The trends indicated a reaction that was initially diffusion or heat loss controlled, which transitioned towards kinetic control at higher strain (flow) rates. This paper details the first comprehensive measurements and analysis of the effects of diffusion based mixing on the interfacial reactions occurring between hypergols.

Facile immobilization of enzyme by entrapment using a plasma-deposited organosilicon thin film

Over the years, immobilization of biologically active species such as enzymes onto solid support gave rise to a wide range of analytical and industrial applications. The development of fast, simple and efficient immobilization strategies is becoming of great importance in specific Biological Micro-Electromechanical Systems (BioMEMS) manufacturing. Thus, the current work focuses on an original methodology and mild procedure for β-galactosidase immobilization. Using as support either silicon or a thin film obtained from polymerization of 1,1,3,3-tetramethyldisiloxane (ppTMDSO) deposited by Plasma Enhanced Chemical Vapor Deposition in afterglow mode, the strategy developed here consisted in adsorption of β-galactosidase followed by its overcoating by the same siloxane plasma polymer. After sample washing, the enzymes were characterized to be efficiently entrapped within the porous polymer matrix while allowing the penetration and hydrolysis of the synthetic substrate ortho-nitrophenyl-β-d-galactopyranoside (o-NPG) with stability over at least 8 assays. The entrapment procedure allowed obtaining bio-functionnal coatings where β-galactosidase was expected to be included in the plasma-polymerized films while preserving its native structure and its activity. This latter was modulated by mass transfer limitations of the substrate according to the thickness of the ppTMDSO coatings. The dry-process-based-preparation of such a thin bio-functional film (from ∼200nm to ∼650nm) is fast and compatible with biochip or microreactor fabrication processes while avoiding the use of lot of chemicals and multi-step treatments commonly encountered in enzyme immobilization procedures.

Surface cell immobilization within perfluoroalkoxy microchannels

Perfluoroalkoxy (PFA) is one of the most promising materials for the fabrication of cheap, solvent resistant and reusable microfluidic chips, which have been recently recognized as effective tools for biocatalytic process development. The application of biocatalysts significantly depends on efficient immobilization of enzymes or cells within the reactor enabling long-term biocatalyst use. Functionalization of PFA microchannels by 3-aminopropyltriethoxysilane (ATPES) and glutaraldehyde was used for rapid preparation of microbioreactors with surface-immobilized cells. X-ray photoelectron spectroscopy and scanning electron microscopy were used to accurately monitor individual treatment steps and to select conditions for cell immobilization. The optimized protocol for Saccharomyces cerevisiae immobilization on PFA microchannel walls comprised ethanol surface pretreatment, 4h contacting with 10% APTES aqueous solution, 10min treatment with 1% glutaraldehyde and 20min contacting with cells in deionized water. The same protocol enabled also immobilization of Escherichia coli, Pseudomonas putida and Bacillus subtilis cells on PFA surface in high densities. Furthermore, the developed procedure has been proved to be very efficient also for surface immobilization of tested cells on other materials that are used for microreactor fabrication, including glass, polystyrene, poly (methyl methacrylate), polycarbonate, and two olefin-based polymers, namely Zeonor® and Topas®.

Surface modification of low and high temperature co-fired ceramics for enzymatic microreactor fabrication

In this work, immobilization of enzyme (urease) on substrates made of low temperature co-fired ceramics (LTCC) and high temperature co-fired ceramics (HTCC) is presented. The research was performed for three various LTCCs (DP951, CeramTec GC, HL2000) and one HTCC (ESL 44000) material system. Investigated ceramic materials were characterized using energy dispersive spectroscopy (EDS) and contact angle measurements. Immobilization method based on APTS (3-aminopropyltriethoxysilane) and glutaraldehyde is proposed for LTCC and HTCC surface modification. Effectiveness of the applied immobilization procedure was examined using Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR) technique. Changes in surface composition of the LTCC and HTCC-based test structures are examined after each step of the immobilization process. On the basis of performed experiments one ceramic material system was chosen for fabrication of the enzymatic microreactor. Performance of the ceramic microreactor with immobilized urease was examined experimentally, as well.

Design, fabrication and characterization of microreactors for high temperature syntheses

Microfluidic reactors offer many potential advantages in several research and industrial fields such as processes intensification, which includes a better reaction control (kinetics and thermodynamics), a high throughput and a safer operational environment (reduced manipulation of dangerous reagents and low sub-products generation). Nevertheless, scaling-down limitations appear concerning the materials used in the fabrication of microreactors for most of the liquid-phase reactions, since they usually require high temperatures (up to 300°C), solvents and organic reagents. In this work, the development of a set of modular and monolithic microreactors based on the integration of microfluidics and a thermal platform (sensor/high-temperature heater) is proposed to perform high temperature reactions. The reliability and performance of both configurations were evaluated through an exhaustive characterization process regarding their thermal and microfluidic performance. Obtained results make the devices viable for their application in controlled and reproducible synthetic processes occurring at high temperatures such as the synthesis of quantum dots. The proposed microfluidic approach emerge as an engaging tool for processes intensification, since it provides better mass and temperature transfer than conventional methods with a reduction not only of the size and energy consumption, but also of by-products and reagents consumption.

Micro-Reactors for Testing Sensor Devices Based on Suspended Carbon Nanotubes

In this work, we report the fabrication of micro-reactors for the characterization of nano-sensors based on suspended nanoparticle-decorated carbon nanotubes (CNTs/NPs). The capsules were fabricated from a single Kovar® piece, having a small volume chamber (100µl). Gold thin films were sputtered onto Si/SiO2 substrates and the electrodes were patterned using electrochemical deposition, photolithography and wet chemical corrosion. In order to obtain devices based on suspended nanotubes, prior to CNTs deposition, a 1µm wide and 5µm deep gap was milled in the substrate by focused ion beam (FIB). The dielectrophoresis (DEP) technique was used for the deposition of the suspended CNTs over the as obtained patterned electrodes. The sensors were tested using oxygen and nitrogen atmospheres, in the pressure range between 10-5 and 10-1mbar. The small chamber volume allowed the measurement of fast sensor characteristic times, with the sensors showing good sensitivity towards gas and pressure as well as high reproducibility.

Design and Packaging of Microreactors for High Pressure and High Temperature Applications

The development of chemically compatible microsystems that can operate across expanded process conditions, such as high pressures (HP) and high temperatures (HT), is of great interest for many applications, including high pressure chemistry and hydrothermal and supercritical fluid processes. We present a methodology for the successful design and use of HP/HT microsystems. Key parameters for the fabrication of microreactors and modular fluidic packaging able to withstand severe pressure and temperature conditions (30 MPa, 400 °C) are described. Applications of these HP/HT plug and play microsystems are illustrated with examples, including multiphase flow visualization through the transition of liquid−liquid immiscible hexane−water segmented flow to homogeneous supercritical flow, on chip supercritical water oxidation, and synthesis of iron oxide nanoparticles.

DEVELOPMENT IN MICROREACTOR TECHNOLOGY FOR NANOPARTICLE SYNTHESIS

Microreactor technology is a new concept of chemical synthesis for nanoparticle production. The "state of the art" in microreactor fabrication and its application to the synthesis of nanoparticles is reviewed. The microfluidic concepts, the materials and technologies for microreactor manufacture, with particular emphasis on polymers and microreplication techniques, and their application to the synthesis of various nanomaterials in microreactors are presented. The unique synthesis properties of various nanoparticles using a microfluidic process as well as broader impact in term of nanomaterials engineering, i.e., selectivity and monodispersity, reduced amount of chemicals, fast reaction, minimum cost, a better control of the process, minimum waste and reduced amounts of reaction byproducts and improved safety, are discussed in comparison with the traditional wet-chemical batch synthesis approach.

Fabrication of Microreactor Using Glass Capillary with Cu/SiO2 Layer

Abstract A catalytic reactor using a capillary column with Cu/SiO2 layer on its inner surface was prepared by injecting a silica sol containing Cu ions in a fused silica capillary and by subsequent gelation under the conditions controlled in order to deposit silica gel uniformly on the inner wall of the capillary. Its catalytic activity was demonstrated in the hydrogenation of propene by constructing a pulse reactor using the catalyst capillary and a separation capillary with pure silica gel layer.

Application Report on Operating Cellular Process Chemistry Plants in Fine Chemical and Contract Manufacturing Industries

AbstractOnly a few microreaction manufacturing plants are being operated to date. The performance of two different microreaction manufacturing plants is discussed, one in a dedicated application, the other in a multi‐purpose environment. Strategies to address the major design and operating challenges for microreactor manufacturing plants to equipartition starting material streams into parallel reaction chambers throughout manufacturing operation are provided for demanding liquid/liquid‐reactions. The importance of minimizing the pressure drop variances between different microreactors or channels by rigorous microreactor fabrication process control is described. A cost/performance balanced microreactor manufacturing strategy is suggested, and the ease of assessing trade‐off decisions is addressed for different manufacturing systems by the use of a case study involving a diffusion controlled Grignard reaction.

Porous anodic alumina microreactors for production of hydrogen from ammonia

AbstractThe synthesis and properties are described of a ruthenium‐impregnated anodic aluminum catalyst for use in microreactors for the production of hydrogen from an ammonia feed. The catalyst structure was synthesized using microelectric discharge machining to create a series of 300 × 300‐μm posts on an aluminum substrate. The posts were anodized to yield a 60‐μm covering of anodic alumina, with an average surface area of 16 m2/gm and an average pore size of 50 nm. Ruthenium metal was dispersed on the alumina using conventional wet impregnation. A 0.9 × 0.9‐cm reactor containing 250 posts decomposed 95% of anhydrous ammonia at 650°C to yield 15 sccm of hydrogen. A possible application of these microreactor fabrication methods is hydrogen generation for fuel cells in mobile power production. 2004 American Institute of Chemical Engineers AIChE J, 50:829–834, 2004