Planar Reactor Research Articles

On-demand in situ generation of oxygen in a nanofluidic embedded planar microband electrochemical reactor.

In situ generation of reagents and their subsequent use downstream presents new opportunities to amplify the utility of nanofluidic devices by exploiting the confined geometry to address mass transport limitations on reaction kinetics and efficiency. Oxygen, an inherently valuable reactant, can be produced from electrolysis of water, a process that can be conveniently integrated within a nanofluidic system. Here, we construct and characterize a nanofluidic device consisting of a planar microband electrode embedded within a nanochannel for in situ electrochemical generation and optical monitoring of O2. Fluorescein, a dye with a pH-sensitive emission intensity, was used to monitor the spatiotemporal characteristics of the oxidation of H2O, using the co-produced H+. Application of anodic potentials at the nanochannel-embedded electrode results in a decrease in fluorescence intensity, which reflects the decreasing solution pH. A combination of fluorescence intensity and chronoamperometric response was used to quantitatively determine proton generation, and the H+/O2 stoichiometry was then used to determine the concentration of the O2 in the channel. Comparison of the experimental results to finite element simulations validates the use of fluorescein emission intensity to spectroscopically determine the local oxygen concentration in the nanochannel. By varying the applied potential, spatially averaged O2 concentrations ranging from 0.13 to 0.41 mM were generated. The results demonstrate a convenient route to in situ modulation of the dissolved O2 level in a nanofluidic device and the use of an optical probe to monitor its spatial and temporal distribution under flow conditions.

Kinetic Modeling of VOC Photocatalytic Degradation Using a Process at Different Reactor Configurations and Scales

Abstract This work investigated the performance of isovaleraldehyde (3-methylbutanal) removal from gas streams in photocatalytic reactors at room temperature. The feasibility of pollutant removal using the up-scaled reactor was systematically assessed by monitoring the removal efficiency at different operational parameters, such as geometries of reactor, air flow rate and inlet concentration. A proposal modeling for scaling up the photocatalytic reactors is described and detailed in this present study. In this context, the photocatalytic degradation of isovaleraldehyde (Isoval) in gas phase is studied. In fact, the removal rate has been compared at different continuous flow reactors: a photocatalytic tangential reactor (PTR), planar reactor and P5000 pilot. The effects of the inlet concentration, flow rate, geometries and size of reactors on the removal efficiency are also studied. A kinetic model taking into account the mass transfer step is developed. The modeling is done by introducing an equivalent intermediate (EI) formed by the photo-oxidation of Isoval. This new approach has substantially improved the agreement between modeling and experiments with a satisfactory overall description of the mineralization from lab to pilot scales.

Treatment of gaseous effluents by using surface discharge plasma in continuous reactors: Process modelling and simulation

In the present work, the oxidation of isovaleraldehyde, a typical pollutant of indoor air, is investigated by using two different plasma DBD reactors: cylindrical and planar reactor. The study of the influence of the specific energy shows that its increment is accompanied by an increase of the removal efficiency. In fact, when specific energy extends three times, the removal efficiency is increased from 5 to 40 %. Moreover an increase of the specific energy induces a higher mineralization due to byproducts oxidation with reactive species production. The same behaviour is observed with ozone production. A generic mathematical model is developed to represent the experimental results obtained. This model is based on several mass transfer steps occurring in series between bulk and plasma phases. The degradation reaction mechanism is supposed to occur on two steps. Firstly, isovaleraldehyde leads to the formation of a fictitious equivalent intermediate (EI). In a second step, EI is transformed into CO and CO2. This approach gives a good agreement between modelling and experiments with a satisfactory overall description of byproducts formation. This original approach allows for the simulation of plasma oxidation kinetics process without knowing the complete chemical pathway.

Microfluidic reactors for visible-light photocatalytic water purification assisted with thermolysis.

Photocatalytic water purification using visible light is under intense research in the hope to use sunlight efficiently, but the conventional bulk reactors are slow and complicated. This paper presents an integrated microfluidic planar reactor for visible-light photocatalysis with the merits of fine flow control, short reaction time, small sample volume, and long photocatalyst durability. One additional feature is that it enables one to use both the light and the heat energy of the light source simultaneously. The reactor consists of a BiVO4-coated glass as the substrate, a blank glass slide as the cover, and a UV-curable adhesive layer as the spacer and sealant. A blue light emitting diode panel (footprint 10 mm × 10 mm) is mounted on the microreactor to provide uniform irradiation over the whole reactor chamber, ensuring optimal utilization of the photons and easy adjustments of the light intensity and the reaction temperature. This microreactor may provide a versatile platform for studying the photocatalysis under combined conditions such as different temperatures, different light intensities, and different flow rates. Moreover, the microreactor demonstrates significant photodegradation with a reaction time of about 10 s, much shorter than typically a few hours using the bulk reactors, showing its potential as a rapid kit for characterization of photocatalyst performance.

Abatement of 3-methylbutanal and trimethylamine with combined plasma and photocatalysis in a continuous planar reactor

This paper deals with the 3-methylbutanal ((CH3)2CHCH2COH) removal with the help of a nonthermal surface plasma discharge coupled with photocatalysis. The capability of this process for gas treatment was studied. A planar reactor system was developed in order to perform the effect of adding photocatalytic material in plasma surface discharge barrier dielectric (SDBD) zone on (i) 3-methylbutanal removal, (ii) selectivity of CO2 and CO, (iii) byproducts formation such ozone formation. It was found that the influence of the UV light generated by SDBD reactor was very low. The activation of the photocatalyst media could be negligible. Whereas, the introduction of external UV light to the process improves significantly the removal efficiency of 3-methylbutanal (3MBA) and the mineralization. A synergetic effect was observed by combining plasma SDBD and photocatalysis from all experiments and with other pollutant such as trimethylamine (N(CH3)3). Moreover, the byproducts of 3MBA were identified and evaluated with plasma SDBD, photocatalysis and plasma SDBD/photocatalysis combination.

Isovaleraldehyde elimination by UV/TiO2 photocatalysis: comparative study of the process at different reactors configurations and scales

A proposal for scaling-up the photocatalytic reactors is described and applied to the coated catalytic walls with a thin layer of titanium dioxide under the near ultraviolet (UV) irradiation. In this context, the photocatalytic degradation of isovaleraldehyde in gas phase is studied. In fact, the removal capacity is compared at different continuous reactors: a photocatalytic cylindrical reactor, planar reactor, and pilot unit. Results show that laboratory results can be useful for reactor design and scale-up. The flowrate increases lead to the removal capacity increases also. For example, with pilot unit, when flowrate extends four times, the degradation rate varies from 0.14 to 0.38 g h(-1) mcat (-2). The influence of UV intensity is also studied. When this parameter increases, both degradation rate and overall mineralization are enhanced. Moreover, the effects of inlet concentration, flowrate, geometries, and size of reactors on the removal capacity are also studied.

Activity of the ZnO–Fe2O3 catalyst on the degradation of Dicamba and 2,4-D herbicides using simulated solar light

In this study, the solar photocatalytic activity of ZnO–Fe2O3 coupled oxide was investigated for the degradation of commercial Dicamba and 2,4-D herbicides. Both pesticides, which are extensively used in agriculture, are active ingredients in water-soluble commercial formulations called Fortune® (480g/L 3,6-dichloro-2-methoxybenzoic acid, Dicamba) and Hierbamina® (479.5g/L 2,4-dichlorophenoxyacetic acid, 2,4-D). The catalyst was synthesized via the sol–gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), and Raman spectroscopy. UV-vis diffuse reflectance spectroscopy (DRS) was used to estimate the band gap energy (Eg) of the prepared material. Photocatalytic tests were conducted in a planar reactor operated in batch-mode using a solar light simulator. Complete degradation of both herbicides was attained for a 10mg/L initial concentration after 300min using 0.5g/L of catalyst loading. Oxalic, formic, and acetic acids were the byproducts identified during the degradation of both herbicides. Dechlorination after photocatalytic decomposition was complete for Dicamba. However, only 70% dehalogenation was attained for 2,4-D under simulated solar light.

Modeling of a continuous photocatalytic reactor for isovaleraldehyde oxidation: Effect of different operating parameters and chemical degradation pathway

An investigation of isovaleraldehyde (ISOV) photocatalytic oxidation was conducted at initial concentrations ranging from 25 to 150mg/m3 and different relative humidities (5–90% RH) in order to characterize the process performances close to indoor air conditions. Experiments were carried out in two different reactors: cylinder and flat-plate photoreactor (planar reactor) at different air gap (20–60mm) and gas residence times (0.67–5.0s). A plug flow reactor system was developed in order to perform kinetic studies of (i) isovaleraldehyde removal, (ii) selectivity of CO2, (iii) by-products formation and removal. It appears that ISOV removal efficiencies increased with lower inlet concentrations, lower air gap and higher gas residence times.In small amounts, the presence of water vapor has a promoting effect on the degradation due to the formation of OH radicals.Evaluating different kinetic models by least squares analysis, it was shown that the Langmuir-Hinshelwood (L-H) model could give a good correlation with the experimental results. Thus, the effect of ISOV gas-phase concentration, air gap and light intensity on chemical conversion rates is discussed.A kinetic model based on Langmuir-Hinshelwood (L-H) approach and taking into account the mass transfer step was developed. This allows us to determine L-H constants regardless of the transfer aspect. This last is estimated by semi-empirical correlation. The separation between the mass transfer and the chemical reaction steps is obtained. The effect of UV light intensity is also considered.

On the application of cw external cavity quantum cascade infrared lasers for plasma diagnostics

Three continuous wave external cavity quantum cascade lasers (EC-QCLs) operating between 1305 and 2260 cm−1 (4.42–7.66 µm) have been tested as radiation sources for an absorption spectrometer focused on the analysis of physical and chemical phenomena in molecular plasmas. Based on the wide spectral tunability of EC-QCLs, multiple species detection has become feasible and is demonstrated in a study of low-pressure Ar/N2 microwave plasmas containing methane as a hydrocarbon precursor. Using the direct absorption technique, the evolution of the concentrations of CH4, C2H2, HCN and H2O has been monitored depending on the discharge conditions at a pressure of p = 0.5 mbar and at a frequency of f = 2.45 GHz in a planar microwave plasma reactor. The concentrations were found to be in the range of 1011–1014 molecules cm−3. In addition, based on the analysis of the line profile of selected absorption lines, the gas temperature Tg has been calculated in dependence on the discharge power. Tg increased with the power values and was in the range between 400 and 700 K. Further, in a pure He/Ar microwave plasma, the wavelength modulation spectroscopy technique has been applied for the sensitive detection of transient plasma species with absorbencies down to 10−5. The typical spectral line width of an EC-QCL under the study was found to be in the range 24 to 38 MHz depending (i) on the chopping technique used and (ii) on a single or averaged measurement approach. Further, different methods for the modulation and tuning of the laser radiation have been tested. Varying the power values of an EC-QCL between 0.1 and 154 mW for direct absorption measurements under low pressure conditions, no saturation effects in determining the concentrations of methane, acetylene and carbon monoxide could be found under the experimental conditions used, i.e. for lines with line strengths between 10−19 and 10−22 cm molecule−1.

Synergistic effect of the combination of immobilized TiO2, UVA and ozone on the decomposition of dichloroacetic acid

The performance of a heterogeneous photocatalytic ozonation system (TiO2/UVA/O3) was evaluated on the degradation and mineralization of dichloroacetic acid as a contaminant in aqueous solutions by means of a planar reactor. The commercial product “Pilkington ActiveTM glass” was used as the immobilized TiO2 photocatalyst and it was irradiated by near UV light in this study. The synergistic interaction between ozone and the photoactivated TiO2 surface was discussed and highlighted. Furthermore, the influences of initial concentration and temperature on the degradation rate of dichloroacetic acid and the ozone consumption level during the oxidation process were investigated. The concentrations of dichloroacetic acid and chloride anions produced during degradation were measured using ion chromatography. The mineralization of dichloroacetic acid was evaluated by Total Organic Carbon (TOC) measurements. The degradation of dichloroacetic acid by photocatalytic ozonation showed good agreement with the kinetics of first-order reactions with respect to dichloroacetic acid.

Catalysts for the conversion of hydrocarbon and synthetic fuels for onboard syngas generators

The use of syngas derived on board a vehicle as a supplement to the main fuel fed to engines ensures engine operation using dilute fuel mixtures. This leads to a decrease in emission toxicity and an increase in the fuel efficiency of the engine. The preparation of new types of efficient catalysts for the conversion of hydrocarbon and synthetic fuels for onboard syngas generators requires the use of new approaches to the design of catalysts not only as catalytically active material, but also as a structural component of a chemical reactor. We prepared and tested a set of catalysts for the conversion of hydrocarbons, i.e., natural gas, diesel and biodiesel fuels, biofuels, and alcohols (ethanol, methanol) to syngas. Primary supports for the catalysts were metals grids and porous tapes; secondary supports were oxides of aluminum and magnesium deposited on or sintered to a primary support. The catalysts exhibited high thermal stability and mechanical strength, and were characterized by the conformity of the coefficients of thermal expansion of the support material and the catalytically active bed. The catalysts can be used as structural components of reactors and as a basis for the preparation of monolithic blocks and planar components of radial and planar reactors. The developed catalysts were subjected to laboratory and bench tests and examined as components of onboard generators of vehicles.

Photocatalytic Microreactor Using Monochromatic Visible Light

A photocatalytic planar reactor with an immobilized nanoporous BiVO4 film has been integrated with a blue-light panel LED, which acts as the light source. The microreactor utilizes two BiVO4-coated glasses as the top and the bottom layer and a UV curable resin layer as the spacer. The UV spacer is patterned with tree-shaped microchannels and a reaction chamber (10 ´ 10 ´ 0.1 mm3). It was found that under blue light of 140 mW/cm2 (the LED is powered at 11 V, 402 nm ) and the flow rate of 37.5 µl/min, the microreactor has the optimum performance with a degradation rate of about 3%/s and a photonic utilization efficiency ³ 0.02%. However, the photonic efficiency can be improved to 0.3% when LED is powered at 9 V.

Optofluidic planar reactors for photocatalytic water treatment using solar energy

Optofluidics may hold the key to greater success of photocatalytic water treatment. This is evidenced by our findings in this paper that the planar microfluidic reactor can overcome the limitations of mass transfer and photon transfer in the previous photocatalytic reactors and improve the photoreaction efficiency by more than 100 times. The microreactor has a planar chamber (5 cm×1.8 cm×100 μm) enclosed by two TiO(2)-coated glass slides as the top cover and bottom substrate and a microstructured UV-cured NOA81 layer as the sealant and flow input∕output. In experiment, the microreactor achieves 30% degradation of 3 ml 3×10(-5)M methylene blue within 5 min and shows a reaction rate constant two orders higher than the bulk reactor. Under optimized conditions, a reaction rate of 8% s(-1) is achieved under solar irradiation. The average apparent quantum efficiency is found to be only 0.25%, but the effective apparent quantum efficiency reaches as high as 25%. Optofluidic reactors inherit the merits of microfluidics, such as large surface∕volume ratio, easy flow control, and rapid fabrication and offer a promising prospect for large-volume photocatalytic water treatment.

Performance and economics of a Pd-based planar WGS membrane reactor for coal gasification

Conceptual 300 tonne per day (tpd) H 2-from-coal plants have been the subject of several major costing exercises in the past decade. Incorporating conventional high- and low-temperature water-gas-shift (WGS) reactors, amine-based CO 2 removal and PSA-based H 2 purification systems, these studies provide a benchmark against which alternative H 2-from-coal technologies can be compared. The catalytic membrane reactor (CMR), combining a WGS catalyst and hydrogen-selective metal membrane, can potentially replace the multiple shift and separation stages of a plant based on conventional technology. CMR-based shift and separation offers several major advantages over the conventional approach, including greater-than-equilibrium WGS conversion, the containment of the CO 2 at high-pressure and a reduction in the number of unit processes. To determine capital costs of a WGS CMR-based H 2-from-coal plant, a prototype planar CMR was constructed and tested with varying catalyst bed depth, residence time and membrane type (commercially-sourced 50 μm Pd or 40 μm Pd-25Ag wt%). Experiments to measure CO conversion, and H 2 flux and yield were conducted at 400 °C with a feed pressure of 20 bar H 2O:C ratio of 3 and a H 2 product pressure of 1 bar. Under the optimum conditions examined (with a 40 μm-thick Pd-25Ag membrane and <3 mm-thick catalyst bed), a membrane surface area of ∼25,000 m 2 would be required to provide a throughput of 300 tpd with 85% H 2 yield. The capital cost of the CMR component of the plant would be around $US 180 million (based on current metal prices), of which 73% can be attributed to the cost of the Pd–Ag alloy membranes. Incorporation of a membrane that meets the 2015 US DOE cost and flux targets would offer cost parity, with a plant cost of $US 44 million and a total membrane area of ∼13,000 m 2. Meeting these performance and cost targets would likely require a shift to very thin Pd-alloy membranes or highly-permeable Group IV, V body-centred-cubic alloys.

３次元立体アルミニウムマスクを用いた石英ガラスの反応性イオンエッチング加工

Three-dimensional microfabrication is an important process for fabricating microelectromechanical systems (MEMS) and optics. This paper describes reactive ion etching of quartz glass using three-dimensional aluminum masks. Aluminum masks were fabricated using photolithography, anodization, and chemical etching, with the mask shape controlled by anodization and chemical etching conditions. By changing the photoresist mask patterns, quadrangular pyramids and cones were fabricated on quartz substrates using the aluminum masks. Etching characteristics of quartz substrates were developed using CHF3 gas in a planar type plasma reactor. When the process pressure was increased, the etching rate of quartz increased and that of aluminum mask decreased. Based on these results, we increased the selectivity of the quartz/aluminum mask from 10 to 37 by adjusting the pressure. Quadrangular pyramids and cones were fabricated on quartz substrates using this method, which was demonstrated as effective for fabrication of three-dimensional microstructures on quartz substrates.

A Microfluidic Approach to the Rapid Screening of Palladium‐Catalysed Aminocarbonylation Reactions

AbstractThe evaluation and selection of the most appropriate catalyst for a chemical transformation is an important process in many areas of synthetic chemistry. Conventional catalyst screening involving batch reactor systems can be both time‐consuming and expensive, resulting in a large number of individual chemical reactions. Continuous flow microfluidic reactors are increasingly viewed as a powerful alternative format for reacting and processing larger numbers of small‐scale reactions in a rapid, more controlled and safer fashion. In this study we demonstrate the use of a planar glass microfluidic reactor for performing the three‐component palladium‐catalysed aminocarbonylation reaction of iodobenzene, benzylamine and carbon monoxide to form N‐benzylbenzamide, and screen a series of palladium catalysts over a range of temperatures. N‐Benzylbenzamide product yields for this reaction were found to be highly dependent on the nature of the catalyst and reaction temperature. The majority of catalysts gave good to high yields under typical flow conditions at high temperatures (150 °C), however the palladium(II) chloride‐Xantphos complex [PdCl2(Xantphos)] proved to be far superior as a catalyst at lower temperatures (75–120 °C). The utilised method was found to be an efficent and reliable way for screening a large number of palladium‐catalysed carbonylation reactions and may prove useful in screening other gas/liquid phase reactions.

Electrochemical reduction of CO and H 2 from carbon dioxide in aqua-solution

This study examined the characteristics of continuous operation in a continuous flow planar electrode reactor, such as Faradaic efficiency, selectivity, and products ratio of carbon dioxide. A silver electrode was found to be useful for the selective formation of carbon monoxide by the electrochemical reduction of carbon dioxide in aqueous electrolytes. The products (CO, H 2) were analyzed by gas chromatography, which was equipped with a thermal conductivity detector (TCD), and the Faradaic efficiency and selectivity were calculated from the data. The yield of monoxide carbon increased with decreasing temperature but the hydrogen yield decreased. The carbon monoxide yield was higher at the lower range of electrolyte concentrations. A graph of the yield as a function of the electrode potential showed a negative parabolic curve. The maximum value is shown at −1.8 V vs. SCE. The optimized carbon monoxide to hydrogen ratio was obtained under the following conditions using a silver electrode: a 0.1 M KHCO 3 electrolyte, 20 °C and a potential of −1.8 V vs. SCE.

Characteristics of dielectric barrier discharge reactor for material treatment

This work reports the development of atmospheric pressure plasma reactor with dielectric barrier discharge DBD for material treatment. The DBD discharge has been generated in planar geometry reactor powered by ac voltage provided by conventional high voltage transformer. The dielectric barrier consisted of two glass slabs, which cover both reactor electrodes. The air discharge gap between the dielectric layers was varied from 1.0 to 3.0mm. The power consumption of the DBD reactor was evaluated by the Lissajous figures method. The optimization of reactor geometry for material processing is discussed.

On the destruction of volatile organic compounds using a dielectric pellet bed reactor

Volatile organic compounds (VOC) are known to be dangerous for human health. If they are part of a precursor gas mixture undesired effects in e.g. industrial processes may occur. Therefore, the destruction of unwanted VOCs in a gas stream is an important aim. For that purpose a five stage planar dielectric barrier discharge reactor working at atmospheric pressure has been developed and tested. Each stage consists of two parallel stainless steel meshes serving as electrodes. The space between them is filled with dielectric beads. The ac voltage applied to the electrodes is in the kV and kHz range and several gas flow rates are possible. The gases of interest have been measured using a Fourier Transform Infrared Spectrometer (FTIR) combined with a 32.5m long path cell. First result showed, that the VOC ethylene (C2H4) can be removed.

Characterization of hydrogen microwave plasmas produced by elementary sources in matrix configuration

In a previous study, a planar plasma reactor comprising 4 × 3 elementary microwave plasma sources distributed according to a square lattice matrix configuration was first characterized with argon. In this work, the objective is to characterize these so-called matrix plasmas with hydrogen in view of surface processing applications. In the absence of a static magnetic field, hydrogen plasmas can be sustained uniformly in the medium pressure range from 10 to 70 Pa. Using a cylindrical Langmuir probe, plasma density and electron temperature have been investigated at a distance of 20 mm from the source plane as functions of pressure and microwave power. The results show that the electron temperature Te is of the order of 1.2 eV and that plasma densities up to a few 1011 cm−3 can be reached. Under the same experimental conditions, optical emission spectroscopy measurements have been performed in order to determine the gas temperature and the degree of dissociation of hydrogen. The gas temperature, calculated from the α–Fulcher Q branch emission band (2–2) , varies from 600 to 850 K ± 50 K. The degree of dissociation has also been determined by using a spectroscopic method based on emission line intensities of Hα, Hβ and H2 (2–2) (N = 1) species. The maximum degree of dissociation of 50% has been obtained for the operating conditions corresponding to the highest plasma density.