Continuous Flow Microreactor Research Articles

Compact Steam-Methane Reforming for the Production of Hydrogen in Continuous Flow Microreactor Systems

The implementation of fuel cell deployment requires efficient conversion of fuels into hydrogen in a distributed energy system. Fortunately, continuous flow and microreactor technology provide unique opportunities for the portable production of hydrogen. This study focuses on determining the operation space for a thermally integrated methane reforming system, thereby providing a theoretical basis for the design and optimization of such systems. The steam-methane reforming over rhodium coupled with methane combustion over platinum in a thermally integrated microchannel reactor arranged with rectangular-shaped protuberances was studied numerically in order to improve its operability and stability. Computational fluid dynamic simulations were carried out with detailed reaction mechanisms to identify conditions for the maximum hydrogen yield and the highest output power. Various operating lines were presented, and various performance metrics were evaluated accordingly. The results indicated that the efficient production of hydrogen is made possible through improving transport performance for highly active catalysts. The flow disturbance elements designed for the reactor are of great benefit to intensification of the reforming process. There exists a trade-off between fuel utilization and output power. Autothermal operation advantages from improved transport performance in small physical dimensions were demonstrated for the system, but careful thermal management is always necessary to ensure its efficient and stable operation. The thermal conductivity of the wall separating the exothermic and endothermic reactions plays a significant role in determining the performance of the system. Highly active catalysts are required to intensify the overall reforming process and to achieve efficient thermal management. Adjustment of fluid velocities can serve as a convenient means to achieve efficient operation of the system.

Modeling of process intensification of biodiesel production from Aegle Marmelos Correa seed oil using microreactor assisted with ultrasonic mixing.

Conventionally, the batch type reactors were used for the production of biodiesel. However, in recent years, the usage of microreactors has started emerging as a significant substitute for biodiesel production due to its higher conversion rate at a short duration. These microreactors have a significantly high surface to volume ratio and high heat-mass transfer rate. The disadvantage of this type of reactors is its low mixing rate of the reagents. This can be overcome with the assistance of ultrasonic mixing. The main objective of this paper is to study the interlaced effect of a continuous flow microreactor and ultrasonic mixing on trans-esterification of Aegle Marmelos Correa seed oil using sodium methoxide catalyst. Results of microreactors with 0.3 mm and 0.8 mm diameter were compared. The effects of process parameters namely, flow rate (2-10 mL/min), reaction temperature (45-65 °C), catalyst amount (0.5-2.5 wt%), oil to methanol molar ratio (1:6-1:18) and ultrasonic mixing time (30-150 s) were studied using response surface methodology (RSM). The biodiesel yield of 98% and 91.8% were obtained for 0.3 mm and 0.8 mm microreactors, respectively. The maximum biodiesel yield observed in 0.3 mm reactor under following optimum conditions: 6.8 mL/min flow rate, 48 °C reaction temperature, 1.3 wt% catalyst, 1:9 oil to methanol molar ratio and 83 s ultrasonic mixing time. The predictive and generalization abilities of RSM and artificial neural network (ANN) models were evaluated and compared. The study showed that ANN and RSM models could predict the yield with an R2 value of 0.9955 and 0.9900 respectively. However, the ANN model predicted the yield with the least mean square error value of 0.00001294, which is much lower than RSM.

Preparation of bimetallic Ni–Fe/MCM-41 catalysts and their catalytic activity for CO methanation

A series of Ni–Fe/MCM-41 bimetallic catalysts and also Ni/MCM-41 and Fe/MCM-41 catalysts were prepared by the incipient-wetness impregnation method and tested for their activity for CO methanation in a continuous-flow microreactor. The results showed that the catalytic activities of the Ni–Fe/MCM-41 bimetallic catalysts were much higher than those of the Ni/MCM-41 and Fe/MCM-41 catalysts at low temperatures (200°C–325°C). The 10%Ni–5%Fe/MCM-41 catalyst showed the best activity with a CO conversion of almost 100% and a CH4 selectivity of 98% at 350°C under a pressure of 1.5 MPa with a 3:1 molar ratio of H2 to CO and a weight hourly space velocity of 12,000 mL h−1 g−1. The catalysts were characterized by N2 physisorption measurements, X-ray diffraction, and H2-temperature-programmed reduction. The results showed that the addition of Fe will lead to the formation of finer Ni particles and Ni–Fe alloy, which were the main reasons for the activity increase in the Ni–Fe/MCM-41 catalysts.

Catalytic Transformation of Biomass Derivatives to Value‐Added Chemicals and Fuels in Continuous Flow Microreactors

AbstractBiomass as a renewable and abundantly available carbon source is a promising alternative to fossil resources for the production of chemicals and fuels. The development of biobased chemistry, along with catalyst design, has received much research attention over recent years. However, dedicated reactor concepts for the conversion of biomass and its derivatives are a relatively new research field. Continuous flow microreactors are a promising tool for process intensification, especially for reactions in multiphase systems. In this work, the potential of microreactors for the catalytic conversion of biomass derivatives to value‐added chemicals and fuels is critically reviewed. Emphases are laid on the biphasic synthesis of furans from sugars, oxidation and hydrogenation of biomass derivatives. Microreactor processing has been shown capable of improving the efficiency of many biobased reactions, due to the transport intensification and a fine control over the process. Microreactors are expected to contribute in accelerating the technological development of biomass conversion and have a promising potential for industrial application in this area.

Ethanol Dehydrogenation to Acetaldehyde over Activated Carbons-Derived from Coffee Residue

This study focuses on the production of acetaldehyde from ethanol by catalytic dehydrogenation using activated carbon catalysts derived from coffee ground residues and commercial activated carbon catalyst. For the synthesis of activated carbon catalysts, coffee ground residues were chemical activated with ZnCl2 (ratio 1:3) followed by different physical activation. All prepared catalysts were characterized with various techniques such as nitrogen physisorption (BET and BJH methods), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), temperature programmed desorption (CO2-TPD and NH3-TPD), X-ray Difraction (XRD), Fourier transform infrared spectrometer (FT-IR), and thermogravimetric analysis (TGA). The dehydrogenation of vaporized ethanol was performed to test the catalytic activity and product distribution. Testing catalytic activity by operated in a fixed-bed continuous flow micro-reactor at temperatures ranged from 250 to 400 °C. It was found that the AC-D catalyst (using calcination under carbon dioxide flow at 600 °C, 4 hours for physical activation) exhibited the highest catalytic activity, while all catalysts show high selectivity to acetaldehyde (more than 90%). Ethanol conversion apparently increased with increased reaction temperature. At 400 ºC, the AC-D catalyst gave the highest ethanol conversion of 47.9% and yielded 46.8% of acetaldehyde. The highest activity obtained from AC-D catalyst can be related to both Lewis acidity and Lewis basicity because the dehydrogenation of ethanol uses both Lewis acid and Lewis basic sites for this reaction. To investigate the stability of catalyst, the AC-D catalyst showed quite constant ethanol conversion for 10 h. Therefore, the synthesized activated carbon from coffee ground residues is promising to be used in dehydrogenation of ethanol.

Preparation and catalytic performance of an efficient Raney nickel catalyst for syngas methanation

A new strategy for preparing Raney nickel catalyst was proposed, which could significantly improve the catalytic activity of the catalyst in the methanation of syngas to substitute natural gas in a continuous flow microreactor. The new preparation strategy includes a hydrochloric acid solution quenching process interpolated between two alkali leaching steps. Raney Ni III catalyst showed the best activity with a CO conversion of almost 100% and a CH4 selectivity of 98% at 548 K under 1.0 MPa with the molar ratio of 3H2:1CO and a gas hourly space velocity of 10000 h−1. The catalysts were characterized by N2 adsorption–desorption, scanning electron microscopy, X-ray powder diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and temperature-programmed desorption of hydrogen. The results of systematic characterization and catalytic activity evaluation show that the formation of 3Ni(OH)2·2H2O in the catalyst is beneficial to the adsorption and activation of hydrogen and the C=O bond, which greatly improves the activity of Raney nickel III in methanation of syngas. Meanwhile, high specific surface area leads to more active sites on the catalyst surface, which is also conducive to the improvement in catalyst activity.

Synthesis of Aluminium Doped Na-Titanate Nanorods and Its Application as Potential CO2 Hydrogenation Catalysts

A series of Al-doped Na-TiO2 nanorods (AlTi-nR-x) varying the Al2O3/TiO2 (Al/Ti) ratio was synthesized by hydrothermal method. TEM results revealed well-defined nanorod like shape morphology. XPS results confirmed the presence of Al inside the samples and a slight increase in electron density around the Ti atom. Calcined materials were evaluated in the CO2 hydrogenation (HYD) in a continuous flow-microreactor at 280–340 °C under atmospheric pressure. Results from this work exposed that all AlTi-nR-x materials have great potential to be used as CO2 HYD catalysts. However, the best catalytic performance was obtained with the AlTi-nR-0.5 catalysts, which also displayed high selectivity (82%) towards methanol.

Identification of kinetic models of methanol oxidation on silver in the presence of uncertain catalyst behavior

AbstractCatalytic oxidation of methanol to formaldehyde is an important industrial process due to the value of formaldehyde either as a final product or as a precursor of numerous chemicals. The study of kinetics in this system is hindered by sources of uncertainty that are inherently associated to the nature and state of the catalyst (e.g., uncertain reactivity level, deactivation phenomena), the measurement system and the structure of the kinetic model equations. In this work, a simplified kinetic model is identified from data collected from continuous flow microreactor systems where catalysts with assorted levels of reactivity are employed. Tailored model‐based data mining methods are proposed and applied for the effective estimation of the kinetic parameters and for identifying robust experimental conditions to be exploited for the kinetic characterization of catalysts with different reactivity, whose kinetic behavior is yet to be investigated.

CO and CO2 Co-Methanation on Ni/CeO2-ZrO2 Soft-Templated Catalysts

Supported nickel catalysts were synthesized, characterized, and employed in the carbon oxides co-methanation process. Five NiO/CeO2-ZrO2 mixed oxides, with the same Ni content and different Ce/Zr molar ratios, were prepared by the soft-template method. They were characterized through ICP-AES, N2 adsorption, XRD, and TPR. Reduced Ni/CeO2-ZrO2 catalysts were obtained by submitting the oxide systems to reduction treatment in H2 at 400 °C. They were characterized by XRD, H2-TPD, and CO2 adsorption microcalorimetry and their catalytic performances in the carbon oxides co-methanation were investigated. Catalytic tests were performed in a fixed-bed continuous-flow microreactor at atmospheric pressure. The effect of experimental conditions (reaction temperature, space velocity, reactants molar ratio) was also studied. Almost complete CO conversion was obtained on any catalyst, whereas CO2 conversion was much lower and increased with Ce content, at least up to Ce/Zr = 1. The beneficial effect of the Ce content could be related to the increased NiO reducibility and to the higher ability to adsorb and activate CO2. However, at high Ce/Zr ratios, it is probably counterbalanced by an interplay of reactions involving CO and CO2.

Heterogeneous singlet oxygen generation: in-operando visible light EPR spectroscopy.

The use of photosensitizers immobilized on mesoporous materials to produce singlet oxygen (1O2) has opened a new way to synthetic and environmental applications due to the fast development of flow photochemistry and continuous-flow microreactors. 1O2-based photosensitized processes can be employed for the degradation of organic pollutants in an aqueous medium and the photosensitizer can be covalently attached to the support and separated from the effluent reducing the environmental impact. The aim of the present paper is to evaluate the 1O2 generation of Rose Bengal (RB) in homogeneous and heterogeneous systems using in-operando evaluation. Mesoporous SiO2 nanoparticles (MSNs) were successfully conjugated with RB (MSN-RB) and electron paramagnetic resonance (EPR) spectroscopy in combination with the spin trap TEMP was employed to obtain paramagnetic TEMPO via generated 1O2 when RB or MSN-RB are exposed to visible light. Additionally, EPR/DMPO was used to exclude the possible generation of other reactive oxygen species (ROS) by the functionalized nanoparticles. We found that in situ 1O2 generation was enhanced when the same amount of RB is immobilized inside of mesoporous SiO2.

Preparation of Pt/CeL reforming catalyst and its performance in the aromatization of naphtha

To solve the problems of chlorine loss and equipment corrosion caused by the conventional alumina-type reforming catalyst, zeolite L was modified with Ce3+ by ion exchange method and with Ce3+-modified L (CeL) as the support, the Pt/CeL reforming catalyst without any chlorine was prepared by impregnation method. The CeL support and Pt/CeL catalyst were characterized by XRD, N2 adsorption-desorption, NH3-TPD and Py-FTIR; the catalytic performance of Pt/CeL in aromatization was investigated in a continuous-flow fixed-bed micro-reactor, with an industrial hydrofining naphtha containing 0.50 μg/mL sulfur as the feedstock. The results indicate that the modification with Ce3+ by ion exchange has little influence on framework structure of zeolite L; however, it can raise the acid content and acid strength of the CeL support and then remarkably enhance the performance of the Pt/CeL reforming catalyst in aromatization. The activity and selectivity of the Pt/CeL catalyst are comparable to those of the commercial alumina-type reforming catalysts, suggesting that proper acidity can facilitate the aromatization reaction.

Ethoxylation of p-Fluoronitrobenzene using phase-transfer catalysts under microflow conditions

Nucleophilic aromatic substitution, one of the most common transformation methods for aromatic organic compounds, is often performed under biphasic conditions using a phase-transfer catalyst. Herein, we investigated the synthesis of 4-nitrophenetole from 4-fluoronitrobenzene in a continuous-flow microreactor, which accelerates mass transfer between the two phases. The reaction proceeded smoothly under slug flow conditions and a slight acceleration effect was observed under ambient pressure. By contrast, high temperature and pressure conditions gave the target compound in good yield within a shorter residence time.

Dynamic characterization of nanoparticles production in a droplet-based continuous flow microreactor

The present work was focused on the dynamic characterization of nanoparticles production under continuous flow in a droplet-based spiral-shaped microreactor. A novel drainage design was incorporated into the microreactor channel network for eliminating the commonly encountered problems of clogging and coalescence of microdroplets containing nanoparticles in the microchannel. Through precise manipulation of droplets formation for investigating the precipitation process of iron oxide, one-to-one pairing and fusion of reactant droplets were obtained and monitored in a real-time manner through digital imaging, where optimised flow rate ratios (in a range of 0.3–0.5) of aqueous phase to oil phase were applied. The nanoprecipitation process was observed and further analysed, indicating that the formation of precipitates was determined by the diffusion of OH− after coalescence of reactants droplets. By characterising the Fe3O4 nanoparticles produced, it demonstrated that smaller droplets were beneficial to obtaining high quality nanoparticles in terms of size control and size distribution. Moreover, the kinetics of the nucleation process was investigated through statistic calculation. Initial results suggested that heterogeneous nucleation occurring inside droplets was likely due to the presence of impurities-mediated (e.g. surfactants) or collision-induced nucleation events.

Continuous and Ultrafast Preparation of In(OH)3, InOOH, and In2O3 Series in a Microreactor for Gas Sensors

In(OH)3 and InOOH were synthesized in a high-temperature continuous flow microreactor, which was much faster than the hydrothermal synthesis in a Teflon-lined autoclave. The phase transition interval of In(OH)3 and InOOH is measured, and the effect of aging temperatures on equilibrium compositions was also theoretically calculated. A transformation from nanorods to nanocubes was observed when the aging temperatures increased. In(OH)3 and InOOH were also synthesized with Sn dopant, which was proven to be beneficial for the transformation from In(OH)3 to InOOH. The sensors based on cubic and hexagonal In2O3 particles showed a fast response (4–5 s) and recovery speed (12–15 s) to acetone vapor at the optimum operating temperature of 290 °C. The sensor based on hexagonal In2O3 showed a higher response than that based on cubic In2O3. This work provided a rapid, continuous, and high-temperature synthesis method of an In(OH)3, InOOH, and In2O3 series.

Process intensification for O2 -dependent enzymatic transformations in continuous single-phase pressurized flow.

Oxidative O2‐dependent biotransformations are promising for chemical synthesis, but their development to an efficiency required in fine chemical manufacturing has proven difficult. General problem for process engineering of these systems is that thermodynamic and kinetic limitations on supplying O2 to the enzymatic reaction combine to create a complex bottleneck on conversion efficiency. We show here that continuous‐flow microreactor technology offers a comprehensive solution. It does so by expanding the process window to the medium pressure range (here, ≤34 bar) and thus enables biotransformations to be conducted in a single liquid phase at boosted concentrations of the dissolved O2 (here, up to 43 mM). We take reactions of glucose oxidase and d‐amino acid oxidase as exemplary cases to demonstrate that the pressurized microreactor presents a powerful engineering tool uniquely apt to overcome restrictions inherent to the individual O2‐dependent transformation considered. Using soluble enzymes in liquid flow, we show reaction rate enhancement (up to six‐fold) due to the effect of elevated O2 concentrations on the oxidase kinetics. When additional catalase was used to recycle dissolved O2 from the H2O2 released in the oxidase reaction, product formation was doubled compared to the O2 supplied, in the absence of transfer from a gas phase. A packed‐bed reactor containing oxidase and catalase coimmobilized on porous beads was implemented to demonstrate catalyst recyclability and operational stability during continuous high‐pressure conversion. Product concentrations of up to 80 mM were obtained at low residence times (1–4 min). Up to 360 reactor cycles were performed at constant product release and near‐theoretical utilization of the O2 supplied. Therefore, we show that the pressurized microreactor is practical embodiment of a general reaction‐engineering concept for process intensification in enzymatic conversions requiring O2 as the cosubstrate.

Online Measurement System in Reaction Monitoring for Determination of Structural and Elemental Composition Using Mass Spectrometry.

The monitoring of chemical reactions is an important task in chemical engineering, especially in quality control, pharmaceutical and biological processes, or industrial production. The development of new reactions such as catalyst-based procedures requires detailed knowledge about process steps and reaction kinetics. For qualitative and quantitative analysis of reactants and resulting products, proprietary online measurement systems are used, which were designed for special applications. A mobile online reaction monitoring system was developed for a flexible coupling to different mass selective measurement systems for structural (ESI-MS) and elemental (ICP-MS) analysis to determine chemical precursors, reaction products, and internal standard compounds and their elemental composition at any stage of the reaction. Chemical reactions take place in a tempered continuous-flow microreactor. The flow rate in the microreactor can be varied to adjust the residence times in the reactor. An online dilution module was integrated to adapt the concentration of the reaction solutions to the working range of the analyzers. The performance and limitations of the online reaction system were determined using standard solutions and a real chemical reaction. The control software with a graphical user interface enables the adjustment of reaction, sampling, and measurement parameters as well as the system and process control.

The convenient Michael addition of imidazoles to acrylates catalyzed by Lipozyme TL IM from Thermomyces lanuginosus in a continuous flow microreactor.

A fast and green protocol for the Michael addition of imidazoles to acrylates catalyzed by Lipozyme TL IM from Thermomyces lanuginosus in a continuous flow microreactor was developed. In contrast with existing methods, this method is simple (35 min), uses mild reaction conditions (45 °C) and is environmentally friendly. This enzymatic Michael addition performed in continuous flow microreactors is an innovation that may open up the use of enzymatic microreactors in imidazole analogue biotransformations.

Hydroxynitrile lyases covalently immobilized in continuous flow microreactors

Enzymes are supreme catalysts when it comes to high enantiopurities and their immobilization will pave the way for continuous operation.

Carbon Dioxide Methanation Over Nickel Catalysts Supported on Activated Carbon at Low Temperature

The methanation of carbon over nickel catalysts supported on activated carbon was investigated using a continuous flow microreactor. Catalysts with nickel loadings of 5, 7, and 10% were synthesised by incipient wetness impregnation methods and characterised using Brunauer–Emmett–Teller (BET), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), H2-temperature-programmed reduction (TPR), BET, XRD, SEM, TEM and H2-TPR. The methanation reaction was studied over the temperature range 200–500°C with a H2 to CO2 ratio of 4:1 in He and at 1 atm. With an increase in Ni content from 5 to 7% both conversion of CO2 and CH4 selectivity increased. Increasing the nickel content to 10%, however decreased conversion and selectivity due to the larger crystallite size and lower surface area of the catalyst. The most active catalyst with 7% Ni does not deactivate during 15h time on stream at 350°C. The high catalytic activity and stability of the studied catalysts is a consequence of the reducibility of Ni and a synergetic effect between the nickel active sites and the activated carbon surface.

The Chapman rearrangement in a continuous-flow microreactor.

The Chapman rearrangement is of practical significance in pharmaceutical and fine chemical industries. It is a high temperature reaction with an exothermic nature in numerous cases. The conventional batch-wise synthesis is limited by its operational complexities, temperature control difficulties and scale-up hurdles. In this work, a microreactor-based continuous-flow approach was developed to perform the rearrangement in a highly controlled and safer manner. High conversions were obtained within short residence times (≤20 minutes). The detailed kinetics of this reaction, using 2,6-dichloro-phenyl N-phenyl benzimidate and 2-carbomethoxy-phenyl N-phenyl benzimidate as the representative reactants, was explored at varying temperatures to understand the intensified reaction behavior, and was modelled based on the obtained experimental data. The continuous process was scaled up to a 16-fold larger reactor volume by increasing the diameter of the microreactor while maintaining the residence time without further optimization. A very slight variation was observed in the conversion for the larger-sized flow system. Upscaling the batch reaction to a 10 times larger volume, by contrast, resulted in a dramatic decrease in the conversion. The simplicity of scaling up continuous-flow system was clearly demonstrated. A CFD model coupled with the obtained rearrangement kinetics was developed and well validated against the experimental data, which provided a robust platform for guiding the relevant process design and optimization of the continuous-flow processes. The results presented shed new light on the developments and applications of continuous-flow method for the classical Chapman rearrangement that require harsh high temperatures.