Catalytic Microreactor Research Articles

ChemInform Abstract: Supported Catalysis in Continuous‐Flow Microreactors

AbstractReview: [136 refs.

Desulfurization of gas oil using a solar photocatalytic microreactor

The present work is devoted to investigate the performance of a homemade Y-shape catalytic microreactor for degradation of dibenzothiophene (DBT), as a model of sulphur compounds including in gas oil, utilizing solar incident energy. The microchannel was coated with TiO2 nanoparticles which were used as a photocatalyst. Performance of the microreactor was investigated using different conditions (e.g., DBT concentration, LHSV, operating temperature, and (H2O2/DBT) ratio). Our experiments show that, in the absence of UV light, no reaction takes place. The results revealed that outlet concentration of DBT decreases as the mean residence time in the microreactor increases. Also, it was noted that operating temperature showed a positive impact on the degradation rate of DBT while LHSV showed a different image. The results reported an optimum (H2O2/DBT) ratio which gave maximum conversion of DBT which vary with initial concentration. Kinetic study was carried out which confirmed that desulfurization of DBT followed a pseudo-first order reaction at 30 and 50oC, respectively. However deviation from linearity was observed at 60oC. Comparison between microreactor´s performance and performance of batch reactors from published literature were illustrated. The Comparison confirmed the unique characteristics of the microreactor.

Chiral Ruthenium Catalyst Immobilized within Magnetically Retrievable Mesoporous Silica Microcapsules for Aqueous Asymmetric Transfer Hydrogenations

The preparation of magnetically separable silica microcapsules that incorporate in their inner shell a chiral catalyst and their application in asymmetric transfer hydrogenation reactions are described. The preparation method is based on the emulsification of an oil phase containing chloroform, a modified Noyori Ru-TsDPEN catalyst, tetraethoxysilane (TEOS), and hydrophobic magnetic nanoparticles in water in the presence of an appropriate surfactant, followed by an interfacial polycondensation process under basic conditions to generate a silica shell around the oil droplets. The resulting catalytic microreactors can be considered a “quasi-homogeneous” system because the immobilized chiral catalyst reacts in a homogeneous zone, the microcapsule core filled with an organic solvent. The catalytic activity was tested in the asymmetric transfer hydrogenation of ketones in an aqueous medium. The catalytic reactions took place only in the presence of surfactants. In addition, the judicious selection of the surfactant plays a crucial role in enhancing the reaction progress through the emulsion-solid transfer (EST) approach. The catalytic activity of the Ru-TsDPEN catalyst immobilized within the silica microcapsules was superior to the same catalyst supported on silica microspheres or linked to the backbone of a silica sol–gel matrix, which indicates the importance of the homogeneous zones for the reactions.

Supported Catalysis in Continuous‐Flow Microreactors

AbstractThis review surveys the recent developments to perform heterogeneous catalysis in continuous‐flow microreactors. Three different types, namely, (i) packed‐bed, (ii) monolithic, and (iii) wall‐coated approaches are discussed to implement various kinds of catalysts in a microreactor. In addition, the applications of these supported catalysts to perform a variety of organic reactions are described. Furthermore, advantages of catalytic microreactors over classical batch reactors on one or more aspects of the reaction, such as rate, conversion, selectivity, and enantioselectivity are presented.magnified image

Mathematical Modeling, Verification and Optimization for Catalytic Membrane Esterification Micro-reactor

AbstractAnalysis of efficient production of ethyl acetate utilizing aCatalyticMembraneMicro-Reactor(CMMR)was theoretically investigated and verified using published results for the esterification reaction. Grafted sulfonic groups in the pores of a polyethersulfone membrane catalyzed the reaction. Theoretical analysis of the catalytic membrane reactor was achieved through development of a lumped parameter model to describe the CMMR behavior and performance. The developed model was solved numerically for different design and operating conditions using MATLAB Simulink software. The model parameters were verified and validated using the experimental results to achieve a reliable tool for design, replication, scaling-up, and optimization. The approach to maximum conversion was simulated. Cumulative yield per unit time was investigated to determine the optimum process time. Membrane regeneration was conducted and the regeneration time was determined as well in order to reuse the membrane for other cycles. Reactor scaling-up was studied using the model for process design.

PH-responsible Pickering emulsion and its catalytic application for reaction at water–oil interface

In this work, pH-responsible Pickering emulsion stabilized by polymer-metal hybrid micelles and its catalytic application for reaction at oil–water interface were presented. Employing Au@poly(ethylene oxide)-b-poly(4-vinylpyridine) polymer-metal hybrid micelles as emulsifier, n-decanol in water Pickering emulsion was first generated. The produced Pickering emulsion displayed reversible emulsification/demulsification with pH variation of the water phase, and this pH-induced emulsification/demulsification could undergo multiple cycles with only a slight reduction in emulsion performance. Dynamic light scattering, zeta potential measurement, and interfacial tension measurement, as well as transmission electron microscopy characterization, all showed that this reversible emulsification/demulsification cycle was the result of the tunable wettabilities of the core cross-linked hybrid emulsifier micelles with pH variation. Benefited from the excellent catalytic performances of the implanted Au nanoparticles at the oil–water interface and the large interfacial area of the emulsion droplets together with the pH-responsible reversible emulsification/demulsification cycle, the generated Pickering emulsion could readily applied as a catalytic microreactor for a broad of organic reactions occurred in water medium. As a proof of the concept, Au catalyzed reduction reaction of p-nitroanisole by NaBH4 was investigated. The catalyst showed both a highly catalytic activity with a good recyclability.

Quantitative carbon detector (QCD) for calibration-free, high-resolution characterization of complex mixtures.

Current research of complex chemical systems, including biomass pyrolysis, petroleum refining, and wastewater remediation requires analysis of large analyte mixtures (>100 compounds). Quantification of each carbon-containing analyte by existing methods (flame ionization detection) requires extensive identification and calibration. In this work, we describe an integrated microreactor system called the Quantitative Carbon Detector (QCD) for use with current gas chromatography techniques for calibration-free quantitation of analyte mixtures. Combined heating, catalytic combustion, methanation and gas co-reactant mixing within a single modular reactor fully converts all analytes to methane (>99.9%) within a thermodynamic operable regime. Residence time distribution of the QCD reveals negligible loss in chromatographic resolution consistent with fine separation of complex mixtures including cellulose pyrolysis products.

A versatile Carberry-type microcatalytic reactor for transient and/or continuous flow operation at atmospheric or medium pressure

A novel catalytic reaction device featuring a Carberry-type well-mixed microreactor built inside a medium pressure leak valve is presented. The complete reaction system allows a broad range of kinetic reaction engineering and heterogeneous catalysis studies for both batch (transient) and continuous operation. Carefully controlled temperature (±0.2K) and pressure (up to 3MPa) conditions can be achieved. The continuous sampling of the reacting mixture permits instantaneous evaluation of the gas phase composition.The device performance was validated by comparing methanol synthesis reaction rates for H2/CO2 mixtures obtained under transient conditions using this catalytic microreactor with steady-state kinetic rate expressions obtained using a conventional plug-flow microreactor employing the same Pd–GaOx/SiO2 catalyst. Excellent agreement was found.The reaction was also studied using a more active commercial methanol synthesis catalyst to assess the impact of heat and mass transfer resistances. For the full range of process conditions that was tested, the microreactor operated well under the kinetic regime.

Immobilization of peroxidase enzyme onto the porous silicon structure for enhancing its activity and stability.

In this work, a commercial peroxidase was immobilized onto porous silicon (PS) support functionalized with 3-aminopropyldiethoxysilane (APDES) and the performance of the obtained catalytic microreactor was studied. The immobilization steps were monitored and the activity of the immobilized enzyme in the PS pores was spectrophotometrically determined. The enzyme immobilization in porous silicon has demonstrated its potential as highly efficient enzymatic reactor. The effect of a polar organic solvent (acetonitrile) and the temperature (up to 50°C) on the activity and stability of the biocatalytic microreactor were studied. After 2-h incubation in organic solvent, the microreactor retained 80% of its initial activity in contrast to the system with free soluble peroxidase that lost 95% of its activity in the same period of time. Peroxidase immobilized into the spaces of the porous silicon support would be perspective for applications in treatments for environmental security such as removal of leached dye in textile industry or in treatment of different industrial effluents. The system can be also applied in the field of biomedicine.

Modelling of the Membrane Permeability Effect on the H2 Production Using CFD Method

Abstract Autothermal reforming of CH4 in a membrane catalytic microreactor for the production of hydrogen at different temperatures over supported Ni catalysts has been studied. A three-dimensional mathematical model was developed using a computational fluid dynamics (CFD) technique. The effect of using different membranes on the performance of the micro-reactor was analysed. The amounts of hydrogen produced and separated in each case, under the same operating conditions, were compared. It was proven that using the porous membrane (Ni–Al2O3) could be an economic solution for the production and separation of hydrogen in membrane reactors.

ChemInform Abstract: On‐Chip Catalytic Microreactors for Modern Catalysis Research

AbstractReview: 103 refs.

A MEMS-Based Catalytic Microreactor for a H$_{\bf 2}$O$_{\bf 2}$ Monopropellant Micropropulsion System

The next generation of miniaturized satellites (`nanosats') feature dramatically reduced thrust and impulse requirements for purposes of spacecraft attitude control and maneuvering. The present study is a joint computational and experimental design effort at developing a new MEMS-based microreactor configuration for incorporation into a monopropellant micropropulsion system. Numerical models of the gas phase catalytic decomposition in microchannel configurations are used to obtain critical sizing requirements for the reactor design. The computational results show that the length scales necessary for complete decomposition are compatible with MEMS-based designs; however, it is also found that the catalytic process is dominated by mass diffusion characteristics within the flow at this scale. Experimentally, a microscale catalytic reactor prototype has been designed and microfabricated using MEMS techniques. The reactor uses self-assembled ruthenium oxide nanorods grown on the wall surfaces as a catalyst. Experimental testing indicates that only partial decomposition of the hydrogen peroxide is achieved. Among the potential sources of the incomplete decomposition, a likely cause appears to be the inability of the H2O2 reactant stream to adequately wet the surface of the catalyst film composed of a high surface density of RuO2 nanorods.

CFD analysis of the effects of the flow distribution and heat losses on the steam reforming of methanol in catalytic (Pd/ZnO) microreactors

A three-dimensional computational fluid dynamics (CFD) simulation study of the effects of the flow distribution and the heat losses on the performance of microchannels and microslits reactors for the steam reforming of methanol (SRM) over Pd/ZnO is presented. Several flow distributing headers covering a wide range of the flow diffuser expansion angle (α) have been considered. Large values of α lead to flow maldistribution characterized by jet flow resulting in negative effects on the SRM conversion and hydrogen yield, especially for the microslits at high reaction temperatures and space velocities. Simulations have also evidenced that heat losses constitute a critical issue for microreactors operation, particularly at low space velocities. Heat losses may reach very high values, above 80–90% of the energy supplied to the microreactor, with the consequence that it may be necessary to provide up to 9times the heat of the SRM reaction to achieve high methanol conversions.

On‐Chip Catalytic Microreactors for Modern Catalysis Research

AbstractOver the past two decades, microfluidics, represented by lab‐on‐a‐chip (LoC) systems, have been developed because of their unique advantages of low reactant consumption, environmental friendliness, high safety, high efficiency, high sensitivity, portability, and easy handling of reactants. The distinguishing features of microfluidics have made the on‐chip reactor a highly efficient platform for general chemical experiments, especially catalysis. In this paper, through a brief review of the recent work on microfluidic catalysis, we highlight the importance of on‐chip catalytic microreactors. New approaches to the fabrication of on‐chip catalytic microreactors and their integration with multifunctional components are briefly introduced. Finally, the current challenges and future perspectives of this up‐and‐coming field are discussed based on our own opinions. It is believed that, with the progress of interdisciplinary cooperation, microfluidics and catalysis could be complementary sciences; catalysts may play a very important role in LoC systems, and on‐chip catalytic microreactors could be a highly efficient experimental platform for modern catalysis research.

Cu, Ce/mordenite coatings on FeCrAl-alloy corrugated foils employed as catalytic microreactors for CO oxidation

The aim of this work was to study different strategies for the synthesis of mordenite coatings on thin FeCrAl alloy foils in order to obtain adherent, stable and homogeneous films for their use as catalytic microreactors. For this purpose, the substrate pretreatments and growth conditions of the films by secondary synthesis were investigated. The best results were obtained by applying a brief calcination of the foils at 700°C that developed a smooth alumina film with hydrophilic properties, followed by immersion in a 0.4wt.% aqueous solution of the cationic polymer poly-(diallyldimethilammoniumchloride), PDDA. The subsequent seeding with diluted nanocristal suspensions (2gL) of Na-mordenite allowed the development of zeolite films with the desired properties and the additional benefit of a marked preferential growth on the metallic surface at the expense of a negligible growth within the synthesis solution. Finally, homogenous zeolite films were obtained in micro-corrugated foils, after which Cu and Ce were incorporated as catalytic ingredients and used in a microreactor for the CO oxidation reaction under different conditions.

Chemical and (Photo)‐Catalytical Transformations in Photonic Crystal Fibers

AbstractThe concept of employing photonic crystal fibers for chemical and (photo)‐catalytical transformations is presented. These optofluidic microdevices represent a versatile platform where light and fluids can interact for spectroscopic or photoactivation purposes. The use of photonic crystal fibers in chemistry and sensing is reviewed and recent applications as catalytic microreactors are presented. Results on homogeneous catalysis and the immobilization of homogeneous and heterogeneous catalysts in the fiber channels are discussed. The examples demonstrate that combining catalysis and the excellent light guidance of photonic crystal fibers provides unique features for example, for photocatalytic activation and quantitative photospectroscopic reaction analysis.

Immobilization of gold nanoparticles on fused silica capillary surface for the development of catalytic microreactors

A new reaction setup using a gold-based catalytic microcapillary reactor was developed. In order to immobilize the gold nanoparticles onto the fused silica inner wall, two different linkers were used: (3-aminopropyl)triethoxysilane (APTES) and (3-mercaptopropyl)triethoxysilane (MPTES). Three different types of gold nanoparticles: (i) Turkevich gold nanoparticles (Citrate–Au), (ii) polyvinylpyrrolidone stabilized gold nanoparticles (PVP–Au) and (iii) polyvinylalcohol stabilized gold nanoparticles (PVA–Au) were synthesized to be anchored on the microcapillary internal surface. The catalytic efficiency of these new microsystems has been investigated for oxidation as a function of the nature of the linkers and/or the type of gold nanoparticles. The oxidation of benzyl alcohol in the presence of H2O2 was used to evaluate the catalytic performance of these microreactors. Under the reaction conditions (80°C, resident time=639s), the Citrate–Au nanoparticles leaked out slightly from the capillary reactor, whereas high conversions (>90%) and high selectivity to benzoic acid were achieved with PVP–Au and PVA–Au nanoparticles. A catalytic microreactor based on MPTES/PVP–Au functionalization proved to be the most effective for this reaction.

The Role of Homogeneous Chemistry during Ignition of Propane Combustion in Pt-Catalyzed Microburners

The aim of this work is to numerically investigate the ignition behavior of homogeneous-heterogeneous (HH) combustion of propane in a Pt-catalyzed microburner to delineate the role of homogeneous chemistry during cold-start ignition. A two dimensional model with one-step homogeneous and catalytic mechanisms in a parallel-plate microburner is considered. The ignition characteristics (ignition temperature and ignition time) are explored for catalytic microreactor with and without homogeneous chemistry. We show that the catalytic reaction lights-off first, followed by the homogeneous reaction. Consequently, the homogeneous chemistry does not affect the ignition behavior of the catalytic microburner. The effect of inlet velocity, wall thermal conductivity and gap size on ignition characteristics is explored. The ignition characteristics are not affected by homogeneous chemistry even at larger gap sizes, despite the fact that the homogeneous contribution at steady state increases with increasing gap size of the microburner.

Enhancement of the Liquid-Side Mass Transfer in a Falling Film Catalytic Microreactor by In-Channel Mixing Structures

Catalytic octanal oxidation with oxygen was performed at 100 °C and the total pressure of 5 and 10 bar in a falling film microreactor with varying reaction plates bearing different in-channel mixing structures. The liquid flow rate was changed in the range of 3.3–17.5 mL/min. The liquid-sided mass transfer over grooved or finned structured plates was enhanced by factors of 1.12 and 1.20, respectively, compared to that on a standard plate with 16 microchannels with dimensions of 1200 μm × 400 μm. The liquid flow rate over the structured plates could be increased by 60%–80% without any loss of octanal conversion. A two-dimensional convection and diffusion model adopted from Al-Rawashdeh et al. [Chem. Eng. Sci. 2008, 63, 5149] was formulated to simulate the reactor behavior, and its predictions describe the experimental results in terms of octanal conversion with an accuracy of 4.3% when the actual temperature distribution in the reactor plate is taken into account.

Characterization of acidic zeolite catalysts by thermodesorption and cracking of n-nonane

The possibility of employing a catalytic microreactor with the quadrupole mass spectrometer detector in characterization of acidic zeolites by means of combined thermodesorption and cracking of nonane was explored. The studied commercial zeolites H-USY (Si/Al=4.5), HY (Si/Al=15), HZSM-5 (Si/Al=15), HMOR (Si/Al=5.7) exhibited differences in catalytic activity, stability and thermodesorption profiles. Conversion of nonane varied from 31% for HY (15) to 80% for HZSM-5 (15) at 500°C. For zeolites H-USY (4.5) and HMOR (5.7) fast deactivation accompanied by substantial coking was observed. For the least acidic zeolite HY (15) thermodesorption profiles of nonane were not affected by the catalytic reactions of desorbing molecules, while for HMOR (5.7) and HZSM-5 (15) cracking of the molecules desorbing from the micropores occurred. Regeneration of the catalysts by temperature programmed oxidation of coke up to 700°C resulted in structural damage of the FAU-type zeolites.