Multichannel Reactor Research Articles

H2-D2 Exchange Activity and Electronic Structure of Ag x Pd1-x Alloy Catalysts Spanning Composition Space.

Many computational studies of catalytic surface reaction kinetics have demonstrated the existence of linear scaling relationships between physical descriptors of catalysts and reaction barriers on their surfaces. In this work, the relationship between catalyst activity, electronic structure, and alloy composition was investigated experimentally using a Ag x Pd1-x Composition Spread Alloy Film (CSAF) and a multichannel reactor array that allows measurement of steady-state reaction kinetics at 100 alloy compositions simultaneously. Steady-state H2-D2 exchange kinetics were measured at atmospheric pressure on Ag x Pd1-x catalysts over a temperature range of 333-593 K and a range of inlet H2 and D2 partial pressures. X-ray photoelectron spectroscopy (XPS) was used to characterize the CSAF by determining the local surface compositions and the valence band electronic structure at each composition. The valence band photoemission spectra showed that the average energy of the valence band, ε̅v, shifts linearly with composition from -6.2 eV for pure Ag to -3.4 eV for pure Pd. At all reaction conditions, the H2-D2 exchange activity was found to be highest on pure Pd and gradually decreased as the alloy was diluted with Ag until no activity was observed for compositions with x Pd < 0.58. Measured H2-D2 exchange rates across the CSAF were fit using the Dual Subsurface Hydrogen (2H') mechanism to extract estimates for the activation energy barriers to dissociative adsorption, ΔE ads ‡, associative desorption, ΔE des ‡, and the surface-to-subsurface diffusion energy, ΔE ss, as a function of alloy composition, x Pd. The 2H' mechanism predicts ΔE ads ‡ = 0-10 kJ/mol, ΔE des ‡ = 30-65 kJ/mol, and ΔE ss = 20-30 kJ/mol for all alloy compositions with x Pd ≥ 0.64, including for the pure Pd catalyst (i.e., x Pd = 1). For these Pd-rich catalysts, ΔE des ‡ and ΔE ss appeared to increase by ∼5 kJ/mol with decreasing x Pd. However, due to the coupling of kinetic parameters in the 2H' mechanism, we are unable to exclude the possibility that the kinetic parameters predicted when x Pd ≥ 0.64 are identical to those predicted for pure Pd. This suggests that H2-D2 exchange occurs only on bulk-like Pd domains, presumably due to the strong interactions between H2 and Pd. In this case, the decrease in catalytic activity with decreasing x Pd can be explained by a reduction in the availability of surface Pd at high Ag compositions.

Innovative fast-dynamic tool to characterize maldistribution in gas-liquid multi-channel reactors

In the field of structured reactors applied to multiphase reactions, the apparatus performance is related to the quality of the spatial distribution of fluids at the reactor inlet. This holds particularly true for monolith-type reactors since no flow redistribution is possible downstream in between the different parallel channels.In order to characterize the gas-liquid flows and their distribution in all the channels, a resistive sensor consisting in a printed circuit board with several annular electrodes has been developed, which can be scanned with high temporal resolution, of up to 20,000 Hz. This technique allows investigating flow features, such as gas holdup, bubble velocity, and bubble frequency, which are assessed in this work by shadowgraphy for a 12-channel monolith fed by air and water.Several treatment methods are evaluated, allowing the flow characteristics to be indirectly measured for Taylor flow regime conditions, with an accuracy of ±10% for bubble frequency and of ±20% for gas holdup and bubble velocity, with respect to the shadowgraphy. Thus, the innovative sensor can be used for industrial applications in order to distinguish the performance of gas-liquid distributors to provide uniform flow in multi-channel structured reactors.

Solar-driven multichannel membrane reactor for hydrogen production from ammonia decomposition

Solar-driven ammonia decomposition is one of the most promising carbon-free pathways to release hydrogen from ammonia. Enhancing the heat and mass transfer processes within an ammonia decomposition membrane reactor is crucial to improve the hydrogen production rate. The multichannel reactors can reduce hydraulic diameters by raising the number of channels while the lateral surface areas of reactors keep the same, which can enhance heat and mass transfer without enlarging re-radiation losses. In this paper, a solar-driven multichannel membrane reactor for ammonia decomposition is proposed, which is promising to improve the conversion without deteriorating the efficiency. Models are developed to simulate the proposed multichannel membrane reactor under solar irradiation. A multichannel membrane reactor with three Pd membrane channels is designed and built. Experiments have been conducted to validate the reactor model. With the validated model, two consecutive parametric studies have been conducted for catalyst volume decreasing and increasing scenarios, respectively. The results show that enlarging permeation area by increasing membrane channels is worthwhile to improve the conversion although the catalyst volume decreases. Under the same solar flux and inlet ammonia properties, a six-channel membrane reactor can achieve a conversion of 0.76, while a single-channel membrane reactor can only achieve a conversion of 0.49. Additionally, the maximum temperature difference within the six-channel reactor is 47 °C lower than that within single-channel membrane reactor, which is favorable for the Pd membrane operating temperature range.

Numerical investigation of a multichannel reactor for syngas production by methanol steam reforming at various operating conditions

A novel multichannel reactor with a bifurcation inlet manifold, a rectangular outlet manifold, and sixteen parallel minichannels with commercial CuO/ZnO/Al2O3 catalyst for methanol steam reforming was numerically investigated in this paper. A three-dimensional numerical model was established to study the heat and mass transfer characteristics as well as the chemical reaction rates. The numerical model adopted the triple rate kinetic model of methanol steam reforming which can accurately calculate the consumption and generation of each species in the reactor. The effects of steam to carbon molar ratio, weight hourly space velocity, operating temperature and catalyst layer thickness on the methanol steam reforming performance were evaluated and discussed. The distributions of temperature, velocity, species concentration, and reaction rates in the reactor were obtained and analyzed to explain the mechanisms of different effects. It is suggested that the operating temperature of 548 K, steam to carbon ratio of 1.3, and weight hourly space velocity of 0.67 h−1 are recommended operating conditions for methanol steam reforming by the novel multichannel reactor with catalyst fully packed in the parallel minichannels.

Thermal‐hydraulic design features of a micronuclear reactor power source applied for multipurpose

Microheat pipe cooled reactor power source (HRP) designed for space or underwater vehicles meets the future demands, such as safer structure, longer operating time, and fewer mechanical moving parts. In this paper, potassium heat pipe cooled reactor power source system which generates 50 kWe electricity is proposed. The reactor core using uranium nitride fuel is cooled by 37 potassium high-temperature heat pipes. The shields are designed as tungsten and water, and reactor reactivity is controlled by control drums. The thermoelectric generator (TEG) consists of thermoelectric conversion units and seawater cooler. The thermoelectric conversion units convert thermal energy to electric energy through the high-performance thermoelectric material. A code applied for designing and analyzing the reactor power system is developed. It consists of multichannel reactor core model, heat pipe model using thermal resistance network, thermoelectric conversion, and thermal conductivity model. Then, the sensitivity analysis is performed on two key parameters including the length of the heat pipe condensation section and the cold junction temperature of the TE cell. Meanwhile, the steady-state calculations are conducted. Results show that the maximum fuel temperature is 938 K located in the center of reactor core and the outlet temperature of coolant reaches 316 K. Both of them are within the limitation. It is concluded that the preliminary design of HPR design is reasonable and reliable. The designed residual heat removal system has sufficient safety margin to release the decay heat of the reactor. This research provides valuable analysis for the application of micronuclear power source.

Continuous-flow liquid-phase dehydrogenation of 1,4-cyclohexanedione in a structured multichannel reactor

A highly selective continuous-flow process is developed for liquid-phase dehydrogenation to produce a high yield of hydroquinone in a millimetre-scale structured multichannel reactor.

Multichannel Open Tubular Enzyme Reactor Online Coupled with Mass Spectrometry for Detecting Ricin.

For counterterrorism purposes, a selective nano liquid chromatography-mass spectrometry (nanoLC-MS) platform was developed for detecting the highly lethal protein ricin from castor bean extract. Manual sample preparation steps were omitted by implementing a trypsin/Lys-C enzyme-immobilized multichannel reactor (MCR) consisting of 126 channels (8 μm inner diameter in all channels) that performed online digestion of proteins (5 min reaction time, instead of 4-16 h in previous in-solution methods). Reduction and alkylation steps were not required. The MCR allowed identification of ricin by signature peptides in all targeted mode injections performed, with a complete absence of carry-over in blank injections. The MCRs (interior volume ≈ 1 μL) have very low backpressure, allowing for trivial online coupling with commercial nanoLC-MS systems. The open tubular nature of the MCRs allowed for repeatable within/between-reactor preparation and performance.

Modeling of carbonaceous feedstock pyrolysis in a multichannel reactor

A mathematical model of unsteady-state carbonaceous feedstock pyrolysis in a multichannel tubular reactor was proposed. It was shown that the conversion of feedstock being heated at periodically varying temperature can exceed the conversion on heating at constant temperature. The main design parameters of the multichannel reactor were determined.

Reactor design and catalysts testing for hydrogen production by methanol steam reforming for fuel cells applications

A tubular-quartz reactor (TQR) and a multichannel reactor (MCR) made of aluminium were employed for methanol steam reforming to perform the kinetic modelling at atmospheric pressure using two commercial catalysts and one new catalyst, respectively. In TQR, the experiments were performed at oven temperatures from 200 to 300 °C, and with different steam to carbon (S/C) ratios. In MCR, the experiments were performed at reactor temperatures from 170 to 210 °C and with S/C ratio equal to 1.5. The experimental data was successfully modeled for the three catalysts. However, the results with TQR revealed that the temperature gradients were formed in the catalyst bed. Thus, the actual representation of the catalyst behaviour neglecting radial temperature gradients is somewhat uncertain. On the other hand, a multichannel reactor (MCR) provided good temperature control through the wall of the reactor and almost isothermal conditions in the catalyst bed which allowed obtaining a reliable model. This kinetic model was used in simulation and designing of a small scale heat exchanger reactor.

Simulation of exhaust gas reforming of natural gas in a microchannel reactor

The present work is aimed to conduct modeling and simulation of exhaust gas reforming of natural gas in a catalytic microchannel reactor. Natural gas, an alternative fuel that can be used in internal combustion engines in compressed form, is modeled as methane only and methane/propane mixtures. The multichannel reactor is composed of a cordierite block with parallel channels, each of which is washcoated with Rh/Al2O3 catalyst. Due to the low thermal conductivity of cordierite, heat transfer between the channels is neglected, and a single, adiabatic microchannel is considered as the modeling domain representing the behavior of the multichannel unit. Two dimensional continuity and conservation equations for the fluid and porous washcoat phases are solved by the finite volume method using the ANSYS Fluent platform. Effects of feed temperature, fuel compositions (i.e. molar inlet steam-to-carbon (H2O/C) and oxygen-to-carbon (O2/C) ratios) and presence of propane in natural gas on temperature and product distribution are investigated in the context of a parametric study. It is observed that temperature is well distributed along the channel and no notable hot spot formation is observed. Increasing feed temperature favors methane conversion and hydrogen production, but results in less uniform temperature distribution. Feeding higher amounts of steam increases hydrogen formation, but slightly dampens methane conversion. Increasing O2/C ratio at the inlet results in a proportional increase in methane conversion and temperature. Even though channel temperature is found to decrease, hydrogen production is favored upon using methane/propane mixture as the fuel.

Dry Methane Reforming Performance of Ni-based Catalyst Coated onto Stainless Steel Substrate

In this work, the Ni-based catalysts (10wt.%Ni/Al2O3-MgO and 10wt.%Ni/MgO) were synthesized by sol-gel method. Each catalyst was prepared as catalyst pellets and catalyst-coated plate, stainless steel plate coated with catalyst. The catalyst-coated plates were fabricated using spray coating. The dry methane reforming (DMR) performances of catalyst-coated plate were investigated and compared with DMR performances of catalyst pellets. As the mass transfer was improved, the methane consumption rate per gram of catalyst coated onto metal plate was ten times greater than those of catalyst pellets approximately. The carbon deposition was also significantly prevented when the catalyst was constructed as a thin-film layer on the plate under our developing condition. Therefore, this catalyst-coated plate can be further developed for multichannel reactor.

Modeling and design of a microchannel reformer for efficient conversion of glycerol to hydrogen

The objectives of this study are to investigate steam reforming (SR) of glycerol, by-product of biodiesel synthesis, in a wall-coated catalytic microchannel by a detailed mathematical model and design an adiabatic microchannel reformer that can be integrated into a biodiesel production plant with an annual capacity of 4 × 103 m3/year. Modeling and simulation studies are based on Finite Element Method (FEM) technique. Sizing and design of the multichannel reactor involving wall-separated arrays of parallel microchannels is based on converting a minimum of 85% of the glycerol obtained as a by-product of the biodiesel production. The results show that the microchannel architecture enables fast and uniform transfer of the sensible heat of the feed stream to the catalyst layer. This phenomenon, which is more pronounced by using thick and high thermal conductivity walls between channels, allows SR to run without external heat supply and leads to glycerol conversions above 85%. It is demonstrated that a multichannel unit of 1 × 10−2 m3 volume, operating without external energy supply, is sufficient to convert ca. 90% of the glycerol produced in a biodiesel plant with a capacity of 4 × 103 m3/year.

Simulation of a shock absorber with vertical buckling tubes welded in the longitudinal direction

The Ignalina Nuclear Power Plant (NPP) has two RBMK-1500 graphite moderate boiling water multi-channel reactors. The Ignalina NPP Unit 1 was shut down at the end of 2004 while the Unit 2 was shut down at the end of 2009. Spent fuel assemblies are located in the pools of Ignalina NPP Units. These spent fuel assemblies will be loaded to the special casks for storage of the spent fuel assemblies. The drop of the cask during the lifting and lowering operation has to be taken into account as an unlikely event.Shock absorbers are mounted on the bottom of the stepped pool. A special shock absorber design using vertical buckling tubes has been developed. In case of a drop of the cask, the buckling tubes dissipate the kinetic and potential energy and reduce the impact force to the floor. These tubes are made of a stainless steel sheet and welded in the longitudinal direction. Therefore, the influence of the weld on vertical buckling of the tubes should be evaluated. Finite element analysis software ABAQUS was used to estimate the influence of the weld on the plastic deformation behaviour of the tubes.

Performance Research on a Methane Compact Reformer Integrated with Catalytic Combustion

AbstractA multichannel reformer integrated with catalytic combustion was investigated for methane steam reforming to produce hydrogen. In this system, the main portion of the required heat was supplied by methane oxidation in the catalytic combustor located on two sides of the reformer. In the compact multichannel reactor, the methane conversion rate is high enough compared to the equilibrium values at different temperatures. The performance of the multichannel reformer was investigated under various operating conditions, such as the reformer temperature and the feed stream ratios in both the reformer and the catalytic combustor. The best feed flow rate ratio of reforming to combustion ranged from 1.3 to 1.5, with &gt; 95 % methane conversion. It is anticipated that this multichannel reformer can generate enough hydrogen for a 30‐W fuel cell system, due to its small volume.

First steps towards a constructal Microbial Fuel Cell.

In order to reach real operating conditions with consequent organic charge flow, a multi-channel reactor for Microbial Fuel Cells is designed. The feed-through double chamber reactor is a two-dimensional system with four parallel channels and Reticulated Vitreous Carbon as electrodes. Based on thermodynamical calculations, the constructal-inspired distributor is optimized with the aim to reduce entropy generation along the distributing path. In the case of negligible singular pressure drops, the Hess-Murray law links the lengths and the hydraulic diameters of the successive reducing ducts leading to one given working channel. The determination of generated entropy in the channels of our constructal MFC is based on the global hydraulic resistance caused by both regular and singular pressure drops. Polarization, power and Electrochemical Impedance Spectroscopy show the robustness and the efficiency of the cell, and therefore the potential of the constructal approach. Routes towards improvements are suggested in terms of design evolutions.

Microwaves and microreactors: Design challenges and remedies

Although microwave enhanced chemistry has become an established research topic, a significant knowledge gap exists with respect to the electromagnetic interactions. This paper aims to address this gap, in particular regarding to small and microstructured processing systems. By means of relatively simple demonstrations, key electromagnetics aspects are highlighted, pointing out the restricted control over operating conditions in familiar microwave systems. In response to these limitations, a radically different approach is presented in the shape of the coaxial traveling microwave multichannel reactor concept. Numerical simulations show that this concept enables controlled and optimized microwave processing.

Single and Multi-Channel Reactor for Oxidative Coupling of Methane

Abstract Management of the produced heat has been one of the challenges encountered in the oxidative coupling of methane (OCM) process. In this study, the influence of the thermal conductive tubular reactor on the total productivity and selectivity of OCM was investigated. The reactors were made from three different metal compounds: two stainless steel tubes and one gold-coated copper tube, and their impact on the operating conditions was compared. 5% Li/MgO was prepared as a catalyst for OCM and characterized by XRD, CO2-TPD, FTIR, and BET. In addition, the effect of reactor geometry on the oxidative coupling process was investigated experimentally in the single channel and multi-channel reactors with different hydraulic diameters.

Computational fluid dynamics model of a modular multichannel reactor for Fischer–Tropsch synthesis: Maximum utilization of catalytic bed by microchannel heat exchangers

A computational fluid dynamics (CFD) model for the Fischer–Tropsch synthesis (FTS) reaction was developed for a compact modular multichannel reactor with microchannel heat exchangers installed between catalytic bed channels. In addition to detailed levels of balance equations, the kinetic parameters for lumped FTS reaction rates and a convective heat transfer coefficient were estimated by fitting experimental data and the validity of model was corroborated by the comparison between experimental and simulated results. The model was used to evaluate the cooling performance of microchannel heat exchangers with varying flow rates, and several reactor specifications including the use of all catalytic bed channels, no inert materials, and reactors arranged in series were considered. When the number of catalytic bed channels was increased, the increase of CO conversion was observed with a maximum temperature within the operating range, but a possible thermal runaway could be expected due to high sensitivity to feed temperature change. In-series reactors also confirmed the increased conversion and the safe operation of the second reactor, and proved to be a major advantage for this reactor arrangement.

A compact highly efficient multichannel reactor with a fixed catalyst bed to produce hydrogen via methanol steam reforming

A new design of the multichannel reactor with a brass catalytic unit (52mmdiameter and 10mm thick) containing 139 short channels (10mm in length and 2mm diameter) for the methanol steam reforming is presented. Compared to the conventional fixed-bed catalytic reactors, the multichannel reactor demonstrates low hydrodynamic resistance and low temperatures gradients. Thus, at the maximal flow rate, the pressure drop was only 0.025torr while the temperature gradient along the catalytic unit axial section was only 0.8°C/cm. The reactor is equipped with an integrated evaporation chamber and a special reagent feeding system to provide uniform flow distribution in all channels. A numerical simulation of the gas flow dynamics, performed with the Fluent 6.3 software package, showed that the maximum flow inhomogeneity in the channels was 0.47%.The tests of the multichannel reactor on the methanol steam reforming showed that at 270°C, the hydrogen production rate was 110.5l/h at the methanol conversion 76.7% and the concentration of carbon monoxide in the output mixture 0.56mol%.

Dynamic analytical and experimental research of shock absorber to safeguard the nuclear fuel assemblies

The Ignalina Nuclear Power Plant (NPP) has two RBMK-1500 graphite moderated boiling water multi-channel reactors. The Ignalina NPP Unit 1 was shut down at the end of 2004 while Unit 2 has been in operation for over 5 years. After shutdown at the Unit 1 remained spent fuel assemblies with low burn-up depth. In order to reuse these assemblies in the reactor of Unit 2 a special set of equipment was developed. One of the most important items of this set is a container, which is used for the transportation of spent fuel assemblies between the reactors of Unit 1 and Unit 2. A special shock absorber was designed to avoid failure of fuel assemblies in case of hypothetical spent fuel assemblies drop accident during uploading/unloading of spent fuel assemblies to/from container. This shock absorber was examined using scaled experiments and finite element analysis.Static and dynamic investigations of the shock absorber were performed for the estimation and optimization of its geometrical parameters. The objective of this work is the estimation whether the proposed design of shock absorber can fulfil the stopping function of the spent fuel assemblies and is capable to withstand the dynamics load. Experimental testing of scaled shock absorber models and dynamic analytical investigations using the finite element code ABAQUS/Explicit were performed. The simulation model was verified by comparing the experimental and simulation results and it was concluded that the shock absorber is capable to withstand the dynamic load, i.e. successful force suppression function in case of accident.