Micro‐packed bed reactors (μPBRs) have the advantages of high heat and mass transfer efficiency and excellent safety, and they have been successfully applied to hydrogenation and oxidation reactions. ...However, the study of gas–liquid flow regimes in the μPBR, which is essential for the mass transfer modeling and reactor scale‐up, is still insufficient due to the limitation of micro‐scale and complexity of capillary force. In this work, the flow regimes in the two‐dimensional μPBR were systematically studied by visual method utilizing a high‐performance camera. Four typical flow regimes and characteristics were captured, and flow regime transition was revealed. Effects of gas and liquid superficial velocities, liquid physical properties, and particle sizes on liquid spreading areal fraction and pressure drop were investigated. Flow regime transition correlation of churn flow and pseudo‐static flow in the μPBR was provided for the first time based on the summary of the current and previous published results.
Selective Oxidation of Sulfides in Flow Chemistry Silva, Filipa; Baker, Alastair; Stansall, James ...
European journal of organic chemistry,
May 15, 2018, Letnik:
2018, Številka:
18
Journal Article
Recenzirano
Odprti dostop
A packed‐bed reactor with oxone has been employed for selective oxidations of sulfur compounds. Various sulfides containing different functional groups are efficiently oxidized to the corresponding ...sulfoxides without formation of sulfones or other side products.
A selective sulfide oxidation has been achieved in flow chemistry by using fixed‐bed oxone reactors.
Flow biocatalysis has emerged as a promising technology for the sustainable production of chemicals. Multiple immobilized enzymes are often used as biocatalysts to perform enzymatic cascade reactions ...in flow biocatalytic systems. When designing packed‐bed reactors with multiple immobilized enzymes, the enzymes are distributed in porous particles, and the porous particles are distributed in catalyst zones. A recently developed methodology is extended for selecting spatial immobilization distributions in batch reactors to packed‐bed reactors. Mechanistic models are used to compare the three most basic designs for a packed‐bed reactor, i.e., mixed individually immobilized enzymes, separated individually immobilized enzymes, and mixed co‐immobilized enzymes. For first‐order microkinetics, the design with co‐immobilized enzymes was found to always outperform the other two. Separating individually immobilized enzymes in two zones was proven to outperform mixing them in one zone for any positive order reaction kinetic.
A recently developed mechanistic modeling methodology for immobilized enzymatic cascades is extended to packed‐bed reactors. In packed‐bed reactors, the enzymes are immobilized in porous particles which are distributed in zones. The theoretical background of this design process is given by examining the most basic cases.
Independent from their intended purpose, the understanding of structural characteristics of random packings of particles having defined shapes is important to understand and optimize fluid dynamic ...behaviour, heat, and mass transfer. The packing structure can be described by the coordination number, local porosity profiles, the average porosity, and pore characteristics, which are influenced by the wall and thickness effect; the material, shape, and size distribution of the packing particles; the packing and compaction mode; and the shape and material of the packing's containing walls. Therefore, existing knowledge on the structure of randomly packed mono‐sized particles is reviewed to provide an updated selection of relevant parameters and their derived correlations obtained by experimental, numerical, and analytical means.
A redox chemical looping process is investigated as an add-on deoxygenation unit for the production of high-purity nitrogen from air using pressure swing adsorption systems. A material screening ...study indicated the non-stoichiometric perovskite oxide Sr0.8Ca0.2FeO3−δ as a promising candidate redox material with fast kinetics and a 75% greater gravimetric oxygen capacity compared to state-of-the-art SrFeO3 at the desired process conditions. Granules of Sr0.8Ca0.2FeO3 were manufactured and characterised according to their thermodynamic and kinetic redox properties. A lab scale packed-bed reactor was experimentally tested as proof-of-concept and used to validate a convection–diffusion model of mass transfer within the reactor. The model was further applied for scaling up to a production of 1000 Nm3h−1 of high-purity nitrogen. The results indicate good performance of the packed-bed configuration and a favourable energy demand compared with existing nitrogen production technologies. The proposed technology could greatly extend the useable oxygen impurity range of pressure swing adsorption systems for nitrogen production.
•Materials screening highlights Sr0.8Ca0.2FeO3 as promising for oxygen separation.•Thermodynamic, kinetic and cycle stability characterisation.•Packed bed reactor experiments at elevated pressure with good performance.•Reactor model and scaled up system analysis show promising results.
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•The utilization of DHBQ as a mediator in the Mediated fuel cell (MedFC).•The DHBQ reduced in a packed-bed reactor has been fed as an anodic fuel in MedFC.•1.12 V of open circuit ...voltage and 282 mW/cm2 power have been obtained in MedFC.
Hydrogen fuel cells, which produce electrical energy and only water as a byproduct, are evaluated for their use in eco-friendly technology. However, there are challenges with using abundant precious metal catalysts for electrodes, particularly regarding hydrogen gas crossover and managing the moisture of the polymer electrolyte membrane. To overcome these challenges, a mediated fuel-cell (MedFC) system, in which hydrogen fuel cells are combined with a redox-flow battery using an oxidation–reduction reaction of an electrolyte, has been recently developed. In a MedFC system, the reduced ions of redox-active materials generated by the oxidation of hydrogen in a packed-bed reactor are fed to the fuel cell electrode as a mediator. In this study, 2,5-dihydroxy1,4-benzoquinone (DHBQ) was used as a anode mediator to operate MedFCs under alkaline conditions. DHBQ and hydrogen were injected with an upward flow into the packed-bed reactor to reduce DHBQ via a chemical reaction. On the anode side of the fuel cell, DHBQ oxidized and transferred the electrons to the cathode. By contrast, an oxygen reduction reaction (ORR) occurred at the cathode under alkaline conditions. The reduction potential of DHBQ was −0.72 V (vs. SHE), and that of ORR was 0.4 V (vs. SHE); thus, the theoretical potential of the cell was 1.12 V. During the MedFC operation, a maximum power density of 282 mW/cm2 was obtained.
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•Identified operating windows for syngas production by calcination of CaCO3 in H2.•Desorption enhanced phenomena occurs when calcination and RWGS eq. are fulfilled.•CaO RWGS catalytic ...activity produces gas close to desorption enhanced RWGS eq.•H2/CO molar ratio below 2 can be obtained under desorption enhanced RWGS cond.
A syngas production method is investigated that combines in a single reactor the enhanced decomposition of CaCO3 with H2 and the reverse water–gas shift (RWGS) of part of the CO2 evolved during calcination. The method exploits Le Chatelier’s principle, to overcome RWGS equilibrium limitations by conducting such reactions with an excess of CaCO3 and at sufficiently high temperatures to maintain the partial pressure of CO2 close to the calcination equilibrium. The decomposition and RWGS reactions result in a ‘desorption-enhanced reverse water–gas shift’ (DERWGS) equilibrium of CaCO3 on H2, observed in experiments performed in a packed-bed reactor operated between 1023 and 1123 K and 1 and 5 atm when feeding H2 to a mixture of CaCO3, with or without a RWGS catalyst. Product gases containing over 25 vol% CO, with an H2/CO molar ratio of 2 and below, were obtained. In experiments without the use of an RWGS catalyst, the DERWGS equilibrium was also approached thanks to the catalytic activity of CaO for RWGS. The syngas analogue obtained from these reactions opens the door to new processes for synthetic fuel production from CaCO3 and renewable H2.
•Reaction-diffusion model explains acid leaching of roasted NdFeB magnets.•REEs can be leached selectively from roasted magnets in stirred tank.•Selective REE leaching in packed bed is demonstrated.
...Acid leaching of Nd and Fe from roasted NdFeB magnet powders was studied in stirred-tank and packed-bed reactors. The experimental data at sulfuric acid concentrations of 0.02–1.0 mol/L and at 80 °C were correlated using a diffusion–reaction model assuming homogeneous distribution of the constituents in the magnet. The results show that the experimental data can be correlated well when formation of NdFeO3 during roasting is taken into account. Decomposition of NdFeO3 to Nd3+(aq) and Fe3+(aq) is the main route in neodymium dissolution from roasted NdFeB. The model parameters derived from stirred-tank data predict reasonable well leaching in packed-bed reactor. In both systems, re-precipitaion of iron due to acid depletion allows selective dissolution of Nd and other rare earth elements.
This paper addresses the experimental demonstration and model validation of chemical looping reforming in dynamically operated packed-bed reactors for the production of H2 or CH3OH with integrated ...CO2 capture. This process is a combination of auto-thermal and steam methane reforming and is carried out at high pressure, as typical for reforming processes, and at relatively low to intermediate temperatures (ranging from 600 to 900°C). The oxidation of the oxygen carrier is performed with air and the hot depleted air stream is fed to a gas turbine, which contributes to reduce the electricity demand. After oxidation, a low-grade fuel is used for the reduction of the oxygen carrier, e.g. off-gas from a PSA unit or non-condensable species from methanol synthesis and, when the bed is completely reduced, natural gas diluted with H2O and CO2 is reformed while the reactor is cooled down.
An experimental campaign has been carried out in a 2kWth packed-bed reactor using 500g of NiO supported on CaAl2O4 as reforming catalyst and oxygen carrier. This material has demonstrated very high stability over >400h of consecutive redox and reforming cycles. Due to the flexibility of the process, dry, wet and steam reforming compositions have been tested during the reforming phase. A 1D reactor model has been validated with the obtained experimental results, including also a detailed thermal model to account for the inevitable heat losses of the system. The experimental and model results are in good agreement in terms of breakthrough curves and temperature profiles. The experimental campaign during reforming also confirmed the possibility to carry out the heat removal phase by means of endothermic methane reforming.
The validated reactor model has subsequently been used for the simulation of different configurations in terms of heat management in which the different phases (oxidation, reduction and reforming) are simulated in series. In these analyses, the reactor design and performance have been compared for two plant configurations based on H2 and CH3OH production integrated with CO2 capture. For the case of H2 production, the CH4 conversion is 92% and all the CO2 is captured from the plant, while for CH3OH production the CH4 conversion reaches 90% and all carbon species, except CH3OH, are converted into CO2, which is separated with high purity.
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•Proof of concept of chemical looping reforming in packed bed reactor.•The model results in very good agreement with the experimental results.•Low grade fuel is used for the OC reduction instead of natural gas.•H2 yield equal to 2.74molH2/molCH4 with 100% of CCR.•CH3OH yield of 89% molCH3OH/molCH4 with 100% of CCR.
In this study, the process optimization of a tri-reformer reactor is conducted for the synthesis of hydrogen gas from natural gas using multi-objective optimization (MOO) approach. Specifically, four ...MOO problems are solved using three objective functions, namely maximization of H2, minimization of CO2, and minimization of power loss. It should be noticed that the power loss is an important economic factor due the large pressure drop and flowrates in packed bed reactors. However, it has not been used as an objective function for the optimization based design and/or operation of fixed bed reactor for reforming process to the best of authors’ knowledge. Three of the four MOO problems are 2-objective in nature with all the permutation and combination of the three objectives. The fourth MOO problem is solved considering all the three objectives, simultaneously. For all the MOO problems, feed conditions of O2, H2O, and Temperature are considered as the optimization variables. The results obtained with 3 objective functions are observed to be superior to the ones obtained from 2 objective problems.
•Two and three-objective optimization of a fixed-bed reactor using NSGA-II.•Study of tri-reformer reactor for the production syn-gas from natural gas.•Maximization of H2 production and minimization of power loss & CO2 emission.•Optimization variables are feed temperature, steam/methane, and oxygen/methane.
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