Oxidation Reactor Research Articles

The analysis of distribution of the reaction mixture in ammonia oxidation reactor

Abstract This article describes the influence of various design modifications of the ammonia oxidation reactor operating in nitric acid plant TKIV in Kędzierzyn-Koźle on flow distribution of an air-ammonia mixture. The CFD (Computational Fluid Dynamics) simulations of turbulent flow were carried out with SST k-ω turbulence model to close the system of RANS (Reynolds Averaged Navier-Stokes) equations. The simulation results show that the properly selected perforated plate screen and the conical diffuser ensure uniform flow of gas on the ammonia oxidation catalysts and on the catalysts for nitrous oxide decomposition. It was proved experimentally achieving uniform temperature of nitrous gases in different locations under the catalytic gauzes and high efficiency of ammonia oxidation and nitrous oxide decomposition

Low Temperature Catalytic Combustion Reactors for High Precision Carbon Isotope Measurements in Gas Chromatography Combustion Isotope Ratio Mass Spectrometry

Metal oxide-filled reactors constructed with ceramic tubes or fused silica capillary are widely used for combustion in gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS). However, they tend to be easily cracked or broken and prone to leaks at operating temperatures of ∼950 °C. Here we introduce a modified commercially available catalytic combustion/reduction methanizer to quantitatively convert organics to CO2 for δ13C analysis while retaining chromatographic resolution. These modified "ARC" reactors operate with a transition-metal catalyst that requires a flowing O2 gas to enable complete conversion to CO2 at lower temperature (620 °C) with acceptable reactor life, reduced complexity, and improved robustness. Performance of two versions of the ARC reactors with different combustion volumes was characterized by analysis of steroid and alkane isotopic standard materials. Linearity of steroid isotopic standards ranged from 0.02 to 0.60 ‰/V in the range of 25 to 200 ng of each steroid injected. Precisions and accuracies of measurements for steroids and alkanes had average standard deviations of SD(δ13C) less than ±0.18 ‰ and average accuracy of better than 0.19 ‰ δ13CVPDB. Peak width expansion within both devices were similar to that in traditionally used metal oxide reactors. These data demonstrate for the first time that novel combustion schemes enable operation at lower temperatures as an alternative approach comparable to high temperature techniques to yield high precision δ13C data with GCC-IRMS.

Thermodynamic assessment of non-catalytic Ceria for syngas production by methane reduction and CO2\u2009+\u2009H2O oxidation

Chemical looping syngas production is a two-step redox cycle with oxygen carriers (metal oxides) circulating between two interconnected reactors. In this paper, the performance of pure CeO2/Ce2O3 redox pair was investigated for low-temperature syngas production via methane reduction together with identification of optimal ideal operating conditions. Comprehensive thermodynamic analysis for methane reduction and water and CO2 splitting was performed through process simulation by Gibbs free energy minimization in ASPEN Plus®. The reduction reactor was studied by varying the CH4/CeO2 molar ratio between 0.4 and 4 along with the temperature from 500 to 1000 °C. In the oxidation reactor, steam and carbon dioxide mixture oxidized the reduced metal back to CeO2, while producing simultaneous streams of CO and H2 respectively. Within the oxidation reactor, the flow and composition of the mixture gas were varied, together with reactor temperature between 500 and 1000 °C. The results indicate that the maximum CH4 conversion in the reduction reactor is achieved between 900 and 950 °C with CH4/CeO2 ratio of 0.7–0.8, while, for the oxidation reactor, the optimal condition can vary between 600 and 900 °C based on the requirement of the final product output (H2/CO). The system efficiency was around 62% for isothermal operations at 900 °C and complete redox reaction of the metal oxide.

Nitrogen Removal Characteristics and Comparison of the Microbial Community Structure in Different Anaerobic Ammonia Oxidation Reactors

Nitrogen removal characteristics and the comparison of the microbial community structure were investigated in different anaerobic ammonia oxidation (Anammox) reactors: an anaerobic sequencing batch reactor (ASBR) and a biofilter reactor. The Anammox systems were inoculated with sludge from the second settling tank of a wastewater treatment plant in Guangzhou, China. After successful start up of Anammox, the microbial community structure of different Anammox reactors were studied through high-throughput sequencing. The results showed that anaerobic ammonium oxidation in the ASBR reactor could successfully start up after 134 days, while Anammox in the biofilter could start up after 114 days. In both systems, total nitrogen removal was at 80% after more than 200 days of operation. The diversity of denitrifying microorganisms was high in both reactors, with Planctomycetes as the main taxa. Anammox bacteria belonging to the genera Candidatus Anammoxoglobus and Kuenenia, were dominant in the ASBR, while all three genera of Candidatus, Anammoxoglobus, Kuenenia, and Brocadia, could be detected in the biofilter reactor. Therefore, the biofilter starts up faster than the ASBR, and contains richer species, which makes it more suitable to domesticate Anammox bacteria.

Power and syngas production from partial oxidation of fuel-rich methane/DME mixtures in an HCCI engine

Polygeneration is the coupling of energy conversion and conversion towards useful chemicals, providing a route towards more flexible and efficient energy systems. In this work, we explore a particular concept of polygeneration using an internal combustion engine as a reactor for partial oxidation to generate synthesis gas in variable combinations with mechanical work and heat. Experiments were performed in a single-cylinder engine operated in homogeneous-charge compression-ignition (HCCI) mode on a mixture of methane and air with dimethyl ether (DME) as a reactivity-enhancing additive. For intake temperature from 100 to 190 °C, the range of stable, non-sooting operation with acceptable pressure-rise rates was determined in terms of equivalence ratio and DME mole fraction in the fuel. At 150 °C intake temperature, 8.7–9.5% DME were needed to stabilize operation at equivalence ratios between about 1.3 and 2.7. Experimental results from fuel-rich conditions with equivalence ratios ranging from 1.65 to 2.34 were compared to simulations with a homogeneous, single-zone engine model. The concept of exergy was used to investigate the thermodynamic performance of the polygeneration engine. The effect of the equivalence ratio on work and heat output, thermal and exergetic efficiency, and selectivity towards useful product species was investigated. In the experiments a work output of up to 160 J (ϕ = 1.65) per cycle (IMEP = 4.82 bar) and exergetic efficiencies of up to 81.5% (ϕ = 2.34) were achieved. The simultaneous generation of synthesis gas had a selectivity of up to 72% for hydrogen and 79% for carbon monoxide (both at ϕ = 2.34).

Simultaneous removal of ammonia and nitrate by coupled S0-driven autotrophic denitrification and Anammox process in fluorine-containing semiconductor wastewater

To achieve the simultaneous removal of NH4+-N and NO3−-N in F−-containing semiconductor wastewater by coupled S0-driven autotrophic denitrification and Anammox process, the effect of variable F− concentration on the Anammox process was investigated by batch experiments. The denitrifying ammonium oxidation (Deamox) reactor was then started-up to explore the feasibility of the coupling of Anammox and sulfur autotrophic denitrification (SADN) for the treatment of semiconductor wastewater. Short-term variation of F− concentration has an obviously effect on the activity of Anammox sludge, but didn't affect the nitrogen conversion rate. The activity of Anammox obviously decreased after long-term operation of the Deamox reactor when influent F− concentrations reached 552 mg/L. The sensitivity of Anammox bacteria to F− concentration is stronger than that of SADN bacteria. Total nitrogen removal efficiency of 98% and total nitrogen removal rate of 4.11 kg/(m3·d) were achieved in the Deamox reactor, when the F− was pre-treated by calcium ions. Moreover, the high-throughput 16S rRNA gene sequence analysis indicated that variation in F− concentrations could influence the structure and functional of microbial communities in the Deamox process. Candidatus Kuenenia, Thiobacillus and Sulfurimonas were main functional bacteria that achieved symbiotic.

Moving Brick Receiver–Reactor: A Solar Thermochemical Reactor and Process Design With a Solid–Solid Heat Exchanger and On-Demand Production of Hydrogen and/or Carbon Monoxide

Three crucial aspects still to be overcome to achieve commercial competitiveness of the solar thermochemical production of hydrogen and carbon monoxide are recuperating the heat from the solid phase, achieving continuous or on-demand production beyond the hours of sunshine, and scaling to commercial plant sizes. To tackle all three aspects, we propose a moving brick receiver–reactor (MBR2) design with a solid–solid heat exchanger. The MBR2 consists of porous bricks that are reversibly mounted on a high temperature transport mechanism, a receiver–reactor where the bricks are reduced by passing through the concentrated solar radiation, a solid–solid heat exchanger under partial vacuum in which the reduced bricks transfer heat to the oxidized bricks, a first storage for the reduced bricks, an oxidation reactor, and a second storage for the oxidized bricks. The bricks may be made of any nonvolatile redox material suitable for a thermochemical two-step (TS) water splitting (WS) or carbon dioxide splitting (CDS) cycle. A first thermodynamic analysis shows that the MBR2 may be able to achieve solar-to-chemical conversion efficiencies of approximately 0.25. Additionally, we identify the desired operating conditions and show that the heat exchanger efficiency has to be higher than the fraction of recombination in order to increase the conversion efficiency.

Hierarchical Fe-ZSM-5/SiC foam catalyst as the foam bed catalytic reactor (FBCR) for catalytic wet peroxide oxidation (CWPO)

Structured Fe-ZSM-5 zeolite supported on silicon carbide (SiC) foam catalyst was develop and applied as the packed foam bed catalytic reactor (FBCR) to the liquid phase catalytic wet peroxide oxidation (CWPO) of phenol under flow conditions. Fe catalysts were uniformly incorporated into ZSM-5 coatings using chemical vapour deposition (CVD). Fluid flow analysis of FBCR was performed by varying liquid flow rate, showing the transition of reactor type from the plug flow reactor to the continuous stirred tank reactor at about 1 ml min−1. Systematic investigation of CWPO within Fe-ZSM-5/SiC FBCRs identified the optimum condition of operating the FBCR (80 mm bed length) as at 60 °C and 1 ml min−1 with the turnover frequency (TOF) of 95 h−1 for phenol degradation (apparent activation energy = 3.4 kJ mol−1) and total organic carbon (TOC) conversion of 45.5%. It was believed that the enhanced macromixing promoted by cellular foam supports was accountable for the observed catalytic performance. The longevity of FBCR under flow conditions was also assessed, showing its good stability over 24 h, as well as the potential for practical adoption.

A Pd-TSH composite membrane reactor for one-step oxidation of benzene to phenol.

Pd membranes with excellent stability and flux were prepared by modified electroless plating, and a loose TSH zeolite with intraparticle hollows was joined on the Pd membrane by a covalent bonding method. The prepared Pd-TSH composite membrane shows outstanding performance for phenol production in the one-step oxidation of benzene to phenol.

A preliminary comparative study between oxide and metallic fuelled ASTRID-like reactor under a B&B strategy

The objective of this paper is to study the reactivity behaviour and the isotopic fuel performance of an ASTRID-like reactor under a breed and burn strategy for two core designs: with oxide and with metallic fuel. The proposed reshuffling scheme was simulated with MCNP6 and the JEFF-3.2 cross-sections library to extend the fuel life by two more cycles. Our findings showed that the implementation of the reshuffling scheme enhanced the fuel utilisation, obtaining cycle extensions of 805 days and 1305 days, over the first 365 days, for the oxide and metallic fuelled designs, respectively. For the metallic-fuelled design the breeding of Pu-239 achieved a production of 577.7 kg, which represents a production rate of 126.3 kg/EFPY. The conversion rate for the metallic-fuelled design was 1.06 and 0.96 for the oxide-fuelled design. Regarding the coolant void reactivity worth, for the oxide-fuelled design it becomes positive after the second fuel reshuffling.

A preliminary comparative study between oxide and metallic fuelled ASTRID-like reactor under a B&B strategy

The objective of this paper is to study the reactivity behaviour and the isotopic fuel performance of an ASTRID-like reactor under a breed and burn strategy for two core designs: with oxide and with metallic fuel. The proposed reshuffling scheme was simulated with MCNP6 and the JEFF-3.2 cross-sections library to extend the fuel life by two more cycles. Our findings showed that the implementation of the reshuffling scheme enhanced the fuel utilisation, obtaining cycle extensions of 805 days and 1305 days, over the first 365 days, for the oxide and metallic fuelled designs, respectively. For the metallic-fuelled design the breeding of Pu-239 achieved a production of 577.7 kg, which represents a production rate of 126.3 kg/EFPY. The conversion rate for the metallic-fuelled design was 1.06 and 0.96 for the oxide-fuelled design. Regarding the coolant void reactivity worth, for the oxide-fuelled design it becomes positive after the second fuel reshuffling.

High-Throughput Production of Heterogeneous RuO2/Graphene Catalyst in a Hydrodynamic Reactor for Selective Alcohol Oxidation

We report on the high-throughput production of heterogeneous catalysts of RuO2-deposited graphene using a hydrodynamic process for selective alcohol oxidation. The fluid mechanics of a hydrodynamic process based on a Taylor–Couette flow provide a high shear stress field and fast mixing process. The unique fluidic behavior efficiently exfoliates graphite into defect-free graphene sheets dispersed in water solution, in which ionic liquid is used as the stabilizing reagent to prevent the restacking of the graphene sheets. The deposition of RuO2 on a graphene surface is performed using a hydrodynamic process, resulting in the uniform coating of RuO2 nanoparticles. The as synthesized RuO2/IL–graphene catalyst has been applied efficiently for the oxidation of a wide variety of alcohol substrates, including biomass-derived 5-hydroxymethylfurfural (HMF) under environmentally benign conditions. The catalyst is mechanically stable and recyclable, confirming its heterogeneous nature.

Hydrothermal ethanol flames in Co-flow jets

Results on the autoignition and stabilization of ethanol hydrothermal flames in a Supercritical Water Oxidation (SCWO) reactor operating at constant pressure are reported. The flames are observed as luminous reaction zones occurring in supercritical water; i.e., water at conditions above its critical point (approximately 22 MPa and 374 °C). A co-flow injector is used to inject fuel (inner flow), comprising an aqueous solution ranging from 20%-v to 50%-v ethanol, and air (annular flow) into a reactor filled with supercritical water at approximately 24.3 MPa and 425 °C. Results show hydrothermal flames are autoignited and form diffusion flames which exhibit laminar and/or turbulent features depending upon flow conditions. Two orthogonal camera views are used; one providing a backlit shadowgraphic image of the co-flow jet and the other providing color images of the flame. In addition, spectroscopic measurements of flame emissions in the UV and visible spectrum are discussed.

Mathematical modeling of isopropylbenzene oxidation reaction and oxidation reactor

In this paper, several kinetic models of isopropylbenzene oxidation are considered. Kinetic model parameters were presented in order to simulate the reaction course in time. The data obtained are may be used to simulate the isopropylbenzene oxidation reactor. This paper represents the results of this computer simulation.

Optimization of structural parameters of an inner preheating transpiring-wall SCWO reactor

A computational fluid dynamics model of an inner preheating transpiring wall reactor for supercritical water oxidation was proposed to optimize the structural parameters. Results showed that higher feed degradation efficiencies and lower inner surface temperatures of the porous wall were obtained at higher reactor diameters. Although the increase in reactor length promoted feed degradation, the increased inner surface temperatures of the porous wall were unsuitable for water film formation. A pyknic-type reactor with a lower length/diameter (H/D) value at a constant volume was more beneficial for water film formation and feed degradation. A higher feed concentration or feed flow required a lower H/D value to ensure an ideal water film formation and feed degradation. We proposed the use of sectional heat load as a new parameter for reactor design based on the similarity between the boiler furnace and the transpiring wall reactor. The sectional heat load in a certain range was calculated to serve as guide in the design of transpiring wall reactors.

The performance of anammox reactor during start-up: Enzymes tell the story

Abstract Start-up is the first and essential step in the operation of anammox (anaerobic ammonia oxidation) reactor. It is helpful to know the progress of start-up for the real-time optimization of reactor performance. In this work, a start-up mode was successfully established, by which the anammox reactor was smoothly put into use, with NLR (Nitrogen Loading Rate) and NRR (Nitrogen Removal Rate) of 11.0 and 10.1 kg-N /(m3 d), respectively. During the start-up, the dehydrogenase, alkaline phosphatase, hydrazine oxidase and heme of the anammox granular sludge were investigated and their activity/content was correlated with the reactor performance. The activity of dehydrogenase and alkaline phosphatase was found to decrease with the elevation of NLR. On the contrary, the hydrazine oxidase activity and heme content were observed to increase with the elevation of NLR. Based on the relative enzyme level, an enzyme indicator system was created to monitor the start-up progress of anammox reactor.

Electrochemical in-situ hydrogen peroxide generation in a packed-bed reactor for Fenton oxidation of p-nitrophenol in aqueous solution

Advancements in electrochemical generation of hydrogen peroxide (H2O2) in Fenton systems hasten the realization of a “chemical-free” treatment of organic pollutants in water. The present study used a novel air-sparged, packed-bed electrode configuration with reticulated vitreous carbon (RVC) as packing material for electrochemical H2O2 generation. The effects of initial pH, applied current, sparging rate, mass of RVC and electrolyte concentration on cumulative H2O2 generation and current efficiency were evaluated. From the results, the operating conditions that gave the optimal cumulative H2O2 generation and current efficiency were pH0 = 2.0, applied current = 50 mA, air sparging rate = 0.5 L min−1, mass of RVC = 0.75 g, and electrolyte concentration = 100 mM Na2SO4. The same reactor configuration was used for the treatment of the model contaminant from aqueous solution and caused the complete removal of p-nitrophenol (pnP) within a 2 h duration. Mineralization of aromatic intermediates was confirmed by gas chromatography – mass spectroscopy analyses of samples and supported by the reduction in chemical oxygen demand and total organic carbon.

The microbial community structure change of an anaerobic ammonia oxidation reactor in response to decreasing temperatures.

In anaerobic ammonium oxidation (anammox) systems, temperature may regulate the activity of functional bacteria (e.g., anammox bacteria) and the composition of the microbial population, ultimately determining the performance of the anammox reactor. Knowledge of the dynamic changes in nitrogen removal rates and the microbial anammox community at low and/or ambient temperature is still limited. This study explored the response of an anammox sequencing batch reactor (SBR) to a gradient of decreasing temperature (33, 25, 20, 15, 10°C), followed by recovery to 22°C, over 360days. Particularly, the specific anammox activity (SAA) and microbial community were assessed. The anammox reaction in the SBR remained stable and efficient at 20-33°C, with a total nitrogen removal load of 0.4g-NL-1day-1 and an SAA of > 0.32g-Ng-VSS-1day-1; 10°C was the turning point for the anammox bacterial metabolic activity, at which the SAA decreased by 91% compared with that at 33°C. After the temperature was returned to 22°C, the anammox activity recovered to 0.24g-Ng-VSS-1day-1. The apparent activation energy for the anammox reaction was 68.4kJmol-1 at 10-33°C and 152.9kJmol-1 at 10-20°C. High-throughput sequencing results revealed that Kuenenia was the dominant species of anammox bacteria, and Kuenenia had a higher tolerance to low temperature than Candidatus Brocadia and Candidatus Jettenia. This study clearly shows the effectiveness of anammox bioreactors for treatment of wastewater at ambient temperatures of 15-33°C.

Formation of concentric shell carbon by homogeneous partial oxidation of methane

It has been shown that the carbon soot produced as a byproduct of partial oxidation of methane consists of carbon nanoparticles of almost ideal spherical morphology and perfect concentric onion-like structure. The particles are unusually big for carbon onions and have outer diameter of 10–50 nm while the inner cage is rather typical for onions and has diameter below 1 nm. The concentric graphitic structure and spherical symmetry along with the absence of amorphous carbon are confirmed by transmission electron microscopy, electron diffraction, EDX spectroscopy and Raman investigation. The spherical particles get deposited on a wall of a partial oxidation reactor as loose particles embedded in a low density organic ovary, which can be detected by its luminescence or by cautious electron microscopy imaging. It is important that unlike literature reports on giant onions, the carbon deposit was dominated by these giant spheres. This process may be considered as a prototype for a production method for giant concentric shell carbon particle black.

Development of a flat membrane microchannel packed-bed reactor for scalable aerobic oxidation of benzyl alcohol in flow

A flat membrane microchannel reactor was designed and demonstrated for the safe and scalable oxidation of solvent-free benzyl alcohol with molecular oxygen on Au-Pd/TiO2 catalyst. The microchannel reactor employed a mesh-supported Teflon AF-2400 membrane, with gas and liquid channels on each side. Catalyst particles were packed in the liquid flow channel. Operation with 20 bara pressure difference between the gas and the liquid phases was possible at 120 °C. Pervaporation of organics through the membrane was experimentally measured to ensure that the organic vapour concentration remained below the lower flammability limit during the reaction. High oxygen pressure was shown to have a positive effect on reactor performance. A conversion of benzyl alcohol of 70% with 71% selectivity to benzaldehyde was obtained at 1150 gcat·s/galcohol, 8.4 bara oxygen pressure and 10 bara liquid pressure. The oxygen consumption rate was not significantly decreased when doubling the membrane thickness, indicating that the membrane generated only low resistance to oxygen mass transfer. When changing the catalyst particle size and the liquid flow rate, no significant effect was observed on the oxidation reaction rate. An effectiveness factor approach is proposed to assess the effect of oxygen permeation and transverse mass transfer on the catalyst packed in the membrane reactor, which suggests that the oxidation of benzyl alcohol on the highly active Au-Pd/TiO2 catalyst is controlled by the oxygen transverse mass transfer in the bulk liquid within the catalyst bed. Scale-up of the flat membrane microchannel reactor was demonstrated through increasing the liquid channel width by approximately ten times, which increased the reactor productivity by a factor of eight.