Reaction of NO and N2O gases with graphite in TGA

Thermal analyses were conducted in a thermogravimetric analyzer by isothermal techniques in order to characterize the carbon-nitrogen oxide reaction. The carbon samples employed in the present study were SP-1 graphite and Micro 450 graphite. Carbon-NO and carbon-N₂O reactions were carried out in a temperature range of 550–900 °C and 5–20 kPa of the partial pressure of reactant. In the NO reaction, reaction orders with respect to NO concentration and activation energy were 0.46-0.92 and 85–102 kJ/mol, respectively. The rate on the monolayer edge was higher than the rate on the multilayer edges. In the N₂O reaction, reaction orders with respect to N₂O concentration and activation energy were 0.55–1.35 and 167–190 kJ/mol, respectively.     

Determination of decomposition rate constants of volatile organic compounds and nitric oxide in a pulsed corona discharge reactor

The decomposition of toluene, propylene and nitric oxide by using a pulsed corona discharge process was investigated. The performance equation of the pulsed corona reactor was derived with the assumption that the decomposition reaction rate is directly proportional to the concentration of the pollutant and the discharge power. From this model equation and the experimental data, the apparent decomposition rate constants of various gaseous organic compounds and nitric oxide were determined. Alkene and substituted alkene were found to have much larger decomposition rate constants than aromatic compounds and substituted alkane, which indicates that the derivatives of aromatics and alkane cannot readily be decomposed in this system. To verify the validity of the model derived, the experimental data in the present study and in the literature were compared with the calculation results using the decomposition rate constants. Despite the different reactor geometry and experimental condition, good agreement between the experimental data and the calculation results was shown.     

Kinetic modeling of CO oxidation on Pt/CeO2 in a gradientless reactor

Cerium oxide is a major additive in three-way catalysts used in emission control of automobile exhaust. Pt/CeO₂ was studied in order to better understand the role of ceria in promoting CO oxidation reaction. The kinetics of carbon monoxide oxidation on Pt/cerium oxide catalyst, was studied over the temperature range 100–170°C. Steady state kinetic measurements of CO oxidation were obtained in a computer controlled micro-CSTR reactor. Activation energies were reported to vary between 39·5 and 51·2 kJ mol⁻¹. At low concentrations of either reactant (CO, O₂) and total conversion, the catalyst exhibited multiple steady states, similar to the multiplicity behavior of Pt/Al₂O₃. The total conversion was reached at 120°C. In comparison, the total conversion at low reactant concentrations was reached at a temperature of 148°C for the alumina-supported catalyst. Langmuir–Hinshelwood mechanisms gave a good fit to the data. However, no single rate expression could effectively describe the CO oxidation data over the whole concentration in the product of the CSTR reactor. The facts gathered indicate that oxygen adsorbed on interfacial Pt/Ce sites and ceria lattice oxygen provides oxygen for CO oxidation. Cerium oxide has been found to lower CO oxidation activation energy, enhance reaction activity and tends to suppress the usual CO inhibition effect.     

Kinetic modeling of hydrocracking reaction in a trickle-bed reactor with Pt/Y-zeolite catalysts

A kinetic model is developed to predict the entire distribution of hydrocarbon products for the hydrocracking reaction with Pt/Y-zeolite catalysts in a trickle-bed reactor. Operating conditions, such as temperature, pressure, and wax and H2 flow rates were varied to evaluate their effects on conversion and distribution, and kinetic parameters were estimated using the experimental data that covers the window of operating conditions. The comparison between experimental data and simulated results corroborated the validity of the developed model, and the quantitative prediction of the reactor performance was clearly demonstrated. To make evident the usefulness of the model, an optimization method, genetic algorithm (GA), was applied, and the optimal condition for the maximum production of C₁₀-C₁₇ was successfully calculated.     

High activity of copper-boralite in the reduction of nitric oxide with propane / oxygen

The activity of ZSM-5 and boralite zeolites (Na, H and Cu forms) in the reduction of nitric oxide with propane / oxygen is compared. Copper ion-exchanged boralite is more active than a corresponding Cu-ZSM-5 sample with the same MFI structure, Si/M (M = Al or B) ratio and copper content, showing that in copper-exchanged samples Brønsted acid sites do not play a key role in the reaction mechanism, in contrast to that found for samples without the exchanged transition metal.     

Selective reduction of nitric oxide with propene over platinum-group based catalysts: Studies of surface species and catalytic activity

The reduction of nitric oxide by propene in the presence of oxygen over platinum-group metals supported on TiO₂, ZnO, ZrO₂, and Al₂O₃ has been investigated by combined diffuse reflectance FT-IR spectroscopy and catalytic activity studies under flow reaction conditions at 523–673 K and atmospheric pressure. The catalytic activity for the selective reduction of nitric oxide and the intensity of the IR bands due to reaction species depended strongly on the nature of the support, type of supported metal, reaction time and temperature. The main surface species detectable by IR were adsorbed hydrocarbons (2900–3080 cm⁻¹), isocyanate (2180, and 2232–2254 cm⁻¹), cyanide (2125 cm⁻¹), nitrosonium (1901 cm⁻¹), CO₂ (2343–2357 cm⁻¹), CO (2058 cm⁻¹) and carbonate (1300–1650 cm⁻¹) species. In the case of rhodium containing catalysts, when supported on Al₂O₃, they exhibited both the highest concentration of surface species and the highest activity for nitric oxide reduction and selectivity to nitrogen. The catalytic activity and the IR intensities of the nitrosonium and isocyanate bands increased with reaction temperature, reached their maximum between 570 and 620 K, and then decreased at higher temperatures. The IR band intensities due to nitrogen containing surface species were found to be strongly correlated to the activity for nitric oxide conversion and only slightly related to the selectivity to dinitrogen.     

Photochemical decomposition of oxalate precipitates in nitric acid medium

This work has been performed as a part of the partitioning of minor actinides. Minor actinides can be recovered from high-level wastes as oxalate precipitates, but they tend to be co-precipitated together with lanthanide oxalates. This requires another partitioning step for mutual separation of actinide and lanthanide groups. Accordingly, the objective of this study was to decompose and dissolve oxalate precipitates into a dilute nitric acid solution by using a photochemical reaction. In order to do this, oxalic acid and neodymium oxalate precipitate were used in this study. Neodymium oxalate was chosen as a stand-in element representing americium, curium and lanthanides. As a result, decomposition characteristics of oxalic acid were first investigated and then on the basis of these results, the decomposition of neodymium oxalate precipitates was evaluated. From results using oxalic acid, the oxalate decomposition appeared to take place due to the reaction between the oxalate ion and hydroxyl radical generated from the nitric acid by photo-radiation. And the oxalate decomposition rate was measured in the experiments for various nitric acid contents when a mercury lamp (λ=254 nm) was used as a light source. The maximum decomposition rate was obtained when the nitric acid concentration was around 0.5 M, while the decomposition rate was reduced with an increase in the nitric acid concentration at more than 0.5 M. The photo-decomposition rate of neodymium oxalate precipitates was found to be 0.0034 M/h at the condition of 0.5 M HNO₃.     

CFD modeling of turbulent reacting flow in a semi-batch stirred-tank reactor

For the mixing-sensitive reactions,both chemical kinetics and mixing conditions of the reactants determine the distributions of products.The direct quadrature method of moments combining with the interaction by exchange with the mean micro-mixing model (DQMOM-IEM) has been validated for the chemical reacting flows in microreactors.Quite encouraging simulation results offer great promise,but the applicability of this method is needed to be explored furthermore,such as in stirred reactors.In this work,the two-environment DQMOM-IEM model was created with C language and used to customize Fluent through the user-defined functions.The mixing effects on the course of parallel competing chemical reactions carried out in a semi-batch single-phase stirred reactor were predicted.The simulation results show that the rising feed velocity enlarges the volume of reaction zone and maximize the yield of the by-product,which also indicates that the feed stream is more difficultly dispersed into the main stream and the zone surrounding feedpipe exit with high turbulent kinetic dissipation rate cannot be efficiently used.     

Qualitative aspects of ethylene oxide oxidation in a well-stirred flow reactor

The slow oxidation of ethylene oxide in a stirred-flow reactor was studied, and accurate, fast-response thermocouples were used for the measurement of temperature rises due to the oxidation. The effects of mixture strength, ambient temperature and total pressure on the temperature rise are illustrated and discussed. Comparisons are made with results previously reported for ethylene oxide when studied in closed vessels.     

Selective catalytic reduction of N2O and NOx in a single reactor in the nitric acid industry

The nitric acid industry is a source of both NO_x and N₂O. The simultaneous selective catalytic reduction of both compounds using propane as a reductant has been investigated. A stacked catalyst bed with first a Co-ZSM-5 catalyst and second a Pd/Fe-ZSM-5 catalyst gives >80% conversion of N₂O and NO_x above 300 °C at atmospheric pressure. At 4 bar absolute pressure (bara) the Co-ZSM-5 DeNO_x catalyst shows higher NO_x and propane conversion. This leaves not enough propane for the Pd/Fe-ZSM-5 DeN₂O catalyst, which causes a ‘dip’ in N₂O conversion. Reducing the space velocity (SV) of the first catalyst bed secures high NO_x and N₂O conversions from 300 °C and up at 4 bara.     

Conversion of nitric oxide and methane over Pd/ZSM-5 catalysts in the absence of oxygen

We have studied the conversion of nitric oxide and methane on several H- and Na-ZSM-5 zeolite catalysts in the absence of oxygen. Our results suggest that the NO-CH₄ reaction can be explained in terms of a mechanism that starts with a nitric oxide decomposition step followed by the surface reaction of methane with the product oxygen regenerating the active site. We have found that reduced Pd/ZSM-5 catalysts are active for the nitric oxide decomposition reaction but deactivate rapidly due to self-poisoning by product oxygen. By contrast, in the presence of methane these catalysts can exhibit high activity and stability under certain conditions. For instance, when the nitric oxide decomposition and the reaction of methane with the surface oxygen proceed at comparable rates the catalyst is stable but when the methane conversion is lower than that required to remove all the oxygen produced (stoichiometric methane conversion) the catalyst rapidly deactivates. Under some conditions the methane conversion may be higher than the stoichiometric requirement leading to the deposition of carbonaceous species. These carbonaceous deposits can promote the reaction by helping to remove the product oxygen.     

Mathematical modeling for chemical vapor deposition in a single-wafer reactor: Application to low-pressure deposition of Tungsten

A mathematical model for low pressure chemical vapor deposition in a single-wafer reactor in stagnation point flow has been developed to investigate the reactor performance. The transient transport equations for a simulated reactor include continuity, momentum, energy, and gaseous species balances. The model equations are simultaneously solved by using a numerical technique of orthogonal collocation on finite element method. Simulation studies have been performed to gain an understanding of tungsten low pressure chemical vapor deposition process. The model is then used to optimize the deposition rate and uniformity on a wafer, and the effects of operating conditions on deposition rate are studied to examine how system responses are affected by changes in process parameters. Deposition rate and uniformity calculated at the steady state are observed to be very sensitive to both temperature and total pressure. In addition, the model predictions for tungsten deposition from hydrogen reduction of tungsten hexafluoride have been compared with available experimental data in order to demonstrate the validity of the model.     

Characterization of the reaction environment in a filter-press redox flow reactor

The characteristics of a divided, industrial scale electrochemical reactor with five bipolar electrodes (each having a projected area of 0.72 m²) were examined in terms of mass transport, pressure drop and flow dispersion. Global mass transport data were obtained by monitoring the (first order) concentration decay of dissolved bromine (which was generated in situ by constant current electrolysis of a 1 mol dm⁻³ NaBr_(aq)). The global mass transport properties have been compared with those reported in the literature for other electrochemical reactors. The pressure drop over the reactor was calculated as a function of the mean electrolyte flow velocity and flow dispersion experiments showed the existence of slow and fast phases, two-phase flow being observed at lower velocities.     

Photochemical production of nitric oxide from a nitrosyl phthalocyanine ruthenium complex by irradiation with light in the phototherapeutic window

The photochemical behavior of [Ru(NO)(NO)₂pc] (pc = phthalocyanine) is reported in this paper. In addition to ligand localized absorption bands (λ < 300 nm), the electronic spectrum of this complex in dichloromethane solution was dominated by an intense absorption at 640 nm characterized as Q-bands. Irradiation of [Ru(NO)(NO)₂pc] at 366 and 660 nm led to the production of nitric oxide (NO) as detected by a NO-sensor. NO production by light irradiation at high energy involved excitation of d_π–π^* transition, while a photoinduced electron transfer occurred at long wavelength irradiation. The NO quantum yields varied from 1.4 × 10⁻³ to 2.3 × 10⁻² mol einstein⁻¹, depending on oxygen concentration.     

Selective reduction of nitric oxide by methane on H-form zeolite catalysts in oxygen-rich atmosphere

Selective reduction of NO by CH₄ in the presence of excess oxygen was investigated using H-form zeolite catalysts. H-ZSM-5, H-ferrierite, and H-mordenite showed high catalytic activity and selectivity. On the contrary, H-USY and Al₂O₃ were not effective for this reaction. Both NO-CH4 and O₂-CH₄ reaction hardly proceeded on H-ZSM-5. Higher NO_x conversion was obtained in the NO₂-O₂-CH₄ and NO₂-CH₄ systems than in the NO-O₂-CH₄ system under high GHSV condition. It seemed that NO₂ plays an important role for selective reduction of NO by CH₄ on H-form zeolites.     

Dynamic mathematical modeling of a novel dual-type industrial ethylene oxide (EO) reactor

In this paper, the dynamic behavior of a novel dual-type industrial ethylene oxide reactor has been proposed with taking catalyst deactivation into account. The configuration of two catalyst beds instead of one single catalyst bed is developed for conversion of ethylene to ethylene oxide. In the first reactor which is an industrial fixed-bed water-cooled reactor, the feed gas is partly converted to ethylene oxide. This reactor functions at very high yield and at a higher than normal operating temperature. In the second converter, the reaction heat is used to preheat the feed gas to the first reactor and a milder temperature profile is observed. The potential possibilities of a two-stage catalyst bed system are analyzed using a 1D heterogeneous dynamic model to obtain necessary comparative estimates. A differential evolution (DE) algorithm is applied as an effective and robust method to optimize the reactors length ratio. The results obtained from the simulation demonstrate that there is a desirable catalyst temperature profile along the dual-type reactor (DR) compared with the conventional single-type reactor (SR). In this way, the catalysts are exposed to less extreme temperatures and thus, diminishing the catalyst deactivation via sintering. Results from this study provided beneficial information about the effects of reactors configuration on catalyst lifetime and ethylene oxide production rate simultaneously.     

Experimental and kinetic modeling study of ethyl butanoate oxidation in a laminar tubular plug flow reactor

This investigation examines the experimental and the kinetic modeling of the oxidation of ethyl butanoate (EB) selected as model molecule for fatty acid ethyl esters (FAEE). New experimental information of EB oxidation was generated from a laminar tubular plug flow reactor (PFR) operating at atmospheric pressure, under dilute conditions, over the temperature range 500–1200 K, with various equivalence ratios ranging from 0.5 to 1.6, and at residence times varying between 0.65 and 1.40 s under STP conditions. Concentration profiles of the reactants, stable intermediates, and final products, identified by GC/MS, were measured by infrared ray absorption and GC/TCD–FID analyses. Experiments of EB oxidation carried out in the tubular PFR were simulated using a detailed chemical kinetic oxidation mechanism (117 species and 1035 reactions) proposed in a previous work [Hakka et al. Int J Chem Kin 2010;42:226] and automatically generated from an improved version of EXGAS software. Globally, good agreement was observed between experimental and simulated results, confirming the validity of the proposed model for EB oxidation. Reaction flux and sensitivity analyses allowed to determine the main reaction pathways involved in the investigated conditions of EB oxidation.     

Computational modeling of gas/particle flow in a riser

Axial solid velocity, solid volume fraction, and solid shear viscosity were computed in the riser of a circulating fluidized-bed reactor using a two-phase 2-D computational fluid dynamic model. The time-averaged model predictions agree well with the experimental data of Miller and Gidaspow (1992). The model predicts a core-annulus flow in the riser, similar to that found experimentally. The maximum velocity in the core agrees well with the measurements, but the downflow in the annulus is somewhat overpredicted. The solid volume fractions profiles agree well in both core and annulus, with discrepancy in the core at the level close to the inlet. The radial profile of solid shear viscosity computed by the turbulent kinetic energy model is ten times lower in the core than that found experimentally, but with a linear function of solid volume fraction in the measurement, the computed profile agrees well with experiments.     

Hydrodeoxygenation of HMF over Pt/C in a continuous flow reactor

The three‐phase hydrodeoxygenation reaction of 5‐hydroxymethylfurfural (HMF) with H₂ was studied over a 10 wt % Pt/C catalyst using both batch and flow reactors, with ethanol, 1‐propanol, and toluene solvents. The reaction is shown to be sequential, with HMF reacting first to furfuryl ethers and other partially hydrogenated products. These intermediate products then form dimethyl furan (DMF), which in turn reacts further to undesired products. Furfuryl ethers were found to react to DMF much faster than HMF, explaining the higher reactivity of HMF when alcohol solvents were used. With the optimal residence time, it was possible to achieve yields approaching 70% in the flow reactor with the Pt/C catalyst. Much higher selectivities and yields were obtained in the flow reactor than in the batch reactor because side products are formed sequentially, rather than in parallel, demonstrating the importance of choosing the correct type of reactor in catalyst screening. © 2014 American Institute of Chemical Engineers AIChE J, 61: 590–597, 2015     

An FT-IR and flow reactor study of the conversion of propane on γ-Al2O3 in oxygen-containing atmosphere

The conversion of propane in the presence of oxygen over alumina has been studied using a fixed bed flow reactor. The interaction of the same catalyst with propane, propene, isopropanol and acetone has also been investigated, with additional gas-phase monitoring, in an FT-IR cell. Alumina looks active in the catalytic conversion of propane to propene, with the production of CO₂, CO, ethylene, methane as the main by-products, depending on the reaction temperature. Higher hydrocarbons such as butenes, butadiene, benzene and toluene are also found.

This reactivity is mainly attributed to the weak but not negligible Brønsted acidity of the surface OH’s of alumina, possibly activating propane in the form of isopropoxides and allowing oligomerization of propene. This shows the detrimental effect of the uncovered alumina support in the case of alumina-supported catalysts for propane oxydehydrogenation and explains the positive role of doping with basic neutralizing agents such as potassium.