Differential Flow Reactor Research Articles

Nickel carbonyl formation in a fluidized bed reactor: experimental investigation and modeling

AbstractBACKGROUNDThe Mond process has been used in the industry for nickel purification over a century. However, theoretical studies on this process are few and primarily based on empirical models. In this article, experimental and theoretical modeling of nickel tetracarbonyl formation through the Mond process under different conditions in a fluidized bed reactor is presented. Nickel tetracarbonyl, known primarily as nickel carbonyl gas, is formed through the reaction between nickel powder and carbon monoxide. The apparent reaction rate is modeled as a function of reaction temperature, inlet gas pressure, and carbon monoxide flow rate. Experimental results were obtained using a fluidized bed reactor. A diffusion‐kinetics and a two‐phase bubbling bed model were developed to compare with experimental results. The reactor is considered as a differential flow reactor for the theoretical modeling.RESULTSRate of reaction is measured in a fluidized bed and used for the verification of the studied models. The best performing model is a kinetic‐diffusion model with a rate of reaction that obeys rem = Kem([CO])n, in which Kem is a function of mass transfer as well as kinetic variables, but is primarily temperature dependent. Also, n for low‐pressure and high‐pressures regions is −1 and −3, respectively.CONCLUSIONSThe reaction rate is strongly dependent on carbon monoxide gas pressure. The models developed are rather simple yet provide significant improvement in predictions of the reaction rate compared to the existing models in the literature. © 2020 Society of Chemical Industry

Transient Kinetic Experiments within the High Conversion Domain: The Case of Ammonia Decomposition

In the development of catalytic materials, a set of standard conditions is needed where the kinetic performance of many samples can be compared. This can be challenging when a sample set covers a broad range of activity. Precise kinetic characterization requires uniformity in the gas and catalyst bed composition. This limits the range of convecting devices to low conversion (generally <20%). While steady-state kinetics offer a snapshot of conversion, yield and apparent rates of the slow reaction steps, transient techniques offer much greater detail of rate processes and hence more information as to why certain catalyst compositions offer better performance. In this work, transient experiments in two transport regimes are compared: an advecting differential plug flow reactor (PFR) and a pure-diffusion temporal analysis of products (TAP) reactor. The decomposition of ammonia was used as a model reaction to test three simple materials: polycrystalline iron, cobalt and a bimetallic preparation of the two. These materials presented a wide range of activity and it was not possible to capture transient information in the advecting device for all samples at the same conditions while ensuring uniformity. We push the boundary for the theoretical estimates of uniformity in the TAP device and find reliable kinetic measurement up to 90% conversion. However, what is more advantageous from this technique is the ability to observe the time-dependence of the reaction rate rather than just singular points of conversion and yield. For example, on the iron sample we observed reversible adsorption of ammonia and on cobalt materials we identify two routes for hydrogen production. From the time-dependence of reactants and product, the dynamic accumulation was calculated. This was used to understand the atomic distribution of H and N species regulated by the surface of different materials. When ammonia was pulsed at 550 °C, the surface hydrogen/nitrogen, (H/N), ratios that evolved for Fe, CoFe and Co were 2.4, 0.25 and 0.3 respectively. This indicates that iron will store a mixture of hydrogenated species while materials with cobalt will predominantly store NH and N. While much is already known about iron, cobalt and ammonia decomposition, the goal of this work was to demonstrate new tools for comparing materials over a wider window of conversion and with much greater kinetic detail. As such, this provides an approach for detailed kinetic discrimination of more complex industrial samples beyond conversion and yield.

Mechanism evolution for the oxidative dehydrogenation of ethyl benzene to styrene over V2O5/TiO2 catalyst: computational and kinetic approach

A kinetic study of the oxidative dehydrogenation of ethylbenzene has been performed in a differential flow reactor over a V2O5/TiO2 catalyst.

Catalytic Ammonia Decomposition during Nanocrystalline Iron Nitriding at 475 °C with NH3/H2 Mixtures of Different Nitriding Potentials

Ammonia is now regarded as an effective source of hydrogen containing no CO. In this paper, we have studied the nitriding of nanocrystalline iron accompanied by catalytic ammonia decomposition reaction. The chemical processes were carried out in a tubular differential flow reactor at 475 °C. NH3/H2 gas mixtures of different compositions viz. different nitriding potentials were let into the reactor. At each nitriding potential the stationary states were observed, when mass of solid and rate of ammonia decomposition were constant. In the whole range of nitriding potentials three regions of different phase composition of solid were observed: α-iron, mixture of α-iron and Fe4N nitride, and Fe4N nitride. It occurred surprisingly that along with increase in nitriding potential the rate of ammonia decomposition decreased when Fe4N nitride phase was present. A model of the process in question was proposed to explain that phenomenon. The decrease in decomposition reaction rate, related with decrease in iron surfac...

Kinetics of hydrogen generation from hydrolysis of sodium borohydride on Pt/C catalyst in a flow reactor

SUMMARY Here, we report the results of a kinetic study on the hydrogen generation from the catalytic hydrolysis of sodium borohydride in a differential flow reactor. As catalyst platinum supported on carbon (Pt/C) was used in two forms: either as powder or coated on carbon cloth. For optimization of the system several parameters such as sodium hydroxide concentration, sodium borohydride concentration and the flow rate of the feed solution were varied. It was found that the H2 generation rate increases with an increase in NaBH4 concentration whereas it shows a slight decrease with variation in NaOH concentration. As an important parameter, an increase in the flow rate of feed solution enhances the hydrogen generation rate. This is an important result as it provides an easy control of reaction or hydrogen generation on demand. Copyright © 2013 John Wiley & Sons, Ltd.

Characterization of carbon deposit with controlled carburization degree

Promoted nanocrystalline iron was carburized in a differential tubular flow reactor with thermogravimetric measurement of mass changes. The carburization process was carried out in the presence of pure methane under atmospheric pressure at 650 °C to obtain different carburization degrees of the sample. The carburized iron samples were characterized by the X-ray diffraction, high-resolution transmission electron microscope in the energy-dispersive X-ray spectroscopy mode, thermoprogrammable oxidation, and Raman spectroscopy. As a result of the methane decomposition on the nanocrystalline iron the following nanocrystalline products were observed: iron carbide Fe3C, graphite, iron and nanotubes. The crystallinity of the samples increased with the carburization degree.

Replication of noise-sustained autocatalytic chemical structures

Autocatalytic systems in a differential-flow reactor may undergo a differential-flow-induced chemical instability toward a convectively unstable regime, in which noise-sustained structures may appear. This is the case of a system with Gray-Scott kinetics in a packed-bed reactor, as reported in [B. von Haeften and G. Izus, Phys. Rev. E 67, 056207 (2003)]. In this work, two identical copies of such a system are coupled in master-slave configuration and submitted to independent spatiotemporal Gaussian white noise sources. Numerical simulation of two-dimensional reactors with uniform and Poiseuille flows reveals that the slave system replicates to a very high degree of precision and the convective patterns arising in the master one due to the presence of noise. The quality of this synchronization is assessed through several measures. A convective instability in the synchronization manifold is theoretically predicted and numerically confirmed.

Methylene blue removal from contaminated waters using O3, natural zeolite, and O3/zeolite

This paper compares experimental results on methylene blue (MB) removal systems based on ozone oxidation, zeolite adsorption, and simultaneous adsorption-oxidation using ozone in the presence of natural zeolite. The effect of pH (2-8), and the presence of radical scavengers (sodium acetate) on process rates and removal efficiencies are assessed at laboratory scale. The experimental system consisted of a 1 L differential circular flow reactor and an ozone generator rated at 5 g O3/h. Results show that ozone oxidation combined with zeolite adsorption increases the overall MB oxidation rate with respect to ozonation process and zeolite adsorption. In presence of free radical scavenger, only a 25% of reduction on MB removal rate are observed in the simultaneous treatment, as compared with 70% when ozonation treatment is used, suggesting that MB oxidation reactions take mainly place on the zeolite surface.

Kinetic studies and Mechanism Evolution of the Ammoxidation of 3-picoline Over V2O5/ZrO2 Catalyst

A kinetic investigation of the ammoxidation of 3-picoline to 3-cyanopyrdine has been studied over V2O5/ZRO2 Catalyst in a differential flow reactor in the temperature range 573-683 K. The partial pressures of 3-picoline, oxygen and ammonia were varied and rates were measured for the formation of 3-cyanopyridine. Kinetics studies reveal that the mechanism of the reaction is of the “Redox” type. The rate equation deduced, assuming a study state involving a three stage oxidation-reduction process, represented the data most satisfactorily for conversion of 3-picoline to nicotinonitrile. Catalysts have been characterized using IR, XRD, ESR, Surface area and ammonia desorption methods with a view to understanding the structure and nature of bonding over the surface of the catalyst. A tentative mechanism of the process has been suggested.

Heterogeneous catalytic ozonation of benzothiazole aqueous solution promoted by volcanic sand

This paper presents experimental results on the catalytic effect of volcanic sands on benzothiazole ozonation. Experiments were assessed at laboratory scale, in a differential circular flow reactor composed of a volcanic sand fixed bed column of 19 cm 3 and a 1 dm 3 storage tank, operated in batch mode at 20 °C and pH 2–7. Experimental results show that ozone self-decomposition is enhanced by the presence of volcanic sand at all pH. At pH > pH PZC, the increase in aqueous ozone decay could be related to ozone interaction with strong Lewis acid on metal oxide surface sites of the volcanic sand. Ozone self-decomposition reactions occurring on the volcanic sand are less affected by the presence of radical scavengers. Benzothiazole removal by ozonation is also enhanced by the presence of volcanic sand. Moreover, the inhibitory effect of free radical scavengers is also impaired by volcanic sand, suggesting that strong Lewis acid surface sites play a key role on the reaction mechanism.

Heterogeneous and homogeneous catalytic ozonation of benzothiazole promoted by activated carbon: Kinetic approach

Ozone oxidation combined with activated carbon adsorption (O 3/AC) has recently started to be developed as a single process for water and wastewater treatment. While a number of aspects of aqueous ozone decomposition are well understood, the importance and relationship between aqueous ozone decomposition and organic contaminant degradation in the presence of activated carbon is still not clear. This study focuses on determining the contribution of homogeneous and heterogeneous reactions to organic contaminants removal in O 3/AC system. Benzothiazole (BT) was selected as a target organic pollutant due to its environmental concern. A reactor system based on a differential circular flow reactor composed by a 19 cm 3 activated carbon fixed bed column and 1 dm 3 storage tank was used. Ozone was produced from pure and dry oxygen using an Ozocav ozone generator rated at 5 g O 3 h −1. Experimental results show that BT removal rate was proportional to activated carbon dosage. Activated carbon surface contribution to BT oxidation reactions with ozone, increased with pH in absence of radical scavengers. The radical reaction contribution within the pH range 2–11 accounted for 67–83% for BT removal in O 3/AC simultaneous treatment. Results suggest that at pH higher than the pH of the point of zero charge of the activated carbon dissociated acid groups such as carboxylic acid anhydrides and carboxylic acids present on activated carbon surface could be responsible for the observed increase in the ozone decomposition reaction rate. A simplified mechanism and a kinetic scheme representing the contribution of homogeneous and heterogeneous reactions on BT ozonation in the presence of activated carbon is proposed.

Advanced treatment of benzothiazole contaminated waters: comparison of O3, AC, and O3/AC processes

Benzothiazole (BT) is a toxic and poorly biodegradable contaminant, usually found in wastewater from rubber related applications. This compound could be effectively eliminated using advanced treatment processes. This paper compares experimental results on detoxification systems based on ozone oxidation, activated carbon adsorption, and simultaneous adsorption-oxidation using ozone in the presence of activated carbon. The effect of pH (2-11), and the presence of radical scavengers (tert-butyl alcohol and sodium carbonate) on process rates and removal efficiencies are assessed at laboratory scale. The experimental system consisted of a 1 L differential circular flow reactor and an ozone generator rated at 5 g O3/h. Results show that ozone oxidation combined with activated carbon adsorption increases the overall BT oxidation rate with respect to the ozonation process and activated carbon adsorption. In the presence of free radical scavenger, only a 44% reduction in BT removal rate is observed in the simultaneous treatment, as compared with 72% when ozonation treatment is used, suggesting that BT oxidation reactions mainly take place on the activated carbon surface.

An investigation of nanostructured vanadia/titania catalysts for the oxidation of monochlorobenzene

In this work, the effects of V/Ti mass ratios in nanostructured V 2O 5/TiO 2 catalysts on catalyst characteristics and catalyst activity were investigated. The destruction of monochlorobenzene was used as a measure of catalyst activity. The V 2O 5/TiO 2 catalysts, which have been traditionally used as de-NO x catalysts and selective oxidation catalysts (e.g. in the production of phthalic anhydride), were made by the wet incipient method. This synthesis method provides nanostructured V 2O 5/TiO 2 catalysts with the vanadium species on the surface of the TiO 2. The catalysts were characterized using X-ray diffraction (XRD), BET surface area, and Raman spectroscopy. The performance of the catalysts for the destruction of organic pollutants was assessed in a differential tube flow reactor for gas-phase thermal oxidation reactions. It was found that the presence of crystalline V 2O 5 on the surface of TiO 2 (V/Ti mass ratio 0.05 and 0.1 ) is necessary for the oxidation of monochlorobenzene at temperatures <300 °C.

Noise-sustained structures in differential-flow reactors with autocatalytic kinetics.

We have studied the formation of noise-sustained structures in a differential-flow reactor with cubic autocatalytic kinetics (the Gray-Scott model). In this system the interplay between advection, diffusion, reaction, and noise fluctuations leads to the formation of noise-sustained patterns in the key species. Numerical integration in one and two spatial dimensions shows that the structures are nonlocally cross correlated. Near threshold, the observed correlation is related to the properties of the convectively unstable critical modes.

Kinetics of the CO+NO Reaction over Bimetallic Platinum–Rhodium on Alumina: Effect of Ceria Incorporation into Noble Metals

The influence of ceria on the kinetic behavior of noble metals in the reduction of NO by CO has been investigated at 120 and 300°C on a freshly prepared Pt–Rh/Al2O3–CeO2 catalyst, and on an aged catalyst after reaction for 16 h at 500°C, within pressure ranges of 2.3–9×10−3 atm for CO and 1.5–8×10−3 atm for NO, using a differential fixed-bed flow reactor. These two temperatures have been selected from temperature-programmed experiments because they correspond to two very different regimes of activity of noble metals with ceria. It has been found that a rate equation derived from a bifunctional mechanism involving reaction paths either on metal or on ceria can correctly fit rate measurements performed at 120°C. In contrast a conventional mechanism earlier proposed for modeling the CO+NO reaction on Pt–Rh/Al2O3 at 300°C, where only noble metals are involved, enables modeling of rate measurements at 300°C on Pt–Rh/Al2O3–CeO2, which suggests that the interaction between ceria and noble metals is suppressed at that temperature. The temperature dependency of the rate constants and equilibrium constants for NO and CO adsorption has been quantified in order to explain such changes in the kinetic behavior of Pt–Rh/Al2O3–CeO2.

Activity and Stability of Molybdenum Carbide as a Catalyst for CO2 Reforming

The activity for CO2 reforming of methane over a Mo2C catalyst was studied at 8 and 1.6 bar total pressure using a plug flow reactor and a differential plug flow reactor with external recycle operated as a continuously stirred tank reactor (CSTR), respectively. In the plug flow reactor, the catalyst deactivation started from the top of the reactor and proceeded downward, while it was stable in the CSTR at high conversions. Comparison of the activity of the Mo2C with that of a 1.8% Ru/MgAl2O4 catalyst demonstrates that this noble metal catalyst is more than two orders of magnitude more active than the Mo2C catalyst on the basis of weight. Thermodynamic calculations of the stability of Mo2C catalysts during CO2 reforming conditions show that Mo2C is only stable at high product concentrations. Finally, the carbon resistance of Mo2C is calculated to be higher than that of nickel-based catalysts. Carbon formation on a Mo2C catalyst at 700°C requires an extra Gibbs-free energy of 4.5 kJ/mole compared to a nickel catalyst with nickel particles up to 2500 Å.

Pattern formation in a differential–flow reactor model

A model for a differential–flow reactor is considered, based on cubic autocatalator kinetics in which the substrate is immobilized and the autocatalyst flows through the reactor at a constant rate. Linear stability analysis shows that there is a critical flow rate above which the spatially uniform steady state becomes convectively unstable. Numerical simulations show that this convective instability leads to the formation of a wave packet propagating through the reactor. The nature of this wave packet depends on the flow rate and on the two cases that are identified for the kinetic parameter μ, namely a generic case for general values of μ and when μ is close to the value which gives a Hopf bifurcation in the kinetic system.

Forced convective structures in a differential-flow reactor

A model of an autocatalytic reaction in a differential-flow reactor is considered in which the reactant is immobilized and the autocatalyst allowed to flow (with uniform velocity) and to diffuse. Consideration is given to the influence that a periodic external signal (fluctuations in the inflow concentration of the autocatalyst) can have upon the convective structures which exist in this model. It is shown that, depending on the frequency of the signal, there are two parameter regions giving distinct spatio-temporal responses. There is a region of high excitation waves (convected forced waves) which appear for a finite range of frequencies. Outside this range there are two domains of natural response waves. Close to the boundary of these regions there are irregular responses suggestive of an excitable system: packets of travelling waves of complex form develop which appear at non-regular intervals surrounded by small amplitude periodic waves.

Combustion and gasification kinetics of pyrolysis chars from waste and biomass

The combustion and gasification of chars from medium temperature pyrolysis of municipal waste, electronic scrap, wood and straw has been investigated in view to potential technical applications. Reaction rate measurements with oxygen and carbon dioxide have been carried out at lower temperatures in the chemical regime, using a thermobalance, a differential flow reactor and a fluidised bed of sand. These chars from waste and biomass belong to the most reactive technical carbon materials. The major reason is the porous and highly disordered carbon structure, catalysts play a minor role. In char incineration tests in a small rotary kiln facility, complete burnout could be attained in 1h at temperatures down to ≈600°C. Use of oxygen-enriched air improves burnout and drastically reduces the flue gas volume and the specific emissions per ton of waste.

Etherification rates of 2-methyl-2-butene and 2-methyl-1-butene with ethanol for environmentally clean gasoline production

Etherification of C5 reactive olefins available in light fluidized catalytic cracking (FCC) gasoline is an attractive way to decrease the olefins and to increase the octane number. The reactivities of 2-methyl-1-butene (2M1B) and 2-methyl-2-butene (2M2B) in the etherification reaction with ethanol catalysed by a strongly acidic macroreticular resin catalyst were investigated in a temperature range of 333–360 K using a liquid phase differential flow reactor. In the presence of excess alcohol, the apparent reaction orders of etherification reactions of isoamylenes were found to be 0.93 and 0.69 with respect to 2M1B and 2M2B concentrations, respectively. 2M1B was shown to be more reactive than 2M2B and its activation energy is also lower in the etherification reaction. It was also shown that diffusion resistances, especially in the macropores of the catalyst, may play an important role on the observed rates. © 1999 Society of Chemical Industry