Reactant Gas Stream Research Articles

Transient Behavior of CO and CO2 Hydrogenation on Fe@SiO2 Core–Shell Model Catalysts—A Stoichiometric Analysis of Experimental Data

The hydrogenation of CO and CO2 from industrial exhaust gases into CH4 represents a promising method for sustainable chemical energy storage. While iron-based catalysts are in principle suitable for that purpose, the active metal Fe undergoes a complex transformation during the chemical reaction process. However, only little is known about the change in catalytically active species under reaction conditions, primarily caused by structural changes in the catalyst material, so far. By using core–shell model materials, factors that alter the catalyst structure can be excluded, making it possible to observe the direct influence of the reactants on the activity in the present work. Furthermore, stoichiometric analysis was used as a key tool for the evaluation of individual key reactions in the complex reaction network purely from experimental data, thus making it possible to draw conclusions about the catalyst state. In the case of CO hydrogenation, the presumed Boudouard reaction and the associated carburization of the catalyst can be quantified and the main reaction (CO methanation) can be determined. The results of the CO2 hydrogenation showed that the reverse water–gas shift reaction mainly took place, but under an ongoing change in the catalytic active iron phase. Due to the systematic exchange between CO and CO2 in the reactant gas stream, a mutual influence could also be observed. The results from the stoichiometric analysis provide the basis for the development of kinetic models for the key reactions in future work.

Numerical simulation of particulate matter interaction with the gas diffusion layer of proton‐exchange membrane fuel cells under various relative humidity conditions

Proton-exchange membrane fuel cell (PEMFC) operation and performance degrade when particulate matter (PM) present in the reactant gas stream is collected in the porous structure of the gas diffusion layers (GDL). Interaction of PM carried by the gas stream and their capture efficiency by fibrous structure of GDLs is numerically investigated at various levels of relative humidity (RH) and different particle sizes. For small particles (sub-micron sizes), the Brownian diffusion mechanism is dominant, while transitioning to interception and inertial impaction mechanisms occur as particle size increases (micron sizes or larger). It is found that high humidity levels result in higher diameter and lower density of PM, lower air density, and lower particle bounce due to the absorption of water vapor in the PM. Of these four effects, the first is the most important and the third is the least important. As humidity level is increased, particle capture efficiency decreases for small particles, but increases for large particles. The present study implies that a filter capable of removing large particles must be installed in the upstream reactant gas supply line to avoid the accumulation/clogging of PM in GDL structure.

Use Of Natural Gas Become a Petrochemical with Zeolite Catalyst

Methane is a hydrocarbon compound that can be used for various purposes. Currently, methane is widely used as fuel, and continues to be developed as a synthetic gas material and petrochemical products that have added value, one of which is formaldehyde. This study aimed to study the partial catalytic oxidation reaction of methane to formaldehyde using MoO3/zeolite as a catalyst. Reactant gas stream consisting of pure O2 and CH 4 were contacted with a rate ratio of 1:20, put into Fixed Bed Reactor therein contained 30 grams of catalyst MoO3/zeolite, and the pressure was maintained at 1 atm. The temperature and flow rate of the incoming reactant gas were used as variables. The main product produced was formaldehyde, besides that there were also CH3 OH, CO, CO2, H2O. The results were analyzed using Gas Chromatography, so it was known that the converted methane was 5.18% and the volume fraction of formaldehyde formed was 1.46%.

Modelling the CO2 hydrogenation reaction over Co, Ni and Ru/Al2O3

The CO2 hydrogenation reaction was experimentally investigated over pristine Co, Ni and an Al2O3-supported Ru catalyst with 0.5 wt% Ru loading. We developed a reaction model which takes the kinetical, diffusional -and thermodynamic reaction regimes into account and enables the description of the reaction over a broad temperature range. The model is based on a fractional rate law with experimentally determined reaction orders. We found that the overall reaction orders on the different catalysts are in proximity to zero order (0.13 for Co, 0.14 for Ni and 0.38 for Ru/Al2O3), which leads to the interpretation that the reaction is limited by the available surface sites in the underlying reaction conditions. We demonstrate on the example of Ru/Al2O3 that the reaction rate strongly depends on the partial pressure of CO2 in the gas phase. Upon reducing the partial pressure of CO2 in the reaction gas stream via He dilution, the reaction approaches a higher reaction order. Furthermore, the supported Ru catalyst is less limited by pore-diffusion compared to pristine Co. With the derived model we can accurately calculate the CO2 conversion over a broad temperature range; the temperature of maximum conversion is predicted within 15 K and the deviation between simulation and experiment is mostly less than 20%. This enables the simple and rapid prediction of the influence of different reaction parameters such as the activation energy or the diffusional limitations on the CO2 conversion.

Modeling and design of PEM fuel cell stack based on a flow network method

Proton exchange membrane fuel cells are usually connected in series to form a fuel cell stack in order to satisfy the power demand of the practical applications. It is necessary to investigate the designs of the fuel cell stack to achieve the uniformity of reactant distributions and maximize the performance of the fuel cell stack. In this study, a fuel cell stack model is established based on the flow network method. The pressure and mass distributions of the reactant gas and coolant streams are determined by the flow network method incorporating the cross flow effect and the minor losses. The temperature distributions are also considered, and the individual cell performances in the fuel cell stack are obtained. The optimization of the fuel cell stack is also carried out after the stack model is validated by the experimental data. The flow channels are optimized in terms of the stack net power considering the pumping power losses and the cooling channels are optimized in terms of minimum power consumption for the same amount of cooling effect. Finally, the optimal designs for the fuel cell stack are obtained.

Nickel oxide as an effective catalyst for catalytic combustion of methane

Coal mine methane can be utilized to produce electrical power even in the case of low concentration by way of catalytic combustion. Simple metal oxides MxOy (M = Fe, Co, Ni, Cu) were tested in the present work as catalysts for catalytic combustion of methane. It is found that the NiO catalyst had a high catalytic activity, superior to the perovskite catalyst LaCoO3 under the same reaction conditions. Amounts of O2 adsorption on the simple metal oxides were measured to reveal the catalytic activities. Furthermore, effect of water vapor in the reaction gas stream on methane combustion was evaluated.

Methanation of carbon dioxide on Ru/Al2O3 and Ni/Al2O3 catalysts at atmospheric pressure: Catalysts activation, behaviour and stability

The methanation of carbon dioxide has been studied over 3% Ru/Al2O3 and 20% Ni/Al2O3 commercial catalysts. Experiments have been performed in diluted conditions in a flow catalytic reactor with a continuous IR detection of products. The data, reported here, confirm that 3% Ru/Al2O3 is an excellent catalyst for CO2 methanation (96% methane yield with no CO coproduction at 573 K at 15,000 h−1 GHSV in excess hydrogen). The performance is better than that of Ni/Al2O3 catalyst. The reaction orders over both catalysts with respect to both hydrogen and CO2 were determined over conditioned catalysts. A conditioning of the Ru/Al2O3 catalyst by reactant gas stream was found to be needed and more effective than conditioning in hydrogen, possibly because water vapour formed during methanation reaction will react to remove chlorine impurities from catalyst surface Conditioned Ru/Al2O3 catalyst was found to retain stable high activity after different shut-down and start-up procedures, thus being possibly applicable in intermittent conditions.

Methane steam reforming in the absence and presence of H2S over Ce0.8Pr0.2O2 − δ, Ce0.85Sm0.15O2 − δ and Ce0.9Gd0.1O2 − δ SOFCs anode materials

We report here on the activity and stability of low-content praseodymium–, samarium– and gadolinium–cerium oxide catalysts for the steam reforming of methane under water deficient conditions. These materials display different methane reforming activities, and remain free of praseodymium, samarium and gadolinium oxide phases respectively after use in a reaction gas stream composed of 50% CH4–5% H2O – (in the absence and presence of 50 or 200ppm H2S) – balance He at 740°C. The results show that Ce0.8Pr0.2O2−δ, Ce0.85Sm0.15O2−δ and Ce0.9Gd0.1O2−δ are effective catalysts for reforming of methane and H2S in the feed promotes the catalytic activity. Ce0.8Pr0.2O2−δ appeared to attain the highest activity for methane reforming, a feature that is associated with the ability of praseodymium to undergo a red–ox (Pr4+/Pr3+) and spreading action in the cerium oxide host structure, possibly resulting in a red–ox relationship between the components.

천연가스의 수증기-이산화탄소 복합개질을 위한 충진층 관형반응기의 전산모사

Abstract >> A 2-dimensional heterogeneous reactor model was developed and simulated for a tube reactorof packed bed where the steam-CO 2 combined reforming reaction of natural gas proceeded to produce synthesis gas. Under the reactor feeding rate, 45 Nm 3 /h, of the reactant gas stream, the 2-dimensional heterogeneous reactor model showed the similar results to those from the ASPEN simulator although there were some discrepancies between the two in the temperature and the H 2 /CO ratio of the reformed gas atthe reactor exit. The calculated enthalpy difference between the reformed gas at the reactor exit and the reactant gas fed to the reactor was closely correspondent to the total amount of heat transferred to the reactorinterior from the furnace. This supports that the 2-dimensional heterogeneous reactor model was reasonablyestablished and the numerical solution was properly obtained. Key words : Simulation(모사), Methane(메탄), Steam-CO 2 reforming(수증기-이산화탄소 개질), Synthesis gas(합성가스), 2-dimensional heterogeneous reactor model(2-차원 비균일 반응기 모델)

Performance Predictions of a Moisture Management Device for Fuel Cell Applications

Moisture management in proton exchange membrane fuel cells is crucial to durability and performance. This frequently requires external humidification of the reactant gas streams to maintain sufficient humidity levels at the membranes, especially at higher operating temperatures. Direct-contact humidifiers using louvered fins brazed to rectangular tubes, similar to those frequently employed in automotive condensers and radiators, can be used to humidify a gas stream. A gas stream in which liquid water is sprayed flows through the passages formed by the louvered fins counter-current to a heating fluid flowing in the rectangular tubes sandwiching the fins. A mathematical model of this type of direct-contact humidifier is presented. The equations of energy and mass conservation are simultaneously solved for a number of segments along the humidifier. An equivalent resistance network is used to capture the temperature profile of the fins and liquid film surrounding them. The thickness of the liquid film is calculated from a shear balance at the film interface. The heat and mass transfer analogy is used with empirically derived transfer coefficients to solve the coupled heat and mass transfer problem in the gas phase. Predicted results are presented for typical operating conditions corresponding to a wide range of fuel cell operating conditions. The results show how the humidification process varies along the length of the humidifier. It is also shown that, although evaporation of the liquid film takes place throughout the entire humidifier, the direction of sensible heat transfer between the gas and liquid film can switch at some distance along the humidifier. This confirms the need for the equivalent resistance network model of the fin and film since simple fin efficiency models would fail in this situation. The model provides a basis for design optimization and performance predictions for this type of direct-contact moisture management device.

Morphology effects of Co3O4 nanocrystals catalyzing CO oxidation in a dry reactant gas stream

Nanocrystals of Co3O4 having different shapes (plates, rods, cubes, and spheres) were synthesized by using a hydrothermal method and their catalytic activities for CO oxidation were measured in dry reactant gas. The plate-like NCs mainly exposing {111} planes showed the highest catalytic activity among the four kinds of NCs.

Experimental study on the effect of reactant flow arrangements on the current distribution in proton exchange membrane fuel cells

Current distribution in a proton exchange membrane fuel cell (PEMFC) is significantly influenced by reactant flow configurations. In this study, the current distribution has been measured experimentally using a segmented flow-field plate and printed circuit board (PCB). Local current distributions for a PEMFC with serpentine flow field and three different flow arrangements including co-flow, cross-flow, and counter-flow arrangements for the anode and cathode streams are investigated along with the effect of flow channel orientation. It is shown that the counter-flow arrangement yields most uniform distribution for the current density, whereas the co-flow arrangement results in a considerable variation in the current density from the reactant gas stream inlet to exit. Flow channel orientation can also impact the cell performance and the current distribution appreciably. The limiting hydrogen concentration at the anode side due to the low stoichiometry condition can have a predominant effect on the current distribution and cell performance.

Photocatalytic Degradation of Chlorinated Ethanes in the Gas Phase on the Porous TiO2 Pellets: Effect of Surface Acidity

The photocatalytic degradation of chlorinated ethanes was studied in a tubular photoreactor packed with TiO(2) pellets prepared by sol-gel method. The steady-state condition was not obtained, but the deterioration in the photocatalytic activity was observed during the irradiation. Effects of mole fractions of water vapor, O(2), and C(2)H(5)Cl or C(2)H(4)Cl(2) and reaction temperature on the photodegradation of C(2)H(5)Cl or C(2)H(4)Cl(2) were examined, and these data were compared with those obtained by the photodegradation of chlorinated ethylenes. On the basis of the products detected with and without oxygen in the reactant's gas stream, we proposed the degradation mechanism. Measurement of diffuse reflectance infrared Fourier transform spectroscopy of pyridine adsorbed on the catalysts showed that decrease in the conversion for the photodegradation of C(2)H(5)Cl was attributable to the formation of Brønsted acid sites. Comparison of the data obtained with the TiO(2) and the sulfated TiO(2) (SO(4)(2-)/TiO(2)) pellets indicated that the photodegradation of C(2)H(5)Cl was suppressed by the presence of the Brønsted sites, but that of trichloroethylene was not affected. Such a difference is attributable to the adsorption process of these reactants on the acid sites on the catalyst surface.

In-situ UV-Raman study on soot combustion over TiO2 or ZrO2-supported vanadium oxide catalysts

UV-Raman spectroscopy was used to study the molecular structures of TiO2 or ZrO2-supported vanadium oxide catalysts. The real time reaction status of soot combustion over these catalysts was detected by in-situ UV-Raman spectroscopy. The results indicate that TiO2 undergoes a crystalline phase transformation from anatase to rutile phase with the increasing of reaction temperature. However, no obvious phase transformation process is observed for ZrO2 support. The structures of supported vanadium oxides also depend on the V loading. The vanadium oxide species supported on TiO2 or ZrO2 attain monolayer saturation when V loading is equal to 4 (4 is the number of V atoms per 100 support metal ions). Interestingly, this loading ratio (V4/TiO2 and V4/ZrO2) gave the best catalytic activities for soot combustion reaction on both supports (TiO2 and ZrO2). The formation of surface oxygen complexes (SOC) is verified by in-situ UV Raman spectroscopy and the SOC mainly exist as carboxyl groups during soot combustion. The presence of NO in the reaction gas stream can promote the production of SOC.

Study on the Reaction Mechanism for Soot Oxidation Over TiO2 or ZrO2-supported Vanadium Oxide Catalysts by Means of In-situ UV-Raman

The reaction mechanisms for diesel soot oxidation over V4/ZrO2 or V4/TiO2 oxide catalysts were studied by the means of in-situ UV-Raman spectroscopy. The results indicate that the formation of surface oxygen complexes (SOC) is a key step and the SOC species mainly exist as carboxyl groups. The presence of NO in the reaction gas stream can promote the formation of SOC species. For soot oxidation over V4/TiO2 catalyst, NO2 can be produced and remarkably accelerate soot oxidation. Based on the UV-Raman experimental results, two different reaction mechanisms are proposed for soot oxidation over V4/ZrO2 or V4/TiO2 samples, respectively.

One-step growth of HfSiON films

Hafnium silicate (HfSiO) has been identified as a promising candidate to replace silicon oxide/oxynitride as a high- κ material for gate dielectric applications. Nitrided hafnium silicate has been found to have a number of advantages in film performance. However, two-step processes have been commonly used, i.e. the first step is the deposition of HfSiO film by CVD, ALD or other techniques, and the second step is film nitridation. In this research, HfSiON films (Hafnium silicon oxynitride, or nitrided HfSiO) were directly deposited on Si substrate by Chem. Vap. Depos. using trisilylamine (TSA) and tetrakis(diethylamido)hafnium(IV) (TDEAH) precursors. TSA, a highly volatile and carbon-free precursor, was used as the Si source and was delivered in pure vapor phase without heating. TDEAH was used as the Hf source and delivered by direct liquid injection (vaporizer). HfSiON films were deposited in a single step with no need of a post treatment process for nitrogen incorporation. The HfSiON films can be tuned in wide compositional (Hf, Si, O, N) ranges and high growth rates were achieved. The addition of NH 3 to the reactant gas stream was found to be able to deposit films with high and controllable N content. It was also found that NH 3 had significant impact on film growth rate and composition.

Reduced dimensional computational models of polymer electrolyte membrane fuel cell stacks

A model of steady state operation of polymer electrolyte membrane fuel cell (PEMFC) stacks with straight gas channels is presented. The model is based on a decoupling of transport in the down-channel direction from transport in the cross-channel plane. Further, cross-channel transport is approximated heuristically using one-dimensional processes. The model takes into account the consumption of reactants down the channel, the effect of membrane hydration on its conductivity, water crossover through the membrane, the electrochemistry of the oxygen reduction reaction, thermal transport within the membrane electrode assembly (MEA) and bipolar plates to the coolant, heat due to reaction and condensation and membrane resistance, electrical interaction between unit cells due to in-plane currents in the bipolar plates, and thermal coupling of unit cells through shared bipolar plates. The model corresponds to the typical operation with counter-flowing reactant gas streams. The model is a nonstandard system of non-smooth boundary value differential algebraic equations (DAEs) with strong, nonlocal coupling. A discretization of the system and a successful iterative strategy are described. Some preliminary analysis of the system and iterative strategy is given, using simple, constant coefficient, linear versions of the key components of the model. Representative computational results, validation against existing experimental data and a numerical convergence study are shown.

A flow channel design procedure for PEM fuel cells with effective water removal

Proper water management in polymer electrolyte membrane (PEM) fuel cells is critical to achieve the potential of PEM fuel cells. Membrane electrolyte requires full hydration in order to function as proton conductor, often achieved by fully humidifying the anode and cathode reactant gas streams. On the other hand, water is also produced in the cell due to electrochemical reaction. The combined effect is that liquid water forms in the cell structure and water flooding deteriorates the cell performance significantly. In the present study, a design procedure has been developed for flow channels on bipolar plates that can effectively remove water from the PEM fuel cells. The main design philosophy is based on the determination of an appropriate pressure drop along the flow channel so that all the liquid water in the cell is evaporated and removed from, or carried out of, the cell by the gas stream in the flow channel. At the same time, the gas stream in the flow channel is maintained fully saturated in order to prevent membrane electrolyte dehydration. Sample flow channels have been designed, manufactured and tested for five different cell sizes of 50, 100, 200, 300 and 441 cm 2. Similar cell performance has been measured for these five significantly different cell sizes, indicating that scaling of the PEM fuel cells is possible if liquid water flooding or membrane dehydration can be avoided during the cell operation. It is observed that no liquid water flows out of the cell at the anode and cathode channel exits for the present designed cells during the performance tests, and virtually no liquid water content in the cell structure has been measured by the neutron imaging technique. These measurements indicate that the present design procedure can provide flow channels that can effectively remove water in the PEM fuel cell structure.

Effect of flow and temperature distribution on the performance of a PEM fuel cell stack

A non-isothermal stack model has been developed to analyze the effects of flow variance and temperature distribution on the performance of a polymer electrolyte membrane (PEM) fuel cell stack. The stack model consists of the flow network solver for pressure and mass flow distributions for the reactant gas streams and cooling water, and the heat transfer solver for temperature distribution among the cells in the stack, as well as the fuel cell model for individual cell performance. Temperature, pressure and concentrations of fuel and oxidant are the most important conditions for the fuel cell operation. In this work, pressure, temperature and concentration distributions are determined incorporating the individual cell performance with the minor losses in stack flow network accounted for. The results indicate that the effect of temperature is dominant on the cell voltage variance when the flow variance is small for sufficiently uniform distribution of reactant flow among the cells in the stack. Sufficient flow uniformity can be achieved by a large manifold that reduces the cell active area, or a small flow channel diameter, the latter may result in excessive pumping power for the anode and cathode gas streams. The manifold and flow channel diameters were optimized considering stack performance and reactant stream pumping power requirement. It is further shown that the flow and temperature distribution have a different influence on the stack performance, and a judicial matching of their distribution can provide the ideal uniform cell voltage distribution. An optimal combination of the flow and temperature distribution along the stack yields the optimal stack performance.

Spinel ferrites of the quaternary system Cu-Ni-Fe-O: Synthesis and characterization

The decomposition of the freeze dried Cu(II)-Ni(II)-Fe(III) formate precursors at 1000°C in air yields complex oxides CuxNi1−xFe2O4±δ (0 ≤ x ≤ 1) with a cubic spinel structure. For x < 0.7, single phase spinels are formed at 1000°C. However, for 0.7 ≤ x ≤ 1, Copper oxide (CuO) is identified as a second phase and the formation of a pure spinel phase requires an increase of the iron content in the mixture. For example, Cu0.81Ni0.1Fe2.09O4 is a single phase at 1000°C/air. Other single spinel phases Cu0.5+yNi0.5−y−zFe2+zO4±δ, 0 ≤ (y + z) ≤ 0.5, in the phase triangle Cu0.5Ni0.5Fe2O4–CuFe2O4–Cu0.5Fe2.5O4 have been synthesized under special p(O2)/T—synthesis conditions. The increase of the iron content requires an increase of the reaction temperature and/or a decrease of the p(O2) in the reaction gas stream. The oxygen exchange between Cu0.9Fe2.1O4.02 and the reducing gaseous phases shows that the non stoichiometry δ of copper ferrite is only about ±0.03. Significant changes in the oxygen content lead to the separation in different phases. The electrical and magnetic properties of copper ferrite samples depend on their chemical composition and preparation conditions.