Reactant Injection Research Articles

Estimating the Interrelation between the Rate of Atomic Layer Deposition of Thin Platinum-Group Metal Films and the Molecular Mass of Reactant Precursors

The published data on the atomic layer deposition of thin platinum-group metal (Ru, Rh, Pd, Os, Ir, and Pt) films with the use of different reactant precursors and second reactants (O2, O3, H2, etc.) are generalized in the context of microelectronic technologies. A procedure for analyzing the data on the atomic layer deposition kinetics is discussed. The rate of atomic layer deposition of metallic ruthenium is not higher than 0.15 nm/cycle. An inverse dependence of the limiting atomic layer deposition growth rate on the precursor molecular mass is established. The rates of atomic layer deposition of thin films of all the remaining metals in the group range between 0.03–0.07 nm/cycle, which is lower than the values for a monolayer of these metals by several times. The methodology and ways of enhancing the reliability of the kinetic data on the atomic layer deposition are discussed, including the need for taking into account the sample surface types and effects of nucleation delays at the initial growth stages of the thin platinum-group metal film. The possible occurrence of chemical deposition reactions with intermediate products involved at the pulsed injection of the reactants is considered.

Clean magnesium production using concentrated solar heat in a high-temperature cavity-type thermochemical reactor

The synthesis of magnesium from the corresponding oxide via a solar carbo-thermal and methano-thermal reduction process using high-temperature concentrated solar heat was investigated. The reduction of magnesium oxide (MgO) was experimentally demonstrated in a directly-irradiated prototype solar reactor at reduced pressure and temperature up to ∼1650 °C. The solar reactor was successfully operated with a variety of reducing agents (carbon and CH4) in batch and continuous modes under atmospheric and low pressure conditions (0.1–0.9 bar), thus representing the first process demonstration of MgO carbothermal reduction with continuous reactant injection in vacuum condition. A parametric study regarding operating pressure, carbon feedstock type, and C/MgO molar ratio was conducted to emphasize their effect on products yield (Mg and CO) and solar reactor performance. MgO conversion, reduction rate, and CO yield increased with decreasing pressure, in agreement with thermodynamic analysis. Utilizing activated charcoal as reducing agent showed the highest MgO conversion and CO yield. High MgO conversion over 99% was demonstrated with maximal CO yield up to 24.59 mmol/gMgO, closely approaching theoretical maximum value (24.81 mmol/gMgO). Employing methane as a reducing agent was also shown to be an alternative option to produce Mg, although methane cracking occurred simultaneously at the elevated reaction temperature. Mg recovery in the outlet products was identified as one of the most critical process challenges because of the pyrophoric property of the produced nanopowder and its strong oxidation reactivity with air.

Effect of Injector Design on the Combustion of Ethanol and Hydrogen-Peroxide Sprays

This paper describes the injection and combustion behavior of liquid reactants—ethanol and hydrogen peroxide—in relevant conditions for storable bi-propellant space thrusters. Particularly, this study points out the comparison between two fundamental injector designs based on impinging-jet atomization. First, like-doublet injection generates separate sprays of oxidizer and fuel that need to undergo vaporization, mixing, and chemical reaction. Second, unlike-triplet injection generates a unique spray of bipropellant mixture that only has to vaporize before burning. The effect of these two injection processes is compared in terms of spray pattern, drop size and velocity, as well as combustion efficiency. For this purpose, direct and -filtered visualizations of the reacting flow are performed, and the characteristic velocity is computed from experiments at combustion pressure 0.6 MPa and overall equivalence ratio in the range 0.5–2.2.

Efficacy of Fe3O4/Starch Nanoparticles on Sporosarcina pasteurii Performance in MICP Process

The microbial induced calcite precipitation (MICP) has been explored using well-known urease producer bacterium Sporosarcina pasteurii for many applications including soil stabilization. Urease enzyme hydrolyzes urea and in the presence of calcium chloride causes calcium carbonate precipitation between sand particles increasing sand stiffness and strength. In this study, the liquefied soil samples from Anzali coast were positioned inside injection columns by standard positioning technique. The columns were treated by injecting S. pasteurii suspension and cementation solution (CaCl2 and urea). The effect of different conditions consisting of number of injections, injection intervals, flow rate, and ratio of injection solution on unconfined compression strength (USC) of sands formed inside the columns were evaluated. The results indicated that soil strength was increased when ratio of reactant solutions and injection time were elevated. Moreover, the maximum Ca-precipitation in MICP reaction in liquid medium was obtained while Fe3O4/starch concentration and time of addition of nanoparticle to culture medium were 10.8 mg/L and 1.4 h, respectively. The USC results showed that the columns injected by bacterial suspension treated by Fe3O4/starch under optimized conditions improved the soil strength up to 1200 kPa in comparison to the control column as 220 kPa.

Transient effectiveness factor. Simultaneous determination of kinetic, diffusion and adsorption equilibrium parameters in porous catalyst particles under diffusion control conditions

A method to determine kinetics, diffusion and adsorption equilibrium parameters simultaneously in porous catalyst particles, where a first order chemical reaction occurs under diffusion control conditions in batch reactor, was proposed. The method is based on the use of observable magnitudes from a few experiments in a well stirred batch reactor. By means of a model considering the accumulation of reactant in the catalyst particles, the transient effectiveness factor allows analyzing the time response of systems with different adsorption capacities. The analysis basis and consequent methodology are more general and precise that those resulting from the conventional assumption, which consider that the concentration profiles in the particles, fulfill the steady state condition. Once an initial period elapsed after the reactant injection, the transient effectiveness factor reaches a pseudo-equilibrium state, condition under which an analytical expression can be used to describe the evolution of the reactant concentration in the fluid phase as a function of time. The parameters characterizing that expression of the dynamic response of the reactor, i.e., the exponential decaying constant and the concentration extrapolated at time zero, allow using data from a few experiments to determine the corresponding system’s diffusion, adsorption and chemical reaction parameters under reaction conditions.

Electrophoretically mediated microanalysis for simultaneous on-capillary derivatization of standard amino acids followed by micellar electrokinetic capillary chromatography with laser-induced fluorescence detection

Amino acids are crucial compounds involved in most biochemical processes essential for life. Since their dynamic turnover reflects the actual physiology of the cell/organism, a turnover assessment may provide valuable information related to multiple physiological and pathophysiological conditions. The sensitive determination of amino acids is predominantly associated with their derivatization which might be laborious, time-consuming and difficult to standardize. However, capillary electrophoresis offers the automatic injection and mixing of reactants, incubation of the reaction mixture, separation and detection of the reaction products in one on-capillary procedure. Among the on-capillary mixing strategies, electrophoretically mediated microanalysis (EMMA) is superior in terms of mixing efficiency. In this paper, we present an optimization of EMMA for the simultaneous derivatization of standard amino acids by naphthalene-2,3-dicarboxaldehyde/NaCN and its application to targeted human embryo metabolomics. For such a purpose, novel separation conditions were developed involving the background electrolyte, comprised of 73mM sodium dodecyl sulfate, 6.7 % (v/v) 1-propanol, 0.5mM (2-hydroxypropyl)-β-cyclodextrin and 135mM boric acid/sodium hydroxide buffer (pH 9.00). Finally, the optimized EMMA was compared to a fundamentally different mixing strategy, namely the transverse diffusion of laminar flow profiles, and proved to be also suitable for human plasma analysis.

Transient effectiveness factor in porous catalyst particles. Application to kinetic studies with batch reactors

The actual transient characteristics of the effectiveness factor for reactions in porous catalyst particles were considered in a model for kinetic studies in gradientless batch reactors. The transient effectiveness factor depends both on the Thiele modulus and the system’s adsorption capacity, a function of the catalyst mass. After the injection of reactant, the transient effectiveness factor reaches a stable value, which is always larger than the conventional factor based on the assumption of steady state in the concentrations in the particle. The steady state approach on classical pseudo-homogeneous models can be used if the adsorption capacity of the system is low. A new pseudo-homogeneous model, where the accumulation of mass in the particle and the transient effectiveness factor approach are considered, extend this limit to systems with medium or high adsorption capacity. The usual interpretation of the Weisz–Prater parameter was reformulated based on this approach, showing that kinetic constants can be determined precisely if the transient effectiveness factor is employed, thus avoiding the errors induced by the accumulation of mass in the catalyst particles. Proper experimental conditions for kinetic studies were suggested.

Steady-State Analysis of Rotating Detonation Engine Flowfields with the Method of Characteristics

A method for modeling the internal flowfield in a rotating detonation engine is developed using shock-expansion theory combined with the steady two-dimensional isentropic method of characteristics. An analytical model using the oblique shock relations, the Prandtl–Meyer function, and the detonation jump conditions is used to determine the basic shock structure. Once the structure is known, a shock-fitted method of characteristics solution is marched out to generate the rest of the flowfield. Reactant injection is handled analytically by solving the conservation equations for a flow undergoing a sudden expansion along with the method of characteristics compatibility relations to provide a new boundary condition. A new solution is then initialized using information from the previous solution to calculate the new shock structure. This process is repeated until the solutions converge. The converged solution is the ideal steady-state solution of a rotating detonation engine in the wave-fixed reference frame. The goal of this model is to provide ideal performance estimates one step up from a basic thermodynamic model that are still fast enough for large parametric studies.

Three-dimensional, numerical investigation of reactant injection variation in a H2/air rotating detonation engine

This study characterizes the mixing performance and non-reacting injection flow field within a rotating detonation engine. Initial reactant mixing is accomplished through a counter-rotating vortex pair developing from a jet-in-a-crossflow situation. Radially injected air wraps around the fuel jet, shearing the hydrogen into the vortex structure. The three-dimensional baseline geometry produces poor hydrogen/air mixing in the injection zone due to low fuel penetration into the wide, cross-flowing air stream and low air entrainment into the vortex structure. Injection parameters, including reactant flow rate, injection area, and fuel injection distribution, are varied to assess the impact on mixing. Decreasing air injection area and fuel injection area improve fuel penetration into the air stream and the vortex mixing mechanism, enhancing the level of mixedness within the annulus. For a given air injection area, an optimized number of fuel injection holes exists that provides the greatest level of mixedness. Variations from the optimized geometry reduce the effectiveness of the vortex mixing mechanism. Staggering fuel injection holes produces a decrease in mixedness when compared to collinear fuel injection.

Large-scale preparation of morphology-controlled microporous silica particles via gradual injection of reactants with different surfactants

Microporous silica particles that are monodispersed and have submicrometer diameters are attracting much attention in many applications, including medicine, environmental technology, cosmetics, and electronics. However, the production of microporous silica particles on an industrial scale comes with some difficulties. We have recently reported that the efficient synthesis of monodisperse and microporous silica particles can be achieved by the gradual injection of reactants into the reaction system. In the present study, we examined the effect of template molecules on the particle morphology via the gradual injection of reactants method. The use of the primary amines is mandatory to obtain the microporous silica particles. Furthermore, the solubility of amines in the reaction solution plays a critical role in the synthesis of monodispersed and microporous silica particles of 100 nm in diameter. Monodisperse silica particles 100 nm in diameter and with a specific surface area of 500 m2/g could be obtained with decylamine as a surfactant. The results indicate that the present synthetic approach is useful for efficient and large-scale production of monodisperse and microporous silica particles with the designated surface area. Microporous silica particles of 100 nm in diameter can be prepared in an industrial scale by the gradual injection of reagent approach. Good dispersibility of particle diameter and effective production can be achieved at the same time.

Numerical investigation of injection within an axisymmetric rotating detonation engine

This investigation characterizes the mixing processes and injection flow field within a rotating detonation engine. The axisymmetric baseline geometry produces poor fuel/air mixing in the immediate injection region due to reduced fuel penetration into the wide, perpendicularly flowing air stream. Injection parameters including reactant flow rate, injection area, and placement of the fuel injection are varied from the baseline geometry to assess the impact on mixing. Decreasing reactant injection areas improves fuel penetration into the cross-flowing air stream, and turbulent diffusion of the fuel is enhanced within the annulus increasing local equivalence ratio. When fuel is injected into the air slot, local equivalence ratio is enhanced due to the increasing mixing length between the recirculation region and fuel injection. Emulating nozzle integration by increasing annulus back-pressure increases local equivalence ratio in the injection region due to increased convection residence time.

Morphology control of microporous silica particles obtained by gradual injection of reactants

Industrial-scale synthesis of fine-tuned monodisperse microporous silica is a central concern on fillers and optical applications. We recently reported that the efficient synthesis of monodisperse microporous silica particles can be achieved by the gradual injection of reactants. In the present study, we investigated the influence of the injection kinetics, the template, and catalyst contents on the morphology of the resulting silica particles. Their specific surface area (SSA) could be tuned from 100 to 500 m2/g by the amount of templating molecule, n-dodecylamine, without changing the particle size and dispersibility. The most important parameters for controlling the particle size were found to be the amounts of catalyst. The resultant microporous and monodisperse silica particles exhibit diameter ranging from 20 to 200 nm and SSA from 50 to 1000 m2/g. These results show that the gradual injection of the reactants in a controlled manner is effective to the industrial-scale synthesis of the silica nanoparticles with expected morphologies.

A beetle's internal bomb

Biomechanics![Figure][1] Bombardier beetle shoots its enemies PHOTO: T. EISNER ET AL. PNAS 96 , 17 (17 AUGUST 1999) © 2015 NATIONAL ACADEMY OF SCIENCES Bombardier beetles shoot a toxic pulse at potential predators and other harassers. The toxic spray is created by a chemical reaction that occurs inside the beetle's body. Although the details of the reaction are known, how the beetle is able to precisely combine the chemicals at appropriate times and release the pulse at regular intervals has remained a mystery. Arndt et al. used synchrotron x-ray imagery to observe the process as it occurs within live beetles. Expansion and contraction of an internal expansion membrane facilitate the precise cyclic injection of reactants and the subsequent ejection of toxic sprays that keep the beetle's predators at bay. Science , this issue p. [563][2] [1]: pending:yes [2]: /lookup/volpage/348/563?iss=6234

Biomechanics. Mechanistic origins of bombardier beetle (Brachinini) explosion-induced defensive spray pulsation.

Bombardier beetles (Brachinini) use a rapid series of discrete explosions inside their pygidial gland reaction chambers to produce a hot, pulsed, quinone-based defensive spray. The mechanism of brachinines' spray pulsation was explored using anatomical studies and direct observation of explosions inside living beetles using synchrotron x-ray imaging. Quantification of the dynamics of vapor inside the reaction chamber indicates that spray pulsation is controlled by specialized, contiguous cuticular structures located at the junction between the reservoir (reactant) and reaction chambers. Kinematics models suggest passive mediation of spray pulsation by mechanical feedback from the explosion, causing displacement of these structures.

Evaluation of Low Temperature TEOS-Ozone Silicon Dioxide Thin Film CVD under Sub-Atmospheric Pressure Using Consecutively Pulsed Reactant Injection

New approach for sub-atmospheric pressure silicon dioxide thin film deposition process at consecutively pulsed injection of tetraethylorthosilicate (TEOS) and ozone is presented. The study was performed with DCVD Centura D×Z tool. Deposition rates (DR) were as low as 0.03–0.1 nm/cycle and similar to those at atomic-layer deposition regime of thin film growth. The effects of deposition temperature, deposition process pressures and total reactant flows, ozone concentration, spacing, process cycle duration and total cycle numbers are presented. Deposition features were similar to those observed using continuous reactant delivery to the process chamber. DR values were found to depend strongly on ozone concentration and the surface of material used for CVD known as so-called “surface sensitivity” effect.

Large-scale synthesis of monodisperse microporous silica nanoparticles by gradual injection of reactants

Monodisperse microporous silica particles were prepared in high yield, by the gradual injection of tetramethoxysilane (TMOS) and template molecules into the reaction system. This resulted in continuous nucleation. The dilute TMOS concentration suppressed silica particle aggregation. The diameters of the microporous silica particles were 100–130 nm. The narrow size distribution resulted from larger particles experiencing smaller growth rates, despite the continuous nucleation occurring during TMOS injection. This method has potential in the industrial-scale preparation of monodisperse silica particles.

Microtomographic Characterization of Dissolution-Induced Local Porosity Changes Including Fines Migration in Carbonate Rock

Summary The microstructure of carbonate rocks experiences substantial changes under reactive processes, in particular chemical dissolution and deposition, including dissolution-released-fines migration occurring during acidizing. A better understanding of such changes at the pore scale and their influences on rock properties is of great value for the effective design and implementation of reactive processes in carbonate reservoirs. In this work, we demonstrate the use of X-ray micro-computed tomography (micro-CT) to quantitatively investigate the local porosity changes in a meso-/microporous carbonate core sample during chemical dissolution. A reactive flooding experiment in a core sample by a nonacidic solution is designed such that changes in pore space from before to after the reactant injection could be imaged in exactly the same locations with micro-CT at a resolution of less than 5 μm. A methodology with three-phase segmentation and 2D histograms of image intensity is used to quantify distributions of the evolution of each image voxel. This technique allows the incorporation of microporosity into the calculation of the evolution regions, including the migration of fines, to accurately quantify the evolution scenarios. The micro-CT images reveal a quasiuniform dissolution pattern and allow characterizing the accompanying migration of fines within the core sample. The 3D pore networks are derived from the image data, which quantify changes in network structure and the pore geometry. The 2D histograms of image intensity derived from the pre- and post-dissolution images show quantitatively how macro- and micropores are enlarged by dissolution close to the inlet, whereas the deposition of fines mainly occurs in pores far from the inlet boundary. These results can explain why permeability of the sample initially decreases and then increases when injection time increases. Pore-surface area between each region is computed on the basis of the spatially resolved voxel evolution scenarios. This allows calculation of local distribution of reactive surface area, which, in turn, will assist in the prediction of local reaction rates in reactive flow simulators.

Effects of compound-specific transverse mixing on steady-state reactive plumes: Insights from pore-scale simulations and Darcy-scale experiments

Transverse mixing is critical for reactions in porous media and recent studies have shown that to characterize such mixing at the Darcy scale a nonlinear compound-specific parameterization of transverse dispersion is necessary. We investigate the effectiveness of this description of transverse mixing in predicting reactive transport. We perform pore-scale numerical simulations and flow-through laboratory experiments to study mixing-limited reactions with continuous injection of reactants that result in steady-state reactive plumes. We consider product mass flux and reactant plume lengths as metrics of reactive transport. This study shows that the nonlinear parameterization of transverse dispersion consistently predicts both product mass flux and reactant plume extents across two orders of magnitude of mean flow velocities. In contrast, the classical linear parameterization of transverse dispersion, assuming a constant dispersivity as a property of the porous medium, could not consistently predict either indicator with great accuracy. Furthermore, the linear parameterization of transverse dispersion predicts an asymptotic (constant) plume length with increasing velocity while the nonlinear parameterization indicates that the plume length increases with the square root of the velocity. Both the pore-scale model simulations and the laboratory experiments of mixing-limited reactive transport show the latter relationship.

Dehydrogenation of methylcyclohexane over Pt/V2O5 and Pt/Y2O3 for hydrogen delivery applications

Dehydrogenation of methylcyclohexane (MCH) for hydrogen transportation and delivery application was carried out over 3 wt% Pt/V2O5 and 3 wt% Pt/Y2O3 catalyst. The catalytic activity was tested using a spray-pulse mode of reactor. Effective dehydrogenation of MCH under spray-pulse mode of reactant injection was observed. In terms of hydrogen evolution rate at 60 min from start of reaction the activity of 958 mmol/g/min was obtained at temperature of 350 °C. Nearly 100% selectivity toward hydrogen was obtained. A relatively high conversion of 98% was observed with 3 wt% Pt/Y2O3 at 60 min using an advanced spray-pulse reactor system. The catalysts were characterized using x-ray diffraction pattern (XRD), CO-chemisorption metal analysis, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis.

NETmix®, a new type of static mixer: Experimental characterization and model validation

AbstractIn a previous article (Laranjeira et al.), a network model was developed to describe and predict the behavior and performance of NETmix®, a new type of static mixer consisting of a network of interconnected chambers and channels. This work reports experimental results on a transparent prototype NETmix® unit constructed to enable the characterization of the mixing mechanisms at the local scale. Tracer flow visualization experiments show that the mixing characteristics in the NETmix® unit depend on the Reynolds number both for macromixing and micromixing. A critical Reynolds number for the onset of mixing was obtained where oscillating flow in the chambers is observed. Chemical reaction experiments were done using test reactions systems that exhibit mixing effects in the final product distribution and selectivity. Reaction selectivity was shown to depend on the reactants injection scheme. Theoretical predictions obtained with the network model were in agreement with experimental data for high Reynolds numbers. © 2010 American Institute of Chemical Engineers AIChE J, 2011