Initial Reactant Concentrations Research Articles

Sonication-assisted synthesis of a new cationic zinc nitrate complex with a tetradentate Schiff base ligand: Crystal structure, Hirshfeld surface analysis and investigation of different parameters influence on morphological properties

A nanostructured cationic zinc nitrate complex with a formula of [ZnLNO3]NO3 (where L = (N2E,N2′E)-N1,N1′-(ethane-1,2-diyl)bis(N2-((E)-3-phenylallylidene)ethane-1,2-diamine)) was prepared by sonochemical process and characterized by single crystal X-ray crystallography, scanning electron microscopy (SEM), FT-IR and NMR spectroscopy and X-ray powder diffraction (XRPD). The X-ray analysis demonstrates the formation of a cationic complex that metal center is five-coordinated by four nitrogen atom from Schiff base ligand and one oxygen atom from nitrate group. The crystal packing analysis demonstrates the essential role of the nitrate groups in the organization of supramolecular structure. The morphology and size of ultrasound-assisted synthesized zinc nitrate complex have been investigated using scanning electron microscopy (SEM) by changing parameters such as the concentration of initial reactants, the sonication power and reaction temperature. In addition the calcination of zinc nitrate complex in air atmosphere led to production of zinc oxide nanoparticles.

CFD‐PBE‐PBE simulation of an airlift loop crystallizer

AbstractA complete solver (CFD‐PBE‐PBE) for crystallization processes in an airlift loop crystallizer is developed in OpenFOAM (open‐source field operation and manipulation) in this work. It combines computational fluid dynamics (CFD) with population balance equations (PBE) for both gas bubbles and crystals. Models for gas‐liquid mass transfer and chemical reaction are included as well in the solver. PBE describing bubble coalescence and breakage is solved by the cell average method. Primary nucleation, secondary nucleation, and particle growth are considered in the PBE describing the crystallization process. The solver is validated with the formation of calcium carbonate via the reaction of CO2 with Ca(OH)2 solution in an airlift reactor. Effects of the chemical enhancement factor and crystallization kinetics on predictions are systematically investigated. Variation of predicted pH value, concentration of Ca2+, mean particle size, and crystal size distribution (CSD) with time is in qualitative and semi‐quantitative agreement with the published experimental data, when the appropriate crystallization kinetics are used. Effects of operation parameters such as initial concentration and superficial gas velocity are further numerically examined. The increase in superficial gas velocity results in the increasing consumption rates of OH‐ and Ca2+, while the particle diameter seems unchanged in the present simulation. A higher initial concentration of reactants will lead to a smaller particle diameter and a narrower CSD. The predicted results indicate that the developed solver is feasible, and can be used for the design and scale‐up of airlift loop crystallizers.

Numerical Simulation of the Behaviors of the Bray-Liebhafsky Oscillating Chemical Reaction by a Four-variable Model

Based on a ten-step chemical model involving the concentrations of I2(aq), O2(aq), and the intermediates of I- and HIO2, four independent variables and seven irreversible steps, the nonlinear behavior of Bray-Liebhafsky (BL) oscillating reaction was investigated. The results showed that with different values of initial concentrations of reactants in the process of simulation, both periodic oscillation and chaotic behavior could be observed. In addition, at the same initial concentrations and rate constants, the system becomes more and more regular after being chaos. That is to say, the translation from chaos to periodic oscillation at the same initial conditions appeared in the BL system. The nonlinear behavior of system was also investigated briefly

Dissipative structures: From reaction-diffusion to chemo-hydrodynamic patterns.

The interplay of reaction and diffusion processes can trigger localized spatiotemporal patterns when two solutions containing separate reactants A and B of an oscillating reaction are put in contact. Using the Brusselator, a classical model for chemical oscillations, we show numerically that localized waves and Turing patterns as well as reaction-diffusion (RD) patterns due to an interaction between these two kinds of modes can develop in time around the reactive contact zone depending on the initial concentration of reactants and diffusion coefficients of the intermediate species locally produced. We further explore the possible hydrodynamic destabilization of an initially buoyantly stable stratification of such an A + B → oscillator system, when the chemical reaction provides a buoyant periodic forcing via localized density changes. Guided by the properties of the underlying RD dynamics, we predict new chemo-hydrodynamic instabilities on the basis of the dynamic density profiles which are here varying with the concentration of one of the intermediate species of the oscillator. Nonlinear simulations of the related reaction-diffusion-convection equations show how the active coupling between the localized oscillatory kinetics and buoyancy-driven convection can induce pulsatile convective fingering and pulsatile plumes as well as rising or sinking Turing spots, depending on the initial concentration of the reactants and their contribution to the density.

Experimental study and numerical simulation of barium sulfate precipitation process in a continuous multi-orifice-impinging transverse jet reactor

Fast jet mixing plays an important role in the intensification of precipitation process. In this work, the precipitation of barium sulfate in a multi-orifice-impinging transverse (MOIT) jet reactor was studied experimentally and numerically. RANS approach coupled with population balance equation (PBE) model was used to predict the process. Large scale variance and small scale variance were solved to evaluate the effect of macromixing and micromixing on the precipitation process, respectively. The influence of Reynolds number (ReM), initial feeding concentration of reactants (C0), and the scale-up of the jet reactor, on the distribution of supersaturation ratio, nucleation rate and crystal growth rate was discussed. The precipitation process can be intensified (here referring to producing smaller nanoparticles with narrower particle size distribution) by increasing ReM at lower ReM region or when the jet reactor is scaled up, or by increasing C0 when C0 is less than 0.4kmol/m3.

A mathematical investigation of the Turkevich organizer theory in the citrate method for the synthesis of gold nanoparticles

Gold nanoparticles are commonly manufactured by the citrate reduction method, a synthesis method pioneered by Turkevich et al. (1951). Based on their experimental evidence, Turkevich et al. (1951) advanced the organizer theory, a nucleation-growth synthesis mechanism. Subsequently, Kumar et al. (2007) developed a mathematical model for the description of the synthesis, basing it on such a theory. However, this model has not been thoroughly tested. Recently, contrary to the evidence provided by Turkevich et al. (1951), other mechanistic descriptions of the synthesis, which emphasize the role of the pH of the solution, have been advanced in the literature. In this paper, we investigated the model of Kumar et al. (2007) for different conditions of pH, temperature and initial reactant concentrations. To solve the model, we used the numerical code Parsival, which is used for solving population balance equations. We tested the model for different synthesis conditions studied experimentally by various researchers, for which results are available in the literature. The model poorly predicted the experimental data because the Turkevich organizer theory does not account for the acid-base properties of chloroauric acid and sodium citrate. A new model, with a more accurate mechanistic description of the synthesis and of the chemistry involved, is therefore required.

Reaction Equilibrium of the ω-Transamination of (S)-Phenylethylamine: Experiments and ePC-SAFT Modeling

This work focuses on the thermodynamic equilibrium of the ω-transaminase-catalyzed reaction of (S)-phenylethylamine with cyclohexanone to acetophenone and cyclohexylamine in aqueous solution. For this purpose, the equilibrium concentrations of the reaction were experimentally investigated under varying reaction conditions. It was observed that the temperature (30 and 37 °C), the pH (between pH 7 and pH 9), as well as the initial reactant concentrations (between 5 and 50 mmol·kg–1) influenced the equilibrium position of the reaction. The position of the reaction equilibrium was moderately shifted toward the product side by either decreasing temperature or decreasing pH. In contrast, the initial ratio of the reactants showed only a marginal influence on the equilibrium position. Further experiments showed that increasing the initial reactant concentrations significantly shifted the equilibrium position to the reactant side. In order to explain these effects, the activity coefficients of the reacting agents ...

Simultaneous formation of nanoscale zero-valent iron and degradation of nitrobenzene in wastewater in an impinging stream-rotating packed bed reactor

A novel process based on an impinging stream-rotating packed bed (IS-RPB) was proposed for preparing nanoscale zero-valent iron (NZVI) and degrading nitrobenzene (NB) simultaneously. The obtained NZVI particles were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy experiments (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The experimental results showed that the NB removal efficiency increased with the augment of liquid flow rate and initial reactant concentrations. The NZVI prepared with Fe2+ as an iron source had high reactive activity and its removal efficiency of NB could be maintained at a high level in acidic or a weakly basic condition (pH<8). Compared with the traditionally mixing method, the IS-RPB could reduce the iron dosing amounts by 49.6% and the prepared NZVI could achieve 100% efficiency of the NB removal. Considering the operational cost and treatment efficiency, the optimal ratio between NaBH4 and iron concentration could be in the range of 2.0–3.0. Through the strong micro-mixing intensification performance of IS-RPB, the reported approach has compensated for the shortcomings of the traditional nanoparticles production such as complicated procedures and the potential oxidation of Fe0. This study encourages further optimization and development of the high gravity system towards industrial production of NZVI and large-scale NB-containing wastewater treatment.

Experimental Study of Batch Reactor Performance for Ethyl Acetate Saponification

Abstract The objective of the current research work is to investigate the performance of batch reactor for saponification of ethyl acetate with sodium hydroxide. Temperature, volume of reaction mixture, rate of agitation, and initial concentration of reactants are the operating conditions considered for analysis. The NaOH concentration decreases from 1.13 × 10−2 mol/L to 0.57 × 10−2 mol/L when reaction temperature increases from 293 K to 313 K after the completion of the reaction. The conversion of NaOH increases with increased reaction temperature under the studied range of reaction temperatures until the stable condition is achieved. Reactant concentration declines with increased volume of reaction mixture from 1.2 L to 1.8 L. Sodium acetate concentration and reaction conversion decrease with increased volume of reaction mixture within the studied range. Concentration of sodium acetate decreases with increased rate of agitation. The conversion of sodium hydroxide declines with increased agitation rate from 70 rpm to 150 rpm. Higher initial reactant concentration leads to decreased reaction conversion. The results obtained may be used to optimize the production of ethanol and sodium acetate using saponification reaction.

Localized stationary and traveling reaction-diffusion patterns in a two-layer A+B→ oscillator system.

When two solutions containing separate reactants A and B of an oscillating reaction are put in contact in a gel, localized spatiotemporal patterns can develop around the contact zone thanks to the interplay of reaction and diffusion processes. Using the Brusselator model, we explore analytically the deployment in space and time of the bifurcation diagram of such an A+B→ oscillator system. We provide a parametric classification of possible instabilities as a function of the ratio of the initial reactant concentrations and of the reaction intermediate species diffusion coefficients. Related one-dimensional reaction-diffusion dynamics are studied numerically. We find that the system can spatially localize waves and Turing patterns as well as induce more complex dynamics such as zigzag spatiotemporal waves when Hopf and Turing modes interact.

Silver sulfide nanoparticles with a carbon-containing shell

Silver sulfide nanoparticles have been synthesized through chemical deposition from aqueous solutions of silver nitrate and sodium sulfide in the presence of sodium citrate as a complexing agent and stabilizer. The nanoparticles have a Ag2S core with a monoclinic crystal structure, covered with a carbon-containing citrate shell. Varying initial reactant concentrations, we can obtain core/shell nanoparticles with a tailored Ag2S core size and carbon-containing shell thickness.

Comparative study on the effects of nitrogen and carbon dioxide on methane/air flames

The measurement of flame temperature profile and flame computation were conducted to analyze the effects of carbon dioxide and nitrogen dilution on methane/air flames. Results indicated that carbon dioxide addition shows more significant effects on the thermal properties of flame, except for flame thickness. Flame kinetic analyses were implemented for the heat release of individual reaction. It is suggested that the heat release contribution of dominant reaction is primarily affected by flame stoichiometry, while the dilution shows weak effect. The concentrations of reactive species play important influences on the progress rate of reaction. The peak product of reactive species concentrations of the dominant reactions could be approximated by an exponent expression of the concentration of initial reactants and dilution rate, and a greater exponential index was obtained for the flames with carbon dioxide addition. The emission indices and combustion efficiency were evaluated to assess the profit in NO suppression and the loss in combustion deterioration. Results indicated that the profit-loss ratio is influenced by both flame equivalence ratio and the component of diluent gas. For rich methane/air flame, nitrogen dilution shows a greater value, while a larger benefit is obtained for stoichiometric flame diluted by carbon dioxide.

Automated Prediction of Catalytic Mechanism and Rate Law Using Graph-Based Reaction Path Sampling.

In a recent article [ J. Chem. Phys. 2015 , 143 , 094106 ], we introduced a novel graph-based sampling scheme which can be used to generate chemical reaction paths in many-atom systems in an efficient and highly automated manner. The main goal of this work is to demonstrate how this approach, when combined with direct kinetic modeling, can be used to determine the mechanism and phenomenological rate law of a complex catalytic cycle, namely cobalt-catalyzed hydroformylation of ethene. Our graph-based sampling scheme generates 31 unique chemical products and 32 unique chemical reaction pathways; these sampled structures and reaction paths enable automated construction of a kinetic network model of the catalytic system when combined with density functional theory (DFT) calculations of free energies and resultant transition-state theory rate constants. Direct simulations of this kinetic network across a range of initial reactant concentrations enables determination of both the reaction mechanism and the associated rate law in an automated fashion, without the need for either presupposing a mechanism or making steady-state approximations in kinetic analysis. Most importantly, we find that the reaction mechanism which emerges from these simulations is exactly that originally proposed by Heck and Breslow; furthermore, the simulated rate law is also consistent with previous experimental and computational studies, exhibiting a complex dependence on carbon monoxide pressure. While the inherent errors of using DFT simulations to model chemical reactivity limit the quantitative accuracy of our calculated rates, this work confirms that our automated simulation strategy enables direct analysis of catalytic mechanisms from first principles.

Numerical study of CO oxidation by N $$_2$$ 2 O reaction over supported catalysts

A mean-field model for study of the CO oxidation with N $$_2$$ O reaction, $$\mathrm {CO\!+\!N_{2}O} \rightarrow \mathrm {N_2+CO_2}$$ , occurring over composite catalysts is proposed. This model involves: the bulk diffusion of both reactants and products, adsorption and desorption of molecules of both reactants, and surface diffusion of adsorbed particles based on the particle jumping mechanism via the catalyst-support interface. The model is solved numerically using a finite difference technique. The influence of the initial concentrations of both reactants, their adsorption and reaction rate constants, and particle jumping rate constants via the catalyst-support interface on the surface reactivity of the composite catalysts is studied.

Decarboxylation of tetrafluorophthalic acid in NH3-enriched high temperature liquid water

2,3,4,5-Tetrafluorobenzoic acid is an important pharmaceutical intermediate. A green technology for the decarboxylation of tetrafluorophthalic acid to 2,3,4,5-tetrafluorobenzoic acid in NH3-enriched high temperature liquid water (HTLW) was developed. Tetrafluorophthalic acid could undergo the decarboxylation with the catalysis of NH3 to 2,3,4,5-tetrafluorobenzoic acid in HTLW. A conversion of 98.1% and selectivity of 96.5% were achieved at 453.15K for 1.5h with an ammonia concentration of 13.4mmol/L. The effects of ammonia concentration, initial concentration of reactant and reaction temperature were then investigated and correlated using a derivated equation. The results indicated that adequate addition of ammonia could adjust the pH of the reaction medium into 2.2–2.4, where the dominant form of the decarboxylation is the monovalent anion. Moreover, the kinetic data at different temperatures were fitted by a first-order equation, and the rate constants at each temperature and an activation energy of 190kJ/mol were obtained.

Chlorine Dioxide–Iodine–Acetylacetone Oscillation Reaction Investigated by UV–Vis and Online FTIR Spectrophotometric Methods

In order to study the chemical oscillatory behavior and mechanism of a new chlorine dioxide–iodine–acetylacetone reaction system, a series of experiments were carried out by using UV–Vis and online FTIR spectrophotometric methods. The initial concentrations of acetylacetone, chlorine dioxide, iodine, sulfuric acid, and the pH value have considerable influence on the oscillations observed at wavelength of 350 nm for the starch–triiodide ion complex (\({\text{QI}{_{3}^-}}\)). There is a pre-oscillatory or induction stage, the amplitude and the number of oscillations are associated with the initial concentration of reactants. Equations were obtained for the starch–triiodide ion complex (\({\text{QI}{_{3}^-}}\)) reaction rate change with reaction time and the initial concentrations in the oscillation stage. The oscillation reaction can be accelerated by increasing the reaction temperature. The apparent activation energies at the induction stage and the oscillation stage are 45.64 and 12.39 kJ·mol−1, respectively. The intermediates were detected by the online FTIR analysis. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction.

Electromagnetic wave propagation characteristics in unimolecular reactions

Microwave-assisted chemical reactions have attracted interests because of their benefits for enhancement of reaction rates. However, the problems, such as hot spots and thermal runaway, limit the application of microwaves in the chemical industry. To study the characteristics of electromagnetic wave propagation in a chemical reaction is critical to solve the problems. The research on the characteristics of electromagnetic wave propagation in the unimolecular reaction that is a simple model reaction, can be generalized to the research in a chemical reaction. The approximate expressions of the attenuation and dispersion characteristics of electromagnetic wave propagation in the unimolecular reaction are derived by the nonlinear propagation theory. Specially, when the reaction rate is zero, the derived approximate expressions can be reduced to the formulas in low-loss dispersive media. Moreover, a 1D mold is used to validate the feasibility of the approximate expressions. The influences of the reaction rate and initial reactant concentration on the characteristics are obtained.

Sonochemical synthesis of a new nano-sized cerium(III) supramolecular compound; Precursor for nanoceria

Using a sonochemical method, nanoparticles of a new Ce(III) supramolecular compound, (NAMH+)2[Ce4(pydc)6(pydcH)2(H2O)8]·8H2O (1), (H2pydc=2,6-pyridinedicarboxylic acid, NAM=nicotinamide), have been synthesized. Compound 1 was characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), FT-IR spectroscopy and elemental analyses, and its structure was determined by X-ray crystallography. It has been revealed that its structure consists of tetra-nuclear building units that extend to a 3D supramolecular network via non-covalent interactions mainly hydrogen bonding. The thermal stability of complex 1 both for its crystals and nanostructures has been studied by the thermal gravimetric (TG) method and compared with each other. The role of ultrasound irradiation power and the concentration of initial reactants on the size and morphology of the nano-structured complex 1, has been investigated. Ceria nanoparticles were obtained upon the calcination of complex 1 at 800°C under atmospheric air. Furthermore, the fluorescent properties of complex 1 at room temperature were studied.

Formation of Bromate and Halogenated Disinfection Byproducts during Chlorination of Bromide-Containing Waters in the Presence of Dissolved Organic Matter and CuO.

Previous studies showed that significant bromate (BrO3(-)) can be formed via the CuO-catalyzed disproportionation of hypobromous acid (HOBr) pathway. In this study, the influence of CuO on the formation of BrO3(-) and halogenated disinfection byproducts (DBPs) (e.g., trihalomethanes, THMs and haloacetic acids, HAAs) during chlorination of six dissolved organic matter (DOM) isolates was investigated. Only in the presence of slow reacting DOM (from treated Colorado River water, i.e., CRW-BF-HPO), significant BrO3(-) formation is observed, which competes with bromination of DOM (i.e., THM and HAA formation). Reactions between HOBr and 12 model compounds in the presence of CuO indicates that CuO-catalyzed HOBr disproportionation is completely inhibited by fast reacting phenols, while it predominates in the presence of practically unreactive compounds (acetone, butanol, propionic, and butyric acids). In the presence of slow reacting di- and tricarboxylic acids (oxalic, malonic, succinic, and citric acids), BrO3(-) formation varies, depending on its competition with bromoform and dibromoacetic acid formation (i.e., bromination pathway). The latter pathway can be enhanced by CuO due to the activation of HOBr. Therefore, increasing CuO dose (0-0.2 g L(-1)) in a reaction system containing chlorine, bromide, and CRW-BF-HPO enhances the formation of BrO3(-), total THMs and HAAs. Factors including pH and initial reactant concentrations influence the DBP formation. These novel findings have implications for elevated DBP formation during transportation of chlorinated waters in copper-containing distribution systems.

Probing structural adaptability in templated vanadium selenites

The structural adaptability of [V3O5(SeO3)3]n2n− layers in organically templated vanadium selenites was determined using a three step approach involving (i) an 84 reaction study with 14 distinct organic amines and 6 different reaction conditions, (ii) decision tree construction using both dependent and independent variables, and (iii) the derivation of chemical hypotheses. Formation of [V3O5(SeO3)3]n2n− layers requires that three criteria be met. First, compound stabilization through hydrogen-bonding with specific nucleophilic oxide ions is needed, requiring the presence of a primary ammonium site on the respective organic amine. Second, layer formation is facilitated through the use of compact ammonium cations that are able to achieve charge density matching with the anionic layers. Third, competition between organic ammonium cations and NH4+, which affects product formation, can be controlled through reagent choice and initial reactant concentrations. This approach to elucidate structural adaptability is generalizable and can be applied to a range of chemical systems.