Rate Constant Data Research Articles

Kinetic modelling of ozonation and photolytic ozonation of metronidazole removal from water

This work addresses the ozonation, photolysis, and photolytic ozonation of metronidazole (MTZ), a widely used antibiotic frequently detected in urban wastewater. A UVA source emitting radiation between 300 and 400 nm was utilized. The presence of scavengers such as t-butanol and sodium azide confirmed the role of hydroxyl radicals in both ozonation and photolysis processes. Conversely, singlet oxygen did not influence the photolytic processes. The average quantum yields of MTZ and ozone were determined to be 1.2 × 10−3 and 0.72 mol/Einstein, respectively, for the 300–400 nm wavelength range. In direct MTZ photolysis, a stoichiometric ratio of 0.34 mol of hydroxyl radicals formed per mol of photolyzed MTZ was observed. However, the effects of hydroxyl radicals on the MTZ photolytic rate were only significant after 45 min of reaction time. Using rate constant data from literature and quantum yields calculated in this study, a kinetic model for both MTZ ozonation and photolytic ozonation was proposed, enabling the prediction of MTZ conversion and degradation rates. This model includes three intermediate compounds that also consume ozone and hydroxyl radicals. The results show that experimental and calculated concentrations of MTZ are within an error margin of less than 14 % in all cases.

Temperature-Dependent Kinetic Study of the Reactions of Hydrogen Atoms with H2S and C2H4S

A discharge-flow reactor combined with modulated molecular beam mass spectrometry technique was employed to determine the rate constants of H-atom reactions with hydrogen sulfide and thiirane. The rate constants for both reactions were determined at a total pressure of 2 Torr from 220 to 950 K under pseudo-first-order conditions by monitoring either consumption of H atoms in excess of H2S (C4H4S) or the molecular species in excess of atomic hydrogen. For H + H2S reaction, a suggested previously strong curvature of the Arrhenius plot was confirmed: kl = 8.7 × 10−13 × (T/298)2.87 × exp(−125/T) cm3 molecule−1 s−1 with a conservative uncertainty of 15% at all temperatures. Non-Arrhenius behavior was also observed for the reaction of H-atom with C2H4S, with the experimental rate constant data being best fitted to a sum of two exponential functions: k2 = 1.85 × 10−10 exp(−1410/T) + 4.17 × 10−12 exp(−242/T) cm3 molecule−1 s−1 with an independent of temperature uncertainty of 15%.

Kinetic Study on Alkaline Hydrolysis of an Ester to Correlate the Solvent Effect with Some Thermodynamic Functions

In the present research paper, second-order rate constants for the alkaline hydrolysis of ethyl benzoate and of ethyl p-nitrobenzoate in ethanol–water mixtures in the ethanol mol fraction range 0.16–0.72 and at 278.15– 318.15 K measured by a specially developed titrimetric technique. The results show interesting variations in the rate constants with ethanol content at the various temperatures, especially over the mol fraction ranges 0.16–0.25 and 0.4–0.5. The rate constant (k2) data, the Arrhenius activation energy (EA) and preexponential factor (A) for ethyl benzoate and the parameters of the fitted polynomials from which other derived thermodynamic functions may be calculated are provided as supplementary material.

Reaction of O(3P) with Carbon Disulfide: Kinetics and Products

The kinetics and products of the reaction of ground-state O atoms with carbon disulfide, of interest for atmospheric and combustion chemistry, were studied using a discharge-flow system combined with modulated molecular beam mass spectrometry. The total reaction rate constant was determined in an absolute way from kinetics of CS2 consumption and reaction product, SO radical formation, and employing a relative rate method with two reference reactions: k1 = (3.35 ± 0.10) × 10–11 exp(−(665 ± 15)/T) cm3 molecule–1 s–1 at T = 220–960 K, with an estimated independent of temperature uncertainty of 15%. The yields of two reaction products, SO and OCS, were determined at T = 220–960 K, resulting in the following expressions for the branching ratio of the corresponding (SO + CS and OCS + S forming) reaction pathways: k1a/k1 = (0.935 ± 0.005) × exp(−(7.4 ± 0.2)/T) and k1b/k1 = (0.067 ± 0.002) × exp(80 ± 8/T), where the uncertainties reflect the statistical 2σ precision. The reaction rate constant and product data from the present work are discussed in comparison with previous experimental and theoretical studies.

A quantitative method of eutectic reaction study between boron carbide and stainless steel

Core Disruptive Accident (CDA) is a critical scenario in the Generation IV sodium-cooled fast reactor development. One of the key issues in the CDA evaluation is the eutectic reaction between Boron carbide (B4C) and Stainless Steel (SS). For developing a physical model in the CDA analysis code, it is necessary to investigate the B4C-SS eutectic reaction. To assess the reaction, one quantitative and high-resolution method using Joule heating is proposed in this study. Experiments were conducted using B4C material and SUS304 tubes. With an originally proposed equation, reaction rate constant data in the 1450 K-1500 K range were obtained, which was scarce in the past. The derived reaction rate constant values are consistent with the reference values. The reaction layer microstructure observation and the associated chemical composition analysis were also conducted. The proposed method is validated by the results. It can be concluded that the new method is credible with high efficiency.

Synthesis of silver nanoparticles anchored on nickel ferrite/oxidized-graphite composite for the efficient reduction of aqueous P-nitrophenol

• Ag-NiFe 2 O 4 /O-graphite exhibits excellent catalytic activity towards reduction of P-NP. • The reduction reaction was performed using sodium borohydride as the reducing agent. • A high normalized reaction rate constant (6.04 ± 0.8 s −1 g −1 ) value was achieved with this catalyst. • The synergistic interaction between nano sized Ag and NiFe 2 O 4 improved the reaction rate. • The material displays improved water cleaning properties. The current study focuses on the synthesis of spherical shaped Ag NPs decorated onto magnetic nickel ferrite/oxidized graphite (NiFe 2 O 4 /O-graphite) support. The synthesized material is thoroughly tested to study the physicochemical properties of the material. The characterization data clearly confirms the successful incorporation of nano sized Ag and NiFe 2 O 4 NPs onto O-graphite surface. Further, the synthesized material is tested as a catalyst towards the reduction of P-nitrophenol (P-NP) with sodium borohydride (NaBH 4 ) as the reducing agent. O-graphite surface failed to reduce P-NP in the presence of NaBH 4. The material (Ag-NiFe 2 O 4 /O-graphite) exhibits excellent catalytic activity with more than 98% reduction of P-NP in less than 1 min with P-NP to NaBH 4 molar ratio of 1:10 and 10 mg of the catalyst. The normalized reaction rate constant data calculated under such reaction condition is 6.04 ± 0.8 s −1 g −1 . The high catalytic activity with an excess of NaBH 4 in the reaction medium is attributed to the synergistic interaction between nano sized Ag NPs and magnetic NiFe 2 O 4 /O-graphite support. Here, Ag NPs acts as an electron transfer medium that transfer electrons to P-NP for the reduction process. In its dual role, NiFe 2 O 4 serves as an electron transfer medium to facilitate the reduction process and separates of the catalyst efficiently from the reaction mixture post catalytic reaction owing to its magnetic nature. Further, FTIR, XRD, and TEM analysis confirms the structural stability of the spent catalyst even after three regeneration cycles. Leaching data confirms that insignificant leaching of Ag NPs from the support material in the aqueous mixture occurred during the reduction reaction. The results clearly indicate that the material may act as an efficient catalyst for the reduction of recalcitrant organic pollutants from water.

Selected Ion Flow Tube – Mass Spectrometry (SIFT-MS) study of the reactions of H3O+, NO+ and O2+ with a range of oxygenated volatile organic carbons (OVOCs)

Selected Ion Flow Tube-Mass Spectrometry (SIFT-MS) uses soft chemical ionisation, typically by H3O+, NO+ and O2+, to analyse trace gases in real time at mixing ratios down to low parts per trillion by volume (pptv) and has recently been demonstrated as an effective method for monitoring volatile organic compounds (VOCs) in the atmosphere. SIFT-MS analysis requires accurate rate coefficient and product ion branching ratio data to allow for accurate mixing ratio calculations without the need for calibration standards. Most rate constant data have been measured using helium as the carrier gas. Here we report rate constants of a number of oxygenated volatile organic compounds (OVOCs) alongside benzene for H3O+, NO+ and O2+ reagent ions in nitrogen carrier gas, using a permeation tube calibration source and a certified gas standard to introduce known concentrations into the SIFT-MS. This includes the first reported literature rate constant for nonanal using SIFT-MS. We found that the rate constants for most compounds measured in nitrogen carrier gas were similar to those measured in helium. However, the NO+ rate constants for ketones measured in nitrogen were 1.2–5 times lower than those measured in helium. We observe higher fragmentation due to changes made to the lens voltages of the instrument in order to tune for higher sensitivity, altering the reagent ion energies. We also show the impact of increasing the flow tube temperature and voltage on the sensitivity and ionisation of benzene, butanone and butanal under both dry and humid conditions. Some of the SIFT-MS compound library entries are data from historic SIFT-MS instruments that lacked a heated flow tube, and therefore suffered from higher water clustering than current commercial SIFT-MS models. We show that a higher flow tube temperature reduces the amount of water adduct formation thereby simplifying compound concentration determination. These results demonstrate the need to ensure that the library data used are acquired under the same conditions as the experiment being performed.

A universal free energy relationship for both hard and soft radical addition in water

AbstractPrioritization of (eco)toxicological risks and technological endpoints among 100,000+ potential substances, conditions and mechanisms requires computationally ‘inexpensive’ and accurate tools to ‘screen’ reactivity and identify reaction products. Such prediction tools are very scarce. Left unresolved, charge‐transfer and hydration complicate predictions. Based on experimental reaction of radicals (3O2, CH3•, CO3•− etc.) with organic substrates, we hypothesized that a universal linear free energy relationship (LFER) can rationalize these reactions to accurately predict addition rates.We calculated free energies of forming charge‐separated intermediates from explicit descriptions of addition reaction products. We combined these energies, via a thermodynamic cycle, with electron transfer energies to calculate product formation energies. All energies include consideration of hydration effects by water. We ascribe feasibilities of ‘hard’ (ionic) and ‘soft’ (covalent) mechanisms to the relevance of the charge‐separated intermediate.Analysis shows that activation energies effectively relate to a combination of product formation energies and charge‐separation energies. The relative importance of these is determined by a mixing parameter, which is mostly constant for a given radical (substrate). Via the Eyring equation, our universal LFER explains up to 94% of the variance in data for rate constants. Prediction error is a factor 5 (2 SD), only slightly larger than variation in experimentation, particularly sensitive to varying reaction conditions.Minimal parametrization ensures that our new framework for calculating reactivity of radical addition is accurate, robust and with satisfactory rational. Calculation time for 100 reactions is <1 h on a standard desktop PC. In anticipation of underpinning with an even wider range of reagents, this ‘inexpensive’ calculus can more easily assess a greater domain of structures and extrapolate to new structures. This helps to better assess and select favourable non‐toxic, environmentally friendly and technologically superior chemical (sub)structures.

Using single fibre electrodes to determine the spatial variability of rate constants across carbon felt electrodes

The spatial variation of rate constants for the ferri/ferrocyanide redox reaction in carbon felt was been determined through the analysis of single fibre electrodes. The rate constant for the reaction at each single fibre electrode was measured using electrochemical impedance spectroscopy (EIS) data. Qualitative rate constant data was also determined from the peak separation extracted from cyclic voltammograms. Both EIS and cyclic voltammetry showed a wide variation in the kinetics for the ferri/ferrocyanide redox reaction over the single fibre samples. Analysis then revealed that fibres taken from one face of the carbon felt sample were statistically different to the other face of the felt, suggesting that the manufacturing process of carbon felt can lead heterogeneity in the activity of the felt. Given the importance of carbon felt electrodes in applications such as redox flow batteries, understanding, controlling and possibly minimising this spatial variation could lead to better flow battery performance.

Segmented flow capillary microreactors for determination of kinetic rate constants of reactive zinc extraction system

Conventional techniques for kinetic rate constant acquisition are limited by diffusive transport, which can be well addressed by microfluidic techniques. Segmented flow capillary microreactors were used for the first time in this study to obtain kinetic rate constants for a reactive zinc extraction system. The influences of initial zinc ion concentration, total flow velocity, pH of the aqueous phase, and ionic strength on the kinetic rate constant determination were investigated. The control regimes were determined with the ratio of reaction to total resistance R, and the Hatta number. The kinetic rate constants obtained at low initial zinc concentrations, low acidity and high flow velocities exhibited minor deviations, indicating that the zinc sulfate/D2EHPA system could be under the kinetic control regime with the capillary microreactors, which also demonstrated the viability of the segmented flow approach. The kinetic rate constant data obtained with the segmented flow capillary microreactor from this work were much higher than those obtained from previous studies, which may be attributed to the fact that the microreactor minimizes the influence of diffusive transport. The purpose of this work was to provide reliable kinetic data of the reactive zinc extraction system and to verify the efficiency and superiority of the segmented flow microreactor approach over other techniques.

Реакционная способность арилсульфонилгалогенидов как функция молекулярного электростатического потенциала реакционного центра

To study the reactivity of arylsulfonyl halides, the molecular electrostatic potential (MEP) was considered for the first time as a descriptor. The reaction of hydrolysis of aromatic sulfonyl halides in the medium of mixed acetone-water solvents (according to the literature data of rate constants) was used as a model. The calculation of the structural parameters of the molecules of substituted arylsulfonyl halides was carried out using the ADF2014 software package at the level of the DFT/M06/6-311+G* (PCM) theory. It was found that the magnitude of the MEP on the sulfonyl sulfur atom is very sensitive to changes in the structure of substrates, which makes it possible to determine the change in the ratio between the rate of nucleophilic attack and anionoid abstraction of the leaving group. In particular, using the example of the hydrolysis reaction of substituted thiophenesulfonyl chlorides, it was shown that the acceleration of the reaction is observed with an increase in the donor properties of the substituents and the associated increase in the negative MEP value on the sulfonyl sulfur atom. The antibate character of the dependence of the hydrolysis constant values on the IEP value indicates that not the nucleophilic attack is the rate determining in the interaction of thiophene sulfonyl chlorides and the hydroxyl anion in this sample, but the abstraction of the chloride anion. This reaction has an unstable mechanism, when the ratio between the degree of S-nucleophile bond formation and S-halogen bond cleavage changes. This makes it possible to use MEP as a descriptor of reactivity in the hydrolysis of aryl sulfonyl halides and to elucidate the details of changes in the structure of transition states during the implementation of mechanisms other than pure SN2 mechanism.

Kinetic Analysis of the Oxidative Conversion of Methane in Slow Combustion. II. Parametric Characteristics of Directional Conversion

The paper presents a kinetic analysis of a model of the oxidative conversion of methane to useful products based on a set of possible elementary reactions that could most fully reflect the chemistry of the process and for which rate constant data are available. The analysis was carried out numerically. Key steps of the mechanism were identified and used to predict conditions under which the process can be effectively carried out in order to obtain a mixture of methanol and formaldehyde or mainly methanol. It is shown that high efficiency can be achieved at increased pressures of the reaction mixture due to the high methane content. The directionality of the process increases with decreasing temperature.

Shock Tube Measurement of the CH3 + C2H6 → CH4 + C2H5 Rate Constant.

The rate constant for the CH3 + C2H6 → CH4 + C2H5 reaction was studied behind reflected shock waves at temperatures between 1369 and 1626 K and pressures from 8.6 to 47.4 atm in mixtures of methane, ethane, and argon. Ethylene time histories were measured using laser absorption of radiation from a carbon dioxide gas laser near 10.532 μm. The resulting rate constant data can be represented by the Arrhenius equation k (T) = 3.90 × 1013 exp(-16670 cal/mol/RT) cm3 mol-1 s-1. We believe this is the first study to extend experimental data for this rate constant to temperatures above 1400 K. The overall 2σ uncertainty of the current data is +18%/-21% resulting primarily from uncertainties associated with the influence of secondary reactions and the fitting of rapidly changing species time histories at the higher temperatures.

A Comparative Study on Photocatalytic Degradation of Pyridinium – Based Ionic Liquid by TiO2 and ZnO in Aqueous Solution

Abstract The photocatalytic degradation of hexylpyridinium bromide (HPyBr) from an aqueous solution was studied by focusing on comparison of the photoactivity of ZnO and TiO2 P25. The process was carried out under different experimental conditions. The results showed that there is no adsorption of pollutant by both catalysts in the dark. The efficiency of P25 Degussa and ZnO photocatalysts were compared, and the photocatalytic kinetics study showed that ZnO is more efficient than TiO2 P25. The HPyBr photodegradation was found to follow a pseudo-first order kinetics, and the higher rates constants were obtained at the alkaline medium for ZnO (pH = 11, kapp = 9.61 × 10–2 min−1) and at acidic medium for TiO2 P25 (pH = 3, kapp = 1.28 × 10–2 min−1). The Langmuir–Hinshelwood model was found suitable to explain the rate constant data for the ionic liquid degradation by both catalysts. The presence of carbonate ions at alkaline medium was found to reduce the HPyBr degradation for ZnO and to enhance the HPyBr degradation for TiO2, this enhancement in TiO2/CO32-/UV system was confirmed by the addition of •OH and hvb+ scavengers. According to TOC and COD results, HPyBr mineralization was faster in ZnO/UV system than in TiO2/UV system.

Effective Mass Transfer Area Measurement Using a CO2–NaOH System: Impact of Different Sources of Kinetics Models and Physical Properties

Absorption of carbon dioxide into sodium hydroxide solution has been extensively used for mass transfer investigation in gas–liquid contacting reactors. To obtain a reliable value of effective mass transfer area (A), the selection of fundamental parameters, such as reaction rate constant, diffusion coefficient, and solubility data, is significant for data processing, and very little literature has been reported on the selection of these parameters. Therefore, an evaluation of the sources of fundamental parameters needs to be given. In this work, six parameter sources, including classic literature and newly published papers, were evaluated for effective mass transfer area measurement in a rotating packed bed. Quantitative comparisons demonstrated that using different reaction kinetics models will cause a large deviation in the values of the effective mass transfer area. Further, the inconsistency between the sources of kinetics models and physical properties can also cause a large deviation, which should b...

General mathematical formula for near equilibrium relaxation kinetics of basic enzyme reactions and its applications to find conformational selection steps

A general mathematical formula of basic enzyme reactions was derived with nearly no dependence on conditions nor assumptions on relaxation kinetic processes near equilibrium in a simple single-substrate-single-product enzyme reaction. The new formula gives precise relationships between the rate constants of the elementary reaction steps and the apparent relaxation rate constant, rather than the initial velocity that is generally used to determine enzymatic parameters according to the Michaelis–Menten theory. The present formula is shown to be complementary to the Michaelis–Menten formulae in a sense that the initial velocity and the relaxation rate constant data together could determine the enzyme–substrate dissociation constant KES, which has been usually conditionally approximated by the Michaelis constant KM within the framework of the Michaelis–Menten formulae. We also describe relaxation kinetics of enzyme reactions that include the conformational selection processes, in which only one enzymatic conformer among a conformational ensemble can bind with either the substrate or product. The present mathematical approaches, together with numerical computation analyses, suggested that the presence of conformational selection steps in enzymatic reactions can be experimentally detected simply by enzymatic assays with catalytic amounts of enzyme.

PHARMACOKINETIC COMPARISON OF MONTELUKAST SODIUM FORMULATIONS AFTER A SINGLE ORAL DOSE IN HEALTHY GUINEA PIGS

Objective: Pharmacokinetic evaluation of montelukast sodium chronomodulated capsules (sustained-release solid dispersion of drug enclosed in pH-sensitive film-coated hard gelatin shell) and marketed tablets has been carried out in this study.
 Methods: A single oral dose of prepared capsules and marketed conventional tablets was administered in healthy male Dunkin-Hartley albino guinea pigs. Blood samples were collected at different time intervals and plasma concentration of drug was determined by reversed-phase high-performance liquid chromatography. Different pharmacokinetic parameters were assessed from plasma drug concentration-time profile by one-compartment model, first-order kinetics.
 Results: Pharmacokinetic parameters such as time to reach maximum concentration, elimination rate constant, elimination half-life, and mean residence time data indicates that drug release from chronomodulated capsules is significantly prolonged with initial release lag time of 3.5–4 h in comparison with marketed conventional tablets. However, maximum drug plasma concentration, area under the concentration-time curve, and apparent volume of distribution values show non-significant difference between capsules and marketed tablets.
 Conclusion: The findings specified that capsules were providing time controlled delivery of drug at a desired rate for prolonged time, which may be helpful for the prevention of episodic attack of asthma in early morning hours.

Towards a kinetic understanding of the NOx sensitization effect on unsaturation hydrocarbons: A case study of ethylene/nitrogen dioxide mixtures

Abstract Ignition delay time (IDT) measurements for ethylene (C2H4)/nitrogen dioxide (NO2)/oxygen/argon mixtures with various blending ratios of NO2/C2H4 = 0/100, 15/85 and 50/50 were performed in a shock tube. The sensitization effect of NO2 on C2H4 ignition was investigated at pressures ranging from 1.2 to 10 atm, in the temperature range 920–1780 K, and at equivalence ratios from 0.5 to 2.0. Similar to our recent studies of NO2 effects on CH4 and C2H6 ignition (Deng et al., 2016; Deng et al., 2017), the effect of NO2 addition on measured IDTs of the unsaturated hydrocarbon C2H4 also exhibits both temperature- and pressure- dependences. NO2 addition generally promotes the reactivity of ethylene and the promotion effect is more pronounced for the mixtures with high NO2 content at higher pressures (p > 4.0 atm), at lower temperatures (T 1250 K). A detailed kinetic mechanism of C2H4/NO2 was proposed by refining critical reactions through incorporating ab-initio calculations from this study and recently published rate constant data. This mechanism is capable of reproducing the new data reported in this work and literature ones as well and has thus been used to perform sensitivity and flux analyses to kinetically interpret the interaction of NO2 with C2H4.

Investigation on adsorption kinetics of heavy metals by rice husk

Removal of heavy metal ions and their derivative forms from the environment has become a priority to safeguard the quality of the ecosystem. In this context, the present study is based on the removal of Cd(II), Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II) from synthetic industrial effluents using heat-treated rice husk, which can be used to develop cost-effective and ecofriendly effluent treatment procedures. The characterisation experiments reveal that Si available in rice husk in high percentage and many chemical functional groups present on the surface are involved in the adsorption mechanism. Metal ions commonly present in effluents of metal finishing industries were specially considered for their removal. The optimum firing temperature of rice husk, determined using 10.0 mg L-1 solutions of each metal ion, was 100 oC. The effect of other experimental parameters, such as contact time and pH were also investigated using rice husk fired at the optimised temperature of 100 oC. Kinetics studies conducted for the interaction of the above metal ions and rice husk lead to the validity of pseudo second order kinetics with high regression coefficients. The initial rate of adsorption ( ho ) of metal ions varies in the order of Pb(II) > Zn(II) > Cd(II) > Cu(II) > Ni(II) > Cr(III). According to the diffusion models investigated, Weber and Morris intraparticle diffusion model supports the data for rate constant of particle diffusion, which varies in the same order as observed in initial adsorption rate measurements ( ho ).

Corrigendum to “The dissolution rates of simulated UK Magnox – ThORP blend nuclear waste glass as a function of pH, temperature and waste loading” [Miner. Mag. 79, (2015) 1529–1542

AbstractWe revise the data fitting in our original paper [The dissolution rates of simulated UK Magnox - ThORP blend nuclear waste glass as a function of pH, temperature and waste loading, Miner. Mag.79 (2015) 1529–1542]. The intrinsic rate constant data were calculated incorrectly, the corrected data are presented herein. To support the corrected analysis we have also taken the opportunity to report some additional 90°C data. The conclusions of the original paper remain sound.