Chemical Kinetics

Introduction to Chemical Reaction Engineering and Kinetics is written primarily for
a first course in chemical reaction engineering (CRE) for undergraduate students in
chemical engineering. The purpose of the work is to provide students with a thorough
introduction to the fundamental aspects of chemical reactor analysis and design. For
this purpose, it is necessary to develop a knowledge of chemical kinetics, and therefore
the work has been divided into two inter-related parts: chemical kinetics and CRE. Included
with this book is a CD-ROM containing computer software that can be used for
numerical solutions to many of the examples and problems within the book. The work
is primarily based on material given to undergraduate students in the Department of
Chemical Engineering and Applied Chemistry at the University of Toronto.

The chemistry and energetics of the Criegee intermediate, a primary product of the ozonolysis of alkenes, are discussed in terms of recent ab-initio calculations and laboratory studies. The experimental observations in O3–alkene systems can be rationalized on the basis of a general mechanism: where the ‡ represents the range of internal excitation energies available to the planar dioxymethylenes (i.e., the Criegee intermediates) initially formed via exothermic O3-alkene reactions. Estimates are given for the rate constants of these reactions, and a critique is provided of the possible role of the Criegee intermediate and its isomers in the formation of alkanoic acid anhydrides in O3–alkene systems and in the formation of H2SO4 aerosols in O3–alkene–SO2 systems.

Shock initiation of the tri-amino-tri-nitro-benzene based explosive PBX 9502 cooled to −55°C J. Appl. Phys. 112, 074909 (2012) One-dimensional plate impact experiments on the cyclotetramethylene tetranitramine (HMX) based explosive EDC32 J. Appl. Phys. 112, 064910 (2012) Imploding water wave: A poppy blossom Phys. Fluids 24, 091113 Non-contact near-field underwater explosion induced shock-wave loading of submerged rigid structures: Nonlinear compressibility effects in fluid structure interaction J. Appl. Phys. 112, 024911 Dynamic mode decomposition analysis of detonation waves Phys. Fluids 24, 066101 Additional information on AIP Conf. Proc.

Previous investigations show that soot particle volume fraction and number density were significantly reduced by exhaust gas recirculation (EGR) diluents CO 2 and H 2 O. However, these investigations were often convoluted by their experimental flame configurations and primarily focused on soot volume fraction rather than soot inception. To isolate the effects on soot inception and the corresponding chemistry, the current study measured the reactivity of CO 2 (up to 9.5% volume fraction) for both C 2 H 2 (1.00% volume fraction) and CH 4 (1.85% volume fraction) fuels in homogeneous mixtures. Computed effect of H 2 O on these and other fuels are also presented. Experiments were performed at high temperature (1640 K and 1770 K) and high equivalence ratios (U = 55 and 75) to understand the effect of CO 2 on polycyclic aromatic hydrocarbons (PAH) and formation of nascent soot particles with negligible oxygen influence. Experimental results show that CO 2 enhanced the soot inception rate when added to C 2 H 2 but had an undetectable affect on CH 4. Gas chromatography confirmed that CO 2 increases CO mole fraction and reduces C 2 H 2 fuel concentration. Chemical kinetic simulations showed that the C 2 H 2 was being converted to soot precursors. CO 2 enhanced the soot inception rate for C 2 H 2 by producing OH radicals. Images of nascent soot particles produced in the presence of CO 2 were used to determine the size of PAH molecules in the particles and particle morphology. Both attributes were similar to particles formed without CO 2. CO 2 had little impact on the long reaction pathway from CH 4 to PAH molecules because H and CH 3 radicals propagated these reactions more readily than OH radicals.

A new two-temperature chemical kinetics model for nitrogen plasmas is presented. The model is used together with the ûibrationally-specific collisional-radiatiûe model to study the effects of ûibrational nonequilibrium distributions on the chemical composition of two-temperature atmospheric pressure nitrogen plasmas. It is found that oûer a wide range of conditions the ûibrational leûels follow Boltzmann distributions and that the ûibrational temperature T v is well approximated by gas temperature T g at low electron number densities and by electron temperature T e at high electron number densities. This result suggests that simple kinetic models with two-temperature rate coefficients can be used to reliably model nonthermal plasmas. The calculation also yields a surprising result that, for a giûen constant gas temperature, the steady-state electron number density exhibits an S-shaped dependence on the electron temperature. This S-shaped behaûior is caused by competing ionization, charge transfer reactions, two-body dissociatiûe recombination, and three-body electron recombination reactions, and therefore is characteristic of molecular plasmas.

The kinetic consequences of resonance tunnelling processes that may occur in chemical reactions are investigated in terms of a multi-centered unsymmetrical Eckart potential barrier. This potential function does not only simulate the possible existence of intermediate wells in the effective potential energy cut along the reaction path, but also is amenable to analytic solutions. The reaction rate as well as its dependence on temperature, reduced mass,Q-value, activation energy and barrier diffuseness are evaluated for successively increasing the number of barrier stages. Comparisons between results due to single and multi-humped potential energy barriers are made and discussed.

The asymptotic structure of laminar, moderately rich, premixed methane flames is analyzed using a reduced chemical-kinetic mechanism comprising four global reactions. This reduced mechanism is different from those employed in previous asymptotic analyses of stoichiometric and lean flames, because a steady-state approximation is not introduced for CH 3 . The aim of the present analysis is to develop an asymptotic model for rich flames, which can predict the rapid decrease of the burning velocity with increasing equivalence ratio . In the analysis, the flame structure is presumed to consist of three zones: a preheat zone with a normalized thickness of the order of unity, a thin reaction zone, and a postflame zone. The preheat zone is presumed to be chemically inert, and in the postflame zone the products are in chemical equilibrium and the temperature is equal to the adiabatic flame temperature T b . In the reaction zone the chemical reactions are presumed to take place in two layers: the inner layer and the oxidation layer. The rate constants of these reactions are evaluated at T 0 , which is the characteristic temperature at the inner layer. In the inner layer the dominant reactions taking place are those between the fuel and radicals, and between CH 3 and the radicals. An important difference between the structure of the inner layer of rich flames and that of lean flames analyzed previously is the enhanced influence of the chain-breaking reaction CH 3 ϩ H ϩ (M) 3 CH 4 ϩ (M) in rich flames. Here M represents any third body. This reaction decreases the concentration of H radicals, which in turn decreases the values of the burning velocity. In the oxidation layer of rich flames, the reactive-diffusive balance of O 2 is considered. This differs from the structure of the oxidation layer of lean flames where the reactive-diffusive balance of H 2 and CO was of primary interest. The burning velocities calculated using the results of the asymptotic analysis agree reasonably well with the burning velocities calculated numerically using chemical-kinetic mechanisms made up of elementary reactions. The values of the characteristic temperature at the inner layer T 0 are found to increase with increasing values of the equivalence ratio and to approach T b at ϭ 1.36. When T 0 is very close to T b , the asymptotic analysis developed here is no longer valid and an alternative asymptotic analysis must be developed for even larger equivalence ratios.

The determination of rate parameters of gas-phase elementary reactions is usually based on direct measurements. The rate parameters obtained in many independent direct measurements are then used in reaction mechanisms, which are tested against the results of indirect experiments, like time-to-ignition or laminar flame velocity measurements. We suggest a new approach that takes into account both direct and indirect measurements and optimizes all influential rate parameters. First, the domain of feasibility of the Arrhenius parameters is determined from all of the available direct measurements. Thereafter, the optimal Arrhenius parameters are sought within this domain to reproduce the selected direct and indirect measurements. Other parameters of a complex mechanism (third-body efficiencies, enthalpies of formation, parameters of pressure dependence, etc.) can also be taken into account in a similar way. A new fitting algorithm and a new method for error calculation were developed to determine the optimal mean values and the covariance matrix of all parameters. The approach is demonstrated on the calculation of Arrhenius parameters of reactions (R1): H + O 2 = OH + O and (R2): H + O 2 + M = HO 2 + M (low-pressure limit, M = N 2 or Ar). In total, 9 direct measurements for reaction (R1) (745 data points), 10 direct measurements for reaction (R2) (258 data points), and 11 ignition time measurements (79 data points) were taken into account. The application of the method resulted in the following rate parameters for the investigated reactions-(R1): A = 3.003 × 10 10 cm 3 mol -1 s -1 , n = 0.

The kinetics of the reduction of chromium(VI) to chromium(III) by D-fructose in HClO 4 was studied at various concentrations of reactants and acidities. The redox reaction takes place through a complex multistep mechanism, which involves the formation of intermediate Cr IV and Cr V species. Cr IV reacts with D-fructose much faster than Cr V and Cr VI do, and cannot be directly detected. Superoxochromium(III), CrO 2 2þ , has been detected by UV spectroscopy, thus evidencing that Cr II is an intermediary in these reactions and provides indirect evidence for the intermediary of Cr IV reaction path. The complete rate law for the Cr VI oxidation reaction is expressed by Àd[Cr VI ]/dt = (a + b [D-Fru])[H + ] 2 [Cr VI ] T , where a = (1.66 ± 0.04) · 10 À4 M À2 s À1 and b = (1.79 ± 0.06) · 10 À2 M À3 s À1 . The EPR spectra show that five-coordinate oxo-Cr V bischelates are formed in rapid pre-equilibria before the redox step: Cr(V) to Cr(III).

Marine aerosols produced by bursting bubbles at the ocean surface are highly enriched in organic matter (OM) relative to seawater. The importance of this OM in the photochemical evolution of marine aerosols and particularly as a source of reactive oxidants are unknown but likely significant. To investigate oxidant production, nascent aerosols were generated by bubbling zero air through flowing Sargasso seawater and photochemical production of OH radical and hydroperoxide were quantified in aqueous extracts exposed to solar radiation. Extrapolation to ambient conditions indicates that OM photolysis was the primary in situ source for OH (1.1 x10 -8 M s -1 ) and hydroperoxides (1.7 x 10 -8 M s -1 ) in nascent aerosols; NO 3 photolysis was the primary source in aged, acidified aerosols (1.4×10 -7 and 4.1×10 -8 M s -1 , respectively). In situ OH photoproduction was comparable to gas-phase uptake whereas H 2 O 2 photoproduction was slower.

Models for the energy profile along the reaction coordinate are utilized to determine the barrier's height and location as a function of ΔG. These form the basis for structure–reactivity correlations and afford a unified formulation for various postulates in the field of physical organic chemistry. Current experimental evidence is examined for the resulting correlations, and some of their applications as an aid to the chemical kineticist are presented.

Smouldering combustion is the driving phenomenon of wildfire in peatlands, like those causing haze episodes in Southeast Asia and Northeast Europe. These are the largest fires on Earth and an extensive source of greenhouse gases, but poorly understood, becoming an emerging research topic in climate-change mitigation. In this work, a series of multistep heterogeneous kinetics are investigated to describe the drying and decomposition in smouldering combustion of peat. The decomposition schemes cover a range of complexity, including 2, 3 or 4-step schemes, and up to 4 solid pseudo-species. The schemes aim to describe the simultaneous pyrolysis and oxidation reactions in smouldering fires. The reaction rates are expressed by Arrhenius law, and a lumped model of mass loss is used to simulate the degradation behaviour seen during thermogravimetric (TG) experiments in both nitrogen and air atmospheres. A genetic algorithm is applied to solve the corresponding inverse problem using TG data from the literature, and find the best kinetic and stoichiometric parameters for four types of boreal peat from different geographical locations (North China, Scotland and Siberia). The results show that at the TG level, all proposed schemes seem to perform well, with a high degree of agreement resulting from the forced optimization in the inverse problem approach. The chemical validity of the schemes is then investigated outside the TG realm and incorporated into a 1-D plug-flow model to study the reaction and the species distribution inside a peat smouldering front. Both lateral and in-depth spread modes are considered. The results show that the drying sub-front is essential, and that the best kinetics is the 4-step decomposition (one pyrolysis, and three oxidations) plus 1-step drying with 5 condensed species (water, peat, α-char, β-char, and ash). This is the first time that the smouldering kinetics and the reaction-zone structure of a peat fire are explained and predicted, thus helping to understand this important natural and widespread phenomenon.

Detailed modeling of complex combustion kinetics remains challenging and often intractable, due to prohibitive computational costs incurred when solving the associated large kinetic mechanisms. The Graphics Processing Unit (GPU), originally designed for graphics rendering on computer and gaming systems, has recently emerged as a powerful, cost-effective supplement to the Central Processing Unit (CPU) for dramatically accelerating scientific computations. Complex scientific computations are now being performed on the GPU in several research fields, such as quantum chemistry, molecular dynamics, and atmospheric modeling. Here, we present methods for exploiting the highly parallel structure of GPUs for combustion modeling. This paper outlines simple algorithm revisions that can be applied to the majority of existing combustion modeling algorithms for GPU computations. Significant simulation acceleration and predictive capability enhancements were obtained by using these GPU-enhanced algorithms for reaction rate evaluation and in ODE integration. For the demonstrations, we implemented the rate evaluation revisions in CHEMKIN and the ODE integration revisions in DASAC and DVODE and we tested the performance for simulating constant-volume ignition using SENKIN. The simulations using the revised algorithms are more than an order of magnitude faster than the corresponding CPU-only simulations, even for a low-end (double-precision) graphics card. Additionally, the computational time scales less than quadratically with the number of chemical species in the kinetic mechanism when using the GPU, as compared to the super-quadratic scaling normally seen with CPU-only chemical kinetics computations; and the GPU-based revisions do not involve approximations to the detailed kinetics. An analysis of the growth rates of combustion mechanism sizes versus computational capabilities of CPUs and GPUs further reveals the important role that GPUs are expected to play in the future of combustion modeling. Finally, we briefly outline practical steps for effectively transitioning from CPU-only to GPU-enhanced combustion modeling.

in a low molecular weight form, a high molecular weight form, and an immobile form where the molecules are bound to the tissue. The model describes how diffusion and absorption gradually reduce the insulin concentrations in the subcutaneous depot and thereby shift the balance between the three forms in accordance with usual laws of chemical kinetics. By presuming that primarily low molecular weight insulin penetrates the capillary walls, the model can account for experimentally observed variations in the absorption rate over a wide range of volumes and of concentrations. The model is used to determine the effective diffusion constant D for insulin in subcutis, the absorption rate constant B for low molecular weight insulin, the equilibrium constant Q between high and low molecular weight insulin, the binding capacity C for insulin in the tissue, and the average life time T for insulin in its bound state. Typical values for a bolus injection in the thigh of fasting type I diabetic patients are D = 0.9• t0-4 cm2/min, B = 1.3 x l O-e/min, and Q = O. 13 (ml/IU) z. Binding of insulin in the tissue is significant only at small concentrations. The binding capacity is of the order of C = 0.05 IU/cm 3 with a typical average life time in the bound state of T = 80,0 rain. Combined with a simplified model for distribution and degradation of insulin in the body, the absorption model is used to simulate variations in plasma free insulin concentrations with different delivery schedules, i.e., bolus injection and dosage by means of an infusion pump. The simulations show that a pump repetition frequency of I-2 per hr is sufficient to secure an almost constant plasma insulin concentration.

Biodiesel has become more attractive recently because of its environmental benefits and the fact that it is made from renewable resources. Esterification of carboxylic acids (specifically free fatty acids) is directly relevant to biodiesel. Non-catalytic esterification reactions lead to much simpler purification and environmentally friendly processes and yield commercial grade biodiesel product with little loss. Moreover, even low grade waste fatty materials such as waste greases can be used as feedstock, which was not permitted in traditional transesterification reaction due to high fatty acid content. In this work, the non-catalytic esterification of sunflower oil, which is readily applicable to actual biodiesel, was investigated. The sunflower oil sample which was chosen included Linoleic acid 72%, Oleic acid 19%, Palmitic acid 6% and Stearic acid 3%.

 The kinetics and mechanism of hydrothermal formation of zeolite A from natural kaolinites have been studied using as starting materials two international kaolinite standards (KGa-1 and KGa-2 from Georgia, USA) exhibiting a different degree of stacking disorder. Precursors utilized for the synthesis were prepared by heating the kaolinites at 800 °C. Metakaolinite was also prepared from KGa-1 by thermal activation at 600 °C. The hydrothermal syntheses were accomplished by heating the samples in NaOH solutions at temperatures between 70 and 110 °C. The kinetic experiments were performed by time-resolved synchrotron powder diffraction in isothermal mode using a transmission geometry and an Image Plate detector. The results of the kinetic analysis are interpreted in the light of the structural state of the starting kaolinite, and of the temperature of activation of the precursor material. For kaolinite activated at high temperature the nucleation and crystallization of zeolite A is essentially independent of the defect density of the original kaolinite, and the thermal history of the precursor seems to be the main controlling parameter. The formation process of zeolite A from metakaolinite materials obtained at lower activation temperatures shows significantly faster reaction rates and lower apparent activation energies. This is again interpreted in the light of the short range inhomogeneities present in metakaolinite. As the reaction proceeds metastable zeolite A transforms into hydroxy-sodalite.

Computer aided process engineering depends much on understanding of chemical and physical processes and their interaction. With this in mind the EU project SAFEKINEX has been designed. Aim of the project is to improve understanding of gaseous hydrocarbon oxidation processes to optimise efficiency and enhance gas explosion safety. Deep knowledge of the chemical kinetics to that end is required. The paper presents an overview of the project and some first results.

The kinetics of the reactions OH ϩ Br 2 : HOBr ϩ Br (1) and OD ϩ Br 2 : DOBr ϩ Br (3) have been studied in the temperature range 230-360 K and at total pressure of 1 Torr of helium using the discharge-flow mass spectrometric method. The following Arrhenius expressions were obtained either from the kinetics of product formation (HOBr, DOBr) in excess of Br 2 over OH and OD or from the kinetics of Br 2 consumption in excess of OH and OD:

Fuel and air staging are used to study the potential for reduction of NOx emissions from biomass fuelled reactors. The two well-known methods to reduce NOx emissions in a combustion process by primary measures are air-and fuel staging. Air staged reactors use primary air injection in the fuel bed, and a secondary air injection in the combustion chamber. A rich combustion in the first stage (close to stoichiometric condition) gives the maximum conversion of fuel-N to N2 (minimum NOx emissions after complete combustion). Fuel staging has been introduced as an alternative emission reduction technique due to the practical demands of air staging (high combustion temperature in the primary zone). Fuel-staging is a method of fuel reburning. The present study shows the effect of different variables on NOx reduction capability. Reactor models consisting of sequences of ideal reactors are employed in combination with a recently available detailed chemical kinetics mechanism, especially suitable for biomass combustion. Nitrogen in the fuel is known to be the largest contributor to NOx emissions; hence the nitrogen content of the fuel is found to be an important parameter in the reduction of nitrogenous emissions. Furthermore, the potential for NOx reduction is found to be highly affected by the amount of excess air in the primary zone, in advance of the secondary air inlet, with a clear optimal reduction close to a primary air excess ratio of 1. Increasing reactor temperature however has an inverse effect on the reduction potential due to the onset of thermal NOx production. Fuel staging is found to have a higher potential for reduction in the majority of the investigated range of primary excess air ratios. Only in the region close to stoichiometric conditions in the primary zone is a higher NOx reduction observed for air staging. The achieved NOx reduction under the optimum conditions was up to 76 percent.

The photochemical box model (PBM) developed in present study is based on the principle of mass conservation. It has a horizontal domain of city size and a vertical dimension of the mixed layer height. The concentration of any pollutant is determined by horizontal advection, vertical entrainment, source emissions, and chemical reactions. A one dimensional high resolution boundary layer model by Blackadar (1976, 1979) has been further developed by considering the effect of urban heat islands to simulate the variation of the mixed layer height and incorporated in the PBM. The simulated pollutant concentration using the predicted mixed layer height compares very well with observations and shows good daytime dynamic variation. The model predicted mixed layer height is a significant improvement over the characteristic mixed layer growth curve used in the original PBM by Schere and Demerjian (1984). The gas phase chemical kinetic mechanism used in the Regional Acid Deposition Study II (RADM2) and Demerjian chemical mechanism have been used to calculate the contributions of chemical reactions to the changes of pollutant concentrations. Detailed analysis and comparisons of the two chemical mechanisms have been made. The simulated pollutant concentration using both chemical mechanisms are in very good agreement with observations. A radiative transfer model developed by Madronich (1987) has been incorporated in the PBM for the calculation of actinic flux and photolytic rate constants. Height averaged and radiation corrected photolytic rate constant are used for the photochemical reactions. The simulated pollutant concentrations for CO, NO, NO_2 and O_3 are in very good agreement with observations. Budget analyses conducted for CO, NO, NO_2 and O_3 have enhanced our understanding of the relative contributions of horizontal advection, vertical entrainment, source emissions, and chemical reactions to the overall rate of change of their concentrations. Sensitivities of model results to the variation of photolytic rate constants, boundary conditions, hydrocarbon speciation factors, and thermal rate constant have been tested.

Densities of sodium chloride in the concentration range (0.010 to 0.090 ( 0.001) mol · dm -3 have been determined in aqueous and aqueous maltose systems [(1.0, 3.0, 5.0, and 7.0) % w/v] at different temperatures [(298 to 323) K] with the interval of 5 K. Apparent molar volume (φ ν ), partial molar volume (φ ν°) and the ion-ion interaction parameter (S V ) have been calculated, using the Masson equation by applying linear regression analysis. Other parameters were also calculated, viz., transfer volume (φ ν°(tr) ) and partial molar expansibility (φ E°) . Values of φ E°s how the presence of caging or packing effects. The data obtained from volumetric studies have been used to investigate the ion-solvent interaction and ion-ion interaction. The structure-breaking capacity of sodium chloride has been inferred in aqueous and aqueous maltose systems from Hepler's criterion, i.e., (∂ 2 φ ν°/ ∂Τ 2 ) Ρ second derivative of partial molar volume with respect to temperature at constant pressure.

Kinetics of acid hydrolysis of seven antibacterial iron(II) Schiff's base complexes has been studied. The Schiff's base ligands were derived from sodium 2-hydroxybenzaldehyde-5-sulfonate and a series of amino acids. The hydrolysis rate is determined by the complex hydrophilicity. Addition of the organic co-solvent, dimethylsulfoxide or n-propanol, significantly accelerates the hydrolysis.

A detailed kinetic, mechanistic and spectroscopic investigation has been made on the oxidation of fosfomycin by potassium dichromate in aqueous perchloric acid medium at 25 oC  and at a constant ionic strength, I = 3.10 mol dm-3. The reaction products were identified and characterized by spectral studies such as GC-MS and IR.  The reaction rate shows first order dependence on both chromium(VI) and fosfomycin concentrations and second order dependence on HClO4 concentration. The addition of chromium(III), which is one of the reaction products, had no significant effect on the reaction rate. The effect of ionic strength and dielectric constant of the medium on the rate of reaction were studied. Based on the kinetic results, spectral evidences, stoichiometry of the reaction and product analysis, a suitable mechanism was proposed. The activation parameters were determined with respect to the slow step of the mechanism. The thermodynamic quantities were also determined and discussed.

To characterize the influence of ionic strength on the kinetics of calcite precipitation from seawater solutions we carried out a set of experiments at four different ionic strengths (I ϭ 0.10; 0.34; 0.55; 0.93 m) in NaCl-CaCl2 solutions, at the temperature of 298.15K and a CO 2 partial pressure of 100 Pa. The constant addition technique was used in order to maintain [Ca 2ϩ ] at Х10.5 mmol/kg, while the [CO 3 2Ϫ ] was varied to isolate its role on the precipitation rate of calcite.

Laminar flame speed measurements of dimethyl ether/air mixtures were made at 1, 5, and 10 atm with equivalence ratios ranging from 0.7 to 1.6. All experiments were performed in a large cylindrical constant-volume bomb with optical access. A new method for converting flame images into flame radii was used. Results reported in other studies were investigated, and some explanations on the disparities found are presented. A full uncertainty analysis was performed combining precision errors from data scatter with predicted systematic errors. Uncertainties ranging between 4.2% and 8.6% were found depending on the equivalence ratio and initial pressure. Experimental results agreed well with some other spherical flame experiments and counterflow flame measurements, but were found to be much lower than PIV-based stagnation flame results. Also, two spherical flame studies deviated significantly both in magnitude and trend. Critical radii and Peclet numbers, defined by the onset of rapid flame acceleration, were recorded for all high-pressure experiments. Markstein lengths were measured and showed a decreasing trend with increasing equivalence ratio. Three different methods were used to define the laminar flame thickness, and large disparities were found between them. In this study, the modeled temperature gradient method for the definition of flame thickness is preferred over other methods. Modeling was performed with the latest version of a C3 chemical kinetics mechanism. Good agreement is seen between the experimental results and the model at all pressures. Emphasis is placed in this paper on reporting experimental uncertainties, calculated density ratios, flame temperatures, and flame radii ranges used for data analysis, and the results resolve some discrepancies seen in the literature for dimethyl ether flame speeds.

Hydrogen peroxide was discovered in 1818 and has been used in bleaching for over a century [1]. H 2 O 2 on its own is a relatively weak oxidant under mild conditions: It can achieve some oxidations unaided, but for the majority of applications it requires activation in one way or another. Some activation methods, e.g., Fenton's reagent, are almost as old . However, by far the bulk of useful chemistry has been discovered in the last 50 years, and many catalytic methods are much more recent.

There is much interest in the combustion mechanism of organophosphorus compounds (OPCs) due to their role as potential halon replacements in fire suppression. A continuing investigation of the inhibition activity of organophosphorus compounds under a range of equivalence ratios was performed experimentally and computationally, as measured by the burning velocity. Updates to a previous mechanism were made by the addition and modification of reactions in the mechanism for a more complete description of the recombination reactions. In this work, the laminar flame speed is measured experimentally and calculated numerically for a premixed propane/air flame, under a range of equivalence ratios, undoped and doped with dimethyl methylphosphonate (DMMP). A detailed investigation of the catalytic cycles involved in the recombination of key flame radicals is made for two equivalence ratios, lean and rich. From this, the importance of different catalytic cycles involved in the lean versus rich case is discussed. Although the importance of certain cycles is different under different stoichiometries, the OPCs are similarly effective across the range, demonstrating the robustness of OPCs as flame suppressants. In addition, it is shown that the phosphorus compounds are most active in the high temperature region of the flame. This may, in part, explain their high level of inhibition effectiveness.

The instantaneous rate of change of rancidity of coconut oil and butter in the acid value scale was determined. These rates of rancidity followed a good second order polynomial fit. The correlation between sampling time and rancidity (A. V. scale) was positive with the correlation coefficient (R 2) 0.958 and 0.984 for coconut oil and butter respectively. The rate of rancidity followed a constant acceleration for both coconut oil and butter. The acceleration rate was found be almost double for butter than that for coconut oil.

A massive air or steam ingress in High Temperature Reactors (HTRs) nominally operating at 600-950 o C is a design-basis accident requiring the development and validation of graphite oxidation and erosion models to examine the impact on the potential fission products release and the integrity of the graphite core and reflector blocks. Nuclear graphite is of many types with similarities but also differences in the microstructure, volume porosity, impurities, type and size of filler coke particles, graphitization and heat treatment temperatures, and the thermal and physical properties. These as well as the temperature, types and partial pressures of oxidants affects the prevailing oxidation mode and kinetics of the oxidation processes of graphite in HTRs. This paper reviews the graphite crystalline structure, the fabrication procedures, characteristics, chemical kinetics and modes of oxidation of nuclear graphite for future model developments.

Experiments have been performed on a Homogeneous Charge Compression Ignition Engine (HCCI) fuelled with natural gas. The in-cylinder pressure has been measured for different engine speeds and fuel-air ratios. Numerical simulations of the ignition process in the engine have been carried out using a detailed reaction mechanism for butane and lower alkanes. The effects of engine speed an fuel-air ratio on autoignition have been calculated and compared with measurements. In addition, calculations have been made of the ignition delay time sensitivity to initial pressure, initial temperature, and quality of gas fuel. Excellent agreement with single-cycle measurements is obtained for the calculated temperature and pressure profiles. The single-cycle temperature simulations show good agreement with 100 cycle-averaged measurements as well, but cycle-to cycle variations flatten out the averaged profiles, and the need for a PDF-based approach to achieve perfection is evident. Furthermore, it was found that the autoignition process in an HCCI engine is extremely sensitive to variations in initial temperature, whereas changes in pressure, fuel-air ratio and engine speed affects the ignition timing to a much lesser extent.

The emergence of methods allowing the simplification of detailed chemical kinetics enables detailed modeling of turbulent diffusion flames. One of these methods, the “Intrinsic Law-Dimensional Manifolds” (ILDM) method and its application to the computation of turbulent reactive flows are described here. A CFD solver and a Monte-Carlo code solving the transport equation of the scalar joint pdf are coupled and

As shown above, each Panel member concentrates his efforts on a given area or type of data. Nevertheless, the Panel's final recommendations represent a consensus of the entire Panel. Each member reviews the basis for all recommendations, and is cognizant of the final decision in every case.

The use of isoconversional, sometimes called model-free, kinetic analysis methods have recently gained favor in the thermal analysis community. Although these methods are very useful and instructive, the conclusion by some that model fitting is a poor approach is largely due to improper use of model fitting, such as fitting a single heating rate or multiple heating rates separately. The current paper shows the ability of model fitting to correlate reaction data over very wide time-temperature regimes for three polymers of interest for formulating high explosives: Estane 5703 P (poly[ester urethane] block copolymer), Viton A (vinylidene-hexafluoropropene copolymer), and Kel-F 800 (vinylidene-chlorotrifluorethene copolymer). The Kel-F required two parallel reactions-one describing an early decomposition process accounting for ∼1% weight loss and a second autocatalytic reaction describing the remainder of pyrolysis. Essentially no residue was obtained. Viton A and Estane also required two parallel reactions for primary pyrolysis. For Viton A, the first reaction is also a minor, early process, but for Estane, it accounts for 42% of the mass loss. In addition, these two polymers yield 2-3% of residue, and the amount depends on the heating rate. This is an example of a competitive reaction between volatilization and char formation, which violates the basic tenet of the isoconversional approach and is an example of why it has limitations. Although more complicated models have been used in the literature for this type of process, we model our data well with a simple addition to the standard model in which the char yield is a function of the logarithm of the heating rate.

The design and operation issues for reactive distillation systems are considerably more complex than those involved for either conventional reactors or conventional distillation columns. The introduction of an in situ separation function within the reaction zone leads to complex interactions between vapor}liquid equilibrium, vapor}liquid mass transfer, intra-catalyst di!usion (for heterogeneously catalysed processes) and chemical kinetics. Such interactions have been shown to lead to the phenomenon of multiple steady-states and complex dynamics, which have been veri"ed in experimental laboratory and pilot plant units. We trace the development of models that have been used for design of reactive distillation columns and suggest future research directions.

The kinetics and nitroarene product yields of the gas-phase reactions of naphthalene-d8, fluoranthene-dl,,, and pyrene with OH radicals in the presence of NO, and in Nz05-NO3-NOz-air mixtures have been investigated at 296 2 2 K and atmospheric pressure of air. Using a relative rate method, naphthalene-d8 was shown to react in Nz05-N03-N0,-air mixtures a factor of 1.22 ? 0.10 times faster than did naphthalene, with the 1-and 2nitronaphthalene-d, product yields being similar to those of 1-and 2-nitronaphthalene from naphthalene. From the measured PAH concentrations and the nitroarene product yields, formation yields of 2-, 7-, and 8-nitrofluoranthene-d, and 2-and 4-nitropyrene of 0.03, 0.01, 0.003, 0.005, and 0.0006, respectively, were determined from the OH radical-initiated reactions. Effective rate constants for the reactions of fluoranthene-d,, and pyrene with N205 in Nz0,-N03-NOz-air mixtures of ca. 1.8 X lo-', cm3 molecule-'^-^ and ca. 5.6 X 10-l7 cm3 molecule-' s-', respectively, were derived. Formation yields of 2-nitrofluoranthene-d9 and 4-nitropyrene of ca. 0.24 and ca. 0.0006, respectively, were estimated for these reaction systems. 2-Nitropyrene was also observed to be formed in these Nz05-N03-NOz reactions, but was found to be a function of the NOz concentration and, therefore, would be a negligible product under ambient NOz concentrations. These product and kinetic data are consistent with ambient air measurements of the nitroarene concentrations. N,O,-NO,-NO,-air systems C41. Continuing studies of these OH radical and Nz05-NO,-NO, reactions with several PAH and monocyclic compounds have led to an initial understanding of the mechanisms involved in the formation of nitroarenes under

The use of numerical models for the design and optimization of UV/H2O2 systems must incorporate both reactor design (hydrodynamics, lamp orientation) and chemical kinetics (reaction mechanisms, kinetic rate constants). This study was conducted to evaluate the performance of comprehensive CFD/UV/AOP models for the degradation of an indicator organic contaminant. The combination of turbulence sub-models, fluence rate sub-models, and kinetic rate equations resulted in a comprehensive and flexible design tool for predicting the effluent chemical composition from a UV-initiated AOP reactor. The CFD model tended to under predict the percent removal of methylene blue compared to pilot reactor trials under the same operating conditions. In addition, the percent difference between the pilot and the CFD results increased with increasing flow rates. The MSSS fluence rate sub-model predicted higher contaminant removal values than the RAD-LSI sub-model while the different two-equation turbulence sub-models did not significantly impact the predicted removal for methylene blue in the tested reactor configuration. The overall degradation of methylene blue was a strong function of the second-order kinetic rate constant describing the reaction between methylene blue and the hydroxyl radical. In addition, the removal of methylene blue was sensitive to the concentration of dissolved organic carbon in the water matrix since DOC acts as a scavenger of hydroxyl radicals.

Determination of experimental kinetic isotope effects (KIE) is one of the most useful tools for the exploration of reaction mecha- nisms in organometallic chemistry. The approach has been further strengthened during the last decade with advances in modern compu- tational chemistry. This allows for the calculation of a theoretical KIE that can often be compared directly to the experimental value. This combined experimental/theoretical approach can be particularly useful in cases where the value of the experimental KIE is not directly associat- ed with one particular reaction step (e.g., in a catalytic reaction). The approach is highlighted by using recent examples from both stoichio- metric and catalytic reactions, homogeneous and heterogeneous catal- ysis, and enzyme catalysis to illustrate the expected accuracy and utility of this approach.

Hydrogen peroxide was discovered in 1818 and has been used in bleaching for over a century [1]. H 2 O 2 on its own is a relatively weak oxidant under mild conditions: It can achieve some oxidations unaided, but for the majority of applications it requires activation in one way or another. Some activation methods, e.g., Fenton's reagent, are almost as old . However, by far the bulk of useful chemistry has been discovered in the last 50 years, and many catalytic methods are much more recent.

iii iv This evolution does present the drawback, however, of increasingly hiding the global and general aspects of the problems. One of the major advantages of analytical solutions is the way in which they can provide insight in these aspects, e.g., by analyzing the limiting behavior of solutions. It is therefore not surprising that we witness today a renewal of interest in analytical methods, which is further supported by the wide availability of symbolic manipulation and computer algebra.

Removal of acid green 25 (AG25) dye onto activated palm ash from aqueous solutions was investigated. Experiments were carried out as function of contact time, initial concentration (50–600 mg/L), pH (2–12) and temperature (30–50 • C). The equilibrium adsorption data of AG25 dye on activated palm ash were analyzed by Langmuir and Freundlich models. The results indicate that the Freundlich model provides the best correlation of the experimental data. The adsorption capacities of the activated palm ash for removal of AG25 dye was determined with the Langmuir equation and found to be 123.4, 156.3 and 181.8 mg/g at 30, 40, and 50 • C, respectively. Adsorption data were modeled using the pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetics equations. It was shown that pseudo-second-order kinetic equation could best describe the adsorption kinetics. Isotherms have also been used to obtain the thermodynamic parameters such as free energy, enthalpy and entropy of adsorption. The positive value of the enthalpy change (26.64 kJ/mol) indicates that the adsorption is endothermic process. The results indicate that activated palm ash is suitable as adsorbent material for adsorption of AG25 dye from aqueous solutions.