Calculation Of Kinetic Parameters Research Articles

Verification of kinetic capabilities of the GNOMER neutron diffusion code

Recently, the GNOMER neutron diffusion code was updated to support kinetic simulations. This direct approach to reactor kinetics is further branched into two operational modes: the so-called Lambda mode and the (normal) implicit mode. Both approaches are described in detail. Also, calculation of point kinetic parameters is implemented and discussed.To verify GNOMER’s new kinetic capabilities, two numerical tests are considered; namely, the point kinetic test case and a rod insertion simulation on a model of a typical pressurised water reactor (PWR). The reference solutions were produced by a point kinetic script and the SKETCH-N diffusion code, respectively. Very good agreement is found for all cases considered. Unusual behaviour and discrepancies – where observed – are explained satisfactorily. With the evidence provided in the paper, GNOMER is deemed to be a reliable tool for (both static and) dynamic simulation.

Thermogravimetric Experiment and Dynamic Analysis on Municipal Sewage Sludge Combustion

The drying and combustion characteristics of sludge may be obtained by the thermogravimetric experiment, then further analysis of their mechanism will provides the basis for the energy utilization of sludge. In this paper, the drying stage, the flammable stage and the nonflammable stage of municipal sludge were studied by the thermogravimetric experiment methodology. The results show the drying stage consists of five stages: preheating stage, rapid weight loss stage, constant-rate weight loss stage, decelerating weight loss stage I and decelerating weight loss stage II. The kinetic process for the drying and for the combustion of sewage sludge should be expressed by phase interface reaction mechanism function g(a)=1-(1-a)n and chemical reaction equation f(a)=(1-a)n respectively. Then kinetic parameter calculation for these three stages of municipal sludge were done. Kinetic parameters reveal that activation energy decreases in the sequence of non-flammable stage, flammable stage and drying stage, and when raising the heating rate, the activation energy increases significantly in flammable stage while nearly remains unchanged in non-flammable stage.

Apparent kinetics of the Bunsen reaction in I2/HI solution for the iodine–sulfur hydrogen production process

Massive hydrogen production featuring high efficiency, CO2 free, and cost effectiveness is a crucial challenge for the hydrogen economy. Nuclear hydrogen production through thermochemical iodine–sulfur (IS) process is a potential candidate for this purpose. Chemical reaction kinetics data are indispensable for developing a high-performance reactor as well as the scaling up of the process. The apparent kinetics of the reaction under simulated recycling conditions of IS closed cycle operation was studied by initial rate method. The effects of key parameters, including agitation speed, SO2 partial pressure, I2 concentration, and reaction temperature, on reaction rate, were systematically investigated by measuring the variation in SO2 pressure with reaction time. Initial rate analysis method indicated that the Bunsen reaction rates were 0.23 ± 0.01 and 0.77 ± 0.01 order with respect to SO2 pressure and I2 concentration. The apparent activation energy was 5.86 ± 0.21 kJ/mol. Based on these results, an exponential rate expression of the Bunsen reaction was established. In addition, a simplified method for calculation of kinetics parameters was proposed and compared with conventional techniques. Experimental results provide theoretical basis for design and development of Bunsen reactors and for elucidating the reaction process.

Comparison of the gasification of coals and their chars with CO2 based on the formation kinetics of gaseous products

The aim of the study was to analyse the kinetics of coal and char gasification in an atmosphere of carbon dioxide. Samples of two Polish coals and their chars were gasified under isothermal conditions at the temperatures of 850, 900 and 950°C and under the pressure of 0.1, 0.6 and 1.1 MPa. Based on the obtained results, curves of the formation rate of gaseous products of gasification such as carbon monoxide, hydrogen and methane were developed and yields of products were evaluated. The influence of temperature, pressure and type of sample on the kinetics of carbon monoxide formation was determined and the reaction rate constant of CO formation for each sample as well as the kinetic parameters (pre-exponential factor and activation energy) were calculated. Firstly, the activation energies both for coal and char gasification with CO2 were calculated based on the isoconversional method. Next, four kinetic models: the n-order volumetric model (NVM), the first order volumetric model (FVM), the grain model (GM) and the random pore model (RPM) were used for the calculation of kinetic parameters. The kinetic curves of gaseous products formation clearly indicate the dominance of the reaction of carbon monoxide formation and its dependence on temperature. The yield of carbon monoxide grows with the increase of the coal rank of the examined sample. The gasification of coals with CO2 is significantly different from the gasification of their chars derived by the ex situ method. Coals are more reactive than chars, and thus, the gasification of coals progresses much faster and, consequently, with a higher formation rate of gaseous products. The analysed coals are characterised by lower values of the parameters A and E compared to their chars. The increasing pressure causes the activation energy decrease, which confirms the positive effect of pressure on reactivity.

Structural, optical and thermoluminescence study of Dy3 + ion doped sodium strontium borate glass

In the present work physical, optical and thermoluminescence studies of Dy3+ ion doped sodium strontium borate glasses have been reported. XRD study confirms the amorphous nature of glass and the increasing concentration of Dy2O3 results in broadening and shifting of the XRD peak. FTIR shows no change in structure with the inclusion of Dy2O3 but the optical band gap is sensitive to dopant concentration. Glow curve possess single prominent peak in the temperature range 390–393 K and the glass sample with 0.4 mol% Dy2O3 concentration has the most appropriate TL response. The Glow curve width also changes with the dopant concentration. The calculation of kinetic parameters shows that all the glass samples exhibit second order kinetics.

Two Energetic Salts based on 5,5′-Bitetrazole-1,1′-diolate: Syntheses, Characterization, and Properties

Two salts based on 1H,1′H-5,5′-bitetrazole-1,1′-diolate (BTO) anion with pyrazole (1) and imidazole (2) cations were synthesized with metathesis reactions. Structural characterization was accomplished for them by using the element analysis, Fourier transform infrared spectroscopy (FT-IR), NMR and mass spectrum, and X-ray single crystal diffraction. Thermal analysis for the title salts were determined by means of differential scanning calorimetry (DSC) and thermogravimetry-derivative thermogravimetry (TG-DTG) as well as the calculation of non-isothermal kinetic parameters. Consequently, both salts shown acceptable thermal stabilities as the decomposition temperatures were over 200 °C. The enthalpies of formation were calculated for these salts using the measured combustion energies with a result of 70.6 kJ·mol–1 for 1 and –47.8 kJ·mol–1 for 2, respectively. Impact and friction sensitivities were also tested and the results indicated that these salts both have low sensitivities (>40 J, 120 N). The title energetic salts possess acceptable performance, they can therefore be applied in the field of energetic materials.

Characterisation of clay samples from minerals–rich deposits for thermoluminescence applications

Thermoluminescent (TL) characteristics of clay samples from Ijero-Ekiti and Isan-Ekiti, Ekiti State, Nigeria were studied for application in retrospective dosimetry. In order to increase the potentials of the clay material for relevant radiation measurement applications, characteristic glow curves of samples from the clay deposits have been obtained using a Victoreen (2800M) TL reader and the TL properties subsequently examined. The variable heating rate method was used to determine the glow peak shape and intensity by estimating the activation energy or trap depth, E and the frequency factor, S. Most samples demonstrated the dependence of their glow curve on the heating rate, with the peak temperature, Tm increasing with the heating rate. These glow peaks were noted to be a complex trapping system, consisting of several overlapping first order peaks and each with different TL behaviour, except for certain samples, which showed independence of peak temperature with dose. While recommending further heating protocol to isolate each peak for the calculation of other kinetic parameters, we present an approximate 0.29–0.84eV for E and 3.7×101 to 4.0×106s−1 for S. Though the samples with the TL dosimetric property of increased peak intensity with increasing excitation dose could be considered for TL applications, the reduction in TL intensity must be considered for high heating rates applications.

Isoconversional analysis of thermal dissociation kinetics of hematite in air and inert atmospheres

Dissociation of hematite is an undesirable reaction for iron ore pelletizing process leading to severe deterioration in compressive cold strength and reducibility factors. It was shown that raising temperature in an induration machine would cause hematite’s dissociation, which is either present in the primary ore or formed by oxidation of magnetite in the feed. The oxidation reaction of magnetite is exothermic, which complicates temperature control within the non-isothermal area of preheating. Kinetics of the dissociation reaction is the temperature’s primary function, which controls the extent of the reaction. Pure hematite samples were subjected to several runs of thermal analysis carried out under both air and inert atmosphere, in order to achieve a comprehensive knowledge about the temperature dependencies of dissociation kinetics. Due to the observed uniformity, isoconversional methods were chosen in the present work over isothermal and non-isothermal for calculation of kinetic parameters of the reaction. Respectively, activation energy values of hematite dissociation were found to be 324 and 382 kJ mol−1 in inert and air atmosphere. The high value of activation energy implies strong dependency of the single-step reaction rate on the temperature. It was also observed that the forward reaction had higher activation energy than the backward reaction; hence, an increase in temperature results in an overall acceleration of the dissociation reaction.

Determination of hydrogen peroxide and organic peroxides in micellar and aqueous–organic media using a spectrophotometric biosensor based on horseradish peroxidase

The expedience of the target-specific control of the properties of a medium (using micellar and aqueous–organic media), in which an indicator process providing the background for the operation of a spectrophotometric sensor based on a polyelectrolyte complex (horseradish peroxidase–chitosan) is conducted, is shown experimentally and proved by calculations of kinetic parameters of the enzymatic reaction. The application of the sensor ensures an increase in the sensitivity of the determination of peroxides of different nature and structures (e.g., hydrogen and urea peroxides, benzoyl peroxide, 2-butanone peroxide and tertbutyl hydroperoxide) in complex matrixes. The proposed approach allows the analyst not only to regulate the performance characteristics of the developed procedures for the determination of peroxides depending on the analytical task, but also to extend the range of test samples (including those insoluble in water) analyzed with no sample preparation.

Determination of activation energy of pyrolysis of carton packaging wastes and its pure components using thermogravimetry

Many processes have been used for recycling of carton packaging wastes. The pyrolysis highlights as a promising technology to be used for recovering the aluminum from polyethylene and generating products with high heating value. In this paper, a study on pyrolysis reactions of carton packaging wastes and its pure components was performed in order to estimate the kinetic parameters of these reactions. For this, dynamic thermogravimetric analyses were carried out and two different kinds of kinetic models were used: the isoconversional and Independent Parallel Reactions. Isoconversional models allowed to calculate the overall activation energy of the pyrolysis reaction, in according to their conversions. The IPR model, in turn, allowed the calculation of kinetic parameters of each one of the carton packaging and paperboard subcomponents. The carton packaging pyrolysis follows three separated stages of devolatilization. The first step is moisture loss. The second stage is perfectly correlated to devolatilization of cardboard. The third step is correlated to devolatilization of polyethylene.

Reactivity and kinetic parameter evolutions for the core height and boron concentration of the fixed bed nuclear reactor

This article focuses on calculation of reactivity and kinetic parameters in different states (different core heights and boron concentrations in the coolant water) of the fixed bed nuclear reactor (FBNR). The numerical calculations are performed with the SRAC code. Uranium dioxide (UO2) with 235U enrichment grade of 5% is used as spherical fuel pellets in the TRISO fuel type. The core height is changed by a core height level limiter. The main results of this study can be summarized as follows: The effective neutron multiplication coefficient is varied with the core height and boron concentration in the coolant water. When there is no-boron in the coolant water and the core height is over 120 cm, the reactor control can be carried out by the movement of a core height level limiter, without the fine control rods in the core center; but when there is a boron concentration, the reactor may be controlled by the level limiter at the lower core heights. The kinetic parameters (the prompt-neutron lifetime and effective delayed neutron fraction) of the reactor also are changed to the reactor core height and to the boron concentration in the coolant water. Copyright © 2016 John Wiley & Sons, Ltd.

Heating rate effect on the thermal behavior of some clays and their blends with oil shale ash additives

The heating rate effect on the thermal behavior of clays from Arumetsa and Kunda deposits (Estonia) and an illitic clay from Fuzerradvany (Hungary) was studied. Experiments were carried out under dynamic heating condition up to 1050 °C at the heating rates of 1.25, 2.5, 5 and 10 °C min−1 in a stream of gas mixture containing 79 % of Ar and 21 % of O2 with Setaram Labsys 1600 analyzer. Two different ashes were used as additives: the electrostatic precipitator ash from the first field and the cyclone ash formed, respectively, at circulating fluidized bed combustion (temperatures 750–830 °C) and pulverized firing (temperatures 1200–1400 °C) of Estonian oil shale at Estonian Power Plant. For calculation of kinetic parameters, the TG data were processed by the differential isoconversional Friedman method. The results of thermal analysis and the variation of the value of activation energy E along the reaction progress α indicated the complex character of decomposition of clays and their blends with Estonian oil shale ashes, and the certain differences in thermal behavior of different clays depending on their origin.

Predictive value of prostate specific antigen kinetics in prostate cancer diagnosis

Background and Aim: Current Australian draft clinical practice guidelines for prostate specific antigen (PSA) testing do not recommend PSA kinetics due to a lack of quality evidence. We investigated the relationship between PSA kinetics and a subsequent diagnosis of prostate cancer. Method: A retrospective audit was conducted of prostate histopathology results from June 2015 with corresponding PSA test results. The laboratory receives both outpatient and hospital referrals. Inclusion criteria for analysis were the availability of ≥3 PSA results each spaced by ≥3 months for reliable calculation of PSA kinetic parameters (linear velocity, doubling time). Total PSA was measured on the Abbott Architect. Results: 512 patient records satisfied the criteria for analysis. PSA linear velocity >0.75 μg/L/year was associated with prostate cancer diagnosis [odds ratio (OR)=1.96, 95% confidence interval (CI)=1.22–3.18], which persisted in the cohort of men with any elevated PSA >3 μg/L (OR=1.80, 95%CI=1.10–2.97). PSA doubling time <3 years was not significantly associated with prostate cancer diagnosis (OR=1.17, 95%CI=0.93–2.17). Discussion: This retrospective analysis confirms the relationship between PSA velocity and prostate cancer, with potential utility of PSA velocity to stratify risk in men with an elevated PSA result.

A sensitivity analysis of thermal lattices kinetic parameters with respect to the spectral weighting function using ultrafine BN method

Accurate calculation of kinetic parameters is of utmost importance in the safety analysis of a nuclear reactor. In the current paper, two approaches are investigated to evaluate these parameters in energy phase space. In the first approach, these parameters are derived from an energy-continuous form of the forward and adjoint transport equations and then integrals with respect to the energy variable are replaced by weighted summations over the energy groups, while in the second approach these parameters are extracted from the multi-group forward equation and its associate adjoint equation in which their multigroup constants are weighted by forward spectrum. The difference of weighting functions in these two approaches would naturally lead to different values for the kinetic parameters. This paper mainly compares the outcome of these two approaches in calculating kinetic parameters for two main types of thermal critical lattices: Mixed Oxide (MOX) and Uranium Oxide (UOX) using ultrafine BN method. The results show that calculations which are based on using the forward weighted spectrum for generating the kinetic parameters underestimate prompt neutron generation time in both thermal lattices, while effective delayed neutron fraction is overestimated in UOX thermal lattice and underestimated in MOX one.

A DFT kinetic study on 1,3-dipolar cycloaddition reactions in solution.

Several popular density functional theory (DFT) methods have been employed to characterize a series of 1,3-dipolar cycloaddition reactions, including the exploration of reaction mechanisms and the calculations of kinetic parameters. Both the gas- and solution-phase translational entropy models have been used to calculate the activation entropies, and the results obtained from the latter method are quite close to the experimental measurements. For some of the reactions studied, e.g., a1 + b9, a1 + b10, a5 + b9 and a12 + b5, the explicit + implicit solvation model, namely, a cluster-continuum type model, should be employed to account for the specific solvent-solute interactions. The quasi rigid-rotor-harmonic-oscillator (qRRHO) small frequency vibrational entropy correction, in conjunction with the conformational entropy correction, could further improve the calculated activation entropy data. The comparison between calculation data with experimental measurements, using 23 activation entropies and 160 reaction rate constants as test benchmark, demonstrated that our present strategy could calibrate the root-mean-square-deviation (RMSD) of activation entropies to be 1.8 cal mol-1 K-1 and that of Gibbs free energy barriers to be 1.8 kcal mol-1.

Thermal Runaway in Lithium-Ion Batteries: Incidents, Kinetics of the Runaway and Assessment of Factors Affecting Its Initiation

A study of thermal runaway phenomena in Lithium-Ion Batteries (LIB) was conducted following different approaches. Risks related to thermal runaway are presented based on a series of incidents involving overheating, fires and explosions with these batteries in different devices; significant cases that have occurred in airplane battery cells are shown. An overview of the possible promoters for the thermal event is presented by studying compounds and reactions involved. Kinetic parameter calculations were performed using Differential Scanning Calorimetry (DSC) data available from the literature. Preliminary molecular simulations were made in order to understand mechanisms and related paths proposed. Finally, the system was studied from the perspective of process safety and the theory of runaway reactions.

Calculation of parameters for the model of an ideal phosphor

Equations for the calculation of kinetic parameters of thermoluminescent processes are theoretically derived for a model of an ideal phosphor. The values used in the calculation are obtained from glow curves and the function that describes the normalized glow curve generated. On the basis of this function, the equations for activation energy, frequency factor, and retrapping factor, were derived. All expressions are valid for a general case, when the filling factor of traps is f0?1. The concept of kinetics order was used for the calculation of parameters and the parameter of kinetics order was defined by means of real physical parameters. Results obtained by the analysis of synthetic curves and experimental glow curves of phosphor materials provide a deeper understanding of thermoluminescent kinetics.

Lipoxygenase inactivation kinetics and quality-related enzyme activities of narrow-leafed lupin seeds and flakes

Abstract Lupin seeds are promising sources for the production of vegetable proteins. However, these proteins are associated with green and bean-like flavour, which is attributed to endogenous enzyme activities. Therefore, the objective was to develop a suitable process for the thermal inactivation of quality-affecting enzymes for lupin (Lupinus angustifolius cv. Boregine) seeds and de-oiled flakes. After monitoring the specific activities of lipoxygenase (LOX), peroxidase (POD) and lipase during seed maturation, LOX was selected as the most appropriate indicator enzyme to assess inactivation as lipase and POD activities extensively declined at full maturity. Effective reduction of LOX activity was achieved by various hydrothermal treatments at 70–100 °C for up to 30 min and 100% relative humidity. The calculation of kinetic parameters revealed a first-order reaction, whereby the k values increased from 0.09 to 0.58 min−1 and 0.06 to 0.62 min−1 for seeds and flakes, respectively. The activation energies were significantly lower for inactivation in seeds (60.5 kJ mol−1) than in de-oiled flakes (78.0 kJ mol−1), suggesting the application of whole seeds for LOX inactivation. Based on these results, a gentle inactivation process at 80 °C for 7 min for lupin LOX is proposed.

Calculating the degradation kinetic parameters of thiamine by the isothermal version of the endpoints method

Thiamine (vitamin B1)'s degradation during thermal processing and storage of foods is known to follow first-order kinetics, where the rate constant's temperature-dependence can be described by the two-parameter Arrhenius equation. In agreement with previous reports, a simpler two-parameter exponential model could replace the Arrhenius equation in thiamine degradation without sacrificing the fit. Theoretically, the exponential model's two parameters can be estimated from the concentration ratios after two isothermal exposures by solving a pair of simultaneous nonlinear algebraic equations of which they are the two unknowns. Once calculated, these two parameters can be used to reconstruct the entire degradation curves to which the two endpoints belonged, and to predict those at any other exposure in a pertinent temperature range. The concept and mathematical calculation procedure were implemented in a freely downloadable interactive Wolfram Demonstration, with which the user solves the equations by moving sliders on the screen to match the reconstructed degradation curves with the experimental endpoints. The method was tested with computer simulations and with published experimental data on thiamine's degradation in a model solution, beef, pasta and salmon, over large temperature ranges and exposure times, and validated by comparing thiamine's predicted final concentration ratios with those reported at temperatures not used in the kinetic parameters calculation. The described method and interactive calculation program can facilitate and economize the study of thiamine degradation in stored foods by eliminating the need to record entire sets of isothermal degradation curves.

The mechanism of Rubisco‐catalysed oxygenation

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is the cornerstone of photosynthetic carbon assimilation because it catalyses the fixation of CO2 onto ribulose-1,5-bisphosphate (RuBP). The enzyme also catalyses RuBP oxygenation, thereby evolving phosphoglycolate which is recycled along the photorespiratory pathway. Oxygenation is quantitatively important, because under ordinary gaseous conditions, more than one third of RuBP molecules are oxygenated rather than carboxylated. However, contrary to carboxylation, the chemical mechanism of oxygenation is not well known, and little progress has been made since the early 80s. Here, I review recent experimental data that provide some new insights into the reaction mechanism, and carry out simple calculations of kinetic parameters. Isotope effects suggest that oxygenation is less likely initiated by a redox phenomenon (such as superoxide production) and more likely involves concerted chemical events that imply interactions with protons. A possible energy profile of the reaction is drawn which suggests that the generation of the oxygenated reaction intermediate (peroxide) is irreversible. Possible changes in oxygenation-associated rate constants between Rubisco forms are discussed.