Kinetic Evaluation Method Research Articles

Kinetics of microwave liquid-phase desorption with chemical dissociation: SO2 desorption of basic aluminum sulfate desulfurization rich liquid

BackgroundReaction kinetics was an important tool for quantitative expression of micro-chemical processes. In this study, a kinetic evaluation method of microwave liquid-phase desorption mechanism was established, which was of great value to reveal the non-thermal effect of microwave desorption. MethodsDesorption kinetics of basic aluminum sulfate (aluminum base) desulfurization rich liquid were monitored with a microwave simultaneous cooling system. The effect of microwave power on its chemical reaction was investigated by linear and nonlinear regression analysis. Significant findingsThe kinetic analysis showed that the pre-exponential factor and activation energy decreased with the increase of microwave power, and the dependence on microwave power was more consistent with the first-order linear model and the second-order polynomial model. At the same temperature, the microwave desorption rate was 1.3–2.6 times that of water bath thermal desorption. At the same desorption reaction rate, the microwave desorption temperature was 10 K–20 K lower than that of thermal desorption. Compared with thermal desorption, although the reaction order did not change under different microwave power, the pre-exponential factor and activation energy decreased, and the reaction rate constant was about 1.1–2.1 times that of the same temperature.

Doubts about the popular Kissinger method of kinetic evaluation and its applicability for crystallization of cooling melts requiring equilibrium temperatures

The famous Kissinger’s kinetic evaluation method (Anal Chem 29:1702, 1957) is examined with respect to the feasible impact of the individual quantities and assumptions involved. It is accentuated that the missing term on heat inertia may change the resulting values when searching for activation energies. Particular attention is paid to the heating rate, β, particularly when applied under opposite process of cooling. In such case of melt solidification, an additional thermodynamic term for the melt undercooling is needed to be incorporated which provides an alternative form of evaluation. Despite as many as 8000 applications caused by the obvious methods simplicity, these affects was overlooked. It is surprising that anybody who evolved various alternatives of the Kissinger method did not find any reasons for its criticism.

Piloyan Method to Determine the Activation Energy from DTA is Defective in Addition to other Methods which do not take into Account the Thermal Inertia

The paper displays that the traditional method of kinetic evaluation of activation energies by simple portioning of the as-cast DTA curves is erroneous because is missing the impact of thermal inertia which is known since the Newton cooling law. This error is interwoven into all methods using thermal measurements. The method derivation is upgraded when using the missing terms.

Imperfections of Kissinger evaluation method and crystallization kinetics

The famous Kissinger’s kinetic evaluation method (Anal. Chem. 1957) is examined with respect to: a) the relation between the DTA signal θ (t) and the reaction rate r(t) ≡ dα/dt; b) the requirements on reaction mechanism model f(α); and c) the relation of starting kinetic equation to the equilibrium behavior of sample under study. Distorting effect of heat inertia and difference between the temperature Tp of extreme DTA deviation and the temperature Tm at which the reaction rate is maximal are revealed. The kinetic equations respecting the influence of equilibrium temperature Teq, especially fusion temperature Tf, are tested as bases for a modified Kissinger-like evaluation of kinetics.

Doubts on Kissinger´s method of kinetic evaluation based on several conceptual models showing the difference between the maximum of reaction rate and the extreme of a DTA peak

The famous Kissinger's kinetic evaluation method (Anal. Chem. 1957) is examined with respect to the feasible impact of the individual quantities and assumptions involved, namely the model of reaction mechanism, f(a) (with the iso- and nonisothermal degrees of conversion, ? and ?) the rate constant, k(T) (and associated activation energy, E), heating/cooling rate, b (supplementing additional thermodynamic term for the melt undercooling, ?T) and above all, the association of the characteristic temperature, Tm, with the DTA peak apex. It is shown that the Kissinger/s equation, in contrary to the results of Vold (Anal. Chem. 1949), is omitting the term of heat inertia arising from the true balance of heat fluxes. The absence of this term skews the evaluated values of activation energies.

Comparison between Continuous and Discontinuous Method of Kinetic Evaluation for Osmotic Dehydration of Cherry Tomato

Discontinuous method is the commonly used method of obtaining the experimental data for osmotic dehydration curves, in which, different samples with similar size are used at different dehydration times. Moreover, the continuous method is based on the measurement of weight loss, in a single sample, at different dehydration times and measurement of the final moisture content at the end of the dehydration process. In this method, one sample is used throughout the osmotic dehydration process. In this paper, continuous and discontinuous methods of kinetic evaluation were compared for water loss and solid gain during osmotic dehydration of cherry tomato in salt solution. The osmotic dehydration experiments were conducted at different solution concentrations (10, 18 and 25% w/w) and temperatures (30 and 40C). The moisture and salt effective diffusivities were estimated using the analytical solution of Fick's second law of diffusion in the spherical coordinate. Although continuous method makes it easier to predict the variations of moisture loss and solute gain as a function of dehydration time, this method predicts the same kinetics for water loss and solid gain and also the same values for moisture and solute diffusivities. The results show that using the discontinuous method results in more dispersion of the experimental data than when the continuous method was employed. Practical Applications The present study compares two well-known method of kinetic evaluation for osmotic dehydration of foodstuff. This comparison shows the shortcoming of the continuous method for prediction of kinetics of water loss and solid gain and also the values of moisture and solute effective diffusivities. These parameters are used in the mathematical modeling of osmotic dehydration process. Mathematical models provide information about the process to which they are applied, and help the designers and researchers find the best design parameters and the most effective process conditions.

The stable isotope ketoisocaproic acid breath test as a measure of hepatic decarboxylation capacity: a quantitative analysis in normal subjects after oral and intravenous administration

There is no generally accepted kinetic evaluation method for the stable isotope [(13)C]ketoisocaproic acid (KIC) breath test. Differences found in the results between women and men are contradictory. Oral and intravenous breath tests using 1 mg/kg stable isotope-labelled KIC were performed in healthy male and female volunteers. A power exponential function was fitted to the mass spectrometric data of breath (13)CO(2) enrichment, allowing mathematical analysis of time-to-peak-excretion, half-excretion time, percent label recovery and parameters describing the shape of the curve. Body composition was determined using bioelectrical impedance analysis. After oral administration, total label recovery after 3 h was about 22% and was not different between men (n=7) and women (n=8). The time to maximal label excretion was 0.67 +/- 0.12 h in men and 0.9 +/- 0.32 h in women (P=0.028) and the excretion curve showed an initially slower rise in women compared with men. Adjusting for lean body mass or body water abrogated the sex differences. Total label recovery after intravenous administration was about 9%, suggesting that the substrate was rapidly catabolized in the muscle compartment after intravenous administration. The modified power exponential function described allows standardized estimates of the KIC breath test results. When corrected for body composition, there are no differences in breath test results between men and women. The comparison between oral and intravenous results provides robust evidence that the KIC breath test measures predominantly hepatic and not muscle decarboxylation and is thus a highly specific liver function test.

Optochemical Film Sensor for the Determination of Free Chlorine in Water

An thin reagent containing optochemical film sensor for detecting and measuring free chlorine in water is described. The film sensor has been manufactured by immobilisation indicator of 3,5-dimethyl-4-hydroxybenzaldazine in a permeable transparent polymeric membrane. A linear calibration for free available chlorine can be obtained in the range between 0.05 and 3ppm. The limit of quantitation is 0.3 ppm, and the accuracy exceeds 7%. It takes about 150s to measure the relatively low occupational exposure concentration of 0.1ppm. The interference of combined chlorine has been studied. The sensor has no response to combined chlorine. And the stability of the sensors and the effect of external parameters like relative humidity (RH), temperature on the sensor response have been investigated. The sensor response is affected by varying the temperature; however, humidity in the range between 0 and 90% RH does not affect sensor response. The 3,5-dimethyl-4-hydroxybenzaldazine remained stable inside the polymeric film and no chemical reaction, crystallization or leaching occurred during 6 months of observation. Proper choice of indicator dye and polymeric material and successful application of kinetic evaluation method for the exposure experiments determine the desired features of the sensor. Introduction

Optochemical sensor for determining ozone based on novel soluble indigo dyes immobilised in a highly permeable polymeric film

An optochemical ozone sensor is described that has been manufactured by immobilisation of novel soluble indigo derivatives in permeable transparent polymeric films of polydimethylsiloxane-polycarbonate copolymer. From a number of investigated indigo derivatives, 4,4',7,7'-tetraalkoxyindigo 9 has been selected for optimal sensitivity and specificity of ozone detection. A linear calibration for ozone can be obtained in the range between 0.01 and 0.5 ppm. The limit of quantitation is 0.03 ppm, and the accuracy exceeds 8%. It takes about 134 s to measure the relatively low occupational exposure concentration of 0.1 ppm. A reduction of the sensor response time could be achieved through application of double-sided coated sensors instead of single-sided variants. The stability of the sensors and the effect of external parameters like relative humidity (RH), temperature and gas flow on the sensor response have been investigated. The sensor response is affected by varying the gas flow or temperature; however, humidity in the range between 0 and 90% RH does not affect sensor response. The indigo derivative 9 remained stable inside the polymeric film and no chemical reaction, crystallisation or leaching occurred during 10 months of observation. Proper choice of indicator dye and polymeric material and successful application of kinetic evaluation method for the exposure experiments determine the desired features of the sensor.

Sensors and analytical chemistry

Instrumental analytical chemistry and chemical sensors, especially biosensors have made remarkable progress in the last decade. With respect to the analytical chemical performance characteristics the sensitivities could be increased drastically. However, the very important comparability of trace and ultra-trace analytical data produced in different laboratories has not been improved to the same degree. The analytical chemical performance characteristics of chemical and biochemical sensors must be judged with those facts in mind when they are validated using such traditional instrumental reference methods. Biosensors based on immune-chemical principles are more versatile in allowing nearly every analyte to be determined and are therefore chosen for this progress report. A recently developed calibration free optical single-use “immuno-chip” is described. This low-cost chip is based on an evanescence field fluorescence detection. The same technique and can also be used for a real-time recording of DNA hybridisation and dissociation events. Multi-analyte devices and DNA-arrays based on this technological platform were developed using a fast kinetic evaluation method. This offers certain advantages to methods detecting only the endpoint of a molecular association reaction especially concerning the detection of mismatches (SNP detection). Finally, a novel and relatively simple micro-electrochemical method based on a microelectrode array in combination with receptor-functionalized magnetic latex beads and an indicating redox system is described which bears in it an alternative to atomic force microscope binding forces measurements. Depending of the numer of individually addressable microelectrodes this method allows the simultaneous study of several hundred to thousands of molecule–molecule interactions within seconds. In addition, a single molecule detection and nearly unlimited multi-analyte, ultra-trace immuno-chemical sensing capabilities seem possible.

Kinetic evaluation method for SPME‐NIR measurements of analytes with long equilibration time

AbstractIn recent years, it has been demonstrated that SPME in polymer‐clad optical fibers can be efficiently combined with NIR evanescent‐wave spectroscopy for on‐site monitoring of apolar hydrocarbons (HCs) in aqueous samples. Typically, the time to reach analyte partition equilibrium between sample matrix and fiber cladding for well‐agitated solutions and low‐molecular‐weight HC species is in the range of 2–20 min. Thus, spectral absorbance data measured in extraction equilibrium are used for calibration and evaluation. However, for samples with no or only low agitation (e.g., in situ measurement in a monitoring well) and even for well‐stirred samples containing HCs with higher molecular weight (>C8–C10), it may take several hours to reach equilibrium, which is by far too long for applications in field analysis. In this context, a calibration and evaluation algorithm based on HC extraction kinetics has been developed, which allows performing quantitative measurements of such samples within 20 min. This method uses the initial gradient of the response curve of a given HC compound or mixture recorded by the SPME‐NIR instrument, which is linearly dependent on analyte concentration. The algorithm has been implemented in the control and evaluation software of an SPME‐NIR photometer system and tested with different aqueous HC samples. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 131–142, 2001

Modification of isotactic poly(propylene) by oxygen and helium plasma with reference to thermo‐oxidative stability

AbstractThe modification of isotactic poly(propylene) (PP) foils by reactive (O2) and inert (He) gas plasma treatment was studied with relevance to surface structure and thermo‐oxidative stability for different treatment times. The following effects were investigated: change of non‐helical (atactic or amorphous) content in the surface region and formation of vinyl and vinylidene groups by frustrated multiple internal reflection Fourier transform infrared spectroscopy (FMIR‐FTIR), formation of peroxyl redicals by electron spin resonance spectroscopy (ESR) and change of the invariant activation energy of degradation by thermogravimetric analysis (TGA). For the latter a new kinetic evaluation method was used based on a selection of multiple step model to determine the invariant Arrhenius constants, e.g., activation energy and preexponential factor, for the weight loss during thermoxidative degradation of untreated and, for the first time, of plasma‐treated PP. Several thermogravimetric curves under different temperature scanning conditions have been evaluated with different solid state models as well as with a selection of different multiple step reaction pathways. With a limitation to total weight loss of 60% of the mass for an untreated PP and applying a most probable kinetic model consisting of one consecutive and one parallel reaction step, the activation energies were found to be 84.2 ± 1.0 and 73.2 ± 1.0 kJ/mol for the initial and the consecutive reaction and 137.8 ± 3.0 kJ/mol for the parallel reaction. The corresponding data of the plasma‐treated samples are 80 ± 1.0 and 71.0 ± 1.0 kJ/mol for the initial and the consecutive reaction, while the activation energy for the parallel reaction remained almost unchanged. Unexpectedly, we found the He plasma treatment to decrease the activation energies of the first and consecutive reaction nonlinearly and within the first 600 s to a larger extent than O2 plasma treatment. Based on this kinetic model, a modified mechanism for the thermo‐oxidative degradation of PP is proposed in terms of elementary degradation reactions and will be discussed with reference to literature data.

Studies on the process of Bi12MO20 (M=Ti, Ge, Si) formation from oxides

Using DSC technique, the chemical interaction in Bi2O3+MO2 mixtures resulting the Bi12MO20 phase, (M=Ti, Ge and Si) was monitored. Kinetic parameters for the primary stage of interaction were yielded by the non-isothermal method of kinetic evaluation of experimental heat flux DSC curves. The model of three-dimensional diffusion according to Jander was fitted as the best in a statistical sense.

Kinetic evaluation method of catalyst.

触媒活性劣化を伴う炭化水素の反応における触媒評価法を, 異なった組成と物性を持つ合成シリカアルミナ触媒における, 酸化エチレン異性化反応によって検討した.析出コークが阻害物として, 主反応に大きな影響を与えるため, 主反応側からの触媒能のみで評価することは, 十分な評価法ではない.そこで, 阻害反応に対する触媒能も含め, 初速度と劣化係数を使って, 総括有効触媒能をrA0αC/rC0αAと定義した.そして, この値によって触媒の評価を行った.また, その適応性を検討した結果, この値と触媒寿命および主反応物生成量との間によい相関が見られた.この値を用いて, 触媒の評価が可能であることが確認された.

Kinetic measurements on polymers — Applications and limits

A modern kinetic evaluation method for nonisothermal reactions measured with TG or DSC is presented. The obtained kinetic data are the basis for computation of a reaction process under any condition, e.g. isothermal or adiabatic. The measurements were performed on a Mettler TA3OOO system with built-in evaluation software. Mainly the following reactions are discussed: polyaddition of an epoxy premix and pyrolysis of polystyrene. To judge the reliability of the results, 4 check procedures are recommended.

On the mechanism of the polymerization of ϵ‐caprolactam. I. The polymerization initiated by ϵ‐aminocaproic acid

AbstractIn this first‐paper of a series of publications on the mechanism of the polymerization of ϵ‐caprolactam (CL), an investigation of the kinetics of the polymerization initiated by ϵ‐aminocaproic acid (ACA) is reported. Experiments were performed at 254°C. for three different initial ratios (ACA/CL)0:0.05, 0.022, and 0.011 mole/mole. The concentration (x) of unconverted CL and that of end groups (c) were determined by extraction with water at room temperature and by potentiometric titration, respectively. The method of kinetic evaluation consists in the direct checking of rate equations making use of the quantities dx/dt and dc/dt which were determined graphically from the curves of x and c versus time. In this way tedious integration procedures are avoided and the testing of rather different mechanisms is much easier. Moreover, it is not necessary to make the assumption of constant rate coefficients which, of course, will seldom apply. Thus the inadequacy of the “polycondensation mechanism” has been proved for every time instant separately, although accidentally the rate constant of the main reaction is fairly constant. In this polycondensation mechanism it is assumed that polymer formation can take place only by polycondensation of ACA, the supply of which is provided for by the reaction of CL with water formed in the process of polycondensation. It turns out that even when the rate of hydrolysis of CL is so high that the polycondensation reaction is rate determining, this latter rate is to small by a factor of 10 or more to account for the rate of CL conversion observed. It is shown that this difficulty can be overcome only by incorporating a third reaction in the mechanism, a reaction which must provide for the main consumption of CL. We have assumed this reaction to be a reversible polyaddition reaction, i.e., a reaction in which CL is added to one of the end groups of the polymer molecules. The rate constant for this reaction derived from the experiments appears to be in good agreement with the value derived from the experiments on the polymerization of CL initiated with water.