Isokinetic Temperature Research Articles

Thermodynamic properties of Anacardium humile St. Hil. (cajuzinho-do-cerrado) achenes

The cajuzinho-do-cerrado is a native species of the cerrado of great potential of use and is threatened of extinction. The aim of this study was to determine and evaluate the thermodynamic properties of Anacardium humile St. Hil. achenes from the different hygroscopic equilibrium points according to the moisture content. To obtain the isotherms, the indirect static method was used at temperatures of 10, 20, 30 and 40 °C and for moisture contents of 13.4, 11.1, 8.7 and 5.3% dry basis (db). The Copace model was used to describe the hygroscopic equilibrium of the achenes. The thermodynamic properties are influenced by the moisture content because the latent heat of vaporization of the water of the achenes increases with the decrease in the equilibrium moisture content, varying between 3,035.63 and 2,510.80 kJ kg-1 for moisture contents of 4.51 to 13.4% db, respectively. The differential enthalpy and entropy are closely related to the moisture content of the achenes. The isokinetic temperature of 304.67 K denotes the linear chemical compensation between the differential enthalpy and entropy of the Anacardium humile St. Hil. achenes, and the desorption process is controlled by enthalpy.

Thermodynamic properties and water desorption isotherms of Golden Delicious apples

Moisture desorption isotherms of apples (Golden Delicious) were determined. Experimental desorption data were fitted by 13 mathematical models. The influence of temperature on desorption isotherms was more indicated at high water activities. The GAB, Halsey, Modified Halsey, Oswin, Chen, Ferro Fontan, Lewicki (1998) and Lewicki (2000) models correlated well to the experimental desorption data over the entire field of temperatures and water activities explored. In order to well understand the water properties and to evaluate the energy requirements for transport phenomena during processing, the thermodynamic properties were evaluated from the experimental desorption data. The enthalpy-entropy compensation theory was validated by the variation of net isosteric heat versus differential entropy. This variation provided the isokinetic temperature and the free energy indicating that the desorption process in apple was a non-spontaneous and enthalpy-driven mechanism.

PH-metric and theoretical studies of the complexation of 2-[α-(o-hydroxyphenyl) ethylidenehydrazino]-4,6-dimethylquinoline and 2-[α-(o-methoxyphenyl)methylidenehydrazino]-4,6-dimethylquinoline

2-[α-(o-hydroxyphenyl)ethylidenehydrazino]-4,6-dimethylquinoline (AHQ) and 2-[α-(o-methoxyphenyl)methylidenehydrazino]-4,6-dimethylquinoline (BHQ) have been synthesized and characterization is performed by elemental analysis and electronic, vibrational and mass spectra. The pKH and log K were gritty in 75% solvent-water pH-metrically for BHQ ligand and at various temperatures for AHQ ligand. The dissociation and stability constants in the aqueous medium for BHQ ligand have been calculated by the relation of pKH or log K with solvent parameters (D, ET, AN and DN). The isokinetic temperature was determined by using a linear regression analysis (LRA) of ΔΗ° vs. ΔS° for AHQ complexes. The thermodynamic parameters of AHQ compounds were analyzed into their electrostatic (el) and non-electrostatic (non) or cratic components. Full geometrical and structural optimizations of the ligands have been performed by a DFT study by using the hyperchem program.

Influence of the activation entropy on the change of the isokinetic temperature in the SN2 reactions in solution

The increase of the changes in the activation entropy $$ \delta \Delta S^{ \ne } $$ value leads to the decrease of the isokinetic temperature Tiso value for the SN2 reaction series in which structure changes are introduced in the substrate, in the reagent or in the solvent. The changes of the free energy of activation $$ \delta \Delta G^{ \ne }_{ \exp } $$ and the activation entropy $$ \delta \Delta S^{ \ne } $$ in the frameworks of the isokinetic relationship $$ \delta \Delta G^{ \ne }_{ \exp } $$ vs. $$ \left( {T_{\text{iso}} {-}T_{ \exp } } \right)\delta \Delta S^{ \ne } $$ were explored quantitatively to predict the isokinetic temperature Tiso for the SN2 reactions in different solvents.

Comparison of the leaving groups during the study of the aquation of halopentaammine cobalt(III) complex in tartarate at different percentage of tert-butanol

The experimental kinetic study of aquation for both complexes bromopentaammine cobalt(III) and chloropentaammine cobalt(III) ions in the presence of tartarate solution in mixed solvent media of water with tert-butanol (10-50%, v:v) was examined spectrophotometrically at different temperatures (30-60 °C) by comparing the special effects of the leaving group of chloro and bromo on the rate constant of aquation. Comparison of kip (rate constant of ion-pairing) for both complexes and show the non-linear plots of log (kip) ion-pair rate constants against the reciprocal of the dielectric constant D. The thermodynamic analyses of the kinetic data for both complexes have been discussed in terms of solvent effect on the ion-pair aquation reactions. The obtained isokinetic temperatures of these systems indicate the existence of compensation effect arising from solute-solvent interaction. The excessive change of ΔHip* and ΔSip* with the mole fraction of the co-solvent can be recognized to the change of the physical properties of the solvent-water mixture with the solvent structure. Undersized changes in ΔGip* with the mole fraction of the co-solvent was found, representing a compensating effects between ΔHip* and ΔSip*.

Meyer-Neldel rule in the conductivity of manganite single crystals

The Meyer-Neldel behavior of conductivity of low-doped manganite ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{\mathit{x}}{\mathrm{MnO}}_{3}$ single crystals has been investigated. The evolution of the isokinetic temperature of conductivity, modified by Ca-doping, hydrostatic pressure, and current bias has been determined. In addition, the evolution of isokinetic temperature with ageing has also been studied. The Meyer-Neldel behavior of the manganite system stems from the multiexcitation entropy mechanism. The isokinetic temperature turned out to be a sensitive parameter characterizing changes in the transport properties of mixed valence manganites, which in the presence of a detailed theoretical model of the excitations coupling in manganites could become a powerful tool for the characterization and investigation of transport properties of manganites.

Kinetic compensation effects in the chemical reaction-controlled regime and mass transfer-controlled regime during the gasification of biochar in O2

This study aims to investigate the kinetic compensation effects during the char-O2 reaction in a fluidised-bed reactor for two particle sizes of 0.80–1.0 mm and 2.0–3.35 mm. The rate of char-O2 reaction was determined by analysing the gasification product gas composition in a quadrupole mass spectrometer. The char-O2 reaction exhibited different kinetic compensation effects between apparent activation energy and apparent pre-exponential factor in the kinetics-controlled, diffusion-controlled and mixed regimes for both particle sizes. The same reaction mechanism is followed during the char-O2 reaction in the kinetic regime at same or at different pyrolysis temperatures as revealed by the kinetic compensation effects. In the mixed regime, higher diffusion limitations increased the m and c values in the kinetic compensation effect lnAapp = mEapp + c for any given particle size. Due to higher rates of reaction at higher char conversions, the char-O2 reaction switched from kinetics-controlled to mixed regimes, resulting in higher slopes ‘m’ and y-intercepts ‘c’ in the kinetic compensation effects. The absence of isokinetic temperature at higher conversions indicates that char properties changed significantly at higher conversions compared with those at lower conversions.

Ligand Sequential Replacement on Chromium(III)-Aqua Complexes by l-Alanine and Other Biological Amino Acids: A Kinetic Perspective.

The ligand sequential replacement on chromium(III)-aqua complexes by l-alanine in slightly acidic aqueous solutions (pH range: 3.55-5.61) has been kinetically followed by means of UV-vis spectrophotometry. A two rate constant model has been applied to fit the absorbance-time data, corresponding to the formation ( k1) and decay ( k2) of an intermediate not reactive enough to be in steady state (long-lived intermediate). The kinetic orders of the amino acid were fractional (0.40 ± 0.03 for k1 and 0.40 ± 0.02 for k2). The two steps showed base catalysis, and the activation energies were 60 ± 3 (for k1) and 83 ± 6 (for k2) kJ mol-1. The rate constants for the coordination of the first l-alanine ligand followed the sequence CrOH2+ < Cr(OH)2+ < Cr(OH)3, Cr3+ being almost inactive. This suggests that the increase in the reaction rate with increasing pH was caused by the enhancement of the lability of the Cr(III)-aqua bonds induced by the presence of hydroxo ligands. The activation parameters for a series of ligand substitution on Cr(III)-aqua complexes by organic molecules yielded a statistically significant enthalpy-entropy linear plot with an isokinetic temperature of 296 ± 21 K.

A new data in the kinetic and thermodynamic analysis of non-isothermal decomposition of super-fine kaolin powder

Abstract Kinetic and thermodynamic analysis of non-isothermal decomposition of super-fine kaolin powder was examined. It was established that the decomposition process proceeds through liberation of adsorbed water, the loss of the water of hydration and dehydroxylation process, which produces highly disordered metakaolin. By applying the distributed reactivity approaches, it was found that dehydroxylation can be described with simultaneous two-parallel reactions model. By applying the Exner-Linert statistical method on estimated Eyring plots, the true isokinetic temperature was confirmed. The appearance of entropy – enthalpy compensation (EEC) showed the direct cause-and-effect relationship between these thermodynamic observables resulting by physically real factors such as the steric factors. It was shown that the phenomenon of true compensation effect arises from conformational (geometrical) changes, which occur during metakaolin formation.

Enthalpy-entropy compensation effect and other aspects of isoparametricity in reactions between trans-2,3-bis(3-bromo-5-nitrophenyl)oxirane and arenesulfonic acids

It was found that as a result of the non-additivity (interaction) of joint effects of structure and temperature on the rate and free energy of activation of the reactions between trans-2,3-bis(3-bromo-5-nitrophenyl)oxirane and Y-substituted arenesulfonic acids YC6H4SO3H in a mixture of dioxane with 1,2-dichloroethane (7 : 3/v : v) at 265, 281, and 298 K, the cross reaction series exhibits isoparametric properties. At a temperature of 265 K, close to the isoparametric temperature point 262 K (isokinetic temperature), the free energy of activation and the rate of oxirane ring opening process do not depend on the structure of the substituent Y due to the enthalpy-entropy compensation effect. At the isoparametric point with respect to the constant of substituent Y (σY = 0.20), the free activation energy does not depend on temperature.

Optimization of the drying of &lt;i&gt;Moringa oleifera&lt;/i&gt; leaves by determination of thermophysical parameters

Moringa oleifera leaves are increasingly used as a dietary supplement. The present study deals with the estimation of its thermophysical properties. It is based on the Clausius-Clayperon and Gibbs-Helmholtz equations. This study required knowledge of the sorption isotherms obtained by the static gravimetric method in the relative humidity range of 5.4 to 97% and the temperatures of 30, 35, 45 and 55 °C. The BET models (1938), Smith (1947), Henderson (1952), Iglesias (1981) and GAB (1985) are used for the smoothing of the experimental points. The isotherms obtained are of type II and characterized by a sigmoid shape. The theoretical curves of GAB and Smith show a better similarity with the experimental curves. The monolayer moisture content (Xm) is 8.54/7.62% at 30 °C; 7.0/5.52% at 35 °C; 6.74/ 5.41% at 45 °C and 5.45/4.65% at 55°C respectively for the GAB and BET models. The net isosteric heat ( qst ) and desorption differential entropy ( ΔS ) tend towards zero for very high moisture contents. The activation energy of desorption of the Moringa oleifera leaves in the temperature range tested is -13.1010 kJ/mol. Isokinetic temperature ( Tβ ) and the average harmonic temperature ( Thm ) are respectively 314.172 K and 314.459 K while the free energy ( ΔGβ ) is 308.18 J/mole. © 2017 International Formulae Group. All rights reserved. Keywords: Desorption isotherm, Modelization, Isosteric heat, Differential Entropy, Activation energy

Enthalpy-entropy compensation and the isokinetic temperature in enzyme catalysis.

Enthalpy-entropy compensation supposes that differences in activation enthalpy ΔH++ for different reactions (or, typically in biochemistry, the same reaction catalysed by enzymes obtained from different species) may be compensated for by differences in activation entropy ΔS++. At the isokinetic temperature the compensation is exact, so that all samples have the same activity. These ideas have been controversial for several decades, but examples are still frequently reported as evidence of a real phenomenon, nearly all of the reports ignoring or discounting the possibility of a statistical artefact. Even for measurements in pure chemistry artefacts occur often, and they are almost inescapable in enzyme kinetics and other fields that involve biological macromolecules, on account of limited stability and the fact that kinetic equations are normally valid only over a restricted range of temperature. Here I review the current status and correct an error in a recent book chapter.

Cross effects of structure and temperature in the reactions of trans-2,3-diaryloxiranes with arenesulfonic acids

Cross effects of the reagent structure and the temperature on the rate and activation parameters of the reactions of symmetrically X-substituted trans-2,3-diaryloxiranes with Y-substituted arene-sulfonic acids have been investigated in the temperature range 265–298 K. The isokinetic temperature of 265 K was reached, at which the rate and the free energy of the ring-opening reaction of trans-2,3-bis(3-bromo-5-nitrophenyl)-oxirane practically do not depend on substituent Y. The transition through the isoparametric points on substituent Y was realized with the inversion of the temperature effect on the free energy of activation for the reactions of oxiranes with X = 4-NO2 and 3-Br-5-NO2.

Kinetics and related studies of the formation of 2,3‐dihydroquinazolin‐4(1H)‐ones in the presence of different benzaldehyde derivatives

AbstractThe kinetics and activation parameters for the reaction between 2‐amino‐benzamide and some benzaldehyde derivatives in the presence of formic acid have been reported and discussed. A linear plot of lnk vs l/T showed that the reactions obey the Arrhenius equation. Both the Arrhenius and the Eyring equations were used to calculate the activation energy. The effect of nitro groups was studied on different positions of benzaldehyde. For all substituents, the reactions followed second‐order kinetics, and the partial orders of reactions were recognized with respect to each reactant. Comparisons between the magnitudes of ΔH‡ and TΔS‡showed that the reactions were enthalpy controlled. The validity of the isokinetic relationship and the compensation effect was tested, and the isokinetic temperature (β) was obtained. A linear enthalpy‐entropy plot (ΔH‡versusΔS‡) showed that the compensation effect is established, and this process occurs via a same mechanism across a series of reactions. From the Van't Hoff and Exner's plots, the isokinetic temperature was obtained.

Propanolysis of arenesulfonyl chlorides: Nucleophilic substitution at sulfonyl sulfur

AbstractWe have studied the mechanism of solvolysis of arenesulfonyl chlorides by propan‐1‐ol and propan‐2‐ol at 303‐323 K. Kinetic profiles were appropriately fit by first‐order kinetics. Reactivity increases with electron‐donating substituents. Ortho‐alkyl substituted derivatives of arenesulfonyl chlorides show increased reactivity, but the origin of this “positive” ortho‐effect remains unclear. Likely, ortho‐methyl groups restrict rotation around the C‐S bond, facilitating the attack of the nucleophile. No relevant reactivity changes have been found with propan‐1‐ol and propan‐2‐ol in terms of nucleophile steric effect. The existence of isokinetic relationships for all substrates suggests a single mechanism for the series. Solvolysis reactions of all substrates in both alcohols show isokinetic temperatures (Tiso) close to the working temperature range, which is an evidence of the process being influenced by secondary reactivity factors, likely of steric nature in the TS. Solvation plays a relevant role in this reaction, modulating the reactivity. In some cases, the presence of t‐Bu instead of Me in para‐ position leads to changes in the first solvation shell, increasing the energy of the reaction (ca. 1 kJ·mol−1). The obtained results suggest the same kinetic mechanism of solvolysis of arenesulfonyl chlorides for propan‐1‐ol and propan‐2‐ol, as in MeOH and EtOH, where bimolecular nucleophilic substitution (SN2) takes place with nucleophilic solvent assistance of one alcohol molecule and the participation of the solvent network involving solvent molecules of the first solvation shell.

Thermophysical characterization of the powder resulting from the solar drying of the Moringa oleifera leaves

This paper presents the results of thermophysical characterization of the powder resulting from the solar drying of Moringa oleifera leaves. The desorption isotherms of the powder, are determined by the gravimetric static method. The models of B.E.T, Smith, Henderson, Iglesias and GAB are used for the smoothing of the experimental points. The Clausius-Clayperon and Gibbs-Helmholtz equation are used for the determination of thermodynamic properties. The isotherms obtained are with type II. The theoretical curves of GAB present a better similarity with the experimental curve at 55°C. The monolayer moisture content (Xm) is 6.32 and 7. 24 % at 30° C; 5.13 and 6.3% at 35 °C; 5.1 and 5.9 % at 45 °C; 4.22 and 4.66 % at 55 °C respectively for BET and GAB models. Isosteric and entropic heats are more important for low values of moisture content. The activation energy of desorption of the powder in the range of temperatures tested is -10.1009539 kJ/mol. Isokinetic temperature (Tβ) and the mean harmonic temperature (Thm) are respectively 301.2435K and 300.12342K and the free energy (ΔGβ) is 302.18 J/mol. The desorption process of the Powder is non-spontaneous and is done by controlled mechanisms enthalpic.Keywords: Moringa oleifera, Thermophysical characterization, Desorption isotherm, Thermodynamic properties, Modelization

Kinetics of water vapor adsorption by vacuum-dried jujube powder

Water vapor adsorption kinetics of vacuum-dried jujube powder were investigated in temperature and relative humidity ranges of 10 to 40℃ and 32 to 75%, respectively. Water vapor was initially adsorbed rapidly and then reached equilibrium condition slowly. Reaction rate constant for water vapor adsorption of vacuum-dried jujube powder increased with an increase in temperature. The temperature dependency of water activity followed the Clausius-Clapeyron equation. The net isosteric heat of sorption increased with an increase in water activity. Good straight lines were obtained with plotting of 1/(m-m0) vs. 1/t. It was found that water vapor adsorption kinetics of vacuum-dried jujube powder was accurately described by a simple empirical model, and temperature dependency of the reaction rate constant followed the Arrhenius-type equation. The activation energy ranged from 50.90 to 56.00 kJ/mol depending on relative humidity. Arrhenius kinetic parameters (Ea and k0) for water vapor adsorption by vacuum-dried jujube powder showed an effect between the parameters with the isokinetic temperature of 302.51 K. The information on water vapor adsorption kinetics of vacuum-dried jujube powder can be used to establish the optimum condition for storage and processing of jujube.

CO2 desorption kinetics for waste ion-exchange resin-based activated carbon by model-fitting and model-free

The CO2 desorption kinetics of waste ion-exchange resin-based activated carbons was analyzed by model-fitting and model-free approaches using thermogravimetric analysis. A non-isothermal method was applied in the temperature range of 303–393K with different heating rates. The experiments were performed under two different inlet CO2 concentrations. The experimental results showed that the extent of conversion of desorption is independent of inlet CO2 concentration during the adsorption process. At the range of 0.2≤α≤0.7, CO2 desorption on chemically activated carbon is complex, while physically activated carbon is simple. The kinetic models comply with Avrami-Eroféev models. The obtained artificial isokinetic temperatures lie in the region of the experimental temperatures, indicating that the reaction model for conversion 0.2 ≤ α ≤ 0.7 remains a proper choice. On the basis of the experimental results, the thermal analysis method can be used successfully in projecting CO2 desorption.

Simple method for determining of the isokinetic temperature value for the SNAr reactions in solution

AbstractThe changes of the free energy of activation δ∆G≠exp and the activation entropy δ∆S≠ in the framework of the isokinetic relationship δ∆G≠exp versus (Tiso − Texp) δ∆S≠ were explored quantitatively to predict the isokinetic temperature Tiso for the aromatic nucleophilic substitution reactions in solution.

Model establishment for the kinetic evaluation of synergistic effect on the coal char gasification with H2O and CO2 mixtures

A kinetic model derived from the classical Šesták-Berggren equation was established to simulate the isothermal gasification process of coal char with different partial pressures of H2O, CO2 and their mixtures. The effects of H2O and CO2 on the reaction could be expressed by the kinetic parameters η and φ which represent the conversion corresponding to maximum reaction rate (xmax) influenced by reactant gas and the gas distribution at the active sites, respectively. The results indicate that the relationship between η and xmax can be expressed as xmax=0.509–0.429η. The parameter φ of co-gasification is superior to that of H2O or CO2 gasification, indicating that the distribution of the gasifying agents during co-gasification is more uniform than that during H2O or CO2 gasification. The synergistic behavior observed during co-gasification was evaluated by the model and it indicates that the interaction between H2O and CO2 results in the improvement of coal physical structure and accelerates the co-gasification reaction rate. Kinetic compensation effect at different partial pressures indicates that the dependence of intrinsic reaction rate on the partial pressures of gasifying agent is gradually weakened as the temperature approaches the isokinetic temperature Tiso for in-situ gasification. It is also confirmed by the nth order reaction rate equation that the reaction order n tends to approach zero when the temperature approaches Tiso. The reaction rate is only affected by the temperature when the gasification temperature exceeds Tiso and the partial pressure of reactant gas is higher than 0.03MPa which is the minimum pressure required for full coverage of all the active sites.