scholarly journals Kinetics of the Release of Nicotinamide Absorbed on Partially Neutralized Poly(acrylic-co-methacrylic acid) Xerogel under the Conditions of Simultaneous Microwave Heating and Cooling

Gels ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 193
Author(s):  
Jelena D. Jovanovic ◽  
Borivoj K. Adnadjevic
Keyword(s):  
Kinetic Parameters ◽  
Microwave Heating ◽  
Model Fitting ◽  
Reaction System ◽  
Release Process ◽  
Exponential Factor ◽  
Heating And Cooling ◽  
Different Temperatures ◽  
First Order Chemical Reaction ◽  
Kinetics Of

The kinetics of release of nicotinamide (NIAM) that was absorbed on partially neutralized poly(acrylic-co-methacrylic) (PAM) xerogel/hydrogel, under the conditions of simultaneous microwave heating and cooling (SMHC) were examined. The kinetics curves of NIAM release into an aqueous solution at temperatures of 308–323 K were recorded. By applying the model-fitting method (MFM), it was found that the kinetics of NIAM release can be modeled by a kinetic model of a first-order chemical reaction. The values of the release rate constants (kM) at different temperatures were calculated, and their values were found to be within the range 8.4 10−3 s −1−15.7 10−3 s−1. It has been established that the Arrhenius equation was valid even in the conditions of SMHC. The values of the kinetic parameters (activation energy (Ea) and pre-exponential factor (A) of the NIAM release process adsorbed on PAM xerogel/hydrogel were calculated as follows: Ea = 25.6 kJ/mol and ln (A/s−1) = 5.21. It has been proven that the higher value of the rate constant at SMHC in relation to CH is not a consequence of the overheating of the reaction system or the appearance of “hot-points”. The values of change of the enthalpy of activation (ΔH*) and the change of entropy of activation (ΔS*) were calculated as follows: ΔH* = +23.82 kJ/mol and ΔS* = −201.4 J/mol K. The calculated higher values of the kinetic parameters and thermodynamic parameters of activation are explained by the formation of a specific activated complex under SMHC, whose structure and degree of order are different than in the one formed under CH.

scholarly journals The kinetics of the extraction of caffeine from guarana seed under the action of ultrasonic field with simultaneous cooling

2019 ◽  
Vol 9 (1) ◽  
pp. 26-36 ◽  
Author(s):  
Biljana Koturevic ◽  
Borivoj Adnadjevic ◽  
Jelena Jovanovic
Keyword(s):  
Activation Energy ◽  
Kinetic Parameters ◽  
Reaction System ◽  
Ultrasonic Field ◽  
Conventional Heating ◽  
Isothermal Kinetics ◽  
Correlation Relationship ◽  
Exponential Factor ◽  
Caffeine Extraction ◽  
Kinetics Of

AbstractThe kinetics of isothermal extraction of caffeine from guarana seed under the action of ultrasonic field with simultaneous cooling (UESC) was investigated. The isothermal kinetics curves were measured at temperatures range T = 17-58°C. Using the model-fitting method it was determined that the kinetics of caffeine extraction can be described by a theoretical Jander three-dimensional diffusional model. The values of the rate constant were calculated for different temperatures, as well as the kinetic parameters (activation energy (Ea) and pre-exponential factor (lnA)). Based on the results obtained, it is concluded that the rate constants of caffeine extraction under UESC are about 2 times higher in comparison to the values obtained for the extraction in the conditions of conventional heating (CH). The activation energy of the caffeine extraction under the UESC $\left( E_{\text{a}}\,^{\text{UESC}}=19.4\,\text{kJ}\cdot \text{mo}{{\text{l}}^{-1}} \right)$is lower than the values are for CH $\left( E_{\text{a}}\,^{\text{CH}}=21.8\,\text{kJ}\cdot \text{mo}{{\text{l}}^{-1}} \right).$Energy consumption for UESC is four times lower than for CH conditions. It is shown that there is a linear correlation relationship between kinetic parameters obtained for UESC and CH conditions. The changes in the values of kinetic parameters are explained by the model of selective transfer of energy from the reaction system to the reactant molecules.

scholarly journals Isothermal green microwave-assisted extraction of caffeine from guarana: a kinetic study

2017 ◽  
Vol 6 (6) ◽  
Author(s):  
Biljana Koturevic ◽  
Borivoj Adnadjevic ◽  
Jelena Jovanovic
Keyword(s):  
Microwave Heating ◽  
Model Fitting ◽  
Water Extract ◽  
Isoconversional Method ◽  
Microwave Assisted Extraction ◽  
Exponential Factor ◽  
Microwave Assisted ◽  
Assisted Extraction ◽  
Caffeine Extraction ◽  
Kinetics Of

AbstractThe kinetics of isothermal green microwave-assisted extraction of caffeine from guarana seed powder with water at a temperature range from 40°C to 60°C was investigated. The caffeine concentration in the water extract was determined by UV-Vis spectrophotometry. By applying the isoconversional method, it was established that the kinetics of the caffeine extraction from the guarana seed powder with microwave heating is an elementary kinetic process. The model fitting method was used to determine the kinetic model of the caffeine extraction under microwave heating. It was found that the kinetics of the caffeine extraction can, under microwave heating, be modeled by the Jander’s model of three dimensional diffusion. The kinetic parameters, activation energy and pre-exponential factor of the caffeine extraction were determined.

scholarly journals Comparative Kinetic Analysis of CaCO3/CaO Reaction System for Energy Storage and Carbon Capture

2019 ◽  
Vol 9 (21) ◽  
pp. 4601 ◽  
Author(s):  
Fedunik-Hofman ◽  
Bayon ◽  
Donne
Keyword(s):  
Activation Energy ◽  
Energy Storage ◽  
Kinetic Analysis ◽  
Kinetic Parameters ◽  
Carbon Capture ◽  
Model Fitting ◽  
Reaction System ◽  
Reaction Model ◽  
Activation Energies ◽  
Exponential Factor

The calcium carbonate looping cycle is an important reaction system for processes such as thermochemical energy storage and carbon capture technologies, which can be used to lower greenhouse gas emissions associated with the energy industry. Kinetic analysis of the reactions involved (calcination and carbonation) can be used to determine kinetic parameters (activation energy, pre-exponential factor, and the reaction model), which is useful to translate laboratory-scale studies to large-scale reactor conditions. A variety of methods are available and there is a lack of consensus on the kinetic parameters in published literature. In this paper, the calcination of synthesized CaCO3 is modeled using model-fitting methods under two different experimental atmospheres, including 100% CO2, which realistically reflects reactor conditions and is relatively unstudied kinetically. Results are compared with similar studies and model-free methods using a detailed, comparative methodology that has not been carried out previously. Under N2, an activation energy of 204 kJ mol-1 is obtained with the R2 (contracting area) geometric model, which is consistent with various model-fitting and isoconversional analyses. For experiments under CO2, much higher activation energies (up to 1220 kJ mol-1 with a first-order reaction model) are obtained, which has also been observed previously. The carbonation of synthesized CaO is modeled using an intrinsic chemical reaction rate model and an apparent model. Activation energies of 17.45 kJ mol-1 and 59.95 kJ mol-1 are obtained for the kinetic and diffusion control regions, respectively, which are on the lower bounds of literature results. The experimental conditions, material properties, and the kinetic method are found to strongly influence the kinetic parameters, and recommendations are provided for the analysis of both reactions.

Kinetics of thermal degradation of wood biomass

2014 ◽  
Vol 68 (12) ◽  
Author(s):  
Ivan Hrablay ◽  
Ľudovít Jelemenský
Keyword(s):  
Kinetic Parameters ◽  
13C Nmr ◽  
Model Fitting ◽  
Isoconversional Method ◽  
Experimental Results ◽  
Pyrolysis Kinetics ◽  
Exponential Factor ◽  
Model Free ◽  
Fitting Method ◽  
Kinetics Of

AbstractPyrolysis kinetics of a hardwood representative, beech (Fagus sylvatica), was investigated by two different kinetic approaches: model-free isoconversional method and model-fitting method. The model-free isoconversional method was used for the determination of apparent kinetic parameters, i.e. the activation energy and pre-exponential factor. The model fitting method was used for the optimization of kinetic parameters of the reaction pathways of three selected reaction mechanisms: one-step, two-step, and three-step one. In both approaches, thermo-gravimetric data were used at five heating rates: 2°C min−1, 5°C min−1, 10°C min−1, 15°C min−1 and 20°C min−1. As the most suitable mechanism, the three-step mechanism containing the intermediate degradation step was chosen. This selection was supported by experimental results from the 13C NMR analysis of solid residues prepared at the key temperatures within the range of 230–500°C. The progress of mass fraction values of each component in this mechanism was simulated. Conclusions from the simulation were confronted with experimental results from the 13C NMR.

scholarly journals SOLVATION OF THE [Cr(NCS)4(IMIDAZOLE)2] ION IN ETHANOL-WATER MIXTURES

2002 ◽  
Vol 10 (11) ◽  
pp. 63-72
Author(s):  
lon Ganescu ◽  
George Bratulescu ◽  
Ion Papa ◽  
Anca Ganescu ◽  
Alin Barbu ◽  
...  
Keyword(s):  
Kinetic Parameters ◽  
Order Reaction ◽  
Water Molecules ◽  
Hydrogen Ions ◽  
Second Order Reaction ◽  
Acidic Solutions ◽  
The Third ◽  
Competitive Reactions ◽  
Different Temperatures ◽  
Kinetics Of

Salvation kinetics of [Cr(NCS)4(imidazole)2]- has been studied in ethanol-water mixtures at different temperatures. The first stage of the solvation consists of two competitive reactions: two NCS- ions are exchanged, presumably, by water molecules and simultaneously an imidazole molecule by ethanol, the latter in a second-order reaction, accelerated by hydrogen ions. The exchange of the amine is followed by the substitution of the first two NCS- ions. The third and fourth NCS- ions are substituted only in neutral and slightly acidic solutions. Kinetic parameters have been determined for reactions (1), (2), and (4). The influence of the solvent composition and acidity is discussed

Thermal Cure and Ceramization Kinetics of Perhydropolysilazane

2013 ◽  
Vol 575-576 ◽  
pp. 81-86 ◽  
Author(s):  
Feng Ling Ma ◽  
Hui Min Qi ◽  
Ya Ping Zhu ◽  
Xiao Wen Ren ◽  
Fan Wang
Keyword(s):  
Activation Energy ◽  
Weight Loss ◽  
Thermogravimetric Analysis ◽  
Kinetic Parameters ◽  
Nitrogen Atmosphere ◽  
Thermal Cure ◽  
Exponential Factor ◽  
Kinetics Of

The kinetics of the thermal cure and ceramization of preceramic prehydropolysilazane (PHPS) was investigated by thermogravimetric analysis (TGA) under nitrogen atmosphere. The results indicated that the gases captured during the thermal cure and ceramization process of PHPS, which had three main weight loss events. The corresponding kinetic parameters including activation energy, pre-exponential factor and empirical order of the thermal cure and ceramization stages were evaluated by using Ozawa and Kissinger metnods, respectively.

Kinetics of Carbothermic Reduction of Ilmenite

2016 ◽  
Vol 852 ◽  
pp. 315-322 ◽  
Author(s):  
Min Chen ◽  
Xuan Xiao ◽  
Xue Feng Zhang
Keyword(s):  
Activation Energy ◽  
Kinetic Parameters ◽  
Carbothermic Reduction ◽  
Reduction Process ◽  
Phase Evolution ◽  
Reduction Kinetics ◽  
Isokinetic Relationship ◽  
Exponential Factor ◽  
Morphology Change ◽  
Kinetics Of

The reduction kinetics of ilmenite was investigated. Phase evolution during the reduction process was identified by XRD and morphology change was observed using SEM. Kinetic parameters of the activation energy and pre-exponential factor were determined by Kissinger-Akahira-Sunose (KAS) method and Coast-Redfern method&artificial isokinetic relationship (IKP) respectively. Results showed that when the reaction of titanium suboxides makes a growing contribution, the conversion dependence of activation energy has an ascending trend. When the conversion exceeded 0.7, the reactants almost consumed, and the process was controlled by diffusion.

scholarly journals Kinetics of the Carbon Monoxide Oxidation Reaction Under Microwave Heating

1996 ◽  
Vol 430 ◽  
Author(s):  
W. Lee Perry ◽  
Joel D. Katz ◽  
Daniel Rees ◽  
Mark T. Paffett ◽  
Abhaya Datye
Keyword(s):  
Activation Energy ◽  
Carbon Monoxide ◽  
Co Oxidation ◽  
Microwave Heating ◽  
Oxidation Reaction ◽  
Reaction Order ◽  
Thermal Gradients ◽  
Exponential Factor ◽  
Co Oxidation Reaction ◽  
Kinetics Of

Abstract915 MHz microwave heating has been used to drive the CO oxidation reaction over Pd/Al2O3 without significantly affecting the reaction kinetics. As compared to an identical conventionally heated system, the activation energy, pre-exponential factor, and reaction order with respect to CO were unchanged. Temperature was measured using a thermocouple extrapolation technique. Microwave-induced thermal gradients were found to play a significant role in kinetic observations.

scholarly journals Influence of Liming on Kinetics of Sewage Sludge Pyrolysis

2019 ◽  
Vol 26 (1) ◽  
pp. 175-188
Author(s):  
Paweł Stolarek ◽  
Stanisław Ledakowicz ◽  
Radosław Ślęzak
Keyword(s):  
Thermal Decomposition ◽  
Sewage Sludge ◽  
Mass Loss ◽  
Kinetic Parameters ◽  
Heating Rate ◽  
Visual Analysis ◽  
Pyrolysis Kinetics ◽  
Exponential Factor ◽  
The Impact ◽  
Kinetics Of

Abstract Thermogravimetry (TG) is the fast and reliable method for characterization of thermal decomposition of any material and in particular to determine the kinetics of pyrolytic decomposition of sewage sludge. Two types of sewage sludge with and without addition of lime were investigated from kinetic point of view. For TG analysis samples of selected sewage sludge were heated under the inert atmosphere of argon with constant heating rate from 303 to 1273 K; the three heating rate β = 5, 10 and 20 K/min were chosen. The iso-conversion methods of Friedman and Ozawa-Flynn-Wall were employed for analysis of TG results. As the sewage sludge decomposition is very complex process it cannot be described by a simple stoichiometric equation, therefore the so called lumping of reactions in the selected temperature ranges were used with detailed principles arising from visual analysis of DTG curve. The deconvolution of DTG curves performed according to Fraser-Suzuki asymmetric profile allowed the identification of number of lumps and their contribution to the overall mass loss. So the decomposition of sewage sludge with lime addition could be described with five groups of reactions while the one without lime by means of six lumps. The thermal decomposition of sewage sludge was assumed to proceed according to the scheme of parallel concurrent independent reactions of n-th order. The values of the apparent activation energies at different constant values of conversion degrees were determined by the iso-conversion analysis. To estimate the kinetic parameters the non-linear regression with Levenberg-Marquart optimization procedure was used. The kinetic parameters such as activation energy, pre-exponential factor, reaction order and fraction of total mass loss associated with a given reaction were determined. The impact of sewage sludge liming revealed in essential differences of pyrolysis products and pyrolysis kinetics of limed sludge and without lime one was highlighted.

scholarly journals Thermal decomposition and their kinetics of mercury(ii) perchlorate complex with 4-aminopyridine and water

2019 ◽  
Vol 8 (3) ◽  
pp. 649-653
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Rapid Heating ◽  
Model Fitting ◽  
Isoconversional Method ◽  
Molecular Formula ◽  
Isothermal Tg ◽  
Different Temperatures ◽  
Kinetics Of ◽  
Perchlorate Complex

Copper perchlorate complex with 4-aminopyridine and water has been prepared with molecular formula [Hg2(C5H6N2)3(ClO4)4].2H2O. It has been characterised by elemental analysis, thermogravimetry, and IR spectroscopic data. Thermal behaviours have been studied by thermogravimetry (TG) in static air and simultaneous thermogravimetry-derivative thermogravimetry analysis (TG-DTG) in flowing nitrogen atmosphere. Complex decomposes in four steps (less resolved). Difference in decomposition under air and inert atmosphere has been also discussed. Kinetics of thermal decomposition has been investigated using isothermal TG data recorded at five different temperatures applying model-fitting as well as isoconversional method on these data. Model-fitting methods have yielded a single value of activation energy whereas isoconversional method has given different values of activation energy for each extent of conversion, α. Response of synthesized complex towards rapid heating has been investigated by recording explosion delay time (DE) at five different temperatures and using these data kinetics of explosion has been analysed. Activation energy for explosion has been also calculated.

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