共查询到20条相似文献,搜索用时 15 毫秒
1.
M. B. Dantas A. A. F. Almeida Marta M. Conceição V. J. Fernandes Jr Iêda M. G. Santos F. C. Silva L. E. B. Soledade A. G. Souza 《Journal of Thermal Analysis and Calorimetry》2007,87(3):847-851
This work presents the characterization and the kinetic compensation
effect of corn biodiesel obtained by the methanol and ethanol routes. The
biodiesel was characterized by physico-chemical analyses, gas chromatography,
nuclear magnetic resonance and thermal analysis. The physico-chemical properties
indicated that the biodiesel samples meet the specifications of the Brazilian
National Agency of Petroleum, Natural Gas and Biofuels (ANP) standards. The
analyses by IR and 1H NMR spectroscopy indicated
the ester formation. Gas chromatography indicated that biodiesel was obtained
with an ester content above 97%. The kinetic parameters were determined with
three different heating rates, and it was observed that both the methanol
and ethanol biodiesel obeyed the kinetic compensation effect. 相似文献
2.
In this research, thermogravimetry (TG/DTG) was used to determine the kinetic analysis of different coals and effect of cleaning process on kinetic parameters of raw and cleaned coal samples from Soma, Tuncbilek and Afsin Elbistan regions. Kinetic parameters of the samples were determined using Arrhenius and Coats and Redfern kinetic models and the results are discussed.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
3.
H. A. Schneider 《Journal of Thermal Analysis and Calorimetry》1993,40(2):677-687
Due to the complex character of the thermal degradation of polymers as a solid-gas chain reaction, an unequivocal kinetic
characteirzation is possible only for stationary states of both radical concentration and reaction mechanism. These conditions
are hardly realizable in non-isothermal thermogravimetry. Additional the weight losses are depedent on the volatility of the
reaction products. That is not always certain in polymer degradation. As a consequence the deduced ‘kinetic parameters’ are
not unequivocal. They are conversion and heating rate dependent and may be influenced by sample shape and size. Thus the ‘kinetic
parameters’ are in fact from the point of view of mathematics the fitting parameters of a ‘rate equation’ like relation, specific
for the used reaction conditions only. From the point of view of chemical kinetics they are neither attributable to a determined
reaction mechanism nor can they be used for predictions.
Dedicated to the 70th Anniversary of Dr. Jo Flynn 相似文献
4.
Kinetic evaluation of thermogravimetry data was used to understand the ageing behavior of beeswax used as an artists’ paint
medium on ancient mummy shrouds and Fayum portraits. Individual components of beeswax were subjected to dynamic thermogravimetry
to assess their evaporation rates, and three methods of kinetic analysis were evaluated for accuracy. The results showed that
although it is impossible to accurately predict the volatility at room temperature for individual components of beeswax due
mostly to their high molecular mass, relative trends and ranking of the volatility of the compounds can be obtained which
may explain compositional changes over time. 相似文献
5.
Maria Luisa A. Gonçalves Deusa Angélica da Mota Pinto Ana Maria R. F. Teixeira M. A. G. Teixeira 《Journal of Thermal Analysis and Calorimetry》2008,91(2):341-346
Dynamic kinetic analyses were performed on different Brazilian petroleum fractions by thermogravimetry. The data were treated
by a multiple heating rate methodology. The apparent activation energies for the light and middle fractions within the range
of 62–74 kJ mol−1 and for heavy distillation residues were within the range of 80–100 kJ mol−1 at lower conversions and 100–240 kJ mol−1 at higher conversions. The kinetic study can be a criterion for tells apart the main phenomena involved in the thermal behavior
of the refinery feedstock. 相似文献
6.
B. A. Howell 《Journal of Thermal Analysis and Calorimetry》2006,85(1):165-167
Thermal
analysis has a long and prominent role in the characterization of materials,
including polymeric materials. Kinetic studies in one form or another have
often been employed in an attempt to assess stability, predict lifetime, establish
degradation pathway, or project suitable processing conditions. The results
of such studies have often formed the basis for the proposal of the ‘mechanism’
of reaction. This despite the fact that the reaction being observed is often
unknown or is not a single process but rather several parallel or consecutive
events. This latter is particularly true for ‘variable temperature kinetics’.
The utility/value of such exercises is marginal at best and contributes nothing
to an understanding of the mechanism of any of the reactions involved. 相似文献
7.
Kinetic Analysis of Thermogravimetric Data XXXI. Derivation of a non-linear kinetic compensation law
The kinetic compensation effect observed in heterogeneous non-isothermal kinetics is only an apparent effect. In general,
the correlation derived between the kinetic parameters E and log A from TG curves can be described by means of a non-linear
compensation law, expressed by Eq. (14). This equation may become approximately linear in certain particular cases, i.e. it
may change into an isokinetic relation. The validity of the non-linear compensation law has been tested by using over 1000
sets of kinetic parameters reported earlier.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
B. Tiţa Eleonora Marian D. Tiţa Gabriela Vlase N. Doca T. Vlase 《Journal of Thermal Analysis and Calorimetry》2008,94(2):447-452
Thermal analysis is one of the most widely used methods for studying the solid state of pharmaceutical substances.
TG/DTG and DSC curves provide important information regarding the physical properties of the pharmaceutical compounds (stability,
compatibility, polymorphism, kinetic analysis, phase transitions etc.).
The purpose of a kinetic investigation is to calculate the kinetic parameters and the kinetic model for the studied process.
The results are further used to predict the system’s behaviour in various circumstances.
A kinetic study regarding the diazepam, nitrazepam and oxazepam thermal decomposition was performed, under non-isothermal
and isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 483, 498, 523, 538 and 553 K. The TG/DTG
data were processed by three methods: isothermal model-fitting, Friedman’s isothermal-isoconversional and Nomen-Sempere non-parametric
kinetics.
In the model-fitting methods the kinetic triplets (f(α), A and E
a) that defines a single reaction step resulted in being at variance with the multi-step nature of diazepines decomposition.
The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation
energies on the extent of conversion.
It is very difficult to obtain an accord with the similar data which resulted under non-isothermal conditions from a previous
work.
The careful treatment of the kinetic parameters obtained in different thermal conditions was confirmed to be necessary, as
well as a different strategy of experimental data processing. 相似文献
9.
A possible deduction is proposed of channel length distribution in one-dimensional porous materials from the kinetic data
obtained in isothermal thermogravimetry (TG). The method utilizes the absorption/desorption of small molecules into one-dimensional
nano-channel. In the surface-controlled absorption/desorption, the second derivative with respect to time is directly proportional
to the channel-length distribution function. Even in the diffusion-controlled case, the second derivative with respect to
the square root of time gives rough information on the distribution function. 相似文献
10.
In this paper, a systematic analysis of the errors involved in the determination of the kinetic parameters (including the
activation energy and frequency factor) from five integral methods has been carried out. The integral methods analyzed here
are Coats-Redfern, Gorbachev, Wanjun-Yuwen-Hen-Zhiyong-Cunxin, Junmeng-Fusheng-Weiming-Fang, Junmeng-Fang and Junmeng-Fang-Weiming-Fusheng
method. The results have shown that the precision of the kinetic parameters calculated by the different integral methods is
dependent on u (E/RT), that is, on the activation energy and the average temperature of the process. 相似文献
11.
The Ni(II), Cu(II) Co(II) and Zn(II) complexes of 2,3‐hydroxyimino‐4‐phenyl‐6‐phenyazo‐1‐thia‐4,5‐diaza‐ cyclohexa‐5‐diene (H2L) were synthesized. Thermal behavior of these complexes was studied in dynamic nitrogen atmosphere by TA (thermogravimetric analysis), DTA (differential thermal analysis) and DTG (differential thermal gravimetry) techniques. The reaction order, the activation energies, the entropies, the enthalpies, the free energies, and the pre‐exponential factors of the thermal decomposition reactions were calculated from the thermogravimetric curves. The kinetic analysis of the thermogravimetric data was performed by using several methods such as MacCallum‐Tanner (MT), van Krevelen (vK), Madhusudanan‐Krishnan‐Ninan (MKN), Wanjun‐Yuwen‐Hen‐Cunxin (WYHC), Horowitz‐Metzger (HM) and Coats‐Redfern method (CR) based on the single heating rate. Most appropriate methods were determined for each decomposition step according to the least‐square linear regression. The Ni(II), Cu(II) Co(II) and Zn(II) complexes displayed one‐ or two‐stage decomposition pattern when heating in a dynamic nitrogen atmosphere and metal oxides remained as end products of the complexes. The characterization of the end products of the decomposition was performed by X‐ray diffraction. 相似文献
12.
The authors recently published works in which the use of two novel equations for modeling the dispersive kinetics observed in various solid-state conversions are described. These equations are based on the assumptions of a ‘Maxwell-Boltzmann (M-B)-like’ distribution of activation energies and a first-order rate law. In the present work, it is shown that it may be possible to expand the approach to include mechanisms other than first-order, i.e. some of those commonly encountered in the field of thermal analysis, thus obtaining ‘dispersive versions’ of these kinetic models. The application of these dispersive kinetic models to the slightly sigmoidal, isothermal conversion-time (x-t) data of Rodante and co-workers for the degradation of the antibiotic, oxacillin, is described. This is done in an effort to test the limitations of the proposed dispersive models in describing kinetic data which is not clearly sigmoidal (i.e. as shown in previous works). Finally, it is demonstrated that, using graphical analysis, the typically sigmoidal x-t plots of first-order dispersive processes are the direct result of (asymmetric) activation energy distributions that are either ‘∩-shaped’ (for heterogeneous conversions) or ‘∪-shaped’ (for homogeneous conversions) in appearance, i.e. when the activation energy is plotted as a function of conversion. This finding lends support to the founding hypothesis of the authors’ approach for modeling dispersive kinetic processes: the existence of ‘M-B-like’ distributions of activation energies. 相似文献
13.
Nataa Stipanelov Vrande
i Branka Andri
i Ivka Klari Tonka Kova
i 《Polymer Degradation and Stability》2005,90(3):455-460
The thermooxidative degradation of poly(vinyl chloride)/chlorinated polyethylene blends of different compositions was investigated by means of isothermal thermogravimetry in flowing atmosphere of synthetic air at temperatures 240–270 °C. The main degradation processes are dehydrochlorination of PVC and CPE. For calculation of the apparent activation energy and apparent pre-exponential factor two kinetic methods were used: isoconversional method and Prout–Tompkins method. True compensation dependency between Arrhenius parameters, obtained using Prout–Tompkins model, was found. Calculated kinetic parameters of isothermal thermooxidative degradation are close to those from non-isothermal degradation and confirm the assumption of the main degradation process in PVC/CPE blends. 相似文献
14.
15.
G. Várhegyi M. J. Antal Jr. Piroska Szabó Emma Jakab F. Till 《Journal of Thermal Analysis and Calorimetry》1996,47(2):535-542
The complexity of the phenomena which arise during the heating of the various substances seldom can be described by a single reaction kinetic equation. As a consequence, sophisticated models with several unknown parameters have to be developed. The determination of the unknown parameters and the validation of the models requires the simultaneous evaluation of whole series of experiments. We can accept a model and its parameters if, and only if we get a reasonable fit to several experiments carried out at different experimental conditions. In the field of the thermal analysis the method of least squares alone seldom can select abest model or abest set of parameter values. Nevertheless, the careful evaluation of the experiments may help in the discerning between various chemical or physical assumptions by the quality of the corresponding fit between the experimental and the simulated date. The problem is illustrated by the thermal de-composition of cellulose under various experimental conditions.This research program was funded by the National Science Foundation (grant INT 8914934), the US Hungarian Science and Technology Joint Fund (grants 90b-22 and 93b-375), the Hungarian National Research Fund (OTKA, grant 3077/91) and the Coral Industries Endowment. 相似文献
16.
Combustion of brick-shaped carbonaceous materials
(carbon deposits from coke oven, coke and electrographite) was carried out
in thermobalance in static air. Analysis of kinetics of the process was carried
out using both classical (Arrhenius law) and newer (three-parametric equation)
methods. In classical approach two types of kinetic equations were used in
calculations: differential and integral. The results obtained show that, independently
on kinetic variables (α – conversion degree or m
– mass of sample) used in differential equations, kinetics of combustion
of brick-shaped carbonaceous materials is characterized by only one pair of
Arrhenius coefficients: activation energy (E)
and pre-exponential constant (A). At the
same time the integral equation demonstrates distinction in relation to methods
based on differential equations, generating higher activation energies and
separate isokinetic effect (IE). Parallel IE shows that kinetic analysis has
to encompass activation energy in connection to second coefficient, pre-exponential
constant A, depending on assumptions made
for kinetic equations. On the other hand three-parametric equation allows
describing kinetic of combustion in alternative way using only one experimental
value – initial temperature in form of point of initial oxidation (PIO)
– and also offers new methods of interpretation of the process. 相似文献
17.
M. Z. Duz Y. Tonbul A. Baysal O. Akba A. Saydut C. Hamamci 《Journal of Thermal Analysis and Calorimetry》2005,81(2):395-398
Summary The relationship between particle size and chemical composition of Hazro coal (origin: SE Anatolia, Turkey) has been examined by elemental analysis and by thermogravimetric pyrolysis. The chemical composition of the coal was determined by grinding sample particles physically and separating according to their size in mm by sieving. Particle size distribution of the coal and chemical composition of these fractions were given. The coal has been non-isothermally pyrolyzed in a thermogravimetric analyzer to determine the kinetic factors. Thermal gravimetric (TG/DTG) experiments were performed from ambient temperature to 800°C under a nitrogen atmosphere at heating rate 10 K min-1 with five different particle size ranges. Kinetic parameters of the samples were determined using a Coats and Redfern kinetic model, assuming a first-order reaction. Depending on the particle size of the coal samples, the mean activation energy values varied between 49.1 and 84.6 kJ mol-1. The results discussed indicate that activation energies increase as the particle size decreases. 相似文献
18.
建立了超高效液相色谱-串联三重四极杆质谱快速筛查和确证食品中的新品种甜味剂爱德万甜的方法。样品经甲醇-水(50:50,v/v)超声提取,离心,取上清液过滤膜。采用Agilent SB-C18(150 mm×2.1 mm,5 μm)色谱柱分离,梯度洗脱,在电喷雾离子源的正离子电离模式下,用多反应监测(MRM)方式采集数据,根据保留时间和定性离子对进行定性筛查,根据峰面积和定量离子进行定量分析。结果表明:方法检出限(LOD)为0.03 mg/kg(信噪比S/N ≥ 3),定量限(LOQ)为0.10 mg/kg(S/N ≥ 10),回收率为80.3%~98.0%,在0.01~1.0 mg/L范围内均有良好的线性,相关系数r2均大于0.997。该方法快速、简便易行、灵敏、准确,适用于饮料、酸奶和果冻中的新品种甜味剂爱德万甜的批量检测。 相似文献
19.
A kinetic study on the thermal behaviour of chitosan 总被引:1,自引:0,他引:1
F. A. López A. L. R. Mercê F. J. Alguacil A. López-Delgado 《Journal of Thermal Analysis and Calorimetry》2008,91(2):633-639
The thermal behaviour of chitosan was studied by means of thermogravimetry, mass spectrometry and infrared spectrometry. Kinetic
parameters were obtained by advanced kinetic evaluation (differential isoconversional analysis) from DSC curves, in non-isothermal
conditions, at several heating rates, between 5 and 30°C min−1. The results showed that the decomposition of chitosan does not follow a single mechanism because both the activation energy
and the pre-exponential factor are not constant during the course of the reaction. A comparison with the results obtained
by applying different conventional calculating methods is also shown. 相似文献
20.
垃圾中可燃物的燃烧动力学研究 总被引:28,自引:2,他引:26
采用热重法对六种垃圾中的可燃物的燃烧过程进行了研究,探讨了垃圾中可燃物燃烧过程的燃烧特性,并由它们的微分热重曲线计算出它们的一级反应动力学参数。各可燃物的燃烧特性可归纳为纤维类与聚合类,可燃物的活化能与着火点温度相对应,活化能与指前因子直接存在补偿效应。 相似文献