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1.
Thermogravimetry is used for regeneration of the alumina catalyst which was deactivated by coke, formed in the transformation
of 1,3-butadiene in a fixed bed continuous flow reactor. The Vyazovkin model-free kinetic analysis has been applied to data
on thermal oxidation of carbonaceous deposits on the catalyst. This analysis has allowed us to estimate the activation energy
( E) as a function of α (conversion) and to predict the time required to remove coke at a given temperature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
A kinetic study on decomposition processes of some penicillin and some commercial drugs was carried out. As expected by the
complex structures of penicillins, several steps with different activation energies occurred in their decomposition processes.
Model-fitting and model-free kinetic approach were applied to non-isothermal and isothermal data.
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 penicillins decomposition.
The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation
energies on the extent of conversion. The complex nature of the multi-step process of the studied compounds was more easily
revealed using a broader temperature range in non-isothermal isoconversional method. The failure in the model fitting method
did not allow calculating storage times. Model-fitting and model-free methods, both isothermal and non-isothermal, showed
that F1 mechanism is able to describe decomposition processes for drugs (having Phosphomycin salts as active component) for
which a single decomposition process occurs. Statistical analysis allowed us to select reliable kinetic parameters related
to the decomposition processes for these last compounds. This procedure showed that the values obtained by extrapolation,
outside the temperature range where the processes occurred must be used with caution. Indeed half-life and shelf-life values,
commonly extrapoled at room temperature, seemed to be unrealistic.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Mold fluxes develop important functions during steel continuous casting process. To obtain a free-defect product the melting
rate of mold flux is an important property to be controlled. The melting rate depends on the reactivity of carbonaceous material
added to these powders as carbon source. In this article, the decomposition kinetic of two carbonaceous materials added to
mold flux: petroleum coke and synthetic graphite, was analyzed. By measuring mass loss at different heating rates the decomposition
reaction was determined on both types of materials. Applying several kinetic models of non-isothermal decomposition, the average
activation energy E = 48 kJ/mol to mold powder with 15 wt% coke and E = 67 kJ/mol to one with 15 wt% graphite was determined. A first order of reaction ( n = 1) associated to the decomposition process was assumed to both types of materials. The lower activation energy presented
by mold powder-15 wt% petroleum coke indicated a higher reactivity of this material. A higher level of variation of E and n values with decomposition degree and temperature observed in the powder with petroleum coke was associated to a less thermally
stable material along with a more complex degradation process. 相似文献
4.
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
5.
The kinetics and mechanism of the structural transformation of 2-(5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-N-(2-phenylethyl)-ethanamide
in non-isothermal conditions were studied by using isoconversion as well as non-isoconversion techniques. It was shown that
the crystal, Z-form of compound, was stable in the temperature range from room temperature to melting point, when E-form of compound was formed. This process involves the breaking of crystal structure and the forming of glass material as
a new phase, which by cooling forms crystal of the E-form of compound very slowly. The dependences of kinetic parameters on fractional extent conversion were determined indicating
a very complex process which involves more than one elementary step, as can be expected for most solid state reactions. The
possible mechanism of the process was discussed according to the algorithm concerning the form of these dependences. The evaluation
of kinetics parameters and isokinetic relationships were done by combination of model fitting and model-free approach. 相似文献
6.
The thermal decomposition of three new reagent cyclohexylamine- p-tolylglyoxime (L 1H 2), tertiarybutyl amine- p-tolylglyoxime (L 2H 2) and secondary butylamine- p-tolylglyoxime (L 3H 2 and their Co-complexes were studied by both isothermal and nonisothermal methods. As expected, the complex structure of Co-complexes,
different steps with different activation energies were realized in decomposition process. Model-fitting and model-free kinetic
approaches were applied to nonisothermal and isothermal data. The kinetic triplet ( f(α), A and E) related to nonisothermal model-fitting method can not be meaningfully compared with values obtained from isothermal method.
The complex nature of the multi-step process of the studied compounds was more easily revealed using a wider temperature range
in nonisothermal isoconversional method. 相似文献
7.
Solid bisphenol-A epoxy resin (DGEBA) of medium molecular mass was cured using o-tolylbiguanide (TBG) as cross-linking agent. In order to improve the kinetics of the reactive system, two Lewis acid catalysts
(erbium(III) and ytterbium(III) trifluoromethanesulfonates) were added in proportions of 1 phr. The kinetic study was performed
by dynamic scanning calorimetry (DSC) and the complete kinetic triplet ( E, A and g(α)) determined. The kinetic analysis was performed with an integral isoconversional procedure (model-free), and the kinetic
model was determined by the Coats-Redfern method and through the compensation effect (IKR). All the systems followed the m=1.5/ n=0.5 isothermal curing model simulated from non-isothermal experiments. The addition of a little proportion of ytterbium or
erbium triflates accelerated the curing process. In order to extract further information about the role of the lanthanide
triflates added to epoxy/TBG systems, the kinetic results were compared with our previous kinetic studies made on DGEBA/lanthanide
triflates initiated systems. 相似文献
8.
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.
The objective of this research work was to investigate the kinetics of esterification of acetic acid with n-butanol through the variation of experimental parameters. The reaction mixture was catalyzed heterogeneously by a sulfonated catalyst in batch mode of operation. The catalyst was prepared from abundantly available agro-waste, Cajanus cajan husk by chemical activation process, which produces a carbon-based solid catalyst with high surface area. The catalyst was characterized by a Brunauer-Emmet-Teller surface analyzer and Fourier transform infrared spectroscopy to know the surface morphology. Process parameters such as contact time, reaction temperature, and catalyst loading, which can influence the extent of conversion of reactants, were studied. Furthermore, the kinetic investigation was also carried out to estimate the kinetic parameters for uncatalyzed and catalyzed reaction using the second-order pseudo-homogeneous (P-H), Eley-Rideal (E-R), and Langmuir-Hinshelwood (LH) kinetic models for this research work. The kinetic parameters such as activation energy, preexponential factor, and the thermodynamic parameters such as enthalpy and entropy were estimated for uncatalyzed and catalyzed reactions using these three models. The process conditions were optimized for catalyzed and uncatalyzed reactions to obtain the maximum product yield by minimizing root mean square error of each experimental data using the MS-excel solver tool. Thus, this study reveals the high potential of an agro-waste, Cajanus cajan husk as raw material for the synthesis of catalyst. The results show that the E-R model is more appropriate for predicting the dynamic data of an esterification reaction, as the forward rate of reaction estimated using the E-R model are more modified than P-H and L-H models. 相似文献
10.
在固定床反应器中研究了甲醇制烯烃反应过程中SAPO-34分子筛催化剂的积炭动力学,分别得到了催化剂积炭量与反应温度、剂醇比的经验关联式。结果表明,催化剂床层存在明显的积炭分布,在450 ℃,甲醇WHSV为15 h-1,催化剂积炭量随催化剂反应运行时间(Time on Stream, TOS)为25 min时,床层入口处的积炭量平均为9.56%,而出口处的积炭量平均为3.20%,属于平行失活,积炭主要来源于甲醇生成的高碳中间体,这些中间体在生成低碳烃的同时生成积炭。从积炭的生成机理出发,得到了SAPO-34分子筛催化剂的积炭动力学机理模型,将催化剂积炭量与一定催化剂停留时间内反应过程中甲醇的转化量相关联,该模型形式同样简单,能够较好地拟合实验数据。 相似文献
11.
The kinetic behavior of partial oxidation of methane to syngas over a LiLaNiO/γ -Al 2O 3 catalyst was investigated under steady-state conditions. Under kinetic control, syngas, to a large extent, is formed via a direct partial oxidation (DPO) scheme. CO and CO 2 are formed in parallel by oxidation reaction over the catalyst. The active sites in the kinetically controlled regime are
different from those in the non-kinetic regime, thus the CO selectivity in the former may not increase with temperature.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
12.
This study describes the physico-geometrical mechanism and overall kinetics for the multistep thermal dehydration of barium titanyl oxalate tetrahydrate (BTO). The thermal dehydration kinetics of BTO was studied at four different linear heating rates under non-isothermal conditions. The reaction kinetics was performed using differential scanning calorimetry (DSC) and the curves obtained were analysed using different isoconversional model-free equations and the values are found to be compatible with each other. The kinetic deconvolution principle is used for identifying the partially overlapped kinetic processes of the thermal dehydration of BTO, and it occurs in two stages. The overall reaction kinetics parameters calculated via kinetic deconvolution of the sample indicate the multistep nature of the process and the kinetic analysis of the non-isothermal data of this reaction model shows that the reaction is best described by Sestak–Berggren (m, n) empirical kinetic model. The prepared sample was identified and characterized by means of FT-IR, XRD, SEM, and TEM. 相似文献
13.
Summary The effect of La 2O 3 and TiO 2 on product selectivity, methane conversion and coke formation over NiO/MgO/ α -Al 2O 3 catalyst were studied in a simultaneous steam and CO 2 reforming of methane to syngas. La 2O 3 and TiO 2 were added to the catalyst via incipient wetness impregnation and bulk precipitation techniques and catalyst activity was tested in a fixed bed quartz reactor. Results reveal that although the addition of these oxides has no effect on the product selectivity and methane conversion, but can reduce coke formation on the surface of the catalysts as it can enhance the mobility of lattice oxygen anions. The results further show that the catalysts prepared by bulk precipitation technique decrease the coke formation more effectively. 相似文献
14.
Carbon deposition via coke formation is one of the critical problems causing catalyst deactivation during the reforming of hydrocarbons. An effort was made to regenerate the catalyst (Ni/γ-alumina) by oxidation methods. Two approaches were carried out for the regeneration of the deactivated catalyst. The first one involves the plasma treatment of the deactivated catalyst in the presence of dry air over a temperature range of 300~500 °C, while the second one only the thermal treatment in the same temperature range. The performance of the regenerated catalyst was evaluated in terms of C 4H 10 and CO 2 conversions and the physicochemical characteristics were examined using a surface area analyzer, an elemental analyzer, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was observed that the carbon deposit (coke) on the catalyst was about 9.89 wt% after reforming C 4H 10 for 5 h at 540 °C. The simple thermal treatment at 400 °C reduced carbon content to 6.59 wt% whereas it was decreased to 3.25 wt% by the plasma and heat combination. The specific surface area was fully restored to the original state by the plasma-assisted regeneration at 500 °C. As far as the catalytic activity is concerned, the fresh and regenerated catalysts exhibited similar C 4H 10 and CO 2 conversion efficiencies. 相似文献
15.
Summary: Thermogravimetric analysis and stirred tank reactor techiques were used to study the kinetic of polycondensation of bis-hydroxy ethylene terephthalate catalyzed by titanium tetrabutylate. Polycondensation reaction can be modelled best with a second order reaction with respect to hydroxyl end groups concentration. Titanium tetrabutylate is a precursor and needs preactivation for polycondensation catalysis. Kinetic data depends on the mode of operation in thermogravimetric analysis. In nonisothermal mode, the overall activation energy was determined by model-free method and the pre-exponential factor was found to be affected by catalyst concentration. The kinetic study of isothermal reaction in thermogravimetric analysis is complex due to lack of a precise way to reach desired isothermal temperature and high activity of the catalyst. Titanium catalyst shows higher activity and lower selectivity than antimony catalyst but its activity is affected by the nature of ligands. 相似文献
16.
The thermal decomposition behavior and kinetic parameters of the exothermic decomposition reactions of the title compound in a temperature‐programmed mode have been investigated by means of DSC, TG‐DTG and lower rate Thermolysis/FTIR. The possible reaction mechanism was proposed. The critical temperature of thermal explosion was calculated. The influence of the title compound on the combustion characteristic of composite modified double base propellant containing RDX has been explored with the strand burner. The results show that the kinetic model function in differential form, apparent activation energy Ea and pre‐exponential factor A of the major exothermic decomposition reaction are 1‐ a,207.98 kJ*mol ?1 and 10 15.64 s ?1, respectively. The critical temperature of thermal explosion of the compound is 312.87 C. The kinetic equation of the major exothermic decomposition process of the title compound at 0.1 MPa could be expressed as: dα/d T=10 16.42 (1–α)e‐2.502×10 4/ T As an auxiliary catalyst, the title compound can help the main catalyst lead salt of 4‐hydroxy‐3,5dinitropyridine oxide to enhance the burning rate and reduce the pressure exponent of RDX‐CMDB propellant. 相似文献
17.
The degradation kinetics of the ABS terpolymer (acrylonitrile-butadiene-styrene) was investigated by means of thermogravimetric
analysis. The samples were heated from 30 to 900°C in nitrogen atmosphere applying three different heating rates: 5, 10 and
20°C min −1. The Vyazovkin model-free kinetic method was used to calculate the activation energy ( E) of the degradation process as a function of conversion and temperature. Between 20 and 80% of conversion, E was calculated
and the figures were: for ABS GP, E is 204.5±11.5 kJ mol −1 (medium value); for ABS HI, E is 239.0±9.8 kJ mol −1; for ABS HH, E is 242.4±5.4 kJ mol −1. 相似文献
18.
Direct catalytic propane dehydrogenation (PDH) to obtain propylene is a more economical and environmentally friendly route for propylene production. In particular, alumina-supported Cr 2O 3 catalysts can have better potential applications if the acidic properties could be tuned. Herein, a series of rod-shaped porous alumina were prepared through a hydrothermal route, followed by calcination. It was found that the acidity of the synthesized alumina was generally lower than that of the commercial alumina and could be adjusted well by varying the calcination temperature. Such alumina materials were used as supports for active Cr 2O 3, and the obtained catalysts could enhance the resistance to coke formation associated with similar activity in PDH reaction compared to the commercial alumina. The amount of coke deposited on a self-made catalyst (Cr-Al-800) was 3.6%, which was much lower than that deposited on the reference catalyst (15.7%). The lower acidity of the catalyst inhibited the side reactions and coke formation during the PDH process, which was beneficial for its high activity and superior anti-coking properties. 相似文献
19.
A novel nanocomposite catalyst for thermal degradation of the ammonium perchlorate (AP) has been synthesized, and its effect on the thermal behavior of AP has been investigated. Preparation of the catalyst was carried out via functionalization of the graphene oxide with phenyl isocyanate and its noncovalent bonding to catocene. The catalytic activity of the catalyst was studied by thermal gravimetric analysis/differential scanning calorimetry at various heating rates. In addition, the effect of the catalyst on the AP thermal decomposition has been investigated by Kissinger and Friedman methods as two model-free methods for calculation of the activation energy parameter. According to the Kissinger method calculations, the Ea of AP decomposition reduced about 151 kJ⋅mol −1 lower than the reported value for pure AP in the presence of the catalyst. Calculation of the Ea value for various reaction conversion rates by the Friedman method also confirmed the Kissinger method results. 相似文献
20.
The thermal polymerization kinetics of dimethacrylate monomers was studied by differential calorimetry using non-isothermal
experiments. The kinetic analysis compared the following procedures: isoconversional method (model-free method), reduced master
curves, the isokinetic relationship (IKR), the invariant kinetic parameters (IKP) method, the Coats-Redfern method and composite
integral method I. Although the study focused on the integral methods, we compared them to differential methods. We saw that
even relatively complex processes (in which the variations in the kinetic parameters were only slight) can be described reasonably
well using a single kinetic model, so long as the mean value of the activation energy is known ( E). It is also shown the usefulness of isoconversional kinetic methods, which provide with reliable kinetic information suitable
for adequately choosing the kinetic model which best describes the curing process. For the system studied, we obtained the
following kinetic triplet: f(α)=α 0.6(1−α) 2.4, E=120.9 kJ mol −1 and ln A=38.28 min −1. 相似文献
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