Kinetic Parameters Of Decomposition Reaction Research Articles

Entropy generation rate minimization for sulfur trioxide decomposition membrane reactor

Sulfuric acid decomposition is the critical reaction in sulfur-iodide thermochemical cycle to produce oxygen. Sulfuric acid can decompose spontaneously into sulfur trioxide (SO3) and water, and SO3 continues to decompose into oxygen and sulfur dioxide. The application of membrane reactor can effectively improve the conversion rate of SO3 and thermal efficiency of sulfur-iodide cycle. The decomposition of SO3 requires the absorption of a large amount of heat due to its highly endothermic properties, and there are many irreversible processes such as heat transfer, mass transfer, chemical reaction and friction flow in the SO3 membrane reactor. Therefore, it is necessary to conduct thermodynamic analysis and optimization of the decomposition process to reduce the irreversible loss of the membrane reactor system. In this paper, a finite time thermodynamic model of SO3 decomposition membrane reactor is established, and the kinetic parameters of decomposition reaction are deduced and calculated based on experimental data. Firstly, the membrane reactor heated by hot helium gas is solved and used as reference reactor. Secondly, optimal control theory is used to optimize the reference reactor under fixed reactant inlet conditions and outlet conversion rate with total entropy generation rate minimization as optimization objective. The total entropy generation rate of Opt-1 reactor is reduced by 32.7% compared with the reference value. For variable reactor length, the total entropy generation rate of Opt-2 reactor is quadratic optimum at L=0.72 m, which is 34.7% less than the reference value. It is found that the reduction of total entropy generation rate in optimal reactors is mainly achieved by minimizing the entropy generation rate in heat transfer process. The distribution of local entropy generation rate is relatively uniform in the middle position, approximately consistent with the principle of equalization of entropy production rate. The conclusions obtained herein can provide guidelines for the energy-saving design of SO3 decomposition membrane reactors.

Solid–liquid equilibrium and thermochemical properties of the TNT–DINA system

Melting is a basic physicochemical process, used in examination of explosive mixtures elaborated by casting. In this paper, the melting process of TNT–DINA two-component mixture was analysed. Phase transformations of the system were investigated by means of differential scanning calorimetry. Several endothermic transformations were observed, with one being associated with the melting process of TNT–DINA eutectic mixture. A phase diagram was developed, which served to determine the composition of TNT–DINA eutectic mixture (DINA mole fraction of 0.69) as well as a melting point value (312.6 K). At high TNT contents, resultant low-temperature endothermic transformations may be associated with the solid-solid transformations. Kinetic parameters of decomposition reaction of TNT–DINA eutectic mixture were determined, which amounted to aEa = 157 ± 4 kJ mol−1, logA = 14.81 (for the degree of conversion of 0.03).

Runaway reaction and thermal hazards simulation of 4-amino-1,2,4-triazole picrate by HP-DSC and ARC

4-Amino-1,2,4-triazole picrate (4-ATPA) is a type of ionic liquids, as well as an explosive with sound thermal stability and low mechanical sensitivity. However, under upset conditions such as high temperature and pressure, an unpredictable explosion would occur and result in huge casualties and property losses. The purpose of this research was to evaluate the thermal hazard and runaway reaction of 4-ATPA through high-pressure differential scanning calorimetry and accelerating rate calorimeter. The kinetic parameters of decomposition reaction under non-isothermal and different pressure conditions were calculated based on the experiment results. Experimental results showed that the β and test pressure had no effect on the amount of heat release. Adiabatic experiments indicated that 4-ATPA had a high onset temperature at 196.8 °C. The maximum self-heating rate (3567.9 °C min−1) and pressure rise rate (202.0 bar min−1) revealed the vulnerability of 4-ATPA to suffer a disastrous explosion. Moreover, the apparent activation energy and pre-exponential factor were evaluated as 110.2 kJ mol−1 and 1.8 × 10−15 s−1 by ASTM E698 method. The correctness of the thermodynamic calculation formula under adiabatic conditions is verified by ARC tests. Finally, the thermal hazard risk of 4-ATPA was classified as unacceptable based on the risk classification criteria.

The Influence of Electrolytes Composition on the Dissociation Rate of Natural Gas Hydrates Obtained in Model Stratum Waters

The study of the hydrates formation and decomposition kinetics in solutions of electrolytes is of interest due to the possibility of natural gas storing and transporting in a hydrate state, since the presence of impurities in water is inevitable under appropriate industrial processes. The kinetic parameters of decomposition reactions of natural gas hydrates obtained in model solutions simulating the composition and concentration of stratum waters of East Siberian fields are studied. These deposits are located within the Leno-Tunguskaya and Lena-Vilyuiskaya oil and gas provinces (OGP). The deposits of the Leno-Tunguskaya OGP are characterized by abnormally low reservoir temperatures and pressures (10° C and 16 MPa). The stratum waters belong to the chloride-calcium type, and by the type of the predominant cation either to the calcium or to the sodium subgroup of waters. The mineralization of stratum water can reach 400 g / l and higher. The abnormal high reservoir pressure is 36.3 MPa, the temperatures reach +66 °C for deposits of the Lena-Viluiskaya OGP. Mineralization of stratum water is from 40 to 180 g / l, there may be waters of chloride-calcium (subgroups of calcium and sodium) and sodium bicarbonate (subgroup of sodium) types. Therefore, hydrates of natural gas were obtained in model solutions of calcium and sodium chlorides, and also in solutions of sodium bicarbonate. The rate constants of hydrate decomposition reactions are determined by the Erofeev equation. The shape of the kinetic curves of hydrate decomposition depends on the type and degree of the model stratum water mineralization. The values of the constants n for the decomposition reactions of all hydrate samples are greater than one. This means that these reactions occur in the kinetic region, that is, the rate of hydrates decomposition is determined by the rate of physical desorption of the gas from the clathrate lattice. It has been established that the rate of hydrates decomposition increases with increasing mineralization, and it is higher in the presence of calcium chloride solutions than sodium chloride.

Thermal decomposition and shelf-life of PETN and PBX based on PETN using thermal methods

The kinetics of exothermic reactions are important in assessing the potential of materials and systems for thermal explosion. In this paper, the thermal behavior and decomposition kinetics of pentaerythritol tetranitrate (PETN) and polymer-bonded explosives (PBXs) based on PETN were investigated using Thermogravimetric analysis (TGA) and Vacuum Stability Test (VST) methods. The Arrhenius activation energies and pre-exponential factors were determined by the Ozawa and Kissinger methods. Based on the overall kinetic parameters of decomposition reactions, the shelf-life of PETN and PBXs based on PETN could be calculated and predicted.

Measurements of H2O2 in low temperature dimethyl ether oxidation

H2O2 is one of the most important species in dimethyl ether (DME) oxidation, acting not only as a marker for low temperature kinetic activity but also responsible for the “hot ignition” transition. This study reports, for the first time, direct measurements of H2O2 and CH3OCHO, among other intermediate species concentrations in helium-diluted DME oxidation in an atmospheric pressure flow reactor from 490 to 750K, using molecular beam electron-ionization mass spectrometry (MBMS). H2O2 measurements were directly calibrated, while a number of other species were quantified by both MBMS and micro gas chromatography to achieve cross-validation of the measurements. Experimental results were compared to two different DME kinetic models with an updated rate coefficient for the H+DME reaction, under both zero-dimensional and two-dimensional physical model assumptions. The results confirm that low and intermediate temperature DME oxidation produces significant amounts of H2O2. Peroxide, as well as O2, DME, CO, and CH3OCHO profiles are reasonably well predicted, though profile predictions for H2/CO2 and CH2O are poor above and below ∼625K, respectively. The effect of the collisional efficiencies for the H+O2+M=HO2+M reaction on DME oxidation was investigated by replacing 20% He with 20% CO2. Observed changes in measured H2O2 concentrations agree well with model predictions. The new experimental characterizations of important intermediate species including H2O2, CH2O and CH3OCHO, and a path flux analysis of the oxidation pathways of DME support that kinetic parameters for decomposition reactions of HOCH2OCO and HCOOH directly to CO2 may be responsible for model under-prediction of CO2. The H abstraction reactions for DME and/or CH2O and the unimolecular decomposition of HOCH2O merit further scrutiny towards improving the prediction of H2 formation.

Estimating the explosion hazard of aromatic azo compounds

This paper gives the results of temperature measurements at the beginning of fast decomposition of nine commercial azo dyes under heating. The enthalpies of formation of three azo dyes are measured, and the parameters of their explosive transformation are calculated. It is shown that for the flash temperatures obtained using the kinetic parameters of decomposition reactions and calculated heats of explosion of azo dyes, the average deviation from experimental values is 4.5%.

The influence of grain size on decomposition reaction of limestone in dispersing state

The thermal behavior and kinetic parameters of decomposition reaction of limestone in a temperature-programmed mode were investigated by means of TG. The experimental results show that the kinetic model functions in different forms for the thermal decomposition reactions of different limestone grain sizes in dispersing state under the atmosphere of static air are 4(1−α)3/4 for small size limestone and (1−α) for large size limestone. Information was obtained on the relationship among the decomposition temperature, decomposition time, decomposition fraction, decomposition reaction rate constant and grain size of limestone.

Theoretical study on the atmospheric fate of carbonyl radicals: kinetics of decomposition reactions

The decomposition kinetics of a large set of representative R–CO carbonyl radicals has been studied theoretically. These radicals can either decompose into R + CO or, in the presence of oxygen, add to O2 to give acylperoxy radicals RC(O)O2. In this work, it is shown, by comparison to available experimental data, that reliable quantitative kinetic parameters for decomposition reactions can be obtained using DFT (B3LYP and BH&HLYP functionals) and ab initio G2(MP2) methods. Moreover, it has been demonstrated, by performing RRKM calculations, that the dissociation of carbonyl radicals under atmospheric conditions is not only governed by the height of the barriers, but that pressure effects can also play an important role and must be taken into account. Structure–activity relationships for the decomposition of R–CO radicals are presented according to the nature of the R group. The R–CO radicals, which are predicted to decompose under atmospheric conditions, contain chlorine or oxygen in the R group.

Analytical techniques estimating kinetic parameters for pyrolysis reaction of scrap tire rubbers

Analytical techniques using derivative thermogravimetry (DTG) and thermogravimetry analysis (TGA) were developed to estimate kinetic parameters for complex decomposition reactions of a heterogeneous substance like scrap tire rubbers. Two methods using non-isothermal techniques were proposed: (1) subtraction method and (2) method utilizing peak properties in a DTG curve. The former method is a reliable tool to determine the kinetic parameters of decomposition reaction of each compositional component, but it may run into a difficulty provided that tire components demonstrate similar thermal stability, thus leading to a complete superposition of peaks in a DTG curve. The subtraction method, however, can be applied after manipulating heating rate, since overlapped peaks can be separated by increasing or decreasing heating rate. Although the peak temperature and height (rate) in a DTG curve in the latter method were closely related to kinetic parameters of a single reaction, they can be rarely utilized to estimate the kinetic parameters of complex reactions because of disturbance arising from peak superposition.

Chromium(III) compounds with valine and 2-amino benzoic (anthranilic) acid ligands: Thermal decomposition and kinetic study in air and argon atmosphere

Thermal decomposition of chromium(III) compounds with valine and 2-amino benzoic (anthranilic) acid ligands has been studied up to 1000°C. Kinetic parameters of decomposition reactions have been calculated according to the Coats-Redfern method. Reaction paths are proposed and their agreement with the data from TG curves is checked.

TG-DSC同時測定による鉱物の熱分解反応の解析-とくにマグネサイトについて

The use of simultaneous TG and DSC data to evaluate kinetic parameters of decomposition reactions has been investigated. The procedure is described as below.1) Based on the method proposed by Achar et al., some probable kinetic equations (Function f(α), α is the fraction reacted) are found from TG or DSC data by trial and error. Then, kinetic parameters (activation energy Eand frequency factor Z) for each mechanism are evaluated. Theoretical TG or DSC curve is calculated from the obtained f(α), E, Z and heating rate q. The above results are examined from the degree of superimposition of the theoretical and experimental curves.2) Activation energy E is calculated by applying the Ozawa's method in a series of TG data obtained under different heating rates.3) The most probable mechanism and kinetic parameters are determined from the results obtained in 1) and 2).The above procedure has been applied to thermal decomposition of magnesite, giving the following results; the most probable kinetic equation R3(α), dα/dtk(1-α)2/3 (the phase boundary reaction of spherical symmetry): activation energy, 40 kcal/mol: frequency factor, about 109. The results are supported by those obtained by the Šatáva and Škvára's method, and are in good agreement with literature data.