Kinetics of propellant decomposition

Equations for solid-state decompositions which are controlled by the phase-boundary movement and nucleation have been examined using ammonium perchlorate/polystyrene propellant decomposition at 503 K and 533 K. It was found that 3 different equations governed by the nucleation process show a good fit of data at these temperatures. However, the best fit was obtained for the following Avrami-Erofeev equation, [-In (1 - α]^1/4=kt.     

Kinetics of the decomposition of perpropionic acid

The decomposition of perpropionic acid, in the presence of manganese propionate catalyst is studied by the capacity-flow method. The reaction is found to be second order with respect to peracid concentration and first order with respect to catalyst concentration. The activation energy is 10.2 kcal/mol. The mechanism of the reaction is discussed along with the possible modes of by-product formation.     

Kinetics of calcium carbonate decomposition

Experiments on thermal decomposition of calcium carbonate were carried out in a thermogravimetric analyser under non-isothermal conditions of different heating rates (10 to 100°C/ min). A new technique for determining the kinetic parameters from non- isothermal thermogravimetric data was described. The activation energy and frequency factors were determined from the proposed method and also by the widely used Coats and Redfern method. The kinetic compensation effect between the activation energy and frequency factors obtained from both the methods were found to be very consistent and are in very good agreement with the literature values. The activation energy and frequency factors were also determined from isothermal experiments in the temperature range from 680 to 875°C. The activation energy and frequency factors determined from isothermal data using initial rate method were also found to be in very good agreement with the above results. It is also found that the kinetic parameters determined by isothermal analysis were consistent with the values determined by non-isothermal analysis.     

Kinetics of methane hydrate decomposition

The kinetics of methane hydrate decomposition was studied using a semibatch stirred-tank reactor. The decomposition was accomplished by reducing the pressure on a hydrate slurry in water to a value below the three-phase equilibrium pressure at the reactor temperature. The data were obtained at temperatures from 274 to 283 K and pressures from 0.17 to 6.97 MPa. The stirring rates were high enough to eliminate mass-transfer effects. Analysis of the data indicated that the decomposition rate was proportional to the particle surface area and to the difference in the fugacity of methane at the equilibrium pressure and the decomposition pressure. The proportionality constant showed an Arrhenius temperature dependence. An estimate of the hydrate particle diameters in the experiments permitted the development of an intrinsic model for the kinetics of hydrate decomposition.     

Kinetics of the heterogeneous catalytic decomposition of methane

Experiments have clearly demonstrated that dissociation of CH₄ on (supported) metal catalyst (e.g. Pt, Ru, Rh, Ir, Pd) occurs to give hydrogen, a small amount of ethane and surface carbonaceous species. For this catalytic decomposition of methane and its conversion into higher hydrocarbons (especially to ethane and surface carbon) model has been developed to investigate the kinetics. Rate constants of the elementary steps have been estimated. The problem with experimental data (especially for the surface species CH_m-s) is also treated for the sake of future improvement in the kinetics studies. A comparison with catalytic hydrogenolysis of ethane kinetics is also outlined.     

Kinetics of thermal decomposition of hydromagnesite

The thermal decomposition of hydromagnesite has been studied using thermogravimetric analysis. The experiments were conducted in a nitrogen atmosphere with pellets of hydromagnesite in the temperature range 300 to 550°C, and also with powder samples under non-isothermal conditions at a heating rate of 10°C/min. It is found that the reaction proceeds in two stages: dehydration followed by decomposition. The dehydration reaction is controlled by external mass transfer whilst the decomposition reaction is controlled by both external and internal mass transfer. The activation energy for the dehydration reaction was found to be 2.67 × 10⁷ J/kmol. From the non-isothermal analysis the activation energy for the decomposition of magnesium carbonate was found to be 1.62 × 10⁸ J/kmol.     

Thermal decomposition of a blackband ironstone. II. Kinetics

Blackband ironstone and siderite have been separately decomposed in a fluidised bed of sand in an atmosphere of nitrogen and the progress of reaction followed by a ‘volatile matter’ test. For the ironstone in the temperature range 370–570°, the residual volatile matter (V_R) after a time (t) between 10 sec and 60 min. was given by the expression V_R = A – B log t, where A and B are constants for a given temperature. The kinetics of decomposition of siderite at 455 and 485° were first-order with an activation energy of 51 kcal. /mole. It is concluded that blackband ironstone appears to decompose by a large number of independent first-order reactions having a range of activation energies showing a peak frequency near 50 kcal.     

Kinetics of enzymatic hydrolysis of polysaccharide-rich particulates

Both pH and volatile fatty acid (VFA) inhibit the hydrolysis of particulate organic waste. It is not clear yet whether VFA or pH is the dominant factor in hydrolysis inhibition. The effects of pH and acetate on the enzymatic hydrolysis of potato samples containing mainly carbohydrate were studied at fixed pH values (5–9) and with/without 20 g L⁻¹ acetate. The leaching liquors were refreshed at prescribed intervals. Experimental results showed that both pH and acetate influenced the hydrolysis of carbohydrate, but that pH was more influential than acetate.     

Kinetics of thermal degradation of semi-stiff macromolecules II. Poly-N-vinyl-carbazol

The thermal degradation of poly-N-vinyl-carbazol (PVK) has been studied using flash pyrolysis, controlled pyrolysis and programmed thermogravimetry analysis techniques. The degradation products have been analyzed using gas-liquid chromatography and mass spectrometry as separation and characterization techniques. The examined PVK has been prepared by free radical polymerization in benzene using AIBN as catalyst. It is shown from experimental results that PVK breaks up almost completely into the monomer through a stepwise unzipping mechanism. The composition of the pyrolyzate allows to propose a mechanism for the polymer degradation. Thermal degradation rates have been analyzed using a multiple heating rates procedure. A value of 40 kcal/mol has been found for the overall activation energy of depolymerization and a value approximately equal to one for the order of reaction. Some thermodynamic considerations have been made in order to explain the value of the activation energy of the whole process. A mechanism is suggested.     

Complex impedance spectra of porous electrode with fractal structure

Transmission line model (TLM) is often used for the analysis of porous electrode since the current distribution in the pore can be calculated. In the present paper, the TLM is applied to the impedance analysis of complicated porous electrode with fractal structure. Activated carbon is used as electrode material for electric double layer capacitor and its pore has branch structure. Considering the fractal structure of the activated carbon, we proposed new equivalent circuit with TLM for three sizes of pores: macropore, mesopore and micropore. In this model, we defined the ratio ξ of electric double layer parts in whole inner wall of the pore because the inner wall is separated to electrolyte/electrode interface and branch base parts. Calculated electrochemical impedance of blocking electrode shows the lumped constant region in low frequency range and the distributed constant region in low frequency range. General TLM yields the straight line with slope of 45° in the distributed constant region on the Nyquist plots. In the present analysis, it was found that the slope was 22.5° at ξ = 0 in the case of double-pores (macropore and mesopore) and 11.25° at ξ = 0 in the case of triple-pores (macropore, mesopore and micropore).     

Kinetics of the thermal decomposition of alkyl hydrogen sulphates

First order rate constants and Arrhenius parameters have been obtained for the thermal decomposition of 1-hexadecyl hydrogen sulphate. From published data on thermal decomposition of lauryl hydrogen sulphate and lauryl ether hydrogen sulphate, first order rate constants and Arrhenius parameters have been obtained. The agreement between the two sets of data for the two alkyl hydrogen sulphates is within the 95% confidence limits, a combined Arrhenius plot giving an activation energy of 12.69 ± 1.97 K cal mol⁻¹ and pre-exponential factor of 10^{(4.68 ± 1.24)} sec⁻¹. For lauryl ether hydrogen sulphate, a 3-point Arrhenius plot gives an activation energy of 9.4 K cal. mol⁻¹ and a pre-exponential factor of 10² sec⁻¹.     

发泡剂AC分解动力学研究

采用正交试验法进行发泡剂AC分解动力学研究。结果表明，发泡剂AC分解速率随温度升高而增大，分解活化能随发泡剂AC含量的增大而增大;橡胶体系中发泡剂AC在160℃分解速率最低，体系中发泡剂AC含量较小导致其分解活化能小于发泡剂AC／发泡助剂混合体系的分解活化能。     

Kinetics of thermal decomposition of unsaturated polyester resins with reduced flammability

In this article, the kinetics of thermal decomposition of unsaturated maleic–phthalic polyester resins, flame‐retarded with zinc hydroxystannate, was studied by thermogravimetric analysis at different heating rates. At the first stage, it was found, on the basis of isoconversional analysis by the methods of Friedman and of Ozawa–Flynn–Wall, that the value of the (apparent) activation energy (E) characteristically changes in three steps during the degradation. Further kinetic studies using nonlinear regression methods revealed the best fits for both pristine and stabilized resins. It was observed that the course of E versus the degree of conversion (α) during degradation of zinc hydroxystannate‐containing resins (α > 0.8) was characterized by higher values of E—this phenomenon can be explained in terms of the flame‐retardation action of zinc hydroxystannate, which is believed to operate primarily in the condensed phase. At the next stage, kinetic analysis by the nonregression method was performed to find the kinetic model [f(α) function] of the decomposition process; hence, for pristine resin, the best fit was found for the Avrami–Yerofeeyev model (nuclei growth), and for stabilized samples, the nth‐order function with catalysis proved to be the best approximation. The obtained kinetic parameters in the form of E, the preexponential factor A, and the model function f(α) allow a prediction of the polyester resin's thermal behavior in an extrapolated range of degree of conversion, time, and temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2851–2857, 2003     

Three-dimensional-printed holistic reactors with fractal structure for heterogeneous reaction

Holistic catalytic reactors with fractal structures have attracted growing attention in heterogeneous reactions because of their advantages of improved mass transfer and easy separation. Herein, a cost-efficient and straightforward design strategy that combined three-dimensional printing and electroless deposition was presented to construct dynamic, holistic stirred reactors with the fractal structure. The conversion factor α of the fractal impeller is 65.01 mmol m⁻² h⁻¹ with a large volume of reactant (80 ml), which is 1.7 times that of the normal impeller with the same loading of Ag catalysts. Experimental results and simulation analysis demonstrate that the fractal impeller significantly improves the catalytic performance by enhancing mass transfer and spatial dispersion in the reaction. Moreover, the holistic impeller could be reused 10 times without obvious loss of catalytic performance, and easily separated from the reaction system. The structural design of fractal reactors will open the way for high-efficiency dynamic heterogeneous catalytic reactors.     

Kinetics of glucose decomposition in formic acid

Cellulose is abundantly available in the form of forestry and agricultural lignocellulosic residues. These residues offer the most potential source for the production of cellulosic glucose, which is a prerequisite for the sustainable production of glucose-based fuels and chemicals. Acid catalysis is one path to lignocellulosic glucose and further to its dehydration end products. Furthermore, many studied lignocellulose pretreatment methods for enzymatic hydrolysis are carried out in acidic conditions, in which the unwanted release of hemicellulose-based glucose and its further reactions to harmful end products are possible. Thus, in order to maximize glucose production from non-food cellulosic raw materials, data on the kinetics of cellulose decomposition and formation rates of end products are required. Glucose decomposition is a complex reaction system that has often been modelled with empirical, simplified models. In this study, a kinetic model was developed for glucose decomposition in formic acid solution. The experimentation was carried out in batch reactors at 180-220 °C in 5-20% (w/w) formic acid. The model developed relies on a mechanistic step through an unknown substance and gives excellent correspondence to the experimental data despite the pseudo-elementary nature of the model structure.     

分形结构二维金属镍枝晶的制备与分析

以环形金属镍为阳极,石墨芯为阴极,利用点电极电沉积法制备了具有明显分形结构的二维金属镍枝晶;再以平行板金属镍为阳极,石墨板为阴极,用自行设计的试验设备,通过喷射电沉积法制备了准二维金属镍枝晶簇。采用计算机软件,求得点电极电沉积和平行板电极喷射电沉积所得沉积物的分形维数分别为1.556387和1.753856。两种电沉积方法都适用于金属枝晶的研究。点电极电沉积过程中,电流随时间的延长而逐渐增大;平行板电极喷射电沉积过程中,电压随时间的延长而逐渐降低。     

氧化铝上吸附平衡与动力学的分形特性

在实验测定氧化铝吸附氮气的平衡和动力学过程的基础上 ,由平衡数据得到分形维数 ,对动力学结果分别用欧氏几何和分形几何的动力学模型进行处理 ,比较两种方法得到的扩散系数之间的差别。结果表明 :粉状氧化铝的分形维数为 2 .12 ;采用分形动力学模型得到的扩散系数同欧氏几何扩散模型的结果不一样 ,扩散系数不随浓度的变化而改变 ;而欧氏几何扩散模型中的扩散系数随浓度变化发生改变 ,且变化符合Darken关系     

Kinetics and mechanism of thermal decomposition of HMX with metal cupferronate additives

The kinetic features of the thermal decomposition of HMX with metal cupferronate additives, in which the nucleophilic detachment of a proton in HMX by a phenylnitric-oxide anion-radical plays an important role, are established. The logarithms of the rate constants for the decomposition of HMX correlate with the ratio of the charge of the metal cation in the cupferronate to its radius, which indicates a different reactivity of the anion-radical owing to the polarizing effect of the cation. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 3, pp. 52–56, May–June 1999.