强酸性阳离子交换树脂催化合成醋酸正丁酯的动力学研究

以强酸性阳离子交换树脂Amberlyst 15作为催化剂,研究了醋酸与正丁醇合成醋酸正丁酯的反应动力学;考察了搅拌速度、催化剂粒径、温度、催化剂用量,以及酸醇物质的量之比对醋酸转化率的影响;建立了拟均相动力学模型,对实验数据进行了拟合,并估算了相应的动力学参数.结果表明,由拟均相动力学模型得到的计算值与实验值吻合较好.     

Cure Kinetics of Poly(acrylonitrile-butadiene-styrene) Modified Epoxy–Amine System

The cure kinetics of epoxy based on the diglycidyl ether of bisphenol A (DGEBA) modified with different amounts of poly(acrylonitrile-butadiene-styrene) (ABS) and cured with 4,4′-diaminodiphenylsulfone (DDS) was investigated by employing differential scanning calorimetry (DSC). The curing reaction was followed by using an isothermal approach over the temperature range 150–180°C. The amount of ABS in the blends was 3.6, 6.9, 10 and 12.9 wt%. Blending of ABS in the epoxy monomer did not change the reaction mechanism of the epoxy network formation, but the reaction rate seems to be decreased with the addition of the thermoplastic. A phenomenological kinetic model was used for kinetic analysis. Activation energies and kinetic parameters were determined by fitting the kinetic model with experimental data. Diffusion control was incorporated to describe the cure in the latter stages, predicting the cure kinetics over the whole range of conversion. The reaction rates for the epoxy blends were found to be lower than that of the neat epoxy. The reaction rates decreased when the ABS contents was increased, due to the dilution effect caused by the ABS on the epoxy/amine reaction mixture.     

Kinetics of Maillard reaction in a chicken meat model system using a multiresponses modeling approach

This research aimed to study the Maillard reaction pathway in chicken meat. Owing to the complexity of real chicken meat, which is composed of many different types of amino acids and reducing sugars, the experiment was initiated with a glucose/lysine model system with the same concentration ratio of reactants as found in chicken meat. By considering glucose as the rate-limiting substrate, a kinetic model of the glucose/lysine model system was developed. Methylglyoxal (MG) was found to be the principal important α-dicarbonyl compound intermediates that further reacted to form melanoidins. Pyridine was a major volatile compound in this model system. The optimized kinetic model was then further validated in a chicken extract, for which the Maillard reaction mechanism has not been elucidated. However, the kinetic model of the glucose/lysine system could not explain the Maillard reaction in the chicken extract, presumably because both types of intermediates and reaction pathway depend on the reactants. Thus, a kinetic model of the Maillard reaction in the chicken extract was developed based on the main types of detected intermediates. Overall, MG was the central intermediate and acted as a substrate for the formation of furfural, volatile compounds, melanoidins, and unknown carbonyl compound(s) (C_n). Pyrazines and aldehydes were the major volatile compounds in the chicken extract.     

Pd/C催化松脂分子间氢转移反应的集总动力学

以Pd/C为催化剂,在改进的动力学实验装置上研究了松脂分子间氢转移反应的集总动力学.在消除内、外扩散影响的条件下,在线跟踪反应产物并用气相色谱法测定反应体系组成随时间的变化,构造了Pd/C催化剂上松脂分子间氢转移集总反应网络,建立了包含单萜烯、枞酸型树脂酸、海松酸型树脂酸、对伞花烃、氢化单萜烯、脱氢枞酸、氢化枞酸型树脂酸和氢化海松酸型树脂酸等复杂反应体系的集总动力学模型,并估算了模型参数.松脂单萜烯和树脂酸的反应级数分别为1和2,并得到了松脂分子间氢转移中各反应过程的活化能.结果表明,所建动力学模型与实验数据吻合良好,并能预测反应在533 K下的集总组分浓度分布.Pd/C催化松脂分子间氢转移反应以脱氢反应为主,树脂酸的氢转移速率大于单萜烯的氢转移速率.     

A comparison of direct methods to determine n-th order kinetic parameters of solid thermal decomposition for use in fire models

Pyrolysis models for burning solids in fire simulations are sensitive to the values of the activation energy, frequency factor, and reaction order that characterize the thermal decomposition of the solid to gaseous fuel, so direct measurement of these kinetic parameters is recommended, and simple methods are preferred. Three direct methods were evaluated with regard to the ability of their kinetic parameters to reproduce the thermal decomposition of five polymers measured by differential thermogravimetric analysis using the reaction order model. It was found that the two multiple heating rate methods produced identical, physically based kinetic parameters, while the peak property method produced non-physical kinetic parameters. However, all of these kinetic parameters in a single-step reaction order model gave reasonably good conversion histories for non-charring and moderately charring polymers. For a highly charring polymer, the conversion histories were poorly described without a multiple step reaction. The temperature at the maximum rate of conversion was found to be essentially independent of the reaction order, which decouples the frequency factor from the reaction order in the direct kinetic methods. Any of the direct methods are sufficiently accurate to obtain kinetic parameters for pyrolysis models because of the inherent spatial and temporal averaging of reaction rates at the burning surface of a thick solid and the uncertainty in the heat transfer mechanisms and thermo-physical parameters used in the models.     

渣油加氢脱残炭的动力学模型研究

以渣油为原料在200 mL反应装置上进行加氢脱残炭试验，同时依据渣油残炭的结构组成以及加氢脱残炭的反应历程，对试验结果进行了分析，在此基础上提出渣油加氢脱残炭的三集总反应动力学模型，并与一集总和二集总加氢脱残炭反应动力学模型进行比较。结果表明，一集总动力学模型不能用来描述渣油加氢脱残炭过程，从二、三集总动力学模型的预测数据与试验值误差来分析，将沥青质与胶质做为一个集总或渣油原料的沥青质含量较少时所建立的动力学模型，两者误差精度相当。用三集总的一级反应动力学模型预测渣油加氢脱残炭过程时，与试验值相比，加氢脱残炭转化率的平均绝对误差为0.005 6，加氢渣油残炭值的平均相对误差为1.01％。     

Kinetic Investigation on the Dehydration of Coprecipitated Mixed Oxide Powders

The authors present an original kinetic model and a computer program in order to determine the mass of various types of water from the oxide powders obtained through co-precipitation, using thermogravimetric data. The model is based on kinetic equations in the framework of the ‘reaction order’ desorption of the water loss. The program minimizes the mean square deviation between the experimental TG curve and the approximation curve; it allows visualizing the experimental and the approximated TG curves for the overall process, as well as the approximated TG and DTG curves for the individual processes. The influence of the aging time and temperature on the mass of various types of water to be found in the co-precipitated manganese ferrite powder was investigated based on this original kinetic model and the suitable computer program. Some correlations between the water release and microstructure changes of the powder during aging in mother solution are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cobalt Ferrite from Citrate Precursor by Self-Propagating Combustion Reaction

A Mangelsdorf's approach to modeling the epoxy-amine cure kinetics has been developed. Analysis of the data by means of Mangelsdorf's approach makes it possible not only to determine the reaction rate constant and the heat of epoxy ring opening, but also to elucidate the reaction mechanism. However, to model the kinetic curves obtained by the calorimetric method for the complicated reaction should be derived an equation expressing the rate of change of the heat with time, as a function of the reaction rate and the extent of conversion. In a detailed examination the thermokinetic data, we found that glassy state transition is kinetically feasible. Using data available in literature, the kinetic model for epoxy-amine cure reaction was developed. Our treatment of glass formation is based on the picture of the reaction system as a miscible mixture of two structurally different liquids. This approach is similar to that presented by Bendler and Shlesinger as a Two-Fluid model. In the application of this model to reaction kinetics, we believe the explanation of glass structure formation lies in the splitting of the homogeneous mixture into two liquid phases. This revised version was published online in August 2006 with corrections to the Cover Date.     

Development of kinetic models for acid‐catalyzed methyl acetate formation reaction: Effect of catalyst concentration and water inhibition

The reaction kinetics of reversible liquid‐phase esterification of acetic acid with methanol is investigated in the temperature range 26–50°C using sulfuric acid catalyst. The main goal of this work is to study the effect of catalyst concentration and sensitivity to the presence of water on the rate expression of this industrially important reaction. Experiments are conducted in an isothermal batch reactor and a second‐order kinetic model is used to correlate the experimental data, which are found to fit well with the assumed kinetic model in terms of the concentrations of reactants and products. Furthermore, an activity‐based kinetic model is also developed employing the UNIQUAC (universal quasi‐chemical equation) model to compute the activities. It is observed that the rate constant is influenced by the concentration of catalyst, and the reaction rate increased with an increase in the catalyst concentration. It is also observed that the catalyst activity is slightly inhibited by the water present in the reaction mixture. The performance of the proposed models is compared with that of other models reported in the literature, and it is found that the proposed models outperformed all the other models reported in the literature. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 263–277, 2011     

Kinetics of gas-liquid ozonization of veratrole and its derivatives

The kinetics was studied for the reactions of ozone with model lignin compounds, viz., phenol, veratrole, veratric aldehyde, and veratric alcohol. Using the mass transfer model for a chemical reaction based on the film theory, the reaction rate constants were calculated. The reaction rate constants determined by both the ozone absorption rate and changes in the substrate concentration coincide satisfactorily, indicating adequacy of the kinetic model chosen. A relationship between the structure of the compounds under study and their reactivity was found. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1941–1946, October, 2007.     

Kinetics of enzymatic reactions in the production of fish protein hydrolysates

The kinetic laws of enzyme hydrolysis of waste products (heads, fins, bones, and muscle tissue) of the Atlantic cod Gadus morhua have been investigated. An enzyme specimen hepatopancreatine was used for the hydrolysis reaction (proteolysis). A kinetic model describing the mechanism of enzyme hydrolysis of fish proteins as a second-order reaction was developed. The proteolysis model was based on the existence of easily hydrolysed and hydrolysis-resistant protein fractions. Autolysis of the enzyme was also taken into consideration. In the context of the developed kinetic model, the second-order rate constants of the intermediate stages of proteolysis were calculated.     

Kinetic method by using calorimetry to mechanism of epoxy-amine cure reaction

A Mangelsdorf's approach to modeling the epoxy-amine cure kinetics has been developed. Analysis of the data by means of Mangelsdorf's approach makes it possible not only to determine the reaction rate constant and the heat of epoxy ring opening, but also to elucidate the reaction mechanism. However, to model the kinetic curves obtained by the calorimetric method for the complicated reaction should be derived an equation expressing the rate of change of the heat with time, as a function of the reaction rate and the extent of conversion. In a detailed examination the thermokinetic data, we found that glassy state transition is kinetically feasible. Using data available in literature, the kinetic model for epoxy-amine cure reaction was developed. Our treatment of glass formation is based on the picture of the reaction system as a miscible mixture of two structurally different liquids. This approach is similar to that presented by Bendler and Shlesinger as a Two-Fluid model. In the application of this model to reaction kinetics, we believe the explanation of glass structure formation lies in the splitting of the homogeneous mixture into two liquid phases.     

New kinetic model for the rapid step of calcium oxide carbonation by carbon dioxide

Carbonation of solid calcium oxide by gaseous carbon dioxide was monitored by thermogravimetry. A kinetic model of CaO carbonation is proposed in order to interpret the first rapid step of the reaction. By taking into account, the existence of large induction period as well as the sigmoidal shape of the kinetic curves in this kinetic-controlled region, a surface nucleation and isotropic growth kinetic model based on a single nucleus per particle is proposed, and the expressions of the fractional conversion and the reaction rate versus time are detailed. The induction period is found to have a linear variation with respect to temperature and to follow a power law with respect to CO₂ partial pressure. The areic reactivity of growth decreases with temperature increase, and increases with CO₂ partial pressure increase. A mechanism of CaCO₃ growth is proposed to account for these results and to determine a dependence of the areic reactivity of growth on the temperature and the CO₂ partial pressure.     

EIS analysis on the anodic dissolution kinetics of pure iron in a highly alkaline solution

The anodic dissolution kinetics of pure iron in a highly alkaline solution was systematically studied by EIS. A model based on its reaction mechanism was proposed, which can well explain the characteristics of EIS. From the model, it was found that the Fe(III) oxide covered on the iron surface was firstly electrochemically oxidized to an adsorbed Fe(V) intermediate, the latter then converted to the final Fe(VI) product and the initial Fe(III) reactant through a disproportionating reaction. The kinetic constants of each step as well as the covering densities of the Fe(III) reactant and the Fe(V) intermediate at different potentials were calculated from the EIS model.     

Computer simulation of the steady state currents at enzyme doped carbon paste electrodes

The plate-gap model of porous enzyme doped electrode has been proposed and analyzed. It was suggested that reaction diffusion conditions in pores of bulk electrode resemble particular conditions in thin gap between parallel conducting plates. The model is based on the diffusion equations containing a nonlinear term related to the Michaelis–Menten kinetic of the enzymatic reaction inside gap. Steady state current was calculated for the wide range of given parameters and substrate concentrations. All dependences of current on substrate concentration were approximated by hyperbolas in order to obtain “apparent” parameters (maximal currents and apparent Michaelis constants) of modelled biosensors. Simple approximate relationships between given and apparent parameters were derived. The applicability of theoretical plate-gap model was tested for the case of carbon paste electrodes which were doped with PQQ – dependent glucose dehydrogenase. It was found, that soluble glucose dehydrogenase based biosensors exhibit characteristic features of the theoretical plate-gap biosensors.     

Kinetic spectrophotometric method for determination of perphenazine based on monitoring the oxidation intermediate by applying a stopped-flow technique

A novel and high-sensitive stopped-flow kinetic spectrophotometic method for the determination of perphenazine based on monitoring the variation of absorbance of the intermediate within a few seconds has been developed. The optimum conditions for various parameters on which the forming of the intermediate depends, were investigated. It was found that the initial reaction rate increased linearly with an increase in the perphenazine concentration in the range from 1.0 x 10(-5) to 1.6 x 10(-4)M. The detection limit was calculated to be 5.3 x 10(-6)M. The kinetics of the reaction was established by the aid of single-mixing or double-mixing stopped-flow techniques, a successive reaction model was proposed to analyze and simulate the reaction. The influence of both ascorbic acid and NADH on the time courses was also investigated.     

环己醇脱氢催化反应本征动力学研究

采用管式连续流动固定床积分反应器,对环己醇在Cu－Co/MgO催化剂上的脱氢反应本征动力学进行了研究,求出幂式速率模型各项参数,得到反应的表观活化能为44.28kJ/mol.将上述实验数据与由似平衡浓度法导出的速控步骤的数学模型相关联,求出各有关参数和物种的吸附烙.结果表明,以环己醇吸附和表面反应为速控步骤的模型可较好地进行关联.对上述模型进行了方差和残差分析,误差在宏观动力学研究允许范围内,实验无系统误差.方差分析表明,表面反应为速控步骤的模型对描述反应具有相对最小误差.