低温条件下二氧化碳存在时羰基硫催化水解本征动力学

在自行设计和安装的一套微反-色谱联用装置上，以TGH为催化剂，进行了二氧化碳对羰基硫催化水解本征动力学影响的研究，得出了在低温50 ℃～70 ℃、高水汽摩尔比(H2O/COS=60～550)，分别对原料气中有无存在CO2的条件下,采用非线性Marquart法对实验数据进行回归，所建立的本征动力学方程式为：     

近临界水中聚丙烯腈无催化水解反应动力学

系统研究了近临界水中聚丙烯腈无催化水解反应动力学.在实验数据重现性和物料配比对PAN水解反应影响的考察基础上,系统测定了210～250℃下聚丙烯腈的水解反应动力学数据,采用元素分析仪、傅立叶变换红外光谱仪、热分析仪、凝胶色谱仪对水解产物进行了表征.结果表明,近临界水中聚丙烯腈无催化水解是可行的,其中温度与物料配比是影响水解速率的主要因素;通过控制不同水解条件,可得到不同含量的腈基(—CN)、酰胺基(—CONH2)和羧基(—COOH)二元或三元共聚物,产物侧基含量的不同有可能在不同的领域得到应用;以一级连串反应动力学模型对实验数据进行了拟合,得到了聚丙烯腈和聚丙烯酰胺水解反应活化能分别为53.37 kJ.mol-1和120.55 kJ.mol-1.     

Estimation of temperature transients for biomass pretreatment in tubular batch reactors and impact on xylan hydrolysis kinetics

A combined heat transfer/kinetic model was developed to quantify temperature variations in small tubular batch reactors and estimate the effect of deviations from isothermal operation on the kinetics of biomass pretreatment. Assuming that heat transfer was dominated by conduction in the radial direction, a classic parabolic time-dependent partial differential equation was applied to describe the temperature in the system and dedimensionalized to provide a single solution for application to all situations. A dimensionless expression for the reaction kinetics for xylan hydrolysis was then developed, and a single parameter expressed as the dimensionless ratio of the first-order rate constant times the tube radius squared divided by the thermal diffusivity was found to control the reaction rate. Three different characterizations of the deviation between the concentration profile predicted for isothermal xylan hydrolysis and that based on the transient temperature were directly related to this dimensionless rate constant parameter for both catalyzed and uncatalyzed hydrolysis kinetics. These results were then used to project the relationship between deviations in yield from isothermal results and the tube radius and reaction time.     

水解制备球形TiO2及其水解过程动力学

以硫酸钛(Ti(SO4)2)为前驱物水解得到超细球形TiO2. 研究了水解过程中前驱物浓度和体系温度对水解速率的影响, 并对实验值进行了拟合, 得到水解TiO2的质量分数与水解时间呈良好的指数关系, 根据Avrami方程进一步验证了拟合的可靠性. 分析了水解介质的影响作用, 确定介电常数和zeta电位也是影响水解速率的重要因素, 因此可通过改变溶剂成分来调节介电常数和zeta电位, 从而达到控制Ti(SO4)2水解速率的目的. 实验结果表明, Ti(SO4)2水解制备TiO2的过程中, 较低的前驱物浓度, 较高的水解温度和合适的溶剂体系有利于得到粒径分布窄、分散性好的TiO2.     

应用阳离子交换树脂催化水解蔗糖Ⅰ.蔗糖非均相催化水解反应动力学

实验选用两种H+型强酸性阳离子交换树脂为催化剂，研究蔗糖在离子交换树脂柱内的非均相催化反应动力学。结果表明，温度每升高10℃，蔗糖在两种离子交换树脂柱内的水解速度分别增加到2．1和3．3倍；蔗糖在两种离子交换树脂柱内水解反应的表观活化能分别为64．96kJ／mol和79．59kJ／mol，其水解反应有明显的扩散控制。     

Kinetics of the hydrolysis of tri- and diethyl phosphite

Conclusions We have studied the kinetics of the hydrolysis of triethyl phosphite in water and dilute KOH, and of the hydrolysis of diethyl phosphite in water and dilute HCl. The temperature dependences of the velocity constants have been determined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2551–2552, November, 1967.     

Studies of the Rate Constant of Levodopa Methyl Ester Hydrolysis by LC

This paper investigates the hydrolysis kinetics of levodopa methyl ester in 0.05–1.5 M HCl between 37 and 75°C. An isocratic HPLC assay was developed for simultaneous determination of levodopa methyl ester and levodopa in the hydrolysate of levodopa methyl ester. A series of hydrolysis rate constants were obtained and the effects of hydrogen ion concentration and temperature on the reaction were evaluated. It was found that pH was a key factor at low temperature, but that when the temperature was raised, temperature became in turn the most influent factor on the hydrolysis. From the measured pseudo-first order reaction rate constants, the activation energy for levodopa methyl ester hydrolysis in 0.5, 1.0 and 1.5 M HCl were calculated to be 71.24, 74.32 and 76.57 kJ mol⁻¹, respectively. Revised: 24 May and 15 August 2005     

Hydrolysis kinetics of silane coupling agents studied by near-infrared spectroscopy plus partial least squares model

Abstract

A method of Fourier transform near-infrared (FT-NIR) spectroscopy combined with partial least squares (PLS) model was successfully applied to investigate the hydrolysis kinetics of four kinds of silane coupling agents (phenyltriethoxysilane, vinyltriethoxysilane, 3-mercaptopropyltriethoxysilane, 3-chloropropyltriethoxysilane) in an acid-catalyzed EtOH system. The fast scanning speed and high sensitivity of the FT-NIR spectroscopy, and the powerful data processing ability of the PLS, enabled the method to quantitatively and accurately catch the fast changing H₂O concentration during the hydrolysis processes without delay, realizing the study of the fast-paced hydrolysis reactions of the silane coupling agents. The results showed that electrophilic substitution occurred in the hydrolysis reactions, which followed second-order reactions and greatly depend on the catalyst concentration and reaction temperature. The hydrolysis rate constants, activation energy, and Arrhenius Frequency factors were gained. In conclusion, the FT-NIR PLS model is a powerful tool for hydrolysis kinetics researching of the silane coupling agents.     

Influence of protein hydrolysis on the growth kinetics of β-lg fibrils

Recently it was found that protein hydrolysis is an important step in the formation of β-lactoglobulin fibrils at pH 2 and elevated temperatures. The objective of the present study was to further investigate the influence of hydrolysis on the kinetics of fibril formation. Both the hydrolysis of β-lactoglobulin and the growth of the fibrils were followed as a function of time and temperature, using SDS polyacrylamide gel electrophoresis and a Thioflavin T fluorescence assay. As an essential extension to existing models, the quantification of the effect of the hydrolysis on the fibrillar growth was established by a simple polymerization model including a hydrolysis step.     

Die Kinetik der alkalischen Hydrolyse von m-und p-substituierten 2,4-Dinitronaphthylthiobenzoaten

The kinetics of alkaline hydrolysis of m-and p-substituted 2,4-dinitronaphthylthiobenzoates were studied. The influence of substituents on the rate of hydrolysis depends mainly on the inductive effect. Isokinetic correlation shows that all members of the series react by the same mechanism. Two typical features are firstly that the reaction constant ρ increases with temperature, and secondly that the isokinetic temperature is below that of the experiment. The kinetic treatment shows that the first step, addition of OH^? to the starting compound, is the slowest and therefore rate-determining.     

On the activation energy for the hydrolysis of bis-(2-chloroethylethyl) sulfide. II

Dilute solutions of mustard, bis-(2-chloroethylethyl) sulfide, hydrolyze to form the chlorohydrin and HCl: the chlorohydrin subsequently hydrolyzes to form the thiodiglycol and another mole of HCl. The kinetics of these reactions constitute consecutive, first-order reactions which past investigators approximated as a single, first-order reaction. In an earlier paper, a non-linear least-squares program was used to refit these data to consecutive, first-order kinetics in order to refine the activation parameters for mustard hydrolysis. It was shown, however, that the early work did not conform to consecutive, first-order reactions, suggesting that dissolution of mustard interfered with the hydrolysis. Only the data of Bartlett and Swain were clearly hydrolysis of mustard: however, rate data were only run at 25°C.This paper reports kinetics of mustard hydrolysis measured in 0.025 mole fraction ethanol-water between 20 and 40°C. Over this temperature range, the enthalpies of activation for mustard and the chlorohydrin are 18.5 and 18.6 kcal mol⁻¹, respectively. These results are similar to enthalpies of activation for other 2-chloroethylalkyl sulfides, but smaller than those reported for mustard hydrolysis in the past.     

单分散SiO2体系制备中TEOS水解动力学研究

采用一种与他人不同的萃取－冷冻分离－气相色谱法，跟踪形成单分散二氧化硅体系条件下正硅酯乙酯（TEOS）的水解过程，考察了温度（25～45℃）、氨浓度（0．5～0．2mol•L－1）、水浓度（6．0～15．0mol•L－1）等实验条件范围内，以上实验参数对TEOS水解速度的影响；并回归得到目前适用于在乙醇介质中氨催化下，形成单分散二氧化硅微粒常用实验条件范围内，唯一的较完整的水解动力学方程式．     

A simple capillary electrophoresis with electrochemical detection method for determination of the hydrolysis rate constant of chlorogenic acid

A method based on the kinetics stability study on hydrolysis of chlorogenic acid by capillary zone electrophoresis with electrochemical detection (CE-ED) has been developed in this paper. Both cyclic and hydrodynamic voltammograms of chlorogenic acid and its hydrolysis product caffeic acid have been investigated. The conditions for separation of chlorogenic acid and caffeic acid, such as the buffer pH and concentration, the separation voltage, and the injection time have been optimized. Under the optimum CE running conditions, the effects of reaction temperature and pH values of the hydrolysis solutions on the hydrolysis rate constants were further studied. The hydrolysis rate constants of chlorogenic acid were obtained from the concentration change of hydrolysis during the process of hydrolysis. Based on the fact, a simple and economical method for the determination of the hydrolysis rate constant and activation energy of hydrolysis reaction has been developed.     

The effect of electron-withdrawing properties of substituents on the hydrolysis of some Schiff bases

The dissociation kinetics of the Schiff bases investigated in the present paper [N,N-bis(X-benzylidenes)ethylenediamine], have been examined under basic and acidic conditions, in aqueous medium 25% acetone in water (wt-wt). The base hydrolysis reaction of these compounds was found to follow second-order kinetics, first-order with respect to each of the Schiff base and the hydroxide ions. The rate-determining step is suggested to be the hydroxide ions attack on the free base. The effect of acetone ratio, in hydrolysis medium, has been studied under alkaline conditions. It is deduced that both the hydrogen bonding formation and solvent-solvent interaction have a pronounced role in such hydrolysis reactions. The acid hydrolysis reaction is strictly second-order kinetics, first-order with respect to the Schiff base and also to the hydrogen ions, and the attack of water molecules on the protonated substrate becomes the rate-determining step. A slower rate of the base hydrolysis was observed through the Schiff base II (p-NO₂), on the other hand, a fast acid hydrolysis rate was detected in the case of compound III (p-COOH). Furthermore, from the effect of temperature on the reaction rate, the various thermodynamic parameters have been also calculated and discussed.     

2,4-二硝基氯苯在微乳液中的水解动力学

十六烷基三甲基溴化铵;正辛烷;正丁醇;2;4-二硝基氯苯在微乳液中的水解动力学     

Selection of the most effective kinetic model of lactase hydrolysis by immobilized Aspergillus niger and free β-galactosidase

The kinetic model of the hydrolysis of lactose by β-galactosidase from Aspergillus niger immobilized on a commercial ceramic monoliths was estimated in the attendance of lactose and its hydrolysis reaction products galactose and glucose. The aim of this work was to developing kinetic model of lactase hydrolysis by Aspergillus niger. The variables in this study are temperature, pH, enzyme concentration, substrate concentration and final product. The optimum temperature used to achieve the best hydrolysis performance in the kinetic model selection was 55 and 60 °C. The optimum pH used for enzyme activity was about 3.5 to 4. Five kinetic models were proposed to confirm experimental data the enzymatic reaction of the lactose hydrolysis by the β-galactosidase. The kinetics of lactose hydrolysis by both Immobilized and soluble lactases were scrutinized in a batch reactor system in the lack of any mass conduction restriction. In both instance the galactose inhibition kinetic models predicted the experimental data. The model is capable to fit the experimental data correctly in the extensive experimental span studied.     

Kinetics and thermodynamics of sucrose hydrolysis from real-time enthalpy and heat capacity measurements

We report a real time study of the enthalpy release and heat capacity during the course of HCl-catalyzed hydrolysis of sucrose to fructose and glucose. Measurements were performed during both isothermal conditions and during slow heating and then cooling at a controlled rate. The reaction rate constant of the first-order kinetics follows an Arrhenius relation with activation energy of 109.2 kJ/mol of sucrose. On hydrolysis, the enthalpy decreases by 14.4 kJ/mol of sucrose at 310 K, and the heat capacity, Cp, increases by 61 J mol-1 K-1 of sucrose in the solution. The enthalpy of hydrolysis decreases with increase in the temperature and DeltaCp on hydrolysis increases. The effects are attributed to change in the configurational and vibrational partition functions as one covalent bond in sucrose breaks to form two molecules, which then individually form additional hydrogen bonds and alter the water's structure in the solution. Cp of the solution increases with temperature less rapidly before sucrose hydrolysis than after it. This may reflect an increase in the configurational contribution to Cp as the hydrogen bond population changes.     

Kinetic Study of the Hydrolysis of Schiff Bases Derived from 2-Aminothiophenol

The kinetics of the hydrolysis of Schiff bases derived from 2-aminothiophenol have been studied in aqueous sodium hydroxide media containing 40?% (v/v) methanol in the temperature range 22?C45?°C. The Schiff base molecular structure-hydrolysis reactivity relationship has been investigated and discussed. Suitable reaction mechanisms have been suggested. From the effect of temperature on the rate constant, various activation parameters have been evaluated. The work has been extended to study the hydrolysis mechanism in buffer solutions of pH?=?2?C13 at 22?°C for Schiff base I (H). A rate profile diagram of pH-rate constant has been proposed.     

Heat transfer considerations in design of a batch tube reactor for biomass hydrolysis

Biologic conversion of inexpensive and abundant sources of cellulosic biomass offers a low-cost route to production of fuels and commodity chemicals that can provide unparalleled environmental, economic, and strategic benefits. However, low-cost, high-yiel technologies are needed to recover sugars from the hemicellulose fraction of biomass and to prepare the remaining cellulose fraction for subsequent hydrolysis. Uncatalyzed hemicellulose hydrolysis in flow-through systems offers a number of important advantages for removal of hemicellulose sugars, and it is believed that oligomers could play an important role in explaining why the performance of flow-through systems differs from uncatalyzed steam explosion approaches. Thus, an effort is under way to study oligomer formation kinetics, and a small batch reactor is being applied to capture these important intermediates in a closed system that facilitates material balance closure for varying reaction conditions. In this article, heat transfer for batch tubes is analyzed to derive temperature profiles for different tube diameters and assess the impact on xylan conversion. It was found that the tube diameter must be <0.5 in, for xylan hydrolysis to follow the kinetics expected for a uniform temperature system at typical operating conditions.     

Kinetic study of a complex triangular reaction system in alkaline aqueous-ethanol medium using on-line transmission FTIR spectroscopy and BTEM analysis

The kinetics of the base-catalyzed reaction of methyl 4-hydroxybenzoate in aqueous-ethanol solvent medium was studied and analyzed via combined on-line transmission FTIR spectroscopy and Band-Target Entropy Minimization (BTEM) technique. This reaction is considered complex since it involves simultaneous hydrolysis and ethanolysis reactions of methyl 4-hydrozybenzoate (MP) to form ethyl 4-hydroxybenzoate (EP) as an intermediate and sodium 4-hydroxybenzoate as a final product. The pure component spectra of the reactive species involved in the reaction were reconstructed using BTEM technique. Their corresponding real concentrations were calculated and subsequently used for analyzing the kinetics of this triangular reaction system. The effects of temperature and solvent mixture compositions were studied. In general, the results show that the rates of both hydrolysis and ethanolysis reactions increase with temperature. Addition of ethanol to the solvent mixture also reduces the rates of the hydrolysis reactions. The effect of solvent mixture on the rate of ethanolysis reaction is more complex and influenced by at least two competing factors, namely the concentration of ethoxide ion in the solution and the stabilization effect on the reactant. The enthalpy and entropy activation parameters, ΔH^‡ and ΔS^‡, of both the hydrolysis and ethanolysis reactions were determined using the Eyring equation and the activation parameters confirm the associative nature in the elementary steps in these reactions. Finally, it is shown that the dominant synthetic pathway in this triangular system changes from direct hydrolysis of methyl 4-hydrozybenzoate to the indirect pathway via ethanolysis and then hydrolysis depending on the solvent mixture composition.