固定床催化反应器中平行反应的飞温现象Ⅰ冷却介质温度恒定

对在固定床催化反应器中冷却介质温度恒定时平行反应的飞温现象做了详尽的理论分析，推导出该系统安全操作所允许的温度上限和临界初始条件。研究结果表明简单反应的飞温理论适用于平行反应，在相同条件下平行反应和简单反应飞温区域之间的差异与主副反应的反应速率和热效应大小有关。对于平行反应系统，判断副反应的取舍，不应只从副反应速率本身的大小来考虑，还应该考虑副反应的热效应。     

Free radicals in coal and coal conversions. 10. Kinetics and reaction pathways in hydroliquefaction

The development is reported of a point rate model for the solubility fractions obtained from Powhatan No.5 coal liquefaction in terms of free-radical concentration. Stepwise regression procedures were used to determine rate constants for general hypothetical rate models. Chemical principles were used at each stage to eliminate terms and to fix others. Rate constant expressions were obtained by fitting In k to the inverse absolute temperature for each solvent. Generalized reaction paths were determined from these individual reactions by combining various reactions. These reactions described the conversion of material between solubility fractions via free-radical interactions. In all three solvents progressive liquefaction reactions that did not involve measured radicals (conventional reaction terms) predominated in the rapid break-up of coal, while free-radical reactions are predominant in retrogressive changes. At higher radical concentrations retrogressive reactions predominated. More reactions of all types became significant with increasing temperature.     

反应条件对甲烷化法去除重整氢气中CO的影响

研究了在采用甲烷化法去除重整氢气中CO的过程中,反应温度、CO浓度和CO₂浓度对3个竞争反应即CO甲烷化反应、CO₂甲烷化反应、逆变换反应（RWGS）的影响。实验结果表明,随着温度升高,CO、CO₂甲烷化反应速率均增大,但CO甲烷化的选择性降低。CO浓度对CO甲烷化反应速率的影响在高温时较为明显,反应速率随CO浓度的升高而增大;CO对CO₂甲烷化反应的影响在较低温度下较为显著,CO₂甲烷化反应速率随CO浓度的升高而减小,表明CO对CO₂的甲烷化具有抑制作用,因而随着CO浓度的升高,选择性增大。另一方面,CO₂浓度对CO甲烷化反应几乎没有影响,而CO₂甲烷化反应速率和RWGS反应速率均随CO₂浓度的升高而增大,该趋势在高温下更加显著,并对3个竞争反应的宏观动力学进行了初步研究。     

Generalized Criteria of Volume Ignition for One‐Stage Exothermic Reations

A method of ignition conditions determination for any type of exothermic reaction is proposed. The method is based on the maximum temperatures equation for any kind of kinetic function, which was obtained using the integral equation for phase trajectories. In this case, the asymptotic ignition criterion is defined by the infinitely high sensitivity of maximum temperature to the change of parameters at the limit of ignition. Hence, the critical ignition conditions are determined by the presence of extreme points on the plane: parameter – maximal temperature. On the strength of these ideas, the universal algebraic set of equations for critical conditions calculation for arbitrary kinetic law of reaction product formation was obtained. The application of this method to calculation of the second order reactions allows to define the thermal explosion degeneration conditions and the regions of critical conditions existence. The maximum discrepancy between the results obtained with the results of numerical calculation does not exceed ten percent.     

Application of parametric sensitivity to batch process safety: Theoretical and experimental studies

The generalised thermal parametric sensitivity criterion is applied to the thermal behaviour of the esterification of 2-butanol with propionic anhydride in a batch reactor under isoperibolic conditions. The reaction is catalysed by sulphuric acid, and the study covered the effects of both catalyst concentration and, in the absence of catalyst, jacket temperature. The experimental location of regions of parametric sensitivity agreed well with theoretical predictions. However, the process conditions that meet conventional standards for safe process design fall into the supercritical sensitivity region of the parametric model. This apparently contradictory result is discussed. The usefulness of the parametric sensitivity approach is illustrated by practical examples of scale-up and heat transfer in reactions prone to thermal runaway.     

Volume reaction model for pyrolysis of a single solid particle accompanied by a complex reaction

A fairly general model is proposed for the pyrolysis of a single solid particle accompanied by consecutive reactions. The model not only takes into consideration the transient heat transfer, mass transfer, and chemical reaction simultaneously but also the functional dependencies of various parameters on the variation of the solids concentration and temperature in the particle. The effects of the heat of reaction, Thiele modulus, and rate of reaction on the solids reactant conversion, concentration profiles and temperature profiles are analyzed and graphically presented.     

Kinetics studies of ketazine formation: Effect of temperature and catalyst concentration

Formation of methyl ethyl ketazine is a distinct case of homogeneous catalyzed gas–liquid–liquid reactions. Kinetics studies of methyl ethyl ketazine formation has been carried out in a semi‐batch reactor. The effects of temperature and catalyst concentration on the percentage yield of ketazine have been studied extensively. The yield of ketazine is found to increase with increase in temperature and then levels off. Increase in catalyst concentration favours the formation of ketazine. The conversion of peroxide is found to increase with increase in temperature thus indicating that chemical reaction is rate‐limiting step in the system. The desired temperature for carrying out the reaction is found to be 60°C and the required catalyst to peroxide ratio is 2.5. The activation energy for the reaction is 24.5 kJ/mol.     

Concentration slip and its impact on heterogeneous combustion in a micro scale chemical reactor

The rarefied gas effect on concentration slip and on heterogeneous combustion in microscale chemical reactors was investigated. First, a concentration slip model to describe the rarefied gas effect on the species transport in microscale chemical reactors was derived from the approximate solution of the Boltzmann equation. Second, the model was verified using the direct Monte-Carlo method for the pure diffusion problems at different Knudsen numbers. The comparison showed that the present analytical model for the concentration slip boundary condition reasonably predicted the rarefied gas effect in the slip regime. Finally, the impact of the concentration slip on the coupling between the surface catalytic reactions and the homogeneous gas phase reactions in a microscale chemical reactor was examined using the one-step overall surface reaction model with a wide range of Knudsen and Damköhler numbers. It was shown that the rarefied gas effect significantly reduced the reaction rate of the surface catalytic oxidization for large Knudsen numbers. Furthermore, it was shown that the impact of slip effects on catalytic reactions strongly depends on the competition between the reaction rate and diffusion transport. It was found that the concentration slip causes a nonlinear reaction rate distribution at large Damköhler numbers. The results also showed that an accurate prediction of the rarefied gas effect on catalytic reactions in microscale reactors has to consider both the temperature slip and the concentration slip.     

SOFC中低浓度干甲烷在Ni/YSZ阳极上的反应

固体氧化物燃料电池(SOFC)趋向于直接使用甲烷天然气为燃料,确定甲烷在固体氧化物燃料电池阳极发生的化学与电化学反应非常重要.以Ni/YSZ为阳极、YSZ板做电解质、LSM为阴极,用涂浆法制作电解质支撑的电池,研究低浓度干甲烷在固体氧化物燃料电池中的反应.改变甲烷浓度、电池工作温度、电解质厚度,用在线色谱测量不同电流密度下,阳极出口气体产生速率.根据阳极出口气体产生速率变化,分析干甲烷在阳极的反应变化.通过氧消耗计算和转移电子数的分析,说明甲烷在电池阳极发生不同类型的反应.电流密度小时,甲烷发生部分氧化反应.电流密度大时,发生氢氧化和CO氧化,部分甲烷发生总反应为完全氧化的反应.部分甲烷发生完全氧化反应的同时,部分甲烷仍发生部分氧化反应,但其反应速率随电流密度增加逐渐降低.甲烷浓度和试验温度增加,甲烷开始发生完全氧化的电流密度增加.     

Kinetics of transesterification of soybean oil

Transesterification of soybean oil with methanol was investigated. Three stepwise and reversible reactions are believed to occur. The effect of variations in mixing intensity (Reynolds number=3,100 to 12,400) and temperature (30 to 70°C) on the rate of reaction were studied while the molar ratio of alcohol to triglycerol (6:1) and the concentration of catalyst (0.20 wt% based on soybean oil) were held constant. The variations in mixing intensity appear to effect the reaction parallel to the variations in temperature. A reaction mechanism consisting of an initial mass transfer-controlled region followed by a kinetically controlled region is proposed. The experimental data for the latter region appear to be a good fit into a second-order kinetic mechanism. The reaction rate constants and the activation energies were determined for all the forward and reverse reactions.     

Nitration of nitrobenzene at high‐concentrations of sulfuric acid: Mass transfer and kinetic aspects

This article reports studies on mass transfer and kinetics of nitration of nitrobenzene at high concentrations of sulfuric acid in a batch reactor at different temperatures. The effects of concentration of sulfuric acid, speed of stirring, and temperature on mass transfer coefficient were investigated. The kinetics of nitration under homogenized conditions was studied at different sulfuric acid concentrations at these temperatures. The reaction rate constants were determined. The variation of rate constant with sulfuric acid concentration was explained by the M_c function. The activation energies of the reactions were determined from the Arrhenius plots. The regimes of the reactions were determined using the values of the mass transfer coefficients and the reaction rate constants. A model was developed for simultaneous mass transfer and chemical reaction in the aqueous phase. The yields of the three isomers of dinitrobenzene were determined, and the variation of isomer distribution with sulfuric acid concentration and temperature was analyzed. This work demonstrates that more than 90% conversion of nitrobenzene is possible at high‐sulfuric acid concentrations resulting in high yield of the product even at moderate temperatures and at low speeds of stirring. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Kinetics of formation of diphenoxymethane from phenol and dichloromethane using phase-transfer catalysis

The reactions of phenol with dichloromethane using quaternary ammonium salts as a liquid–liquid phase-transfer catalyst in an organic solvent/alkaline solution were investigated. The technique of phase-transfer catalysis had a dramatic accelerating effect on the reaction and increased the yield of diphenoxymethane by more than 95%. The effects of catalysts, temperature, and basic concentration on reaction rate were studied in order to find the optimum operating conditions for this reaction. Experimental results indicated that a potassium hydroxide was preferred over sodium hydroxide in order to enhance the reactivity of the reaction. The reaction rate constant and the distribution coefficient of the intermediate product were obtained. During the reaction, the concentration of the intermediate product was also measured in order to study its behavior in the liquid–liquid system.     

椰壳酸水解制备木糖的反应动力学

本文研究了椰壳经酸水解制备木糖的反应温度、反应时间和酸浓度对水解液中木糖浓度的影响,探讨了椰壳酸水解反应的机理,建立了木聚糖降解与木糖分解的均相不可逆连串水解反应动力学模型,求出了反应活化能Ea,木糖生成与分解反应速率常数k_1、k₂,建立了k₁ 与酸浓度C和反应温度T的关系式,分析了提高k₁与k₁/k₂比值的酸水解条件,其规律可供实现工业化生产借鉴。     

Kinetics of catalytic esterification of terephthalic acid with methanol vapour

This paper describes the investigations carried out on the kinetics of the solid-gas reaction between terephthalic acid and methyl alcohol in presence of phosphoric acid as the catalyst. As phosphoric acid itself reacts with the alcohol forming methyl phosphates, the kinetic data obtained have been analysed taking this reaction into account. The rate of formation of monomethyl phosphate has been found to be proportional to the square of the mole fraction of the acid present at any instant. The activation energy involved in this reaction is 11.3 kcal/g mole. The data obtained on terephthalic acid esterification show that; (i) the conversion sharply increases with an increase in the catalyst concentration between 30–35 per cent (w/w), (ii) the ‘shrinking particle’ model, proposed by Levenspiel for solid-gas reactions, can be conveniently adapted to represent the reaction, and (iii) the temperature dependency of the reaction follows the Arrhenius law, with activation energy being 11.5 kcal/g mole.     

Hydrogenation Characteristics of High Erucic Rapeseed Oil

Twenty-seven experiments were done to study the hydrogenation characteristics of high erucic rapeseed oil, with the experiments being designed systematically according to orthogonal test. The characteristics include the influence of operating variables on the reaction rate (average reaction rate and instantaneous reaction rate) and on the relationship between melting point and iodine value of the finished product, and the induction time of reactions under different conditions. Reaction rate and melting point models were generated from the experimental data. The results show that temperature has the most significant effect on the reaction rate, followed by catalyst concentration and hydrogen pressure. The correlation between melting point and iodine value of the hydrogenated product was greatly affected by the operating variables, especially temperature. Melting point will decrease as temperature increases at a given iodine value. Induction time is relatively long at temperature below 170°C.     

Temperature effect on polymer mechanochemistry

The influence of temperature is a fundamental variable for the mechanochemical processes of high polymers. However, it is generally recognized that the effect of temperature in this process is not always direct, as in normal chemical reactions, but is mainly indirect involving change in the properties (principally elastic and viscous), in the physical state of the system, and consequently in the mechanism of rupture. The negative temperature coefficient has been considered a prime criterion of a mechanochemical reaction by many researchers. Recently, it has been suggested that the negative temperature coefficient is really due to the viscous heating during polymer deformation and the low thermal conductivity of polymers. The aim of this paper is to reevaluate the role of temperature on mechanically induced reactions of polymers. In light of evidences published in the last 30 years, the dependence of mechanochemical reaction on temperature must involve the overlapping of the following factors: (1) the usual positive dependence of rate on temperature, as predicted by Arrhenius equation; (2) the true experimental temperature, which depends on viscous heating and on thermostatting efficiency; and (3) the breaking tension at the center of the polymer chain which is inversely dependent on temperature, i.e., greater at the higher viscosity and the slower relaxation at the lower temperatures, this last factor being dominant in determining the characteristic negative temperature coefficient for polymer mechanochemistry.     

Theoretical and experimental analysis of capsule membrane phase transfer catalysis: Selective alkaline hydrolysis of benzyl chloride to benzyl alcohol

Intensification of and selectivity in multiphase reactions catalysed by phase transfer catalysts can be greatly improved by the use of the so-called capsule membrane-PTC (CM-PTC) technique in comparison with the L-L PTC. We report here the theoretical and experimental analysis of the CM-PTC and inverse CM-PTC for exclusively selective formation of benzyl alcohol from the alkaline hydrolysis of benzyl chloride. The theoretical analysis shows that it is possible to simultaneously measure the rate constant and equilibrium constant under certain conditions. The effects of speed of agitation, catalyst concentration, substrate concentration, nature of catalyst cation, membrane structure, nucleophile concentration, surface area for mass transfer and temperature on the rate of reaction are discussed.     

First order kinetics in continuous reactors

It is shown that for any continuous flow reactor, isothermal or not, supporting any system of first order reactions, there exists always a batch reactor or plug flow reactor whose performance is better (or at least no worse) for that reaction system. The performance criterion (a higher value to indicate better performance) may be any convex function of the concentrations of the various species.     

Erweiterung des Semenov‐Kriteriums auf konzentrationsabhängige Reaktionen

Exothermic reactions in liquid phase are often performed in a batch reactor with cooling. To avoid runaway, suitable conditions of the reaction and its performance must be selected. It is shown that in the case of liquid phase reactions these conditions should not be determined by the Semenov criterion but by its extension, the sensitivity, which regards the concentration dependency of the reaction. The theoretical relationships are derived on the basis of the heat and mass balances. The results are illustrated by numerical calculations.