A kinetic model for enzymatic reactions in a reverse micellar system,involving water-insoluble substrate

A kinetic model was proposed for enzymatic reactions in a reverse micellar system, involving a water-insoluble substrate. Though surfactant is one of the main structural components of reverse micelles, an increase in the surfactant concentrations affects the enzyme activity remarkably. A relationship between the enzyme activity and the surfactant concentration is discussed. In this study it was assumed that free substrate in the organic phase was in adsorption equilibrium with the surface of the micellar surfactant, and that the adsorption coefficient and the true K_m value (Michaelis constant) were independent of the surfactant concentration. The validity of this model was verified by data on the hydrolysis of olive oil, catalyzed by Chromobacterium viscosum lipase (Glycerol-ester hydrolase; EC 3.1.1.3) in an AOT/isooctane reverse micellar system. The activity value predicted by the model equation agreed well with the experimental data.     

A kinetic model for enzymatic reactions in reverse micellar systems involving water‐insoluble substrates and enzyme activators

The activity of Chromobacterium viscosum lipase (glycerol‐ester hydrolase, EC 3.1.1.3) entrapped in AOT/isooctane reverse micelles was significantly increased by the addition of short chain polyethylene glycols (PEGs) or methoxypolyethylene glycols (MPEGs) for the hydrolysis of olive oil. To understand enzyme activity in the presence of PEG 400 or MPEG 550 molecules, a kinetic model was proposed. The validity of this model was verified by experimental data on the lipase‐catalyzed hydrolysis of olive oil in AOT/isooctane reverse micellar systems, in which PEG 400 or MPEG 550 had been added. The large value of the equilibrium constant (k_D) for enzyme activation indicated that the affinity between C viscosum lipase and PEG 400 or MPEG 550 molecules was very strong. The Michaelis constant (K_m) predicted by the proposed model explained enzymatic reactions more exactly than that by the previously published model. Copyright © 2003 Society of Chemical Industry     

Estimation of kinetic constants for reactions in thin films

The problem of synthesizing a product in thin films taking into account a finite reaction rate at the phase boundaries is considered. Formulas are derived that determine the dynamics of synthesis in the diffusive regime and in the regime controlled by the boundary kinetics. Based on these formulas, procedures are proposed for estimating the parameters of the boundary kinetics.     

Improvement of mass transfer coefficient in reverse osmosis by oscillatory flow

This paper describes a laboratory apparatus for confined feed liquid reverse osmosis operation. In this apparatus, the mass transfer coefficient on the high pressure side of the membrane is increased by sweeping the membrane surface at a predetermined frequency by a back and forth movement of the feed liquid itself through an adjustable narrow channel in the cell. The utility of the technique for improving membrane performance is illustrated.     

A kinetic model for curing reactions of epoxides with amines

Curing reactions of epoxy resins are accelerated by added hydrogen-bond donor solvent and hydroxyl groups produced during the course of polymerization. A kinetic model comprising several different polycondensation and polyaddition reactions that occur simultaneously is developed. The concept of diffusion controlled reactions is employed to describe the change of reaction rate constants with conversion after the formation of an infinite crosslinking network. Good agreement is obtained between the model predictions and experimental data available in the literature.     

Dehydration reactions and kinetic parameters of gibbsite

Dehydration reactions and the corresponding kinetics of gibbsite [γ-Al(OH)₃] were analyzed using non-isothermal thermoanalysis and the Kissinger equation. It is concluded that the starting temperature of the dehydration reaction of γ-Al(OH)₃ rises with increasing heating rate of the system. At a heating rate of 10 °C min⁻¹, γ-Al(OH)₃ has lost part of its crystalline water, and was completely transformed into boehmite (γ-AlOOH)) at about 317 °C. However, γ-AlOOH did not lose the residual crystalline water entirely, and did not change into amorphous Al₂O₃ until the system was above 700 °C. The kinetic energy needed to convert γ-Al(OH)₃ to γ-AlOOH, and γ-AlOOH to amorphous Al₂O₃, was calculated by differential scanning calorimetry (DSC) with activation energies of 108.50 and 217.24 kJ mol⁻¹, pre-exponential factors of 2.93 × 10⁹ and 8.30 × 10¹³, and reaction orders of 0.96 and 1.06, respectively. The kinetic parameters of dehydration reactions for γ-Al(OH)₃ obtained using the derivative thermogravimetric method (DTG) are very similar to that of obtained by DSC.     

对流扩散化学反应动力学方程的流动坐标解法

对于两种介质并行流动的对流扩散化学反应问题,给出了在流动坐标系下的化学反应动力学方程的解法.在这个坐标系下,对流项消失了,只是一个化学反应、扩散方程,即在每个时间步的计算只有反应扩散而没有流动.流体的流动体现在计算域随时间步的增加而增加;并且,流体流进计算域的时间就是其化学反应和扩散的时间,因此流体各个质点的反应、扩散时间是不同的.本算法克服了因流体介质前端物理量分布的间断引起的计算上的数值虚假摆动,进而避免了对化学反应计算的不利影响.算例表明,该算法是有效的.     

Some strategies for the kinetic study of complex heterogeneous catalytic reactions

This paper presents a method of transforming the non-liner regression problem in the kinetic study of complex heterogeneous catalytic reactions into a linear regression problem. Application of this method reduced the number of parameters to be estimated by n-1, where n is the number of independent reactions. In addition, a stepwise model discrimination strategy in introduced to reduce the number of equation sets ad equations in the set undergoing parameter estimation. These two new approaches are very advantageous in reducing the computation effort, especially when the number of independent reactions is large. The linear regression method and the stepwise model discrimination strategy are successfully applied in the kinetic study of the methanol synthesis system in which the formation rates of methanol, methane, ethanol and ethane are considered.     

微型流化床反应动力学分析仪的研制与应用

本文首次研发了一种用于测定气固反应速度、求算反应动力学参数的微型流化床反应分析仪器（MFBK）。该仪器利用流化床强化反应过程的热量与质量传递过程,通过气体脉冲输送在给定温度下瞬时进样,根据在线监测的气体组分浓度变化,测试反应速度、推导反应动力学参数和分析反应机理。利用该仪器测定氩气气氛中碳酸钙的分解反应表明：其表观活化能与指前因子分别为142.73kJ.mol^-1和399777s^-1,活化能在文献报道范围之内,且小于热重分析仪测定的184.3kJ.mol^-1,并建立了反应模式函数f(α)=(1-α)0.86,对应的拟合线性相关系数达到0.99。测定煤和生物质热解反应过程表明：MFBK测试的反应完成时间在15s左右,且揭示了生成气关键组分具有不同的释放时间和生成量,为深入探讨热解反应机理提供了新的证据。     

Automatic data-driven stoichiometry identification and kinetic modeling framework for homogeneous organic reactions

Data-driven and knowledge-driven methods are two approaches used in studying reaction kinetics. This article proposes a hybrid-modeling framework for homogeneous synthesis reactions, which combines the advantages of high level of automation in the data-driven approach and improved accuracy in the knowledge-driven approach. A constrained enumeration method is proposed to generate possible candidate stoichiometries, and dynamic response surface methodology, target factor analysis, and mass balance are used together for identifying stoichiometries one-by-one, without the necessity of an expert-generated candidate list. Then, the previously screened stoichiometries are formed into different groups that represent candidate reaction systems, and the group (or groups) with the greatest likelihood will be identified, based on kinetic fitting and reaction dynamic criteria. This framework has been demonstrated by several examples of different reaction systems. The true reaction stoichiometries are all correctly identified, and the accurate kinetic models are obtained, showing satisfactory performance of the proposed method.     

A logistic kinetic model for isothermal and nonisothermal cure reactions of thermosetting polymers

A model describing the low‐temperature crystallization kinetics observed for thermoplastic polymers from the melt by differential scanning calorimetry (DSC) was shown to accurately predict the cooling curves as a function of time and temperature. The model was successful for treating data for several cooling rates as well as for isothermal DSC data. In this article, we extended the model to cure reactions of thermosetting polymers. The parameters representing lower and upper exotherm reference temperatures in crystallization events have a different meaning for curing events. Thus, the model was modified to account for this change of context. The new model was tested for exothermic reactions of a Hysol® FP4527 epoxy adhesive system using data from DSC ramp heating experiments at several heating rates and also from isothermal experiments. Good fits were obtained for all the varied experimental conditions. The model made use of three fitting parameters with physical significance: a lower critical temperature (T_c) an activation energy (E_b), and a reaction order (τ + 1). Additionally, to complete the kinetic fitting, the dependence of the time to reach the reaction peak maximum for isothermal cure was considered. That dependence was found to follow a more simple model which is formally equivalent to that observed in isothermal crystallization, and which makes use of two parameters related to the limits of the temperature range in which the polymerization may occur. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40670.     

Rotating nanoparticle array electrode for the kinetic study of reactions under mixed control

A method for the determination of the intrinsic electrocatalytic activity of metal nanoparticles for reactions under mixed diffusion-activation control is proposed. The working electrode consists of a nanoparticle array supported on a rotating disc of an inert conducting substrate. This electrode configuration reduces significantly the contribution of the reactant diffusion to the experimental current-potential curves and consequently, the kinetic parameters of the reaction can be evaluated more accurately. A model was developed for the diffusion process in the proposed configuration, which includes a parameter related to the degree of dispersion of the nanoparticles on the electrode surface (active area factor). It allows one to evaluate changes in the current-potential plot under conditions of constant particle diameter, which is essential for the appropriate analysis of the electrocatalytic activity of nanoparticles. On this basis the dependences of the current and current density for the hydrogen oxidation reaction on overpotential, rotation rate, particle size and active area factor were derived. The validity of these expressions was verified through the analysis of experimental results.     

Selective exothermic catalytic reactions in a reverse heat front

A model system of exothermic reactions of selective and complete catalytic conversion is considered. The system comprises the reactions A + m[B] C + [], C + n[B] D + [], and B + [] [B], where A and B are the initial reactants, C is the desired product (of the selective conversion), D is the undesired side product (of the complete conversion), [B] is the reactant B chemisorbed on the catalyst surface, and [ ] is a free catalytic active site. Numerical study of the system of reactions in an adiabatic catalyst bed shows that the yield of the desired product and the specific performance of the catalyst can be significantly increased if the reactions are performed not under steady-state conditions but in unsteady-state modes involving periodic time-separated introduction of the reactants A and B. Of greatest interest is to carry out the process in a reverse heat front propagating upward the flow of the gaseous reaction mixture, since, in this front, the maximal catalyst temperature is much lower and also the conversion selectivity is high.Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 1, 2005, pp. 72–79.Original Russian Text Copyright © 2005 by Zagoruiko.     

Monte Carlo simulation of kinetic discontinuities in hydrocarbon hydrogenation reactions

Recent experimental studies of alkene and alkyne hydrogenation reactions have shown the presence of a transition between a reactive regime at low hydrocarbon surface coverage and a less reactive regime in which the catalyst surface is saturated with the hydrocarbon. This transition is discontinuous but reversible. Langmuir-Hinshelwood rate expressions cannot account for this discontinuity between the two regimes, indicating that the origin of the transition is related to the non-random distribution of reactants on the catalyst surface. Time-dependent Monte Carlo simulations of ethylene hydrogenation have been used to predict the presence of this transition and investigate the complex dynamics of the reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparison between simulated moving bed and reverse flow chromatographic reactors for equilibrium limited reactions

A staged linear model, containing five parameters, is developed to compare equivalent simulated moving bed chromatographic reactors (SMBCR) and reverse flow chromatographic reactors (RFCR). A first order reversible reaction and linear adsorption equilibrium, with preferential adsorption of the reactant is assumed. The analysis uses simple, easily computable analytical solutions that rigorously represents the transients in the cyclic steady state for both the RFCR and the SMBR. A comparison between the two types of reactors is carried out to determine the maximum conversion attainable and the range of operation where these systems have advantages over conventional steady state reactors. It is found that the maximum conversion of both reactors is similar. The range of operation in terms of amount of catalyst and range of switching times favors the RFCR, while the conversion at low separation factors favors the SMBCR.