Kinetics of alkaline hydrolysis of 2-ethylbutylformate

The theory of mass transfer accompanied by chemical reaction has been used for studying the kinetics of alkaline hydrolysis of 2-ethylbutylformate at different temperatures and ionic strengths of aqueous alkaline solution. Experiments have been conducted in a stirred cell having a flat liquid-liquid interface. For aqueous phases containing 1–3 kmol/m³ sodium hydroxide, the alkaline hydrolysis conforms to the fast pseudo-first order reaction regime. The system is of considerable practical importance and can be successfully employed for the measurement of the interfacial area of a mechanically-agitated and flooded packed-bed liquid-liquid contactor.     

KINETICS OF ALKALINE HYDROLYSIS OF ISOAMYLACETATE

The theory of mass transfer accompanied by chemical reaction has been used to determine the kinetics of alkaline hydrolysis of isoamylacetate. The rate constant for the alkaline hydrolysis is around 9.52 cm³/(mole)(sec). This is much lower than the rate constant for alkaline hydrolysis of n-amyl acetate, which is about 85 cm³/(mole)(sec). The presence of an electrolyte like sodium chloride in the aqueous phase reduced the rate of extraction to some extent. The rates of extraction with sodium chloride in the aqueous phase and the corresponding rate constant values have been reported.     

Mass transfer behavior of liquid–liquid slug flow in circular cross-section microchannel

An alkaline hydrolysis reaction was used as the model reaction to investigate the performance of liquid–liquid slug flow microchannel. The specific interfacial area was determined through the photographic snapshot method physically by means of measuring the lengths of relevant slugs. The overall volumetric mass transfer coefficients were calculated through the Danckwerts’ model chemically. The influences of various operating conditions on the slug length, the overall volumetric extraction rate and the mass transfer coefficient were investigated quantitatively. A decreasing trend of volumetric mass transfer coefficients along the channel length was found. The linear dependence of the volumetric extraction rate on the volumetric mass transfer coefficient indicates that the overall rate of the process is determined by the mass transfer process. In addition, the volumetric mass transfer coefficients were correlated for different channel lengths.     

Alkaline hydrolysis of isoamylformate: Effect of dissolved electrolytes on kinetics

The kinetics of alkaline hydrolysis of isoamylformate with aqueous solutions of sodium hydroxide and pottassium hydroxide has been determined by using the theory of mass transfer with chemical reaction; the effect of presence of electrolyte salts such as sodium chloride and sodium sulfate in aqueous alkaline solution has been assessed. Experiments have been conducted in a stirred cell having a flat liquid—liquid interface. For the different aqueous phases employed, the alkaline hydrolysis conforms to the fast pseudo‐first order reaction regime. The system is of considerable practical importance and has been successfully employed for the measurement of the interracial area of a flooded packed bed contactor that contained cation exchange resin particles having a diameter of approximately 0.5 mm as packing particles.     

EXTRACTION RATE OF W-AMYL ACETATE WITH ALKALINE HYDROLYSIS IN AQUEOUS PHASE

It is confirmed experimentally that a “Diffusion controlled slow reaction model'“ explains very well the alkaline hydrolysis of n-amyl acetate at constant inlerfacial area. Mass transfer coefficient obtained from the model agrees well with that obtained from pure mass transfer experiment. Mass transfer coefficient can be correlated against Reynolds number, Schmidt number and vessel dimensions. Effect of diluents and solutes can also be explained using the above model. From the extraction rate of H-amyl acetate dispersed in aqueous phase in an agitated vessel, the second order reaction rate constant for hydrolysis of the ester with alkali in aqueous phase is estimated based on the above model. The estimated value of second order reaction rate constant for H-amyl acetate is almost identical to that for iso-amyl acetate or n-butyl acetate.     

EXTRACTION RATE OF W-AMYL ACETATE WITH ALKALINE HYDROLYSIS IN AQUEOUS PHASE

It is confirmed experimentally that a “Diffusion controlled slow reaction model'“ explains very well the alkaline hydrolysis of n-amyl acetate at constant inlerfacial area. Mass transfer coefficient obtained from the model agrees well with that obtained from pure mass transfer experiment. Mass transfer coefficient can be correlated against Reynolds number, Schmidt number and vessel dimensions. Effect of diluents and solutes can also be explained using the above model. From the extraction rate of H-amyl acetate dispersed in aqueous phase in an agitated vessel, the second order reaction rate constant for hydrolysis of the ester with alkali in aqueous phase is estimated based on the above model. The estimated value of second order reaction rate constant for H-amyl acetate is almost identical to that for iso-amyl acetate or n-butyl acetate.     

合成丁基多苷反应动力学模型

在描述固 -液非均相反应的缩芯模型的基础上对丁基多苷反应动力学进行研究 ,提出的包含传质步骤的固 -液界面反应模型能准确地描述合成烷基多苷的第 1步反应———形成丁基多苷的反应体系 .由界面反应模型推导的化学反应速度常数k_r 与传质系数k_B 的比值能直观地反映出化学反应速度与传质速度的相对大小 ,并得出反应体系的动力学参数     

Kinetics of fast alkaline hydrolysis of esters

The kinetics of alkaline hydrolysis of a variety of esters (liquid and solid), which are sparingly soluble in water, was studied by using the theory of mass transfer accompanied by fast pseudo first-order reaction. This method, under certain conditions, can cover a wide range of second-order rate constants (～ 1 to 10⁴ 1/g mole sec). Whenever possible the values of the rate constants obtained by the above method were compared with those obtained by a study of the kinetics in the homogeneous phase.     

The resistance of interphase mass transfer in colloidal liquid aphron systems

Colloidal liquid aphrons (CLAs) provide very large interfacial area and thus could enhance interphase mass transfer in multiphase processes. This work characterized the mass transfer behavior of CLAs during mass transfer of benzoic acid from cyclohexane in CLAs to water in a small stirred vessel. From experimental data the overall mass transfer coefficient K_L of the surfactant-stabilized CLAs was determined. The influence of stirring speed and concentration of surfactant used for formulating CLAs on K_L was investigated. The experimental results show that surfactant adsorbed on the interface of CLAs influences greatly the value of K_L, and when the surfactant concentration is below its CMC, the overall CLAs mass transfer coefficient K_L (mainly varying with the interfacial mass transfer resistance) could be fitted to the following expression:

K_L=H₁+H₂ln[C+H₃].     

Mass transfer with chemical reaction in liquid foam reactors

Mass transfer studies were conducted in a stable liquid foam reactor under various operating conditions to evaluate gas holdup, effective interfacial area, liquid-phase mass transfer coefficient and a modified interfacial mass transfer coefficient to include the surface-active agents employed. Gas holdup and effective interfacial area were evaluated experimentally. The interfacial mass transfer coefficient was evaluated semitheoretically, by considering the interfacial region as a separate phase and using the experimental data developed for mass transfer accompanied by a fast first-order chemical reaction. The liquid-phase mass transfer coefficient was also evaluated semitheoretically, using Danckwert's theory for the liquid phase and the experimental data on mass transfer accompanied by a slow pseudofirst-order chemical reaction. An experimental unit was set up to provide a stable flowing foam column, simulating the foam reactor. Mass transfer rates were studied for superfacial gas velocities in the range from 1.5 × 10⁻² m/s to 5 × 10⁻² m/s, giving gas residence times in the range from 20 to 55 seconds. A cationic and nonionic surface-active agent and three different wire mesh sizes, giving bubble size distributions in the range from 2.2 to 5.4 mm Sauter mean diameters, were employed. It is observed that gas holdup is insensitive to the type of surface-active agent; it is however, dependent on wire mesh size and gas velocity. The bubble diameter and, hence, the interfacial area are found to be insensitive to gas velocity in the range studied; they are, however, strong functions of wire mesh size. The liquid-phase mass transfer coefficient increases with increase in gas velocity. The surface-active agent introduces additional resistance to mass transfer in both reaction cases, this being the controlling one in the case of the fast reaction. A comparison with conventional packed bed contactors indicates the mass transfer rates to be about 8 times lower for the foam reactor, for the fast reaction case; for slow reactions, the foam reactor has mass transfer rates approximately 2-4 times higher than those for conventional packed bed contactors.     

Soil Clean-Up by Surfactant Washing. IV. Modification and Testing of Mathematical Models

Abstract

Three models for the operation of surfactant washing/flushing columns or test beds are developed. These differ in the manner in which hydrophobic contaminant is held in the soil and, therefore, in the nature of mass transfer of contaminant from the stationary phase to the advecting surfactant solution. The fitting of parameters to experimental results is addressed, following which the parameters obtained are used to simulate operation of laboratory columns and a pilot-scale test bed. The results are compared which experimental data from the column and test bed. The air stripping of biphenyl from spent surfactant solution is modeled using a local equilibrium approach to see if air stripping could account for observed losses. The air stripping of toluene from the surfactant solution is modeled using a local equilibrium approach or a lumped parameter method to model diffusion-limited kinetics.     

OXIDATION OF MENTHOL: REACTION-RATE DETERMINATION BASED ON THERMODYNAMIC PROFILES

This study investigated the reaction kinetics of menthol oxidation. For this purpose the thermal profiles obtained from the measurements within the reaction calorimeter were used for the first time. In our case the reaction was performed under isothermal conditions using potassium dichromate as a catalyst. Due to the low solubility of menthol in water, acetone was added to the diluted sulfuric acid as a co-solvent. This caused the reaction medium to become more homogeneous and thus more appropriate for kinetic analyses without considering a mass transfer term.     

Influence of surface-active agents on the mass transfer from gas bubbles in a liquid—II

The mass transfer from a gas bubble in water is calculated for the important case where this mass transfer is decreased by the presence of surfactant in the liquid phase. In the calculation it is assumed that a stationary situation has been established as regards the exchange of surfactant between interface and bulk. The calculation takes as its starting point the equilibrium of forces existing between the drag force and the surface tension gradient at the bubble surface. The penetration theory is applied, allowance being made for the ‘stretching’ of the surface. Use is also made of Gibb's equation.It seems probable that the group c (dσ/dc)² is not only a measure of the influence of surface-active material on the mass transfer, but can also be characteristic of other processes, this group indicating the deceleration of the interfacial flow for a ‘stretching’ surface.This model only holds when the mass transfer is decresed less than about 30 per cent.     

Effect of surface properties of activated carbons on surfactant adsorption kinetics

This research investigates the adsorption properties of three activated carbons (AC) derived from coconut, coal, and wood origin. A linear relationship exists between the number of water molecules adsorbed onto each AC and the oxygen content determined elemental analysis and XPS. An inverse linear relationship exists between the plateau amount of dodecanoic acid anionic surfactant and the oxygen content on the surface of ACs. The surface charge on each AC’s surface had a linear relationship with the plateau amount of dodecanoic acid. A plug-flow heterogeneous surface diffusion model (PFHSDM) for a fixed-bed adsorption process was developed to describe the adsorption kinetics in a fixed-bed column. The model represents axially dispersed plug-flow, external mass transfer, adsorption equilibrium on the fluid-particle interface, and intraparticle diffusion. The larger molecular dimension of the dodecanoic acid as a more hydrophobic entity than octanoic acid led to a faster external mass transfer rate but a slower surface diffusion rate as estimated from the PFHSDM. The interaction between the organic moiety of surfactant and the AC surface chemistry such as surface oxygen content and surface charge contributes to the adsorption performance in both to the adsorption equilibrium and kinetics.     

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.     

Near-critical carbon dioxide extraction of khoa (Satureja boliviana Benth Briq) using ethanol as a co-solvent: Experiment and modeling

In this work the volatile oil from khoa was extracted using pressurized CO₂ with and without ethanol as co-solvent. Kinetic experiments were performed at pressures of 6.5 and 7 MPa and temperatures of 294.15 K. The composition of the volatile oil was determined using gas chromatography. The volatile oil was formed predominantly by cymene, 1-8 cineole, isomenthone, pulegone, thymol and caryophyllene. Consequently, we present a mathematical modeling study of the extraction of essential oil from khoa. The overall extraction curves (OECs) obtained for khoa oil were modeled considering the mass transfer based on local equilibrium between solvent and a solid. The influence of pressure and co-solvent on the extraction kinetics was evaluated using a mathematical modeling. The model was solved numerically and validated with experimental data. A novel method for calculating the initial mass fraction of khoa-extract is proposed; data of the proposed model are in excellent agreement with the experimental data. Furthermore, the influence of fluid flow rate and particle size has been studied on the extraction efficiency. Finally, a methodology has been established to estimate extraction yield curves in large scale using the data obtained in small-scale experiments.     

On the use of internal mass transfer coefficients in modeling of diffusion and reaction in catalytic monoliths

We utilize the recently developed concept of internal or intraphase mass transfer coefficient to simplify the problem of diffusion and reaction in more than one spatial dimension for a washcoated monolith of arbitrary shape. We determine the dependence of the dimensionless internal mass transfer coefficient (Sh_i) on washcoat and channel geometric shapes, reaction kinetics, catalyst loading and activity profile. It is also reasoned that the concept of intraphase transfer coefficient is more useful and fundamental than the classical effectiveness factor concept. The intraphase transfer coefficient can be combined with the traditional external mass transfer coefficient (Sh_e) to obtain an overall mass transfer coefficient (Sh_app) which is an experimentally measurable quantity depending on various geometric and transport properties as well as kinetics. We present examples demonstrating the use of Sh_app in obtaining accurate macro-scale low-dimensional models of catalytic reactors by solving the full 3-D convection-diffusion-reaction problem for a washcoated monolith and comparing the solution with that of the simplified model using the internal mass transfer coefficient concept.     

A kinetic study of the depolymerisation of poly(ethylene terephthalate) by phase transfer catalysed alkaline hydrolysis

BACKGROUND: Chemical or tertiary recycling of waste polymers including PET, poly(ethylene terephthalate), leads to the formation of raw starting monomers by different depolymerisation routes. This work was focused on the identification of the catalytic behaviour, if any, of a series of quaternary phosphonium and ammonium salts as phase transfer catalysts for the alkaline hydrolysis of PET, and on the determination of the kinetics of the phase transfer catalysed process. RESULTS: Among the salts examined tributylhexadecylphosphonium bromide was found to be the most effective catalyst. The proposed kinetic model accounted for the uncatalysed and catalysed reactions and predicted a linear correlation for the reaction rate with the concentration of the quaternary salt. The notable increase in the phase transfer catalysed reaction rate was related mainly to the greater value of the pre‐exponential factor while the value of the activation energy was hardly modified by the presence of the quaternary phosphonium salt, thereby suggesting a similar mechanism for the alkaline hydrolysis with or without phase transfer catalyst. CONCLUSIONS: The use of selected phosphonium quaternary salts exhibited a remarkably positive effect on the experimental conditions under which the depolymerisation of poly(ethylene terephthalate) by alkaline hydrolysis can be carried out, especially in terms of low operating temperature. Kinetic correlations provided a reliable mathematical reaction model for this recycling process, which is in agreement with the principles of sustainable development. Copyright © 2008 Society of Chemical Industry     

油水分层流条件下腐蚀动力学特性模拟

当石油输送管道内处于油水分层流条件时,管道底部与酸性水层接触极易造成内腐蚀,严重威胁管道安全,传统的静止和单相流条件的腐蚀预测方法已不能指导管道的安全运行,而多相流动、离子传质、化学反应及电极动力学等多种不同尺度的物理化学过程对多相流腐蚀预测提出了挑战。本文基于多相流动特性及电化学腐蚀特性的耦合机理提出了分层流条件下腐蚀动力学模型,首先建立油水三层流传质计算模型,进而基于溶液区域和产物膜内部的传质计算,依据阴阳极电化学反应电流密度与传质通量之间的平衡关系,形成多相流条件下腐蚀预测方法。探究了离子传质、电极反应以及产物膜动态生长的耦合过程对腐蚀行为的作用机理,揭示了CO₂分压、温度对腐蚀发展规律的影响机制。研究发现温度、CO₂分压的改变会导致平衡反应方向的移动,从而改变离子浓度;离子的扩散系数是决定传质系数变化的内在原因;腐蚀速率的变化规律由产物膜生长和电极反应两种因素共同决定：腐蚀产物膜的生长会阻碍反应离子的传质效应,从而抑制腐蚀;而离子浓度的升高或传质增强会加快电极反应,促进腐蚀。     

The effects of reactant starvation and mass transfer in the rate measurement of fluid-solid reactions with small equilibrium constants

The purpose of this article is to analyze critically and quantitatively the effect of fluid reactant supply rates and mass transfer on the measurement of the rates of fluid-solid reactions, particularly those with small equilibrium constants. It is shown through a mathematical analysis that the measurement of the intrinsic kinetics of a reaction with a small equilibrium constant (a positive standard free energy of reaction) requires much larger rates of fluid reactant supply and mass transfer rates than that of a reaction with a large equilibrium constant. The overall reaction rate of the former also tends to be slow. Furthermore, the apparent activation energy of such a reaction approaches the standard enthalpy of reaction (ΔH⁰), rather than the true activation energy of the chemical reaction.