乳状液膜分离Zn^2＋的界面传质阻力及传质模型

用Ｌｗｅｉｓ恒界面传质池对乳状液膜分离Ｚｎ＾２＋的传质阻力进行实验研究，结果表明由于表面活性剂单分子层的形成，使界面传质阻力占整个传质阻力的８５％。在此基础上所建立的既考虑界面传质阻力又考虑膜破碎的液膜传质模型能使用理论计算值与实验测定值符合较好。     

Interfacial Mass Transfer in Ligand Accelerated Metal Extraction by Liquid Surfactant Membranes

Abstract

Interfacial mass transfer rates were determined for the extraction of Co(II), Ni(II), and Cu(II) by di-(2-ethyl hexyl) phosphoric acid by using a modified Lewis cell. This allowed us to elucidate the effect of ligands on liquid surfactant membrane extraction of heavy metal ions by ligand addition to the external aqueous phase. The effects of different ligands on the kinetics of extraction and the influence of surfactant on interfacial resistance to mass transfer were then examined.     

Mass Transfer Rate with Liquid Ion Exchangers. The Role of Interfacial Chemical Reactions in the Extraction Kinetics by Dinonylnaphthalenesulphonic Acid and Trilaurylammonium Salts

Kinetics and interfacial tension studies concerning the liquid cation exchanger dinonylnaphthalene sulphonic acid (HD) and the liquid anion exchangers trilauryl-ammonium chloride and nitrate (TLAHCI and TLAHNO₃), performed in the laboratory, are reviewed. The interfacial tension studies have shown that, due to the very strong surface active properties of these compounds, even at very low bulk organic concentrations, the interfacial plane gets completely saturated with a strongly adsorbed monomolecular layer of the exchanger. The structure of the interface is such that the ion-exchange group faces the aqueous phase while its organic part is completely immersed in the organic diluent. Extraction kinetic experiments performed with a quiescent interface cell (Lewis cell) as a function of the stirring speed, interfacial area and volume of the phases have shown that (a) a region always exists where the extraction kinetics is independent of the stirring speed and (b) the exchange kinetics is directly proportional to the interfacial area and inversely proportional to the volume of the phases. These two facts, together with the knowledge of the interfacial structure of the exchanger, are a strong indication that interfacial chemical reactions can have a predominant effect in determining the extraction kinetics. Experiments performed at relatively high stirring speeds of the phase as functions of the chemical composition of the system have produced a set of interfacial chemical reactions which completely describe the kinetics of the liquid ion-exchange process. This set of reactions consists basically of the following steps: (a) formation of an interfacial complex between the interfacially adsorbed molecules of ion-exchanger and the metal cation or complex present in the aqueous solution, (b) replacement at the interface of the interfacial complex with bulk organic molecules of the ion-exchanger; this process, with a rate which is proportional to the organic concentration of the exchanger, occurs through the reaction with bulk molecules of the extractant, and (c) the reverse steps occur when organic to water transfer takes place. By applying the stationary condition to the interfacial complex its concentration has been evaluated and a rate expression derived which has led to the calculation of the rate constants of the chemical reactions. The following metal ions have been studied experimentally: Fe+³, Eu+³, Ce+³, Gd+³, Tm+³ with HD; FeCln³-n with TLAHCI and Pu(NO₃)n⁴-n with TLAHNO₃. By using the derived rate expressions and rate constants, distribution laws have been obtained to calculate equilibrium distribution data in good agreement with experimental results.     

湍球塔气液相界面结构及传质面积

湍球塔因其防堵塞、强湍动、传质面积大等特点,可作为烟气氨法脱碳后用磷石膏浆料净化尾气微量氨的气液传质设备。本文基于湍球塔液滴团聚分散理论研究了液滴和液膜形成的气液相界面结构,并得到气液传质面积的数学模型。在磷石膏浆料吸收氨法脱碳尾气微量氨的湍球塔实验装置中,在气体Re_g157~475、液气比1~6范围内进行实验研究,从实验数据回归得到的气液传质面积与理论计算值吻合。结果表明,湍球塔气液传质面积以团聚分散的液滴为主,湍球表面积占比不足25%。     

High Diffusion Permeability of Anion-Exchange Membranes for Ammonium Chloride: Experiment and Modeling

It is known that ammonium has a higher permeability through anion exchange and bipolar membranes compared to K⁺ cation that has the same mobility in water. However, the mechanism of this high permeability is not clear enough. In this study, we develop a mathematical model based on the Nernst–Planck and Poisson’s equations for the diffusion of ammonium chloride through an anion-exchange membrane; proton-exchange reactions between ammonium, water and ammonia are taken into account. It is assumed that ammonium, chloride and OH⁻ ions can only pass through membrane hydrophilic pores, while ammonia can also dissolve in membrane matrix fragments not containing water and diffuse through these fragments. It is found that due to the Donnan exclusion of H⁺ ions as coions, the pH in the membrane internal solution increases when approaching the membrane side facing distilled water. Consequently, there is a change in the principal nitrogen-atom carrier in the membrane: in the part close to the side facing the feed NH₄Cl solution (pH < 8.8), it is the NH₄⁺ cation, and in the part close to distilled water, NH₃ molecules. The concentration of NH₄⁺ reaches almost zero at a point close to the middle of the membrane cross-section, which approximately halves the effective thickness of the diffusion layer for the transport of this ion. When NH₃ takes over the nitrogen transport, it only needs to pass through the other half of the membrane. Leaving the membrane, it captures an H+ ion from water, and the released OH⁻ moves towards the membrane side facing the feed solution to meet the NH₄⁺ ions. The comparison of the simulation with experiment shows a satisfactory agreement.     

3D Modeling and Simulation of Mass Transfer in Vapor Transport through Porous Membranes

A 3D mathematical model is developed to predict the transport of water vapor through porous membranes. The model is based on solving the continuity, momentum as well as energy equations for water in the membrane contactor. The model's equations are numerically solved using the finite element method to obtain the concentration and temperature distributions of water in the membrane contactor. The model findings were in good agreement with experimental data. The proposed 3D model proved to be appropriate for predicting the performance of a membrane evaporator. Simulations were carried out in order to study the influence of different operating parameters and membrane structure on the membrane evaporation effectiveness. The results of simulation indicate that the gas velocity is a favorable parameter in the membrane evaporation process due to its tendency to keep the process far from the thermodynamic equilibrium.     

Overall Rate Analysis of the Gaseous Reduction of Stable Oxides Incorporating Chemical Kinetics, Mass Transfer, and Chemical Equilibrium

A unified mathematical relationship for the overall rate of gaseous reduction of a stable oxide that produces a volatile suboxide has been derived including the effects of a product gas in the bulk stream, chemical kinetics, mass transfer, and chemical equilibrium. The important effect of the small equilibrium constant is quantified. How the reaction conditions affect the overall rate at different asymptotic conditions is also elucidated. By using the obtained results, the conflicting previous claims on the rate-controlling mechanism for the hydrogen reduction of silica has been critically examined and reconciled. The small equilibrium constant of this reaction causes it to be rate controlled by mass transfer under typical conditions and its rate to be slow. How the presence of even a small amount of water vapor in the bulk gas greatly enhances the effects of the small equilibrium constant is elucidated from the mathematical derivation. In addition, the small equilibrium constant also causes the apparent activation energy of silica reduction by wet hydrogen to approach the Δ H ° of reaction and that by dry hydrogen to approach     Δ H °. Because of the large positive Δ H ° value associated with reactions with a large positive Δ G ° value, such a reaction has been mistaken to be rate controlled by chemical kinetics.     

Hydraulic Permeability,Mass Transfer,and Retention of PEGs in Cross-flow Ultrafiltration through a Symmetric Microporous Membrane

Abstract

The flow and retention of 0.1% w/w aqueous solutions of several polyethylene glycols with molecular weights ranging from 3,000 to 35,000 dalton are studied when they are tangentially filtered through a nuclear track-etched symmetric microporous membrane made from polycarbonate with transmembrane pressure differences going up to 200 kPa. The work was done within the framework of the film layer theory for the concentration polarization phenomenon which allows one to obtain the mass transfer coefficient for the cell used as a function of the feed circulation speed and the molecular weight of the solute. The retention curves obtained lead to a sieve radius smaller than the nominal one.     

Resistance and Mass Transfer Control through Passive Porous Films. I. A Transport Model for Diffusive Permeability

Abstract

The first part of this work describes a model for the passive transport of solutes through membrane systems formed by a low porosity film and the adjacent boundary layers. Model equations allow correlation of the overall phenomenological coefficient of diffusive resistance with the morphological and structural characteristics of the membrane system. Based on the general solution, the total resistance appears to be the result of three contributions related to the membrane itself, the associated boundary layers, and the pore end effects. Under specific conditions it is possible to obtain an explicit and simple functional dependence for each of these contributions as well as to express the solute concentrations in the membrane-boundary layer interfaces.     

A Combined Mass Transfer Coefficient Model for Liquid‐Liquid Systems under Simultaneous Effect of Contamination and Agitation

The simultaneous effect of contamination and agitation was investigated using a pilot rotating disc contactor and mass transfer in both directions with single drops in the absence of drop break‐up and coalescence. It is ideally required to account for the extent of contamination in a quantitative manner and in both phases with a single parameter. In this work, a combined mass transfer model is applied and an improvement is made using an empirical coefficient and having mathematical consistency. Based on 120 experimental data series obtained for each mass transfer direction, a correlation is proposed for the coefficient of this model.     

Separation of Toluene and n‐Heptane through Emulsion Liquid Membranes Containing Ag+ as Carrier

Using silver ions as carrier in oil/water/oil‐type emulsion liquid membranes, batch wise extraction experiments were carried out to separate toluene from a mixture of toluene and n‐heptane. The separation performances, represented by the permeation rate, emulsion stability, and separation factor, were analyzed systematically by varying the operating parameters, viz., contact time, concentration of Ag⁺, emulsification time, surfactant concentration, membrane stabilizer concentration, relative amount of solvent, and initial feed phase concentration. The emulsion liquid membranes thus formed are stable, and Ag⁺ and surfactant concentrations strongly affect the permeation behavior of toluene.     

Separation Behavior of Composite Polyamide Membranes from Mixed Amines: Effects of Interfacial Reaction Condition and Chemical Post-Treatment

Abstract

Composite polyamide membranes are prepared using in-situ interfacial polymerization using mixed amine system comprising 1,4-phenylene diamine and pipperazine. Separation performance of the membranes are studied as a function of the concentration of amine and acid chloride, the concentration ratio of the amines, nature of the acid chloride, and the presence of surfactant and acid acceptor in the aqueous reagent. The effect of esterification and hydrazide reactions involving residual carboxylic acid groups in the polymeric membranes on the co-polymeric composite membrane performance is also studied. The membrane performance can be tailored easily by conversion of the residual reactive functional groups in post-treatment.     

Oilfield Produced Water Treatment by Ceramic Membranes: Mass Transfer and Process Efficiency Analysis of Model Solutions

This work evaluated the performance of ceramic membranes in removing dispersed oil present in oilfield produced water, seeking to advance knowledge of the process, and identify the conditions for its application. The effect of the operating conditions and effluent characteristics were evaluated across a wide range, enabling establishment of operational limits for the permeation process. It was demonstrated that a flow regime corresponding to a Reynolds number (Re) greater than 6,000 does not imply significant improvements in membrane permeability. It was further found that the permeate flux exhibits a slight linear dependence with the salt concentration (C_S).     

Resistance and Mass Transfer Control through Passive Porous Films. II. Applications of a Two-Dimensional Model to Salt Transport through Porous Membranes of Moderate Porosity

Abstract

In a previous study we dealt with the practical equations and the range of validity of a two-dimensional model for the diffusive flux of a solute through a membrane system. In the present study we apply the equations to the results of the experimental determination of the flux of LiCl solutions through different types of polymeric microporous membranes (Nuclepore) at several temperatures between 25 and 50°C. Thus, we have established the concentration profiles in the membrane-boundary layers interfaces, the thickness of these boundary layers, the apparent pore diffusivities, and their temperature dependence. The values of each term of the diffusive resistance have been calculated, and the relative importance of each term on the total resistance of the barrier has also been analyzed.     

Modeling of Gas‐Solid Reactions: Kinetics,Mass and Heat Transfer,and Evolution of the Pore Structure

Mathematical models for simulating heterogeneous gas‐solid reactions must describe a complex set of physicochemical and thermal phenomena. These include the chemical reaction itself, at an interface whose area varies during the conversion, the transport of gaseous species by diffusion in the pores of the solid, whose size and number generally change in the course of reaction, diffusional transport in the layer of solid product, the evolution or consumption of heat by the reaction and its transport in the porous solid, etc. The present paper gives details of the equations employed to model each of these processes. Some computed results illustrate how increasingly sophisticated recent models describe the gradual obstruction of pores during reactions, such as the sulfation of lime, or the thermal effects related to the exothermic nature of the oxidation of zinc sulfide.