Numerical study of the coupling between reaction and mass transfer for liquid‐liquid slug flow in square microchannels

While the benefits of miniaturization on processes have been widely demonstrated, its impact on microfluidics and local mechanisms such as mass transfer is still little understood. The coupling between reaction and mass transfer in microchannels is simulated for liquid‐liquid slug flow. First, the extrapolation to confined flow of the classical model used to calculate interfacial mass fluxes in reactive infinite media was studied. This model consists in estimating transferred fluxes between two phases as a function of the enhancement factor E. Its expression depends on the model used to represent interfacial mass transfer. In infinite media, Lewis and Whitman's stagnant film theory is generally preferred for its simplicity and its reliability. In the case of confined slug flow, the limitation of such a model to predict interfacial fluxes is highlighted. Second, the case of liquid‐liquid competitive consecutive reactions in microchannels is considered. The unfavorable impact of the length between droplets on selectivity is emphasized. This is a direct consequence of mass‐transport mechanisms in microchannels. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

DIFFUSION AND MASS TRANSFER IN MICELLAR SYSTEMS

Research on diffusion and mass transfer in micellar systems is reviewed. Models for interfacial transport at liquid/liquid interfaces, solubilization at solid/liquid and at liquid/liquid interfaces, and for detergency are discussed and similarities between these phenomena are elucidated. The literature on diffusion in micellar systems is discussed, especially in the region of the critical micelle concentration where previous investigators have presented results in disagreement with each other. Finally, the mechanism of micellar transport through membranes is also reviewed.     

双子表面活性剂溶液胶束微观结构研究

双子表面活性剂因其高界面活性、低临界胶束浓度、低浓度时增粘效果明显,在清洁压裂液增稠方面潜力巨大。而溶液胶束结构的形态及变化与溶液粘度密切相关,因此准确表征不同浓度下双子表面活性剂溶液胶束微观结构形态及变化特征具有重要理论指导意义。在大量调研表面活性剂溶液胶束结构形态检测方法与表征的基础上,重点阐述了可用于双子表面活性剂溶液胶束微观结构表征的研究方法及其研究发展现状。     

Flow behavior of sucrose stearate/water systems

The aim of this work was to carry out a rheological study of aqueous systems containing a nonionic surfactant derived from sugar. The compositions studied ranged from the micellar region up to the occurrence of fully developed liquid crystals. This study was carried out at 50°C. Systems up to 2% (wt) sucrose stearate exhibited a power-law decrease in the steady-state apparent viscosity with shear rate. At higher sucrose stearate concentrations, the flow curves exhibited two well-defined regions depending on shear rate, so that the apparent viscosities fitted the Carreau model A [Carreau, P.J., D. De Kee and M. Daroux,Can. J. Chem. Eng. 57:135 (1979)]. The existence of three composition ranges is proposed. An increasingly stronger micellar structure, as surfactant concentration rises, extends up to 10% (wt) sucrose stearate. Between 15% and 35% (wt) sucrose stearate, the results obtained are consistent with the occurrence of a lamellar liquid-crystal dispersion in an isotropic micellar solution. The liquid crystalline content in the dispersion steadily increases with surfactant concentration up to reaching a fully developed lamellar liquid crystal at 40% (wt) sucrose stearate.     

An overview of the mathematical modelling of liquid membrane separation processes in hollow fibre contactors

Liquid membranes have traditionally been employed for liquid/liquid mass transfer and have found applications in industrial, biomedical and analytical fields as well as in hydrometallurgical processes, wastewater treatment and remediation of polluted groundwater. However, in spite of the known advantages of liquid membranes, there are few examples of industrial application. The development of reliable mathematical models and design parameters (mass transport coefficients and equilibrium or kinetic parameters associated with the interfacial reactions) is a necessary step for design, cost estimation, process optimisation and scale‐up. This work reports an overview of the different approaches that have been proposed in the literature to the mathematical modelling of liquid membrane separation processes in hollow fibre contactors providing, at the same time, a useful guideline to characterise the mass transport phenomena and a tool for the optimal design and intensification of separation processes. Copyright © 2009 Society of Chemical Industry     

Effect of photoinitiator segregation on polymerization kinetics in lyotropic liquid crystals

Through photopolymerization lyotropic liquid crystalline (LLC) phases may be templated onto organic polymers to yield highly complex nanostructures. In order to understand the unique polymerization behavior controlling structural development in LLC media, the polymerization kinetics in these systems have been studied using several commercially available photoinitiators. Although monomer segregation and diffusional restrictions largely govern the kinetics in these systems, the initiation may also be influenced by changing LLC order and composition. Nonpolar monomers, which partition to the oil soluble domains of the LLC phase typically display the fastest rate of polymerization in micellar aggregates. The rate decreases in phases with larger nonpolar domains due to decreasing localized double bond concentration. Polar monomers exhibit the opposite behavior. However, the segregation of photoinitiator may contribute to significantly different trends in polymerization behavior. Relatively mobile initiators, displaying favorable interaction with water, yield a trend in polymerization that is governed primarily by monomer and diffusional effects. When bulkier, hydrophobic initiators are used, the polymerization appears much less dependent on these effects. Rather than the decreasing rate usually observed at higher surfactant concentrations, polymerization of oil soluble monomers with the less mobile initiators shows the opposite trend of increasing rate at higher surfactant concentration. This behavior likely results from increasing initiator efficiency of the bulky, hydrophobic initiator in the surfactant rich environment.     

Separation of liquid–liquid dispersion in a batch settler: CFD-PBM simulations incorporating interfacial coalescence

Several commercially important chemical processes involve liquid–liquid phase separation. In the present work, we have developed a multi-fluid Eulerian CFD model using OpenFOAM that incorporates binary and interfacial coalescence processes. We simulated separation of kerosene dispersed in water in a batch settler and validated the predictions using the measurements of time-evolution of coalescing and settling interfaces, local dispersed-phase volume fraction (α_O) and drop size distribution (DSD). Simulations are performed to understand the contributions of binary and interfacial coalescence processes to the phase separation process. While the time-evolution of coalescing and settling fronts can be predicted reasonably well using the two-fluid model with empirically-corrected drag models, local α_O and DSD could not be predicted. We have shown that the comprehensive multi-fluid Eulerian model, which incorporates binary and interfacial coalescence, predicts the time-evolution of the coalescing and settling fronts, local α_O and the DSD in an excellent agreement with the measurements.     

Interfacial properties of cationic and anionic Gemini surfactant mixtures

The possibility and the prospect of cationic/anionic (“catanionic”) surfactant mixtures based on sulfonate Gemini surfactant (SGS) and bisquaternary ammonium salt (BQAS) in the field of enhanced oil recovery was investigated. The critical micelle concentration (CMC) of SGS/BQAS surfactant mixtures was 5.0 × 10⁻⁶ mol/L, 1–2 orders of magnitude lower than neat BQAS or SGS. A solution of either neat SGS or BQAS, could not reach an ultra-low interfacial tension (IFT); but 1:1 mol/mol mixtures of SGS/BQAS reduced the IFT to 1.0 × 10⁻³ mN/m at 100 mg/L. For the studied surfactant concentrations, all mixtures exhibited the lowest IFT when the molar fraction of SGS among the surfactant equaled 0.5, indicating optimal conditions for interfacial activity. The IFT between the 1:1 mol/mol SGS/BQAS mixtures and crude oil decreased and then increased with the NaCl and CaCl₂ concentrations. When the total surfactant concentration was above 50 mg/L, the IFT of SGS/BQAS mixtures was below 0.01 mN/m at the studied NaCl concentrations. Adding inorganic salt reduced the charges of hydrophilic head groups, thereby making the interfacial arrangement more compact. At the NaCl concentration was above 40,000 mg/L, surfactant molecules moved from the liquid–liquid interface to the oil phase, thus resulting in low interfacial activity. In addition, inorganic salts decreased the attractive interactions of the SGS/BQAS micelles that form in water, decreasing the apparent hydrodynamic radius (D_{H, app}) of surfactant aggregates. When the total concentration of surfactants was above 50 mg/L, the IFT between the SGS/BQAS mixtures and crude oil decreased first and then increased with time. At different surfactant concentrations, the IFT of the SGS/BQAS mixtures attained the lowest values at different times. A high surfactant concentration helped surfactant molecules diffuse from the water phase to the interfacial layer, rapidly reducing the IFT. In conclusion, the cationic-anionic Gemini surfactant mixtures exhibit superior interfacial activity, which may promote the application of Gemini surfactant.     

Effects of 1-Alkyl-(and 1-Benzyl)-2,3-Dimethylimidazolium Ionic Liquids as Additives on the Micellar Behavior of Surfactant SB-12

The micellization and surface-active behavior of zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SB-12) in aqueous media were investigated in the absence and presence of different alkyl-appended and benzyl-appended ionic liquids (IL) 1-butyl-2,3-dimethylimidazolium chloride [bdmim][Cl], 1-butyl-2,3-dimethylimidazolium bromide [bdmim][Br], 1-hexyl-2,3-dimethylimidazolium bromide [hdmim][Br], and 1-benzyl-2,3-dimethylimidazolium chloride [bzdmim][Cl]. The characteristics of self-organization processes in SB-12 + IL/water systems include critical micelle concentration (cmc), aggregation number (N_agg), micellar size (D), surface, and adsorption parameters. These parameters were determined by the fluorescence and surface tension measurements. In SB-12 solutions, cmc were found to be decreasing to different extents in the presence of all the studied IL than in pure water. The addition of IL [hdmim][Br] decreases the cmc of aqueous SB-12 to rather a low extent. The other three IL show a prominent lowering in cmc of surfactant SB-12 to different magnitude. The maximum lowering in cmc was observed due to addition of benzyl-appended IL [bzdmim][Cl]. The aggregation number of aqueous SB-12 solution obtained in general is higher at high wt.% of added IL. The average micellar size was also found to increase upon addition of IL. Both IL anions and cations interacted with the charged centers present on the zwitterionic surfactant SB-12, which caused a substantial increase in the surface activity.     

离子液体表面活性剂的合成与应用(Ⅷ)——在分析中的应用

离子液体表面活性剂同时具有有机溶剂的属性和优良的表面活性,在分析中得到了广泛应用。在微波/超声波辅助下,利用离子液体表面活性剂水溶液的胶束增溶作用,可对各种固体中的有机物进行萃取,同时也可以在萃取结束后加入化学试剂使水溶性表面活性剂变成水不溶性表面活性剂,实现原位预浓缩提高分析的灵敏度。离子液体表面活性剂可以作为HPLC的固定相、胶束动电毛细管色谱的准固定相等实现有机物的分离和手性拆分。离子液体表面活性剂通过与金属离子形成络合物实现增敏光谱测定金属离子。离子液体表面活性剂修饰电极后能够促进电子传递和提高电分析灵敏度。     

表面活性剂浓度对泡沫体系稳定性的影响

主要探讨了在泡沫体系内,表面活性剂对泡沫稳定性的影响,以表活剂浓度为主要研究点,总结了不同表活剂浓度下气泡的聚并过程,还分析了液膜的排液过程,指出界面流变学因素以及表活剂高浓度情况下的胶束分层现象是影响泡沫稳定的主要因素.表活剂浓度低于CMC时,界面流变学因素起主要决定作用;表活剂浓度高于CMC时,胶团分层起主要决定作用.     

Enzyme Separation Using Supported Liquid Membrane Filled with Reversed Micelles

Abstract

A phenomenological model describing the transfer of lysozyme between a bulk aqueous phase and a reversed micellar phase in a stirred membrane cell has been confirmed. Transport of the enzyme at the interface at low surfactant concentrations is dominant, while that through the membrane is the rate-determining step at high surfactant concentrations. Complete separation of α-chymotrypsin from lysozyme using a supported liquid membrane filled with reversed micelles demonstrates the feasibility of the present process for enzyme separation.     

Drop rise velocities and fluid dynamic behavior in standard test systems for liquid/liquid extraction—experimental and numerical investigations

The fluid dynamic behavior of single organic droplets rising in a quiescent ambient liquid is investigated experimentally and numerically. Three standard test systems for liquid/liquid extraction recommended by the European Federation of Chemical Engineering (EFCE) but without the respective transfer component have been chosen for the investigations: toluene/water, n-butyl acetate/water, and n-butanol/water, representing systems with high, medium, and low interfacial tension. Simulations are performed using the academic code Navier, which features a sharp interface representation and a variational formulation of the curvature. The validity of both correlations and the results obtained by dynamic numerical simulation is discussed in terms of terminal rise velocity, aspect ratio, and the onset of shape oscillation. The numerical results show excellent agreement with experiments in all three test systems, and with simulations in the n-butanol/water system published recently by Bertakis et al. (2010). The presented numerical method is applicable for a wide range of interfacial tension, whereas the investigated correlations lose accuracy with decreasing interfacial tension.     

On the permeation rate of copper extraction through liquid membranes

The understanding of the permeation rate of metal ions through liquid membranes is important for the design of such systems. In this paper, the permeation rates of copper ions through liquid surfactant membranes, including interfacial reaction rates and the diffusion rate of the copper ion, were analyzed using a model based on a mobilized hollow spherical globule configuration. The analysis shows that the extracting reaction is dominant at the external interface of the membrane and the stripping reaction is dominant at the internal interface; this means the reactions at both interfaces are not in equilibrium during the course of extraction. It also shows that the extraction rate, the diffusion rate and the stripping rate are not of equal value, especially at the early stage of the run.     

Interaction between reverse micelles as a key factor governing back-extraction of proteins and its control systems

The interfacial transport processes of proteins from a reverse micellar phase to an aqueous phase have been investigated focusing on micellar-micellar interaction. The proteins solubilized into reverse micelles were back-extracted to the aqueous phase depending on the concentration of reverse micelles in organic phase. This fact seems to suggest the importance of micellar-micellar interactions in back-extraction processes. The interactions induced by various alcohol addition and temperature change could be evaluated easily and quantitatively by the percolation phenomena in reverse micellar systems (RVMS). The interactions were influenced considerably by the presence of small amount of alcohol and temperature in the RVMS. The addition of alcohols promotes the back-extraction of proteins depending on their species and concentrations. In particular, the alcohols that suppress the cluster formation of reverse micelles, remarkably improve the back-extraction processes. With a small amount of alcohol (20 mM OctOH), Bovine carbonic anhydrase (CAB) can be back-extracted completely from reverse micelles to aqueous solution at the optimal temperature, in which the so high concentration of salt is not necessary.     

Insights Into Molecular Interaction of Antitumor Drug Mitoxantrone With Anionic Surfactant Sodium Dodecyl Sulfate at Different Temperatures

A study of the interaction of antitumor drug mitoxantrone with anionic surfactant sodium dodecyl sulfate (SDS) has been carried out by UV–Vis absorption spectroscopy at submicellar and micellar surfactant concentrations, pH 7.4 and 10, and over a temperature range of 293.15–323.15 K. The variation of the monomer drug absorbance as a function of SDS concentration indicates, at pH 7.4 and all investigated temperatures, two definite processes: process I in the submicellar range, attributed to the electrostatic interaction between mitoxantrone and SDS monomers; and process II in the micellar range, when the drug is incorporated into SDS micelles in monomer form. At pH 10, the results have indicated only the process II at micellar SDS concentrations. The monomer absorbance changes occurring as a result of the interactions between mitoxantrone and SDS were rationalized in terms of binding constant, micelle/water partition coefficient, and the corresponding thermodynamic parameters for binding and partitioning processes. Thermodynamic parameters indicate that at pH 7.4 both binding process of mitoxantrone to SDS and partition process of mitoxantrone between micellar and bulk aqueous phases are spontaneous and enthalpy controlled, while at pH 10 both processes are spontaneous and entropy controlled.     

Extraction of erythromycin‐A using colloidal liquid aphrons: I. Equilibrium partitioning

Colloidal liquid aphrons (CLAs) are surfactant‐stabilised solvent droplets which have recently been explored for use in pre‐dispersed solvent extraction (PDSE). In this work, the equilibrium partitioning of a microbial secondary metabolite, erythromycin, has been studied using both CLAs (formulated from 1% (w/v) Softanol 120 in decanol and 0.5% (w/v) SDS in water) and surfactant‐containing, two‐phase systems. The equilibrium partitioning of erythromycin was found to be strongly influenced by the extraction pH, and exhibited a marked change either side of the pK_a of the molecule. A modified form of the Henderson–Hasselbach equation could be used as a simple design equation to predict the equilibrium partition coefficient (m_eryt = C_org /C_aq) as a function of pH. For extraction experiments with dispersed CLAs where pH > pK_a, m_eryt values as high as 150 could be obtained and the erythromycin could be concentrated by factors of up to 100. Experiments were also carried out in surfactant‐containing, two‐phase systems to determine the effect of individual surfactants used for aphron formulation on erythromycin partitioning. For extraction at pH 10 neither the Softanol (a non‐ionic surfactant) nor SDS (an anionic surfactant) had any influence on the equilibrium erythromycin partition coefficients. For stripping at pH 7, however, it was found that recovery of erythromycin from the organic phase decreased with increasing concentration of SDS, although again the Softanol had no influence on the equilibrium. The effect of SDS was attributed to a specific electrostatic interaction between individual erythromycin and SDS molecules under stripping conditions. The m_eryt values and concentration factors achievable in the two‐phase systems were considerably less than those for the PDSE experiments. The physical properties of the two‐phase systems, ie density, viscosity, interfacial tension, etc, and the equilibrium distribution of the surfactants were also determined in relation to subsequent studies on the kinetics of erythromycin extraction. © 2000 Society of Chemical Industry     

激光诱导荧光技术测量规整填料内的液体分布

介绍了利用激光诱导荧光技术（LIF）测量规整填料内的液体分布的实验方法,实现了液体分布的可视化,得到了液膜厚度和持液量等定量信息。利用LIF技术分别测量了3种物系在750Y型规整填料的实验装置内的液体分布。结果表明,表面张力和黏度都对填料表面上的液体分布有影响,但表面张力对液膜厚度和持液量的影响较大,是主要影响因素。     

Colloid‐Enhanced Ultrafiltration of Chlorophenols in Wastewater: Part IV. Effect of Added Salt on the Surfactant Leakage in Surfactant Solutions and Surfactant–Polymer Mixtures

Abstract

The critical aggregation concentration (cac) in surfactant–polymer mixtures approximates a lower limit to the surfactant concentration in the permeate (surfactant leakage) in polyelectrolyte micellar‐enhanced ultrafiltration. Here, the cac was measured at different salinities by using surface tension measurements. It was found that the cac increases slightly with the addition of simple salt, then the cac value decreases at higher salt concentration. The critical micelle concentration (CMC), which approximates surfactant leakage in micellar systems (no polymer), decreases monotonically with increasing salinity for ionic surfactants. The surfactant leakage in colloid‐enhanced ultrafiltration (CEUF) processes is investigated by using a dialysis method in the presence of three phenolic solutes with various degrees of chlorination: 2‐monochlorophenol (MCP), 2,4‐dichlorophenol (DCP), and 2,4,6‐trichlorophenol (TCP). Cetylpyridinium chloride (CPC) or n‐hexadecylpyridinium chloride is used as a cationic surfactant; and sodium poly(styrenesulfonate) (PSS) is used as an anionic polyelectrolyte. The effect of salinity and type of colloid is focused on here. In the absence of added salt, the cac can be over an order of magnitude less than the CMC, as can be surfactant leakage with added polymer. The added salt reduces the surfactant leakage in the micellar solution due to CMC reduction in the presence of electrolyte. In the surfactant–polymer mixture, the surfactant leakage is dramatically affected by salinity.     

On the Relationships between the Hydrophilic–Lipophilic Balance and the Nanoarchitecture of Nonionic Surfactant Systems

Building links between established parameters for the characterization of surfactant systems is useful not only for the understanding of the underlying phenomena but also for the judicious formulation of products. Herein, we review comprehensively the literature data to find correlations between the hydrophilic–lipophilic balance (HLB) and the molecular packing parameter (CPP) for a variety of nonionic surfactants in water. The interfacial area per surfactant molecule, a fundamental variable to calculate CPP, follows a power law as a function of the number of ethylene oxide (EO) groups in the surfactant. The exponent ranges from 0.3 to 0.7, which may reflect changes in the conformation of the EO chain depending on the nature of the hydrophobic group; there is also apparently a transition toward a collapsed conformation of the EO chains at high surfactant concentrations. CPP is found to change linearly with HLB in the range of data studied, although the parameters of the linear fitting depend on the nature of both hydrophobic and hydrophilic moieties of the surfactant; this would also imply a linear relationship between CPP and the HLB temperature (i.e., Phase Inversion Temperature) according to the Kunieda–Shinoda equation. Analysis of the liquid crystal regions of the surfactant phase diagram at constant temperature indicates that the HLB values required for the morphological phase transitions defined by CPP increase with surfactant concentration. The present report may serve as a contribution to the programmed design of nanoarchitectures in surfactant systems.