Phase Behavior of Supercritical CO2 Microemulsion with AOT and its Solubilization Properties of 1,3-propanediol

The phase behaviors of three microemulsion systems were studied in a custom-made volume-variable view cell, including the ternary system of CO₂/EtOH (ethanol)/1,3-PDO (1,3-propanediol), quaternary system of CO₂/EtOH/H₂O/1,3-PDO and quinary system of AOT/CO₂/EtOH/H₂O/1,3-PDO, using 1,3-PDO as the model compound, AOT (sodium bis(2-ethylhexyl) sulfosuccinate) as surfactant and ethanol as co-solvent in the CO₂ continuous phase. The phase behaviors of the AOT/CO₂/EtOH/H₂O/1,3-PDO quinary system were mainly discussed in the temperature range of 29.1°C–44.3°C and pressure range of 6.41 MPa-15.95 MPa. The result shows that a thermodynamically stable microemulsion can be formed by controlling the operating pressures and temperatures, which can provide basic thermodynamics data for industrial design and proper operating conditions for selectively solubilizing 1,3-PDO from dilute aqueous solution.     

Comparison of the Composition and Structural Parameters of W/O Microemulsions Containing Gemini Imidazoliums with Those Containing Monomeric Analogues

The composition and structural parameters of W/O microemulsions containing the gemini surfactant 1,4‐bis(3‐alkylimidazolium‐1‐yl) butane bromide [(C_n‐4‐C_n)Br₂, n = 12, 14, 16] + pentan‐1‐ol + octane + water and W/O microemulsions containing the ionic liquid surfactant 1‐alkyl‐3‐methylimidazolium (C_nmimBr, n = 12, 14, 16) + pentan‐1‐ol + octane + water were studied and compared. The mole fractions of the n‐alkyl alcohol at the interfacial layer in (C_n‐4‐C_n)Br₂ based microemulsion systems are always larger than those in C_nmimBr based microemulsion systems. However, the mole fractions of the n‐alkyl alcohol in the oil phase are nearly the same for both the microemulsion systems. The (C_n‐4‐C_n)Br₂ based microemulsion systems have greater absolute values of the free enthalpy values than that for C_nmimBr based systems. In the (C_n‐4‐C_n)Br₂ based microemulsion systems, a large number of cosurfactants at the interfacial layer is conducive to the formation of a smaller droplet W/O microemulsion. The effects of n‐alkyl alcohols, alkanes, salinity and temperature on the composition and structural parameters of the (C_n‐4‐C_n)Br₂ based and C_nmimBr based microemulsion systems were also investigated and discussed.     

正丁醇对二(2-乙基己基)琥珀酸酯磺酸钠微乳液体系的影响

通过在二(2-乙基己基)琥珀酸酯磺酸钠(AOT)/正庚烷/水的三元体系中加入正丁醇,得到了新的四元体系。绘制了25℃时AOT/正丁醇/正庚烷/水四元体系能够稳定存在的相图,发现在一定R值(水和AOT的摩尔比)条件下该相图出现了分为两个区域的现象。利用电导率数据研究了由W/O型微乳液→双连续微乳液→棒状液晶→层状液晶→双连续微乳液→O/W型微乳液的结构转变。通过稀释法求得AOT/正丁醇/正庚烷/水微乳液体系的结构参数,结果表明:含水量增加,两个区域的自由能-△G0c→i都减小,对微乳液体系的稳定不利;含水量越低,越有利于微乳液的形成和稳定;AOT/正丁醇/正庚烷/水四元体系比以AOT作表面活性剂的三元体系有更大的微乳液区域,是一个适合制备所需功能性纳米粒子的体系。     

Inverse microemulsion polymerization of acrylamide in the presence of N,N-dimethylacrylamide

The presence of N,N-dimethylacrylamide (NDA) influences the stability of initial, clear, single-phase Winsor IV inverse microemulsion composed of toluene/AOT (sodium salt of bis(2-ethylhexyl) sulfosuccinate)/NDA/water/acrylamide (AAm). For a molar fraction of NDA, n_NDA = [NDA]/([NDA] + [AAm]) = 0.200 a single-phase system turned to a milky one during polymerization initiated by oil-soluble dibenzoyl peroxide or water-soluble ammonium peroxodisulfate, and finally a two-phase system was formed. For n_NDA values greater than 0.200 also the precipitation of a polymeric product was observed during polymerization. The (co)polymerization rate of AAm and NDA exponentially decreases with increasing value of n_NDA, while the reverse is true for the (co)polymer particle diameter. The results support the idea of simultaneously proceeding free-radical polymerization initiated by free radicals in continuous oil and dispersed water phase of the inverse microemulsion system.     

Extraction with Water-in-Carbon Dioxide Microemulsions: A Case Study on Steviol Glycosides

This work explores the use of water-in-supercritical carbon dioxide (scCO₂) microemulsions for the extraction of polar metabolites from plants. Stevia rebaudiana Bertoni leaves and polyethylene glycol trimethylnonyl ether (TMN) surfactants were selected for a case study. A CO₂-water-TMN 10 mixture at 35 °C and 30.0 MPa extracted 7 mg target analyte/g dry leaves. The extraction was proven to occur due to a water-surfactant liquid solution rather than a water-in-CO₂ microemulsion. Using a modified extraction setup, the microemulsion was created prior to extraction. TMN 6 was able to dissolve enough water in CO₂ to extract steviol glycosides, in detectable but very small amounts.     

Preparation of partly hydrophobized,crosslinked polyacrylamide particles by terpolymerization of acrylamide/ N,N‐methylenebisacrylamide/styrene in inverse microemulsion

Free‐radical polymerization of a termonomer system comprising acrylamide (AAm) N,N ′‐methylenebisacrylamide (MBAAm) and styrene (S) initiated by water‐soluble ammonium peroxodisulphate (APS) or by toluene‐soluble dibenzoyl peroxide (DBP) in inverse microemulsion (toluene/S/AOT//water//AAm/MBAAm), leads to the formation of partly hydrophobized crosslinked polymer particles of tailored chemical composition, degree of crosslinking and polymer particle size. Styrene strongly decreases the rate of terpolymerization, while the presence of MBAAm has almost no effect on the polymerization rates observed. This conclusion is valid for both APS and DBP initiators. Increase of the S/T mass ratio (T is toluene) in inverse microemulsion leads to an increase of polymer particle diameter from about 20 nm to about 50 nm attributed to toluene swelling of the styrene‐rich structural moieties of AAm‐co‐S copolymer located on the surface of polymer particles. Polymerization kinetics measurements pointed to the important role of exiting water soluble AAm and MBAAm monomer radicals generated by thermal decomposition of APS in water pools of inverse micelles for initiation of polymerization reactions of sparingly water‐soluble S monomer in the oil‐phase of the inverse microemulsion. It was shown that the polymerization and copolymerization reactions of S in the presence of AAm and/or MBAAm are effectively initiated by water‐soluble APS and also by oil‐soluble DBP initiators. During dialysis the polymerized single‐phase water/oil Winsor IV inverse microemulsion gradually converts itself into a two‐phase oil/water Winsor I dispersion system with volume fraction of aqueous phase Φ_aw ≈ 0.950. The water phase contains water swelled, crosslinked polymer particles of diameters 80–300 nm. During dialysis, toluene and the sodium salt of bis(2‐ethyl hexyl)sulphosuccinic acid (AOT) partition between the oil phase of the dialysed dispersion system and the water dialysate. After evaporation of water from the dialysed inverse microemulsion, solid, dried, crosslinked polymer particles in the form of a transparent film, almost uncontaminated by AOT surfactant, were obtained. © 2000 Society of Chemical Industry     

Extraction of Uranium and Thorium from Nitric Acid Solution by TODGA in Ionic Liquids

Extraction of uranium (UO₂²⁺) and thorium (Th⁴⁺) from a nitric acid solution into an imidazolium-type ionic liquids (ILs) of 1-alkyl-3-methylimidazolium hexafluorophosphate ([C_nmim][PF₆], n = 6 or 8) was carried out using N,N,N′,N′-tetraoctyl-3-oxapentanediamide (TODGA) as an extractant. It was found that the extraction efficiencies of UO₂²⁺ and Th⁴⁺ ions are higher in comparison with that done in n-dodecane. The extraction mechanism was deduced by the slope analysis and extraction experiment. Transfer of both ions is assumed to proceed predominantly through the neutral solvation mechanism from nitric acid solution into ILs. The UO₂²⁺ ion forms a 1:2 complex with TODGA in ILs at lower acidity, and a 1:1 complex in ILs and in n-dodecane at higher acidity. The Th⁴⁺ ion forms a 1:2 complex with TODGA in C₆mimPF₆ IL or a 1:1 complex in C₈mimPF₆ IL at lower acidity and a 1:1 complex in both ILs, and n-dodecane at higher acidity. Stripping studies were conducted using sodium salt of EDTA as a stripping ligand. The thermodynamics of extracting UO₂²⁺ ions and Th⁴⁺ ions from a 3 M HNO₃ solution was also studied. The results indicated that the extraction reactions are spontaneous and go through an exothermic process.     

Microemulsion polymerization in the water,aerosol-OT,tetrahydrofurfuryl methacrylate system

Summary Part of the phase diagram at low (<10%) oil content and 25°C has been mapped in the water, Aerosol-OT (AOT), tetrahydrofurfuryl methacrylate (THFM) ternary system. Sodium persulfate/sodium metabisulfite was used as a redox initiator to induce polymerization in this microemulsion system at 7.8% (w/w) THFM and 4.4% AOT. Conversions in excess of 90% were obtained. The parent microemulsion droplets have diameters on the order of 5 nm. The resulting latexes have average particle diameters of 37–39 nm. The latex particles are cross-linked as a result of radical induced opening of the tetrahydrofurfuryl ring, and exhibit nearly the same density (1.216 g/cm³) and glass transition temperature (67°C) as material (1.222 g/cm³; 62°C) produced by solution polymerization. This three-component microemulsion, and the corresponding latexes, have been imaged directly by cryo-electron microscopy. The first reports of three-component polymerized (oil in water) microemulsions, stabilized by cationic surfactants, were made by Murtagh, Ferrick, and Thomas [ACS Polymer Preprints 1987, 28, 441] and more recently by Perez-Luna, Puig, Castano, Rodriguez, Murthy, and Kaler [Langmuir 1990, 6, 1040]. this report appears to be the first such polymerization in a three-component system stabilized with an anionic surfactant. These latexes are cross-linked beads, and are the first such examples to be prepared by microemulsion polymerization.     

Fluorometric analysis on physicochemical properties of phosphatidylcholine-based W/O microemulsion involved with enzymatic reactivity in phospholipid hydrolysis

Interfacial tension and fluorometric analysis were employed for the investigation of the interfacial local fluidity and the hydrophobicity of the micro water pool in the PC-based water-in-oil (W/O) microemulsion. These microenvironment properties strongly influenced the phospholipase A₂ reactivity for phospholipid hydrolysis in the W/O microemulsion. The organic phase was prepared by mixing of isooctane as a main solvent and 1-butanol as a co-solvent. The critical micelle concentration (CMC) was dramatically decayed from 9mM to 0.025mM by the increasing of the 1-butanol content. The local interfacial fluidity of the micro water pool was measured by using fluorescence polarity indicated by 1,6-Diphenyl-1,3,5-hexatriene-4′-trimethylammonium tosylate (TMA-DPH) and Coumarin 343 (C343). It was apparently increased with increasing the molar ratio of additive 1-butanol. In contrast, the hydrophobicity of the water pool measured by C343 was almost constant throughout the molar ratio of additive 1-butanol. Additive alcohol influenced the micro fluidity and enhanced reactivity of phospholipase A₂ in lipid hydrolysis. This work was presented at 13 ^th YABEC symposium held at Seoul, Korea, October 20–22, 2007.     

Synthesis and evaluation of a ruthenium–copper oxide/silica catalyst derived from microemulsion processing

Bimetallic Ru–Cu catalysts supported on SiO₂ have been synthesized in microemulsions using sodium metasilicate (Na₂SiO₃), copper nitrate (Cu(NO₃)_2·3H₂O) and ruthenium chloride (RuCl₃) at 28 °C. The microemulsion system consists of sodium 1,4‐bis(2‐ethylhexyl) sulfosuccinate (AOT) and sodium dodecyl sulphate (SDS), cyclohexane, and an aqueous solution of sodium metasilicate or metal salts. The catalysts have been characterized by XPS, EDX/SEM with line scanning and they possess a very narrow pore size distribution (around 38 Å) and relatively high specific surface areas (around 400 m²/g). The catalytic results of the N₂O decomposition reveal that higher conversions of N₂O can be achieved by the catalysts synthesized from the microemulsion process at lower temperatures (around 400 °C).     

Extraction of Europium(III) into W/O Microemulsion Containing Aerosol OT and a Bulky Diamide. I. Cooperative Effect

Abstract

The extraction of Eu(III) from aqueous HNO₃ solution into a water‐in‐oil (W/O) microemulsion occurring in hexane was studied. Aerosol OT (AOT^?) was used as an anionic surfactant, and a bulky diamide (DA), N,N ^′‐dioctyl‐N,N ^′‐dimethyl‐2‐(3^′‐oxapentadecyl)propane‐1,3‐diamide, was employed as an electrically neutral extractant. The combination of AOT^? and the DA shows a very strong cooperative effect on the metal extraction. The microemulsion containing AOT^? alone in hexane, equilibrated with the acidic solution, is unstable. However, in the presence of the electrically neutral extractant acting as a “masking” ligand to H⁺, the microemulsion in the hexane phase is dramatically stabilized, which enhances the distribution of Eu(III) to the organic phase. The distribution of the metal in the micellar extraction system is also greatly affected by the concentration of an electrolyte, such as HNO₃ or NaNO₃, playing two important roles, i.e., the formation of the microemulsion, “promoting” the metal extraction, and the ion‐exchange of the metal ion for the cation yielded from the electrolyte, contrarily, “suppressing” the metal extraction.     

Antiradical Efficiency of Essential Oils from Plant Seeds Obtained by Supercritical CO2, Soxhlet Extraction,and Hydrodistillation

The effect of supercritical CO₂ (SCCO₂) extraction conditions (pressure and temperature) on the system performance as well as the antiradical efficiencies of the essential oils from Japanese pepper (Xanthoxylum piperitum DC.), cardamom (Elettaria cardamomum Maton), and fennel (Foeniculum vulgare) seeds were investigated. A control study with the conventional Soxhlet extraction and hydrodistillation was also conducted to compare the performance of those processes. Antiradical efficiencies were investigated by utilizing 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay with a UV-vis spectrophotometer. Higher pressure and temperature had positive effects on the supercritical process performance due to higher CO₂ density and substrate solubility in SCCO₂. Antiradical efficiencies of cardamom and pepper were almost the same, being significantly higher than that of fennel seeds. However, this effect decreased dramatically for all the spices when the extraction method was changed to Soxhlet extraction and hydrodistillation. SCCO₂ extraction was found to yield more quality and effective essential oils than Soxhlet extraction and hydrodistillation.     

Solubilisation of water in alkanes using nonionic surfactants

Nonionic surfactants are frequently used as emulsifiers in nonpolar oil + water systems and as solubilisation agents for oil in water, or vice versa. In the latter application the amount of, say, water that can be solubilised in nonpolar oil (to give microemulsion droplets) depends on: (a) the capacity of the micelles to incorporate water; and (b) the fraction of surfactant originally present as micelles. This paper is concerned with the single-phase water-in-oil (W/O) microemulsion regions enclosed by the haze and solubilisation boundaries at the oil-rich end of Shinoda-type phase diagrams. The systems studied contain the nonionic surfactant C₁₂H₂₅(OCH₂CH₂)₅OH (C₁₂E₅), normal alkane (heptane, decane or tetradecane) and water. Critical microemulsion concentrations (cμc) and droplet compositions for w/o microemulsions formed from C₁₂E₅ in alkane have been determined at phase boundaries over a range of temperatures. The results show how the maximum extent of water solubilisation is determined jointly by the cμc and the maximum droplet size for a given temperature. It appears that for larger (microemulsion) droplets, the cμc is determined by temperature rather than by droplet size. However, along part of the haze curves, aggregates form with only small amounts of water (less than four molecules per ethyleneoxy group on the surfactant head groups). For a given temperature, in the small range where either micelles or microemulsion droplets can exist, reverse hydrated micelles have much higher critical micelle concentrations (cmc) than the cμc of the larger microemulsion droplets.     

Electropolymerization of pyrrole in ionic liquid microemulsion

The direct electropolymerization of pyrrole in [BMIM]PF₆ microemulsion was investigated for the first time. The H₂O/TX-100/[BMIM]PF₆ (W/IL), bicontinuous (BC), [BMIM]PF₆/TX-100/H₂O (IL/W) subregions can be used as electrolytes for pyrrole electropolymerization. The use of IL microemulsion remarkably reduces the amount of IL. Furthermore, electrochemical measurements indicated that W/IL microemulsion was the optimal medium and its polymerization rate was the fastest. Compared with molecular solvent system (0.25 mol L⁻¹ [BMIM]PF₆/acetonitrile) and neat [BMIM]PF₆, the resultant films electrodeposited in W/IL microemulsion possessed excellent electrochemical activity and uniform morphology. All the results indicated that the H₂O/TX-100/[BMIM]PF₆ microemulsion as electrolyte medium is the most suitable for electropolymerization of pyrrole. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Separation of Gallium and Aluminum from HCl Solution by Microemulsion

Gallium was separated from aluminum in hydrochloric acid medium by a steady microemulsion. In the cetyltrimethylammonium bromide (CTAB)/n-pentanol/n-heptane/HCl/tributyl phosphate (TBP) system, TBP was introduced as the modifier to avoid emulsification of the microemulsion. The extraction efficiency on gallium was also improved by adding TBP. The factors that influenced the separation efficiency were explored. The results of the experiments showed that the gallium and aluminum were effectively separated within a very short time, and the extraction efficiencies of gallium and aluminum were 92% and 5%, respectively. The maximum back-extraction efficiency of gallium was 92% in HCl solution (4 M).     

Extraction of Lysozyme Using Reverse Micelles and Pressurized Carbon Dioxide

Abstract

Lysozyme was forward extracted in a reverse micellar process under conditions of varying ionic strength, pH, AOT level, and temperature both with and without high‐pressure CO₂. It was found that high‐pressure CO₂ reduced the extraction time under all conditions tested and increased the amount of protein transferred. Reasons for this are discussed. In addition, the CO₂ stripped lysozyme from the micelles efficiently, avoiding the need for the usual back extraction for purification.     

Preparation of tungsten borides by combustion synthesis involving borothermic reduction of WO3

An experimental study on the preparation of two tungsten borides, WB and W₂B₅, was conducted by self-propagating high-temperature synthesis (SHS), during which borothermic reduction of WO₃ and elemental interaction of W with boron proceeded concurrently. Powder mixtures with two series of molar proportions of WO₃:B:W = 1:5.5:x (with x = 1.16–2.5) and 1:7.5:y (with y = 0.5–1.33) were adopted to fabricate WB and W₂B₅, respectively. The starting stoichiometry of the reactant compact substantially affected the combustion behavior and the phase composition of the final product. The increase of metallic tungsten and boron reduced the overall reaction exothermicity, leading to a decrease in both combustion temperature and reaction front velocity. The initial composition of the reactant compact was optimized for the synthesis of WB and W₂B₅. In addition to small amounts of W₂B and W₂B₅, the powder compact of WO₃ + 5.5B + 2 W produced WB dominantly. Optimum formation of W₂B₅ was observed in the sample of WO₃ + 7.5B + 0.85W. Experimental evidence indicates that an excess amount of boron about 10–13% is favorable for the formation of WB and W₂B₅.     

Synergism Between Ni and W in the Niw/ γ-Al2O3 Hydrotreating Catalysts

A series of NiW/ γ-Al₂O₃ catalysts (20 and 30 wt% W and 1–5 wt% Ni) have been prepared and studied by TPR and XPS. HDS activity has been tested in the thiophene conversion. The effect of Ni and W loadings on the formation of different structures is presented. In the calcined catalysts several phases coexist, concentrations of which depend on the Ni/(Ni+W) atomic ratio. The Ni synergistic effect in the HDS reaction is confirmed by the increase in the HDS activity (~10–15 times). This effect is ascribed to the formation of an active NiWS phase of high dispersion from the mixed NiW oxide precursors. At higher Ni/Ni+W ratio a redistribution of active components in additional amount ofNiWS phase during sulfidation is suggested.     

Electrochemical behavior of K<Subscript>4</Subscript>Fe(CN)<Subscript>6</Subscript> in [bmim]PF<Subscript>6</Subscript>/TX-100/H<Subscript>2</Subscript>O based microemulsions

The electrochemical behavior of potassium ferrocyanide [K₄Fe(CN)₆] at Pt/ionic liquid (IL) microemulsion interfaces was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). H₂O/TX-100/bmimPF₆ was used to prepare three IL microemulsions: water in 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF₆) (W/IL), bicontinuous (WIL) and bmimPF₆ in water (IL/W). The results show that the IL microemulsion systems have relatively narrower potential windows compared with the pure IL system. The redox potential gap is about 100 mV in the pure water and the three IL microemulsions. The redox potentials of K₄Fe(CN)₆/K₃Fe(CN)₆ and the redox peak currents decrease in the order pure water, IL/W, WIL, W/IL. Furthermore, the peak currents increase linearly with the square root of the scan rate, while the diffusion coefficient increased in the order W/IL, WIL, IL/W. The Nyquist plots obtained in the WIL and IL/W systems show capacitive resistance arcs at high frequencies and 45° straight lines at low frequencies, implying that the electrochemical reactions are controlled by charge transfer and diffusion steps. For the W/IL system there is only a 45° straight line in the Nyquist plot, indicating that diffusion is the controlling step at all frequencies.     

Polymerization of acrylamide in single-phase in-verse dispersion systems at high volume fractions of dispersed phase

The preparation of single-phase inverse microemulsions of toluene/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/water/acrylamide (AAm) is described and their properties prior to polymerization (macro and microviscosity as a function of volume fraction Φ_aw of the dispersed aqueous (water + acrylamide) phase, of the [to-luene]/[AOT] molar ratio and of the acrylamide/water mass ratio) were studied. The polymerization of acrylamide in dispersion systems was initiated by the oilsoluble initiator dibenzoyl peroxide at 60°C. The polymerization rate of acrylamide for a given [toluene]/[AOT] molar ratio and AAm/water mass ratio monotonically decreases beyond a Φ_aw value of 20%. The polymer particle size in polymerized systems as well as the molecular mass of polymer in the polymer particles increase on increasing the acrylamide concentration in the aqueous phase and/or the Φ_aw values of the dispersion system. On increasing the surfactant AOT concentration both polymer particle size and polymer molecular mass decrease for a given set of other relevant parameters of the dispersion system (i.e. [toluene]/[AOT] and AAm/water ratios). The polymerized inverse dispersion system can be converted to an oil-in-water dispersion by addition of water.