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.     

A study of the photocatalytic degradation of metamitron in ZnO water suspensions

The photocatalytic degradation of the herbicide metamitron in water using ZnO under Osram ULTRA-VITALUX® lamp light was studied. The effect of the operational parameters such as initial concentration of catalyst, initial metamitron concentration, initial salt concentration (NaCl, Na₂CO₃ and Na₂SO₄) and pH was studied. The optimal concentration of catalyst was found to be 2.0 g/l. First-order rate constants were calculated for the uncatalysed reactions. On the base of the Langmuir-Hinshelwood mechanism, a pseudo first-order kinetic model was illustrated and the adsorption equilibrium constant and the rate constant of the surface reaction were calculated (0.119 l mg^− 1 and 0.836 mg l^− 1 min^− 1, respectively). The photodegradation rate was higher in acidic than in alkaline conditions. When salt effect was studied, it was found that sodium carbonate was the most powerful inhibitor used, while sodium chloride was the weakest one. A negligible inhibition was observed when the concentration of sodium chloride was 20 mM.The rate of photodecomposition of metamitron was measured using UV spectroscopy and HPLC, while its mineralization was followed using ion chromatography (IC), as well as total organic carbon (TOC) and total nitrogen (TN) analysis.Under the employed conditions, almost complete disappearance of 9 mg/ml of herbicide, 56% TOC and 34% TN removal, occurred within 4 h. The ion chromatography results showed that the mineralization led to ammonium, nitrite and nitrate ions during the process.     

Preparation, characterization and photoactivity of TiO2 obtained by a reverse microemulsion route

TiO₂ was synthesized by a reverse microemulsion route. By using different water contents in the reverse microemulsion, we obtained three different materials named R = 10, R = 20 and R = 30. The reverse microemulsion synthesis has the advantage that the kind of the crystalline titania structure obtained may be changed by simply modifying the water content in the microemulsion.The synthesized materials were characterized by nitrogen adsorption, scanning and transmission electron microscopy, and X-ray diffraction. Methylene blue (MB) was used as testing dye; we studied the pH effect and catalyst dosage in the MB photodegradation. The degradation kinetics was also studied.     

Phase diagram, viscosity and conductivity of α-sulfonate methyl esters derived from palm stearin/1-butanol/alkane/water systems

Phase diagrams of sodium salt α-sulfonate methyl esters derived from palm stearin (α-SMEPS)/1-butanol/alkane/water systems were constructed at 30.0±0.1°C. The presence and changes in the isotropic region of the quaternary mixtures of surfactant, co-surfactant, alkane (oil) and water were mapped with different oil compound (different hydrocarbon chain lengths). An attempt to elucidate the self-association behavior of α-SMEPS in the presence of butanol as co-surfactant and the effect of different alkane chain lengths was conducted by studying the viscosity and electrical conductivity behavior. Preliminary investigation suggested that the formation of oil-in-water (o/w) microemulsion, bicontinuous structure and water-in-oil microemulsion were based on the composition of mixtures in the isotropic region.     

Interfacial tension and the behavior of microemulsions and macroemulsions of water and carbon dioxide with a branched hydrocarbon nonionic surfactant

Measurements of interfacial tensions for 2-ethyl-hexanol-(propylene oxide)∼_4.5-(ethylene oxide)∼₈ (2EH-PO_4.5-EO₈) at the planar water-CO₂ interface and the surfactant distribution coefficient are utilized to explain microemulsion and macroemulsion phase behavior from 24 to 60 °C and 6.9 to 27.6 MPa. A CO₂ captive bubble technique has been developed to measure the interfacial tension γ at a known surfactant concentration in the aqueous phase, with rapid equilibration at the water-CO₂ interface. The surface pressure (γ_o − γ) decreases modestly with density at constant temperature as CO₂ solvates the surfactant tails more effectively, but changes little with temperature at constant density. The area per surfactant at the CO₂-water interface determined from the Gibbs adsorption equation decreases from 250 A²/molecule at 24 °C and 6.9 MPa, to 200 A²/molecule at 27.6 MPa. It was approximately twofold larger than that at the water-air interface, given the much smaller γ_o driving force for surfactant adsorption. For systems with added NaCl, γ decreases with salinity at low CO₂ densities as the surfactant partitions from water towards the W-C interface. At high densities, salt drives the surfactant from the W-C interface to CO₂ and raises γ. Compared with most hydrocarbon surfactants, this dual tail surfactant is unusually CO₂-philic in that it partitions primarily into the CO₂ phase versus the water phase at CO₂ densities above 0.8 g/ml, and produces γ values below 1 mN/m. With this small γ, a middle phase microemulsion and a C/W microemulsion were formed at low temperatures and high CO₂ densities, whereas macroemulsions were formed at other conditions.     

Synthesis of nanocrystalline 8 mol% yttria stabilized zirconia by the oleate complex route

Nanocrystalline 8 mol% yttria stabilized zirconia (YSZ) powder has been synthesized by the oleate complex route. Oleate complexes of zirconium and yttrium were formed in the hexane rich layer by the reaction of sodium oleate with zirconyl chloride and yttrium chloride at the interface of the two ternary solutions in water–ethanol–hexane system. The zirconyl oletae and yttrium oleate complexes on heating decomposed to oxide through the formation of carbonate intermediates. The powder obtained by calcination at 600 °C for 2 h was cubic YSZ with surface area of 42 m²/g. The YSZ powder contained primary particles of ∼300 nm size and the primary particles were aggregate of crystallites of 5–10 nm. The compacts prepared from the YSZ powder were sintered to ∼99% TD (theoretical density) at 1400 °C. The sintered YSZ had a low average grain size of 0.73 μm.     

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.     

Hydroisomerization-cracking of gasoline distillate from Fischer-Tropsch synthesis over bifunctional catalysts containing Pt and heteropolyacids

A gasoline distillate from the Fischer-Tropsch synthesis (so-called as F-T gasoline) was collected in a cold trap set in a gas-flowed slurry reaction system. The F-T gasoline contained 92.8 wt.% n-alkanes (ranged from n-C₄H₁₀ to n-C₁₄H₃₀), 2.4 wt.% 1-alkenes, and 4.8 wt.% iso-alkanes. By the hydroisomerization-cracking in an atmospheric flowed fixed-bed reactor over the catalysts containing Pt and heteropoly compound Cs_2.5H_0.5PW₁₂O₄₀ (abbreviated as Cs2.5), the F-T gasoline was converted to gasoline distillated mixed alkanes with a high iso/n ratio. A mechanical mixture of Pt/Al₂O₃ and Cs2.5 (noted as Pt/Al₂O₃ + Cs2.5) showed the highest catalytic performance among various catalysts. The product over Pt/Al₂O₃ + Cs2.5 after 5 h on-steam at 523 K contained 94.4% C₅-C₉ (gasoline components) with a high iso/n ratio of 8.45. The co-grinding time of Pt/Al₂O₃ and Cs2.5 influenced the catalytic performance when the time was shorter than 10 min but gave little influence on the catalytic performance when the time was longer than 10 min. Because the iso/n ratio of products over Pt/Al₂O₃ + Cs2.5 increased by adding Pt in Cs2.5 and decreased with increasing H₂/feedstock, the reaction proceeded through a bifunctional mechanism in which Pt sites achieved a hydrogenation/dehydrogenation function and acid sites achieved an isomerization/cracking function. The balance of Pt and solid acids was important to obtain a high catalytic performance in the hydroisomerization-cracking of F-T gasoline. Because Cs2.5 possessed moderate acidic strength and uniformly distributed acidic sites, Pt/Al₂O₃ + Cs2.5 showed a higher catalytic stability than that over Pt/Al₂O₃ + SO₄/ZO₂ and showed a higher catalytic activity than that over Pt/Al₂O₃ + H-ZSM-5.     

TritonX100微乳液体系溶水性能研究

研究了非离子表面活性剂TritonX 100与不同助表面活性剂、油相形成的微乳液体系的溶水能力,并考察了温度、pH对微乳液体系稳定性的影响。分别绘制了不同体系的拟三元相图。研究结果表明,当TritonX 100与异戊醇质量比为1∶1,(TritonX 100+异戊醇)与正庚烷质量比为4∶1时,TritonX 100/异戊醇/正庚烷/水微乳液体系具有较大的稳定区域,其最大溶水量在50%左右。该微乳液体系在温度低于80℃时,随温度增加,其稳定区域有所增大;pH对该体系稳定性影响较小。     

Measurement and prediction of CO2 solubility in sodium phosphate monobasic solutions for food treatment with high pressure carbon dioxide

Two experimental systems were designed and tested to measure the CO₂ solubility in pure water and sodium phosphate monobasic solutions (0.240, 2.40 and 4.80 g/100 g water) at different pressures (7.5 and 15.0 MPa) and temperatures (35, 40 and 50 °C).The solubility experimental results were compared with the equilibrium conditions evaluated by applying three different thermodynamic models by means of the process simulation software Aspen Plus^®: (1) the Peng-Robinson equation of state (EOS), with the Wong and Sandler mixing rules (PRWS) and the excess Gibbs free energy calculated according to the UNIFAC method; (2) the Electrolytic Non-Random Two Liquids (ELECNRTL) with the Redlich-Kwong equation of state for aqueous and mixed solvent applications; (3) the completely predictive Soave-Redlich-Kwong (PSRK) equation of state.CO₂ solubility appeared to be a strong function of sodium phosphate monobasic concentrations. The predictions of the PRWS EOS agreed well with the experimental data in the pressure and temperature ranges tested. Larger differences between experimental and predicted results were observed for conditions close to the CO₂ critical point and for low sodium phosphate monobasic concentrations. Predictions of thermodynamic models 2 and 3 had much larger deviations from experimental data.     

Cosurfactant effects on the polymerization of vinyl acetate in anionic microemulsion media

The polymerization of vinyl acetate at 60 °C in microemulsions stabilized with the anionic surfactant, Aerosol OT, with or without cosurfactant (n-butanol) is examined. Partial phase diagrams at 60 °C show that the addition of n-butanol enhances the one-phase microemulsion region. Results indicate that the reaction rate is not affected by the presence of the alcohol. However, average molar masses are smaller although particles are bigger throughout the reaction compared to those values obtained in the absence of n-butanol. An explanation for these results is presented.     

U型微乳水相增溶过程微观结构的模拟

利用耗散粒子动力学（DPD）方法对丁酸乙酯/无水乙醇/Tween80/水四组份微乳体系形成过程进行了模拟,其模拟内容包括水相增溶过程中微乳体系的微观结构和微乳液滴的形态特征变化、微乳体系内有效区域与无效区域的分界线等。模拟结果表明：水相增溶过程中,微乳体系能够在含水量为50%和70%时发生相的转变以及微乳液滴形态结构的变化：柱状→球状→柱状→球状。在油相与表面活性剂质量比小于等于5：5时,微乳体系水相可无限增溶;当油相与表面活性剂质量比为10：0,9：1,8：2,7：3,6：4时,微乳体系的最大增溶水量分别为25%,30%,35%,45%和50%,均为油包水型微乳,当水容量大于最大增溶水量时,微乳体系被破坏,分层。试验结果也发现：当含水量小于55%时,微乳体系电导率表明,微乳体系为油包水型;当含水量为55%-70%时,微乳体系为双连续型;当含水量大于70%时,微乳体系为水包油型。微乳体系的三相图也显示出微乳的有效区域。试验结果很好的吻合了模拟结果。     

Electrochemical performances of poly(3,4-ethylenedioxythiophene)-NiFe2O4 nanocomposite as electrode for supercapacitor

Poly 3,4-ethylenedioxythiophene (PEDOT)-based NiFe₂O₄ conducting nanocomposites were synthesized and their electrochemical properties were studied in order to find out their suitability as electrode materials for supercapacitor. Nanocrystalline nickel ferrites (5-20 nm) have been synthesized by sol-gel method. Reverse microemulsion polymerization in n-hexane medium for PEDOT nanotube and aqueous miceller dispersion polymerization for bulk PEDOT formation using different surfactants have been adopted. Structural morphology and characterization were studied using XRD, SEM, TEM and IR spectroscopy. Electrochemical performances of these electrode materials were carried out using cyclic voltammetry at different scan rates (2-20 mV/s) and galvanostatic charge-discharge at different constant current densities (0.5-10 mA/cm²) in acetonitrile solvent containing 1 M LiClO₄ electrolyte. Nanocomposite electrode material shows high specific capacitance (251 F/g) in comparison to its constituents viz NiFe₂O₄ (127 F/g) and PEDOT (156 F/g) where morphology of the pore structure plays a significant role over the total surface area. Contribution of pseudocapacitance (C_FS) arising from the redox reactions over the electrical double layer capacitance (C_DL) in the composite materials have also been investigated through the measurement of AC impedance in the frequency range 10 kHz-10 mHz with a potential amplitude of 5 mV. The small attenuation (∼16%) in capacitance of PEDOT-NiFe₂O₄ composite over 500 continuous charging/discharging cycles suggests its excellent electrochemical stability.     

Friedel–Crafts green alkylation of xylenes with tert-butanol over mesoporous superacid UDCaT-5

Friedel–Crafts green alkylation of xylenes with tert-butanol was investigated in the presence of mesoporous superacidic catalysts named as UDCaT-4, UDCaT-5 and UDCaT-6. The catalysts are modified versions of zirconia showing high catalytic activity, stability and reusability. The catalytic activity is in the order: UDCaT-5 (most active) > UDCaT-6 > UDCaT-4 > sulfated zirconia (least active). Synergistic effect of very high sulfur content present (9% (w/w) S) and preservation of tetragonal phase in UDCaT-5, in comparison with sulfated zirconia (4% (w/w) S), were responsible for higher catalytic activity. The performance of UDCaT-5 in alkylation of xylenes was studied with tert-butanol with reference to selectivity and stability. Alkylation of m-xylene over UDCaT-5 gives 96% conversion of tert-butanol with 82% selectivity towards 5-tert-butyl-m-xylene (5-TBMX) under optimum reaction conditions. The formation of products is correlated with the acidity of the catalyst. The reactions were conducted in liquid phase at relatively low reaction temperatures (130–160 °C). A systematic investigation of the effects of various operating parameters was done to describe the reaction pathway. The reaction was carried out without any solvent in order to make the process cleaner and greener. An overall second order kinetic equation was used to fit the experimental data, under the assumption that both xylene and tert-butanol are weakly adsorbed. An independent study of dehydration of tert-butanol (TBA) was also done. Alkylation of o-xylene and p-xylene with tert-butanol was also studied. The overall process is green and clean.     

Thermodynamic modeling of dealcoholization of beverages using supercritical CO2: Application to wine samples

The supercritical removal of ethanol from alcoholic beverages (brandy, wine, and cider) was studied using the GC-EoS model to represent the phase equilibria behavior of the CO₂ + beverage mixture. Each alcoholic drink was represented as the ethanol + water mixture with the corresponding ethanol concentration (35 wt% for brandy, 9-12 wt% for different wines and 6 wt% for cider). The thermodynamic modeling was based on an accurate representation of the CO₂ + ethanol and CO₂ + water binary mixtures, and the CO₂ + ethanol + water ternary mixture.The GC-EoS model was employed to simulate the countercurrent supercritical CO₂ dealcoholization of the referred beverages; the results obtained compared good with experimental data from the literature. Thus, the model was used to estimate process conditions to achieve an ethanol content reduction from ca. 10 wt% to values lower than 1 wt%. The model results were tested by carrying out several extraction assays using wine, in a 3 m height packed column at 308 K, pressures in the range of 9-18 MPa and solvent to wine ratio between 9 and 30 kg/kg.     

Stabilization of aviation gasoline as detergent emulsion for lead determination by electrothermal atomic absorption spectrometry

The present work reports the development of a method for the determination of lead in aviation gasoline samples by electrothermal atomic absorption spectrometry (ETAAS). The samples were emulsified before injecting into the spectrometer in order to avoid the high instability observed in the signals when the samples were injected directly without any treatment. Stable detergent emulsions were obtained by mixing 1 mL of a 7% m/v Triton X-100 solution containing 10% v/v HNO₃ with 4 mL of aviation gasoline. These emulsions generated constant integrated absorbance signals for 5 h at least. Several parameters related to the emulsion formation (Triton X-100 and HNO₃ concentrations) and temperature program (pyrolysis and atomization temperatures and heating rate and the final temperature of the drying step) were evaluated. Both Triton X-100 and HNO₃ concentrations in the solution used to form the emulsion influenced the sensitivity of the lead measurements as well as the heating rate utilized in the drying step. The use of a chemical modifier was necessary, being that the Pd conventional modifier presented better performance than the permanent Ir modifier. The limits of detection and quantification derived for the methodology were 1.2 and 4.0 μg L^− 1. Six samples of aviation gasoline were analyzed and the lead concentrations varied between 11.6 and 64.2 μg L^− 1. A recovery test was performed in order to attest the accuracy of the procedure and recovery percentages between 88 and 112% were observed.     

Considerations on formation and stability of Oil/Water dispersed systems

Two systems: (a) a costabilized system of toluene/water/1-propanol, and (b) an emulsion system of toluene/sodium dodecyl sulfate/1-butanol/NaCl solution are used as examples to provide some general observations on emulsion formation and stability. Phase volume and interfacial tension measurements indicate that the requirement for formation of O/W systems is low γ_i, but for overall stability, γ_i must be positive and of significant value in addition to any steric barrier at the interface. An approximate calculation of the amount of surfactant needed to fill the interface provides a guide for preparation of such systems.     

Effect of Ethylene Oxide Group in the Anionic–Nonionic Mixed Surfactant System on Microemulsion Phase Behavior

The phase behavior of microemulsions stabilized by a binary anionic–nonionic surfactant mixture of sodium dihexyl sulfosuccinate (SDHS) and C12-14 alcohol ethoxylate (C_{12 − 14}E_j) that contains an ethylene oxide (E_j) group number, j, of either 1, 5, or 9 was investigated for oil remediation. The oil–water interfacial tension (IFT) and optimal salinity of the microemulsion systems with different equivalent alkane carbon numbers (EACN) were examined. The anionic–nonionic surfactant ratio was found to play a pivotal role in the phase transition, IFT, and optimal salinity. The minimum IFT of mixed SDHS − C_{12 − 14}E_j systems were about three times lower than those of neat SDHS systems. A hydrophilic–lipophilic deviation (HLD) empirical model for the mixed anionic–nonionic surfactant system with the characteristic parameter was proposed, as represented in the excess free energy term . The results suggested that the mixed system of SDHS − C_{12 − 14}E₁ was more lipophilic, while SDHS − C_{12 − 14}E₉ was more hydrophilic than the ideal mixture (no excess free energy during the microemulsion formation), and the SDHS − C_{12 − 14}E₅ system was close to the ideal mixture. The findings from this work provide an understanding of how to formulate mixed anionic–nonionic microemulsion systems using the HLD model for oils that possess a wide range of EACN.     

A comparison between lipase-catalyzed esterification of oleic acid with glycerol in monolayer and microemulsion systems

Lipase-catalyzed synthesis-esterification of oleic acid with glycerol-was carried out in L2 microemulsions and in monolayers. The microemulsions were based on isooctane as a nonpolar component and various water-glycerol mixtures as polar component. The substrate, oleic acid/sodium oleate, constituted the microemulsion surfactant. The lipase resides mainly in the water pools. Monolayers of oleic acid/sodium oleate were formed on subsolutions of glycerol and water, and the enzyme solution was injected under the compressed monolayers. Thus, the arrangement of the reactants at the oil-water interface of the microemulsion can be regarded as analogous to that at the airwater interface of the monolayer. The microemulsion structure was characterized by self-diffusion nuclear magnetic resonance. It was found that the higher the glycerol-to-water ratio, the lower are the water D-values. The reactions in microemulsions generally gave a low degree of oleic acid conversion. The yield increased with increasing glycerolto-water ratio. Monoglycerides were the main product, and no triglyceride could be detected. The monolayer experiments gave a somewhat higher degree of conversion, with tri- and diglycerides being the major reaction products. The reason why triglycerides are formed in monolayer experiments but not in microemulsions is believed to be due to an unfavorable partitioning of the diglyceride in the microemulsion systems. Once formed, the diglyceride will partition into the hydrocarbon domain and become inaccessible for reaction with the enzyme-O-acyl intermediate at the oil-water interface. In addition, the interfaces in the two systems are different. The monolayer interface is static, whereas the microemulsion interface is highly dynamic, and this difference may also influence the product patterns.     

Adhesion of air bubbles to a fluorite surface in the presence of oleate species

Measurements of the detachment force of air bubbles from a surface of fluorite covered with an oleate film immersed in an aqueous sodium oleate solution or water were carried out. The contact angles for the systems fluorite/oleate film-drop of aqueous sodium oleate solution-air, fluorite/oleate film-air bubble-aqueous sodium oleate solution, and fluorite/oleate film-air bubble-water were also measured. The detachment forces were also calculated from the measured contact angles. It was found that the adhesion of air bubbles to the fluorite surface increased considerably in the presence of an oleate film on the fluorite surface, but decreased if the oleate film was at the water-air interface. Good agreement between the theoretically calculated and the measured values of the detachment force for the system fluorite/oleate film-air bubble-sodium oleate aqueous solution when the concentration of this latter solution was in the range 0 to 87.1 mg/dm³ was also found, but for concentrations over 87.1 mg/dm³ the calculated values of the detachment force were higher than the measured values. The calculations and measurements indicate that the most favourable condition for the adhesion of air bubbles to fluorite grains is the presence of a chemisorbed film of oleate without surface precipitation of calcium oleate salt at low concentrations of oleate species in water.