Kinetics of gas-phase photocatalytic oxidation of heptane over TiO2

In this paper, gas-phase photocatalytic oxidation of heptane over UV-illuminated TiO₂ was carried out in a batch reactor. A Langmuir-Hinshelwood kinetic equation was observed from the results at different initial concentrations of heptane, oxygen, water vapor, and light intensity.     

Long-range Lennard-Jones and electrostatic interactions in interfaces: application of the isotropic periodic sum method

Molecular dynamics (MD) simulations of heptane/vapor, hexadecane/vapor, water/vapor, hexadecane/water, and dipalmitoylphosphatidylcholine (DPPC) bilayers and monolayers are analyzed to determine the accuracy of treating long-range interactions in interfaces with the isotropic periodic sum (IPS) method. The method and cutoff (rc) dependences of surface tensions, density profiles, water dipole orientation, and electrostatic potential profiles are used as metrics. The water/vapor, heptane/vapor, and hexadecane/vapor interfaces are accurately and efficiently calculated with 2D IPS (rc=10 A). It is demonstrated that 3D IPS is not practical for any of the interfacial systems studied. However, the hybrid method PME/IPS [Particle Mesh Ewald for electrostatics and 3D IPS for Lennard-Jones (LJ) interactions] provides an efficient way to include both types of long-range forces in simulations of large liquid/vacuum and all liquid/liquid interfaces, including lipid monolayers and bilayers. A previously published pressure-based long-range LJ correction yields results similar to those of PME/IPS for liquid/liquid interfaces. The contributions to surface tension of LJ terms arising from interactions beyond 10 A range from 13 dyn/cm for the hexadecane/vapor interface to approximately 3 dyn/cm for hexadecane/water and DPPC bilayers and monolayers. Surface tensions of alkane/vapor, hexadecane/water, and DPPC monolayers based on the CHARMM lipid force fields agree very well with experiment, whereas surface tensions of the TIP3P and TIP4P-Ew water models underestimate experiment by 16 and 11 dyn/cm, respectively. Dipole potential drops (DeltaPsi) are less sensitive to long-range LJ interactions than surface tensions. However, DeltaPsi for the DPPC bilayer (845+/-3 mV proceeding from water to lipid) and water (547+/-2 mV for TIP4P-Ew and 521+/-3 mV for TIP3P) overestimate experiment by factors of 3 and 5, respectively, and represent expected deficiencies in nonpolarizable force fields.     

Stability and disintegration of ultrathin heptane films in water: molecular dynamics simulations

Molecular dynamics simulations of ultrathin heptane films (less than 5 nm in thickness) in water were conducted to study their stability and disintegration behavior. The density distributions of heptane and water molecules across the film were determined for different equilibrium film thicknesses ranging from 1.5 to 4 nm. The potential energy of the system was computed as a function of the heptane number fraction, and the results were employed to determine the excess energy of mixing of heptane in water. The diffusion coefficients of heptane and water obtained from the MD simulations were also compared with experimental data. A good agreement was found between the heptane self-diffusivity obtained from the MD simulations and its literature reported value. Following an analysis of the equilibrium properties of the heptane films and associated structures, we performed simulations where the shapes of the heptane films were initially perturbed. Different perturbations of these ultrathin films led to formation of various associated structures, including cylindrical rodlike heptane droplets, films with holes, and intact films. The different shapes are formed in systems with the same heptane/water composition. An analysis of this behavior is presented showing the possibility of multiple associated structures with similar total energy in these highly confined systems.     

Dielectric relaxation studies of 1-hexanol and 1,2-hexanediol in heptane

Solutions of 1-hexanol and 1,2-hexanediol in heptane have been investigated tigated by means of dielectric time domain spectroscopy (TDS). The permittivity spectrum of 1-hexanol in heptane is characterized by a model function containing a sum of three elementary Debye dispersions, while 1,2-hexanediol in heptane is best described by a Cole-Davidson model function. It is shown that dilute solutions of 1-hexanol in heptane have a completely different behavior to that of 1,2-hexanediol. For the diol, the relaxation time levels off at a high value indicating an existence of higher hydrogen bonded complexes. It is possible to quantify the relative amount of monomeric 1-alcohol molecules from the dielectric spectrum. The monomerization rate for 1-hexanol upon dilution with heptane is initially low, but increases rapidly for mole fractions of heptane exceeding 0.4.     

Microscope measurements for the transient formation of W/O emulsions of sodium bis(2-ethylhexyl) sulfosuccinate in the dodecane/water interfacial region

The present study investigated the transient formation of water-in-oil (W/O) emulsions of sodium bis(2-ethylhexyl) sulfosuccinate (aerosol OT, AOT) in a dodecane/water interfacial region and the anomalous uptake of water in the dodecane phase by in situ bright-field optical microscopy and water concentration measurements in detail. The hydrodynamic radius of the individual W/O emulsions in the dodecane phase was determined to be 0.1-1.2 μm from the analysis of their diffusion behavior; they are much larger than common W/O microemulsions (a few nanometers in radius). At first, they were formed spontaneously in the dodecane/water interfacial region without shaking, and they diffused away into the dodecane phase. Then, almost all of them vanished at the interface by fusion. Their number and the water concentration in the dodecane phase increased first and then decreased gradually. The formation mechanism was discussed with estimated concentration profiles of AOT and water molecules, which suggests that larger W/O emulsions of 0.01-0.44 μm in radius can be formed in the dodecane phase near the interface (within 2 μm) because the concentration of AOT becomes lower than that of water there.     

Measurement of critical heat flux conditions under vacuum

Determination of optimum conditions for waste oil (used motor oils, transformer oils) regeneration using vacuum distillation was attempted including the search for the optimum temperature difference between the heating surface and the boiling point of the liquid. Optimum temperature allowed the distillation equipment to operate at maximum performance. Equipment suitable for the measurement of boiling curves under atmospheric pressure and vacuum conditions was assembled. These curves were used to determine the optimum temperature difference of various substances including waste oils. Properties of pure substances, for example water, ethanol, hexane, heptane, isooctane, decane, or dodecane, were measured with this equipment under atmospheric pressure. Results of various liquids measurements under vacuum and atmospheric pressure are presented.     

Tuning aggregation of microemulsion droplets and silica nanoparticles using solvent mixtures

The effect of solvent on stability of water-in-oil microemulsions has been studied with AOT (sodium bis(2-ethylhexyl)sulfosuccinate) and different solvent mixtures of n-heptane, toluene and dodecane. Dynamic light scattering DLS was used to monitor the apparent diffusion coefficient D(A) and effective microemulsion droplet diameter on changing composition of the solvent. Interdroplet attractive interactions, as indicated by variations in D(A), can be tuned by formulation of appropriate solvent mixtures using heptane, toluene, and dodecane. In extreme cases, solvent mixtures can be used to induce phase transitions in the microemulsions. Aggregation and stability of model AOT-stabilized silica nanoparticles in different solvents were also investigated to explore further these solvent effects. For both systems the state of aggregation can be correlated with the effective molecular volume of the solvent V(mol)(eff) mixture.     

Group contributions to the infinite dilution partial molar volumes of alkanes, alcohols, and glycols in polar organic solvents

Densities of binary mixtures of polar organic solvents with alcohols were measured at 25‡C. The solvents studied were N,N-dimethylformamide, dimethylsulfoxide, and formamide while alcohols were butanol, pentanol, hexanol, and 1,4-butanediol. Density measurements of hydrocarbons (from pentane to dodecane and some heptane isomers) + N,N-dimethylformamide were also performed. From these data the apparent molar volumes of alcohols and hydrocarbons as functions of concentration were calculated. The standard partial molar volumes were obtained by extrapolation to infinite dilution and are discussed in terms of group contributions.     

Calorimetric Investigation of the Monolayers Formed At Solid-liquid Interface

Heat capacity measurements have been made to investigate the formation of two solid monolayers each of n-pentane, n-heptane and n-dodecane adsorbed on graphite, one at submonolayer coverages and the other coexisting with the liquid. At submonolayer coverages the monolayers are found to melt respectively at 99.8, 151.6, and 217.3 K, well below the bulk melting points. The monolayers coexisting with the liquid melted at 205.6 for heptane and at 287.8 K for dodecane, whereas no evidence was obtained for pentane on the formation of such solid monolayer above the bulk melting point. The order persisting in the liquid near the interface depends upon the length of the molecules. The dodecane monolayers showed another transitions below the melting points both at submonolayer and multilayer coverages.This revised version was published online in November 2005 with corrections to the Cover Date.     

Formation of n-alkane layers at the vapor/water interface

We present a study on the initial wetting behaviors of two low molecular weight alkanes, heptane and octane, at the vapor/water interface using both neutron and X-ray reflectometry. Combined X-ray and neutron reflectivity studies data showed that a uniform film, which has never been reported, was formed continuously at 25 degrees C. As the adsorptive deposition continued, each adsorbed film was saturated at a specific equilibrium thickness: 48 and 36 A for deuterated heptane and octane, respectively, and 21 A for hydrogenated octane. The thickness of the adsorbed layer measured by neutron reflectivity is in agreement with that measured using X-ray reflectivity. Our observations of continuous and saturated adsorption behaviors are analyzed qualitatively using a kinetic adsorption model.     

超临界正十二烷-醇溶液体系的Monte Carlo模拟

用ＭｏｎｔｅＣａｒｌｏ 方法研究了超临界正十二烷－醇溶液的分子质心Ｃ－ Ｃ、Ｃ－ Ｏ原子间的径向分布函数． 结果表明, 在临界压力下, 在临界温度附近改变温度时, 十二烷－十二烷分子质心Ｃ－ Ｃ原子间的径向分布函数变化不大, 即温度对十二烷分子间聚集的影响不明显． 在临界温度下, 当压力在临界压力附近变化时, 十二烷－十二烷分子质心Ｃ－ Ｃ原子间的径向分布函数发生了显著变化, 十二烷分子在临界压力以下聚集最强． 在临界状态下, 对于十二烷分别与甲醇、乙醇、正丙醇和异丁醇构成的溶液, 十二烷在异丁醇周围的聚集最强, 在乙醇周围的聚集次之, 在甲醇和正丙醇周围聚集较弱．     

Water vapor sorption and desorption behavior of some keratins

Summary Sorption and desorption isotherms of water vapor in a number of keratin substrates including excised human stratum corneum, guinea pig and neonatal rat corneum and human hair have been obtained and the data compared to the information available on wool. An attempt was made to analyze the data according to the BET and D'Arcy-Watt equations, Flory-Huggins polymer solution theory and Zimm's clustering function. The results suggest strong binding between the sorbate and keratins in the low relative vapor pressure range, reflecting a sorption process on primary reactive sites (Langmuir) which proceeds up to 0.2-0.3 relative vapor pressure. More confirmation is obtained from isosteric heat of sorption measurements. Extensive clustering and multilayer formation occur in the higher relative vapor pressure range.With 10 figures     

Isotropic raman scattering study of the ν1 mode of OCS and CS2 in n-alkanes

The isotropic Raman bandwidths of ν₁ of OCS and CS₂ in n-heptane and of OCS in n-dodecane have been measured at variable temperature and of OCS in the n-alkane series at ambient temperature. Results are compared to Oxtoby's hydrodynamic theory for vibrational dephasing. Agreement if good in heptane and bad in dodecane. Conclusions are derived on the applicability of the theory.     

Phase behavior and rheology of oil-swollen micellar cubic phase and gel emulsions in nonionic surfactant systems

We have studied the phase behavior and rheological property of the cubic phase and related gel emulsions in water/nonionic/dodecane systems. In the phase behavior study, it is pointed out that the formation of the discontinuous cubic phase (I₁) is not common in all nonionic surfactant systems; however, a cubic phase (I₁) with oil-swollen micelles or a cubic phase microemulsion is found in the water/C₁₆EO₆/dodecane system, which can solubilize large amount of oil. It was also observed that water/C₁₆EO₆/dodecane system forms stable gel emulsion. In the rheological study we have found an anomalous behavior of the I₁ phase in the water/C₁₂EO₆/dodecane and the water/C₁₆EO₆/dodecane systems. In the water/C₁₂EO₆/dodecane system, the viscoelastic nature of the I₁ phase has been observed, which is shifted to the elastic nature with the addition of dodecane, whereas, highly elastic nature was observed in the water/C₁₆EO₆/dodecane system. In both the cases shear-thinning behavior were seen. The elastic modulus, G′ and complex viscosity, |η1| of the I₁ phase increase with the dodecane concentration in the water/C₁₂EO₆/dodecane system, whereas, decreasing trend have been observed in the water/C₁₆EO₆/dodecane system. This anomalous behavior is suggested due to the nonspherical shape of micelles or polydispersity of the micelles in the water/C₁₆EO₆/dodecane system. The rheological behavior of the O/I₁ gel emulsion was also studied in both the systems.     

Activity coefficient at infinite dilution, azeotropic data, excess enthalpies and solid–liquid-equilibria for binary systems of alkanes and aromatics with esters

Binary azeotropic data have been measured at different pressures for ethyl acetate + heptane, methyl acetate + heptane, isopropyl acetate + hexane and isopropyl acetate + heptane by means of a wire band column. Additionally activity coefficients at infinite dilution have been determined for ethyl acetate and isopropyl acetate in decane and dodecane in the temperature range between 303.15 and 333.15 K with the help of the dilutor technique. Furthermore excess enthalpies for the binary systems methyl acetate + hexane, methyl acetate + decane, ethyl acetate + hexane and ethyl acetate + decane at 363.15 and 413.15 K have been studied with the help of isothermal flow calorimetry. Finally solid–liquid equilibria for the systems ethyl myristate + benzene and ethyl myristate + p-xylene have been investigated by a visual technique. All these data have been used for the revision and extension of the group interaction parameters of the group contribution method modified UNIFAC (Dortmund) and the group contribution equation of state VTPR. The experimental data was compared with the results predicted using the group contribution method modified UNIFAC (Dortmund) and the group contribution equation of state VTPR.     

Molecular aggregation in the ternary system deca glycerol dioleate/heptane/water

The phase diagram for the ternary system deca glycerol dioleate(DGD)/heptane/water was established at 25 °C. In this phase diagram it was seen that the reverse micellar solution phase extends in its area until the water content reaches 35–45 wt%, at which a liquid crystalline phase begins to appear. On the basis of the experimental results of specific conductivity, viscosity, etc. for the samples containing a definite amount of DGD (0,1 M), and varying relative amounts of heptane and water, the mechanism of the transition of reverse micellar structures to liquid crystalline phase is discussed.     

Comparison of liquid chromatographic separations of geometrical isomers of substituted phenols with β- and γ-cyclodextrin bonded-phase columns

The capacity factors (k′) of several substituted phenols were measured by using β- and γ-cyclodextrin bonded-phase columns with mobile phases varying from the classical normal-phase conditions (e.g., heptane/2-propanol) to the reversedl-phase conditions (e.g. water/2-propanol). The cyclodextrin columns have unusual selectivities in both normal- and reversed-phase separations because of their large number of hydroxyl functional groups and their ability to form inclusion complexes with substrates. The occurrences of minima in plots of log k′ vs. percent organic modifier for various substituted phenols are considered to result from solute/solvent competition for interaction with the stationary phase and from the relative hydrophobicity of the stationary and mobile phases.     

Microemulsions studies: Correlation between viscosity,electrical conductivity and electrochemical and fluorescent probe measurements

Microemulsion systems involving brine and dodecane, and stabilized by sodium dodecylsulfate and both pentanol and heptanol have been investigated. Results of various experiments including conductivity and viscosity measurements, electrochemical diffusion coefficients and fluorescent probe studies have been gathered and compared in order to gain additional understanding of the microemulsion structure. The diffusion coefficients of hydrophilic hydroquinone and hydrophobic ferrocene obtained from the Levich equation at the rotating disc electrode, vary as the self-diffusion coefficients of water and dodecane, respectively; the results are consistent with those obtained by other workers from tracer or NMR self-diffusion studies. The fluorescence analysis of the polarity sensed by pyrene and the microviscosity felt by dipyrenylpropane suggests that the progressive addition of pentanol and dodecane to SDS micelles leads to solubilizate the probes more in the droplet interior where they experience a more hydrophobic environment. The systematic study of the two microemulsion systems provides insight into the microscopic properties of the oil domains in which the fluorescent probes are assumed to be located. In the system stabilized by n-heptanol as cosurfactant, the microviscosity sensed by P(CH₂)₃P is shown to be much lower than the bulk viscosity of the microemulsion. All the results evidence the well-known structural transitions: water continuous, bicontinuous and oil continuous in the single monophasic area of the brine/ SDS/n-pentanol/dodecane system; premicellar aggregates and water swollen micelles in the W/O area of the brine/SDS/n-heptanol/dodecane system.     

Use of HMDS/hexane double layers for obtaining low cost selective membrane

Sheets of paper commonly used for filtration were coated with double layers of HMDS (hexamethyl disilazane) and n-hexane using a low pressure plasma reactor. The organic compounds formed a thin film with very good adhesion to the substrate; the process produced water-repellent surfaces, with apparent water-contact angles higher than 100° and water adsorption around 15 g/m². The paper porosity was not altered, indicating that the depositions were conformal. Preliminary tests to investigate the possibility of using the modified paper as a selective membrane for separation of water and organic-polar and non-polar compounds of different chain length were conducted. The non-polar compounds tested were: n-hexane, cyclohexane, heptane, dodecane, benzene and poly(dimethylsiloxane). The polar organic liquids were ethanol, 2-propanol, carbon tetrachloride, acetophenone and phenol. Three types of behaviour were observed: (a) in the case of water/non-polar mixture, the non-polar compound passed through the modified paper whereas water did not; (b) in the case of acetophenone, phenol and carbon tetrachloride, neither the water nor the polar compound percolated through the modified paper; (c) in the case of water/2-propanol or ethanol solution, it was observed that a minimum concentration of alcohol was necessary in order for both the alcohol and water to percolate through the paper; in this case the alcohol percolates first, followed by water.     

Physicochemical investigations of anionic–nonionic mixed surfactant microemulsions in nonaqueous polar solvents: I. Phase behavior

Phase behaviors of AOT/heptane (Hp)/formamide (FA), ethylene glycol (EG), propylene glycol (PG), triethylene glycol (TEG) and glycerol (GLY) have been investigated in the absence and presence of a nonionic surfactant, polyoxyethylene(2) cetyl ether (Brij-52) at 303 K. The phase characteristics of (AOT+Brij-52)/Hp/(EG or PG or TEG) have been found to be different from that of AOT/Hp/FA systems in respect of both the area of monophasic domain and the appearance of other mesophases. The area of monophasic domain of (AOT+Brij-52)/Hp/EG depends on the content of Brij-52 (X _Brij-52) and shows a maximum at X _Brij-52=0.4. A negligible effect on the area of the monophasic domain has been shown by more hydrophobic surfactants, polyoxyethylene(2) stearyl ether (Brij-72) and polyoxyethylene(2) oleyl ether (Brij-92). The effect of oils (dodecane and hexadecane) on the mixed systems stabilized by (AOT+Brij-52) in EG has been investigated. The area of monophasic domain has been found to be dependent on the type of nonaqueous solvents and follows the order GLY>EG>PG>TG. A systematic investigation on the measurement of phase volumes of mixed surfactant systems [AOT+nonionic surfactant(s)] stabilized in oils of different chain lengths (heptane, dodecane and hexadecane) and polar solvent (EG) has been carried out at different compositions of the ingredients to identify the phase transitions of these systems as a function of X _Brij-52. The threshold point of phase transition (both W I→W IV and W IV→W II transitions) has been found to be a function of the configuration of added nonionic surfactant, nature of the polar solvent and oil. The conversion of the initial oil/EG droplets into EG/oil droplets with increasing X _nonionic has been facilitated for hydrophobic surfactants polyoxyethylene(4) lauryl ether (Brij-30), Brij-52, and Brij-72 in comparison to the hydrophilic surfactants polyoxyethylene(10) cetyl ether (Brij-56) and polyoxyethylene(20) cetyl ether (Brij-58).