Excess heat capacities and orientational order in systems containing hexadecane isomers of different molecular structure

Using the Picker flow microcalorimeter, excess heat capacities have been obtained at 25°C throughout the concentration range for 2,2-dimethylbutane,n-hexane, and cyclohexane each mixed with a series of hexadecane isomers of increasing degrees of orientational order, as determined by depolarized Rayleigh scattering. The isomers are 2,2,4,4,6,8,8-heptamethylnonane, 6-, 4-, and 2-methylpentadecane, andn-hexadecane. Thec _p ^E values are negative, increasing rapidly in magnitude with increase of orientational order, and are not predicted by the Prigogine—Flory theory which neglects order. Values ofc _p ^E are obtained at 10, 25, and 55°C for cyclohexane +6-, 4-, and 2-methylpentadecane which with other literature data lead to the temperature dependence of the thermodynamic excess functions for cyclohexane solutions of the five C₁₆ isomers. The excess enthalpy and entropy vary with the C₁₆ isomer and with temperature, but the corresponding variation of the excess free energy is small, indicating a high degree of enthalpy-entropy compensation. This is consistent with a rapid decrease with temperature of orientational order in the C₁₆ isomers.     

Alkylation of cyclododecanone with α,ω-dibromoalkanes under conditions of phase-transfer catalysis

Alkylation of cyclododecanone with ,-dibromoalkanes Br(CH) _n Br (n=3, 4, 5) under conditions of phase-transfer catalysis in the presence of KOH results in the formation of either bicyclic ketones forn=3 and 5 or a mixture of bicyclic and spirocyclic ketones forn=4.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1436–1438, August, 1994.     

聚合物流变特性标准物质的研制

介绍聚合物流变特性标准物质的研制过程。聚合物流变特性标准物质主要由聚异丁烯和十六烷组成。研制的该标准物质具有良好的均匀性、稳定性。经对测定数据进行统计处理,确定了该标准物质在不同静态剪切速率下粘度和第一法向应力差的标准值并给出了其相对扩展不确定度。     

Determination of the regime in the reverse wilson chamber at critical supersaturation measurements

The pressure in the Reverse Wilson Chamber (RWC) was directly measured at different rates of compression of the gas mixture. It was shown that at compression time in the range from 0.06 to 0.3 s an intermediate, between adiabatic and isothermal, process took place in the chamber. To obtain the relative pressure increase P _m /P _at from the values of the relative gas compression V/V, a calibration of the experimental set-up was carried out. The calibration showed that the values of critical supersaturationSc for water condensation on hexadecane, estimated for intermediate regime of the gas compression, were reduced with respect to the values calculated when the adiabatic regime was assumed. This fact confirmed the conclusions made earlier [1–3] that the classical theory was not applicable in this case of heterogeneous phase formation and that the line tension < 0 should be taken into account. Moreover, in an atmosphere of very pure argon (instead of room air [1–3]) the critical supersaturation turned out to be independent of the initial state of undersaturationS _o . The more accurate values obtained for condensation of water on hexadecane were: lnS _c =0.204 (instead of the maximum value obtained earlier: lnS _c =0.26) and=–1.9×10^–5 dyne (instead of=–1.5×10^–5 dyne).     

Biodegradation of n-hexadecane by bacterial strains B1 and B2 isolated from petroleum-contaminated soil

Two hydrocarbon-biodegrading bacterial strains,B1 and B2,were isolated from petroleum-contaminated soil collected from Tianjin,China.The strains were identified as Pseudomonas aeruginosa(B1) and Acinetobacter junii(B2).The degradation rate of n-hexadecane by B1 and B2 reached 96% and 78% respectively after 7 days,though the strains employed different mechanisms of degradation.The results showed that B2 was not able to use glucose as carbon source.B1 could produce glycolipid surfactants using glucose as the carbon source,according to the results of blue agar plate analysis and thin layer chromatography(TLC),and the bacterial culture of B1 had a high oil discharge and emulsification activity.Both B1 and B2 could produce biosurfactants with hexadecane as the sole carbon source,but their modes of action were different.The carbon source was found to affect the cell surface hydrophobicity.Cell surface hydrophobicity was poor with glucose as the carbon source,but enhanced when hexadecane was used as the carbon source.     

分子筛催化剂上正十六烷的临氢异构化反应

 对分子筛催化剂上正十六烷的临氢异构化反应进行了研究，考察了不同分子筛催化剂的活性和选择性，并对临氢异构化反应的产物分布进行了分析．在此基础上，对正十六烷的临氢异构化反应机理进行了初步探讨．结果表明，正十六烷在中孔分子筛催化剂上的临氢异构化反应主要在分子筛外表面和孔口进行，分子筛的择形作用对异构选择性的影响有限．这与一般情况下低分子量正构烷烃在择形分子筛上的临氢异构化反应有所不同．临氢异构化反应的异构选择性主要取决于催化剂酸性组分的酸性质，弱酸和中等强度的酸对异构化反应有利，而催化剂的活性则由酸性组分中B酸中心的数量和加氢组分的活性共同决定．     

Predicting hexadecane–air equilibrium partition coefficients (L) using a group contribution approach constructed from high quality data

A group contribution-based quantitative structure–property relationship (QSPR) for the hexadecane–air equilibrium partition coefficients (L) of organic chemicals is developed using the iterative fragment selection (IFS) approach. This new QSPR includes in its training and external validation data sets L values for a large number of structurally complex chemicals measured by the same group using consistent methods. The resulting QSPR has better predictive power than other prediction methods trained primarily using data for chemicals of simpler structures, and measurements of L values from diverse sources. For a subset of chemicals in which the L values have non-additive effects caused by intramolecular hydrogen bonds, the new QSPR gives much better performance in comparison to the most commonly used prediction method.     

Recent developments in manufacturing emulsions and particulate products using membranes

Membrane emulsification (ME) is a relatively new technique for the highly controlled production of particulates. This review focuses on the recent developments in this area, ranging from the production of simple oil-in-water (O/W) or water-in-oil (W/O) emulsions to multiple emulsions of different types, solid-in-oil-in-water (S/O/W) dispersions, coherent solids (silica particles, solid lipid microspheres, solder metal powder) and structured solids (solid lipid microcarriers, gel microbeads, polymeric microspheres, core-shell microcapsules and hollow polymeric microparticles). Other emerging technologies that extend the capabilities into different membrane materials and operation methods (such as rotating membranes, repeated membrane extrusion of coarsely pre-emulsified feeds) are introduced. The results of experimental work carried out by cited researchers in the field together with those of the current authors are presented in a tabular form in a rigorous and systematic manner. These demonstrate a wide range of products that can be manufactured using different membrane approaches. Opportunities for creation of new and novel entities are highlighted for low throughput applications (medical diagnostics, healthcare) and for large-scale productions (consumer and personal products).     

Volumes of mixing and the isomeric effect. Part I. Nonane Isomers withn-nonane andn-hexadecane

Molar excess volumes of four nonane isomers mixed with n-nonane and n-hexadecane were obtained from precise density measurements over the complete mole fraction range at 25°C. Good agreement was found between the experimental molar excess volumes and those predicted by the Flory theory. This work shows the importance of the three contributions to V _m ^e , the heat of mixing X₁₂, the differences in free volume, and the P^* effect.     

Dispersion of TiO2 on high‐surface‐area mesoporous silica: functionalization with tungstophosphoric acid and application in solvent‐free,aerobic oxidation of n‐hexadecane

Imidazole type ionic liquid, 1‐hexadecyl‐3‐methylimidazolium chloride, was used to template the synthesis of high‐surface‐area mesoporous silica under acidic conditions and crystalline titanium dioxide (TiO₂) nanoparticles of anatase phase were inserted utilizing a solvent evaporation‐induced method. The surface area of more than 700 m² g^?1 was obtained after TiO₂ impregnation. Further, the polyoxometalate, 12‐tungstophosphoric acid (PW₁₂) was dispersed on the surface of TiO₂ to form PW₁₂–TiO₂–silica hybrid catalytic materials. The catalytic activity of this hybrid material was tested for solvent‐free, aerobic oxidation of n‐hexadecane. The experimental investigation shows that PW₁₂–TiO₂ nanocrystals did not block the pore channels and gave good conversion. Copyright © 2012 John Wiley & Sons, Ltd.