Volume expansion behavior of water–hydrocarbon mixtures at high temperatures and pressures as studied by infrared spectroscopy

Infrared spectra of binary mixtures of water with toluene and ethylbenzene have been measured at temperatures and pressures in the 473–623 K and 100–350 bar ranges, respectively. Concentrations of water and hydrocarbons in the hydrocarbon-rich phase have been estimated from the integrated band intensities, and using these results, densities of the hydrocarbon-rich phase have been obtained as a function of temperature and pressure. In order to characterize the density of the hydrocarbon-rich phase, the experimental densities have been compared with the average densities before mixing, which were calculated from the literature densities of pure water and pure hydrocarbon with the experimental concentrations. All the experimental densities of the mixtures are lower than the average densities before mixing at the same condition. Relative volume change for mixing has been estimated and an anomalously large increase in volume has been found in the vicinity of the critical region of the water–hydrocarbon mixtures. This volumetric behavior is very similar to that previously found for water–benzene mixtures, and may be characteristic of the critical behavior of fluid mixtures of water and hydrocarbons.     

Role of aluminum ions on the dielectric and conducting properties of multiferroic Tb1−xAlxMnO3: Study at high temperatures

Dielectric and conducting properties of Tb_1−xAl_xMnO₃ (x = 0, 0.05) synthesized by the solid–state reaction method have been investigated. The Al ion has the same valence as substituted Tb but is nonmagnetic and its small size gives rise to microstructural strain which affects the multiferroic properties of the parent compound. Samples were characterized by means of complex impedance spectroscopy (CIS) in the frequency range from 40 Hz to 5 MHz, at temperatures above room temperature. The conductivity curves for the two samples are well fitted by the Jonscher law σ(ω) = σ_dc + Aωⁿ. Results of the fitting procedure indicate that for the studied samples, the hopping motion involves localized hopping without the species leaving the neighbors. Frequency dependence of the dielectric constant (ε″) and tangent loss (tan δ) display a dispersive behavior at low frequencies that can be explained on the basis of the Maxwell–Wagner model and Koop's theory. The relaxation dynamics of charge carriers has been studied by means of the electric modulus formalism. In turn, the variation of the imaginary part of the complex impedance, Z″, shows a peak at a relaxation angular frequency (ω_r) related to the relaxation time (τ) by τ = 1/ω_r. The complex impedance spectra (Nyquist plots) show well-defined semicircles which are strongly dependent on the Al-doping level and temperature. The complex impedance data have been modeled using electrical equivalent circuits.     

Molar conductivities of concentrated lithium chloride–glycerol solutions at low and high temperatures: application of a quasi-lattice model

Conductivities of concentrated solutions of lithium chloride in glycerol were measured for concentrations ranging from 0.005 to 1.5 mol.dm^?3. The conductivity dependencies were analysed successively using the Debye–Huckel–Onsager limiting law (DHO) at very low concentrations, the Fuoss equation of 1978 up to 0.1 mol.dm^?3, the Casteel–Amis empirical equation and the quasi-lattice model (QLM) at moderate and higher concentrations. The molar conductivities at infinite dilution, obtained using DHO and QLM were quite different from each other, because the salt forms contact pairs which were underestimated in the Λ = f(C^1/3) in QLM, as it may well be proved by Raman spectroscopy. Besides, the value of Madelung constant suggests that LiCl crystallises face centred cubic (FCC) at higher concentrations. On the basis of Raman spectroscopy analysis of previous lithium salts, we assume that the dissociation coefficient varies slightly with concentration and fraction of paired ion constant, the QLM equation is applied successfully in the concentration range used in this study. The temperature dependency of conductivity was also described using the Vogel–Tamman–Fulcher (VTF) empirical equation where the Arrhenius type was found. The results also suggest that as NaCl, LiCl can be considered as a structure maker electrolyte.     

Photo-oxidative degradation of polyethylene: Effect of polymer characteristics on chemical changes and mechanical properties. Part 1—Quenched polyethylene

Photo-oxidative degradation of quenched samples of linear low density (LLD), medium density (MD) and two kinds of high density (HD) polyethylene (PE) films was studied using a medium-pressure mercury lamp. Greater amounts of crosslinking and build up of oxidation products were noticed in LLDPE than the other samples. The primary products of interaction between dienes and oxygen are considered to participate in the initiation of the photo-oxidation reactions. Using the FT-IR difference spectrum technique, the amount of branch concentration in the photo-irradiated PE samples was determined. Oxidation damage at the boundary region between crystalline and amorphous phases is considered to be important in determining the embrittlement time.     

Structure and stability of halogenated polymers: Part 1—Ring-chlorinated polystyrene

Ring-chlorinated polystyrene has been prepared by reaction between polymer and chlorine at −20°C in the presence of iodine, using a 1·2:1 molar ratio of chlorine to styrene units. Although the product has a composition corresponding precisely to 1 Cl atom per styrene unit and the predominant site of chlorination is the para position in the aromatic ring, some ortho chlorination, backbone chlorination and unchlorinated structures have been shown to be present by characterisation spectroscopically and from degradation experiments.The chlorinated polymer loses the backbone chlorine readily as HCl at temperatures from 200°C. The resulting unsaturation in the backbone appears to destabilise the polymer towards chain scission and the main breakdown process, which resembles that of polystyrene in consisting of depolymerisation and transfer reactions, occurs over a wider temperature range and at lower temperatures than the decomposition of polystyrene. Products have been identified and estimated quantitatively.     

Mass spectrometric studies at high temperatures—XV: Sublimation pressures of chromium,manganese and iron trifluorides and the heat of dissociation of Fe2F6(g)

Vapours effusing from Knudsen cells containing CrF₃, MnF₃ and FeF₃ have been analysed mass spectrometrically. Only monomers of CrF₃ and MnF₃ were observed in the vapour phase, while the mass spectrum of the vapour over FeF₃ showed the presence of both monomers and dimers. The sublimation pressures and heats of sublimation of CrF₃, MnF₃ and FeF₃ were measured and the dissociation energy of Fe₂F₆(g) was determined.     

Inorganic ion exchangers — VIII The purification of water at elevated temperatures by a combination of zirconium phosphate and zirconium hydroxide gels

Zirconium phosphate gels of different crystallinities have been prepared with the view of finding a sorbent which combines a low phosphate release with a high affinity for ions formed by corrosion reactions, such as copper(II), nickel(II) and iron(III). The best sorbent achieved still releases small amounts of phosphate. These may be sorbed on a zirconium hydroxide gel which has to be prepared in such a way that it does not itself release any acid or basic species. Sorption experiments with combinations of zirconium phosphate and hydroxide have been carried out at 20° and 127°C according to a batch technique, and at 100°C by means of consecutive columns. The sorption characteristics are very favourable on the whole. As far as column operation is concerned, the draw-back exists that high loads of metal ions tend to increase the flow resistance, especially for the more crystalline gels.     

Influence of dissolution processing of PVA blends on the characteristics of their hydrogels synthesized by radiation—Part I: Gel fraction,swelling, and mechanical properties

In this work several hydrogels were obtained with two different poly(vinyl alcohol)s/PVAs as the main polymer in aqueous solutions containing 10% of PVA, 0.6% of agar, and 0.6% of κ-carrageenan (KC), cross-linked by gamma-rays from a ⁶⁰Co irradiation source. The PVAs tested have different degrees of hydrolysis and viscosities at 4% with values closed to 30 mPa s. The aqueous polymeric solutions were prepared using two distinct processes: the simple process of heating–stirring and that of making use of an autoclave. The purpose of this study was to evaluate the influence of the dissolution process by means of both methods on the hydrogels’ properties obtained. These were investigated by means of degree of cross-linking/gel fraction, degree of swelling in water, and some mechanical properties. The results that are obtained for hydrogels synthesized from solutions of PVA, agar, KC, and blends thereof prepared by both dissolution processes showed higher degrees of swelling for hydrogels from the autoclaved polymer solutions than those from the solutions prepared by simple heating–stirring process. Furthermore, their hydrogels containing totally hydrolyzed PVA displayed higher tensile strength and lower elongation properties.     

The mobility of cations in synthetic zeolites with the faujasite framework — II: The mobility of calcium,strontium and barium ions in zeolite X at high temperatures

A radiochemical method has been used to examine the mobility of the Sr²⁺ and Ba²⁺ cations between high-energy sites in zeolite X. Thermodynamic parameters have been estimated and comparisons made to other cation self-diffusion measurements [1–3].     

Mass spectrometric studies at high temperatures—X: The sublimation pressures of scandium (III), yttrium (III) and lanthanum (III), trifluorides

Sublimation pressures of ScF₃, YF₃ and LaF₃ were measured by mass spectrometric and semi-microbalance studies via the Knudsen and Langmuir techniques. The mass spectrometric work established ScF₃(g), YF₃(g) and LaF₃(g) as the major vapour species over their respective solid trifluorides. For ScF₃ the results are represented by: log P_atm = −(1·938 ± 0·042) × 10⁴/T + 9·43 ± 0·33; (1172° < T° < 1402°K) for YF₃ by log P_atm = −(2·185 ± 0·030) × 10⁴/T + 9·77 ± 0·23; (1256° < T° < 1434°K) and for LaF₃ by log P_atm = −(2·02 ± 0·02) × 10⁴/T + 8·20 ± 0·15, (1200° < T° < 1434°K) where the errors quoted are standard deviations from the least-square fits.The heat of sublimation for ScF₃ at 1290°K is 89 ± 3 kcal mole⁻¹; for YF₃ at 1332°K, ΔH° = 100 ± 3 kcal mole⁻¹; and for LaF₃ at 1324°K, ΔH° is 92 ± 2 kcal mole⁻¹.     

Thermal characterization and compounds identification of commercial Stevia rebaudiana Bertoni sweeteners and thermal degradation products at high temperatures by TG–DSC,IR and LC–MS/MS

Journal of Thermal Analysis and Calorimetry - The thermal behavior of two commercially available sweeteners based on Stevia rebaudiana Bertoni was studied by TG–DSC and EGA. The composition...     

Homogeneous multimetallic catalysts: Part 10. Formylation of aryl and alkenyl iodides by palladium—ruthenium bimetallic catalysts

The PdCl₂(PPh₃)₂—Ru₃(CO)₁₂ bimetallic system exhibited higher catalytic activity for the formylation of aryl and alkenyl iodides than PdCl₂(PPh₃)₂ or Ru₃(CO)₁₂ alone. Thus, in the formylation of iodobenzene (at 70 °C for 1.5 h under 50:50 atm of CO:H₂), the yield of benzaldehyde by PdCl₂(PPh₃)₂—Ru₃(CO)₁₂ catalyst (Pd:Ru = 1:2) was about four times as high as that by PdCl₂(PPh₃)₂ alone. Carbonyl complexes of other metals, such as Mn₂(CO)₁₀, Co₂(CO)₈, Cr(CO)₆, Fe(CO)₅, Mo(CO)₆ and W(CO)₆ were ineffective as the second component of the catalyst. To clarify the mechanism of the synergistic effects, the reaction of PdI(CO-p-Tol)(PPh₃)₂ with [HRu₃(CO)₁₁]⁻ or [HRu(CO)₄]⁻, ruthenium hydride species known to be generated under the catalytic formylation conditions, was performed. The reaction rapidly proceeded at 40 °C by dinuclear reductive elimination to form p-tolualdehyde, although the reaction with molecular hydrogen was very slow. These results strongly suggest that the improved catalytic activity of the Pd—Ru system is attributable to the high hydrogenolysis activity of in-situ-generated ruthenium hydride species.     

414 — Surface and/or Donnan potentials at the thylakoid membrane?: Part I. Calculation of light-induced Donnan potential changes and corresponding ion movements for A 1 : 1 electrolyte

The majority of the protons which are actively transported into the thylakoids of chloroplasts are buffered by endogenous compounds either at the internal surface or by molecules dissolved in the inner aqueous phase. Accordingly, the light-induced transmembrane potential changes have to be interpreted as changes of a surface or a Donnan potential.Here, in Part I of this series, the Donnan representation is given. Whereas the dark state corresponds to a Donnan equilibrium, the light state is stationary, for which a generalized Donnan potential is defined. The light-induced potential change and ion transport are calculated for the case of constant volume and the volume change for the case of zero difference is osmotic pressure. In addition, allowance is made for proton binding to the Donnan groups.     

Thermal and photo-chemical degradation of nylon 6,6 polymer: Part 1—Influence of amine-carboxyl end group balance on luminescent species

Nylon 6,6 polymers of different degrees of polymerisation have been characterised by ultra-violet (uv) absorption, fluorescence and phosphorescence emission spectroscopy, viscosity number and amine end-group balance and the data related to their subsequent thermal and photo-chemical stabilities. The latter, determined by the percentage change in viscosity number, clearly shows that in both cases polymer stability is markedly influenced by the final stages of polymerisation under both steam and nitrogen atmospheres, the latter being the most detrimental. During both of these processes the molecular weight increases, as indicated by an increase in viscosity number, as does the concentration of fluorescent and phosphorescent impurities and products absorbing uv at 294 nm. Extraction of some of these species by 2-propanol results in a marked improvement in polymer photo-stability, implicating the involvement of these chromophores in initiation of photo-oxidation. Thermal degradation at 120°C confirms the presence of two types of fluorescent species. The first is reactive, rapidly diffuses out of the polymer and is associated with cyclic α, β-unsaturated carbonyl compounds; the second is non-volatile in-chain in type, increases in concentration and is associated with α-ketoimide structures. However, whilst correlations between the presence of light absorbing/luminescent carbonyl species is evident to some extent another, more important, factor based on the concentration of amine end-groups appears to be dominant. In this case a higher concentration of amine end-groups at lower degrees of polymerisation results in an increase in polymer stability, both thermally and photo-chemically and is associated with the radical/oxygen scavenging ability of the amine end-group, not unlike that of the well-known hindered piperidine light stabilisers. This is confirmed by the observation that treatment of nylon 6,6 films with sulphur dioxide gas, which reacts with the amine groups, thus generating sulphonamides, sensitises the photo-chemical oxidation of the polymer, an effect which contrasts with that found earlier for polyolefins.     

NO-NH_3-O_2 reaction catalyzed by V_2O_5/AC at low temperatures——Effects of SO_2, V_2O_5 loading and reaction temperature

The effects of SO2, V2O5 loading and reaction temperature on the activity of activated carbon supported vanadium oxide catalyst have been studied for the reduction of NO with NH3 at low temperatures (150-250℃). It is found that SO2 significantly promotes the catalyst activity. Both V2O5 loading and reaction temperature are vital to the promoting effect of SO2. The catalysts with V2O5 loadings of 1 -5 weight percent have a positive effect on the promotion of SO2, while the catalysts with V2O5 loadings of above 7 weight percent have not such an effect or show a negative effect. At lower temperatures (<180℃) SO2 poisons the catalyst but at higher temperatures promotes it. The reason of the SO2 promotion was also discussed; it may results from the formation of SO42- on the catalyst surface, which increases the surface acidity and hence the catalytic activity.     

415 - Surface and/or Donnan potentials at the thylakoid membrane?: Part II. Calculation of light-induced surface potential changes and corresponding ion movement for a 1 : 1 electrolyte

The surface potential at the inner side of the thylakoid membrane in the dark and in the light state is calculated using the simple Gouy-Chapman theory, together with modifications to allow for proton binding to the surface. The corresponding transmembrane potential change and the ion transport, necessary for ion redistribution in the diffuse double layer, are formulated. the steady-state generalized Donnan potential is shown to be negligible. Finally, the surface potential representation is compared with the Donnan potential representation, given in the preceding paper. On the basis of the formula derived, measurements are discussed which will help to decide between the different concepts.     

Specific Role of Reactor Configurations on the Mass Transfer and Energy Yield: Case of “Batch” and "Circulating” Gliding arc Liquid–Gas Reactors—Part 1: Experimental Study

Plasma Chemistry and Plasma Processing - The mass transfer and energy efficiency in the “batch” and “Circulating” gliding arc configuration reactors for the direct...