Modelling the phase equilibria of multicomponent mixtures containing CO2, alkanes,water, and/or alcohols using the quadrupolar CPA equation of state

ABSTRACT

In this work, a quadrupolar cubic plus association (qCPA) equation of state is evaluated for its ability to predict the phase equilibria of multicomponent mixtures containing CO₂ and alkanes, alcohols, and/or water. A single binary interaction parameter is employed in qCPA for all binary combinations. All parameters are based solely on pure fluid or binary mixture data and multicomponent data are used only to evaluate the predictions. The performance of qCPA is, for all mixtures, compared to CPA where CO₂ is considered to be either non-associating (inert), solvating or self-associating. In the latter two approaches, an additional adjustable parameter is employed for binary pairs of CO₂ and an associating compound. The results show that the predictions with qCPA are very similar to the best performing CPA approaches, even though the model uses fewer adjustable binary parameters. The predictions with qCPA and the best CPA approaches are typically satisfactory and predict the general behaviour of the systems. As expected, qCPA and CPA with solvation or association typically performs better than inert CPA for two- and three phase vapour–liquid and vapour–liquid–liquid equilibria. However, inert CPA yields the best results of all the models for the prediction of dew point pressures.     

Emission characteristics of an ultraviolet emitter based on mixtures of krypton with low-aggressive halogen carriers pumped by a barrier discharge

The emission characteristics of a pulse-periodic excilamp with three dielectric barriers based on the 222-nm KrCl(X-B) and 248-nm KrF(X-B) emission bands have been investigated. The working gases of the lamp were mixtures of krypton with low-aggressivity halogen carriers (SF₆, CCl₄). Optimal compositions of Kr-SF₆ and Kr-CCl₄ mixtures for obtaining the maximum intensity of the system of 222-nm KrCl(X-B) and 248-nm KrF(X-B) bands have been determined. The results of lamp optimization depending on the parameters of the source of pulse-periodic short-duration barrier discharge are presented.     

The concentration susceptibility in He3He4 mixtures near the superfluid transition

We report direct measurements of the concentration susceptibility in He³He⁴ mixtures by observing the gravity-induced concentration change δX₃ over a height of 2 mm in the mixture. The predicted peak at the superfluid transition is observed for the investigated mixtures, 0.60 ? X₃ ? 0.67.     

X-ray photoemission spectra of valence electrons in V3X and Nb3X compounds

The X-ray photoemission spectra (XPS) of the A15 type compounds V₃Au, Nb₃Os, Nb₃Ir, Nb₃Pt and Nb₃Au have been studied. The inner level binding energies of the different components and the valence electron distribution were measured. The Nb4d and the X5d energy bands of the Nb₃X compounds appear to be more and more separate with increasing atomic number of the X component. The comparison between the results from X-ray emission spectroscopy (XES) and X-ray photoelectron spectroscopy (XPS) of corresponding V₃X and Nb₃X compounds points out the similarity of their electronic structures.     

New compounds in the Mn-X-Bi system where X = Ni, Cu, RhorPd

A new class of magnetic compounds has been discovered in the temary system Mn-X-Bi where X is Ni, Cu, Rh or Pd. The approximate compositions of these compounds are Mn₅Ni₂Bi₄, Mn₃Cu₄Bi₄, Mn₅Rh₂Bi₄, and Mn₅Pd₂Bi₄. The Bravais lattice is face-centered cubic, and the lattice constants are 12.16 Å (X = Ni), 12.18 Å (X = Cu), 12.31 Å (X = Rh) and 12.44 Å (X = Pd). These compounds are probably ferromagnetic and have Curie temperatures in the range -7°C to 183°C. A crystal structure is proposed for these compounds which contains 88 atoms/unit cell.     

The virial coefficients of hard hypersphere binary mixtures

The third, fourth and fifth virial coefficients of hard hypersphere binary mixtures with dimensionality d = 4, 5 have been calculated for size ratios R ≥ 0.1, R = ≡ σ₂₂/σ₁₁, where σ _ii is the diameter of component i. The composition independent partial virial coefficients have been evaluated by Monte Carlo integration of the corresponding Mayer modified star diagrams. The results are compared with the predictions of Santos, S., Yuste, S. B., and Lopez de Haro, M., 1999, Molec. Phys., 96, 1 of the equation of state of a multicomponent mixture of hard hyperspheres, and the good agreement gives strong support to the validity of that recipe.     

A high-pressure study of Th3P4 and some U3X4 compounds

Abstract

The high-pressure crystal structures of Th₃P₄ and U₃X₄, where X = P, As and Sb, have been studied by means of synchrotron x-ray diffraction in the pressure range up to 50 GPa. The cubic phase of these compounds is retained in the whole pressure range. The bulk modulus B₀ and its pressure derivative B₀’ have been determined for each compound. A log-log plot of B₀ versus unit-cell volume gives a straight line for the uranium pnictides, with a slope about -5/3.     

Optimization of high pressure bioactive compounds extraction from pansies (Viola × wittrockiana) by response surface methodology

Response surface methodology (RSM) was employed for the first time to optimize high pressure extraction (HPE) conditions of bioactive compounds from pansies, namely: pressure (X₁: 0–500?MPa), time (X₂: 5–15?min) and ethanol concentration (X₃: 0–100%). Consistent fittings using second-order polynomial models were obtained for flavonoids, tannins, anthocyanins, total reducing capacity (TRC) and DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity. The optimum extraction conditions based on combination responses for TRC, tannins and anthocyanins were: X₁?=?384?MPa, X₂?=?15?min and X₃?=?35% (v/v) ethanol, shortening the extraction time when compared to the classic method of stirring (approx. 24?h). When the optimum extraction conditions were applied, 65.1?mg of TRC, 42.8?mg of tannins and 56.15?mg of anthocyanins/g dried flower were obtained. Thus, HPE has shown to be a promising technique to extract bioactive compounds from pansies, by reducing the extraction time and by using green solvents (ethanol and water), for application in diverse industrial fields.     

Study of phase behavior in a system of linear hydrogen-bonded carboxylic acid homologues

The system of hydrogen-bonded liquid crystals formed from binary mixtures p-n-heptyloxybenzoic (I) acid and p-n-undecloxybenzoic (II) acid has been investigated by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction, and scattering and dielectric measurements. The T–X phase diagram was obtained for this system. All mixtures show enantiotropic smectic and nematic phases. The crystalline phase represents a (α, β) solid solution. At the 2:1 ratio of I to II, an intermediate phase – co-crystal γ – is formed. The co-crystal γ possesses a much wider mesophase range than the corresponding initial components. In contrast to mixtures based on the solid solutions having a positive anisotropy, the co-crystal shows a negative dielectric anisotropy in the mesophase.     

Infrared Spectroscopic Study of Td‐Type Piperazinemetal(II) Tetracyanometallate(II) Benzene(1/1) Clathrates: Cd(C4H10N2)Cd(CN)4·C6H6 and Cd(C4H10N2)Hg(CN)4·1,25 C6H6

Abstract

The title compounds have been prepared in powder form. Their spectral data have been compared with those of the corresponding host complexes and found to be consistent with the host structure found in T_d‐type clathrates.     

Spectral characteristics of a broadband exciplex spontaneous emission source upon mixtures of the cadmium dibromide vapor with gases

The spectral characteristics of radiation from atmospheric-pressure gas-discharge plasma in mixtures of cadmium dibromide vapor with gases (Ne, Ar, Kr, Xe, and N₂), as well as the temporal characteristics of the voltage and current, have been investigated. A barrier discharge at the repetition frequency of sine voltage pulses up to 140 kHz has been used to create the gas-discharge plasma and excite the components of the working mixture. The discharge radiation has been analyzed in the spectral range 200–900 nm with a high resolution (0.05 nm). In the spectra, we have revealed radiation from exciplex molecules CdBr(B → X) and CdBr(C → X), atomic lines of cadmium and inert gases, and, in mixtures with xenon, radiation of exciplex molecules XeBr(B → X, B → A). The XeBr(B → X) radiation prevailed in the spectra at mixture temperatures up to 200°C. The further increase of the temperature resulted in the prevalence of the CdBr(B → X) radiation. The most intense CdBr(B → X) radiation was observed in mixtures of CdBr₂/Xe. When the temperature of the mixture was higher than 250°C, the discharge radiation had a silvery-white color. Regularities in the spectral characteristics of the radiation from the gas-discharge plasma are discussed. The high-frequency atmospheric-pressure barrier discharge in mixtures of cadmium dibromide with gases, excited by sine voltage pulses, can be used in multiwave and broadband excilamps, operating in the UV and visible regions.     

Ferroelectric phase transition in deuterated dihydrogen phosphate,studied by infrared spectroscopy

Abstract

The temperature dependence of polar phonon spectra of K(H_1?X D_X)₂ PO₄ single crystal with x = 0.9 for the electric field polarised parallel and perpendicular to the ferroelectric axis is reported between 7 and 300 K, in the para- and ferroelectric phase.     

Hypersonic wave anomalies in Cs3H(SeO4)2 at the transitions above room temperature

The elastic properties of Cs3H ( SeO4 ) ₂ are investigated by Brillouin spectroscopy in the temperature range 20-220 covering the two transitions III II and II I occurring at and , respectively. Phase I is known to be a protonic conductive one. Discontinuities of elastic constants are generally observed at both transitions, implying first orderness. In phases II and I, a slight broadening of the Brillouin lines is detected. The results are discussed in comparison with compounds of the families XHSeO4 (X = NH4, Rb and Cs) and CsH2BO4 (B = As and P) which also undergo a transition to a superionic phase. In the conductive phase, it appears that the lattice anharmonicity is weaker in Cs3H ( SeO4 ) ₂ than in these other compounds. Received 16 October 1998     

Spectral characteristics of a barrier discharge in cadmium dihalide vapor-inert gas mixtures

Spectral characteristics of a barrier-discharge plasma produced in atmospheric-pressure mixtures of cadmium diiodide and cadmium dibromide vapors with neon, krypton, and xenon at a repetition rate of sine voltage pulses up to 130 kHz are studied. The emission from the discharge is studied within the spectral range 200–900 nm with a resolution of 0.05 nm. Emission of exciplex molecules CdI(B → X) and CdBr(C, B → X), and cadmium and inert gas atoms is revealed, as well as emission of exciplex molecules XeI(B → X, A) and XeBr(B → X, A) in xenon-containing mixtures. The emission of xenon halides prevails in the spectra at a mixture temperature up to 200°C. With a further temperature increase, the emission of cadmium halides becomes dominating. It is ascertained that the most intense emissions of CdI(B → X) and CdI₂/CdBr₂/Xe/Kr and CdBr(B → X) molecules are observed, respectively, in CdI₂/CdBr₂/Xe/Kr and CdI₂/CdBr₂/Xe mixtures. The cadmium dihalide-inert gas mixtures are of interest for the use as a radiating gas in a multiwavelength and broadband excilamp emitting in the UV and visible spectral ranges.     

Effect of silane addition on acetylene ignition behind reflected shock waves

Ignition delay time and species profile measurements are reported for the combustion of C₂H₂/O₂/Ar mixtures with and without the addition of silane for temperatures between 1040 and 2320 K and pressures near 1 atm. Characteristic times, namely ignition time and time to peak, were determined from the time histories of CH* (A²Δ → X²Π) and OH* (A²Σ⁺ → X²Π) emission near 430 and 307 nm, respectively. For the cases without silane, there is good agreement between the present data and some recent acetylene oxidation results. Small SiH₄ additions (<10% of the fuel) reduced the ignition time in stoichiometric mixtures by as much as 75% for shocks near 1800 K. Similar reductions were seen in the fuel-lean mixture, although the effect was less temperature dependent. Several detailed chemical kinetics mechanisms of hydrocarbon oxidation were compared to the ignition delay-time data and species profiles for C₂H₂/O₂/Ar mixtures without silane. All models under-predicted ignition time for the 98% diluted stoichiometric mixture but matched the fuel-lean ignition data somewhat better. Two of the models displayed the shift in activation energy at lower temperatures seen in the data, although no one model was able to reproduce all ignition times over the entire range of mixtures and conditions.     

A comparative study of cationic distribution in the systems Li1+5XM1−XO3 and Li1+XM1−XM′ XO3 (M=Nb,M′=Ti; M=Ta,M′=Ti,Zr, Sn)

Abstract

A comparative ferroelectric and NMR studies of the systems Li_1+5X M_1?XO₃ and Li_1+XM_1?XM^′ _XO₃ (M=Nb, M′=Ti M = Ta; M′=Ti, Zr, Sn) have indicated that plot of T_C versus composition can be qualitatively explained on the basis of cationic distribution. The strong drop of T_C has been found in systems with all cations in octahedral sites, whereas little change of T_C was observed along the solid solutions with Li-ions in interstitial tetrahedral sites.     

Dielectric behaviour of propylene glycol-water mixtures studied by time domain reflectometry

Dielectric relaxation measurements on water mixtures of propylene glycol across the entire concentration range were carried out using time domain reflectometry at 25°C over the frequency range from 10 MHz to 4 GHz. For all the mixtures, only one dielectric loss peak was observed in this frequency range. The relaxation in these mixtures can be described by a single relaxation time using the Debye model. A plot of the calculated relaxation time of the mixtures gives a straight line against the mole fraction of water, X_w. It is reasoned that the diameter of the water cluster is nearly the same as the length of propylene glycol. Further, a plot of the dielectric relaxation strength δ? against X_w suggests that there is a changing pattern of dielectric behaviour from below X_w = 0.5 to higher values of X_w. The excess permittivity, the excess inverse relaxation time and the activation free energy have been determined, to confirm the formation of hydrogen bonded homogeneous and heterogeneous cooperative domains, the dynamics of solute-solvent interaction and the hindrance to molecular rotation in the hydrogen bonded glass forming propylene glycol-water system.     

Pulsed-periodic UV emitter tunable near the main absorption maximum of a DNA molecule

The spectral characteristics of a pulsed-periodic lamp with three dielectric barriers are presented for the range 220–250 nm. As the active media of the lamp, krypton (Kr)-sulfur hexafluoride (SF₆) and krypton-carbon tetrachloride (CCl₄) mixtures are tested. The use of Kr-SF₆ and Kr-CCl₄ binary mixtures in two noncommunicating volumes is shown to be more effective than the use of a Kr-SF₆-CCl₄ ternary mixture with the same amount of Kr, SF₆, and CCl₄ constituents. The emission spectrum of the lamp near the maxima of the KrF(X-B) 248-nm and KrCl(X-B) 222-nm bands can be controlled by varying the partial pressures of halogen carriers and krypton.     

Conversion ratio to F-H center pairs from self-trapped excitons in alkali chloride crystals

Abstract

The time delayed double excitation spectroscopy has been utilized to determine the conversion ratio to F-H center pairs from self-trapped excitons(STE_L) at the lowest state (1s[sgrave]_g;a_1g). The final conversion ratios, η_F/(η_F+η_X), were 0.86, 0.49 and 0.20 for NaCl, KCl and RbCl at 14K, respectively. The conversion efficiency (η =η_F+η_X) from STE_L to F-H center pairs(η_F) and to unknown states(η_X) were 0.25, 0.90 and 0.76 for the hole excitation to π_g, while 0.03, 0.01 and 0.01 for the electron excitation to b_1u, b_2u or b_3u, in NaCl, KCl and RbCl, respectively.