Calculation of high pressure vapour—liquid equilibria for systems containing polar substances with the use of an augmented van der Waals equation of state

An augmented van der Waals equation of state based on a perturbation theory has been applied to the calculation of high pressure vapour—liquid equilibria for systems containing polar substances. The equation of state comprises four terms, which imply the contributions from repulsion, symmetric, non-polar asymmetric, and polar asymmetric interactions. The characteristic parameters of each pure substance have been determined by three methods with the use of vapour pressures and saturated liquid densities. Mixing models for the terms of the repulsion, symmetric, and non-polar asymmetric interactions are the same as used previously. Two types of mixing models based on a three-fluid model and/or a one-fluid model are developed for the polar asymmetric term. The polar asymmetric term has a large effect on the prediction of the vapour—liquid equilibrium. With the introduction of a binary interaction parameter, the equation is found to be useful in correlating the vapour—liquid equilibria for a system containing a polar substance except near a critical region.     

A new procedure for consistency testing of binary vapour—liquid equilibrium data

A procedure has been proposed for testing the thermodynamic consistency of low-pressure binary vapour—liquid equilibrium data. The method, employing the idea of local defects due to Mc Dermott and Ellis, is based on the statistical nature of consistency and is systematically formulated using the methods of mathematical statistics. It provides well-defined limits for the test quantities and consequently is superior to all empirically evaluated tests. In addition, the proposed procedure provides an estimate of experimental error and enables any systematic characteristic to be identified. The efficiency of the method developed here has been investigated through Monte Carlo simulations and its applicability to actual vapour—liquid equilibrium data has been demonstrated using a number of examples. A comparison with the methods of Ulrichson and Stevenson and Samuels et al., which also utilize a statistical treatment of the local defects, reveals a serious error involved in both. For the case when credit is placed in the vapour—liquid equilibrium data, the consistency may be used to draw some conclusions on the vapour phase non-ideality. In this respect, minimization of the consistency criterion proposed is shown to lead to the maximum likelihood estimate of the second-cross virial coefficient.     

Moderated pressure microwave digestion system for preparation of biological samples

A new type closed digestion vessel was constructed for digestion of biological samples. In this the vapour pressure can be maintained on moderated level (150-300 kPa) by means of an internal cooling spiral. During the operation the reflux of the condensed acid and water vapour continuously renews the liquid phase over the sample. By this way a less expensive microwave system may be applied. The performance of this instrument is practically equal to the commercial systems. The digestion time of plant and tissue samples is 5-10 min and the analytical results for reference materials are in good agreement with the reference values.     

Vapour pressures,densities, and viscosities of the aqueous solutions containing (triethylene glycol or propylene glycol) and (LiCl or LiBr)

In this work, new results for density, viscosity, and vapour pressure of (triethylene glycol or propylene glycol) in H₂O with LiCl or LiBr systems over temperatures ranging from 303.15 K to 343.15 K are presented. For each ternary system, four systems of which (4 to 25) mass% salt mixed with various glycols (50 to 80) mass% were studied. Incorporated with the pseudo-solvent approach, a vapour pressure model based on the mean spherical approximation for aqueous electrolyte solutions was used to represent the measured vapour pressure of the investigated systems. The present density and viscosity results were also correlated as a function of temperature and composition. The correlations yield satisfactory results. Compared to the conventionally used liquid desiccants, the vapour pressures of the systems studied yield smaller values of vapour pressures. The properties presented in this work are, in general, of sufficient accuracy for most engineering-design calculations.     

An equipment for dynamic measurements of vapour–liquid equilibria and results in binary systems containing cyclohexylamine

A computer-aided equipment for precise measurements of vapour–liquid equilibrium (VLE) data at normal and low pressures using the dynamic method will be introduced. The apparatus consists of a circulation still which allows isothermal and isobaric measurements. The digital measurement and control system is accomplished by a multimeter coupled with a PC via IEEE-card. The quality of the measurement data is demonstrated by a comparison of the measured vapour pressure data of the pure substances toluene, n-octane and cyclohexylamine with the vapour pressure equation of Daubert and Danner. Furthermore, vapour–liquid equilibrium data were measured in the binary systems cyclohexylamine + aniline or water or n-octane. The measured data were regressed according to the activity coefficient models NRTL, UNIQUAC and to the Elliott–Suresh–Donohue-equation of state (ESD-EOS).     

Vapour pressures and densities of the mixed-solvent desiccants (glycols + water + salts)

The vapour pressures and densities of the mixed-solvent desiccants have been studied for temperatures ranging from (303.15 to 343.15) K. The mixed-solvent desiccants investigated were aqueous-organic systems with salt. The studied organic solvents were diethylene glycol, tetraethylene glycol, and dipropylene glycol. The chosen salts were lithium chloride and lithium bromide. Six ternaries (glycol/water/salt) were selected for this study. For each ternary system, four systems of which (4–25) mass% salt mixed with various glycols (50–80) mass% were investigated. Incorporated with the pseudo-solvent approach, a vapour pressure model based on the mean spherical approximation for aqueous electrolyte solutions was used to represent the measured vapour pressure of glycol/water/salt systems. A simplified density equation was applied to model the measured density of glycol/water/salt systems. Satisfactory results were obtained for vapour pressure and density calculations. The vapour pressures of the aqueous-organic systems with salt yield smaller values of vapour pressures compared to the conventionally used liquid desiccants. The properties obtained and presented in this study are, in general, of sufficient accuracy for most engineering-design calculations, such as the design of dehumidifier process using mixed-solvent desiccants as absorbents.     

The vapour pressure of naphthalene

Measurements of the vapour pressure of naphthalene over the temperature range 263 to 343 K are reported. These have been correlated with data from the literature, and an equation is given from which recommended values are calculated for the vapour pressure of solid naphthalene from 230 K to the triple point. An equation is given also for the vapour pressure of liquid naphthalene from the triple point to the critical point. The enthalpy of melting obtained by differentiating these two equations is in good agreement with a measured value.     

Effect of small amounts of methanol on the vapour—liquid equilibrium for the water-formaldehyde system

The total vapour pressures of three mixtures of the water-methanol-formaldehyde system have been measured over the range of temperatures 55–95°C. The formaldehyde composition was in the range 34–44 wt.%, while that of methanol was <1 wt.%. These measurements were carried out with the aim of demonstrating that, for studying the vapour—liquid equilibrium for the water—formaldehyde system, it is necessary to eliminate methanol to a greater extent than is usual.The experimental results compare favourably with those calculated by a predictive thermodynamic model which explains nonideality in the liquid phase in terms of chemical forces for the binary systems water—formaldehyde and methanol—formaldehyde and in terms of physical forces (Wilson equation) for the binary system water—methanol.The proposed model was also utilized in bubble-point calculations for the binary system methanol-formaldehyde and for the ternary system over a large range of compositions. The results were compared with literature data.     

Review of non-reactive and reactive wetting of liquids on surfaces

Wettability is a tendency for a liquid to spread on a solid substrate and is generally measured in terms of the angle (contact angle) between the tangent drawn at the triple point between the three phases (solid, liquid and vapour) and the substrate surface. A liquid spreading on a substrate with no reaction/absorption of the liquid by substrate material is known as non-reactive or inert wetting whereas the wetting process influenced by reaction between the spreading liquid and substrate material is known as reactive wetting. Young's equation gives the equilibrium contact angle in terms of interfacial tensions existing at the three-phase interface. The derivation of Young's equation is made under the assumptions of spreading of non-reactive liquid on an ideal (physically and chemically inert, smooth, homogeneous and rigid) solid, a condition that is rarely met in practical situations. Nevertheless Young's equation is the most fundamental starting point for understanding of the complex field of wetting. Reliable and reproducible measurements of contact angle from the experiments are important in order to analyze the wetting behaviour. Various methods have been developed over the years to evaluate wettability of a solid by a liquid. Among these, sessile drop and wetting balance techniques are versatile, popular and provide reliable data. Wetting is affected by large number of factors including liquid properties, substrate properties and system conditions. The effect of these factors on wettability is discussed. Thermodynamic treatment of wetting in inert systems is simple and based on free energy minimization where as that in reactive systems is quite complex. Surface energetics has to be considered while determining the driving force for spreading. Similar is the case of spreading kinetics. Inert systems follow definite flow pattern and in most cases a single function is sufficient to describe the whole kinetics. Theoretical models successfully describe the spreading in inert systems. However, it is difficult to determine the exact mechanism that controls the kinetics since reactive wetting is affected by a number of factors like interfacial reactions, diffusion of constituents, dissolution of the substrate, etc. The quantification of the effect of these interrelated factors on wettability would be useful to build a predictive model of wetting kinetics for reactive systems.     

Vapour—liquid equilibria in binary systems formed by N-Methylpyrrolidone with hydrocarbons and hydroxyl derivatives

The vapour—liquid equilibria (VLE) determined by an ebulliometric total pressure method under isothermal conditions for binary systems formed by N-methylpyrrolidone with hexane (333.25 and 343.15 K), dodecane (393.25 K), cyclohexane (333.25 and 354.15 K), methyl-cyclohexane (354.15 and 373.25 K), benzene (333.25 and 354.15 K), toluene (362.15 and 383.35 K), propylbenzene (352.15 and 373.75 K), butylbenzene (352.15 and 373.75 K), propanol-1 (354.15 K), hexanol-1 (351.75 and 393.35 K) and at 393.55 K for cyclohexanol, 4-methylphenol and 2,4-dimethylphenol are reported. The vapour pressures of the pure substances are given. The least squares analysis of VLE data by means of the Redlich-Kister equation is given.     

Separation of systems based on uranium hexafluoride and some of halogen fluorides

The purpose of this paper is to present the results of the comprehensive study of the phase equilibriums liquid-solid and liquid-vapour in binary and ternary systems, formed by uranium hexafluoride, bromine trifluoride and iodine pentafluoride.Investigation of the phase equilibriums in condensed systems is done by methods of differential thermoanalysis and visual polythermal analysis. All systems belong to simple eutectics; formation of the compounds is not detected. For all systems under investigation diagrams of the phase equilibrium liquid-solid are plotted.Phase equilibriums liquid-vapour in studied systems were studied by statistical method. All systems are non-aseotropic. The article presents diagrams of the phase equilibrium liquid-vapour in binary systems, pressure of the saturated vapour dependences on liquid composition, surface of the boiling liquid and lines of the constant content of uranium hexafluoride and iodine pentafluoride in vapour phase of the ternary system UF₆-BrF₃-IF₅.     

Photodynamic actinometry using microspheres: concept, development and responsivity

Photodynamic therapy (PDT) relies on three main ingredients, oxygen, light and photoactivating compounds, although the PDT response is definitively contingent on the site and level of reactive oxygen species (ROS) generation. This study describes the development of a novel, fluorescent-based actinometer microsphere system as a means of discerning spatially resolved dosimetry of total fluence and ROS production. Providing a high resolution, localized, in situ measurement of fluence and ROS generation is critical for developing in vivo PDT protocols. Alginate-poly-L-lysine-alginate microspheres were produced using ionotropic gelation of sodium alginate droplets, ranging from 80 to 200 microm in diameter, incorporating two dyes, ADS680WS (ADS) and Rhodophyta-phycoerythrin (RPE), attached to the spheres' inside and outside layers, respectively. To test the responsivity and dynamic range of RPE for ROS detection, the production of ROS was initiated either chemically using increasing concentrations of potassium perchromate or photochemically using aluminum tetrasulphonated phthalocyanine. The generation of singlet oxygen was confirmed by phosphorescence at 1270 nm. The resulting photodegradation and decrease in fluorescence of RPE was found to correlate with increased perchromate or PDT treatment fluence, respectively. This effect was independent of pH (6.5-8) and could be inhibited using sodium azide. RPE was not susceptible to photobleaching with light alone (670 nm; 150 Jcm(-2)). ADS, which absorbs light between 600 and 750 nm, showed a direct correlation between radiant exposure (670 nm; 0-100 Jcm(-2)) and diminished fluorescence. Photobleaching was independent of irradiance (10-40 mW cm(-2)). We propose that actinometer microspheres may provide a means for obtaining high spatial resolution information regarding delivered PDT dose within model systems during investigational PDT development and dosimetric information for clinical extracorporeal PDT as in the case of ex vivo bone marrow purging.     

Vapour—liquid equilibrium in binary mixtures formed by benzene or cyclohexane with 1-chloropropane or 1-chlorobutane

The vapour—liquid equilibria (VLE) for the binary systems formed by 1-chloropropane with benzene and cyclohexane at 308.15 K and 318.15 K, and for systems formed by 1-chlorobutane with the same hydrocarbons at 308.22 K, 328.27 K and 348.31 K have been determined by a total pressure ebulliometric method. The accuracy of these results was proved by comparing the heat of mixing data calculated from these VLE results with those obtained by direct measurements (Amaya, 1961; Grolier et al., 1973). The experimental data and the results of correlation by means of the Redlich—Kister equation are given. The systems with benzene were found to be nearly ideal, while those with cyclohexane exhibit positive deviations (G^E = 220–260 J mole^?1 for an equimolar mixture). New vapour pressure versus temperature data for 1-chlorobutane are reported.     

QUANTUM YIELDS OF TRIPLET FORMATION OF SOME DERIVATIVES OF ANTHRAQUINONE

Abstract— Quantum yields of triplet formation for five amino substituted anthraquinones have been determined by the comparative actinometer method using laser flash photolysis. Substitution reduces the yields to values of ˜10^--². and the requirement of low laser intensities required high sensitivity of detection of triplet absorption. The ø_T values are compared with the quantum efficiencies of fluorescence and decomposition for the compounds, and the criteria for light stability discussed.     

Modelling (vapour + liquid) and (vapour + liquid + liquid) equilibria of {water (H2O) + methanol (MeOH) + dimethyl ether (DME) + carbon dioxide (CO2)} quaternary system using the Peng–Robinson EoS with Wong–Sandler mixing rule

The (vapour + liquid) equilibria (VLE) and (vapour + liquid + liquid) equilibria (VLLE) binary data from literature were correlated using the Peng–Robinson (PR) equation of state (EoS) with the Wong–Sandler mixing rule (WS). Two group contribution activity models were used in the PRWS: UNIFAC–PSRK and UNIFAC–Lby. The systems were successfully extrapolated from the binary systems to ternary and quaternary systems. Results indicate that the PRWS–UNIFAC–PSRK generally displays a better performance than the PRWS–UNIFAC–Lby.     

A NEW REUSABLE CHEMICAL ACTINOMETER FOR UV IRRADIATION IN THE 248 - 334 nm RANGE

The highly reversible thermally stable photochromic system consisting of heterocoerdianthrone-endoperoxide (HCDPO) and its parent compounds HCD and 0₂ is proposed as a new reusable liquid chemical actinometer in the UV region 248 ≤λ≤ 334 nm. The foremost advantageous features of this new system are: (1) high reproducibility and accuracy, (2) high sensitivity, (3) almost wavelength independent quantum yields, (4) no loss in accuracy even after 100 repeated actinometric cycles and (5) very easy handling and straightforward calculability of the radiation quantum flux.     

Interfacial phase transitions in conducting fluids

We present a review, largely based on recent experimental work of our group, on phase transitions at interfaces of fluid metals, alloys and ionic liquids. After a brief analysis of possible experimental errors and limitations of surface sensitive methods, we first deal with first-order wetting transitions at the liquid/vapour and liquid/wall interface in systems such as Ga-based alloys, K-KCl melts, and fluid Hg. The following chapter refers to surface freezing or surface induced crystallization in different metal alloys. The respective surface phase diagrams are discussed in comparison with their bulk counterpart. In the last part we present very recent investigations of ionic liquid interfaces, including order-disorder transitions at the liquid/vapour interface and examples of two-dimensional phase transitions at the electrified ionic liquid/metal interface. Finally, a simple electrowetting experiment with an ionic liquid droplet under vacuum is described which gives new insight into the contact angle saturation problem. The article ends up with a few perspective remarks on open problems and potential impact of interfacial phenomena on applied research.     

Evaluation of translational friction coefficients of macroscopic probes in nematic liquid crystals

We present a study of the translational friction coefficients of spherical and ellipsoidal probes in nematic liquid crystalline fluids, based on the numerical treatment of Leslie-Ericksen equations [Q. J. Mech. Appl. Math. 19, 357 (1966); Adv. Liq. Cryst. 4, (1979); Trans. Soc. Rheol. 5, 23 (1961); Adv. Liq. Cryst. 2, 233 (1976)] for incompressible nematic fluids. Simulations of director dynamics in a local environment surrounding the moving probe are presented, and the dependence of translational diffusion on liquid crystal viscoelastic parameters is discussed. The time evolution of the director field is studied in the presence of an orienting magnetic field in two characteristic situations: Directors of motion parallel and perpendicular with respect to the field. In the particular case under investigation, a detailed analysis is given for the case of spherical, prolate, and oblate ellipsoidal probes in rectilinear motion in nematic (4-methoxibenzylidene-4'-n-butylaniline), together with a comparison with other nematogens, namely, 4,4'-dimethoxuazoxy benzene and (4'-n-pentyl-4-cyanobiphenil). A discussion of the general methodology presented in this work is given for the case of colloidal dispersions in nematic liquid crystals, which are considered as model systems of dispersions of particles in host media with anisotropic physical properties.     

CHEMICAL ACTINOMETRY IN THE VISIBLE (475 - 610 nm) BY meso-DIPHENYLHELIANTHRENE

Abstract The self-sensitized photooxidation of meso -diphenylhelianthrene to its endoperoxide was kincticallv examined. It is recommendable as a convenient, reliable, and wavelength independent actinometer for the visible wavelength range. The calibration values, the actinometric procedure and the evaluation method are given in detail.     

Monte Carlo simulations of squalane in the Gibbs ensemble

We investigate the liquid–vapour coexistence curve of 2,6,10,15,19,23-hexamethyltetracosane (squalane) near the critical point with a new Lennard–Jones parameter set and compare our results to existing simulation data as well as to recent experimental vapour pressure data. Comparison of the liquid–vapour coexistence curve to previous simulation data reveals that this new force field, which includes tail corrections to the truncation of the non-bonded interactions increases the liquid density. We determine the critical temperature to 829 K and 825 K (with roughly 1% error) for two different system sizes, 72 and 108 molecules, and the critical density to 0.211 g/cm³ and 0.228 g/cm³, respectively. We extrapolate experimental vapour pressure data by use of Antoine's law to the temperature range covered by simulation and yield good agreement between simulation and experiment. We note that the vapour pressure in simulation is essentially governed by the ideal vapour pressure.