Phase Equilibria Of Water Research Articles

Predicting the high-pressure phase equilibria of binary aqueous solutions of 1-butanol, n-butoxyethanol and n-decylpentaoxyethylene ether (C10E5) using the SAFT-HS approach

The phase equilibria of water + n-butan-1-ol is characterized by the presence of so-called closed-loop curves which represent regions of liquid-liquid immiscibility in the phase diagram. The system exhibits lower critical solution temperatures (LCSTs), which denote the lower limit of immiscibility together with upper critical solution temperatures (UCSTs). This behaviour can be explained in terms of the competition between the incompatibility of the water with the alkyl chain and the hydrogen bonding between water and the hydroxyl group. To study the phase equilibria we have used a simplified version of the statistical associating fluid theory (SAFT), which is based on the thermodynamic perturbation theory of Wertheim for associating fluids: the original SAFT-LJ equation of state treats the molecules as chains of Lennard-Jones segments, while the simplified SAFT-HS equation treats molecules as chains of hardsphere repulsive segments with van der Waals interactions. The water molecules are modelled as hard...

Predicting the high-pressure phase equilibria of binary aqueous solutions of 1-butanol, n-butoxyethanol and n-decylpentaoxyethylene ether (C10E5) using the SAFT-HS approach

The phase equilibria of water + n-butan-1-ol is characterized by the presence of so-called closed-loop curves which represent regions of liquid-liquid immiscibility in the phase diagram. The system exhibits lower critical solution temperatures (LCSTs), which denote the lower limit of immiscibility together with upper critical solution temperatures (UCSTs). This behaviour can be explained in terms of the competition between the incompatibility of the water with the alkyl chain and the hydrogen bonding between water and the hydroxyl group. To study the phase equilibria we have used a simplified version of the statistical associating fluid theory (SAFT), which is based on the thermodynamic perturbation theory of Wertheim for associating fluids: the original SAFT-LJ equation of state treats the molecules as chains of Lennard-Jones segments, while the simplified SAFT-HS equation treats molecules as chains of hardsphere repulsive segments with van der Waals interactions. The water molecules are modelled as hard spheres with four association sites to treat the hydrogen bonding; the dispersion forces are treated at the van der Waals mean-field level. The 1-butanol molecules are modelled as chains of hard-sphere segments with two/three bonding sites to treat the terminal hydroxyl group; the dispersion forces also are treated at the mean-field level. The work has been extended to examine water + n-butoxyethanol (C4E1) and water + n-decylpentaoxyethylene ether (C10E5), which are n-alkyl polyoxyethylene ethers (C i E j ). Both of these systems exhibit closed-loop behaviour. These longer chain molecules also are modelled as chains of hard spheres with bonding sites to treat the terminal hydroxyl group, but with an additional three sites per oxyethylene group. For appropriate choices of the intermolecular parameters, the SAFT-HS approach predicts cloud curves with both a UCST and an LCST. The critical temperatures and the extent of immiscibility are in very good agreement with experimental data. The high-pressure critical behaviour is also well described by the theory, including the critical dome for H2O + C4E1.

Phase equilibria of water + methanol + hexyl acetate mixtures

Liquid-liquid equilibrium data at 25, 35 and 45 °C, and isobaric vapour-liquid equilibrium data at 101.32 kPa, were determined for the ternary system water + methanol + hexyl acetate. The data were correlated using the Wilson, NRTL and UNIQUAC models and were predicted using the UNIFAC and ASOG methods.

Critical curves and phase equilibria of water- n-alkane binary systems to high pressures and temperatures

The critical curves of the six binary systems water-methane to water-hexane and water-dodecane have been calculated up to 200 MPa and, in part, to 670 K. An equation of state of the perturbation type with a repulsion and an attraction term with square-well potential for intermolecular interaction is used. With pairwise combination rules for these potentials, three adjustable parameters are needed. The values of these parameters for the series of alkanes obtained from comparison with experiments are given and discussed. For water with methane, butane, and hexane the extent of the three-dimensional two-phase regions is calculated. It is suggested to use this procedure as a basis for predictions for analogous binary polar-nonpolar systems to high pressures and temperatures.

Phase equilibria of absorbed liquids and the structure of porous media

The phase equilibria of water within porous silica has been studied by proton and deuteron magnetic resonance. Proton signal amplitude as a function of filling factor was measured. These protons arise from the proton-deuterium equilibrium that is established between the liquid and the absorbed layer on the pore wall. The results for temperatures below 0°C show a maximum as a function of filling factor, Θ. This suggests that the pores fill from either a surface layer or from the crevices and interstices into the center. Another experiment used cryoporometry to study the size of crystals formed within the pores as a function of Θ and leads to the same conclusion.

Fluid phase equilibria in water: natural gas component mixtures and their description by the hole group-contribution equation of state

Fluid phase equilibria in water: natural gas component mixtures and their description by the hole group-contribution equation of state

Modeling and simulation of the operation of an AFC cathode by using concentrated electrolyte solution transport theory

A mathematical model for alkaline fuel cell cathodes was developed by using concentrated solution transport theory to simulate and study the electrode operation. The model assumed an electrode with two layers: gas-supply layer and reaction-active catalyst layer. The processes considered in the model include: Multiple component gas diffusion in both the gas-supply and catalyst layers, multicomponent transport in the concentrated electrolyte of the catalyst layer, phase equilibrium of water in the gas and liquid phases of the catalyst layer, reactant gas transport both in the electrolyte film and agglomerates within the catalyst layer, the electrochemical reaction of oxygen on the catalyst, and electronic conduction within the solid phase of the catalyst layer. The emphasis of the model simulation was given to study the effect of humidity content in the inlet reactant gas, electrode operating current density, and electrode operating temperature on the details of the electrode operation. The details considered comprise water flux transport in gas and liquid phase, both reaction and electrolyte concentration distributions inside the electrode, and electrode output potential. The results give interesting aspects of the water movement in the catalyst layer with important implications for the water balance of the electrode. Application of this model should be especially beneficial to the understanding of humidity content management during electrode operation.

Fluid phase equilibria in water: natural gas component mixtures and their description by the hole group-contribution equation of state

Victorov A.I., Fredenslund Aa. and Smirnova N.A., 1991. Fluid phase equilibria in water:natural gas component mixtures and their description by the hole group-contribution equation of state. Fluid Phase Equilibria, 66: 187-210. Experimental data on fluid phase equilibria in binary mixtures of water with typical natural gas and oil components (light and heavy alkanes, nitrogen, hydrogen sulfide, carbon dioxide) have been examined and the phase behavior of these mixtures over wide ranges of temperature and pressure is reviewed. A quasi-chemical group-contribution hole model is used for calculating the phase equilibria in these systems. With few exceptions the model predicts correctly the basic types of phase behavior and, except for gas-gas equilibria, the accuracy for all the binaries and two multicomponent aqueous mixtures tested is satisfactory.

Phase equilibria of water + γ-butyrolactone system

Vapor pressures over the range 392–555 K, saturated liquid densities from 353 to 453 K for pure γ-butyrolactone (GBL), and total pressure ( PTx) data for water + GBL mixtures are reported for four mixture compositions over the pressure range from 0.5 to about 16 bar. Experimental data have been fitted to Peng-Robinson and Patel-Teja equations for pure components and mixtures.

Influence Of Ice Sheets On Climate and Ice-Sheet Dynamics

Influence Of Ice Sheets On Climate and Ice-Sheet Dynamics

Influence Of Ice Sheets On Climate and Ice-Sheet Dynamics

Influence Of Ice Sheets On Climate and Ice-Sheet Dynamics

Phase equilibria in water, pentanol, tetradecyltrialkylammonium bromide systems

Phase equilibria in water, pentanol, tetradecyltrialkylammonium bromide systems

Role of phase equilibrium in frost heave of fine-grained soil under negligible overburden pressure

The role of the phase equilibrium of water in frost heave was studied for two kinds of soil. The rate of frost heave and the rate of water intake were measured simultaneously under various rates of heat removal. The experimental data revealed a trend common for both soils that the rate of water intake attains its maximum at a certain critical rate of heat removal. The data were analyzed by using equations accurately describing the relation between these rates. The results of the analysis indicate a serious doubt about the validity of phase equilibrium in the system. Alternatively, an assumption was introduced that supercooling occurred between a frost front and an unfrozen part of the soil. It was shown that supercooling could explain the data well under certain conditions.

Thermodynamic compatibility of proteins in aqueous media. Part. I. Phase diagrams of some water--protein A--protein B systems.

The thermodynamic compatibility of proteins belonging to different classes according to Osborne has been investigated in aqueous media. Phase equilibrium for water--ovalbumin--soybean globulin fraction, water--ovalbumin--casein, water--casein--gliadin and water--casein--soybean globulin fraction systems has been investigated. The data obtained were analysed according to the theoretical concepts of Scott, Patterson and Prausnitz concerning the effect of polymer molar masses and the solvent quality on the phase equilibrium in similar systems. The analysis performed indicates that these concepts can be applied to the water--protein A--protein B systems. The phase equilibrium in water--protein A--protein B systems has some distinctive features as compared to that in systems containing two synthetic polymers in the single solvent. Firstly, proteins are usually compatible in a broader concentration range as compared to common polymers. Moreover, the separation of water--protein A--protein B systems into two phases often results in a considerable concentration of one of the protein components. Apparently, the latter fact can be associated with the marked difference in the interaction parameter of proteins belonging to different classes with the solvent, and, hence, with the marked difference in the hydrophilicity of the proteins investigated.

Phase equilibria in water, pentanol, tetradecyltrialkylammonium bromide systems

Three tetradecyltrialkylammonium bromides (trimethyl, triethyl and tripropyl) were combined with water and pentanol and the phase regions determined. Increasing the chain-length of the trialkyl part gave a pronounced reduction of the regions for liquid-crystalline phases, especially the lamellar variety, but gave only insignificant distinction of the geometric characteristics once the liquid-crystalline phase was formed.

Solid-liquid phase equilibria in water + ethylene glycol

Thermal methods were used to determine with high precision the solid-liquid phase equilibria diagram for water + ethylene glycol. A stable 1−1 solid hydrate forms. Because of supercooling, the hydrate is difficult to obtain; a cooling procedure was devised to initiate its crystallization. The two eutectics are at (224.12 ± 0.05) and (230.22 ± 0.05) K and mole fractions 0.288 and 0.541 of ethylene glycol, respectively. We also obtained a metastable phase diagram with a single metastable eutectic at (209.5 ± 0.5) K and mole fraction 0.335 of ethylene glycol.

Activation of Atmospheric Particles as Ice Nuclei in Cold and Dry Air

Abstract Ice nucleation and subsequent phase equilibrium in water held in the micro-capillaries of atmospheric particles are examined. It is found that ice formed in the micro-capillaries of certain particles may exist in equilibrium with a dry atmosphere, where particles preactivated by Fournier's effect are expected to lose their activity. A possible mechanism of activation of the particles as ice nuclei in a cold dry atmosphere is suggested.