Phase equilibrium measurement

Since these mixing processes occur at constant pressure, // is the heat evolved or absorbed upon mixing. It is usually measured in a mixing calorimeter. The excess Gibbs free energy, is usually obtained from phase equilibria measurements that yield the activity of each component in the mixtureb and S is then obtained from equation (7.17). The excess volumes are usually obtained... 

The liquid-liquid phase equilibria measurements under ambient pressure and temperature (288.2 K) were carried out using an apparatus of a 300 ml glass cell. The temperature of the cell was controlled by a water jacket and measured with a copper-constantan thermocouple and was estimated to be accurate within + 0.1 K. A series of liquid-liquid equilibria measurements were performed by changing the composition of the mixture. 

Huo, Z., Hydrate Phase Equilibria Measurements by X-Ray Diffraction and Raman Spectroscopy, Ph.D. Thesis, Colorado School of Mines, Golden, CO (2002). 

The following two subsections consider the apparatuses used for most phase equilibria measurements, namely, the three-phase (Lw-H-V and I-H-V) regions, respectively. Similar equipment have been used to measure three-phase (Lw-H-Lhc), and four-phase (Lw-H-V-Lhc) conditions. For two-phase (H-Lhc and H-V) regions, different apparatuses have been used as discussed in Section 6.1.1.4. 

In general, stirred autoclave cells with P, Tcontrol are used for hydrate phase equilibria measurements. Over the last 50 years, hydrate phase equilibria apparatuses have been developed with the above three principles. As a consequence of reading... 

Therefore, key advantages of the QCM method are that much smaller samples (one drop of water) and hence shorter times (15 min/temperature step versus several hours for conventional methods) are required for these hydrate phase equilibria measurements. The authors applied this system to measure dissociation temperatures of gas hydrates, such as methane, nitrogen, and oxygen hydrates. 

J. David Raal and Andreas Muhlbauer, Phase Equilibria Measurement and Computation, Taylor and Francis, London, UK, 1998. 

In this paper first results of the solubility and extraction of low molecular weight polymers and plasticizers with supercritical carbon dioxide are presented and compared to the results of phase equilibria measurements. Additionally the formation of sub-micrometer particles during polymerization of acrylic acid and derivatives thereof in scCC are examined and compared with recent works [2], Finally there are some aspects to modification of polymers by absorption of scC02 and reactive components solved therein. 

Extraction and phase equilibria measurements have shown, that in the temperature range with good extraction rates the solubility is rather poor. Nevertheless it was possible to extract 70 vol.% of the binder within one hour without damaging the parts. This is a good improvement compared to usual pyrolysis or extraction processes with organic solvents or water, which last 1-2 days for parts of the described geometry. 

Initial values of the binary interaction parameters were obtained from vapor-liquid equilibrium data for ternary mixtures (9). These interaction parameters were then adjusted to minimize the difference between calculated and measured phase compositions for the three-phase equilibria measured at 50 C. 

AjH" is based mainly on two sets of gas-phase equilibria measured mass spectrometrically by Hildenbrand ( 1) and, to a lesser extent, on the analogous data of Potter et al. (2). Analyses of the mass-spectrometric data ( - ) are summarized below. 

The thermodynamic properties of clay minerals have been obtained from calorimetric measurements (cf. Robie et al. 1978), from laboratory solubility and phase equilibria measurements (Aja and... 

Eq. (1.24) is used as a consistency test of excess molar Gibbs energies obtained from phase equilibria measured over an extended temperature range, by comparing with calorimetric measurements of molar excess enthalpies (Chap. 1.10). 

ABB1 Abbott, M.M. Low pressure phase equilibria measurement of VLE. Fluid Phase Equilib. 29 (1986) 193-207. 

RAA1 Raal, J.D. Muhlbauer, A.L. Phase Equilibria, Measurement and Computation. Taylor Francis, Washington, 1998. 

Fig. 15.1 Schematic flow chart of the high-pressure view cell used for the phase equilibria measurements...

For reasons of experimental or instrumental limitations, phase equilibria measurements are usually possible only over restricted ranges of pressure and temperature. If the equilibrium has been achieved at one point P-iT-i, it can be extrapolated to another point P2T2 by evaluation of a relation of the type -... 

The data reported show that ethyl lactate weight fractions in the liquid phase increase when temperature increases and pressure deereases. On the other hand, the weight fractions of ethyl lactate in the C02-rich phase increase with pressure, and the effect of temperature depends on pressiue. Nevertheless, some diserepancies could be observed between the data reported by Villanueva et alT and the liquid phase compositions reported by the other authors which could be due to the difference in the experimental methodology used or even in the quality (purity) of the ethyl lactate solvent employed. As mentioned before, ethyl lactate is a very hydroscopic substance and the presence of water can greatly influenee solubility and phase equilibria measurements (see for example Figure 20.4.12). 

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