Vapor Pressures for

When the critical constants for a pure substance or the pseudocritical constants for a petroleum fraction are known, the vapor pressure for hydrocarbons and petroleum fractions can be calculated using the Lee and Kesler equations ... 

Regarding product characteristics, European specifications were established in 1992. They concern mainly the motor octane number (MON) that limits the olefin content and which should be higher than 89, and the vapor pressure, tied to the C3/C4 ratio which should be less than 1550 mbar at 40°C (ISO 4256). On the other hand, to ensure easy vehicle start-ups, a minimum vapor pressure for winter has been set which is different for each country and depends on climatic conditions. Four classes. A, B, C, and D, are thus defined in Europe with a minimum vapor pressure of 250 mbar, respectively, at -10°C (A), -5 C (B), 0°C (C) and -t-10°C (Z)). France has chosen class A. 

The Kelvin equation (Eq. HI-18), which gives the increase in vapor pressure for a curved surface and hence of small liquid drops, should also apply to crystals. Thus... 

To achieve sufficient vapor pressure for El and Cl, a nonvolatile liquid will have to be heated strongly, but this heating may lead to its thermal degradation. If thermal instability is a problem, then inlet/ionization systems need to be considered, since these do not require prevolatilization of the sample before mass spectrometric analysis. This problem has led to the development of inlet/ionization systems that can operate at atmospheric pressure and ambient temperatures. Successive developments have led to the introduction of techniques such as fast-atom bombardment (FAB), fast-ion bombardment (FIB), dynamic FAB, thermospray, plasmaspray, electrospray, and APCI. Only the last two techniques are in common use. Further aspects of liquids in their role as solvents for samples are considered below. 

Ref. 87. Test method ASTM E96-35T (at vapor pressure for 25.4 p.m film thickness). Values are averages only and not for specification purposes. Original data converted to SI units using vapor pressure data from Ref. 90. 

Vapor Pressures and Adsorption Isotherms. The key variables affecting the rate of destmction of soHd wastes are temperature, time, and gas—sohd contacting. The effect of temperature on hydrocarbon vaporization rates is readily understood in terms of its effect on Hquid and adsorbed hydrocarbon vapor pressures. For Hquids, the Clausius-Clapeyron equation yields... 

Figure 1 shows the density of sulfur trioxide as a function of temperature. This curve (42) is a composite of data taken from the Hterature (43—46). The vapor pressures of sulfur trioxide s a-, P-, and y-phases are presented in Figure 2 (47). Different values of SO vapor pressure for a-, P-, and y-phases have been reported in References 30 and 32 (Table 2).

A tabulation of the partial pressures of sulfuric acid, water, and sulfur trioxide for sulfuric acid solutions can be found in Reference 80 from data reported in Reference 81. Figure 13 is a plot of total vapor pressure for 0—100% H2SO4 vs temperature. References 81 and 82 present thermodynamic modeling studies for vapor-phase chemical equilibrium and liquid-phase enthalpy concentration behavior for the sulfuric acid—water system. Vapor pressure, enthalpy, and dew poiat data are iacluded. An excellent study of vapor—liquid equilibrium data are available (79). 

Vapor pressure has also become a means of regulating storage tank design by the EPA. Because increasing vapor pressure tends to result ia an iacrease ia volatde emissions, the EPA has specific maximum values of vapor pressure for which various tank designs may be used. 

The vapor pressure for the soHd at 25°C has been calculated from the value for the Hquid at 70°C and the heats of vaporization and fusion using the Clausius-Clapeyron relationship. 

The hquid vehicle in a slurry should have a low vapor pressure for Hquid extraction and drying be compatible with the soHds and casting mold be inexpensive and be capable of dissolving and dispersing deflocculants and other additives. Distilled or deionized water is generally used as the Hquid vehicle, however, organic Hquids must be used for such moisture sensitive oxide powders as CaO and MgO, and for oxidation sensitive nonoxide powders, eg, AIN. 

Figure 6.5 Vapor pressures for x,c-C6HnCH +. v c-C(,Hi2 at T= 308.15 K. The symbols represent the experimental vapor pressures as follows , vapor pressure of c-C6Hi2 , vapor pressure of c-C6HnCHi , total vapor pressure. The dashed lines represent the ideal solution prediction.

This procedure is commonly used to calculate vapor pressures and activities for volatile mixtures. For example, it was used to determine the vapor pressures for the (ethanol + water) system shown in Figure 6.7. 

One of the most Important thermophysical properties of reactor fuel In reactor safety analysis Is vapor pressure, for which data are needed for temperatures above 3000 K. We have recently completed an analysis of the vapor pressure and vapor composition In equilibrium with the hypostolchiometric uranium dioxide condensed phase (1 ), and we present here a similar analysis for the plutonium/oxygen (Pu/0) system. 

Since we did not measure the conversion during the experiment, we computed the equilibrium vapor pressure at the average solution temperature. We believe that, for safety design, the equilibrium vapor pressure is an adequate estimate of the styrene vapor pressure. For example, even at a 50% conversion, the difference is only 10 at the experimental temperatures. Figures 6, 7 and 8 compared the observed pressures with the computed total pressures. The latter were based on the equilibrium vapor pressure. As expected, there were increasing variations in Tests 1, 2 and 3 respectively because of their higher initial conversions. From these figures we can verify that our pressure and temperature measurements were in phase with respect to time. 

As an example, the ratio of the equilibrium vapor pressures for water, Pi6 and water. Pig, depends on temperature and is expressed by the following equation, derived from Faure (1977) (temperature is in kelvins) ... 

The system is dynamic because molecular transfers continue, and it has reached equilibrium because no further net change occurs. The pressure of the vapor at dynamic equilibrium is called the vapor pressure (v p) of the substance. The vapor pressure of any substance increases rapidly with temperature because the kinetic energies of the molecules increase as the temperature rises. Table lists the vapor pressures for water at various temperatures. We describe intermolecular forces and vapor pressure in more detail in Chapter 11. 

The trapping efficiency of polymeric, microporous adsorbents [e.g., polystyrene, polyurethane foam (PUF), Tenax] for compound vapors will be affected by compound vapor density (i. e., equilibrium vapor pressure). The free energy change required in the transition from the vapor state to the condensed state (e.g., on an adsorbent) is known as the adsorption potential (calories per mole), and this potential is proportional to the ratio of saturation to equilibrium vapor pressure. This means that changes in vapor density (equilibrium vapor pressure) for very volatile compounds, or for compounds that are gases under ambient conditions, can have a dramatic effect on the trapping efficiency for polymeric microporous adsorbents. 

Vapor pressure. The vapor pressure at working conditions should preferably be low if an organic solvent is to be used. High vapor pressure for an organic solvent will lead to the emission of volatile organic compounds (VOCs) from the process, potentially leading to environmental problems. VOCs will be discussed in more depth later when environmental issues are considered. 

A foam is a colloidal dispersion of gas bubbles trapped in a liquid. To produce a stable foam, several characteristics of the liquid are necessary. For example, a viscous liquid facilitates the trapping of gas bubbles. The presence of a surface active agent or stabilizer that, for structural reasons, preferentially locates on the surface of the gas bubble also provides a more permanent foam. A low vapor pressure for the liquid reduces the likelihood that the liquid molecules (particularly those surrounding the bubble) will easily evaporate, thus leading to the collapse of the foam. 

As described above, the precursors traditionally employed for preparation of III-V films have been group 13 metal alkyls (Me3Ga, Me3Al, Me3In) in combination with the group 15 hydride gases (Table 2). These are available on a commercial scale and have appropriate vapor pressures for both atmospheric pressure and low-pressure applications. 

Bidleman, T. F. (1984) Estimation of vapor pressures for nonpolar organic compounds by capillary gas chromatography. Anal. Chem. 56, 2490-2496. 

Burkhard, L. P, Andren, A. W., Armstrong, D. E. (1985a) Estimation of vapor pressures for polychlorinated biphenyls A comparison... 

Hinckley, D. A., Bidleman, T.F., Foreman, W.T. (1990) Determination of vapor pressures for nonpolar and semipolar organic compounds from gas chromatographic retention data. J. Chem. Eng. Data 35, 232-237. 

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