Vapor pressure at temperatures below

Lanthanide and actinide complexes. Ln(L-L)) and An(L-L)4, of sterically hindered diketonates [e.g.. [Me3CC(0)CHC(0)CMej] fdpm) and [F CCF2CF2-CfOICHQOJCMeJ (fed)], are of considerable interest because of their volatility. Despite their high molecular weights, they have measurable vapor pressures at temperatures below the boiling point of water. This volatility has been exploited in... 

M(BH4) (M = Zr, Hf and Al ) with a significant vapor pressure at temperatures below which the product thermally decomposes, can be purified by considering the vapor pressure and temperature. The vapor pressures of Zr(BH4)4, Hf(BH4)4 and A1(BH4)3 are shown in Table 15.3. For example, pure Zr(BH4)4 was isolated from the products of reaction (15.6), i.e. mixture of Zr(BH4)4 and 4LiCl, because Zr(BH4)4 sublimed whereas 4LiCl remained in the container by evacuation using a rotary pump (under approximately... 

Uranium Isotope Separation. The successful industrial separation of uranium isotopes results from (a) UFg having a substantial vapor pressure at temperatures below 100°C, and (b) fluorine being monoiso-topic. However UFg is a toxic, highly corrosive gas which decomposes on contact with water. As a result its use, on an industrial scale, gives rise to plant problems in selecting materials for construction and containment. 

Hence, for temperatures very close to the boiling point, we integrate Eq. 4-7 by assuming that Avap//,(T) = AvapH,(Tb) = constant (see Section 4.2). However, in most cases, one would like to estimate the vapor pressure at temperatures (e.g., 25°C) that are well below the boiling point of the compound. Therefore, one has to account for the temperature dependence of Avap// below the boiling point. A first approximation is to assume a linear temperature dependence of Avap/7, over the temperature range considered, that is, to assume a constant heat capacity of vaporization, A Cpi (the difference between the vapor and liquid heat capacities). Thus, if the heat capacity of vaporization, AvapCpi(Tb), at the boiling point is known, Avap/7,(7) can be expressed by (e.g., Atkins, 1998) ... 

Many elements evaporate, but many such as chromium (Cr), cadmium (Cd), magnesium (Mg), arsenic (As), and carbon (C) sublime, and many others such as antimony (Sb), selenium (Se), and titanium (Ti), are on the borderline between evaporation and sublimation. For example, chromium, which has a vapor pressure of 10 Torr 600°C below its melting point, is generally vaporized by sublimation. Carbon cannot be melted except under high hydrostatic pressure. Materials such as aluminum, tin, gallium, and lead have very low vapor pressures at temperatures above the points at which they are just-molten. For example, tin has a vapor pressure of lO Torr 1000°C above its melting point. Aluminum and lead have vapor pressures of 10 Torr at about 500°C above their melting points. 

Properties. Tetrafluoroethylene (mol wt 100.02) is a colorless, tasteless, odorless, nontoxic gas (Table 1). It is stored as a Hquid vapor pressure at —20° C = 1 MPa (9.9 atm). It is usually polymerized above its critical temperature and below its critical pressure. The polymerization reaction is highly exothermic. 

These reactions are thermodynamically unfavorable at temperatures below ca 1500°C. However, at temperatures in the range from 1000 to 1200°C a small but finite equiUbrium pressure of barium vapor is formed at the reaction site. By means of a vacuum pump, the barium vapor can be transported to a cooled region of the reactor where condensation takes place. This destroys the equiUbrium at the reaction site and allows more barium vapor to be formed. The process is completely analogous to that used in the thermal reduction of CaO with aluminum to produce metallic calcium (see Calcium AND CALCIUM alloys). 

When the reboiler was brought back on line, the water was swept into the heat transfer oil lines and immediately vaporized. This set up a liquid hammer, which burst the surge tank. It was estimated that this required a gauge pressure of 450 psi (30 bar). The top of the vessel was blown off in one piece, and the rest of the vessel was split into 20 pieces. The hot oil formed a cloud of fine mist, which ignited immediately, forming a fireball 35 m in diameter. (Mists can explode at temperatures below the flash point of the bulk liquid see Section 19.5.)... 

This chart is applicable only to flammable liquids or gases in equilibrium In a closed container. Mixtures of vapor and air will be too lean to burn at temperatures below and at pressures above the values shown by the line on the chart for any substance. Conditions represented by points to the left of and above the respective lines are accordingly nonflammable. Points where the diagonal lines cross the zero gauge pressure line (760 mm of mercury absolute pressure) indicate flash point temperatures at normal atmospheric pressure. 

In Figure 8.15, a two-phase (liquid + vapor) region is again enclosed by a liquid line and a vapor line. However, the lines have inverted from those in the pressure against mole fraction phase diagram, with the vapor line now on top and the liquid line on the bottom. At temperatures below the liquid line, only liquid is present while above the vapor line, only vapor is present. 

If a liquid near its boiling point at one pressure is let down to a reduced pressure, vapour flashing will occur. This will cease when the liquid temperature is reduced, due to removal of the latent heat of vaporization, to a temperature below the saturation temperature at the new pressure. As a result ... 

Pervaporation. Pervaporation differs from the other membrane processes described so far in that the phase-state on one side of the membrane is different from that on the other side. The term pervaporation is a combination of the words permselective and evaporation. The feed to the membrane module is a mixture (e.g. ethanol-water mixture) at a pressure high enough to maintain it in the liquid phase. The liquid mixture is contacted with a dense membrane. The other side of the membrane is maintained at a pressure at or below the dew point of the permeate, thus maintaining it in the vapor phase. The permeate side is often held under vacuum conditions. Pervaporation is potentially useful when separating mixtures that form azeotropes (e.g. ethanol-water mixture). One of the ways to change the vapor-liquid equilibrium to overcome azeotropic behavior is to place a membrane between the vapor and liquid phases. Temperatures are restricted to below 100°C, and as with other liquid membrane processes, feed pretreatment and membrane cleaning are necessary. 

Although thermally rather unstable at room temperature, liquid diboron tetrachloride decomposes relatively slowly at temperatures below 0°. In the gas phase, the substance may be exposed to ambient temperatures for periods as long as 5 to 10 minutes without the risk of appreciable deterioration. The colorless substance melts5 at —93.0° and its vapor pressures in the interval —63.5 to 22.5° are given by the equation 3... 

To confirm the above reasoning, use boiling points given below to indicate strengths of intermolecular forces. Remember, the lower the boiling point is, the weaker the intermolecular forces present in the liquid, and the higher the vapor pressure at a specific temperature. 

As mentioned in the previous section, the condition for vapor phase combustion versus heterogeneous combustion may be influenced by pressure by its effect on the flame temperature (Tvol or Td) as well as by its effect on the vaporization temperature of the metal reactant (Th). For aluminum combustion in pure oxygen, combustion for all practical conditions occurs in the vapor phase. In air, this transition would be expected to occur near 200 atm as shown in Fig. 9.15 where for pressures greater than —200 atm, the vaporization temperature of pure aluminum exceeds the adiabatic flame temperature. This condition is only indicative of that which will occur in real particle combustion systems as some reactant vaporization will occur at temperatures below the boiling point... 

At the critical temperature, Tc, and critical pressure, Pc, a liquid and its vapor are identical, and the surface tension, y, and total surface energy, as in the case of the energy of vaporization, must be zero (Birdi, 1997). At temperatures below the boiling point, which is 2/3 Tc, the total surface energy and the energy of evaporation are nearly constant. The variation in surface tension, y, with temperature is given in Figure A.l for different liquids. 

Ammonium bisulfate is a corrosive salt that sublimes from a vapor to a solid at temperatures below its dew point. The salt will foul downstream equipment resulting in higher pressure drops across economizers and preheaters. Ammonium bisulfate can be returned to its vapor state if the temperature is increased above its ABS dew point. 

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