Vapor Pressure and Liquids

Verevkin, S.R et al.. Thermodynamic properties of mixtures containing ionic liquids. Vapor pressures and activity coefficients of n-alcohols and benzene in binary mixtures with l-methyl-3-butyl-imidazolium bis(trifluoromethyl-sulfonyl)imide. Fluid Phase Equilib., 236, 222, 2005. 

Utilization of the Kelvin Effect for ILM Stability. One possible method for reducing the vapor pressure of immobilized liquids involves the expanded use of the capillpy forces res nsible for immobilization. The reduction of the size of the pores in which the liquid is immobilized can have a significant effect on the liquid vapor pressure, and ultimately on ILM stability. This vapor-pressure/pore-size relationship was derived by Lord Kelvin and is known as the Kelvin effect... 

The search for T begins with the evaluation of the pure-liquid vapor pressures and fugacity coefficients. The temperature dependence of each vapor pressure is invariably represented by some relative of an Antoine equation. Values for fugacity coefficients are computed from a PvTx equation of state the same equation should be used for q), and for (p . Then, with values for the activity coefficients computed from the model chosen for g, the liquid-phase fugacity can be computed. 

Available net positive suction head The available NPSH is the net pressure available in a given system, based on vessel pressure and static head, minus the liquid vapor pressure and functional losses in the system. The goal is to maintain equipment heights and minimi /se pump. suaion piping to ensure that the available NPSH is greater than tlie required NPSH. Insufficient NPSH can reduce pump capacity and efficiency and lead to cavitation damage. 

This new Internet edition has added 13 new subsections that can be accessed as interactive tables. These include tables on atomic and molecular polarizabilities, diffusion in gases and liquids, vapor pressure and density of mercury, ionic radii in crystals, surface tension, and other topics. All material in the printed Handbook is accessible in the Internet version as interactive tables and/or pdf displays. 

According to (16.4) (in combination with (16.1)), a smaller mass flux density results for higher liquid vapor pressure and hence liquid temperature Tq. Furthermore, it has to be considered that higher pressure losses result in lower liquid velocities for the same given pressure difference Apeff (16.5). The pressure loss is determined by the effect of a flow separation at the nozzle inlet due to a constriction ( q), and the pressure loss attributed to friction (fp). 

FIGURE 3.11 Computed liquid vapor pressure and vapor mol% benzene, according to Raoult s law, for a mixture of benzene and toluene at a constant temperature of 20°C. (Here we use mol percent instead of mol fraction on the ordinate so that both curves plot on the same scale.) The line for mol% benzene in the liquid is shown because it is traditionally shown in this type of diagram. 

Adsorption may occur from the vapor phase rather than from the solution phase. Thus Fig. Ill-16 shows the surface tension lowering when water was exposed for various hydrocarbon vapors is the saturation pressure, that is, the vapor pressure of the pure liquid hydrocarbon. The activity of the hydrocarbon is given by its vapor pressure, and the Gibbs equation takes the form... 

Equations for four-parameter vapor pressure, Hadacher vapor pressure, and liquid volume can be found in Refs. 36, 34,... 

Flash Point. As a liquid is heated, its vapor pressure and, consequendy, its evaporation rate increase. Although a hquid does not really bum, its vapor mixed with atmospheric oxygen does. The minimum temperature at which there is sufficient vapor generated to allow ignition of the air—vapor mixture near the surface of the hquid is called the dash point. Although evaporation occurs below the dash point, there is insufficient vapor generated to form an igrhtable mixture below that point. 

In order to ensure thermodynamic consistency, in almost all cases these properties are calculated from Tr. and the vapor pressure and liquid density correlation coefficients listed in those tables. This means that there will be slight differences between the values listed here and those in the DIPPR tables. Most of the differences are less than 1%, and almost all the rest are less than the estimated accuracy of the quantity in question. 

Liquid viscosity is accurately correlated as a function of temperature by the modified Riedel equation previously discussed for correlation of vapor pressure and shown by Eq. (2-96). 

Figure 2. Determine the vapor pressure/critical pressure ratio by dividing the liquid vapor pressure at the valve inlet by the critical pressure of the liquid. Enter on the abscissa at the ratio just calculated and proceed vertically to intersect the curve. Move horizontally to the left and read r< on the ordinate (Reference 1).

The nomograph combines all of these corrections (4) except the one for higher liquid vapor pressures. Physical properties of each of the inorganic gases are incorporated in the primary and secondary scales identifying the dissolved gas. 

Usually, the closed liquid drain header is run as a separate line to the drum and provided with a high level cut-off valve with local manual reset. In some cases the closed drain system is segregated into a number of subheaders, as described earlier. Hydrocarbon liquids may be bypassed around the drum through a connection from the closed drain header directly to the pumpout pump suction, provided that the liquid can be routed to a safe disposal location, considering its vapor pressure and temperature. Emergency liquid pulldown connections, if provided, are routed to the blowdown drum via the closed drain header. 

The inherent error between true vapor pressure and RVP means that a stabilizer designed to produce a bottoms liquid with a true vapor pressure equal to the specified RVP will be conservatively designed. The a[>or pressures of various hydrocarbon components at 100°F are given in Table 6-1. 

The amine cooler is typically an air-cooled, fin-fan cooler, which low-er.s the lean amine temperature before it enters the absorber. The lean amine entering the absorber should be approximately 10°F warmer than the sour gas entering the absorber. Lower amine temperatures may cause the gas to cool in the absorber and thus condense hydrocarbon liquids. Higher temperatures would increase the amine vapor pressure and thus increase amine losses to the gas. The duty for the cooler can be calculated from the lean-amine flow rate, the lean-amine temperature leaving the rich/lean exchanger and the sour-gas inlet temperature. 

The first step in a gas processing plant is to separate the components that are to be recovered from the gas into an NGL stream. It may then be desirable to fractionate the NGL stream into various liquefied petroleum gas (LPG) components of ethane, propane, iso-butane, or normal-butane. The LPG products are defined by their vapor pressure and must meet certain criteria as shown in Table 9-1. The unfractionated natural gas liquids product (NGL) is defined by the properties in Table 9-2. NGL is made up principally of pentanes and heavier hydrocarbons although it may contain some butanes and very small amounts of propane. It cannot contain heavy components that boil at more than 375°F. 

The flammable liquid itself does not burn only the vapors emitted from the liquid burn. The vaporization of a liquid depends on its temperature and corresponding vapor pressure and increases as the temperature of the liquid increases. Thus, the warmer the liquid, the more potentially hazardous it becomes. 

Use a sealing liquid that has a relatively low vapor pressure, and is not readily combustible, and will not readily freeze. Quite often glycol or mixtures are... 

The bottom tray of a tower must have its downcomer sealed to prevent upflow of reboiled vapors. The downcomer of this tray is usually equal to or 6 in. longer than the other downcomers to ensure against bottom vapor surges or pulses in pressure breaking the seal. The seal pan is designed to avoid liquid back pressure and minimum restrictions to liquid flow. 

Two sources of absorption oil are normally utilized in this tower. The first is the hydrocarbon liquid from the main fractionator overhead receiver. This stream, often called wild, or unstabilized, naphtha, enters the absorber a few trays below the top tray. The second absorbent is cooled debutanized gasoline, which generally enters on the top tray. It has a lower vapor pressure and can be considered a trim absorbent. The expression lean oil generally refers to the debutanized gasoline plus the unstabilized naphtha from the overhead receiver. 

We have already noted that if we place liquid water in a flask at 20°C and seal the flask, some water molecules leave the liquid and enter the gas phase. The partial pressure rises as more and more water molecules become part of the gas. Finally, however, the pressure stops rising and the partial pressure of water becomes constant. This partial pressure is the vapor pressure and equilibrium now exists. 

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