Saturation pressures

The constants in Equation (5) are not the same as those in Equation (4). Using this saturation pressure, the pure-liquid reference fugacity at zero pressure is then calculated from the equation... 

In the first type of method, the density at saturation pressure is calculated, then this density is corrected for pressure. The COSTALD and Rackett methods belong to this category. Correction for pressure is done using Thompson s method. These methods are applicable only if the reduced temperature is less than 0.98. 

For our needs, the saturation pressure of a mixture will be defined as the vapor pressure of a pure component that has the same critical constants as the mixture ( JT... 

The saturation pressure, P, is different from the bubble point pressure (see. Vidal, 1973) and has no physical reality it merely serves as an intermediate calculation. 

The density at saturation pressure is expressed as a function of reduced temperature ... 

The density of a liquid depends on the pressure this effect is particularly sensitive for light liquids at reduced temperatures greater than 0.8. For pressures higher than saturation pressure, the density is calculated by the relation published by Thompson et al. in 1979 ... 

At the saturation pressure, the viscosity variation with temperature follows a law analogous to that of Clapeyron for the vapor pressure f ) ... 

P = saturation pressure for the petroleum fraction at T P = pseudocritical pressure for the petroleum fraction... 

LPG, stored as a liquid at its saturation pressure, is vaporized and introduced as vapor in conventional spark ignition motors. These motors are not modified with the exception of their feed system. Moreover, in the majority of cases, dual fuel capabilities have been adapted, that is, the vehicle can use either LPG or liquid fuel. 

When the pressure of a volatile oil or black oil reservoir is above the bubble point, we refer to the oil as undersaturated. When the pressure is at the bubble point we refer to it as saturated oil, since if any more gas were added to the system it could not be dissolved in the oil. The bubble point is therefore the saturation pressure for the reservoir fluid. 

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... 

Fig. IX-1. Variation of AG with droplet size for water vapor at 0°C at four times the saturation pressure. (From Ref. 2.)...

Frequently, vapor-phase supersaturation is studied not by varying the vapor pressure P directly but rather by cooling the vapor and thus changing If To is the temperature at which the saturation pressure is equal to the actual pressure P, then at any temperature T, Pjf = x is given by... 

There is always some degree of adsorption of a gas or vapor at the solid-gas interface for vapors at pressures approaching the saturation pressure, the amount of adsorption can be quite large and may approach or exceed the point of monolayer formation. This type of adsorption, that of vapors near their saturation pressure, is called physical adsorption-, the forces responsible for it are similar in nature to those acting in condensation processes in general and may be somewhat loosely termed van der Waals forces, discussed in Chapter VII. The very large volume of literature associated with this subject is covered in some detail in Chapter XVII. 

In molecular distillation, the permanent gas pressure is so low (less than 0 001 mm. of mercury) that it has very little influence upon the speed of the distillation. The distillation velocity at such low pressures is determined by the speed at which the vapour from the liquid being distilled can flow through the enclosed space connecting the still and condenser under the driving force of its own saturation pressure. If the distance from the surface of the evaporating liquid to the condenser is less than (or of the order of) the mean free path of a molecule of distillate vapour in the residual gas at the same density and pressure, most of the molecules which leave the surface will not return. The mean free path of air at various pressures is as follows —... 

If the number of molecular layers, even at saturation pressure, is restricted to the finite number N (by the walls of a narrow pore, for example), the BET treatment leads to the modified equation... 

Several of the lower alkanes, from C2 to C7, have been used from time to time for surface area determination. They possess the virtue of chemical inertness towards the majority of adsorbents, and their saturation pressures... 

The model proposed by Zsigmondy—which in broad terms is still accepted to-day—assumed that along the initial part of the isotherm (ABC of Fig. 3.1), adsorption is restricted to a thin layer on the walls, until at D (the inception of the hysteresis loop) capillary condensation commences in the finest pores. As the pressure is progressively increased, wider and wider pores are filled until at the saturation pressure the entire system is full of condensate. 

The hysteresis loops to be found in the literature are of various shapes. The classification originally put forward by de Boer S in 1958 has proved useful, but subsequent experience has shown that his Types C and D hardly ever occur in practice. Moreover in Type B the closure of the loop is never characterized by the vertical branch at saturation pressure, shown in the de Boer diagrams. In the revised classification presented in Fig. 3.5, therefore. Types C and D have been omitted and Type B redrawn at the high-pressure end. The designation E is so well established in the literature that it is retained here, despite the interruption in the sequence of lettering. 

Type I isotherms are characterized by a plateau which is nearly or quite horizontal, and which may cut the p/p° = 1 axis sharply or may show a tail as saturation pressure is approached (Fig. 4.1). The incidence of hysteresis varies many Type I isotherms exhibit no hysteresis at all (Fig. 4.1), others display a definite loop, and in others there is hysteresis which may or may not persist to the lowest pressures ( low-pressure hysteresis ) (Fig. 4.2). Type 1 isotherms are quite common, and are no longer restricted, as seemed at one time to be the case, to charcoals. Many solids, if suitably prepared, will yield Type 1 isotherms the xerogcls of silica, titania, alumina... 

Occasionally the DR plot falls into two straight lines (cf. Fig. 4.20), and the question again arises as to the significance of the different values of the uptake at p°jp = 1, derived by extrapolation of the respective branches, ( te often, the DR plot displays an upward turn as saturation pressure is approached (Fig. 4.18 and 4.21), a feature which can readily be understood in terms of multilayer adsorption and capillary condensation in mesopores. 

Both Type III and Type V isotherms are characterized by convexity towards the relative pressure axis, commencing at the origin. In Ty )e III isotherms the convexity persists throughout their course (Fig. 5.1(a), whereas in Type V isotherms there is a point of inflection at fairly high relative pressure, often 0-5 or even higher, so that the isotherm bends over and reaches a plateau DE in the multilayer region of the isotherm (cf. Fig. 5.1 (b)) sometimes there is a final upward sweep near saturation pressure (see DE in Fig. 5.1(b)) attributable to adsorption in coarse mesopores and macropores. 

Relative Humidity (rh). Relative humidity is the ratio of the mole fraction of water vapor present in the air to the mole fraction of water vapor present in saturated air at the same temperature and barometric pressure it approximately equals the ratio of the partial pressure (or density) of the water vapor in the air to the saturation pressure (or density) of water vapor at the same temperature. 

---