Phase behavior pure components

Equatioa-of-state theories employ characteristic volume, temperature, and pressure parameters that must be derived from volumetric data for the pure components. Owiag to the availabiHty of commercial iastmments for such measurements, there is a growing data source for use ia these theories (9,11,20). Like the simpler Flory-Huggias theory, these theories coataia an iateraction parameter that is the principal factor ia determining phase behavior ia bleads of high molecular weight polymers. 

The Class I binary diagram is the simplest case (see Fig. 6a). The P—T diagram consists of a vapor—pressure curve (soHd line) for each pure component, ending at the pure component critical point. The loci of critical points for the binary mixtures (shown by the dashed curve) are continuous from the critical point of component one, C , to the critical point of component two,Cp . Additional binary mixtures that exhibit Class I behavior are CO2—/ -hexane and CO2—benzene. More compHcated behavior exists for other classes, including the appearance of upper critical solution temperature (UCST) lines, two-phase (Hquid—Hquid) immiscihility lines, and even three-phase (Hquid—Hquid—gas) immiscihility lines. More complete discussions are available (1,4,22). Additional simple binary system examples for Class III include CO2—hexadecane and CO2—H2O Class IV, CO2—nitrobenzene Class V, ethane—/ -propanol and Class VI, H2O—/ -butanol. 

Fig. 6. Qualitative piessuie—tempeiatuie diagiams depicting ctitical curves for the six types of phase behaviors for binary systems, where C or Cp corresponds to pure component critical point G, vapor 1, Hquid U, upper critical end point and U, lower critical end point. Dashed curves are critical lines or phase boundaries (5). (a) Class I, the Ar—Kr system (b) Class 11, the CO2—CgH g system (c) Class 111, where the dashed lines A, B, C, and D correspond to the H2—CO, CH —H2S, He—H2, and He—CH system, respectively (d) Class IV, the CH —C H system (e) Class V, the C2H -C2H OH...

Pure-component vapor pressures can be used for predicting solu-bihties for systems in which RaoiilFs law is valid. For such systems Pa = Pa a, where p° is the pure-component vapor pressure of the solute andp is its partial pressure. Extreme care should be exercised when attempting to use pure-component vapor pressures to predict gas-absorption behavior. Both liquid-phase and vapor-phase nonidealities can cause significant deviations from the behavior predicted from pure-component vapor pressures in combination with Raoult s law. Vapor-pressure data are available in Sec. 3 for a variety of materials. 

A wide variety of physical properties are important in the evaluation of ionic liquids (ILs) for potential use in industrial processes. These include pure component properties such as density, isothermal compressibility, volume expansivity, viscosity, heat capacity, and thermal conductivity. However, a wide variety of mixture properties are also important, the most vital of these being the phase behavior of ionic liquids with other compounds. Knowledge of the phase behavior of ionic liquids with gases, liquids, and solids is necessary to assess the feasibility of their use for reactions, separations, and materials processing. Even from the limited data currently available, it is clear that the cation, the substituents on the cation, and the anion can be chosen to enhance or suppress the solubility of ionic liquids in other compounds and the solubility of other compounds in the ionic liquids. For instance, an increase in allcyl chain length decreases the mutual solubility with water, but some anions ([BFJ , for example) can increase mutual solubility with water (compared to [PFg] , for instance) [1-3]. While many mixture properties and many types of phase behavior are important, we focus here on the solubility of gases in room temperature IFs. 

OC10H21)], in which rearrangement does not occur. All the mixtures studied display liquid crystal behavior with improved properties with respect to the pure components. A representative binary phase diagram and their corresponding DSCtraces are presented in Figures 8.24 and 8.25 respectively, and reveal the eutectic nature ofthese systems. 

A distillation column uses a partial condenser as shown in Figure 9.19. Assume that the reflux ratio and the overhead product composition and flowrate and the operating pressure are known and that the behavior of the liquid and vapor phases in the column is ideal (i.e. Raoult s Law holds). How can the flowrate and composition of the vapor feed to the condenser and its liquid products be estimated, given the vapor pressure data for the pure components. Set up the equations that need to be solved. 

One major question of interest is how much asphaltene will flocculate out under certain conditions. Since the system under study consist generally of a mixture of oil, aromatics, resins, and asphaltenes it may be possible to consider each of the constituents of this system as a continuous or discrete mixture (depending on the number of its components) interacting with each other as pseudo-pure-components. The theory of continuous mixtures (24), and the statistical mechanical theory of monomer/polymer solutions, and the theory of colloidal aggregations and solutions are utilized in our laboratories to analyze and predict the phase behavior and other properties of this system. 

Eutectic diagrams (from Greek svtt]ktoo- easily melted ) represent the T-x melting behavior for binary systems with completely immiscible solid phases a, /3. The solid a, /3 phases often correspond to (virtually) pure components A, B, respectively, so we may treat phase and component labels (rather loosely) as interchangeable in this limit. 

We will first consider systems which consist of a single, pure substance. These systems behave differently from systems made up of two or more components. In particular, we will be interested in phase behavior, that is, the conditions of temperature and pressure for which different phases can exist. 

After a careful examination of the phase behavior of a pure substance, we will discuss the behavior of systems which contain two or more components and point out the differences between multicomponent behavior and pure substance behavior. 

Next we will consider the phase behavior of mixtures of two components. The petroleum engineer does not normally work with two-component systems usually mixtures consisting of many components are encountered. However, it is instructive to observe the differences in phase behavior between two-component mixtures and pure substances. These differences are amplified in multicomponent mixtures. 

In mixed bilayer vesicles diacetylenic and natural lipids exhibit the same miscibility behavior as in monomolecular films. This can be demonstrated using differential scanning calorimetry (DSC). The neutral lipid (23) is immiscible with DSPC or DOPC as indicated by the two phase transitions of the mixed liposomes which occur at the same temperatures as those of the pure components (Fig. 33 a). 

Ideal Adsorbed Solution Theory. Perhaps the most successful general approach to the prediction of multicomponent equilibria from single-component isotherm data is ideal adsorbed solution theory. In essence, the theory is based on the assumption that the adsorbed phase is thermodynamically ideal in the sense that the equilibrium pressure for each component is simply the product of its mole fraction in the adsorbed phase and the equilibrium pressure for the pure component at Ike same spreading pressure. The theoretical basis for this assumption and the details of the calculations required to predict the mixture isotherm are given in standard texts on adsorption. Whereas the theory has been shown to work well for several systems, notably for mixtures of hydrocarbons on carbon adsorbents, there are a number of systems which do not obey this model. Azeotrope formation and selectivity reversal, which are observed quite commonly in real systems, are not consistent with an ideal adsorbed phase and there is no way of knowing a priori whether or not a given system will show ideal behavior. 

The macroscopic properties such as mechanical behavior of block copolymers or polymer blends depend directly on the relative concentrations of different constituents and their meso-structures. How to predict the exact macroscopic properties of polymer blends or block copolymers with meso-phase separation structures from pure component properties remains a big challenge. Some theoretical efforts have been explored. For example, Buxton et al. found that the deformations and fractures of polymer blends can be described by the... 

The behavior of solid phase activity coefficients is a more complex issue. We can view this behavior in two ways. The first is where only a trace mole fraction of component i ("trace component") is coprecipitated in a relatively pure component j ("carrier component"). The activity of the carrier component is well approximated as being equal to unity. When this is true, the activity coefficient of the trace component in the solid is given by the following relation ... 

From the pure component data it is possible to calculate the expected a behavior as a function of temperature for a blend of the two polymers using the equation ah = sas + < rar, where the subscripts b, s, and r refer to the blend, polystyrene, and rubber, respectively, and the < s represent the volume fractions of the two components in the blend. The calculated curves (Figure 7) are reasonably smooth and exhibit only the polystyrene Tg. The calculated curve for TR-41-2445 is in good agreement with that found experimentally for the solution-blended material. The only significant difference is that below the polystyrene Tg the calculated values of a are about 0.5 X 10 4 deg1 lower than the experimentally determined data points. This may be attributable to the density differences in the samples, particularly for the blended material where density variations and void formation can occur at the interfaces between the polymer phases. 

For this mixture it is not possible to isolate the pure components in a batch rectifier or batch stripper. The use of additional equipment such as a decanter to exploit liquid-liquid phase behavior or the addition of a fourth component or chemical reactions can sometimes be used to effect the separation. 

---