Phase behavior types

Fig.1 Phase behavior types of surfactant-oil-water systems as Winsor Diagrams for difer-ent cases of the ratio R of interactions between the surfactant adsorbed at interface and the oil and water molecules...

The alkane mixtures provide the prototypical examples of type I type V behavior. Methane + hexane (and higher alkanes), ethane + octadecane, and propane + pentatriacontane are all type V. The upper LL regions of these systems are noteworthy in that the temperature difference between the UCEP and the LCEP seems to monotonically increase with increasing carbon number. Ultimately, this trend must reverse as type III behavior sets in, but no indication of this reversal has been observed experimentally. Mixtures of methane with hexane isomers provide unusual examples of type V phase behavior. Type V behavior is exhibited for all isomers except 2,2-dimethyl butane. Ternary mixtures of methane with the 2,2 and 2,3-isomers provide a rare example of tri-critical behavior. Turning to another example, the type V LLV locus becomes extremely short as the asymmetry of the mixture increases to the point where transition to type III behavior is approached. Ethane + p-dichlorobenzene provides an example of this phenomenon, with an LLV locus extending over a mere 0.6K.[ Such an odd effect may seem to have little practical significance, unless one considers the impact of an unexpected precipitation on a critical pipeline. 

Measurement and prediction of transitions from one type of phase behavior to another are key to our understanding of the physical properties of hydrocarbon mixtures. One can examine phase behavior type transitions for binary mixtures from the perspective of the solute or the solvent while varying the other. Both approaches are found in the literature. The solvent fixed approach is shown in Fig. 5 for carbon dioxide + n-alkane binary mixtures. The anthracene... 

Although the classification of ternary phase behavior is described here at a fixed temperature, it is important to remember that a single ternary system can exhibit all three types of phase behaviors as the temperature of the system changes. Based on our classification of binary phase behavior, type-I ternary phase behavior above the critical temperature of the SCF solvent may revert to type-II or type-III ternary phase behavior if the operating temperature and pressure are adjusted to values near the critical point of the SCF solvent. 

Each phase behavior type is associated with an emulsion type, but near optimum formulation either a monophasic (micioemulsion) or triphasic (microemulsion at equilibrium with excess oil and water) is exhibited, dqiending on the amphiphile surfactant/alcohol mixture (S -f- A) concentration. When lempenituie... 

The complete form of the liquid-liquid immiscibility region can be achieved only if there is no interference of immisci-bihty region and crystallization surface, and this region does not touch the crystallization surfaces but exists only in solid unsaturated solutions (the main types of fluid phase behavior). Types lb, Ic and Id are the versions of complete phase diagrams with three different types of immiscibility region in their complete form. 

To illustrate, predictions were first made for a ternary system of type II, using binary data only. Figure 14 compares calculated and experimental phase behavior for the system 2,2,4-trimethylpentane-furfural-cyclohexane. UNIQUAC parameters are given in Table 4. As expected for a type II system, agreement is good. 

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...

There are many types of phase diagrams in addition to the two cases presented here these are summarized in detail by Zief and Wilcox (op. cit., p. 21). Solid-liquid phase equilibria must be determined experimentally for most binaiy and multicomponent systems. Predictive methods are based mostly on ideal phase behavior and have limited accuracy near eutectics. A predic tive technique based on extracting liquid-phase activity coefficients from vapor-liquid equilib-... 

Of course, LC is not often carried out with neat mobile-phase fluids. As we blend solvents we must pay attention to the phase behavior of the mixtures we produce. This adds complexity to the picture, but the same basic concepts still hold we need to define the region in the phase diagram where we have continuous behavior and only one fluid state. For a two-component mixture, the complete phase diagram requires three dimensions, as shown in Figure 7.2. This figure represents a Type I mixture, meaning the two components are miscible as liquids. There are numerous other mixture types (21), many with miscibility gaps between the components, but for our purposes the Type I mixture is Sufficient. 

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. 

Smits first established experimentally that phase behavior of the type shown in Fig. 8 is possible, with his classic investigation of the system ethyl ether + anthraquinone.76-83 83 84 The temperature and pressure of the principal points of the phase diagram are... 

Aughel and coworkers [63] studied the phase behavior of hydrocarbon-water mixtures in the presence of alkyl(aryl)polyoxyethylene carboxylates for enhanced oil recovery and found good salt tolerance with an alkyl ether carboxy-late (C13-C15) with 7 mol EO and a good microemulsion forming effect with the 3 EO type. 

From phase behavior studies of hydrocarbon-water mixtures in the presence of ether carboxylates it was concluded that C13-C15 ether carboxylic acids with 3 and 7 mol EO were more suitable than the nonylphenol ether carboxylates with 5.7 and 10 mol EO and the tridecyl ether carboxylic acids with 6.5 mol EO. However, with the use of cosolvents these types were also acceptable [191]. 

Tailoring block copolymers with three or more distinct type of blocks creates more exciting possibilities of exquisite self-assembly. The possible combination of block sequence, composition, and block molecular weight provides an enormous space for the creation of new morphologies. In multiblock copolymer with selective solvents, the dramatic expansion of parameter space poses both experimental and theoretical challenges. However, there has been very limited systematic research on the phase behavior of triblock copolymers and triblock copolymer-containing selective solvents. In the future an important aspect in the fabrication of nanomaterials by bottom-up approach would be to understand, control, and manipulate the self-assembly of phase-segregated system and to know how the selective solvent present affects the phase behavior and structure offered by amphiphilic block copolymers. 

Micellar flooding is a promising tertiary oil-recovery method, perhaps the only method that has been shown to be successful in the field for depleted light oil reservoirs. As a tertiary recovery method, the micellar flooding process has desirable features of several chemical methods (e.g., miscible-type displacement) and is less susceptible to some of the drawbacks of chemical methods, such as adsorption. It has been shown that a suitable preflush can considerably curtail the surfactant loss to the rock matrix. In addition, the use of multiple micellar solutions, selected on the basis of phase behavior, can increase oil recovery with respect to the amount of surfactant, in comparison with a single solution. Laboratory tests showed that oil recovery-to-slug volume ratios as high as 15 can be achieved [439]. 

A brief discussion of sohd-liquid phase equihbrium is presented prior to discussing specific crystalhzation methods. Figures 20-1 and 20-2 illustrate the phase diagrams for binary sohd-solution and eutectic systems, respectively. In the case of binary solid-solution systems, illustrated in Fig. 20-1, the liquid and solid phases contain equilibrium quantities of both components in a manner similar to vapor-hquid phase behavior. This type of behavior causes separation difficulties since multiple stages are required. In principle, however, high purity... 

The values of the elements of the weighting matrices R, depend on the type of estimation method being used. When the residuals in the above equations can be assumed to be independent, normally distributed with zero mean and the same constant variance, Least Squares (LS) estimation should be performed. In this case, the weighting matrices in Equation 14.35 are replaced by the identity matrix I. Maximum likelihood (ML) estimation should be applied when the EoS is capable of calculating the correct phase behavior of the system within the experimental error. Its application requires the knowledge of the measurement... 

The interaction parameters for binary systems containing water with methane, ethane, propane, n-butane, n-pentane, n-hexane, n-octane, and benzene have been determined using data from the literature. The phase behavior of the paraffin - water systems can be represented very well using the modified procedure. However, the aromatic - water system can not be correlated satisfactorily. Possibly a differetn type of mixing rule will be required for the aromatic - water systems, although this has not as yet been explored. 

---