Phase behavior study

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]. 

In the Will case, provided that there is enough surfactant but not too much, e.g., 1 wt. %, the system splits into three phases, i.e., a microemulsion in equilibrium with excess water and excess oil. At a higher surfactant concentration than the top vertex of the 3

single phase microemulsion often called WW behavior is attained. However, this occurrence generally requires a large amount of surfactant, e.g., 20 wt. %, which is in most practical cases too much for cost reasons. At a very low surfactant concentration, around the CMC, only two phases are in equilibrium, and the tension is not necessarily very low. Hence, the convenient surfactant concentration to carry out a phase behavior study is in the range 0.5-3 wt. % for which three-phase behavior and a very low inter facial tension is exhibited in most Will cases. 

Thus, surfactant enhanced subsurface remediation is a mature technology for remediating hydrophilic NAPL, as displayed at the field level. These successful field demonstrations provide encouragement for further evaluation of hydrophobic oils with a similar goal of field deployment. To this end, the current research evaluated laboratory batch and column studies for surfactant enhanced remediation of hydrophobic oil contamination, including phase behavior studies, column studies, and evaluating separation... 

The hydrophobic oils evaluated in phase behavior studies were diesel, dodecane, and hexadecane. A commercial Diesel was selected based on its occurrence as a subsurface contaminant and its hydrophobicity. Based on... 

Previous work has shown that binary surfactant systems containing Dowfax 8390 and the branched hydrophobic surfactant AOT can form Winsor III systems with both PCE and decane whereas DOWFAX 8390 by itself cannot (Wu et. al. 1999). This binary surfactant system was used in conjunction with hydrophobic octanoic acid to help with phase behavior and lessen the required concentration of CaCl2. Since this formulation is rather complicated, questions about field robustness arise. Thus, for the phase behavior studies presented here, we used the simple binary system of the nonionic TWEEN 80 and the branched hydrophobic AOT, and we optimized the NaCl concentration to give the Winsor Type III system. The lesser electrolyte concentration requirement for the binary TWEEN 80/ AOT system helps to decrease the potential for undesirable phase behavior such as surfactant precipitation, thereby increasing surfactant system robustness. 

Phase behavior studies with poly(ethylene-co-methyl acrylate), poly (ethylene-co-butyl acrylate), poly(ethylene-co-acrylic add), and poly(ethylene-co-methacrylic acid) were performed in the normal alkanes, their olefinic analogs, dimethyl ether, chlorodifluoromethane, and carbon dioxide up to 250 °C and 2,700 bar. The backbone architecture of the copolymers as well as the solvent quality greatly influences the solution behavior in supercritical fluids. The effect of cosolvent was also studied using dimethyl ether and ethanol as cosolvent in butane at varying concentrations of cosolvent, exhibiting that the cosolvent effect diminishes with increasing cosolvent concentrations. 

A novel approach to reduce the experimental effort associated with constructing pseudoternary phase diagrams is by using expert systems to predict the phase behavior of multicomponent ME-forming systems. Artificial neural networks have been investigated and were shown to be promising in phase behavior studies [17,35,36] as well as in the process of ingredient selection [37]. 

Robledo-Muniz, J. G. Tseng, H. S. Lloyd, D. R., "Phase Behavior Studies of the System Polystyrene-Polybutadiene- Chloroform. I. Application of the Flory-Huggins Theory," Polym. Eng. Sci., 25, 934 (1985). 

Spectroscopic and phase behavior studies were conducted using a fixed path length cell. Pressure was increased by adding pure solvent to the cell, so molar concentrations were constant while mole fractions varied. Additional phase behavior studies and solubility studies were conducted in a variable volume view cell, based on an existing design(24), in which mole fractions were held constant but molarities varied. 

Phase behavior studies of oil-brine-surfactant systems have shown that the ultralow interfacial tension (less than 0.01 dyne/cm) necessary for EOR is very sensitive to salinity changes (2 3). Such low tensions are obtained only within a small range of salinity near the point of "optimum salinity" where equal amounts of oil and brine are solubilized. The tolerance of ultralow tensions to divalent ions is still less. 

The results from aqueous solution phase behavior studies show that phase separation takes place only when aqueous solutions are liquid crystalline. A schematic of a lamellar phase is shown in Figure 9. For the lamellar structure of the systems investigated, the bilayer thickness is about 10 to 30 °A while the thickness of the brine layer does not exceed 100 to 200 °A. Hence, the size of the polymer molecule is too large to be accommodated into the brine spacing in lamellar structure. 

Most of the studies reported in this chapter fail to include the phase behavior of the reacting mixture. Since multiple phases can occur in the mixture critical region, reaction studies need to be complemented with phase behavior studies so that we may gain an understanding of the fundamentals of the thermodynamics and kinetics of chemical reactions in solution. Chapter 5 describes how a simple cubic equation of state can be used to extend and complement the phase behavior studies. An equation of state can be used to determine the location of phase-border curves in P-T space and, with transition-state theory, to correlate the pressure dependence of the reaction rate constant when the pressure effect is large (i.e., at relatively high pressures). 

Niswonger, D. C., C. A. Plank, and W. L. S. Laukhuf. 1985. Vapor-liquid equilibria of the system trimethyl borate (l)-n-heptane (2). J. Chem. Eng. Data 30 209-211. Occhiogrosso, R. N. 1985. Phase behavior studies of organic hydrocarbon-supercritical carbon dioxide mixtures. M.S. thesis, Univ. of Notre Dame. 

Examples of Combined Reaction/Phase Behavior Studies... 

Phase behavior studies showed that the substrate methyl acrylate is fully miscible with CO2 in the pressure range 9-29.5 MPa, whereas the product dihydromuconates are only fully miscible at the concentrations required above a density of 0.4 g cm" ... 

MAH Mahdavi, H., Sadeghzadeh, M., and Qazvini, N.T., Phase behavior study of polyCA-tert-butylacrylamide-co-aciylamide) in the mixture of water-methanol The role of polymer-nonsolvent second-order interactions, J. Polym. Sci. Part B Polym. Phys., 47, 455, 2009. 

Two main conclusions may be drawn from the phase behavior studies ... 

The investigation technique is the unidimensional formulation scan as in the phase behavior. studies discussed in the previous chapter. For the sake of simplicity, the scanned variable is often taken as the salinity for ionic surfactant systems, and as surfactant EON or temperature for nonionic systems, but it should be well understood that other formulation variables would produce exactly the. same effects. In the reasoning, the formulation will be referred to a.s SAD, the deviation from optimum formulation, whatever the variable used to produce the scan. 

Whether the low-concentration or the high-concentration system is selected, the system is made up of several components. The multicomponent facet leads to an optimization problem, since many different combinations could be chosen. Because of this, a detailed laboratoiy screening procedure is usually undertaken. The screening procedure typically involves three types of tests (1) phase behavior studies, (2) interfacial tension studies, and (3) oil displacement studies. 

Phase behavior studies are typically conducted in small (up to 100 mL) vials in order to determine what type, if any, of microemulsion is formed with a given micellar-cmde oil system. The salinity of the micellar solution is usually varied around the salt concentration of the field brine where the process will be applied. Besides the microemulsion type, other factors examined could be oil uptake into the microemulsion, ease with which the oil and aqueous phases mix, viscosity of the microemulsion, and phase stability of the microemulsion. 

In the preceding section, it was seen that the monoglycerol fatty acid esters could not form any liquid-crystalline phases in liquid paraffin, squalane, and squalene. Phase-behavior studies have shown that the surfactants of this class do not form any liquid-crystalline phases in n-alkanes also. At normal room temperature, there is a solid phase in equilibrium with an excess oil phase in glycerol a-monolaurate... 

With all due respect, I (LKS) would like to dedicate this chapter to my first PhD advisor, late Prof Hironobu Kunieda. I happened to be the final student to join his group, and although, I could not complete my PhD under his supervision, he introduced me to several interesting features of surfactants in a short period of time. He also highlighted the importance of phase behavior study to understand fundamental science and also its significance in the practical applications. I still remember his common advice to his students You have to improve yourself and he independent . I hope many of his students recall these words and I am quite sure he will be remembered for a long time due to his important contribution to colloid and interface science society. I pray to the God to keep his soul in rest and peace. 

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