Effect of phase behavior

Fig. 35. Effect of phase behavior on palladium-catalyzed oxidation of benzyl alcohol to benzaldehyde in supercritical CO2 characterized by transmission- and ATR-IR spectroscopy combined with video monitoring of the reaction mixture (102). The figure at the top shows the pressure dependence of the reaction rate. Note the strong increase of the oxidation rate between 140 and 150 bar. The in situ ATR spectra (middle) taken at 145 and 150 bar, respectively, indicate that a change from a biphasic (region A) to a monophasic (B) reaction mixture occurred in the catalyst surface region in this pressure range. This change in the phase behavior was corroborated by the simultaneous video monitoring, as shown at the bottom of the figure.

A high-pressure micromodel system has been constructed to visually investigate foam formation and flow behavior. This system uses glass plates, or micromodels, with the pattern of a pore network etched into them, to serve as a transparent porous medium. These micromodels can be suspended in a confining fluid in a pressure vessel, allowing them to be operated at high pressure and temperature. Because of this pressure capability, reservoir fluids can be used in the micromodel, and any effects of phase behavior or pressure- and temperature-dependent properties on foam flow can be examined. 

Abstract Supercritical (SC) CO2 and ionic liquids (ILs) are two types of solvents witli special properties, which have been used as reaction media for different chemical reactions. In this chapter, some recent work about the effect of phase behavior on chemical reactions in SC CO2 and SC CO2/IL biphasic systems are discussed. 

Many elegant researches have been carried out for chemical reactions in SC CO2 and SC CO2/IL system, and huge nmnber of papers have been published on this. Study on effect of phase behavior of reaction system on... 

Earlier investigators generally attributed this kind of phenomenon to the effect of phase behavior. Figure 8.9 shows that in Case C2 [type II(+)], water break through later (longer low water-cut period) than in Case Cl (type III). In Case C3 [type II(-)], a high aqueous phase saturation in the two-phase flow... 

Novosad, J., 1982. Surfactant retention in Berea sandstone—effects of phase behavior and temperature. SPEJ (December), 962-970. 

MISCIBLE FLOODING AND EFFECT OF PHASE BEHAVIOR ON OIL RECOVERY... 

This chapter explores solutions. Its main emphasis is on aqueous solutions, because water is the most important solvent for life. We first describe the nature of solutions. Then we examine the molecular features that determine whether one substance dissolves in another. We introduce some characteristic properties of solutions, including effects on phase behavior. The chapter concludes by looking more closely at dual-nature molecules such as those present in shampoos. 

Isotactic PHEMA was found to possess negative temperature dependence in water (Oh and Jhon, 1989). While atactic PHEMA is not expected to have a strong negative temperature dependence, the mechanisms of this behavior can still exist over short ranges and may effect the phase behavior. As such, increased temperatures may also function to control the pore morphology by allowing the polymer to phase separate early on in the reaction. 

The regioselective course of the Diels-Alder reaction in supercritical carbon dioxide was investigated. The analysis failed to confirm the previously reported dramatic effect of reaction conditions on Diels-Alder regiochemistry. The results highlighted the importance of verifying phase behavior when sampling CO2 reaction mixtures and the utility of a view-cell reactor that allows direct monitoring of phase behavior (Ren-slo et al., 1997). 

Effect of Phase Transition on Swelling and Mechanical Behavior of Synthetic Hydrogels... 

Product operators can thus be used to predict the behavior of an NMR experiment. The calculations are relatively simple to perform. Computer programs are available that also take into account the effects of phase-cycling to select the desired terms and reject unwanted ones. A drawback of the product operators approach is that, in its simplest version, it does not take into account the effect of relaxation. This is a must when dealing with paramagnetic substances. Exponential decay terms can be introduced to multiply each term and take relaxation into account. The method then becomes more cumbersome, and the effect of relaxation is introduced in a phenomenological way. A more detailed approach is that of using the concept of Redfield density matrix [1,2]. 

Computer simulation is invariably conducted on a model system whose size is small on the thermodynamic scale one typically has in mind when one refers to phase diagrams. Any simulation-based study of phase behavior thus necessarily requires careful consideration of finite-size effects. The nature of these effects is significantly different according to whether one is concerned with behavior close to or remote from a critical point. The distinction reflects the relative sizes of the linear dimension L of the system—the edge of the simulation cube, and the correlation length —the distance over which the local configurational variables are correlated. By noncritical we mean a system for which L E, by critical we mean one for which L [Pg.46]

Computationally, polydispersity is best handled within a grand canonical (GCE) or semi-grand canonical ensemble in which the density distribution p(a) is controlled by a conjugate chemical potential distribution p(cr). Use of such an ensemble is attractive because it allows p(a) to fluctuate as a whole, thereby sampling many different realizations of the disorder and hence reducing finite-size effects. Within such a framework, the case of variable polydispersity is considerably easier to tackle than fixed polydispersity The phase behavior is simply obtained as a function of the width of the prescribed p(cr) distribution. Perhaps for this reason, most simulation studies of phase behavior in polydisperse systems have focused on the variable case [90, 101-103]. 

The surface force apparatus (SFA) has been used extensively over the past 30 years to measure the force directly as a function of separation between surfaces in liquids and vapors. If the force-measuring spring is replaced with a mechanically more rigid support, the two opposing surfaces become an ideal model pore for the study of confinement effects on phase behavior [16], A detailed review can be found in reference ]. Briefly, the shift of the melting temperature AT can be related to the size h of the condensate measured with SFA according to... 

Heifetz, Y Miloslavski, I., Aizenshtat, Z. and Applebaum, S. W. (1998). Cuticular surface hydrocarbons of desert locust nymphs, Schistocerca gregaria, and their effect on phase behavior../. Chem. Ecol., 24,1033-1046. 

The irradiation of micellar solutions effects the phase behavior and the critical micelle concentration (CMC). Because radiation sterilization of biopharmaceutical products is a common routine it is important to investigate the influence of radiation on surfactants that are widely used in the pharmaceutical industry for formulations as wetting agents, emulsifiers, or solubilizers. In particular, in drug formulations... 

Song J, Shi T et al (2008) Rigidity effect on phase behavior of symmetric ABA triblock copolymers a Monte Carlo simulation. J Chem Phys 129 054906... 

Miscible blends of poly(vinyl methyl ether) and polystyrene exhibit phase separation at temperatures above 100 C as a result of a lower critical solution temperature and have a well defined phase diagram ( ). This system has become a model blend for studying thermodynamics of mixing, and phase separation kinetics and resultant morphologies obtained by nucleation and growth and spinodal decomposition mechanisms. As a result of its accessible lower critical solution temperature, the PVME/PS system was selected to examine the effects of phase separation and morphology on the damping behavior of the blends and IPNs. 

An understanding of the phase behavior of surfactant-supercritical fluid solutions may be relevant to developing efficient secondary oil recovery methods because oil displacing fluids, such as a C02/surfactant mixture, may be supercritical at typical well conditions. In addition, the original oil in the well may contain dissolved gases such as ethane, propane, or butane, which may effect the phase behavior of the surfactant solution used to sweep out remaining oil. 

Equation (1) is used to determine equilibrium between free products and dilute aqueous phases in terms of pure compound properties (solubility) adjusted for the composition of the product (mole fraction). The activity coefficient reflects the effect of phase composition on the equilibrium relation (nonideal behavior). If = 1, then Equation (1) reduces to Raoult s law, which states idealized... 

Many of the basic concepts of micellar-polymer flooding apply to alkaline flooding. However, alkaline flooding is fundamentally different because a surfactant is created in the reservoir from the reaction of hydroxide with acidic components in crude oil. This reaction means that the amount of petroleum soap will vary locally as the water-to-oil ratio varies. The amount of petroleum soap has a large effect on phase behavior in crude-oil-alkali-surfactant systems. 

The above results of phase behavior as summarized in Table I suggest that the observed macroscopic phase separation is directly related to the structure of the surfactant solution. There is no phase separation when the solutions are isotropic. But the added polymer induces phase separation only when a single liquid crystalline phase or a stable dispersion of liquid crystal particles in brine is present in the absence of polymer. The effect is the same for two different types of polymer and is independent of the polymer concentration over a fair range of composition. 

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