Miscibility, conditions for

In two of the precipitation tests, the asphalts were first precipitated by addition of n-butane and n-pentane to the tank oil. After separation of asphalts from the crude, the deasphalted crude was analyzed by gas-liquid chromatography. Table 2 shows that the original oil composition is considerably altered by asphalt precipitation. The amount of heavier ends in the deasphalted crude is less than in the original crude. Also, n-butane removed greater amount of heavier fraction iC y + ) than n-pentane. The deasphalted crude has lower density than original crude. This Indicates that in a miscible process, asphaltene precipitation can alter the composition of crude oil which needs to be accounted for in prediction of solvent-oil phase behavior, compositional path and miscibility conditions for solvent-oil systems. 

Asphaltene precipitation results in removal of heavier fractions of the crude leaving behind lighter deasphalted crude. This indicates that in a miscible process, the alteration of crude composition needs to be accounted for in prediction of phase behavior, compositional path and miscibility conditions for solvent-oil systems. 

Equation 2.36 gives the miscibility conditions for systems with species of different molecular weight. The relations are rather accurate, as they are markedly insensitive to the FH assumptions and approximations (Fig. 2.6). Three special cases can be distinguished ... 

Oil is miscible with all the refrigerants except ammonia. This may create foaming in the crankcase and an unsatisfactory compression condition for reciprocating compressors. 

An interface between two immiscible electrolyte solutions (ITIES) is formed between two liqnid solvents of a low mutual miscibility (typically, <1% by weight), each containing an electrolyte. One of these solvents is usually water and the other one is a polar organic solvent of a moderate or high relative dielectric constant (permittivity). The latter requirement is a condition for at least partial dissociation of dissolved electrolyte(s) into ions, which thus can ensure the electric conductivity of the liquid phase. A list of the solvents commonly used in electrochemical measurements at ITIES is given in Table 32.1. 

The information available on aqueous polymer blends is qualitative in nature because of the lack of a suitable theory to interpret the experimental observations. Mixed gels can be comprised of an interpenetrating network, a coupled network (as discussed above), or a phase-separated network [2]. The latter is the most common as the blends have a tendency to form two phases during gelation. In such cases the miscibility and thermodynamic stability have to be empirically investigated and proper conditions for miscible blends identified. This involves a phase diagram study as is described in [3]. 

The structural constraints used in the first case study namely, Eqn s 27,28 and 29 are used again. The melting point, boiling point and flash point, are used as constraints for both solvent and anti-solvent. Since the solvent needs to have high solubility for solute and the anti-solvent needs to have low solubility for the solute limits of 17 <8 < 19 and 5 > 30 (Eqn s. 33 and 37) are placed on the solubility parameters of solvent and anti-solvents respectively. Eqn.38 gives the necessary condition for phase stability (Bernard et al., 1967), which needs to be satisfied for the solvent-anti solvent pairs to be miscible with each other. Eqn. 39 gives the solid-liquid equilibrium constraint. 

The 500 and 600 series methods provide parameters and conditions for the analysis of drinking water and wastewater, respectively. One method (EPA SW-846) is focused on the analysis of nearly all matrixes, including industrial waste, soil, sludge, sediment, and water-miscible and non-water-miscible wastes. It also provides for the analysis of groundwater and wastewater but is not used to evaluate compliance of public drinking water systems. 

AHM will be zero when the two liquids are identical, and it is obvious that under such conditions the two liquids must be completely miscible. Also, liquids which are very similar to one another and have practically identical values of L, D and K will be miscible. It is, however, not a sufficient condition for solubility that the two molecules have equal heats of evaporation. We now return to the example of water and hexane. The boiling points are not markedly different and consequently their heats of evaporation are of the same order. For hexane AH — A, and D and K are both zero, while for water the K term is so predominant that, as a good approximation, AH — K. AHM, which then has its largest possible value... 

All experiments in this study were carried out under conditions where C02 and styrene are miscible. The solubilities of C02 and ethylbenzene (a model for styrene) in HDPE were determined at 80 °C and 243 bar. The HDPE samples were immersed in either pure C02 or a 36 wt % ethylbenzene/C02 solution within pressure vessels under these conditions for various times. Figure 10.1 shows results of a typical desorption experiment to determine the mass uptake of ethylbenzene for a given soak time the equilibrium mass uptake was found to be 4% and this was reached after approximately 5 h. Figure 10.2 illustrates the mass uptakes as a function of soak time the diffusivity of ethylbenzene in C02-swollen HDPE under these conditions was calculated by curve fitting to be 9.23 x 10 7 cm2/s. Attempts to determine the equilibrium mass uptake of neat ethylbenzene in HDPE at 80 °C failed because ethylbenzene dissolves polyethylene under these conditions. 

Consider a binary solution of two components -A and B which are completely miscible with one another. On heating under constant pressure, it will boil at a temperature at which its total pressure becomes equal to the atmospheric pressure. If pA and pB represent the partial pressures of the two components A and B, then conditions for boiling is that... 

The condition for complete miscibility of two liquids is simply that the interfacial tension between them should be zero or negative. If this is so, then the molecular forces no longer operate to keep the liquids apart, for each liquid attracts the molecules of the other as much as, or more than, they are attracted by their own liquid. WAB becomes equal to, or greater than, Ya+Yb > and therefore molecules move across from one liquid to the other quite freely. 

Popular conditions for the hydrolysis of dioxolane derivatives involve treatment of the substrate with either p-toluenesulfonic add monohydrate or camphorsul-fonic acid together with a small amount of water in a water-miscible solvent such as acetonitrile, THF, 1,4-dioxane, or acetone. Under these conditions secondary fert-butyldimethylsilyl ethers21 and primary ferf-butyldtphenysilyl ethers22 survive [Scheme 2,5]. If acetone is used as solvent, the deprotection can be carried out without the addition of water by a transacetalisation reaction [Scheme 2.6].23... 

We can now summarize our conditions for forming a single phase or miscible mixture (Figure 11-21) ... 

The temperature dependence of the total interaction parameter shows that there exists an optimum condition for the composition at a given temperature (Fig. 3). Binary blends of PEO/PS and PEO/PAA are immiscible and miscible, respectively, at room temperature. The shape of curves implies that the homopol-ymer/homopolymer blends will exhibit UCST behaviors. A drastic effect of the sequence distribution on the miscibility can be found in Fig. 4. As the AA content in SAA increases from 5 mol% (Fig. 4a) to 7 mol% (Fig. 4b) to 10mol% (Fig. 4c), the blend becomes more miscible. The blend with random copolymers becomes miscible at a composition between 5 and 7 mol%, which agrees well with the experimental results [15]. At 7 mol%, the blend with block copolymers shows positive x> while the blend with random copolymers has negative y. This is very interesting because the miscibility could be controlled only by the change of copolymer sequence distributions. 

For operational reasons it is important to look at detection properties, purity, recycling ability and viscosity of the mobile phase. If solvent mixtures are used as mobile phase, the miscibility of the solvents is an absolute condition for their use, which has to be guaranteed for the whole concentration range of the solute as well (Fig. 4.6). For example, acetonitrile and water are miscible, but when sugars are added at high concentrations (e.g. fructose) the system demixes. 

Preconcentration of analytes in aqueous solution may be performed by a miscible organic phase followed by salting out. Thus, microextraction of anionic solntes snch as phenol, cresols and xylenols in industrial effluents can be carried ont with a small amonnt of isopropyl alcohol, followed by demixing of the phases with ammoninm snlfate. End analysis of the extract by GC-MS in the selected ion monitoring (SIM) mode allowed a LOD of 1 ppb for 50 mL samples . The best conditions for eliminating petrolenm prodncts from the concentrate were found for the GC determination of volatile phenols in natnral waters. Losses of volatile phenols due to preconcentration were insignificant and cansed no increase in the relative error of determination by the internal-standard method. The concentration of phenol in the atmosphere can be determined by sorption on Chromosorb 102, desorption with benzene and 0.1 M NaOH and GC nsing a capillary colnmn. LOD was abont 1 p,gm, with accuracy within 15% . 

Knowing the thermal stability of clathrates permits the prediction of experimental conditions for polymerization (8). A detailed analysis of this problem requires the examination of all the involved phases, particularly the solid and liquid phases. Equations for phase equilibria were derived from within the framework of the regular solution theory they contain an interaction parameter W, (whose value is always positive or zero for ideal solutions), which measures the tendency of host and guest to segregate in the liquid phase. The melting or decomposition point is very sensitive to the value of W, especially when it exceeds 2 RT, i.e. when a miscibility gap is observed in the liquid phase. For this reason the PHTP-hydrocarbon clathrates melt congruently between 115 and 180 C, whereas the urea-hydrocarbon... 

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