Heterogeneous water systems

Fig. 6. Boiling point (a) and phase diagram (b) for the heterogeneous a2eotropic system, water/ 1-butanol at atmospheric pressure, yi, B and C, D are representative equiUbrium points Z is the a2eotropic point M and N are Hquid miscibility limits.

FIG. 13-13 Vap or-liqiiid equilibrium data for an n-biitanol-water system at 101.3 kPa (1 atm) phase splitting and heterogeneous-azeotrope formation. 

The present procedure affords a simple and general method for preparing bromohydrins from alkenes which avoids the heterogeneous solvent systems often used in such reactions. Labeling experiments have demonstrated that the oxygen from the dimethyl sulfoxide appears in the hydroxyl group of the bromohy-drin. Therefore the role of the water is to hydrolyze the intermediate /3-bromodimethylsulfoxonium ion. 

Evidence exists that the relative solubility of amines and inhibitors in heterogeneous oil-water systems could be decisive in formation of nitrosamines and blocking these reactions, Nitrosopyrrolidine formation in bacon predominates in the adipose tissue despite the fact that its precursor, proline, predominates in the lean tissue (5,6,7). Mottram and Patterson (8) partly attribute this phenomenon to the fact that the adipose tissue furnishes a medium in which nitrosation is favored, Massey, et al, (9) found that the presence of decane in a model heterogeneous system caused a 20-fold increase in rate of nitrosamine formation from lipophilic dihexylamine, but had no effect on nitrosation of hydrophilic pyrrolidine. Ascorbic acid in the presence of decane enhanced the synthesis of nitrosamines from lipophilic amines, but had no effect on nitrosation of pyrrolidine. The oil-soluble inhibitor ascorbyl palmitate had little influence on the formation of nitrosamines in the presence or absence of decane. 

Ice cream serves as a wonderful (and tasty) example of a complex, dynamically heterogeneous food system. A typical ice cream mix contains milk or cream (water, lactose, casein and whey proteins, lipids, vitamins, and minerals), sucrose, stabilizers and emulsifiers, and some type of flavor (e.g., vanilla). After the ingredients are combined, the mix is pasteurized and homogenized. Homogenization creates an oil-in-water emulsion, consisting of millions of tiny droplets of milk fat dispersed in the water phase, each surrounded by a layer of proteins and emulsifiers. The sucrose is dissolved in... 

H. Kato, M. Hori, R. Konta, Y. Shimodaira, A. Kudo, Construction of Z-scheme type heterogeneous photocatalysis systems for water splitting into H2 and 02 under visible light irradiation, Chem. Lett. 33 (2004) 1348-1349. 

A similar heterogeneous photocatalytic system was applied for the study of the decomposition of the anthraquinone dye, Acid blue 25 (AB25). The chemical structure of the dye and those of the first intermediates tentatively identified by HPLC-MS are shown in Fig. 3.55. RP-HPLC-DAD analysis of AB25 was carried out in a C4 column (250 X 4 mm i.d. particle size 5 //m) at ambient temperature. The isocratic mobile phase was composed of ACN (solvent A)-water (pH adjusted to 4.5 with acetic acid and ammonium acetate) (42 58, v/v). 

Phosphate is widely used as a chemical stabilization agent for MSW combustion residues in Japan and North America and is under consideration for use in parts of Europe. The application of this technology to MSW ashes generally parallels its application to contaminated soils. Metal phosphates (notably Cd, Cu, Pb and Zn) frequently have wide pH distribution, pH-pE predominance, and redox stability within complex ash pore water systems. Stabilization mechanisms identified in other contaminated systems (e.g., soils), involving a combination of sorption, heterogeneous nucleation, and surface precipitation, or solution-phase precipitation are generally observed in ash systems. 

Koide (1996) recommended that for air—water systems, if D 8 >2x10 4 m2, the flow can be considered to be in the heterogeneous regime. In this relationship, D is the column diameter and 8 the nozzle or hole diameter of the gas distributor. The transition region can be defined in terms of gas holdup by using Marrucci s and Akita-Yoshida equations as presented in Figure 3.28 (Koide, 1996). 

For batch liquid, usG f = usG. The subscript w in symbols denotes water property. SI units are used in this equation. For the derivation of this correlation, air velocities up to 0.305 m/s and liquid velocities up to 0.09 m/s were used. The Hughmark correlation has been derived for the heterogeneous flow regime. In Figure 3.31, the effect of liquid flow on gas holdup for the air-water system is presented. 

McClements, D.J., Decker, E.A. (2000). Lipid oxidation in oil-in-water emulsions impact of molecular environment on chemical reactions in heterogeneous food systems. Journal of Food Science, 65, 1270-1282. 

As can be seen in figure 6.1 and 6. 2 a heterogeneous system exhibits interfaces or planes of separation whereas a homogeneous one does not. By increasing the temperature of the alcohol - water system, we can create a vapour phase next to the liquid phase (figure 6.3). Vapours are completely miscible which means that at most one vapour phase can occur in a system. 

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