Condensation Immiscible condensates

Condensed phases of systems of category 1 may exhibit essentially ideal solution behavior, very nonideal behavior, or nearly complete immiscibility. An illustration of some of the complexities of behavior is given in Fig. IV-20, as described in the legend. 

Figure 4d represents in situ encapsulation processes (17,18), an example of which is presented in more detail in Figure 6 (18). The first step is to disperse a water-immiscible Hquid or soHd core material in an aqueous phase that contains urea, melamine, water-soluble urea—formaldehyde condensate, or water-soluble urea—melamine condensate. In many cases, the aqueous phase also contains a system modifier that enhances deposition of the aminoplast capsule sheU (18). This is an anionic polymer or copolymer (Fig. 6). SheU formation occurs once formaldehyde is added and the aqueous phase acidified, eg, pH 2—4.5. The system is heated for several hours at 40—60°C.

This system requires direct steam injection into the still with the liquid, all the steam leaves overhead with the boiled-up vapors (no internal condensation) in a steady-state operation, and system at its dew point. Steam is assumed immiscible with the organics. Steam distillation is usually applied in systems of high boiling organics, or heat sensitive materials which require separation at vacuum conditions. 

Nn = Number of theoretical trays above feed, or reference plate, n, but not including n Nm = Number of theoretical trays before feed tray Njra = Mols of immiscible liquid No = Mols of non-volatile material present or, number of theoretical trays/stages in column only, not reboiler or condenser Ng = Mols of steam... 

When the distribution ratio is low, continuous methods of extraction are used. This procedure makes use of a continuous flow of immiscible solvent through the solution if the solvent is volatile, it is recycled by distillation and condensation and is dispersed in the aqueous phase by means of a sintered glass disc or equivalent device. Apparatus is available for effecting such continuous extractions with automatic return of the volatilised solvent (see the Bibliography, Section 9.10). 

Take the non-condensables (ethylene and inerts) as the tie substance. Treat gas phase as ideal, and condensed EDC-water as immiscible. 

In steam distillation, steam is introduced into the column to lower the partial pressure of the volatile components. It is used for the distillation of heat sensitive products and for compounds with a high boiling point. It is an alternative to vacuum distillation. The products must be immiscible with water. Some steam will normally be allowed to condense to provide the heat required for the distillation. Live steam can be injected... 

Chemical separations are often either a question of equilibrium established in two immiscible phases across the contact between the two phases. In the case of true distillation, the equilibrium is established in the reflux process where the condensed material returning to the pot is in contact with the vapor rising from the pot. It is a gas-liquid interface. In an extraction, the equilibrium is established by motion of the solute molecules across the interface between the immiscible layers. It is a liquid-liquid, interface. If one adds a finely divided solid to a liquid phase and molecules are then distributed in equilibrium between the solid surface and the liquid, it is a liquid-solid interface (Table 1). 

Ohno T (2002) Morphology of composite nanoparticles of immiscible binary systems prepared by gas-evaporation technique and subsequent vapor condensation. J Nanoparticle Res 4 255-260... 

Such behavior occurs when the two components either form an ideal mixture or are immiscible. Before drawing conclusions concerning molecular interactions (12, 13), it is clearly important to establish that homogeneous mixed films have been formed. Any deviation from line LM is, of course, indicative of both mixing and nonideality. In discussing such effects, we define any negative deviation from LM as a "condensation and any positive deviation as an "expansion. Our results fall into three distinct categories. 

SURFACE CHEMISTRY. This topic deals with the behavior of matter, where such behavior is determined largely by forces acting at surfaces. Since only condensed phases, i.e., liquids and solids, have surfaces, studies in surface chemistry require that at least one condensed phase be present in the system under consideration, The condensed phase may be of any size ranging from colloidal dimensions to a mass as large as an ocean. Interactions between solids, immiscible liquids, liquids and solids, gases and liquids, gases and solids, and different gases on a surface fall within the province of surface chemistry. 

Investigations at Cornell University are based on process concepts in which an ice slurry is produced from saline water by evaporation of a suitable immiscible refrigerant. After washing, the ice crystals are melted by direct condensation on the ice of the compressed refrigerant vapors. Potable water is the product, and the immiscible refrigerant recycles to the process. 

The two designs of the Dean and Stark apparatus (Fig. 2.31(a) and (b) available from Bibby Science Products) carry a flask on the lower cone and a reflux condenser on the upper socket. They are used for the automatic separation of two immiscible components in a distillate and the subsequent return of the upper layer (a) or the lower layer (b) to the reaction flask. 

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