Two-Phase Layer Systems

Fig. A.2. Two-phase layer system representative for a partially crystalline polymer. Electron density distribution Ape(z) = pe z) — (pe) and the associated onedimensional correlation function K(z) for a perfectly ordered system (a). Effects of varying intercrystalline spacings (6), varying crystallite thicknesses (c) and diffuse interfaces (d)...

Acrolein reacts slowly in water to form 3-hydroxypropionaldehyde and then other condensation products from aldol and Michael reactions. Water dissolved in acrolein does not present a hazard. The reaction of acrolein with water is exothermic and the reaction proceeds slowly in dilute aqueous solution. This will be hazardous in a two-phase adiabatic system in which acrolein is suppHed from the upper layer to replenish that consumed in the lower, aqueous, layer. The rate at which these reactions occur will depend on the nature of the impurities in the water, the volume of the water layer, and the rate... 

TIPSH (0.25 mol) was added to a mixture of anhydrous copper(n) chloride (0.55mol) and MeCN (250ml), resulting in a two-phase liquid system. This was heated under reflux for 16h, and then chilled to precipitate copper(i) chloride. The supernatant, consisting of a dark MeCN layer and a colourless phase of TIPSCl, was separated, and the MeCN phase was extracted with pentane. The pentane extract and the TIPSCl phase were combined, concentrated and distilled, to give the product (0.25 mol, 100%), b.p. 88-92 °C/18 mmHg. 

A schematic illustration of the method, and of the correlation between binary phase diagram and the one-phase layers formed in a diffusion couple, is shown in Fig. 2.42 adapted from Rhines (1956). The one-phase layers are separated by parallel straight interfaces, with fixed composition gaps, in a sequence dictated by the phase diagram. The absence, in a binary diffusion couple, of two-phase layers follows directly from the phase rule. In a ternary system, on the other hand (preparing for instance a diffusion couple between a block of a binary alloy and a piece of a third... 

We know from thermodynamics that spontaneous processes occur in the direction of decreasing Gibbs free energy. Therefore we may conclude that the separation of a two-phase dispersed system to form two distinct layers is a change in the direction of decreasing Gibbs... 

The use of NBD-Cl for the fluorescence analysis of alkylamine-generating pesticides has been investigated [173]. A two-phase reaction system is employed for the hydrolysis and labeling of N-methyl- and N,N-dimethyl-carbamate pesticides. The residue is hydrolyzed in 0.1 M sodium carbonate and the liberated amine is treated with NBD-Cl in an organic phase (IBMK, isobutyl methyl ketone) above the aqueous layer. An aliquot portion of the organic layer is used for chromatography. The reactions involved are shown in Fig. 4.65. 

FIGURE 10.2. Schematic diagram of the centrifugal liquid membrane (CLM) method apparatus. The glass cylinder cell (i.d., 19 cm) was rotated at a speed of 7000-10,000 rpm. Introduction of 50-200 pi of the organic and the aqueous phase generated a two-liquid layer system with a thickness of 50-100 pm for each phase. 

Another feature of two-phase colloidal systems (lyophobic colloids) is their sensitivity to flocculation by small amounts of added electrolyte. The electrolyte causes the diffuse part of the double layer to compress. When the double layer is reduced in thickness, the colloid floes because the particles approach close enough for London forces to take over. 

Tokeshi et al. reported the first two-phase microextraction system on a microchip in 2000. An Fe(II)-complex was extracted from an aqueous solution into a chloroform solution with a simple Y-shaped chip (see Figure 50.28). The solvents were introduced with two syringe pumps, and a parallel two-layer fiow was formed in the microchannel because the surface tension and frictional forces are much stronger than that due to the specific gravity. The extraction of Fe(II)-complex from aqueous... 

Furthermore, the growth of the layer may involve two boundaries and, consequently, two diffusion coefficients. Similarly, the diffusion in the adjoining layers is dependent of their thickness, which, in turn, may partly depend on diffusion in yet other layers. Solutions of the diffusion equations, for given boundary conditions, have been evaluated [66]. Van Horn [96] and others have obtained equations, together with nomographic solutions, relating the motion of a phase boundary to the diffusion rates in a simple two-phase binary system using the parabolic law as a basis. A relationship between the diffusivities in each phase was found ... 

One of the most important quantities of the two-phase layer on a tray is the size of the interfacial area contributing to mass transfer. Present knowledge on inteifacial area on trays is rather poor and contradicting. Figure 5.4-8 shows the result of a theoretical estimation (Stichlmair 1978 Stichlmairand Fair 1998) of the relative irrterfacial area a (i.e., interfacial area referred to the volume of the two-phase layer) for three systems with different siuface tensions. This rough estimation shows that in aqueous sys-... 

The components of two-phase reaction systems usually differ in density and viscosity, which is the reason for flow layering, especially at high flow rates. This is the lower limit of the output of a tubular turbulent reactor for fast chemical processes, including the interphase boundary. 

We thus see that the elimination procedure firstly gives a certain justification for introducing a separate term — coacervate — for the colloid-rich layer, secondly opens perspectives for studying macromolecular two phase colloid systems of the type liquid/liquid from general physical chemical points of view. 

Fig.23. Relative interfacial area in the two-phase layer on trays.Comparison of data from the literature for air/ water system. (Numbers refer to various authors (12i).

The thin-layer apparatus were developed for use with two-phase aqueous systems for both liquid-liquid... 

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