Possible three phase systems

It was shown in section 4.3 that there are seven possible combinations of three phases, and for each combination ten configurations are theoretically possible. Only a limited number of these 70 possibilities are of practical importance. One further practical distinction may be made  

In three phase systems there can be either three or two interfaces. In most cases, one dispersed phase is completely wetted by one continuous phase, so that there are only two interfaces. Systems with partial wetting of, e.g., a solid phase by a liquid and a gas do exist, e.g, in some trickle flow columns, but this is usually an undesired situation. Then in a first approximation the transport through one of the wetting phases, usually the gas phase (depending on the solubility of the transported component), is neglect.  

In a three-phase system with two interfaces, two different mass transfer situations can be distinguished  

Situation b is encountered frequently, e.g., in catalytic hydrogenations and oxidations of liquid phase components. Situation a is less common but occurs, e.g., in processes where a solid and a gas both dissolve in a liquid and react there. 

Since there are so many possible configurations for three-phase systems, it would appear that a systematic treatment of mass transfer of all possible three-phase configurations would become excessively complicated. However, many if not most 

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The use of a fluidized-bed reactor is possible only when the reactants are essentiaUy in the gaseous phase. Eluidized-beds are not suitable for middle distiUate synthesis, where a heavy wax is formed. Eor gasoline synthesis processes like the MobU MTG process and the Synthol process, such reactors are especiaUy suitable when frequent or continuous regeneration of the catalyst is required. Slurry reactors and ebuUiating-bed reactors comprising a three-phase system with very fine catalyst are, in principle, suitable for middle distiUate and wax synthesis, but have not been appHed on a commercial scale. 

In order to understand the mechanisms governing the mass transfer in three-phase systems, the distribution of organic and water phases near the gas-liquid interface has been estimated using various possible mechanisms for mass transfer. 

Figure 6 is a graphic representation of foam structures in which the microspheres are dispersed randomly (a) and uniformly in close packing (b). In both structures, the two phases fill completely the whole volume (no dispersed air voids) and the density of the product is thus calculated from the relative proportions of the two. Measured density values often differ from the calculated ones, due to the existence of some isolated or interconnected, irregularly shaped voids as shown in Fig. 6c. The voids are usually an incidental part of the composite, as it is not easy to avoid their formation. Nevertheless, voids are often introduced intentionally to reduce the density below the minimum possible in a close-packed two-phase structure. In such three-phase systems the resin matrix is mainly a binding material, holding the structure of the microspheres together.

In the diagram in Figure 29.2(b) we display a three-phase system (with phases labelled a, p and y) each phase containing two components (labelled 1 and 2). Since the phases are open then transfer of material is possible between some of the phases present. Thus d//)7 1 signifies the amount of material / which is removed from phase f > phase to y, as is shown. The following transfers occur in Figure 29.2(b) ... 

Microemulsions are thermodynamically stable dispersions of oil and water stabilized by a surfactant and, in many cases, also a cosurfactant.1-4 The microemulsions can be of the droplet type, either with spherical oil droplets dispersed in a continuous medium of water (oil-in-water microemulsions, O/W) or with spherical water droplets dispersed in a continuous medium of oil (water-in-oil microemulsions, W/O). The droplet-type microemulsions can be either a single-phase system or part of a two-phase system wherein the microemulsion phase coexists with an excess dispersed phase (an upper phase of excess oil in the case of O/W and a lower phase of excess water in the case of W/O microemulsions). There are also nondroplet-type microemulsions, referred to as middle-phase microemulsions. In this case, the microemulsion phase is part of a three-phase system with the microemulsion phase in the middle coexisting with an upper phase of excess oil and a lower phase of excess water. One possible structure of this middle-phase microemulsion, characterized by randomly distributed oil and water microdomains and bicontinuity in both oil and water domains, is known as thebiccntinuous microemulsion. Numerous experimental studies have shown1 2 4 that one can achieve a transition... 

S. A system composed of ethane hydrate, water, and ethane is classed aa a two-component system when Gibbs phase rule is applied since it could be formed from water and ethane. What is the variance of this system when a solid, a liquid, and a vapor phase coexist in equilibrium If the temperature of this three-phase system is specified, would it be possible to alter the pressure without the disappaaranoe of a phase ... 

Rigorous distillation models can be used to model absorber columns, stripper columns, refluxed absorbers, three-phase systems such as extractive distillation columns, many possible complex column conflgurations, and columns that include... 

In the case of adsorption of a vapor by a porous material, a three phase system in terms of SAS is produced pore/adsorbed film or capillary condensed vapor/solid. Since the s.l.d. of H2O and D2O are known while the pore space s.l.d. equals to zero, contrast matching conditions are achieved if an appropriate mixture of H2O/D2O that has the same s.l.d. as the solid is used as the adsorbate. In this case the adsorbed film as well as the condensed cluster of pores will cease to act as scatterers, and only the remaining empty pores will produce measurable scattering. In terms of SANS, contrast matching reduces the solid/film/pore system to a binary one [1]. By determining a number of scattering curves corresponding to the same sample equilibrated at various relative pressures, for both the adsorption and desorption branches of the adsorption isotherm, a correlation of the two methods could be possible. If the predictions of the Kelvin equation are in accordance with the SAS analysis, a reconstruction of the adsorption isotherm can be obtained from the SAS data [2]. 

Under certain temperature and pressure conditions, it is possible for some binary solutions to form two liquid phases along with one vapor phase. Under these conditions, only one degree of freedom exits for the solution. Therefore, for a given pressure, the temperature and composition of all the phases are fixed. For a given temperature, the three phases will all occur in equilibrium. At a temperature greater than this, the system may be a single liquid two phases, a vapor and liquid phase or three phases, a vapor and two liquid phases. At low pressure, the composition of the three phase system may be calculated as shown in the following section. 

The theory for BOHLM is developed for flat thin uncharged symmetric membranes without variation in porosity and pore sizes across the membrane thickness. To develop a three-phase system model [1,2], the transport model simpUfication analysis, developed by Hu [68] for the two-phase system, is used. Titanium(IV) was chosen, as an example for transport model verification, because of the extensive experimental data available on Uquid-Uquid extraction and membrane separation [1, 2, 64, 65] and for its extraction double-maximum acidity dependence phenomenon [63]. The last was observed for most extractant famUies basic (anion exchangers), neutral (complexants), and acidic (cation exchangers). So, it is possible to... 

Two possible scenarios can be envisaged for the structure of the hybrid material (see Fig. 11). The poly(ethylene oxide) block, albeit strongly interacting and partially penetrating, forms a pure PEO layer at the interface to the hydrophobic poly(isoprene) (Fig. 11, left-hand sketch) ( three-phase system). The other possibility is the complete dissolution of the PEO chains in the aluminosilicate, which results in the two-phase system depicted in the right-hand sketch of Fig. 11. Spin-diffusion NMR experiments showed that there appears to be no dynamic heterogeneity in the poly(ethylene oxide) chains, as would be expected for a three-phase system, giving rise to the conclusion that the hydrophilic... 

The electrochemical deposition of lead dioxide provides an example of a three-phase system which is so nearly perfect that it can be analysed by the foregoing techniques, but which has some instructive non-idealities. Divalent lead ions from a wide variety of salts can be oxidised electrochemic-ally in acid or alkaline solution to give a smooth adherent deposit on inert surfaces such as platinum. Either of the two crystalline forms a or j , or possibly a mixture of them, make up the layer, according to the ionic environment. If a mixture of sodium acetate, acetic acid, and plumbous acetate is aqueous solution is used, the a form is thought to be produced exclusively [12] and ellipsometry has been used to learn more about the growth details [13]. 

Despite the limitations of available data with RDC (three different TPC systems were investigated), it was possible to suggest a first generalization (Glatzer and Doraiswamy, 2001). The key idea for a general correlation for TPC systems is to break up the three-phase system (L-L-S) into two L-S systems and correlate the data for each side of the three-phase system separately. 

Extensive experimental work showed that a three-phase system with type III phase behavior was attained whenever a certain relationship, termed the correlation for optimum formulation, was satisfied. The term optimum came from the fact that this formulation was also associated with the lowest possible interfacial tension value in the scan, which led to the most reduction in capillary forces and maximum oil recovery. It is worth mentioning that type III sj tems are now recognized as corresponding to the bicontinuous microemulsions that exhibit the highest solubilization of oil and water per unit weight of amphiphile and thus also the optimum situation whenever the solubilizing ability is sought after, which is probably the most important application of microemulsions outside the petroleum industry. 

In other cases, operating with one fluid phase is possible but too expensive. As a matter of fact, the use of three phase systems is often the most economical way to realize a large number of catalytic reactions. That is the reason why increased use of two fluid phase reactors will result from economical as well as from technical reasons. 

The intrinsic complexity of three phase systems creates some difficulties in the scale-up and in the prediction of performances of three phase reactors. But this complexity is also often a serious advantage, as the simultaneous occurrence of three phases offers such a large number of design possibilities that almost all technical and chemical problems (heat removal, temperature control, selectivity of the catalyst, deactivation, reactants ratio etc..,) can be solved by a proper choice of the equipment and of the operating conditions. For example, countercurrent flow of gas and liquid can be used to overcome thermodynamic limitations and solvent effects can be used to improve selectivity and resistance to poisoning of the catalyst. 

When a three phase system seems to be the best (or the sole) solution for a specific application, there remains the difficult task of selecting the most suitable reactor type among the numerous possibilities of contacting a gas and a liquid in the presence of a solid catalyst. Several papers have been devoted to this problem (see for example references 2,3, and 5) Fundamental characteristics such as residence time distribution are as important as technological aspects such as tightness of pressure vessels. Main features on which can be based a comparison between the two broad classes of three phase reactors - slurry and fixed bed-have been collected in Tables 2 and 3. Of course, such a general comparison is very rough and each mentioned item has to be discussed for every specific case. 

The main effort of researchers was initially oriented to exploring the possibilities and the characteristics of catalytic membrane reactors, especially in three-phase systems. Only a few papers are devoted to the application of catalytic membrane reactors to liquid-liquid systems. An excellent and comprehensive review of three-phase catalytic membrane reactors has been published by Dittmeyer et al. (2004). This exhaustive review covers several aspects of the application of catalytic membranes as three-phase reactors and critically discusses some examples in the literature. 

Homopolymer PP exists as a two- and possibly a three-phase system of crystalline and amorphous phases with the amorphous phase being comprised of a crystalliz-able isotactic portion and a noncrystallizable atactic portion. The noncrystalliz-able, gummy, atactic PP phase has small amounts of a low molecular weight oily material at a level of 1% and lower. The latter has been characterized in some products as having some structural inversions of propylene monomers and some branches other than methyl. Typical levels of crystallinity in extruded PP pellets are in the 60-70% range. One way to describe the morphology of PP is to consider it an assemblage of crystallites that act as physical cross-links in an amorphous matrix. 

In three-phase systems the individual phase voltages (230 V) are equally displaced timewise (phase displacement of 120°) and because of this the voltage across phases is higher. Three-phase supplies can be used to supply both singlephase equipment (with the loads balanced as equally as possible between the three phases) or three-phase equipment such as to large motors. 

In three-phase systems the number of possible configurations is at least ten. These can be summarized as follows ... 

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