Mixtures separating into components

Figure 8.17 Vapor fugacity for component 2 in a liquid mixture. At temperature T, large positive deviations from Raoult s law occur. At a lower temperature, the vapor fugacity curve goes through a point of inflection (point c), which becomes a critical point known as the upper critical end point (UCEP). The temperature Tc at which this happens is known as the upper critical solution temperature (UCST). At temperatures less than Tc, the mixture separates into two phases with compositions given by points a and b. Component 1 would show similar behavior, with a point of inflection in the f against X2 curve at Tc, and a discontinuity at 7V...

If we could prevent the mixture from separating into two phases at temperatures below Tc, we would expect the point of inflection to develop into curves similar to those shown in Figure 8.17 as the dotted line for /2, with a maximum and minimum in the fugacity curve. This behavior would require that the fugacity of a component decreases with increasing mole fraction. In reality, this does not happen, except for the possibility of a small amount of supersaturation that may persist briefly. Instead, the mixture separates into two phases. These phases are in equilibrium so that the chemical potential and vapor fugacity of each component is the same in both phases, That is, if we represent the phase equilibrium as... 

Hofmann amine separation org chem A technique to separate a mixture of primary, secondary, and tertiary amines they are heated with ethyl oxalate there is no reaction with tertiary amines, primary amines form a diamide, and the secondary amines form a monoamide when the reaction mixture is distilled, the mixture is separated into components. haf-mon am,en, sep-3,ra-sh3n ... 

Mechanical activation apphed to the mentioned reaction was found to be very efficient [45]. For example, molybdenum oxide mechanically activated for several seconds is readily dissolved in hot solution of phosphoric acid to give heteropolyacid. By varying the interaction conditions, one succeeds in obtaining heteropolyacids with different molybdenum to phosphorus ratios. H3PM012O40 can be synthesized in the individual pure state, and HgP2Mo,gOj2 with the purity of 94-98 %. Mo - P mixtures, which are most easily prepared, can be used as acid catalysts without separating into components. Besides the simplicity of preparation. 

Through the process of paper chromatography, mixtures can be separated into components. 

Many different methods for the deconvolution of the components of combinatorial libraries exist today. An active mixture of peptides can be separated into components. Conventional reverse-phase HPLC (columns with Cjg) has been used successfully for the separation of peptide mixtures. 

Zone electrophoresis is used extensively in modem research and clinical laboratories. In this technique, the components of the analyte mixture separate completely to form discrete zones, or bands, that may be stabilized by a support medium or may exist as free zones. The analyte solution is applied to the medium as a spot or band, and the electric field causes the initial band to separate into component bands through migration, as shown in Figure 9.4. 

For the extraction of proteins, aqueous two-phase systems (ATPS) are preferred over organic solvents, which usually denature the proteins and render them biologically inactive. They consist of polyethylene glycol (PEG), and a salt (e.g., potassium phosphate) or dextran in water. At concentrations above a critical value, the mixture separates into two phases—one rich in PEG and the other in dextran or salt. In industrial systems, salts are more commonly used because they are relatively inexpensive as compared to dextran. The MW, charge and surface properties of the protein decide how the protein partitions in the system. The nature of the phase components, the MW of the polymer, and the concentration and type of salt used also affect the distribution. ... 

However, as the pressure is increased above about 10 to 15 atmospheres, especially when metallic oxide catalysts or metal-alkali catalysts are used, the product tends to become more and more oxygenated in character and exceedingly complex mixtures may be obtained. Such products, because of their complexity and difficulty of separation into components, are of little commercial value from the standpoint of being sources of valuable oxygenated organic compounds. 

Polymer-solvent mixtures can be separated and the polymer recovered from solution at the lower critical solution temperature (LCST). This is the temperature at which the miscible polymer-solvent mixture separates into a polymer-rich phase and a solvent-rich phase. LCST phenomena are related to the chemical nature of the mixture components, the molecular weight of the mixture components, especially the polymer, and the critical temperature and critical pressure of the solvent (Allen and Baker, 1965). As the single-phase polymer solution is isobarically heated to conditions near the critical point of the solvent, the polymer and solvent thermally expand at different rates. This means their free volumes change at different rates (Patterson, 1969). The thermal expansion of the solvent is much greater than that of the polymer. Near its critical point, the solvent has expanded so much that it is no longer able to solubilize the polymer. Hence, the polymer falls out of solution. If the molecular weight of the polymer is on the order of 10 a polymer-solvent LCST can occur within about 20-30°C of the solvent s critical temperature. If the molecular weight of the polymer is closer to 10, the LCST phase... 

In Fig. 2-30, this rectification separation process, in two columns operated at two different pressure levels, is explained as a tv/o pressure process for a binary mixture. The binary mixture consists of components 1 and 2, with mole fraction Xp of the low-boiling component 1. In the first column, operated at a lower pressure Pqj, the binary mixture is separated into component 2 as the bottom product, and an azeotropic mixture of composition, as an overhead product. In the second column, operated at a pressure Pg2 > Pgi l he azeotropic mixture is separated into component 1 (at the bottom) and azeotropic mixture x 2 the top). The azeotropic mixture of the second column is then fed into the side of column 1 at an appropriate location. 

Practically, all natural substances and substances produced in the chemical reactors are mixtures that do not have the properties required for using them in techniques and for household needs. These mixtures should be separated into components or groups of components. 

The diagrams of reversible distillation were constructed for some types of three-component azeotropic mixtures. It is interesting that some types of mixtures with one binary azeotrope and with two distillation regions [types 3 and 5 according to classification (Gurikov, 1958)] permit sharp separation into component and binary zeotropic mixture at some feed compositions. The mixture acetone(l)-benzene(2)-chloroform(3) is an example of such mixture. 

The formation of IL/O microemulsions in mixtures of [bmim][BFJ (IL) and cyclohexane, stabilized by the nonionic surfactant, TX-lOO has been proved [30]. Three-component mixtures could form IL/O microemulsions of well-defined droplet size determined by fixing the water content (mole ratio of IL to TX-lOO) [30,48,49]. An upper critical point (T) was observed in the mixture [([bmim][BFJ/ TX-lOO)-I-cyclohexane] with fixed water content (mole ratio of [bmim][BFJ to TX-lOO) [50]. The mixture separated into two microemulsion phases of different composition but with the same composition below as occurred in other systems [48]. The microemulsion system, [bmim][BF ]/TX-100 +cyclohexane, could be regarded as a pseudobinary mixture of [bmim][BF ]/TX-100 IL droplets dispersed in the cyclohexane continuous phase. Therefore, the phase behavior could be depicted in a two-dimensional diagram with concentration of droplets along the abscissa and temperature along the ordinate. A coexistence curve of temperature (T) against a concentration variable, such as volume fraction ( ), could then be drawn in the same way as it was done for pseudobinary mixtures in AOT/water/decane micro-emulsions [48]. 

Fractionation may be broadly defined as any method by which a liquid or vapor mixture may be separated into individual components by vaporization or condensation. The components may be pure compounds or if the original material is a complex mixture, the components may be products that are stUl mixtures but whose distillation range is limited by the fractionation process. In a more detailed way the various means of separation have been given special names. Distillation is usually considered to refer to a complete operation in which heating, vaporization, fractionation, condensation, and cooling are practiced. DephlegmaMon is a particular kind of fractionation in which a vapor mixture is separated into components by partial condensation. In this operation... 

In the first class, azeotropic distillation, the extraneous mass-separating agent is relatively volatile and is known as an entrainer. This entrainer forms either a low-boiling binary azeotrope with one of the keys or, more often, a ternary azeotrope containing both keys. The latter kind of operation is feasible only if condensation of the overhead vapor results in two liquid phases, one of which contains the bulk of one of the key components and the other contains the bulk of the entrainer. A t3q)ical scheme is shown in Fig. 3.10. The mixture (A -I- B) is fed to the column, and relatively pure A is taken from the column bottoms. A ternary azeotrope distilled overhead is condensed and separated into two liquid layers in the decanter. One layer contains a mixture of A -I- entrainer which is returned as reflux. The other layer contains relatively pure B. If the B layer contains a significant amount of entrainer, then this layer may need to be fed to an additional column to separate and recycle the entrainer and produce pure B. 

Example 5.1 Each component for the mixture in Table 5.2 is to he separated into relatively pure products. Use the heuristics to determine sequences which are candidates for further evaluation. 

In the petroleum refining and natural gas treatment industries, mixtures of hydrocarbons are more often separated into their components or into narrower mixtures by chemical engineering operations that make use of phase equilibria between liquid and gas phases such as those mentioned below ... 

Gas is produced to surface separators which are used to extract the heavier ends of the mixture (typically the components). The dry gas is then compressed and reinjected into the reservoir to maintain the pressure above the dew point. As the recycling progresses the reservoir composition becomes leaner (less heavy components), until eventually it is not economic to separate and compress the dry gas, at which point the reservoir pressure is blown down as for a wet gas reservoir. The sales profile for a recycling scheme consists of early sales of condensate liquids and delayed sale of gas. An alternative method of keeping the reservoir above the dew point but avoiding the deferred gas sales is by water injection. 

Another important class of materials which can be successfiilly described by mesoscopic and contimiiim models are amphiphilic systems. Amphiphilic molecules consist of two distinct entities that like different enviromnents. Lipid molecules, for instance, comprise a polar head that likes an aqueous enviromnent and one or two hydrocarbon tails that are strongly hydrophobic. Since the two entities are chemically joined together they cannot separate into macroscopically large phases. If these amphiphiles are added to a binary mixture (say, water and oil) they greatly promote the dispersion of one component into the other. At low amphiphile... 

A mixture can often be separated into its components by utilising their selective adsorption from solution by a suitable substance, such as active alumina the separation can be readily followed if the components are coloured. 

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