Degree of separation

In practice the efficiency of plates is usually less than 100%, with the result that the number required to achieve a given degree of separation or absorption is greater than the theoretical number. 

A first approach to testing, ASTM D 1094, is to create, using a potassium phosphate reagent, a separation between two layers, hydrocarbon and aqueous. The degree of separation of the two phases is estimated by attributing a grade from 1 to 3 and the appearance of the interface by five levels of observation 1, lb, 2, 3, and 4. The specifications establish both the quality of separation (2 is the maximum) and the appearance of the interface (lb maximum). 

Separations based upon differences in the physical properties of the components. When procedures (1) or (2) are unsatisfactory for the separation of a mixture of organic compounds, purely physical methods may be employed. Thus a mixture of volatile liquids may be fractionally distilled (compare Sections 11,15 and 11,17) the degree of separation may be determined by the range of boiling points and/or the refractive indices and densities of the different fractions that are collected. A mixture of non-volatile sohds may frequently be separated by making use of the differences in solubilities in inert solvents the separation is usually controlled by m.p. determinations. Sometimes one of the components of the mixture is volatile and can be separated by sublimation (see Section 11,45). 

Resolution. The degree of separation or resolution, Rs, of two adjacent peaks is defined as the distance between band peaks (or centers) divided by the average bandwidth using 14), as shown in Fig. 11.3. 

The goal of chromatography is to separate a sample into a series of chromatographic peaks, each representing a single component of the sample. Resolution is a quantitative measure of the degree of separation between two chromatographic peaks, A and B, and is defined as... 

As shown in Figure 12.8, the degree of separation between two chromatographic peaks improves with an increase in R. For two peaks of equal size, a resolution of 1.5 corresponds to an overlap in area of only 0.13%. Because resolution is a quantitative measure of a separation s success, it provides a useful way to determine if a change in experimental conditions leads to a better separation. 

The choice of a mass spectrometer to fulfill any particular task must take into account the nature of the substances to be examined, the degree of separation required for mixtures, the types of ion source and inlet systems, and the types of mass analyzer. Once these individual requirements have been defined, it is much easier to discriminate among the numerous commercial instruments that are available. Once suitable mass spectrometers have been identified, it is then often a case of balancing capital and running costs, reUability, ea.se of routine use, after-sales service, and manufacturer reputation. 

The general formula for the initiator species can be written H B, where the degree of separation or ion pairing depends on the polarity of the medium and the possibility of specific solvation interactions. If we represent the equilibrium constant for the reactions in (6.DD) and (6.EE) by K, the initiator concentration can be written as... 

Diafiltration is an ultrafiltration process where water or an aqueous buffer is added to the concentrate and permeate is removed (50). The two steps may be sequential or simultaneous. Diafiltration improves the degree of separation between retained and permeable species. 

A Barrier Efficiency Eactor. In practice, diffusion plant barriers do not behave ideally that is, a portion of the flow through the barrier is bulk or Poiseuihe flow which is of a nonseparative nature. In addition, at finite pressure the Knudsen flow (25) is not separative to the ideal extent, that is, (M /Afg) . Instead, the degree of separation associated with the Knudsen flow is less separative by an amount that depends on the pressure of operation. To a first approximation, the barrier efficiency is equal to the Knudsen flow multiphed by a pressure-dependent term associated with its degree of separation, divided by the total flow. 

Separation by distillation is dependent on the fact that when a Hquid is partially vaporized the vapor and Hquid compositions differ. The vapor phase becomes enriched ia the more volatile components and depleted ia the less volatile components with respect to its equiUbrium Hquid phase. By segregating the phases and repeating the partial vaporization, it is often possible to achieve the desired degree of separation. One measure of the degree of enrichment or the ease of separation is the relative volatiHty defined as ... 

The ratio of wash solvent to extraction solvent is the same in the enriching section as in the stripping section if no solvent is added in the feed. The degree of separation to be achieved can be chosen for the process design, such as 99 percent of component b into the extrac-t stream and 99 percent of component c into the raffinate stream. Then the feed rate can be chosen so that the solute loadings in the extrac-t stream and... 

Feed Preparation and Feed Size The ability to achieve a separation of different solid particles on the basis of density, as in all physical separation, depends on the degree to which the particles are liberated (detached) from each other. Liberation can be achieved by breaking the material in a manner that causes it to fracfure and free the individual grains of the constituents to be recovered. The degree of separation that can be realized by the dense-media process will depend on the degree of hberation of the individual grains. 

J. Chem. Educ., 50, 864 (1973)], theory shows that the degree of separation that is obtained increases as the liquid column is made taller. But unfortunately it decreases as the column is made wider. In simple terms, the latter effect can be attributed to the increase in the dispersion coefficient as the column is widened. 

Since the boiling point properties of the components in the mixture being separated are so critical to the distillation process, the vapor-liquid equilibrium (VLE) relationship is of importance. Specifically, it is the VLE data for a mixture which establishes the required height of a column for a desired degree of separation. Constant pressure VLE data is derived from boiling point diagrams, from which a VLE curve can be constructed like the one illustrated in Figure 9 for a binary mixture. The VLE plot shown expresses the bubble-point and the dew-point of a binary mixture at constant pressure. The curve is called the equilibrium line, and it describes the compositions of the liquid and vapor in equilibrium at a constant pressure condition. 

Note that filter aid selection must be based on planned laboratory tests. Guidelines for selection may only be applied in the broadest sense, since there is almost an infinite number of combinations of filter media, filter aids, and suspensions that will produce varying degrees of separation. The hydrodynamics of any filtration process are highly complex filtration is essentially a multiphase system in which interaction takes place between solids from the suspension, filter aid, and filter medium, and a liquid phase. Experiments are mandatory in most operations not only in proper filter aid selection but in defining the method of application. Some general guidelines can be applied to such studies the filter aid must have the minimum hydraulic resistance and provide the desired rate of separation an insufficient amount of filter aid leads to a reduction in filtrate quality — excess amounts result in losses is filtration rate and it is necessary to account for the method of application and characteristics of filter aids. 

The degree of separation required for both the liquid and the solid... 

In EUROVENT 4/9 the dust spot efficiency has been replaced by measurement of the degree of separation of particles within the 0.2-3 pm range, with a particle size of 0.4 pm used for classification of the filter. 

As described above, the application of classical liquid- liquid extractions often results in extreme flow ratios. To avoid this, a completely symmetrical system has been developed at Akzo Nobel in the early 1990s [64, 65]. In this system, a supported liquid-membrane separates two miscible chiral liquids containing opposite chiral selectors (Fig. 5-13). When the two liquids flow countercurrently, any desired degree of separation can be achieved. As a result of the system being symmetrical, the racemic mixture to be separated must be added in the middle. Due to the fact that enantioselectivity usually is more pronounced in a nonaqueous environment, organic liquids are used as the chiral liquids and the membrane liquid is aqueous. In this case the chiral selector molecules are lipophilic in order to avoid transport across the liquid membrane. 

The degree of separation achieved in this system can be calculated according to... 

Generally the maximum allowable velocities are lower under conditions of pressure, and higher under conditions of vacuum. The limits and ranges of each area being determined by the relative operating densities of the vapor and liquid, the nature of the entrainment, and the degree of separation required. 

Some experimental results for the helium-xenon system are shown in Fig. 25. (The critical temperature of xenon is 16.6°C.) At temperatures several degrees above the critical of xenon, the two phase-compositions are significantly different even at pressures as low as 200 atm. However, to obtain the same degree of separation at higher temperatures, much higher pressures are required. 

The value of a12 affects the total pressure required to achieve any specified degree of separation. This is illustrated in Fig. 32. A binary solvent separates into phases a and b at lower pressures as oc12 increases. This follows from the fact that a large ac12 indicates that the gas is much more soluble than predicted by Henry s law. 

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