Extraction dispersion number

Although solvent samples have been observed for approximately one year without any solids formation, work was completed to define a new solvent composition that was thermodynamically stable with respect to solids formation and to expand the operating temperature with respect to third-phase formation.109 Chemical and physical data as a function of solvent component concentrations were collected. The data included BC6 solubility cesium distribution ratio under extraction, scrub, and strip conditions flowsheet robustness temperature range of third-phase formation dispersion numbers for the solvent against waste simulant, scrub and strip acids, and sodium hydroxide wash solutions solvent density viscosity and surface and interfacial tension. These data were mapped against a set of predefined performance criteria. The composition of 0.007 M BC6, 0.75 M l-(2,2,3,3-tetrafluoropropoxy)-3-(4-.sw-butylphenoxy)-2-propanol, and 0.003 M TOA in the diluent Isopar L provided the best match between the measured properties and the performance criteria. 

When evaluating whether or not an aqueous and organic (solvent) pair is suitable for carrying out a solvent extraction, the most important characteristic is the distribution ratios of the components to be extracted and of those to be left in the fluid. Once the distribution ratios are found to be favorable, the immiscible liquid-liquid pair must be characterized to determine if the pair can be used in commercial solvent-extraction equipment. This characterization is best done by the batch dispersion-number test (Leonard, 1995). This test can be performed easily and quickly with no special equipment. If the results are favorable, the densities of the two phases need to be considered. If the difference is less than 10%, plant operation could be difficult. As a rule of thumb, the density difference should be 15% or greater. The liquid viscosity is important in that more power will be required to turn the rotor if the viscosity is higher. The liquids also need to be able to flow easily from stage to stage. 

Equation 9 is plotted in Figure 2 for several values of the axial dispersion number, /mL,—i.e., the reciprocal of the above-mentioned axial Peclet number. E/uL approaches zero as piston-type or plug flow is approached, and approaches infinity as a completely mixed condition is approached. It is seen that axial dispersion has an increasingly detrimental effect on devolatilization as the extraction number, increases. The applicability of Equation 9 and the validity of some of the assumptions contained therein will be tested experimentally in the section on Results. 

The choice of PEG-2000 for metal ion partitioning studies is perhaps not too surprising. This polymer is inexpensive, commercially available, nonflammable, nontoxic, and durable. The ABSs formed with PEG-2000 are easily separated by centrifugation and the phases have manageable viscosities [7,11]. Phase separation times are dependent on system composition and temperature, but dispersion numbers for many of these ABSs are comparable to those of many oil/water systems utilized in traditional solvent extraction [11]. The dispersion number [34], a unitless quantity, is used to... 

It is seen that there are a large number of compounds capable of dispersive interactions with the reverse phase, contained in the serum that have been extracted and separated. Again the results have been obtained, partly as a result of the extraction and concentration properties of the sampling system, and partly as a result of the high mass sensitivity of the small bore columns. 

The effectiveness of a number of crude oil dispersants, measured using a variety of evaluation procedures, indicates that temperature effects result from changing viscosity, dispersants are most effective at a salinity of approximately 40 ppt (parts per thousand), and concentration of dispersant is critical to effectiveness. The mixing time has little effect on performance, and a calibration procedure for laboratory dispersant effectiveness must include contact with water in a manner analogous to the extraction procedure otherwise, effectiveness may be inflated [587]. Compensation for the coloration produced by the dispersant alone is important only for some dispersants. 

A technique that attempts to combine the extraction and SPE into a single step is matrix solid-phase dispersion (MSPD). In this technique, a nonpolar (such as Cig) SPE sorbent is blended directly into tissue matrix, the mixture is packaged into an SPE cartridge, and the cartridge is eluted like a typical SPE cartridge. The advantage of MSPD is reduced sample size and increased efficiency due to a reduced number of steps. 

Approximate number of theoretical stages for extraction and stripping The necessity or desirability of a scrub stage between extraction and stripping The physical characteristics of the system i.e., dispersion requirements and settling rates, emulsion tendencies, viscosity, etc. 

Nondispersive solvent extraction is a novel configuration of the conventional solvent extraction process. The term nondispersive solvent extraction arises from the fact that instead of producing a drop dispersion of one phase in the other, the phases are contacted using porous membrane modules. The module membrane separates two of the immiscible phases, one of which impregnates the membrane, thus bringing the liquid-liquid interface to one side of the membrane. This process differs from the supported liquid membrane in that the liquid impregnating the membrane is also the bulk phase at one side of the porous membrane, thus reducing the number of liquid-liquid interfaces between the bulk phases to just one. 

We find that long-range interactions responsible for decoherence can be modeled by dispersion forces U(r) = C(f6 and show no dependence on the number of degrees of freedom in the buffer gas molecules. Dispersion force parameters Cg were extracted (see Table 1) according to the equation ... 

It should be pointed out that for a low pressure gas the radial- and axial diffusion coefficients are about the same at low Reynolds numbers (Rediffusion effects may be important at velocities where the dispersion effects are controlled by molecular diffusion. For Re = 1 to 20, however, the axial diffusivity becomes about five times larger than the radial diffusivity [31]. Therefore, the radial diffusion flux could be neglected relative to the longitudinal flux. If these phenomena were also present in a high-pressure gas, it would be true that radial diffusion could be neglected. In dense- gas extraction, packed beds are operated at Re > 10, so it will be supposed that the Peclet number for axial dispersion only is important (Peax Per). 

A number of authors [46 to 48] employ the single sphere model in which the packed bed is considered as a set of equal spheres that are under the same state of extraction, and the fluid flowing around them is solute-free. That is, equation (3.4-90) would be valid, but without the generation term [46], The transport at the solid-fluid interface obeys the boundary condition (Eqn. 3.4-94) with C = 0 (fluid-flows at a large velocity). Under these assumptions, there is an analytical solution to the above problem (without axial dispersion) in terms of the Biot number (Bi = k, R/De), included in the following equation ... 

Such reactions can take place predominantly in either the continuous or disperse phase or in both phases or mainly at the interface. Mutual solubilities, distribution coefficients, and the amount of interfadal surface are factors that determine the overall rate of conversion. Stirred tanks with power inputs of 5-10 HP/1000 gal or extraction-type equipment of various kinds are used to enhance mass transfer. Horizontal TFRs usually are impractical unless sufficiently stable emulsions can be formed, but mixing baffles at intervals are helpful if there are strong reasons for using such equipment. Multistage stirred chambers in a single shell are used for example in butene-isobutane alkylation with sulfuric acid catalyst. Other liquid-liquid processes listed in Table 17.1 are numbers 8, 27, 45, 78, and 90. 

When component C is added to the continuous phase this component is extracted to the dispersed phase, but chemical reaction can take place only in drops containing component A. By continuously coalescing and redispersing, the number of drops containing component A is increasing, however, and therefore, the over-all conversion rate will increase. It is required in this method that the order of drop conversion in component A be equal to zero, so that the drop conversion rate be independent of the concentration in the drop. 

In their experiments water was the dispersed phase and toluene the continuous phase. Iodine was dissolved in the toluene, while a concentrated sodium thiosulfate solution was introduced into the reactor at the beginning of the experiment. The free iodine was extracted from the continuous phase to the sodium thiosulfate-containing drops, the number of which was continuously increasing by coalescence and redispersion. The progress of the extraction process was followed by withdrawing samples of the continuous phase and analyzing the iodine content by light absorption. When M is the number of drops which contain thiosulfate, N the total number of drops,... 

In the last entry in Table III more than 50 samples were extracted in an experiment surveying the performance of laboratory robotic equipment. These included 2.0 gram samples of soils extracted with pure C02,2.5 gram samples of a reverse phase material extracted with C02 and mixtures of C02 with various modifiers, 2.0 gram samples of ground coffee plus aliquots of modifiers dispersed on the samples within the sample thimble extracted with pure CO and 20 microliter aliquots of performance evaluation standard (PES, octadecane in isooctane) on simple matrices extracted with pure C02. The variety of analytes and complex matrices along with the number of different runs clearly show that the instrumentation is reliable. 

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