Extraction processes packed columns

In this process, the two streams flow countercurrently through the column and undergo a continuous change in composition. At any location are in dynamic rather than thermodynamic equilibium. Such processes are frequently carried out in packed columns, in which the liquid (or one of the two liquids in the case of a liquid-liquid extraction process) wets die surface of the packing, thus increasing the interfacial area available for mass transfer and, in addition, promoting high film mass transfer coefficients within each phase. 

Liquid-liquid extraction is carried out either (1) in a series of well-mixed vessels or stages (well-mixed tanks or in plate column), or (2) in a continuous process, such as a spray column, packed column, or rotating disk column. If the process model is to be represented with integer variables, as in a staged process, MILNP (Glanz and Stichlmair, 1997) or one of the methods described in Chapters 9 and 10 can be employed. This example focuses on optimization in which the model is composed of two first-order, steady-state differential equations (a plug flow model). A similar treatment can be applied to an axial dispersion model. 

Activity coefficients at infinite dilution, of organic solutes in ILs have been reported in the literature during the last years very often [1,2,12,45,64, 65,106,123,144,174-189]. In most cases, a special technique based on the gas chromatographic determination of the solute retention time in a packed column filled with the IL as a stationary phase has been used [45,123,174-176,179,181-187]. An alternative method is the "dilutor technique" [64,65,106, 178,180]. A lot of y 3 (where 1 refers to the solute, i.e., the organic solvent, and 3 to the solvent, i.e., the IL) provide a useful tool for solvent selection in extractive distillation or solvent extraction processes. It is sufficient to know the separation factor of the components to be separated at infinite dilution to determine the applicability of a compound (a new IL) as a selective solvent. 

These materials are commonly used in the chemical processing industry as packing for extraction and distillation columns. In a subsequent chapter, we will discuss the relevance of void volume, but it relates to the size of the equipment. A higher void volume is a more efficient use of usable space in a column. It is clear... 

Organic substances can be extracted from aqueous samples by solid-liquid (known as solid phase) extraction. The process is simple, fast, and cost effective in comparison to LLE. In addition, the analysis can be carried out using a smaller volume of sample. By using a suitable capillary column, a detection level comparable to LLE-packed column could be readily attained. The method requires a... 

Eckert [9] showed that a relative height equivalent to a theoretical stage (HETS) vs. the dispersed-phase velocity revealed the packed-column efficiency, or simply the required height, to make one theoretical stage. (See Fig. 7.10). Eckert and others [6, 8] have shown that normally the theoretical packed-column stage requires 2.5 ft of column packed height. All this of course refers strictly to liquid-liquid extraction processing. Also, the continuous-phase velocity Vc (ft/h) and the dispersed-phase velocity VD (ft/h) are referenced to the liquid-phase... 

Determination of theoretical stage number and stage efficiency, or more simply HETS, has been established for any extraction process. The next item of order is the packed extractor column flooding limit. Just as fractionation columns must be sized for vapor and liquid, liquid-liquid extraction columns must be sized for flood limits. 

Dried residues of extracts, processed from volumes of urine containing 25 mg of creatinine, were dissolved in 50 yl of BSTFA (containing 1% TMCS) in dimethylfor-mamide (1 1) and heated at 70°C for 5 minutes. Five microliter aliquots were injected into a 180 cm x 0.2 cm ID pyrex column packed with 1.5% OV-17 on 100/120 mesh HP chromosorb G held isothermally at 275°C with nitrogen carrier gas flow of 30 ml/minute. Each sample was automatically screened by PBM for A -THC and seven of its metabolites (cf. Figure 9) using assay programs consisting of 10 carefully selected characteristic ions for each compound (7). 

Besides fluid mechanics, thermal processes also include mass transfer processes (e.g. absorption or desorption of a gas in a liquid, extraction between two liquid phases, dissolution of solids in liquids) and/or heat transfer processes (energy uptake, cooling, heating, drying). In the case of thermal separation processes, such as distillation, rectification, extraction, and so on, mass transfer between the respective phases is subject to thermodynamic laws (phase equilibria) which are obviously not scale dependent. Therefore, one should not be surprised if there are no scale-up rules for the pure rectification process, unless the hydrodynamics of the mass transfer in plate and packed columns are under consideration. If a separation operation (e.g. drying of hygroscopic materials, electrophoresis, etc.) involves simultaneous mass and heat transfer, both of which are scale-dependent, the scale-up is particularly difficult because these two processes obey different laws. 

Liquid-liquid systems are encountered in many practical applications involving physical separations of which extraction processes performed in both sieve-tray and packed columns are well-known examples. In principle, all three methods discussed in Section III,B,2 can be used to model liquid-liquid two-phase flow problems. The added complexity in this case is the possible deformation of the interface and the occurrence of flow inside the droplet. 

Supercritical fractionation of a liquid lipid feed material is usually carried out in a packed column. Standard columns are not available commercially and have to be custom built either in-house or by manufacturers of extraction units. Lab-scale and pilot-scale supercritical columns, 0.6-13.6 m high with internal diameters of 14.3-68 mm are available in research labs around the world and have been used for the processing of deodorizer distillates (56, 57, 86-90), vegetable and fish oils (91-105), cocoa butter, and milkfat (106-109). A schematic diagram of a typical SCCO2 fractionation column (2.8 m, 2.54 cm o.d.), which was designed and built... 

Timothy C. Frank, Ph.D. Research Scientist and Sr. Technical Leader, The Dow Chemical Company Member, American Institute of Chemical Engineers (Section Editor, Introduction and Overview, Thermodynamic Basis for Liquid-Liquid Extraction, Solvent Screening Methods, Liquid-Liquid Diversion Fundamentals, Process Fundamentals and Basic Calculation Methods, Dual-Solvent Fractional Extraction, Extractor Selection, Packed Columns, Agitated Extraction Columns, Mixer-Settler Equipment, Centrifugal Extractors, Process Control Considerations, Liquid-Liquid Phase Separation Equipment, Emerging Developments)... 

The transfer of mass within a fluid mixture or across a phase boundary is a process that plays a major role in various engineering and physiological applications. Typical operations where mass transfer is the dominant step are falling film evaporation and reaction, total and partial condensation, distillation and absorption in packed columns, liquid-liquid extraction, multiphase reactors, membrane separation, etc. The various mass transfer processes are classified according to equilibrium separation processes and rate-governed separation processes. Fig. 1 lists some of the prominent mass transfer operations showing the physical or chemical principle upon which the processes are based. 

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