Column extraction

The simplest form of extractor is a spray column. The column is empty one liquid forms a continuous phase and the other liquid flows up, or down, the column in the form of droplets. Mass transfer takes places to, or from, the droplets to the continuous phase. The efficiency of a spray tower will be low, particularly with large diameter columns, due to back mixing. The efficiency of the basic, empty, spray column can be improved by installing plates or packing. 

Sieve plates are used, similar to those used for distillation and absorption. The stage efficiency for sieve plates, expressed in terms the height of an equivalent theoretical stage (HETS), will, typically, range from 1 to 2.5 m. 

Random packings are also used they are the same as those used in packed distillation and absorption columns. The properties of random packings are given in Table 11.3. Proprietary structured packing are also used. 

Mass transfer in packed columns is a continuous, differential, process, so the transfer unit method should be used to determine the column height, as used in absorption see Section 11.14.2. However, it often convenient to treat them as staged processes and use the HETS for the packing employed. For random packings the HETS will, typically, range from 0.5 to 1.5 m, depending on the type and size of packing used. 

No simple correlation is available to predict the flooding velocities in extraction columns, and hence the column diameter needed. The more specialised texts should be consulted to obtain guidance on the appropriate method to use for a particular problem see Treybal (1980), Perry et al. (1997) and Humphrey and Keller (1997). 

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Fig. 8. UOP Parex simulated moving bed for adsorptive separation. AC = adsorbent chamber RV = rotary valve EC = extract column ...

Fig. 13. UOP Penex-Molex process. AC = adsorbent chamber, EC = extract column, RC = raffinate column.

Extraction, a unit operation, is a complex and rapidly developing subject area (1,2). The chemistry of extraction and extractants has been comprehensively described (3,4). The main advantage of solvent extraction as an industrial process Hes in its versatiHty because of the enormous potential choice of solvents and extractants. The industrial appHcation of solvent extraction, including equipment design and operation, is a subject in itself (5). The fundamentals and technology of metal extraction processes have been described (6,7), as has the role of solvent extraction in relation to the overall development and feasibiHty of processes (8). The control of extraction columns has also been discussed (9). 

Coalescence and Phase Separation. Coalescence between adjacent drops and between drops and contactor internals is important for two reasons. It usually plays a part, in combination with breakup, in determining the equiHbrium drop si2e in a dispersion, and it can therefore affect holdup and flooding in a countercurrent extraction column. Secondly, it is an essential step in the disengagement of the phases and the control of entrainment after extraction has been completed. 

Kuhni contacters (Eig. 15e) have gained considerable commercial application. The principal features are the use of a shrouded impeller to promote radial discharge within the compartments, and a variable hole arrangement to allow flexibility of design for different process applications. Columns up to 5 m in diameter have been constmcted (176). Description and design criteria for Kuhni extraction columns have been reported (177,178). 

K. Najim, Control of Eiquid—Eiquid Extraction Columns, Gordon and Breach, New York, 1988. 

Scale-Up Proceduresfor a Scheibel Extraction Column, NTIS Report No. DE3-013576, National Technical Information Service, U.S. Department of Commerce, Washington, D.C., 1983. 

In addition, solvent extraction is appHed to the processing of other metals for the nuclear industry and to the reprocessing of spent fuels (see Nuclearreactors). It is commercially used for the cobalt—nickel separation prior to electrowinning in chloride electrolyte. Both extraction columns and mixer-settlers are in use. 

L. Burkhart, A. Survey of Simulated Methods for Modeling Pulsed Sieve-Plate Extraction Columns, UCRL-15101, Ames Laboratory, Iowa State University, Ames, Iowa, 1979. 

Modem commercial wet-acid purification processes (see Fig. 4) are based on solvents such as C to Cg alcohols, ethers, ketones, amines, and phosphate esters (10—12). Organic-phase extraction of phosphoric acid is accompHshed in one or more extraction columns or, less frequently, in a series of countercurrent mixer—settlers. Generally, 60—75% of the feed acid P2 s content is extracted into the organic phase as H PO. The residual phosphoric acid phase (raffinate), containing 25—40% of the original P2O5 value, is typically used for fertilizer manufacture such as triple superphosphate. For this reason, wet-acid purification units are almost always located within or next to fertilizer complexes. 

Differences based on ends of extraction column 100 measured values 2% deviation. Based on area oblate spheroid. 

E] Used with a log mean mole fraction difference. Based on ends of extraction column. 

The hydrolysis of fats is improved by running in a counter-current extraction column (Donders et al., Proc. 4th Europ. Symp. Chem. React. Eng., Pergamon, 1968, pp. 159-168). 

One of the components, A (not necessarily the most volatile species of the original mixture), is withdrawn as an essentially pure distillate stream. Because the solvent is nonvolatile, at most a few stages above the solvent-feed stage are sufficient to rectify the solvent from the distillate. The bottoms product, consisting of B and the solvent, is sent to the recoveiy column. The distillate from the recoveiy column is pure B, and the solvent-bottoms product is recycled back to the extractive column. 

The solvent must be higher boiling than the key components of the separation and must be relatively nonvolatile in the extractive column, in order to remain largely in the liquid phase. 

The extractive column must be a double-feed column, with the solvent feed above the primary feed the column must have an extractive section. 

Bi-functional radio-analytical scheme, based on exchange and extraction column chromatography, which provides the reliable information on molybdenum and uranium contents in biological materials has been elaborated. The contribution of uranium fission reaction has been strictly monitored. The uncertainty of the results of Mo determination by the presented method is very low. 

Microwave extraction realized at 120 °C for 30 min with Hexane -Acetone (3 2 V/V) as the extraction solvent was identified as the most effective extraction procedure for isolation of TPH from biotic matrices. The aim of this research is to develop a silica gel and alumina fractionation procedure for plant sample extraction. Column chromatography with two solvents (chloroform and hexane dichloromethane) as a mobile phase were used for clean-up of extract. In this research the efficiency of recovery received from chloroform as a mobile phase. 

Reactive distillation is a technique for combining a number of process operations in a single device. One company has developed a reactive distillation process for the manufacture of methyl acetate that reduces the number of distillation columns from eight to three, also eliminating an extraction column and a separate reactor (Agreda et al., 1990 Doherty and Buzad, 1992 Siirola, 1995). Inventory is reduced... 

Wiped film stills in place of continuous still pots —Centrifugal extractors in place of extraction columns —Flash dryers in place of tray dryers —Continuous reactors in place of batch —Plug flow reactors in place of CFSTRs —Continuous in-line mixers in place of mixing vessels... 

A A multistage extraction column uses gas oil for the preliminary removal of phenol from wastewater. The flowrate of wastewater is 2.0 kg/s and its inlet mass fraction of phenol is 0.0358. The mass fraction of phenol in the wastewater exiting the column is 0.0168. Five kg/s of gas oil are used for extraction. The inlet mass fraction of phenol in gas oil is 0.0074. The equilibrium relation for the transfer of phenol from wastewater to gas oil is given by... 

H. G. J. Mol, H.-G. Janssen, C. A. Cramers and U. A. Th Brinkman, On-line sample enrichment-capillary gas clir omatography of aqueous samples using geometr ically deformed open-tubular extraction columns , 7. Microcolumn Sep. 7 247-257 (1995). 

Figure 12-10. The Inventa-Fisher process for producing nylon 6 from caprolactam (1) Melting station, (2,3) polymerization reactors, (4) extruder, (5) Intermediate vessel, (6) extraction column, (7,8) extraction columns, (9) cooling silo.

Fig. 7.12. Countercurrent extraction column with material balance in the ternary diagram.

Counter-current extraction columns are used. Figure 7.12 shows the counter-current extraction column with a ternary diagram for material balance and equilibrium curve. 

FIG. 4 Sorbex-simulated bed for adsorptive separation. AC, adsorbent chamber RV, rotary valve EC, extract column RC, raffinate column. (From Ref. 32.)... 

FIG. 11 Production of linear olefins from linear paraffins. AC, adsorbent chamber EC, extract column GLS, gas-liquid separator H, heater Rx, reactor RC raffinate column ST, stripper column LE, light end. (From Ref. 10.)... 

FIG. 24 Manufacture of p-toluenesulfonic acid. R, reactor S, separator E, extraction column D, distillation column (From Ref. 162.)... 

In a liquid-liquid extraction column, the process is similar to that occurring in an absorption column except that both streams are liquids, and the lighter liquid rises through the denser one. 

The basic process outline is depicted in Figure 5.2 moist un-roasted coffee beans and CO2 are fed counter-currently into the extractor under supercritical conditions. Caffeine is selectively extracted into the CO2 and this stream is led to a water-wash column to remove caffeine at a reduced pressure, the CO2 being recycled back to the extraction column. Extraction of the caffeine into water is necessary to avoid dropping the CO2 pressure too low, since compression is energy-intensive. There is now the problem of separating the caffeine (which is used in soft drinks and pharmaceu-... 

For stirred tanks with hold-ups up to 0.35 the constant K = 0.024 ( 1For reciprocating-plate extraction columns K = 0.I8, while for pulsed perforated-plate columns AT = 0.18 Kirk-Othmer Encyclopedia of Technology, 1978-1984). 

Extractors with mechanical agitation, such as mixer-settlers, Kuhni columns, York-Schiebel columns, etc., should be avoided as much as possible. Up to seven theoretical stages packed extraction columns can be conveniently adopted. Sieve-plate extractors can be used up to 20 stages. When a very efficient extraction has to be carried out with expensive solutes, and for reasons of material stability and requirements of low expensive product inventory, we may have to use centrifugal extractors or hollow-fibre extractors. 

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