Types of Extractors

The earliest large-scale continuous industrial extraction equipment consisted of mixer—settlers and open-spray columns. The vertical stacking of a series of mixer—settlers was a feature of a patented column in 1935 (96) in which countercurrent flow occurred because of density difference between the phases, avoiding the necessity for interstage pumping. This was a precursor of the agitated column contactors which have been developed and commercialized since the late 1940s. There are several texts (1,2,6,97—98) and reviews (99—100) available that describe the various types of extractors. 

Types of extractor General features Fields of industrial appHcation... 

The simple box-type mixer—settler (113) has been used extensively in the UK for the separation and purification of uranium and plutonium (114). In this type of extractor, interstage flow is handled through a partitioned box constmction. Interstage pumping is not needed because the driving force is provided by the density difference between solutions in successive stages (see Plutoniumand plutonium compounds Uraniumand uranium compounds). 

Density. The difference in density between the two hquid phases in eqiiilibrium affects the countercurrent flow rates that can be achieved in extrac tion equipment as well as the coalescence rates. The density difference decreases to zero at a plait point, but in some systems it can become zero at an intermediate solute concentration (isopycnic, or twin-density tie line) and can invert the phases at higher concentrations. Differential types of extractors cannot cross such a solute concentration, but mixer-settlers can. 

Karr, Holmes, and Cusack have given comparisons of the Karr column volumetric efficiency with other types of extractors. In Table 15-10 are data showing the values of HETS and volumetric efficiency over a range of column diameters from 1-36 in (0.025-0.9 m) Fig. 15-51... 

The alternative is hexane, which because of the explosion hazard requires a more expensive type of extractor construction. After the extraction the product is dull gray. The continuos sheet is slit to the final width according to customer requirements, searched by fully automatic detectors for any pinholes, wound into rolls of about 1 m diameter (corresponding to a length of 900-1000 m), and packed for shipping. Such a continuous production process is excellently suited for supervision by modern quality assurance systems, such as statistical process control (SPC). Figures 7-9 give a schematic picture of the production process for microporous polyethylene separators. 

This is a slow process, and the extraction time depends on the type of extractor used. With stirring as described in Note 10, practically quantitative extraction of jb-hydroxy phenyl pyruvic acid can be achieved within 6 hours. Extremely long extraction times may cause decomposition of the product. 

The modelling approach to multistage countercurrent equilibrium extraction cascades, based on a mass transfer rate term as shown in Sec. 1.4, can therefore usefully be applied to such types of extractor column. The magnitude of the... 

If it is necessary or desirable, water can be extracted from unsaturated soils in the laboratory. This requires either pressure or suction to move water from the soil. A common laboratory method for removing water from unsaturated soils is the pressure plate (see Figure 7.13). Plates for this type of extractor can be used for extraction of water at field capacity 33 kPa and at permanent wilting point - --1500 kPa.3... 

The modelling approach to multistage countercurrent equilibrium extraction cascades, based on a mass transfer rate term as shown in Section 1.4, can therefore usefully be applied to such types of extractor column. The magnitude of the mass transfer capacity coefficient term, now used in the model equations, must however be a realistic value corresponding to the hydrodynamic conditions, actually existing within the column and, of course, will be substantially less than that leading to an equilibrium condition. 

Figures 7 and 8 show one of the pump-mix types of extractors (C5, S2). In this case each stage consists of a mixing chamber and a settler. Ad-...

Some novel types and variations of basic types of extractors have been developed, most of which have not found wide acceptance, for instance pulsed rotary towers. The literature of a few of them is listed by Baird (in Lo et al., 1983, pp. 453-457). Here the extractors illustrated in Figure 14.15 will be described. 

Extraction and finisher pressures can greatly influence the flavonoid content of citrus juices. Generally, as the fruit is squeezed harder more juice is recovered. However, excessive extractor pressures produce juice of a lower quality (35). As shown in Figure 8, grapefruit flavanone glycoside concentrations increase with increasing extractor pressures. In the early portion of the season almost twice as much naringin was obtained under hard squeeze conditions than was obtained with the soft squeeze. The effect of finisher pressure is not as clear, and is dependent on the composition of the raw juice which, in turn, is dependent on the type of extractor used. 

Thus, the type of extractor, extractor pressure, juice pulp contact time as well as ultimate juice pulp content will all alter the amount of flavanone glycosides found in the juice. 

There are three types of nonproprietary nonagitated types of extraction columns (see Figure 12). The spray columns are the simplest type of extractors, containing only distributors for the feed (often through perforated pipes). This... 

An extractor column is generally a tall, vertical packed tower that has two or more bed sections. Each packed bed section is typically limited to no more than 8 ft tall, making the overall tower height about 40 to 80 ft. Tower diameter depends fully upon liquid rates, but is usually in the range of 2 to 6 ft. Liquid-liquid extractors may also have tray-type column internals, usually composed of sieve-type trays without downcomers. These tray-type columns are similar to duoflow-type vapor-liquid separation, but here serve as contact surface area for two separate liquid phases. The packed-type internals are more common by far and are the type of extractor medium considered the standard. Any deviation from packed-type columns is compared to packing. 

Rather expensive in capital as well as recurring costs compared to other types of extractors... 

A small-scale chain conveyor type of extractor was developed in the 1940s at Iowa State University with the intent of using trichloroethylene solvent to extract soybeans. Crown Iron Works of Minneapolis, Minnesota, licensed the technology and extractor design, and supplied several continuous solvent extraction plants in 1951 using the new extractor and trichloroethylene solvent (6). The meal from these plants proved detrimental to animals, so the plants were either closed or converted to petroleum-based solvents (7). The chain-type extractor apparatus continued on and is the basis of the modern Crown Iron Works Model III extractor used today. 

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