Extractor column extraction efficiency

A-l. Extractor Column Extraction Efficiency. Extraction of the PAHs from the generated solutions was accomplished by pumping volumes varying between 5.0-25.0 mL through the extractor column. Over this range, extraction efficiencies are quantitative for 11 of the 12 compounds studied in this investigation. Benzene was not extracted efficiently by the extractor column. The solubility of benzene, therefore, was determined by direct injection of 23.2 /xL of the generated solutions via a sample loop. 

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. 

For column extractors Decrease in extraction efficiency agitator speed to fast/ex-cessive backmixing/flooding. 

After microwave irradiation, each brown mass was dissolved in approximately 100 mL of deionized water and allowed to cool to room temperature. The resulting solutions were adjusted to pH 8 with 6N NaOH to enhance the extraction efficiency of nitrogen-containing heterocyclic compounds. The aqueous solution was extracted with 50 mL of dichloromethane using a liquid-liquid continuous extractor for 6 h and then dried over anhydrous sodium sulfate for 12 h. After removal of sodium sulfate, the dichloromethane extract was concentrated to 1 mL by fractional distillation with a Vigreux column at atmospheric pressure. 

Fig. 18-1. (a) The glass continuous extractor is shown without boiling flask, reflux condenser and thermometer. To improve the extraction efficiency the vacuum-jacketed distillation column may be filled with glass helices. The lower flat stopcock is used do drain the column, (b) The extractor configured for fractionated distillation. The upper flat stopcock is used to adjust the reflux ratio. 

The advantages of using XAD-2 resin, as we see them today, are the large volumes that can be processed per unit time (90L/h, Le., 5 bed volumes/min), and the use of several extractors in series, if necessary. The extraction efficiency of a single column is 70-90 %, if the capacity of the column is not exceeded (Schulz, 1990). This is in good agreement with the results of another study (Gomez-Belinchon etal., 1988). 

The basic design of Uquid-Hquid-extraction test plant with packed columns is shown in Fig. 7-1. It largely corresponds to the structure commonly used for gas/Hquid systems. A distributor with bore holes is used for the pre-distribution of the dispersed phase, with the hole diameter roughly matching the expected droplet size. A distributor is also used for the pre-distribution of the continuous phase, in order to achieve an even flow of both phases in the packed extractor. Practical experience has shown that a poor pre-distribution of the continuous and dispersed phases results in strong back-mixing, which, in turn, leads to a significant reduction of the extractor s separation efficiency [3,4, 10,21],... 

FIG. 23-38 Efficiency and capacity range of small-diameter extractors, 50 to 150 mm diameter. Acetone extracted from water with toluene as the disperse phase, V /V = 1.5. Code AC = agitated cell PPC = pulsed packed column PST = pulsed sieve tray RDC = rotating disk contactor PC = packed column MS = mixer-settler ST = sieve tray. (Stichlmair, Chem. Ing. Tech. 52(3), 253-255 [1980]). 

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. 

The need to use multiple extraction to achieve efficient extraction required the development of new types of continuously working extractors, especially mixer-settlers and pulsed columns, which were suitable for remotely controlled operations. These new extractors could be built for continuous flow and in multiple stages, allowing very efficient isolation of substances in high yield. A good example is the production of rare earth elements in >99.999% purity in ton amounts by mixer-settler batteries containing hundreds of stages. These topics will be further developed in Chapters 6 and 7. 

If a rapid, reciprocating motion of relatively short amplitude is applied to the liquid contents of an extraction column, the column is said to be pulsed. The agitation thus provided has been found to give improved extraction rates. Devices of this sort were suggested as early as 1935 (VI), but it was not until the atomic energy programs in the United States and Great Britain developed a need for efficient extractors of low... 

If the solvent is nonvolatile, it can cause accumulation of heavy impurities in an extraction loop that are surface-active. Even in trace concentrations, these culprits can have a devastating effect on extractor performance. They can reduce the coalescing rates of drops—and thus reduce column capacity. Since most flooding models are based on pure-component tests, these models tend to be overly optimistic. Relative to a clean system, the presence of impurities can lower column capacity by 20% or more and efficiency by as much as 60%. 

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