Continuous extractors efficiencies

Contimious liquid extraction techniques are used when the sample volume is large, the distribution constant is small, or the rate of extraction is slow. The efficiency of extraction depends on many factors including the viscosity of the phases, the magnitude of the distribution constant, the relative phase volumes, the interfacial surface area, and the relative velocity of the phases. Numerous continuous extractors using llghter-than-water and heavier-than-water solvents vee been described [3,2 7,42,73,74]. Generally, either the ligi Pr or heavier density... 

Solvent extraction. The press cake emerging from a screw press still retains 3 to 15 percent of residual oil. More complete extraction is done by solvent extraction of the residues obtained from mechanical pressing. The greater efficiency obtained in the solvent extraction process encouraged the industry for direct application to oilseeds. In the United States and Europe, continuous extractor units are used in which fresh seed flakes are added continuously and are subjected to a counterflow of solvent by which intimate contact is achieved between the seeds and solvent. The common solvent for edible oil is commercial hexane or heptane, commonly known as petroleum ethers, boiling in the range of 146 to 156°F (63.3 to 68.9°C). After extraction, maximum solvent recovery is necessary for economical operation. The solvent is recovered by distillation and is reused. The extraction oil is mixed with prepress oil for refining. The extracted meals contain less than 1 percent of residual oil. 

In a continuous extraction, crude lecithin and acetone are simultaneously metered into a vessel. Within limits, acetone consumption can be decreased by increasing residence time in the continuous extractor, increasing raw material efficiency (33). 

The efficiency of continuous extractors is measured by the half extraction volume, determined as shown in Figure... 

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. 

If the desired product is fairly water soluble, simple extraction into organic solvents may not be an efficient means of recovery. In that case, continuous extraction of the aqueous solution with an organic solvent may be necessary to effect the recovery. Either of two types of apparatus are normally employed, and the correct design depends on the density of the organic solvent. For solvents less dense than water, the apparatus should be set up as in Fig. A3.11a. The barrel of the extractor is charged with the... 

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. 

Ahnoff and Josefsson [18] built a solvent extraction apparatus for river work which was later modified into their in situ extractor [ 17]. The unit as described in the earlier work could easily be adapted for seawater analysis. A unit based on a Teflon helix liquid-liquid extractor, some 332 feet (101.5 metres) in length, was constructed by Wu and Suffet [19]. The extractor was optimized for the removal of organophosphorus compounds, specifically pesticides, with an efficiency of around 80%. For some compounds, these continuous extraction methods should be the methods of choice and should be explored. 

Prepared cottonseed meats containing 35 per cent of extractable oil are fed to a continuous countercurrent extractor of the intermittent drainage type using hexane as the solvent. The extractor consists of ten sections and the section efficiency is 50 per cent. The entrainment, assumed constant, is 1 kg solution/kg solids. What will be the oil concentration in the outflowing solvent if the extractable oil content in the meats is to be reduced by 0.5 per cent by mass ... 

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. 

Pulsing means that either the whole liquid content of a sieve tray column is continually pushed up and down by a piston that moves to and fro, or the whole plate package is moved up and down [3]. Figure 9.5 illustrates the two extractor constructions schematically. They show about the same efficiency... 

Laboratory Extractors. Pilot-Scale Testing, and Scale-Up. Several laboratory units arc useful in analysis, process control, and process studies. The AKUFVE contactor incorporates a separate mixer and centrifugal separator. It is an efficient instrument for rapid and accurate measurement of partition coefficients, as well as for obtaining reaction kinetic data. Miniature mixer-settler assemblies set up as continuous, bench-scale, multistage, countercurrent, liquid-liquid contactors are particularly useful Tor the preliminary laboratory work associated with flow-sheet development and optimization because these give a known number of theoretical stages. 

Continuous glycerin washing of soap produced by saponification has been demonstrated in a countercurrent centrifugal extractor (38). The device achieves phase separation with as little as 0.02 specific gravity difference and accomplishes up to 10 theoretical stages of extraction. Some of the advantages over prior operations reportedly include flexibility in feed, low holdup, less waste due to more efficient separation, simple operation, rapid startup, and small space requirements. 

Gamiz-Gracia and de Castro (2000) devised a subcritical extractor equipped with a three-way inlet valve and an on/off outlet valve to perform subcritical water extractions in a continuous manner for the isolation of fennel essential oil. The target compounds were removed from the aqueous extract by a single extraction with 5 ml hexane, determined by gas-chromatography-flame ionization and identified by mass spectrometry. This extraction method is superior to both hydrodistillation and dichloromethane manual extraction in terms of rapidity, efficiency, cleanliness and the possibility of manipulating the composition of the extract. 

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