Batch extractors

Holdup and Flooding. The volume fraction of the dispersed phase, commonly known as the holdup can be adjusted in a batch extractor by means of the relative volumes of each Hquid phase added. In a continuously operated weU-mixed tank, the holdup is also in proportion to the volume flow rates because the phases become intimately dispersed as soon as they enter the tank. 

Batch Extractors. Coarse soHds are leached by percolation in fixed or moving-bed equipment. Both open and closed tanks (qv) having false bottoms are used, into which the soHds are dumped to a uniform depth and then treated with the solvent by percolation, immersion, or intermittent drainage methods. 

The NaCl-KCl eutectic is used when the pregnant extraction salt is to be processed by aqueous recovery (this is the salt currently used at Rocky Flats because calcium follows americium in the present aqueous recovery process). The NaCl-CaCl system is used when the salt is processed by pyrochemical means to recover the americium and residual plutonium. When the pyrochemical recovery technique is used, the NaCl-CaCl2-MgCl2 salt is contacted with liquid calcium metal at approximately 850°C in a batch extractor. The calcium reduces A111CI3,... 

This example considers the interactions involved in multicomponent extraction as shown in Sec. 3.3.1.2 and takes the particular case of a single batch extractor with two interacting solutes. 

Batch esterification, 10 478—480 Batch experimental reactor, 21 352 Batch extraction, 10 756 Batch extractor, holdup in, 10 764 Batch fermentation, 10 267 Batch filter cycles, 11 344, 345-346 Batch furnaces, 12 288—289 Batch gasoline blending, 12 413 Batch hydrogenation, 10 811 Batching, ceramics processing, 5 648 Batch injection analysis (BLA) technique, 9 586-587... 

We, at IIP carried out certain oxidation studies and report the results on oxidation of sulfur compounds present in gas oil using carboxylic acid / H2O2 system. Extent of sulfur removal in gas oil after oxidative desulfurization was monitored by sulfur analysis. Oxidation and solvent extraction reduced sulfur in gas oil from 1.5% to 0.20% in single stage batch extractor. 

In the ALCELL process, conventional hardwood chips are cooked in batch extractors with an aqueous ethanol liquor at appropriate temperatures, pH, and time. In the process lignin, hemicellulose and other various components of wood are extracted from the chips into the aqueous ethanol forming a black liquor. 

An extraction system set up to take advantage of solvent reuse is designated as countercurrent extraction. A battery of batch extractors is provided and the solvent is used to treat the contents of each extractor in succession. Each time a batch of miscella is drained from an extractor, it is sent to another extractor containing material previously extracted with a richer miscella. 

Batch Extractors. The first solvent-extraction systems consisted of batch vessels charged with a material that was washed, batchwise, with progressively leaner miscellas, and, finally, with clean solvent. Plants of higher capacity used banks of batch vessels, loaded one at a time, and sequenced with the wash cycles so that the whole bank was handled in a countercurrent flow pattern. Batch extractors are no longer used for oilseeds, but some batch extractors are still used for special materials such as coffee, pharmaceuticals, and other high-priced materials. 

Batch extractors mix a charge of solids and solvent and then let it drain. Immersion extractors cause the solids to pass through a pool of solvent. Percolation extractors carry the solids through a vapor-light chamber where solvent rains down through the solids, dissolving out the oil, similar to the way a coffee percolator works. There are hve major types of percolation extractors basket, rotary, perforated belt, slid-ing-bed, and rectangular loop (151). 

A Canadian group of entrepreneurs and scientists decided in 1985 to install an industrial extraction centre in Edmonton, Alberta, for research, product development and plant design. The centre is equipped with 5 units from laboratory size to commercial plants. Not only are batch extractors installed, but also columns for treating liquid materials are available. The maximum capacity for continuous extraction is about 50 tons/yr. 

The simplest type of extraction equipment is the stirred tank, coupled with a solid-liquid separation step such as a screen, filter, or centrifuge to separate the marc from the extract. This equipment is readily available in a wide variety of sizes and can be operated as a single-batch extractor or run in series in a countercurrent mode as shown in Figure 11.6. 

One mode of operation is described here. A batch extractor is charged with the mixture to be separated. Gas is passed through the charge and the extract phase passes overhead to a rectifying. The process operates in the retrograde condensation region. Thus, a hot finger causes some of the heavier components to precipitate. Part of the condensate can be withdrawn and the remainder is refluxed back to the extractor. The depleted gas stream is lowered in pressure and temperature to liquid conditions and passed into a separator. The liquefied gas is vaporized and recycled via a compressor and the product is withdrawn. 

One example gives quantitative data. 450 g of hexane-extracted soy bean flake with a residual hexane content of 228 ppm was contacted with 4,250 ml of liquid CO2 for 72 hrs at 22 °C and 65 to 75 atm in a batch extractor. The flakes were separated, air dried, and the residual hexane content measured as 44 ppm. (The background section of the patent stated that 60 ppm is the maximum allowed by FDA and, thus, the single extraction was satisfactory to produce material within specifications.) Subsequent extractions lowered the hexane content to 0.7 ppm. 

The ratio of the amount extracted to the amount remaining is called the distribution ratio. There are many situations in which the distribution ratio is low, which would require large amounts of solvent if separatory funnels were used exclusively. This can be very expensive in both chemical and labor costs, and the additional cost of solvent disposal is now often prohibitive. Continuous extractors, in which a small volume of solvent is used to extract a portion of the compound, then evaporated, condensed, and used again, are an ideal solution. This process can be repeated for days if necessary and at the end, there is only a small volume of solvent to remove and dispose of Continuous extractors that involve solvents both heavier and lighter than water are discussed in Chapter 10. A widely used apparatus for continuously extracting components from solids is the batch extractor developed by Soxhiet. The sample is placed in a porous paper thimble and then placed in a horizontal tube with a closed bottom. The extraction solvent is dripped onto the top of the solid, percolates through it, and siphons off after a short time, the process is repeated as often as necessary. Soxhiet extraction is covered in Chapter 10. 

Batch extractors are used Tor single-stage extraction. In most of these tha solid-liquid mixture is agitated (e.g., by slowly turning, large-diameter propellers) to suspend the solids in the liquid. In other cases the solids settle and are resuspended by conveying mixers (e.g., Naula mixers). In other batch extractors a... 

Extraction is carried out batchwise or continuously. For batch extraction, rotating extractors are frequently used, serving both for extraction and the subsequent separation of the solvent from the extraction residue by distillation. Batch extractors are simple and robust, but have a limited capacity, and the periodic filling and emptying is time consuming. Consequently, for bulk materials continuous countercurrent extractors with a capacity of up to several 1000 td are widely used to process oilseeds, but they are also used for coffee and tea (Figure 3.3.54). 

Discontinuous recovery of CO2. This is required whenever the contents of a batch extractor are discharged or whenever the contents of an activated carbon or ion resin adsorber require changing. In order to minimise the downtime associated with the above operations, the expansion should take place as rapidly as possible, but subject to the following restraints. 

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