Continuous extraction of solids

APPARATUS FOR THE CONTINUOUS EXTRACTION OF SOLIDS OR LIQUIDS BY SOLVENTS... 

APPARATUS FOR THE CONTINUOUS EXTRACTION OF SOLIDS OR LIQUIDS BY SOLVENTS Solids by solvents. The various forms of Soxhlet apparatus illustrated in Section 11,44 can be purchased with groimd glass joints. A simplified form, in which the fragile side tubes are absent, is shown in Fig. 77,58,1. The material to be extracted, if of granular form, may rest upon a sintered glass disc or upon a removable septum ... 

Apparatus for the continuous extraction of solids or liquids by solvents 222... 

Continuous extraction of solids is commonly used to separate one solid from another by means of a solvent in which their solubilities are quite different. If the desired solid is quite soluble in the solvent, con-... 

Continuous extraction of solids is not easily achieved in a high pressure environment, but can be achieved in certain cases. These favourable cases are met when the solids can be ground to a small size (below 1 mm) and a diluted suspension of the solid material in the solvent can be used. As this possibility is of fundamental importance, an experimentally verified example is treated here in some detail. 

Unfortunately the continuous extraction of solids at high pressures presents many very difficult engineering problems which have not so far been fully overcome. The design of solid product entry and exit valves for high pressure vessels has been described by Eggers et al. [2] and is also discussed in chapter 8, which contains an account of a pilot plant for the continuous extraction of oil seeds. However, the use of true continuous dense gas extraction processes does not appear to be a commercial practicality at present. 

Table 8.5 High pressure lock systems for continuous extraction of solid material...

For the continuous extraction of a solid by a hot solvent, the Soxhiet extraction apforotua, shown in Fig. 11, 44, 4, is usually employed. The... 

Many continuous extractions involving solid samples are carried out with a Soxhiet extractor (Figure 7.18). The extracting solvent is placed in the lower reservoir and heated to its boiling point. Solvent in the vapor phase moves upward through the tube on the left side of the apparatus to the condenser where it condenses back to the liquid state. The solvent then passes through the sample, which is held in a porous cellulose filter thimble, collecting in the upper reservoir. When the volume of solvent in the upper reservoir reaches the upper bend of the return tube, the solvent and any extracted components are siphoned back to the lower reservoir. Over time, the concentration of the extracted component in the lower reservoir increases. 

This mode of chromatogram development is, in principle, almost identical with continuous development. The only feature that varies is the length of the developing path. In short bed-continuous development (SB/CD), this path is very short, typically equal to several centimeters [23-25]. This is the reason why this mode is preferentially applied for analytical separations. However, a similar technique is applied for zonal sample application and online extraction of solid samples, which are described in the following text. 

Studies designed to improve the determination of environmental contaminants will continue to provide refinements and improvements in the determination of acrylonitrile. The current high level of activity in supercritical fluid extraction of solid and semisolid samples should yield improved recoveries and sensitivities for the determination of acrylonitrile in solid wastes, and the compound should be amenable to supercritical fluid chromatographic analysis. Immunoassay analysis is another area of intense current activity from which substantial advances in the determination of acrylonitrile in environmental samples can be anticipated (Vanderlaan et al. 1988). 

Soxhlet extraction Continuous extraction of sample with boiling solvent Organic compounds in solid samples (e.g. plasticizers in PVC)... 

Figure D1.1.1 Soxhlet lipid extraction unit used for continuous extraction of analytes from a solid into an organic solvent. As the flask containing the solvent is heated, vapors rise in the larger outside tube, through the thimble containing the sample, enter the water-cooled condenser, and liquefy. When the liquid level in the extractor reaches the top of the siphon arm, the extract-enriched solvent returns to the flask.

For the continuous extraction of a solid by a hot solvent, it is better to use a Soxhlet extraction apparatus such as that shown in Fig. 2.96. The solid substance is placed in the porous thimble A (made of tough filter paper) and the latter is placed in the inner tube of the Soxhlet apparatus. The apparatus is then fitted to a round-bottomed flask C of appropriate size containing the solvent and boiling chips, and to a reflux condenser D (preferably of the double surface type). The solvent is boiled gently the vapour passes up through the tube E, is condensed by the condenser D, and the condensed solvent falls into the thimble A and slowly fills the body of the Soxhlet. When the solvent reaches the top of... 

The turn-key multipurpose high pressure pilot unit shown in picture 1 can be used for the continuous extraction of liquid products in a column with structured packings and for the batch extraction of solids in a extraction vessel. It is assembled using the following proven basic modules (see also figure 1) ... 

As reported in a lot of reviews, extractions with supercritical solvents have a very promising commercial potential. Until now the commercialization is mainly restricted to batchwise extraction of solids with carbon dioxide (e g. decaffeination of coffee and tea, extraction of hop). Laboratory experiments and operation of small-scale pilot plants gave favourable economic values for continuous extraction of liquids with C02 and other gases. Only a few extractions with C02 or C HS are performed already on a small industrial scale. For research purposes and product development a new high pressure counter-current extraction plant was erected. To get greater amounts of product the explosionproof plant was constructed in pilot scale using a special modular concept and an effective visual control system. 

The apparatus for Soxhiet extraction is shown in Fig. 14.5 and comprises a flask containing the solvent, a Soxhiet extractor and a reflux condenser (p. 116). The sohd to be extracted is placed in a porous thimble, made from hardened filter paper, and the solvent is heated so that its vapour flows past the thimble, condenses and fills the extractor with hot solvent to extract the solid. When the extractor is full, the solvent (together with the extracted material) siphons back into the solvent flask and the process is repeated automatically. The advantage of this procedure is that fresh solvent continually extracts the solid, which is concentrated in the flask. The disadvantage is that the compound extracted is kept at the boiling point of the solvent for a prolonged period. Soxhiet extractors come in sizes of lOmL to 5000 mL, based on the volume of solvent contained in the extractor. The procedure for using a Soxhiet extraction system is described in Box 14.2. 

In order to extend the range of applications of SCF extraction of natural substances, there are developmental trends towards the construction of systems for the continuous transport of solid materials through pressure vessels. According to the natural substance concerned, a decision must be made between ... 

Soxhlet extraction Equipment used for the continuous extraction of a solid by a solvent. The material to be extracted is placed in a porous cellulose thimble, and continually condensing solvent is then allowed to percolate through it, and return to the boiling vessel, either continuously or intermittently. 

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