Extraction continuous

Many materials have such low distribution ratios that neither separatory funnels nor the older, no longer commercially available, Craig apparatus are practical to use. What is needed is a continuous extraction with an apparatus that can be left unattended for long periods of time. Several different approaches are described in this chapter. 

To have a high efficiency in a continuous extraction, the following factors are beneficial  

With low D s, a large volume of extracting solvent is needed. However, it can be the same solvent used over and over, if it is evaporated from the extract between uses. A 50 mL sample may have 50 mL of extraction solvent initially employed for an actual ratio of 1 1. If however, the solvent is redistilled and reused 20 times, then the relative volume is 1,000 to 50 or a 20 1 ratio. A high D is desirable, but if you had a high D, then a continuous extraction probably would not be necessary. 

This is the volume of extracting solvent required to reduce the amount of the desired compound in the sample to one-half of its original concentration. A distribution factor, k, can be used to evaluate individual systems. 

Concentration of solute in the extracting solvent Concentration of solute in the original solution W = the original solution volume and V = the half extraction volume. 

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A drop of an aqueous solution of the mixture to be separated is now placed near the bottom of the paper strip and allowed to evaporate in the air. The strip is now again suspended in the closed cylinder, but with the bottom of the strip just immersed in the solvent. The capillary action of the paper will cause the solvent to rise steadily up the strip, and during this process the solvent, which now contains the mixture in solution, is continuously extracted by the retained water molecules in the paper. A highly hydrophobic (water-repellent) solute will move up closely behind the solvent-front, whereas a highly hydrophilic solute will barely leave the original point where the drop of the mixed solutes in solution has been dried. In an intermediate case,... 

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... 

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

Attention is directed to the great advantage of continuous extraction over manual shaking in a separatory funnel for liquids or for solutions which tend to froth or which lead to emulsification comparatively little difficulty is experienced in the continuous extraction process. 

Extraction of steam distillates by solvents. The apparatus, depicted in Fig. 11,58, 7, may be employed for the continuous extraction of substances which are volatile in steam from their aqueous solutions or suspensions. Solvents of the ether type (i.e., lighter than water) or of the carbon tetrachloride type (i.e., heavier than water) may be used. A reflux condenser is inserted in the Bl9 socket, whilst flasks of suitable capacity are fltted into the lower B24 cone and the upper. B19 cone respectively. For extraction with ether, the flask attached to the upper. B19 cone contains the ether whilst the aqueous solution is placed in the flask fltted to the lower B2i cone the positions of the flasks are reversed... 

Alternatively, the following procedure for isolating the glycol may be used. Dilute the partly cooled mixture with 250 ml. of water, transfer to a distilling flask, and distil from an oil bath until the temperature reaches 95°. Transfer the hot residue to an apparatus for continuous extraction with ether (e.g.. Fig. II, 44, 2). The extraction is a slow process (36-48 hours) as the glycol is not very soluble in ether. (Benzene may also be employed as the extraction solvent.) Distil off the ether and, after removal of the water and alcohol, distil the glycol under reduced pressure from a Claisen flask. 

Hexamethylene glycol, HO(CH2)gOH. Use 60 g. of sodium, 81 g. of diethyl adipate (Sections 111,99 and III,100) and 600 ml. of super-d ethyl alcohol. All other experimental detaUs, including amounts of water, hydrochloric acid and potassium carbonate, are identical with those for Telramelhylene Glycol. The yield of hexamethylene glycol, b.p. 146-149°/ 7 mm., is 30 g. The glycol may also be isolated by continuous extraction with ether or benzene. 

Better results are obtained if a continuous extraction apparatus (e.g. Fig. II, 44, 2) is employed. Ether may also be used as the solvent. 

Place 200 g. (172 -5 ml.) of redistilled furfural (1) in a 1 litre beaker, provided with a mechanical stirrer and surrounded by an ice bath. Start the stirrer and, when the temperature has fallen to 5-8°, add a solution of 50 g. of sodium hydroxide in 100 ml. of water from a separatory funnel at such a rate that the temperature of the reaction mixture does not rise above 20° (20-25 minutes) continue the stirring for a further 1 hour. Much sodium furoate separates during the reaction. Allow to cool to room temperature, and add just enough water to dissolve the precipitate (about 65 ml.). Extract the solution at least five times with 60 ml. portions of ether in order to remove the furfuryl alcohol the best results are obtained by the use of the continuous extraction apparatus (charged with 350 ml. of ether) depicted in Fig. //, 44, 2. Keep the aqueous layer. Dry the ethereal extract with a httle anhydrous... 

Vote 2. With diethyl ether continuous extraction has to be performed. 

Mote 4. Continuous extraction with diethyl ether can also be carried out. 

Continuous Extractions An extraction is still feasible even when the component of interest has an unfavorable partition coefficient, provided that ah other components in the sample have significantly smaller partition coefficients. Because the partition... 

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. 

Miscellaneous Pharmaceutical Processes. Solvent extraction is used for the preparation of many products that ate either isolated from naturally occurring materials or purified during synthesis. Among these are sulfa dmgs, methaqualone [72-44-6] phenobarbital [50-06-6] antihistamines, cortisone [53-06-5] estrogens and other hormones (qv), and reserpine [50-55-5] and alkaloids (qv). Common solvents for these appHcations are chloroform, isoamyl alcohol, diethyl ether, and methylene chloride. Distribution coefficient data for dmg species are important for the design of solvent extraction procedures. These can be determined with a laboratory continuous extraction system (AKUEVE) (244). 

In the continuous process for producing phosphatidylcholine fractions with 70—96% PC at a capacity of 600 t/yr (Pig. 5) (16), lecithin is continuously extracted with ethanol at 80°C. After separation the ethanol-insoluble fraction is separated. The ethanol-soluble fraction mns into a chromatography column and is eluted with ethanol at 100°C. The phosphatidylcholine solution is concentrated and dried. The pure phosphatidylcholine is separated as dry sticky material. This material can be granulated (17). 

Aroma Distillate. Used by the flavor industry, aroma distillates are the product of continuous extraction of the plant material with alcohol at temperatures between ambient and 50°C followed by steam distillation, and, lastly, concentration of the combined hydro—alcohoHc mixture. On cooling, terpenes often separate from the aroma distillate and are removed. 

Hydrolysis by Steam. High pressure steam, 4.5—5.0 MPa (650—725 psi), at 250°C in the absence of a catalyst hydroly2es oils and fats to the fatty acids and glycerol (20). The reaction is commonly carried out continuously in a countercurrent method. The glycerol produced during the reaction is continuously extracted from the equiUbrium mixture with water. A yield of 98% can be achieved. Currentiy, the preferred method to produce soaps is steam hydrolysis of fats followed by alkaU neutrali2ation of the fatty acids. 

Karr and Scheihel [Chem. Eng. Frvg., 50, Symp. Set 10, 73 (1954)]. Continuous extraction of acetic acid between methyl isohiityl ketone and water, and... 

FIG. 15-21 Continuous extraction of n-hiitylamine from kerosine into water. T = 1.23 ft, Z = 1.56 ft, no air-liquid interface, impellers centered, Vr/Ve X 1-57, residence time X 1.08 min. To convert feet to meters, multiply hy 0.3048 to convert inches to centimeters, multiply hy 2.54 and to convert horsepower to kilowatts, multiply hy 0.746. [Overcashiet Kingsley, and Olney, Am. Inst. Chem. Eng. J., 2, 529 (1.956), with permission.]... 

Flynn and Treybal [Am. Inst. Chem. Eng. J., I,. 324 (1955)]. Continuous extraction of benzoic acid from toluene and kerosine into water baffled vessels, turbine agitators. Stage efficiency is correlated with agitator energy per unit of liquid treated. 

Ryon, Daley, and Lowrie [Chem. Eng. Ftog., 55(10), 70, (1959), U.S. AFC ORNL-2951, I960]. Continuous extraction of uranium from sulfate-ore-leach liquors and kerosine -t- trihiityl phosphate and di(2-ethylhexyl)-phosphoric acid baffled vessels, turbine agitated. There is strong evidence of the influence of a slow chemical reaction. 

Ryon and Lowrie (U.S. AEC ORNL-3.381, 1960). Batch and continuous extraction of uranium from aqueous sulfate solutions into kerosine -t- amines, stripping of extract with aqueous sodium carbonate baffled vessels, turbine agitated. A detailed process study. 

Simard et al. [Can. J. Chem. Eng., 39, 229 (1961)]. Continuous extraction of uranium from aqueous nitrate solutions into kerosine -t- trihiityl phosphate and from sulfate solutions containing tricaprylamine unbaffled vessel, propeller agitated. Process details for high recovery and low reagent costs. 

Once the value of k is obtained from the batch data, it can be related to a continuous extraction via the correlation ... 

A monoacetate can be isolated by continuous extraction with organic solvents such as cyclohexane/CCl4. 

The solution is then placed in a continuous extraction apparatus (Org. Syn. 3, 88) and the 2-furylcarbinol is extracted with 1500-2000 cc. of ether (Note 4). The extraction is complete after six to seven hours. 

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