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A large Soxhlet-Type Extractor E. V. P.41WTER1, University of Texas, Austin, Texus
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a series of investigations involving the removal of *DURING wax from cotton fabric and yarn in various stages of manu-
facture, a need developed for a large Soxhlet-type extractor. Large extractors have been described (1, d ) , but they are only about 40 times the capacity of the standard Soxhlet (about 200 ml.) while a capacity of approximately 200 times was desired. The extractor described here was designed to handle 100 to 200 skeins of yarns or 3 to 5 pounds of raw cotton, sliver, or fabric. The extractor was operated successfully with nine different solvents, from diethylether (boiling point 34.4" C., 93.9" F.) to a light naphtha (boiling point 150" C., 302" F,), The operation was similar t o a standard Soxhlet, the solvent being "dumped" from the sample and renewed every 4 minutes for 8 hours. Ethyl and methyl alcohols had minimum cycle times of 8 1
minutes because of their relatively high heats of vaporizatiori Carbon tetrachloride gave some trouble due t o the slow formation of hypochlorous acid which attacked the galvanized sheet iron, the copper tubes, and rondensers. ('hloroform gave no difficultv. DESIGN
The principal features and general dimensions of the extractor are illustrated in Figures 1 t o 3.
Present address, Fabric Research Laboratories, Inc., Boston, Mass
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t Figure 2. Detail of Sample Tra>A.
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i Figure 1. A. B. C.
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Cut-Away View of Soxhlet-Type Extractor
Glans condenser Removable lid Cooling water inlet with pressure gage D . Automobile radiator condensers E . Water outlet with temperature gage F. Deflector skirt c. Body of 24-gage galvanized sheet iron, 18 inches wide to fit snug OD both sidea of radiator#
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Sample tr2y-and rack 1-inch angle iron supports for tray K. Steam coils with prrqnurr gage trap L. steam
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M . Angle iron legs
N- Drain P.
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Observation port C clamps on lid
Sample rack Sample spare
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Sample tray Siphon
Two automobile radiator cores provided adequate condenser capacity. It was not necessary to seal these radiators to the extractor, since a snug fit on all sides retained all the vapors. The glass condenser on top of the extractor served t o indicate by cloudy vapors when the boiling rate was in excess of the condenser capacity. The condensed solvent poured off the deflector into the sample tray across its entire width, thus reducing the possibility of any channeling through a large sample. The liquid was boiled in the bottom by the steam coil (15 feet of 6/g inch copper tubing) and the vapors rose from a surface area of 540 square inches (0.35 square meter), reducing entrainment and ensuring a pure solvent feed t o the sample. The sample tray was simply a box with a siphon tube in one side. Tests of several different sizes and numbers of siphon tubes resulted in the selection of the 6/8 inch copper tube as shown. This tube proved the most satisfactory, emptying 3 gallons of solvent from the tray in little more than one minute. As the liquid level reached the bottom of the tray, the siphon was broken because the open end of the tube cleared the bottom of the tray by 0.125 inch. With some solvents, as in the conventional Soxhlet extractor, it was possible t o condense liquid into the tray so rapidly that the liquid could not be removed fast enough to break the siphon. However, this presented no serious difficulty, since this condition occurred only for cycle times less than the standard time of 4 minutes. The cycle time was regulated by adjusting the steam supply. The sample wa6 held on a rack which had a screen bottom and no sides and was providkd with a handle a t the top t o facilitate convenient carrying. The bottom of the rack cleared the tray bottom by 1 inch, leaving a drain space which aided in removing dirty solvent from the sample each time the tray emptied. The total contact volume available for sample and filled with solvent was 11 x 17 X 4 inches or 748 cubic inches (12 liters). It would be a simple matter to provide screen sides and top for the rack to hold chips, leaves, or pieces of any other material one desired to extract. The principal difficulty in design was the lid seal. Several modifications were tried until the one shown proved satisfactory. The lid seat, J in Figure 3, was made from four pieces of angle iron laid carefully in a square on a flat surface and gas-welded a t
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ANALYTICAL CHEMISTRY
378 the mrners with the upright web on the inside. The upper edge was then squared and finis d flat with a hand file. The lid frame H in Figure 3, was made rom four pieces of 1 X 2 inch steel, slotted and clamped in place on top of the angle-iron frame, in which position the four frame pieces were electric-welded to one another. These two surfaces (inside the slot) were then sufficiently true; a double gasket of felt l/16 inch thick and a/l6 inch wide provided a seal that prevented the escape of any solvent vapors from the edge of the lid during operation. An 18-inch square sheet of copper was laid on top of the lid frame and bolted to it every 3 inches, and the seam was soldered over to prevent leaks.
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solvent in the bottom of the extractor, pure vapors were boiled off and condensed into the tray, leaving about a quart of concentrated solution containing the impurities. This residue was then drained off and the bottom washed with about a pint of pure solvent from the tray by raising the check valve slightly. The drain valGe was closed and all t h e clean solvent drained back into the bottom. Cooling water was then circulated through the steam coils for several minutes in order t o cool the solvent enough t o aklow removal of the lid without excessive vapor loss. The special tray could then be removed and the sample tray inserted ready for operation. At the end of the extraction the solvent was cooled as above prior to removal of the lid and sample. The steam was always turned off just as the tray began to empty, in order to allow for complete drainage of solvent from the sample. CONCEYTRATION OF EXTRACT
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Figure 3. Detail of Lid Section A - A of Figure 1 * A. B. C. D.
Steel ring of '/c inch plate iron Steel ring of '/2 inch plate iron Steel ring of s/s inch plate iron 10-inch diameter glass disk 1/1 inch thick E. 10-inch diameter glass disk a / g inch thick F. Felt or neoprene gaskets G. Cover sheet of lid H . Lidframe J . Lid seat of 1-inch angle iron ' K . Extractor body
The porthole in the lid enabled the entire interior, boiling solvent, and solvent level in sample tray, t o be observed during operation. Thus the cycle time was determined by watching the rise and fall of solvent in the sample tray and taking the time between two rises. The 18-inch square opening provided by the lid facilitated easy charging and removal of the trays used. EXTRACTION OF SAMPLE
-4s with the laboratory Soxhlet, operation consisted of adjusting the heat input for proper solvent rate. The factor limiting solvent rate was the condensing capacity of the radiators, which in turn depended upon the rate of flow and temperature of the inlet cooling water. The maximum operating pressure of the inlet water to the radiators was about 20 pounds per square inch (58 kg. per sq. cm.) gage. With most solvents the pressure was set a t 15 pounds per square inch (44 kg. per sq. em.) gage, but with the alcohols it was necessary t o operate a t maximum. With most solvents 0.5 t o 2 pounds per square inch (0.15 t o 6 kg. per sq. cm.) gage steam pressure was sufficient t o maintain. optimum solvent rate, but with the highLboiling naphtha it was necessary to use 125 pounds per square inch (366 kg. per sq. cm.) gage steam. The solvent rate was never allowed t o get any higher than that which gave an outlet cooling qater temperature 20' F. (11' C.) below the boiling point of the solvent.
After the 8-hour extraction period, the steam was turned off and the solvent cooled as described above. The sample tray with sample was then removed and the special square tray inserted. ill1 but about 2 or 3 pints (1 to 1.5 liters) of the solvent were then boiled off and collected in the tray. These 2 or 3 pints still in the bottom and containing the extracted wax were then drained into an appropriate container, and an extra pint of clean solvent from the tray above was allowed to wash over the bottom and also drain into the container. Since this left practically no wax in the extractor, a fairly accurate estimate could be made of the amount of extract. Each time the extractor was started, the body n-as full of air which had to be expelled from the .top by the rising vapors. Some vapors were entrained by this air and the solvent odor was strong for a few minutes. ;Is soon as the air was out, however, no more odors could be detected. After the rate was adjusted by the steam valve, the extractor required no more attention for the $-hour extraction period. COST
The Chevrolet radiators used cost about $20 each and the galvanized sheet iron, steel, glass, and fittings cost about $30. A mechanic assembled the unit in two weeks. The total cost, then, was approximately $150. Stainless steel would be more satisfactory but was unavailable a t the time. Had it been used the cost would have been roughly doubled. Cooling R-ater was available from a circula ing system utilizing a cooling tower supplying water to this and other units. Should it be necessary, however, t o use tap water and discard the effluent, the maximum consumption would be approximately 250 gallons per hour. At 30 cents per 1000 gallons, the cost would amount to about 70 cents for one 8-hour extraction period, including.solvent purification and concentration of extracts. SUMMARY
A large-size Soxhlet-type extractor provides very thorough solvent extraction of samples up to 748 cubic inches (12 liters) in volume a t atmospheric pressure. Three gallons of hot solvent are added t o and removed from the sample every 4 minutes (for most solvents, 8 minutes for alcohols) from a total solvent volume of about 38 liters (10 gallons). The large condensing capacity is obtained by means of two automobile radiators. ,4special tray in place of the sample tray facilitates purification of solvent prior to extraction and concentration of extract afterwards. A large lid with vapor-tight seal provides easy charging of sample. ACKNOWLEDGMENT
Acknowledgment is hereby made t o J. W. Moore and C. M. Furgason for many helpful ideas and suggestions.
PURIFICATION OF SOLVENT
Prior to the extraction of a sample, the solvent was purified by use of a special tray (not shown in figures) in place of the sample tray. This was 18 inches square and 10 inches deep and had a 1-inch bronze check valve soldered in the middle of the bottom. A piece of string was clipped t o a short wire loop soldered t o the seat of the check valve and run out through the condensers at the top. Pulling the string raised the valve seat and drained the tray. Starting with about 10 gallons of impure
LITERATURE CITED
(1) Jonnard, R.,IND. ENG.CHEM.,A N ~ LED., . 16,61 (1944). (2) Smallwood, E.,Ibid., 14,903 (1942). RECEIVED January 11, 1946. Developed for a project sponsored by the Texas Cotton Research Committee at the Bureau of Industrial Chemistry, University of Texas, Austin, Tex.
