Countercurrent Liquid-Solid Extraction

recovery of zein from corn proteins. The commercial solvent extraction plant for the recovery of cocoa butter from flaked cocoa beans, expeller cake, ...
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Countercurrent Liquid-Solid Extraction THE KENNEDY CONTINUOUS PILOT PLANT FRANK LERMAN, ANGUS B. KENNEDY, AND JEROME LOSHIN Vrclcan Copper and Supply Company, Cincinnati, Ohio Numerous pilot plant runs on over 20 dieerent lcinds of extractable solids have been made to demonstrate the effectiveness of the Kennedy extraction system for continuous, countercurrent extraction and product recovery. The continuous pilot plant, of type 316 stainless steel construction, has proved the versatility, efficiency, and flexibility of the Kennedy extractor, and has indicated the quality of the products obtainable. The pilot plant has been an invaluable demonstration unit and also has given excellent data for use in design of commercial units. iMaterials heretofore considered unsuitable fbr continuous solvent extraction have been readily and thoroughly extracted. A full program of pilot plant work has been scheduled for the coming months, involving several new extractable materials.

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ARLY in the development work on the Kennedy extraction system a t the Vulcan Copper and Supply Company, the need was recognized for a continuous pilot plant that could duplicate closely commercial solvent extraction and recovery operations. Previous pilot plant and commercial installations built by Angus B. Kennedy, inventor of the extractor, already had indicated the versatility and flexibility of the Kennedy extractor. The first installation of this type was built in 1927 i n Charlottesville,Va., for the extraction of natural dyes and tanning extracts from bark and wood. This machine was of rather crude construction, but clearly demonstrated a considerable saving over the leach tubs and autoclave methods of extraction in general use. I n later years, the extractor was redesigned for the solvent extraction of vegetable oils, and a number of patentable improvements were incorporated at t h a t time; these greatly increased the efficiency of the apparatus. I n 1941, a small brass extractor of this improved design was installed a t the WoIf Company’s plant, Chambersburg, Pa. The capacity of this small pilot extractor was approximately 1 cubic foot of solids per hour for a throughput time of 1hour. I t s prime purpose was t o furnish design data for the large commercial plant, which was subsequently installed a t Hershey, Pa., for the extraction of cocoa butter from cocoa residues. This extractor was used also to solvent extract various vegetable oilbearing materials, such as tung kernels ( I ) , soybeans, and flaxseed, and t o rarrv out certain special liquid-solid contacting op-

erations, such as the water washing of cellulose acetate and the recovery of zein from corn proteins. The commercial solvent extraction plant for the recovery of cocoa butter from flaked cocoa beans, expeller cake, filter cake, hulls, and foots has been in operation for 6 years a t the soap plant of the Hershey Estates, Hershey, P a It has a capacity of 50 tons per day of expeller cake. A small brass extractor was installed a t the Eastern Regional Research Laboratory of the U. S. Department of Agriculture a t Philadelphia, Pa., to extract vitamins from various vegetable materials. Its capacity is approximately 1 cubic foot per hour of solids for 1 hour’s throughput contacting time. Recently, a pilot plant of steel construction, with a n extractor of about four tinies the capacity of the previous pilot units, was built and operated a t the Northern Regional Research Laboratory of the U. S. Department of Agriculture a t Pcoria, Ill., for tho extraction of soybeans with alcohol. A large srale Kennedy extractor mas built and installed on the West Coast for the acid M ashing and water neutralization of pectin for peal: war requiremonts. Cypress wood was used as the substitute construction material; it resisted the acid corrosion for the emergency period. It was to extend and confirm these previousextractions, to tect extractions of numerous other materials using various solvents, and to obtain basic operating data for the design of commercial installations for processing specific materials t h a t the present continuous extraction and recovery pilot plant has been built on the grounds of the Vulcan Copper and Supply Company in Cinrinnati. DESCRIPTION OF THE KENNEDY PILOT PLANT

The pilot plant is installed in a concrete building, 35 feet long by 19 feet 6 inches wide, with a roof of corrugated sheet metal sloping from 22 feet to 15 feet above the concrete floor. An adjacent concrete building, 22 feet 6 inches long by 18 feet wide, with the roof sloping from 23 feet to 14 feet high, houses the preparation equipment. This equipment consists of a corrugated roller mill and a flaking mill for cracking and flaking the seeds, beans, or kernels i n preparation for extraction. Near these joint buildings is a solvent storage building of similar construction. The layout of equipment in the preparatioii and extraction buildings is shoi5 n in Figures 1, 2, and 3.

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The drained rcsitiuc is batch fed int.0 the solvent dryer n-here solvent vaporization takes place scmicontinuously under either atmospheric or vacuum condition$. The vapor is carried from the dryer through a stcamjacketed filter drum. Here, in passing through a cloth-covered, perforated metal cartridge, the vapors deposit the entrained dust before flowing int,o the condensVAPOR ing system. DETECTOR The solvent feed to the extractor is pumped from the weigh tanks by a proportioning pump through the tubes of a heat exchanger where, by controlled hot water F L O O R PLAN or steam flow into the KENNEDY PI LOT SOLVENT EXTRACTION PLANT shell side, the solvent leaves a t the desired temFigure 1 perature for extraction. It then flows into the drag chain conveyer section of the extractor at. a n intermediate level and gives a final The Kennedy extraction syst,em is designed around the Kenwash t,othe extracted residue on t,he lower flights of the conveyer nedy extractor, a cross section of which is shon-n in Figure 4. as they are carried upward. The solvent collects at the boot of The continuous extractor consists of a series of enclosed exthe conveyer, which serves as the last wsidue extraction section, and then overflow from seciion t,o section of the extractor traction chambers or sections; into each of these is fitted an imin countercurrent movement t,o the solids. peller wheel assembly for moving the solid materials through The solvent, containing the extracted material in solution, the liquid. Each impeller wheel assembly consists of an enleaves the filter section with a small content of fines, in no way closed hub (the lower portion of the hub is partially submerged comparable t,o thc amount of fines in the solid feed material, as most of the smaller particles are carried along with the coarser in the liquid), four curved blades of perforated metal, and a shaft solid residues. A large portion of the fines entrained in the extending through bearings in the sides of the extractor n-alls. liquid are removed in the self-filtering operation in the extractor The impeller wheel assemblies are driven from the outside by a as the solvent fiows through tlie solid materials betxeen sections common drive shaft through a xyorm and gear arrangement. of the extractor; also the coarser fines settle out' of the liquid in the sections (particularly the filter section) and are carried back. On leaving the extractor, the extract liquor flows by gravity into SXTRACTIOS AKD RECOVERY PROCESS the miscella receiver; from the bottom of the receiver it,ispumped by a proportioning pump through a laboratory Sparkler filter. The process is as shown in Figure 5. K h e n the solid material Here the remaining fines are deposited on the prccoated paper being processed is required in flake form for extraction, IL 1s disks covering the filter plates. The f i h a t e flo~vsinto a iveigh first put through tlie corrugated rolls of the cracking mill. S e x i , tank. the moisture content is adjusted to give the best, flaking propThe solvent recovery unit of the pilot plant was designed t o erties, and then t,he ma,t,erialis flakcd i o the desired thiclrness by separate vater-immiscible solvents from nonvolatile liquid passing it one or more times through the smooth rolls of the extracts, such as is normally the case in extracted vegetable oil flaking mill. and animal fat recovery operations. Extractions involving waterThe material, reduced to the most suitable form and size for miscible solvents, or volatile or solid extracts, require special extraction, is placed in the feed'hopper of the Kennedy extractor. recovery equipment, axmilable in t,he laboratories and distillaFrom here, controlled quantities are fed a t a COnSTant rate b>- a tion pilot plant elsen-here in the VuIcan plant. feed screm conveyer into the first extraction section of tlie cxI n . normal retractor. The material then is carried through the extraccoveries. t,he actor in countercurrent flow t o t.he solvent. cumulai'ed quantity Each portion of immersed solid material in a section is of solvent extract collected by a n ,impeller blade and carried through the liquor is pumped or liquid in that section. As the solids are carried up the carried by vacuum curved wall of that section, they are slightly compressed from the weigh tank between the wall and the curved blade to form a wedge, a t a constant ratewhich is lifted above the liquid level and sloughs off the usually thr ec or blade into the next section. This slight compression and more times the rate draining, through lifting the solids above the liquid level, of inflow t o the tank reduce t8heamount of entrained liquid carried over t o t,he -throughthe single succeeding section. of the vel tical, tube On striking the liquid surface i n the succeeding section, rising-film cvaporathe wedge readily breaks up and disperses. The solids tor and through its immersed in the liquid of this section as distinct particles entrainment pepaare again collected by an impeller blade and moved through rator. From here, the liquid. thc vaporized solThe cycle in each section of dispersion, immersion, and vent iscarried to the collection of the solid in the liquid, of movement t,hrough condensers, and the the liquid, and of the compression, lifting, and draining of liquid, often conthe solids is the basis of the intimate and thorough concentrated t o above tacting betm-een solid and liquid for exhaustive extraction 90% extract in low of solute. temperature vacThe extracted solids arc gravity drained of a good part u u m operation, of the entrained solvent while being carried up the drag flows t o the top of chain conveyer, and then are dropped into a collecting can the stripping Figure 2. View in Preparation with a perforated false bottom for separating additional column. R iiilding liquid drainings.

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Figure 3.

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View i n Extraction Building

Here, the liquid flows down through the packed stripping column (filled with Raschig rings) in countercurrent flow t o stripping steam. T h e stripping column is jacketed so t h a t the heat required t o vaporize the residual solvent may be added through the shell of the column. T h e vaporized solvent and the stripping steam pass through a n entrainment separator above t h e stripping column and from there to the condensing system. T h e solvent-free extract flows into a vacuum oil receiver. The condensate is collected in one of two vacuum condensate receivers and flows from them t o a decanter for separating water from solvent so t h a t the latter may be re-used. The vapors from these condensers flow t o a large water-cooled, tube-in-shell vent condenser before venting to the air. When the condensation is under vacuum, the vapors are carried through a steam jet ejector t o the vent condenser. SPECIAL DESIGN FEATURES

In the pilot plant all items that contact solvent, miscella, or oil are made of type 316 stainless steel. This material was chosen because i t is resistant to the widest variety of liquids, solids, or vapors that may be involved in the processing. The extractor throughput time can be varied from 30 to 90 minutes by adjusting the variable speed drive. The capacity of the extractor ranges from 1 to cubic foot per hour of solid material, depending on the throughput time. With the usual oil-bearing materials, having densities from 20 to 30 pounds per cubic foot, this amounts to about 7 t o 30 pounds per hour. The feed screw and drag chain conveyer are synchronized with the extractor drive. To meet special requirements outside the operating ranges mentioned, adjustments and changes in the extractor can be made readily by changing sprockets and gears.

The number of sections in thc pilot extractor are fixed. However, means are available to determine the proper number of sections for a commercial machine. T o decrease the number of effective extraction sections, the feed hopper assembly of the pilot unit may be moved to discharge into a n intermediate section. To increase the number of extracting sections, the extracted solids discharged from one run may be used ns the feed material for a subsequent run. The solvent feed rate can be varied froin 0.5 to 11 gallons per hour by adjusting the solvent feed pump. The solvent rate used depends on the concentration of solute desired i n the extract liquor and the amount of solvent carried from the extractor by the wet extracted material. In the design of the vacuum dryer, the advantages of operating on a continuous basis were counterbalanced by the high cost of devices for continuously charging and discharging the material into and from a vacuum. A compromise between batch and continuous operation was obtained by uring a continuous dryer with a throughput capacity of about G times t h a t of the extractor and providing vapor-tight feed and discharge hoppcrs with cnough volume to allow a n 8-hour run of wet extracted material. T h e holdup time in the drying section can be varied from 20 t o 90 minutes. The oil and solvent recovery system, when operating at 10 inches of mercury absolute pressure, can recover from 3 to 15 pounds of oil per hour, depending on the original concentration of oil i n the miscella. Both the evaporator and stripping column heating jackets are piped to allon the use of either steam or hot water as a heating medium.

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the solids work through t,lie ext,ractor and start to discharge, solvent flow is resumed a t the required rate and proper temperat,ure. This start-up procedure is used t o build up equilibrium concentrations quickly. Another 2 to.4 hours are required normally to reach dynamic equilibrium in the eatraetor. Runs are then continued from 4 to 24 hours, depending on what specific information or quantity of product is desired. The recovery syabems can be operated concurrently with t'he extractor, but are frequently operated during the clean-out period 01' the preparatory period for a succeeding ruii.

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RECEIVER ___

Figure 4.

Schematic Drawing of

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Solids impeller dimensions: 14 impellers are 8 inches in diameter X 6 inches in width: 1 impaller is 11 25 inches in diameter X 6 inches in w.idth: each impeller has 4 blades of 24-gage stainless steel, perforated with 1/16-inch holes, on '/sa-inch centers

The introduction of complete and modern safety eyuipnient, and practices mas one of the foremost considerat,ions in the design of the plant. Electrical equipment in the extraction and solvent storage buildings is of Class I, Group D rating. A flammable vapor detector samples the air in sequence from eight critical points in the pilot plant. If the flammable solvent concentration in t,he air reaches 40% of the lower explosive limit, an alarm sounds, all motors are shut' off, vent louvres below the windows autoinatically open, and the vent,ilation blower changes rhe air in the building 30 times a n hour instead of the 10 times an hour for normal operation. All equipment, mctal supports, and window frames are grounded positively. TThcncvcr flanimahle solvent is present, in the building, only nonspariting tools are used and only minor repairs are permitted. Other safety features, important but beyond t>hescope of t,his paper, were incorporated in the extraction plant'. As careful a safety engineering job was done for the preparation and solvent.storage buildings. OPERATION O F THE UNIT

The pilot plant' was operated for the first, 6 months on one, two, and occasionally three %hour shifts per day for a 5-dag XI-eek. Hoviever, the demand for applying the Kennedy system to an increasing number of extraction problems has necessit,ated a 3shift, 24-hour per day operation of the pilot plant since the first of this year. Operation for 5 days per week has been continued, except on special, urgent occasions. The extraction pilot plant is under the direct control of the head of the Research and Development Department; he is responsible also for the operation of the Dist'illation Pilot Plant and Laboratory, and the Fermentation and Biochemical Laboratory of the Vulcan organization. The engineers of the Kennedy Extraction Division work closely with him in coordinating and scheduling the pilot plant runs. Close contact is kept also with representatives of various companies interested in the specific runs or for whom the investigations are being made. The shift supervisors are graduate chemical engineers. They are assisted by chemical engineering students of two or more years' training in the cooperative course a t the University of Cincinnati. The shift supervisor and a n assistant operator are assigned for each shift t,o run the plant,. Another assistant is scheduled each shift to carry out the required analyt,icalwork on solid and liquid samples of materials, taken prior to and after processing, or from intermediate processing steps. Anot,her engineer on the day shift correlates these data and prepares the formal reports. I n starting up, the solvent is pumped from a drum outside the building: by a hand pump into one of the weigh tanks. The extractor sections are filled wit,h solvent. Then wit,hout further solvent flow, the snlid material is fed into the extractor. -4fter

DATA OBTAINED

During extraction operation, hourly weight madings are taken for solids and solvent feed rates and extract liquor and solids residue discharge rates to obtain material balances. Samples of the liquid and solid discharged materials also are taken hourly for analysis to obtain a niaterial balance for the extract material. Fines remaining in the exti~actliquor can he measured by weighing the cake of the filter plates after the run or, better, by eollecting a gall011 or more liquid saniple during the run for laboratory filtration, drying, and iveighing. Liquid and solid saniples at intermediate stages of extraction are taken through thr quick-opening st~mplingp x t s located above the junction point between Pach pair of extraction sections. These saniples are taken only at the end of each run t o avoid upsetting material equilibrium during that run. The solid samples are drained to a uniform extent by placing on absorbent paper toweling before analysis. The liquid saniples are settled or filtered free of fines before analysis. Analyses of feed material and final extracted material are run in t,riplicate. Concentrations in intermetliat,e srctioris are usually the result of single analysis. The recovery equipment, both for the estracttd residue and t'he ext,racted material, is operated chiefly to duplicate, on a continuous basis, cornniercial operations to ensure t,hat comparable product quality may be attained. Ternpcrature wid vacuum conditions are measured and maintained cloaely. The concent,ration of the extract liquor after evaporation and before stripping is an example of t>hegood agreement between theory, pilot plant operat,ion, and coinmercial design. From laboratory equilibrium data for a typical vegetable oil in a given petroleum solvent (Sj, the equilibrium concentration at. 180" F. and 20 inches of mercury vacuum is 9394 oil. In the design of a commercial installation for these conditions, a value of 90% oil concentration was used. The pilot plant evaporator, when operated a t this given temperature and vacuum, consistently discharges a concentrated oil-solvent liquor containing From 90 to 927,oil. For each series of runs made on a given type of material (covering a period from 2 days t o a month or more), a Rcsearch Department report is prepared, This report presents briefly but thoroughly t,he n-ork accomplished, the data obbined, and the conclusions drawn. Data usually are prepared as follows: a general summary of conditions and results for each run; an over-all material balance sheet of input and output of the extract,or; and the analytical results on concentrations of solute in solid and liquid at, intermediate and terminal points of the extractor. An over-all solube balance sheet is then presented. Examples of thcse data sheets are shown in Tables I to IV. Charts which show the solute concent,rations plotted against extractor section number on semilog paper are included with the data sheets. Such charts are valuable for design purposes, as ext,rapolation or interpolation of the curves indicates the effect of increasing or decreasing the number of extraction sections. Comparison between curves shows the effects of changes made

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DIAGRAMMATIC FLOW SHEET PILOT SOLVENT EXTRACTION PLANT Figure 5

in the operating variables from one run to another. Typical charts are shown in Figures 6 and 7. When quality determinations are made on the solvent-free extracted residues discharged f i om the dryer or the recovered solute from the distillation unit, these data are recorded in the report. Generally material or heat quantity measurements are not made on either the dryer or distillation unit operations, as these pilot units were not designed for such purposes. This information is unnecessary for design of commercial units because accepted and proved methods of calculation from chemical engineering principles are available. However, careful control of pressure and temperature is carried out in the drying, evaporating, and stripping so t h a t the quality of the products obtained may be an indication of performance in large commercial installations of similar design and under the same operating conditions. EVALUATION OF PILOT PLANT WORK

After 10 months of operation, a review of the results shows that the extraction pilot plant has lived up t o all expectations and justified t h e purposes for which it was built. I n operations with a number of different extractable solids and several solvents, it hm proved versatile and flexible. It has made apparent the extractive actions of the Kennedy system with sufficient clarity t o give a good indication of their effectiveness even when extrapolated t o large scale operation It has supplied the basic infor-

TABLEI.

GENER.4L SUMMARY FOR

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TABLE 11. SUMMARY O F AN.4LYTICAL RESULTS= 1/22/48 45 9.5 40.9 32.0

5.6 1.2

Solvent ratio Solvent feed temperature, F. Extractor temperature F. Oil in extracted meal (dry basin). % Oil in oI .-. ... miscc”. 5U*, ,o Fines in unfiltered miscella, % Fines in unfiltered miscella (after settling 1 lir.), % Solids in drained meal, % . . . - oil in mRrc b ~~

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mation on a large number of extraction pioblenis to permit design of commercial installations with guaranteed performance. Approximately 115 runs on over 20 different kinds of solid material (some prepared several ways) and using various solvents or solvent mixtures have been completed in this continuous pilot plant during operation for less than a year. Materials oi vegetable origin from which oils have been recovered include soybeans of various flake thickness, ground or flaked cottonseed (both cooked and uncooked and containing a wide range of fines content), castor bean flakes and pomace, sunflower seed, and flaxseed. Tallow and grease have been extracted from various packing house materials containing from 5 t o 607, animal fat. Animal tissues processed include both pressed and unpressed cracklings, steamed bones i n the dry and wet states, and dried pancreas fines. Water extractions have been accomplished on coffee, seaNTeed, and paper pulp. Special extracts, such as carotene, chlorophyll, and cholesterol have been recovered in the pilot plant. Petroleum fractions, acetone, alcohols, trichloroethylene, and hot and cold water, as well as mixed solvents, have been used as extractants. Granular, powdery, flaky, gelatinous, fibrous, stringy, and pulpy material all have been handled readily in the extractor. The settling action in the sections of the extractor, particularly in the filter section, and the filtering action of the solids on the

14.9 1.57 135 135

0.7 24.6

0.3 0.04 51 X 100) 98.5

Data sheet taken from research department report on extraction of rolled and cooked cottonseed meats as normally prepared for hydraulic pressing. b Lb. of oil per Ib. of dry oil-free meal.

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Feed Water (as received), % Fat, % Miscella Fat. % Fines, % Fat in,mrtrc, % Section 1 3 5

7 9

13 Fat in final mar0 % F a t in solvent drhned from marc,

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:amed bone.

43.4 ”O 31

15 0.61 0.61

4.8 0,083

40.0 33.0 21.3 14.4 7.4

11.7 8.6 5.1 2.9

2.4 1.73 1.04 0.923 0.60

1.14

11

%

3

2.2 11.3

4.0

1.6 0.82

1.7 1.5 0.22

0.49 0.6 0.46

37.3 4.5

0.60

0.41 0.5

0.46

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H M L i E i U RATE 7 . 1 L B E . / H R . S O L V E K T F E E D R l T E 17.3 L B S . l H R . EXTRACTOR TE"PER4TURE 128°F. P E R C E Y i O I L l i l MEAL U H ? R I BASIS H E A L ENTERS AT 7 . 7 P E R C E N T kdTsR H E A L DATA FO? H E A L L E A Y I N O S E C l l O Y H

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EXTRACTOR S E C T I O N II-IhCTSi SEC-lln

Figure 6. Extraction Profile on Rolled and Uncooked c'Bollie" Cottonseed M e a t s

Figure 7.

Extraction Profile for Partially Pressed Meat Cracklings

Flake thickness, 0.013 0.0059 inoh; oil i n micella leaving extractor, 24.6%

counterflowing liquid especially during the movement from section to section, keep the solid fines of the miscella t o a minimum. Normally the tines content is appreciably below 1% by weight of the miscella leaving the extractor; this indicates ready removal of the fines in large scale operations by ordinary clarification methods . As a source of design data for comniercial installations, the pilot plant has proved invaluable. Test runs on extractable material, prepared in various ways, permit determinztion of the most suitable preparation procedure for extraction of the material. Similarly, the optimum extraction temperature, the minimum acceptable throughput time for the solids, and the best solvent t o solids feed ratio may be determined for each inaterial by varying these extraction factors.

TABLE 111.

SUNIVIARYOF hI.4TERI.4L

BALANCES~

Run ______ _~___ 1 2 3 4 Input 7.9 6.2 Feed meal Ib./hr. 5.9 9.1 16.7 13.6 Solvent, ld./hr. 13.0 18.7 Total, Ib/hr. 19.8 18.9 27.8 24.6 output 14.3 9.2 Misoella, Ib./hr. 8.6 13.2 Wet meal Ib./hr. 8.4 10.3 7.9 8.8 Freesolv&drainedfroin\rermeal,lb./hr. 1.2 2.5 1.6 1.6 Total, Ib./hr. 18.1 26.0 23.7 19.6 0.8 1.8 0.9 0.2 Input-output Ib./hr Material unaccounted f o r , % b 4 6 4 1 a Data sheet on over-all material balance for extraction of various preparations of flaxseed. b Material unaccounted for is vented solvent-usually high for pilot operations.

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Run b 2

8

Input Oilin meal, lb./hr. 1.05 0.82 0.74 output Oil in rnisella lb./hr. 1.02 0.81 0.72 Oilin drained marc lb./hr. 0.02 0.01 0.003 0.002 0.0005 0.0005 0ilinfreesolventd;ained froin marc, lb./hr. Total output, lb./hr. 1.04 0.82 0.72 Input-output lb./hr. 0.01 0 0.02 Material unaccounted for 1 0 3 a D a t a sheet on oil balanoes for extraction of soybeans. b Run 1 = flake thickness, 0.012 inoh. run 2 = flake thickness, 0.0098 inch; run 3 = flake thickness, 0.0064 inbh.

As a denionstratiori unit for the benefit of the operator and engineer of the Vulcan Copper and Supply Company, as weH as visiting representatives of other companies, who view the operations through the glass top and the opened sample holes, the pilot extra.ctor exhibits the easy handling of the materials being tested. The extraction cycle in each section can be observed and results compared with those obtainable in a commorcia1 extractor to provide convincing evidence t h a t the large scale unit, of similar construction and under identical operation, n d l give as thorough a n extract'ion and as concentrated a n extmractliquor as t'his pilot extract'or. h large amount of work has been completed in this pilot plant; more remains to be done. The schedule for this extraction plant is filled for the next 3 months with enough work on new mat,eriale tentatively considered to carry the program through the year. X.uns cont'emplated include tests on peanuts, copra, and palm kernels. These runs are expected to show t h a t each of these high oil-content materials can be thoroughly extracted without preliminary pressing operations. It is hoped that suficient time can be allotted for thorough and basic st,udies on a given material with careful variat'ion of all the extraction factors t,o permiE the development of a general extraction theory. Through this work,completed and proposed, the pilot plant is proving that continuous, countercurrent extraction is not a specialized process for a limited number of carefully prepared materials, but that i t is a unit' operation of general application t o ext,ractable solids. ACKNOWLEDGMENT

Credit' is due Newton J. Krug for the mechanical design and supervision in t'hc fabrication of the pilot extractor. The writers acknowledge with full appreciation the expert work of William R. Ludlia, head of the Research and Development Department of Vulcan Copper and Supply Company, and his assistants, particularly Robert E. Benge and Gordon A. Hughmarlr, for their skilled supervision and operation of the extraction pilot plant and their preparation of the Research Department reports. LITERATURE CITED

(1) McIiinney, R. S., Rose, W . G., and Kennedy, A. B., IND. ENE. CHEM.,36, 138 (1944). ( 2 ) Pollard, E. P., S'ix, H. L. E., and Gnstrock. E . A . . I b i d . , 37, 1022 (1946). RECEIVED May 10, 1948.