SELECTIVE EXTRACTION OF VEGETABLE OILS WITH FURFURAL

SELECTIVE EXTRACTION OF VEGETABLE OILS WITH FURFURAL. Richard L. Kenyon, S. W. Gioyer, C. C. Georgian. Ind. Eng. Chem. , 1948, 40 (7), pp 1162– ...
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Selective Extraction of Vegetable Oils with Furfural I

Control Panel for Demon-

* RICHARD L. KENYON Associate Editor

W

In collaboration w i t h

ITH the rise of the soybean aa a major crop in the United States, there has become available a large and dependable supply of soybean oil. In the form in which it is taken from the bean this oil is valuable as a food but is not a good drying oil for paint and v d h uses. However, certain of its constituents are of high value in the latter respect and proper fractionation of soybean oil can yield B superior drying oil. Inasmuch as there is normally an excesa of food oils and a deficiency of high grade drying oils in this country, and as the growing of k x must he subsidized in order to make linseed oil avabble to the paint industry, in su5cient mounts, domestically, the manufacture of drying oil from soybean oil is highly desirable. For more than ten years the Pittsburgh PlateGlasaCompanyhas been following a research program directed at this problem. The project has been suoeeasful in yielding a method for separating the glyceride oils of high iodine value, which are desirable in drying oils, from those of low iodine value which are desirable for processing into food products. Thia has been accomplished through the liquid-liquid extraction of the oils, using furfural as a solvent (14). Although hindered during the war by a shortage of soybean oil, during which tlme the method was applied to hseed oil, it has now been developed to a commercial plant scale. A semicommercisl plant has been in operation with soybean oil sines Boon after the war. Separation of oils into their component glycerides, or groups of glycerides, offers outatanding advantages: production of entirely new oils, not hitherto available; control of characteristies

S. W. GLOYER AND C. C. GEORGIAN Pittsburgh Plate Gloss Co., Milunukee. Wis.

without the variations found in natural products; production from domestic sources of substitutes for unavailable oils. A number of methods have been applied with tbe aim of achieving these or similar purposes. Fractional crystahation (1, 8, 4, 8, l7,29, $9, 61) involves repeated crystallizations from dilute organic solvents, usually at low temperatm. The crystslline materials are filtered with difficulty at low temperatures after long periods of solid phase formation. Although molecular distillation ( 9 , 19, 96) has been s u c c e s ~ fuUy used for the removal of highly valuable minor ingrediedts in oils, it has not been applied on a commercial scale to the fractionation of the component glycerides. Separation has been aebieved by hydrolysis, fractionation of the acids, and reconstitution (%,&). Di5culty is encountered in the separation of acids of different uneatmtion and similar chain length. Although the dehydration of castor oil ( 4 2 , P ) and the isomerization of nonconjugated oils (6, $0, SS, $4, 60) have been studied, no commercially satisfactory chemical means for increasing the unsaturation of the fatty acid radicals of glyceride oils haa been found. A number of techniques have taken advantage of the varying solnhility of glycerides of diEerent degrees of unsaturation in organic solvents. Methods have been developed for the fractional precipitation of glyceride esters from organic solvents ( S I , @ ) and for the solvent fractionation of partially polymerized highly unsaturated glycerides from thoee of lower unaaturation (S,IO).

July 1948

INDUSTRIAL AND ENGINEERING CHEMISTRY

One of the most,recently developed systems employs the variation of solubility in liquid propane to effect fractionation. This method has been applied to the fractionation of fatty acids and their glycerides (21, 22, 24) as well as to the separation of fatty acids and rosin acids in tall oil (23, 26) and the fractionation of oleoresinous gum (26). The principle of liquid-liquid extraction (11, 18, 27, 88, 47, 48) 49) has been well developed, but until recently its application was limited chiefly to the recovery of organic solvents from water, dehydration of acetic acid, purification of rosin, and refining of petroleum. Solvent extraction with furfural is now being applied successfully by the Pittsburgh Plate Glass Company to the separation of vegetable oils of high and low iodine value. As a result of this work, some of the important products which can be made are: a soybean oil of high iodine value that can compete successfully as a replacement for linseed oil; a soybean oil of low iodine value superior to the unfractionated oil for use in food products; a linseed oil of high iodine value with properties similar to those of perilla oil; and a fish oil of high iodine value useful in varnish preparation (18). Furthermore, the method has been made applicable t o the separation of free fatty acids of varying degrees of unsaturation (16,18) and the separation of the fatty acids of tall oil from the rosin acids (16). EXTRACTION PROBLEMS

The separation of two components by means of liquid-liquid extraction is dependent upon the formation of a two-phase system with a partially miscible solvent in which one of the components is preferentially soluble. Certain underlying principles in liquidliquid extraction are analogous to distillation (28, S9, 46)namely, the use of reflux, or the return of part of the extract product to the bottom ofJhe extraction column where it isinequilibrium with the extract solution being removed. On the above basis liquid-liquid extraction was approached by S. E. Freeman, of the Pittsburgh Plate Glass Company, as a possible solution to the problem of separating the component glyceridesof vegetable oils. Early batchwise experiments, using polar solvents, showed that the separation of relatively high and low unsaturates could be effected. Extensive tests aimed a t se'fection of the most desirable solvents followed a systematic procedure: testing for miscibility a t -20 O C. and above with refined soybean oil of iodine value 136; determination of critical solution temperatures; and selectivity tests, to show the spread of iodine value effected in one extraction. These tests and the elimination of solvents requiring low temperatures of operation, and consequently expensive refrigeration, removed from consideration all but a few solvents. Of those remaining, furfural was found to have every desired advantage, except stability, as it had a tendency to form dark, tarry residues when not properly handled. These residues, the formation of which is promoted by the exposure of furfural to heat, light, and oxygen, produce inhibition to oxidation in the oils, which retards the formation of paint films. Experience has shown that furfwal which is carefully distilled, blanketed with an inert gas, and kept from contact with oxygen, light, and excessive heat will not form these deleterious by-products (29). Furfural was selected as the most desirable solvent with the conviction that stabilization could be effegted satisfactorily in an industrial plant, a belief that was later borne out in practice. In developing a continuous process, it was necessary to adapt the system to a countercurrent extraction column. Liquidliquid extraction columns, dealt with extensively in the literature (6, 20, S 7 , 58, 48, 47), were studied in the laboratory, beginning with small units 9 feet high by 2 inches in diameter. These were increased in the pilot plant to &foot height and 3-inch diameter, then carried to the semicommercialscale described below. The three factors considered in column design are height of packing, column diameter, and type of packing. The packing height problem in relation to solvent and reflux ratios was

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studied in the laboratory by the methods of Varteressian and Fenske (49),using equilibrium data obtained in the laboratory and plotted on triangular graph paper. The iodine values of the oils in the conjugate phases were used as the additive physical characteristic. These studies indicated that maximum fractionation of soybean oil would be obtained under the conditions of Table I. TABLEI. CONDITIONS FOR MAXIMUM FRACTIONATION Solvent Ratio

Refluxa Ratio

Column Height Feet of Packing!

14 10 8

4.0 2.6 1.8

72 87 95

reflux feed r a t e , Reflux ratio = extract production r a t e

Some of the results of experimental work on fractionation, which led to the present state of development, have been described by Gloyer (18). SEMlCOMMERCIAL PLANT

I n the process under discussion, fractional extraction is effected in one unit, the extraction column, and the remainder of the plant is devoted to the isolation of the two desired products from their respective solvent fractions and the reclamation and drying of solvent for reuse. A demonstration of the process currently in use by the Pittsburgh Plate Glass Company is found in the semicommercial plant at Milwaukee, Wis. I n this unit 500 to 2000 gallons of feed oil can be processed per day, depending on the solvent ratio used. The plant is described here as a basic illustration of the process. The extraction column is a cylindrical carbon steel vessel 87 feet high and 22 inches in diameter. ft is packed with 0.5inch ceramic Berl saddles to a height of 75 feet, leaving clearance sections of 3 feet at the top and 6 feet at the bottom and open sections for distributors. The column is insulated with a 2inch exterior layer of asbestos paper. Three streams enter this column: feed 041, solvent (furfural), and reflux, which is a portion of the high iodine value oil. These streams are pumped by multistage turbine pumps. Before entering the column each passes through a Brown fin tube preheater, from which the rates of flow and temperature are automatically controlled. These automati'c control instruments, as well as those described later, have 0 to 150% throttling range with automatic reset. Electronic temperature controllers are used for flexibility and low maintenance. The column temperature is controlled by the temperature of the feed materials and ranges from 80" to 125" F., depending upon the oil being fractionated. The oil enters the column through one of three inlets at positions 10, 20, and 30 feet above the bottom of the packing; furfural enters through one of three inlets 10, 20, and 30 feet below the top of the packing; the reflux feed stream enters on a level with the bottom of the acking. These variable inlets allow variation of the effectiveReight of the column packing. Each feed stream enters throu h a hub from which perforated fingers radiate. The rate of oil feed varies, depending upon the solvent ratio (ratio of furfural to feed oil, volumetric) being maintained, from 25 to 80 gallons per hour. Furfural is introduced in a selected ratio of 6 to 14 parts per part of feed oil, traveling downward countercurrent to the rising oil. The feed oil is introduced a t such a height that i t is in equilibrium, within practical limits, with respect to iodine value, with the oilin the raffinate phase flowin past the point of introduction. The rate of addition of reflux oifdepends, of course, upon the reflux ratio to be maintained. (Solvent ratios and reflux ratios used are illustrated b> Tables I1 and 111.) An interface is maintained in the extraction column between the oil feed inlet and the solvent feed inlet; the oil-predominant phase exists in the upper part of the system, the furfural-predominant phase in the lower part. The entering furfural then falls in droplets through the upper, oil-predominant, phase while the entering oil rises in droplets through the furfural-predominant phase. Two products flow out of the column, the raffinate solution, containing the low iodine value oil, flowing from the top and the

INDUSTRIAL AND ENGINEERING CHEMISTRY

1164 TABLE11.

FRSCTIONATIOX

OF

DEGUMMED SOYBEAK

OIL

(In column 87 feet by 22 inches, containing 75 feet of packing) Iodine Values Yields, yo Solvent Reflux ExRaffiExRaffiByRatio Ratio* Feed tract nate tract nate product 2 134.5 152.8 107.8 59 2 40.15 0.65 14 8.33 1.1 134.8 150.9 113.3 57.5 41.9 0.60 a Reflux

feed rate

=

oil feed rate

'

TABLE 111. FRACTIONATION O F RXFINED LINSEEDOIL I N SAXE COLUMN AS TABLE TI Solvent Ratio 7.3 6.0

Reflux Ratio 0.73 0.60

Extract yield,

Iodine Values Feed 179.5 179.5

Extract 195.6 196.1

Rsffina e 121.7 128.6

% 78.5 75 5

extract solution, containing the high iodine value oil, floring from the bottom. In the fractionation of soybean oil, the raffinate solution is comprised of 60 to 70% oil by weight and the extract solution 10 to l5y0oil by weight. The yield of low iodine value raffinate is 30 to 407, and the yield of high iodine value extract is 60 to 70% on the basis of the feed oil (18). The extract stream flows out through EXTR-~CT TREATJIENT. an adjustable overflow leg, where choice of the take-off level controls the height of the interface between the oil- and furfural-predominant phases in the column. The exact position of the interface is not especially important to yield or fractionation, but it must be held constant, as the yield changes during its movement. From the overflow leg the extract is piped down to the level of the bottom of the column, thence up to the extract evaporator, oper-

ating under vacuum. This evaporator is located high enough to create a barometric leg between it and the overflow lcg. Before reaching the evaporator, the extract passes through a rotameter type flowmeter and a Brown fin tube preheater, in which the temperature is brought to the boiling point. The evaporator is a vertical tube, rising film type unit. Extract solution a t the boiling point enters a t the bottom of the tube bundle. Solvent vapors, oils, and unevaporated solvent from the top of the bundle are separated by means of a tangential type vapor-liquid separator. The tube bundle has a heat transfer area of 85 square feet. The arrangement and size of the tubes are chosen to give a compromise between high vapor velocities, desired for maximum heat transfer coefficients, and lo& vapor velocities desired to give low pressure drop. Heat transfer coeficients of 100 B.t.u. per hour per square foot per degree F. are obtained a t optimum operating conditions. The operating pressure is 100 mm. of mercury, absolute. Solvent vapors from the evaporator pass into a horizontal, short tube, drip type condenser. In this unit water flows inside the tubes and is baffled to give countercurrent flow. The solvent vapors a t about 220°F. enter the top of the shell and pass directly domn-ward. Total condensation of the vapors is accomplished a t about the mid-point, below which subcooling to m ithin 10 of the temperature of the cooling water (60' to 80' F.)of the liquid takes place. The condensate flows directly to the furfural storage tank, through a barometric leg. The extract concentrate from the evaporator, containing 80 to 90% oil, flows down through a barometric leg, up through a rotameter, and into the top of a bubble plate stripper. This column is a steel tower containing 12 bubble plates and is designed to keep the vapor velocity low enough to prevent entrainment and minimize pressure drop. The temperature of the oil is maintained by heating coils located on the bubble cap plates. The pressure a t the top of the column is 50 mm. with 1 to 2 mm. increase pes plate, proceeding downward. The vacuum in the stripper is maintained by a tvio-stage steam jet ejector, located high enough to provide a barometric leg drain on the condenser. The vacuum is controlled by an absolute pressure controller operating a diaphragm control valve which throttles the flow of noncondensables from the condenser to the ejector. The oil entering the stripper is introduced onto the top plate pLnd f l o m down from plate to plate; dry superheated steam, at about 300 F., is introduced into the column just below the bottom plate and passes upward, removing all furfural from the oil as indicated by a standardized test with aniline acctate. The solvent-free oil is pumped out a t the bottom of the stllpper, by means of a gear pump, through a steel fin tube cooler, to a 600-gallon vertical cylindrical steel storage tank. At this point a portion, dependent upon the reflux ratio being maintained, piped back t o the extraction column its reflux feed. TWOreceiving tanks are maintained for the extract oil. After one has been filled, a control analysis is run and the product is pumped to a 9000-gallon storage tank while the other is being filled. Yield checks are made at 4-hour intervals. The handling of the raffinate soluRAFFINATE TREATMENT. tion is similar to that of the extract, The solution is piped out of the top of the extraction column, through a barometric leg, flowmeter, and preheater, then into an evaporator, where it is concentrated to a eolution containing about 90% oil. This passes through a stripper and cooler, then into storage tanks. All the equipment units involved are virtually identical with those described for the extract processing, except that the evaporator is of the falling film type. Wovever, it has been concluded on the basis of this operation that the rising film is generally more satisfactory, as it gives better heat transfer. This evaporator is smaller than the extract evaporator, having 11 square feet of tube surface. The furfural from the raffinate evaporator goes to the same condenser as does the solvent from the extract solution. The O

Extract Solvent Recovery Equipment of Single-Column Commercial Plant Left. Furfural dryer Center. Evaporator liquid-vapor separator Right. Evaporator tube bundle

Vol. 40, No. 7

INDUSTRIAL AND ENGINEERING CHEMISTRY

July ' 1948

Extract and Raffinate Strippers (Upper Sections) of Semicommercial Plant Fine tube

preheater for extract evaporator i n lower foreground. ' Extract evaporator tube bundle a t left

furfural-water vapors from the stripper also pass through the same condenser as do those from the extract stripper system. CONTROL ANALYSIS. An extensive schedule of standard control tests is applied to feed, extract, and raffinate: Tests On control lots Iodine value % free f a t t y acid iMoisture Color 70furfural On tank car lots Gardner break test Peroxide value Heat bleach test Hydrogenation and deodorization

Feed Oil

Extract

Raffinate

X X X X

X X X X X

X

X X

X X X

X

..

....

..

X X X X ~~

X

..

X

Oil is tested for furfural by shaking a 25-ml. sample with an equal volume of 10% isopropyl alcohol in water, and withdrawing 10 ml. of the water layer that separates; to this solution is added 1 ml. of a solution of 50% by volume of aniline, 40% acetic acid, and 10% water. The presence of furfural produces a pink color. By matching color against that produced in samples of known strength, the amount of furfural present can be determined. This test will readily detect traces of furfural. SOLVENT RECLAMATION AND DRYINQ. Condensed solvent from the evaporators goes directly to storage for reuse. The furfural-water condensate from the stripper condensers is led, through a barometric leg, to a decanting tank. Here the furfural layer, containing about 5% water, is drawn from the bottom of the tank. Furfural going directly from the evaporators to storage contains a trace of water. T o remove this water, furfural from storage is added to that from the decanting tank before drying, in such quantities that the mixture has a water content of 2 to 3%. It is then fed into a stainless steel bubble plate column, entering about the middle of the column. I n this unit the pressure is maintained at 100 mm. of mercury absolute , with a maximum drop of 10 mm. across the column. The temperature is

1165

automatically controlled. The control temperature a t the third plate is 210" F., while the overhead temperature is 110' t o 150" and that of the bottoms 215'. This 10-plate column, operating a t a reflux ratio of approximately 0.25 to 1, gives a near-azeotrope of furfural and water (approximately 40% furfural and 60% water) as overhead and dry furfural as bottoms. The bottoms are drained through a cooler and barometric leg to storage. The vapors of the azeotropic mixture pass out the top of the column, through a condenser, and into a decanting tank. The water layer from the decanting tank, containing about 8% furfural, overflows into a pumping tank and thence is pumped by means of a turbine pump into the top of a tower, packed with 0.5-inch Berl saddles, which operates a t atmospheric pressure. The feed enters cold, and saturated steam a t about 5 pounds per square inch pressure is introduced a t the bottom. All the furfural is carried out in the vapors from the distillation of the azeotropic mixture, while the water runs out the bottom of the" tower to the sewer. The vapors pass through a condenser and return to the decanting tank. HANDLING OF FURFURAL. All liquid surfaces of furfural or oil and furfural are kept blanketed with an atmosphere of inert gas produced by a commercial inert gas generator using butane as a fuel. STEAMAND WATER. Throughout the plant, heat is furnished by steam. The maximum pressure needed a t any of the points described is 125 pounds per square inch. Condenser water is collected in a hot well, from which it is pumped to a spray pond on the roof and cooled for reuse. MATERIALS OF CONSTRUCTION. The extraction, evaporation, and stripping systems of this plant are constructed of carbon steel. All units in which wet furfural is handled are of type 304 stainless steel. No brass or other copper alloys are allowed to come into contact with the oil or solvents, as there are widely accepted indications that traces of. copper may cause oil rancidity (?', 62). FULL SCALE COMMERCIAL PLANT

The semicommercial plant described has been operating on nonbreak soybean oil. A commercial plant in Milwaukee, capable of processing 1 to 1.5tank cars of oil a day, has operated since 1943 on the principles described for the semicommercial plant. A full scale commercial plant, using a less refined grade of degummed soybean oil has been planned. In this type of operation it has been found (18)that the use of naphtha in connection with furfural is more satisfactory than furfural alone. The naphtha generally used is a mixture of paraffinic hydrocarbons with a distillation range of 290 ' to 360 F. and a kauri-butanol value of 36 to 39; however, m y mixture of hydrocarbons which is immiscible with furfural may be used with varying degrees of success. The naphtha effects separation of by-products of value, and produces a purer extract oil. I n such a fractionation a two-column system is used, a relatively large amount of naphtha being fed into the bottom of the second, or backwash, column to remove most of the extract oil from the furfural solution. This leaves in the furfural, as a by-product, a concentration of coloring pigments, free fatty acids, traces of break constituents, and unsaponifiable matter. The planned commercial plant, as outlined in the accompanying flowsheet, follows the semicommercial plant that has been described in principle and for the most part in practice. It differs in that it employs two extraction columns and a stepwise process in the recovery of the solvent from the by-product. At the present time, the semic'ommercial plant has been converted t o the two-column system and is operating in the fashion described for the contemplated commercial plant. EXTRACTION COLUMN.Maximum fractionation conditions from experimental studies are shown in Table I. Runs made at a O

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INDUSTRIAL A N D ENGINEERING CHEMISTRY

Vol. 40, No. 1

By-product Recovery System 14 to 1 solvent ratio (18)in a column with 75 feet of packing gave nearly maximum separation of a nonbreak soybean oil. Maximum separation, as applied to soybean oil, is defined as the maximum spread in iodine values of the extract and raffinate products, while a minimum extract product iodine value of 150 is maintained. If maximum fractionation i s not desired, for economic or technical reasons, lower solvent ratios can be used. Under these conditions of operation, the iodine value of the extract is maintained a t 150 minimum with a sacrifice in extract yield. The raffinate iodine value is higher under these conditions than under those of maximum fractionation. Thus, operating with any solvent ratio lower than that for which a plant is designed, a lower unit processing cost will be possible, as a greater amount of oil can be processed for nearly the same utility, labor, and overhead charges. The column diameter is determined from flood rate data for given conditions of operation. Operation at a processing rate of 200,000 pounds per day of degummed soybean oil and a solvent ratio of 8.3 to 1 requires two extraction columns 5.5 feet in diameter operating in parallel. The use of two columns in parallel increases the plant flexibility and decreases the phase distribution problem a t only a slight increase in plant costs. The type of packing used depends on the stage efficiency and the flood rate desired. I n general, the selection depends on a balance between the cost of Berl saddles and Raschig rings, and the construction costs. Berl saddles have been found experimentally to give a shorter stage height and higher flooding rate, but cost about twice as much as Raschig rings.

Two-Column System for Extraction of Vegetable Oils with Furfural

Feed flow rates to the column and temperatures are automotically controlled. The column interface is controlled by means of an automatic flow controller, which throttles the flow of the extract solution from the bottom of the No. 1 column to the top of the No. 2 column. The actual location of the interface is easily determined by sampling and, as all flows to the column are held constant, it can be raised or lowered by resetting the interface control instrument to give a smaller incremental increase or decrease in extract solution output. Experience has shown that an increase or decrease of 0.5 to 1% ' of the total flow from the column gives satisfactory control. The actual temperature of extraction in the column is followed by means of thermocouples inside the column, spaced 15 feet apart. Column temperatures are read by means of a multiple point indicating Electronik potentiometer and recorded hourly by the plant operator. Surge capacity for the extraction column is provided by the raffinate solution receiver. The reflux feed to the No. 1 column is different from that described for the semicommercial plant in that naphtha is added t o it. Where 1.1 parts of extract oil are returned to the extraction column, as reflux, per part of feed oil entering the column employing a n 8.3 to 1 furfural ratio, 0.2 part of naphtha is incorporated with the reflux oil before it enters the column. This aids in the separation in the first column. About 10% of this naphtha is carried into the backwash column, where a larger quantity is added to effect separation of the extract oil from the by-products. (For compositions of the solutions from this column see Table IV.) BACKWASH COLUMN.The extract solution from the No. 1 column at 120" F. is pumped to the top of the No. 2 column through a heat exchanger and then through a cooler which brings the extract solution temperature down to 70". The heat exchanger takes care of the major cooling duty by transferring heat to the furfural being fed to the No. 1column. Naphtha, a t an automatically controlled flow rate and a tem-

I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY

14 to 1 solvent ratio (18) in a column with 75 feet of packing gave n e d y maximum separation of a nonhresk soybean oil. M&um separation. as applied to s o y h oil, is defined 88 the madmum spresd in iodine values of the extract and r a h t e prcducta, while a minimum extract product iodine value of 150

.-&ni If maximum fractionation is not deaired, for economic or technical reasons, lower solvent ratios can be wed. Under thesa conditions of operation. the iodine value of the extract in maintained at 150 minimum with a sacrifice in extract yield. The rstlhte iodine value is higher under these conditions than under t h m of maximum fractionation. Thus, operating with any advent ratio lower than that for which a plant is designed, a lower unit proceseing cost will be possible, as a greater amount of oil can be proceaasd for nearly the m e utility, labor, and owrhead C ~ g e s . The column diameter is determined from flood rate data for given conditions of operation. operation at a proceasing rate of zoO,ooO pounds per day of degummed soybean oil and a solvent ratio of 8.3 to 1 requiree two extraction columne 5.5 feet in diameter operating in parallel. The uea of two columna in parallel increase8 the plant aexibility and decreases the phase distribution problem at only a alight increaae in plant caste. The type of packing used depends on the stage efficiencyand In reneral. the selection denends on a the flood rate d&d. balance between the cost of k r l BBkdles and Raschii rings, and the construction costa. Berl saddles have been found experimentally to give a shorter stage height and higher floodmg rate, hutocstabout twiceasmnchasRaschigrings.

* Two-Column System for Extraction of Vegetable Oils with Furfural

1161

Feed flow rates to the column and temperatures are automatic d y controlled. The column interface is controlled by means of an automatic Bow controller, which throttles the flow of the extrnct solution from the bottom of the No. 1 column to the top of the No. 2 column. The actual location of the interface in w i l y determined by sampling and, as all flows to the mlumn rue held constant, it can be &d or lowered by resetting the interface control instrument to give a smaller incremental increaea or decrease io extract solution output. Experience haa shown that an increase or deereaes of 0.5 to 1% of the total flow from the column gives satisfactory control. The actual temperature of extraction in the column is followed by means of thermocouples inside the column, spaced 15 feet apart. Column temperaturea are read by meam of a multiple point indicating Electron& potentiometer and recorded hourly by the plant operator. Surge capacity for the extraction column is provided by the raEinate solution receiver. The reflux feed to the No. 1 column is different from that de. scribed for'the semicommercial plant in that naphtha in added to it. Where 1.1parta of extract oil are returned to the extrsction column, as reflux, per part of feed oil entering the column employing an 8.3 to 1 furfursl ratio, 0.2 part of naphtha ia incorporated with the reflux oil before it enters the column. This ai& naphtha in the separation in the first column. About 10% of thi~ is carried into the backwash column. where a lareer ausntitv is added to effect separation of the extract oil from the by-products. (For compositionsof the solutions from this column see Table IV.) BACKWASE COLUMN.Th0 extract solution from the No. 1 column at 120" F. is pumped to the top of the No. 2 column through a heat exchanger and then through a cooler which brings the &act solution temperature down to 709 The heat exchanger takes cam of the major cooling duty by transferring heat to the furfuralbeing fed to the No. 1column. Naphtha, at an automatically controlled flow rate and a tem~~

1169

INDUSTRIAL A N D ENGINEERING CHEMISTRY

,

directly dependent on the rate of evaporation, is controlled by manually m t t i n g the steam prrssure controller on the first efiect evaporator tube bundle. Evaporator load balance is obtained aa above and by minor adjustments in the v m u m used in each efiect. The second, third, and fourth stages are single effect evaporators. Evaporation rate is controlled by means of a steam pressure controller. The control point is reset manually to give the desired flow rate of unevaporated material from each unit. The control point could be r m t automatically from a flow controller on the unevaporated liquid line if desired, but experience has shown that operations are sufficiently stable for manual reset. The second and third stage evaporators an operated at 100 mm. of mercury absolute premure. The fourth stage operates at 50 mm. to provide the lowest possible evaporation temperature, so aa to minimize decompition and polymerisation of tbe furfural and by-product. The discharge from this point is 90 to 95% by-product containing 5 to 10% furfural. The concentrated by-product solution has foaming c h a c teristieebut can be satisfactorilystripped in a bubble cap stripperwithsuperheatedsteamat 50mm.ofmercuryabsolutepressure. An theee strippers become fouled after a relatively short period of operation, two unitsare provided for continuity of operations. Foulingra~onallotherstrippersandevaporatorsare relstivelylow, cleaningcyclesofStol2monthabeinormal. Exmm OIL RXUVERY. The extract oil recovery syatem mneistSof 8 double efiect evaporator and 8 bubble cap stripper in the commercial plant. whereas a single effect evaporator is d in semicommercial operations. The former is found to efiect appreciable steam economy. Operation and control are similar to that of the double efiect evaporator used in the byproduct system, except that a temperature controller is usad to controlthe steam to the first efiect. This is poasible b u s e of tbe rapid cbange in boiling point, with concentration, in a 75 to 907"oil solution. The comDoBition of the concentrated oil&lntion is easily controlled at-90 1%oil with this type of instrument. ' and The combined naphtha-furfural vapors are condensed led to the dry deranter tank. where they are semated and Dimd

74-

&-

STEAM

SUPERHEATED STEAM

11

**INDICATING LEVEL CONTROLLER

f

Rsffinste R-very

System

to Storage.

A controlled amount of the So.% oil solution from the first e6ect evaporator is precooled, and then mixed with a metered m o u n t of naphtha to glve the desired compition for reflux feed. The mixture is cooled to the desired temperature and pumped to the No. 1 column where it is fed in aa reEux. A satisfactory reEux solution is one whose composition fa& outado the range of immiscibility on the oil-rich side of the triangular phase diagmm. T h e oil in this solution baa the Bame iodine value aa the extract oil. The type of operation described reduces the extract oil stripping load considerably and still provides satisfactory d u x . The balance of the discharge stream of the evaporator Eows by gravity to the extract stripper through a barometric leg. The extract stripper design and operation are essentially the name aa tbwa previously described. Enough bead is provided for the &ha& gear pump to allow the installation of an oil cooler ahead of the pump. RAFFINATE 01L RECOVERY. The r a f f i t e oil recovery system fdbws that of the semicommercial plant. A rising film evaporator that is used is a Bingle efiect vertical tube evaporator with a temperature controller contrelling the composition of the diPchar@3. The unit is operated at 50 mm. of mercury absolute pressure. Flow from.& evaporator to the stripper iS by p a n t y t h g b a hammetric leg. The d i n a t e atripper is a bdbble cap unit similar in deaign to the extract stripper. W m Fwmani REcowa~. The wet furfural recovery system is somewhat different from that used with the single solvent System. Two decanters are needed, one wet and one dry. A

difierent tvtx of reboiler is d on the furfural drver. an improvement heveloped since the building of the semi&nknereial plant. The remainder of the system is effectivelythe name. All the dry solvents, from the evaporator condensers, are separated into a furfural phase and a naphtha phase in the dry decanter, and each phase flows by gravity into ita respective storage tank. The wet decanter receives the distillate from both the extract and r a f f i t e strippers and distillate from the water still. The wet mixture separates into naphtha, water, and furfural phases. The naphtha flow by gravity through an o d o w leg to naphtha storage, p&ng through an auxiliary decanter on the way, where any entrained wster is separated. The Water Bows by gravity, thmugh an overflow leg, to a small surge tank,from which it is pumped under controlled conditions to the water still. The furfurallayer overEows by gravity to ita surge tenk. Flow from the surge tank to the furfhral dryer is controlled by an indicating level controller. The dryer consiata of a l&plate bubble cap fractiomting column and a once-tbmugb type reboiler similar in design to a vertical tube evaporator. The feed enters the fractionating column on the fifth plate, close to ita boiling p i n t . Reeux is pmvided by an internal reflux coil above the t a t b plate. Temperature and pressure data here are directly comparable with those for the Semicommercial plant. An the feed travele downward, the water is removed by an upward flow of furfural vapors provided by the reboiler by gravity flow. Partial vaporisation tdea place, and the liquid and vapns are separated

INDUSTRIAL AND ENGINEERING CHEMISTRY

1170 TABLE V.

MAJOROPERATING COSTFACTORS

(Plant, operating a t a solvent ratio of 8.3 to 1, fractionating and refining 200,000 pounds of degummed soybean oil per day) A. Services Steam, 125 lb./sa. in. and less 30,000 lb./hr. Water 1280 gal./min. Cooling tower 60D F. supply 100 gal./min. Eleotrio power (connected load) 200 kw.-hr. 75 cu. ft./min. Compressed air 15 cu. ft./min. Inert gas B. Supervision One chemical engineer C. Direct labor Foreman One, 40 hours/week Operators Two continuously (plant operates 24 hours/day, 7 days/week) Oil and raw materials handler One, 40 hours/week Control technician One, 2 hours/day D. Solvent loss 800 gal./month Furfural 350 gal./month Naphtha

in the tangential separator located below the bottom plate. Hot, dry furfural drains back t o furfural storage through a barometric leg. A heat exchanger cools the bottoms and heats the feed. Overhead composition is modified somewhat by the presence of naphtha, but in general is close to that of the water-furfural system. The reboiler rate is controlled by means of an Electronik temperature controller. The thermocouple is located on the third plate. The control temperature is 3 to 5 F. lower than the temperature on the bottom plate, which corresponds t o the boiling point of dry furfural at the operating pressure (100 mm. of mercury absolute). FUTUREPOSSIBILITIES. The fractionation of soybean oil into a drying oil fraction that is not significantly different from linseed oil and into a n improved food oil fraction has extremely important potentialities. The very rapid growth of the soybean oil industry in the past 10 to 15 years has ensured a large supply of this oil. The production of crude soybean oil doubled in volume during the years 1942 to 1946; 761,582,000 pounds were produced in 1942 and 1,454,339,000 in 1946 (46). Under normal economy, farmers have not been desirous of growing the large acreage of flax needed t o ensure sufficient linseed oil to meet the domestic demand. As an incentive the Government finds it necessary to set a minimum price per bushel on flaxseed. On the other hand, the farmers have readily accepted the growing of soybeans, so that a constant supply of oil is assured in large quantities. A portion could be easily fractionated to supplement the demands for linseed oil. Up t o the present time, soybean oil, as such, has been essentially a food oil and relatively insignificant quantities have been used by the paint, varnish, and allied drying oil industries. Only 2 to 3% of the total soybean production for 1946 was used by the paint and varnish industry. It is possible to produce large quantities of drying oil from soybean oil by the use of selective solvent fractionation, and thus to aid this country greatly in becoming more self-sufficient in respect to drying oils. The process may also be applied t o the refining of glyceride oils without the use of alkali. Tank car quantities of degummed soybean oil have been fractionated and refined by this process a t relatively low solvent ratios to yield relatively small amounts of paint oil and substantially larger amounts of fully refined food oil. This food oil or raffinate fraction has been processed directly to hydrogenated products of excellent color and quality. It is conceivable that this process may supplement some of the normal alkali refining of soybean or other glyceride oils. In addition to soybean oil, many other glyceride oils may be fractionated on the basis of carbon chain length or unsaturation. The fractionation of fatty acids to yield highly unsatuO

Vol. 40, No. 7

rated acids for specialty purposes offers a challenge t o every oil chemist. The concentration of minor ingredients of fats and oils into a small by-product fraction which becomes a potential source of sterols and tocopherol has considerable promise of being reduced t o commercial practice. LITERATURE CtTED

Amberger, C., 2. Untersuch. Nahr. u . Genussm., 40,192 (1920). Baldwin, W. H., and Parks, L. E., Oil & Soap, 20,101 (1943). Behr, 0. M. (to Vegetable Oil Products Co.), U. S. Patents 2,166,103 (July 18, 1939); 2,239,692 (April 29, 1941). Brown, J. B., Chem. Rev., 29,333 (1941). Burr, G. 0. (to Regents of University of Minnesota), U. S. Patent 2,242,230 (May 20,1941). Cannon, M.R., and Fenske, M. R., IND. ENG.CHEM.,28, 1035 (1936). Cowan, J. C., paper presented before meeting of American Oil Chemists’ Society, Chicago, November 1947. Demmerle, R. L., IND. ENG.CHEM.,39, 126 (1947). Detwiler, S.B., Bull, W. C., and Wheeler, D. H., Oil & Soap, 20, 108 (1943). Eibner, A . (to T . Kotthof), U. S.Patent 1,870,614 (Aug. 9,1932) ENG.CHEM., 40, 53 (1948). Elgin, J. c.,IND. Elgin, J. C., “Perry’s Handbook of Chemical Engineering,” 2nd ed., p. 1213, New York, McGraw-Hill Book Co., 1941. Embree, N. D., Chem. Rev., 29,317 (1941). Freeman, S. E. (to Pittsburgh Plate Glass Co.), U. S. Patents 2,200,390, 2,200,391 (May 14, 1940). Freeman, S. E. (to Pittsburgh Plate Glass Co.), U. S. Patents 2,278,309 (March 31, 1942); 2,313,636 (March 9, 1943). Freeman, S.E., and Gloyer, S. W. (to Pittsburgh Plate Glass Co.), U. S.Patent 2,423,232 (July 1,1947). Fritzweiler, R., Arb. kaiserl. Gesund., A18, 371 (1902). Gloyer, S. W., IND. ENG.CHEM.,40, 228-36 (1948). Heise, R., Arb. kaiserl. Gesund., A12, 540 (1896). Hersh, R. E., Varteressian, K. A., Rusk, R. A,, and Fenske. M. R., IND. ENG.CHEM.,ANAL.ED., 10,86 (1938). Hixson, A. K., and Drew, D. A., Ibid., 40,675 (1944) Hixson, A. W., and Bockelmann, J. B., Trans. Am. Inst. Chem Engrs., 38, 891 (1942). Hixson, A. W., and Hixson, A. N., Ibid., 37,927 (1941). Hixson, A. W.,and Miller, Ralph (to Chemical Foundation). U. S. Patent 2,219,652 (Oct. 29, 1940). Ibid., 2,226,129 (Dee. 24, 1940). Ibid.,, 2,247,496 (July 1, 1941); 2,344,089 (Mar. 14, 1944); 2,388,412 (Nov. 6, 1945). Hunter and Nash, IND. ENG.CHEM.,27,836 (1935). Hunter and Nash, J . SOC. Chem. Ind., 53,95T (1934). Jenkins, J. D. (to Pittsburgh Plate Glass Co.), U. S. Patent 2,352,546 (June 27, 1944). Kass, J. P., and Burr, G. O., J. Am. Chem. Soc., 61, 3292 (1939). Kleinsmith, A. W.,and Kraybill, H. R., IND.ENG. CHEW, 35, 674 (1943). Klimont, J. I., 2. Untersuch. Nahr. u. Genussm., 12, 359 (1906). Miller, E. S., and Burr, G. O., Chem. Rev., 29, 419 (1941). Moore, Biochem. J.,31, 138 (1937). Potts, R. H., and McKee, J. E. (to Armour and CO.), U. S. Patents 2,224,984-6 (Deo. 17, 1940) ; 2,212,127 (Aug. 20, I

1940). _- _I .

Riemenschneider, R. W., Swift, C. E., and Sando, C. E., Oil & Soap, 17, 145 (1940). Row. S. B., Koffalt, J. H., and Withrow, J. R., Xrans. A m . Inst. Chem. Engrs., 37, 559 (1941). Rushton, J. H., IND. ENG.CHEM.,29, 309 (1937). Saal and van Dyck, Proc. World Petroleum Congr., 11, 352 (1933). Schaafsma, A. (to Shell Development Co.), U. S. Patent 2,118,454 (May24, 1938). Scheiber, J., U. S. Patent 1,942,778 (Jan. 9, 1934). Schicktanz, S. T., J.Research Xatl. Bur. Standards, 20,83 (1938). Schwarcman, A. (to Spencer Kellogg & Sons), U. S. Patent 2,140,271 (Dee. 13, 1938). Stingley, D. V., IND. ENG.CHEM.,32, 1217 (1940). Thiele, E. W., Ibid., 27, 392 (1935). U. S. Dept. Commerce, Bulletin, “Animal and Vegetable Fats and Oils,” Series M17-7-06 (1947). Varteressian and Fenske, IND. ENG.CHEM.,28, 928 (1936). I b i d . , 28, 1353 (1936). Ibid., 29, 270 (1937). Von Mikusch, J. D., J.Am. Chem. Soc., 64,158 (1942). Yamada, T., J . SOC.Chem. I n d . J a p a n , 37 (suppl. binding). 190-2 (1934). Ziels, N. W., and Schmidt, W. H., Oil & Soap, 22,327 (1945). RECEIVED M a y 10, 1948.